PAINTING INSPECTION GRADE 3/2 - NIORDCen.niordc.ir/uploads/94_79_paint.pdfThe BS 4800 colour system 2 The BS 5252, framework for colour co-ordination for building purposes 3 HEALTH

PAINTING INSPECTION

GRADE 3/2

(ATC88)

TWI Ltd, Training and Examination Services

WORLD CENTRE FOR MATERIALS JOINING TECHNOLOGY

CORROSION 1 Electrical Circuit 1 The Chemical Reaction 2

SURFACE PREPARATION METHODS & STANDARDS 1 Dry abrasive blast cleaning 1

Abrasives 2 Sizing of abrasives 4 Adhesion and Profile 4 Profile 4 Shot blasted profile 5 Profile measurement 5 Assessing a profile to BS 7079 Pt C ISO 8503.1 11 Use of the comparators 11 Using the comparators 11 Preparation of steel substrate before application of paints and related products 12 Abrasive Blasting Grades 13 Equipment 13 Considerations 14 Air Blasting 14 Water Blasting 17 High pressure water blasting up to 30 000 psi (water jetting) 17 High pressure water plus abrasive injection 17 Low pressure water plus abrasive injection 17 Steam Cleaning 18 Air blasting with water injection 18

Hand and power tool cleaning. 7079 Pt A, ISO 8501, SS 05 59 00 18 Flame cleaning 19

Method 19 Pickling 20 Vapour degreasing 21

SURFACE CONTAMINANTS AND TESTS FOR DETECTION 1 Test for soluble iron salts 1 Test to detect soluble chlorides 1 Other tests for salts 2 Test to detect the presence of millscale 2 Test to detect the presence of dust on a substrate 3 Test to detect the presence of moisture on a substrate 3 Test to detect the presence of oil or grease 3

PAINT CONSTITUENTS AND BASIC TECHNOLOGY 1 Binder 2

Binder – solvent groups and compatibility 5 Polymers 6 Oils 10

Pigments 10 Rust inhibitive pigments. Anticorrosive 11 Metallic Pigments 11 Opaque pigments 12 Extender pigments 12 Laminar pigments 12 PVC 12

Solvents 13 Other Additives 14

Anti settling agents 14 Plasticisers 14 Driers 15 Anti skinning 15

SOLUTIONS AND DISPERSIONS 1 Solutions 1 Dispersions 1 A suspension 1 An emulsion 1

DRYING AND CURING OF PAINT FILMS 1 PAINT SYSTEMS 1

Primer 1 Mid-coats 2 Finishing coats 2 Moisture tolerant systems 2 Powder coating materials 3 Thermosetting 3 Thermoplastic 3 Sacrificial coatings 3

WATER BORNE COATINGS 1 PAINT MANUFACTURE 1

Direct charge dispersing mills 1 TESTING OF PAINTS FOR PROPERTIES AND PERFORMANCE 1

Tests done on paint 1 Determination of volatile, non volatile 1 Flash point determination 1 Paint density 2 Relative density or specific gravity 3 Hegman grind gauge 4 Viscosity 5 Kinematic viscosity 7 Flow viscometers (Flow cups) 7

FILM THICKNESSES 1 Wet film thickness measurement 1 Tests done on dry paint films 3

Dry film thickness 3 Test panels 3 Calculations 4 Destructive test gauges 5 Non destructive test gauges 6

Tests for mechanical properties on paint films 8 Abrasion resistance 8 Hardness 9 Flexibility BS 3900 E1 9 Impact resistance 9 Accelerated testing 9

Drying and curing tests 10 Ballotini test 11

BK drying recorders 11 Other tests 11

Mechanical thumb test 11 Pencil scratch test (Wolff-Wilborn) 12 Mechanical scratch test 12 Gold leaf test 12 Thumbnail test 12

Opacity 12 Hiding power charts and micrometer adjustable film applicator 14 Degree of Gloss 14

Adhesion 15 ‘V’ cut test 15 Cross cut (cross hatch test) 16 Dolly test 16 Hydraulic adhesion test equipment 16

SPECIFIED COATING CONDITIONS 1 Relative Humidity 1 Dew Point 1 The Whirling Hygrometer, Aspirated Hygrometer or Psychrometer 2 Steel temperature measurement 2

CATHODIC PROTECTION 1 Sacrificial anode systems 1 Impressed current system 2 Interference 3 Monitoring CP 3 Cathodic disbondment 4

HOLIDAY/PINHOLE DETECTION 1 Voltage setting 1

PAINT APPLICATION 1 Brush application 1 Roller application 1 Spray application 2

Conventional spray 2 Airless spray 3 Safety considerations 5 Electro-static spray 6

Other paint application methods 6 METAL COATINGS 1

Galvanising 1 Sheradising 1 Calorising 1 Anodising 1 Electro-plating 1 Hot metal spraying 2

Powder system 2 Electric arc system 2

Wire and pistol system 2 COATING FAULTS 1 COLOUR 1

The Munsell colour system 2

The BS 4800 colour system 2 The BS 5252, framework for colour co-ordination for building purposes 3

HEALTH AND SAFETY 1 Hazard warning symbols 1 Responsibilities 2 Dräger tube and Dräger bellows 3 Using the tubes and bellows 4

DUTIES OF AN INSPECTOR 1 LIST OF SPECIFICATION AND BS NUMBERS 1 QUALITY 1

Quality assurance 1 Quality control 1 Quality related standards 1 Quality related definitions (from the above) 2

REVISION QUESTIONS 1 Corrosion OP – Monday 1 Surface preparation - Monday 2 Surface preparation – Tuesday 3 Paint technology (1) - Wednesday 5 Paint technology (2) - Wednesday 6 Paint testing – Thursday 8 Revision questions general – Friday 10 Revision questions PA 10 specific 12 B. Gas 3.2 Maths Exercises 14 Density and SG exercise 15 RH and DP exercise 16

Appendix A 1 Appendix B 3

INSULATION 3 General 3 Acoustic cladding 3

General 3 Materials 4 Application of materials 4

Thermal insulation 5 General 5 Materials 5

Insulating materials 5 Protective coverings 6 Fixing materials 6

Application of materials 6 Appendix C 1

DATA SHEET EXAMPLES 1

Painting Inspection Grade 3/2. Rev 1 April 2004 Corrosion 1.1 Copyright © 2003, TWI Ltd


CORROSION Corrosion can be generally defined as “Degradation of a metal by chemical or Electro-chemical means”. From this definition it is obvious that two mechanisms are involved, firstly an electrical circuit and secondly a chemical reaction.

Electrical Circuit In a corrosion circuit the current is always D.C. (Direct Current). It is conventionally thought that a current passes from positive + to negative -, i.e. from anode to cathode. In fact electrons are flowing in exactly the opposite direction, from cathode to anode. For corrosion circuit to exist three things are needed: a) Anode An anode is a positively charged area. It becomes positively charged because the atoms release two electrons each, thus causing an imbalance between protons and electrons, positive and negatively charged units. In it’s passive state, the iron atom has 26 of each, protons and electrons, when the two electrons are released the atom still has it’s 26 protons, but now only 24 electrons. In this state the atom is now an ion, overall positively charged by two units and written as Fe++. (An ion is a charged particle, and can be positive or negative, a single atom or a group of atoms, known as a molecule.) This losing of electrons can be shown as: - Fe Fe++ + 2e. The Fe++ is called a positive iron ion. An ion can be positive or negative and is a charged particle, an atom or a group of atoms.

A passive iron atom Fe 26 protons and 26 electrons.

An iron ion Fe++, 26 protons and only 24 electrons

Figure 1.1 iron atoms

Nucleus



b) Cathode A cathode is a negatively charged area where there are more electrons than needed in its passive state. These are electrons released from the anode. At the cathode the electrons enter into the electrolyte to pass back to the anode. c) Electrolyte An electrolyte is a substance, which will conduct a current and be broken down by it, (dissociate into ions). Water is the most abundant electrolyte and also very efficient. Acids, alkalis and salts in solution are also very efficient electrolytes. As the electrons pass into the electrolyte it is dissociated into positive and negative ions, as shown by the formula: -2H2O 2H+ + 2OĦ. Simultaneously the electrons couple back with the Hydrogen ions to form two full Hydrogen atoms, which join together diatomically to form Hydrogen gas. This is termed as being evolved, or given off from the cathode. The hydroxyl ions return to the anode through the electrolyte carrying the electrons. The corrosion triangle, as shown below, can illustrate the electrical circuit. The electron circuit can be seen to be from anode A, to cathode C, through the electrolyte E, back to A. Figure 1.2 The corrosion triangle

The Chemical Reaction From the above we can see that no chemical reaction, (combination of elements) has occurred at the cathode, or in the electrolyte. The chemical reaction, the formation of corrosion products, only occurs at the anode. The positive iron ions, Fe++, receive the returning hydroxyl ions and ionically bond together to form iron hydroxide, which is hydrous iron oxide, rust, and is shown by the formula: Fe++ + 2OĦ Fe (OH)2 It is now apparent that corrosion only occurs at the anode, never at the cathode. Hence the term cathodic protection. If a structure can be made to be the cathode in a circuit, it will not corrode. The corrosion triangle shows the three elements needed for corrosion to occur, anode, cathode and electrolyte. If any one of these three is removed from the triangle, corrosion cannot occur. The one most commonly eliminated is the electrolyte. Placing a barrier between the electrolyte and the anodic and cathodic areas, in the form of a coating or paint system does this. If electrolyte is not in direct contact with anode and cathode, there can be no circuit, and so no corrosion.

E

A C



The basic corrosion reaction, as explained above, occurs fairly slowly at ambient temperatures. In common with all chemical reactions certain factors can increase the reaction rate, listed below are some of these. 1 Temperature. Steel, in common with most metals, is thermodynamically unstable. The

hotter the steel is the faster the corrosion will occur. 2 Hygroscopic Salts. A hygroscopic salt is one, which will attract water and dissolve in it.

When salts are present on a substrate and a coating is applied over them, water will be drawn through the film and the resulting solution builds up a pressure under the film. Eventually the film is forced up to form blisters. These blisters are called osmotic or hygroscopic blisters, and are defined as ‘pinhead sized water filled blisters’. Sulphates and Chlorides are the two most common salts, chlorides predominant in marine environments, and sulphates in industrial areas and sometimes agricultural.

3 Aerobic conditions, (presence of oxygen). By introducing oxygen into the cathodic reaction the number of Hydroxyl ions doubles. This means that double the number of iron ions will be passivated and therefore double the corrosion rate. Shown by :- 2H2O + O2 + 4e 4OH-

4 Presence of some types of bacteria on the metal surface, for example Sulphur Reducing Bacteria, better known as SRBs, or MEMs, Metal Eating Microbes.

5 Acids and alkalis 6 Bi-metallic contact. Otherwise known as Bi-Metallic Corrosion. Metals can be listed in order of nobility. A noble metal is one, which will not corrode. In descending order, the further down the list the metal is, the more reactive it is, and so, the more anodic it is, the metal loses its electrons to become reactive ions. The degree of activity can be expressed as potential, in volts. The list can be called a Galvanic List, but when the free potentials of the metals are known it can also be called the Electro Motive forces series or the Electro-Chemical series. Below is a list of some metals in order of nobility with potentials as measured using a copper/copper sulphate half cell reference electrode, in seawater at 25oc.

MATERIAL KNOWN POTENTIAL AV. VALUES Graphite + 0.25 v Titanium 0.0 v Silver - 0.1 v Nickel 200 - 0.15 v Lead - 0.2 v Admiralty Brass - 0.3 v Copper - 0.35 v Tin - 0.35 v Mill Scale - 0.4 v Low Alloy Steel - 0.7 v Mild Steel - 0.7 v Aluminium Alloys - 0.9 v Zinc - 1.0 v Magnesium - 1.6 v



From the list above it can be seen that millscale is immediately above steel on the galvanic list. This means that millscale is cathodic to steel, and if left on the surface of steel will accelerate the corrosion of the steel substrate. Millscale is formed during the rolling operation of steel sections e.g. RSC, RSA, RSJ. The oxides of iron form very quickly at temperatures in excess of 580c. The first oxide formed is FeO, iron oxide, the next is Fe3O4 and last of all Fe2O3. Common names in order are Wustite, Magnetite and Haematite. These oxides are compressed during the rolling operation to produce blue millscale. The thickness of millscale varies from 25 to 100 um. Because millscale is only produced during rolling, when it has been removed by any surface preparation method, it can never re-cur.

Painting Inspection Grade 3/2. Rev 1 April 2004 Surface Preparation 2.1 Copyright © 2003, TWI Ltd


SURFACE PREPARATION METHODS & STANDARDS If the products of the corrosion reactions, and other contaminants, were left on a substrate and paint applied over them, the adhesion of the coating and thus the coatings life would be far from satisfactory. Surface preparation involves removing these contaminants, and in some instances increasing the area available for adhesion by roughening up the substrate. A good surface preparation grade (degree of cleanliness) along with a suitable surface profile can give 10 years life from a typical four coat paint system. The same system applied over a substrate with little or no profile and contaminant remaining might give four to six years, or even less. Therefore two factors need to be considered when inspecting a surface preparation. 1. Degree of cleanliness 2. Surface Profile (degree of roughness) If a specification gives criteria for both of these factors, then quality is not achieved until both criteria are satisfied. Surfaces can be prepared for paint application in several different ways, each one varies in cost, efficiency, ease and suitability. a) Dry Abrasive Blast Cleaning b) Water Blasting c) Hand and Power Tool Cleaning d) Flame Cleaning e) Pickling f) Vapour Degreasing g) Weathering

Dry abrasive blast cleaning Dry abrasive blast cleaning involves compressing air and forcing it along a hose and out of a small aperture called a nozzle. A pressure of 100 psi results in the air exiting the nozzle at approximately 450 mph. If abrasive particles are mixed in with the air and travel at the same speed, they will carry a lot of work energy. This energy is used in chipping away millscale and other detritus from the substrate. With some abrasives part of the energy is used in shattering into small pieces and with others all the energy is used in impinging into the steel surface, roughening the surface and increasing the surface area to increase adhesion properties. Because all standards refer to the amount of contamination remaining on the surface, the longer the time spent on this operation, the higher the degree of cleanliness.



Abrasives Abrasives come in many forms and can be classified in several different ways, as shown below. None metallic (Mineral) expendable

Metallic (Recyclable) Agricultural by-product

Copper Slag Nickel Slag Boiler Slag Glass Bead Aquamarine (Olivine) Garnet Sand

ACI (Angular Chilled Iron) Steel Grit Steel Shot Grit and Shot Mix Garnet

Walnut Shell Coconut Shell Eggshell Corn Cob Husk Peach Husk

It can be seen that the recyclable abrasives are the more costly, and therefore justify a cleansing operation before re-use. In the context of this course we are considering the following: - a) Sand It is not permitted to use sand. SI 1657 states that any mineral used as an abrasive must release less than 1% free silica on impact. (Silica causes preumonicosis or silicosis). COSHH REGS does not allow the use of sand containing silica for dry blasting. Sand itself is perfectly safe, but shattering on impact releases silica which can be inhaled. b) Copper Slag Although the name implies metallic content the amount of copper in the structure is extremely minute. Minerals smelted with the copper, liquefy and form a protective cover over the molten copper to prevent reaction with the atmosphere like slag on a weld. When the copper metal is run off the slag is rapidly cooled in cold running water, which causes it to shatter. The material is supplied in grit form (random, sharp edges, amorphous) and is very brittle, shatters into smaller pieces on impact, and should be used only once and then discarded and so classed as expendable. c) Garnet A natural mineral classed as being “of a diamond type hardness” can be either expendable or recyclable. If the situation justifies, cleansing units are available to extract contamination so that the material can be reused, usually up to three times. Doesn’t shatter on impact but does suffer some “wear”. Supplied in Grit form.



d) Metallic Grit In this context, steel and iron are both metallic. Cast steel grit being the softer of the two tends to round off on impact and loses its sharp edges. Angular Chilled Iron chips off small slivers on impact to produce sharp cutting surfaces on its next cycle. The finings so produced are extremely abrasive and cause extreme wear on moving parts of the recovery systems. Metallic abrasives are recyclable because the particles reduce in size slowly. Hence it can be re- used many times and still perform a useful function in a '‘working mix’. A working mix is an accepted ratio of large and small particles, where the large particles cut the profile and the smaller particles clean out the troughs. e) Metallic Shot Shot is spherical and doesn’t shatter (otherwise it would form grit). When supplied the particles are virtually uniform in size and shape, (not a working mix) but like the grit they wear down slowly in size. Regular addition of new abrasive as with grit, will then maintain a working mix. The particles are worn down eventually to finings, and are drawn out of the system during cleansing. f) Metallic Shot and Grit Mixed A mix of shot and grit results in a more uniform profile. The grit cuts the profile and the shot, being unable to enter the troughs produced, controls the peak height and so greatly reduces the number of ‘rogue peaks.’ A rogue peak is one, which is well proud of the acceptable profile range, and if painted over due to contraction of the paint, will leave bare metal in contact with the atmosphere, thus allowing corrosion to occur. When rogue peaks are in concentrated area the effect is of a rash, hence rust rashing or rust spotting. A typical mix ratio of Shot to Grit as used in a pipe coating mill would be 70 – 80 % shot to 20 –30 % grit. Other properties of an abrasive have an effect on the resulting substrate also, these being. Size of the particles Hardness of the material Density of the material Shape of the particle For example steel has a density of approximately 7.6 gm/cc and copper slag, depending on composition, approximately 4.2 gm/cc. If one particle of each material, of identical size, hit a steel substrate, then it would be logical to say that the steel would impinge further into the substrate, resulting in a deeper trough. A spherical particle would not impinge as deeply because the large smooth surface area would use its energy up in peening or work hardening the surface rather than cutting into it. So a shot blasted surface is different in appearance and texture to that of a grit blasted surface.



Sizing of abrasives G Prefix = Grit amorphous, points and cutting edges, irregular profile. S Prefix = Shot spherical, smoother profile. The G or S notation is followed by a number, which denotes the particle size. E.g. G24 or S330. From system to system the number can represent vastly different values, e.g. with the now defunct BS 2451 the 24 means nominally 24 thousandths of an inch where as in the SAE system it represents 1/24

" = approximately 40 thou. The new BS ref. 7079 pt E uses a different method again, in metric units. G140 would mean a nominal particle size of 1.4mm Adhesion and Profile A commonly used definition of adhesion is: - The force required to separate two surfaces in touch. A newly rolled plate, perfectly smooth, 1m x 1m has an apparent surface area of 1m2 and an actual area of 1m2. Abrasive blasting roughens the surface and increases the actual area, (the apparent area is still 1m2), thus increasing the adhesion. Two theories of adhesion are: - 1 Molecular Interference. Because the surface is rough and uneven the paint wets, and locks

into the profile, analogy Velcro. Physical. 2 Molecular Attraction. Negatively charged particles attracted to positive areas, and vice

versa. Analogy Magnet (sometimes called Ionic Bonding). Chemical. Profile Surface profile, anchor pattern, key, peak to trough height and amplitude are all expression meaning the cross section of a blasted area, as measured from the top of the peaks to the bottom of the troughs. The surface profile requirements are given on the specification for the job, e.g. for B. Gas 30 – 75 microns.



Shot blasted profile Also amplitude, key, anchor pattern, surface profile. Figure 2.1 Terms relating to preparing surfaces Other terms relating to preparing surfaces are illustrated below. Figure 2.2 Grit blasted profile Hackle – A small surface lamination, which stands upright like a needle after blasting. Approximately ≤ 13 mm. Easily removed. Lamination – Appears to be a longitudinal ‘crack’, one lip curling back, any laminations (slivers) found must be referred to engineer for ultrasonic check. Profile measurement If a profile requirement is specified, it is the inspector’s duty to ensure that the specification requirements are met. This can be done in two ways. a) By measuring – using gauges with and without replica tape. b) By assessing – using surface comparators.

Peak to trough

Hackle Rogue Peak

Lamination or Sliver



Digital gauges are common nowadays, but refineries, gas plants etc have stringent safety requirements and batteries can produce sparks, so the dial gauges are still very often used. The dial gauges fall into two categories, Surface Profile Needle Gauge and Dial Micrometers and Replica Tape. i Surface Profile Needle Gauge. The gauge is applied to the blasted substrate and the needle can be felt to locate a trough. Then by applying a slight pressure to allow the flat ‘foot’ of the gauge to sit firmly on the peaks of the blasted substrate, the needle will pass into the trough as far as it can Figure 2.3 Surface profile needle gauge In order to measure the difference from peak to trough we need to zero the gauge when the point of the needle is on the same plane as the flat foot, i.e. on a smooth piece of glass. This is done by applying slight pressure to the foot to ensure that it is perfectly flat on the glass. By loosening the locking screw, the bezel can now be moved easily in any direction. Still applying the slight pressure, the bezel should be moved so that the zero on the gauge is immediately behind the needle, then tighten the locking screw and the gauge is ready for use. When using this type of gauge it is normal to work to an average figure. Several readings are taken, usually more than ten, in random positions over the substrate, and the average calculated. This type of gauge is not ideally suited for curved areas such as pipes.

Foot

Plane for zero

Distance travelled by needle from zero = profile depth

Needle



ii Dial Micrometer and Replica Tape Replica tape, more often referred to by its trade name “Testex”, is also sometimes called ‘cornplaster method’. Although more costly than the needle gauge this method provides a permanent record and the traceability required from quality systems. The tapes are supplied in two grades: - Coarse Grade and Extra Coarse Grade, to cover two different ranges of blasted profiles. Coarse Grade for measuring profiles 0.8 to 2 Thou". 20-50um Extra Coarse Grade for measuring profiles 1.5 to 4.5 Thou" 37-115um The correct tape should be selected otherwise the readings will not be accurate. Figure 2.4 Cross section of a replica tape The procedure for using replica tape is as follows 1 Zero the dial micrometer. Clean the anvils (paper or fingers) an d allow the contacts to

come together, release the locking screws and adjust the bezel so that the zero is immediately behind the large needle.

2 Remove the backing paper from the replica tape, ensure that the small white disc with the black ring is detached also. Stick the replica tape to the area to be measured.

3 Using a pen or pencil end, or the specially provided plastic stick, rub firmly and evenly all over the area of the mylar. This causes the testex paste to pass into the troughs and the peaks of the blast will butt up to the transparent mylar.

4 Remove the replica tape and check. The mylar area should no longer be white (now grey), and pinpricks of light should be visible through the mylar when held up to the light.

5 Place the testex paste area between the anvils of the micrometer and allow them too gently

close together. From the final reading on the gauge deduct two thou if using an imperial gauge or 50um if using a metric gauge. The balance figure is the peak to trough height of the profile.

Mylar tough transparent Polyester plastic

Testex Paste Paper



Figure 2.5 Metric micrometer for testex measurement in microns 1 mm = 1000 um 25.4 um = 0.001" (1 Thou.) 40 Thou" = 1 mm 25.4 mm = 1 inch Micrometer is reading 93 um, subtract 50 um for testex plastic backing. The surface amplitude is therefore 43 u

Testex (allow 50 um for plastic backing)

10 um

2 um



Figure 2.6 Metric micrometer for testex measurement in microns

Testex (allow 50 microns 0.05 mm for plastic backing

1 100 mm

10 microns

100 microns

0.10 mm

Micrometer is reading 80 microns (0.080 mm) subtract 50 microns (0.050 mm) for testex plastic backing, the surface amplitude is therefore 30 microns.



Figure 2.7 Imperial micrometer for testex measurement in 1000 of an inch Reading the gauges. There are four common scales for dial micrometers, one of which, the 2um scale is also used on the needle gauge. The common scales are: - 0.01 mm = 10 microns / small division 0.002 mm = 2 microns / small division 0.001” = 1 thou / small division 0.0001” = 1/10 thou / small division

Micrometer is reading 4.6 Thou (0.0046"), subtract 2 thou (0.002") for testex plastic backing, the surface amplitude is therefore 2.6 thou (0.0026")

1 10 Thou 0.0001"

1 Thou

0.001"

Testex (allow 2 Thou (0.002") for plastic backing



With all four scales the value given represents the smallest increment on the periphery of the large scale. The small dial at 11 or 1 o-clock position gives the number of complete revolutions of the needle on the main scale. Typically the 2 um scale is 200 um per full revolution. Most profiles are around 75 – 100 um. Therefore the small dial can be virtually ignored for normal use. Useful conversion factors are: - 1 mm = 1000 um 1 thou = 25.4 um 25.4 mm = 1 inch 2.54 cm = 1 inch Assessing a profile to BS 7079 Pt C ISO 8503.1 Grit and shot abrasives produce different surface profiles, therefore two comparators are specified. One for grit blasted profiles, G. and one for shot blasted profiles, S. When a mix has been used then the reference comparator should be G. In all instances the entire area should be blasted to SA21/2 or SA3 grade. (discussed later) Use of the comparators There are three methods which can be employed to assess the roughness characteristics of blast cleaned steel. 1 Naked Eye 2 Visual Aid, not exceeding 7x magnification 3 Tactile (N.B. the comparators are not for assessing cleanliness.) The comparators to BS 7079 are approximately 8 cm square with a 2 cm diameter hole in the middle, and are divided into four segments, by smooth strips. On each strip is an arrow indicating the segment number. Segment one is the smoothest and the degree of roughness progressively increases up to segment four. Using the comparators With all three methods it is important to remember that the prepared surface should not be touched (contamination). For the tactile method the fingernail or a clean wooden stylus may be used. The principle is to compare the surface profile of the blasted steel with the segments on the ISO/BS comparator, looking for two segments between whose profile the test surface lies.



The grading used is: - Fine - Profiles equal to segment one and up to, but excluding segment two. Medium - Profiles equal to segment two and up to, but excluding segment three. Coarse - Profiles equal to segment three and up to, but excluding segment four. Any profile below the lower limit for ‘Fine’ grading is referred to as finer than fine. Any profile above the upper limit for ‘Coarse’ grading is referred to as coarser than coarse. Because the blasted surface is considered to be a secondary profile, the primary profile is the surface of the steel prior to abrasive blasting. The primary profile is therefore going to have an effect on the secondary profile. It is customary to report on the condition of the substrate before preparation in the following manner. Preparation of steel substrate before application of paints and related products Rust Grades. BS 7079 Pt A, ISO 8501, SS 05 59 00 The numbers given all refer to the same book, which gives high quality pictorial standards for condition and cleanliness before and after surface preparation, by abrasive blasting, hand and power tool cleaning and flame cleaning. The steel can then be graded. E.g. B. SA 3, from the definitions below. Rust Grade A - Steel surface largely covered with adherent millscale with little if any

rust. Rust Grade B - Steel surface, which has begun to rust and from which the millscale has

begun to flake. Rust Grade C - Steel surface on which the millscale has rusted away or from which it

can be scraped, but with slight pitting visible under normal vision. Rust Grade D - Steel surface on which the millscale has rusted away and on which

general pitting is visible under normal vision. The original rust grade is then given a degree of cleanliness, i.e. a grading relating to how much contaminant is left on the surface after preparation. The degree of cleanliness is mainly dependent on the time spent on the area and the velocity of the particles.



Abrasive Blasting Grades Before surface preparation commences any oil or grease should be removed (by specified solvent or proprietary degreaser) and heavy rust and scale removed by chipping. After preparation the surface should be free from dust and debris. Sa 1 - Light Blast Cleaning. When viewed without magnification, the surface shall

be free from visible oil grease and dirt and from poorly adhering mill scale, rust, paint coatings and foreign matter.

Sa 2 - Thorough Blast Cleaning. When viewed without magnification, the surface shall be free from visible oil grease and dirt and most of the millscale, rust, paint coatings and foreign matter. Any residual contamination shall be firmly adhering.

Sa 21/2 - Very Thorough Blast Cleaning. When viewed without magnification, the surface shall be free from visible oil grease and dirt and from millscale, rust, paint coatings and foreign matter. Any remaining traces of contamination shall show only as slight stains in the form of spots or stripes.

Sa 3 - Blast Cleaning to Visually Clean Steel. When viewed without magnification the surface shall be free from visible oil grease and dirt, and shall be free from millscale, rust, paint coatings and foreign matter. It shall have a uniform metallic colour.

From the above definitions it can be seen that Sa 1 and Sa 2 are not achievable on rust grade A and consequently there are no photographs for the grades. The American SSPC and NACE (Steel Structures Painting Council and National Association of Corrosion Engineers) have their own systems and compare as below.

BS 7079 PtA SSPC NACE Sa 3 White Metal SP5 Grade 1 Sa 21/2 Near White Metal SP10 Grade 2 Sa 2 Commercial Finish SA6 Grade 3 Sa 1 Light Blast and Brush of SP7 Grade 4

Equipment 1 Wheelabrators Wheelabrators, sometimes known as centrifugal blast units are a mechanised way of preparing components for coating. They are ideal for long production runs on similar section components such as pipes in a pipe coating mill, or bridge steelwork. They are usually referred to by the number of ‘wheels’ which they operate e.g. 6 wheel. Special machines are designed for special circumstances e.g. flat steel plated for fabrication yards or ship yards, pneumatically driven operator controlled machines for blasting decks or internal tanks, magnetic crawlers for tank externals.



The operators of these machines prefer shot as an abrasive, grit cuts the impellers and entails large amounts of downtime, but when the specification demands, it must be used. The abrasive is gravity fed into the centre of the wheel. Centrifugal forces carry it to the end of the impeller where it is impelled at the component to be cleaned at a speed of 220 mph app. in a fan pattern. The fast moving metallic abrasive shatters millscale, cuts a profile etc., ricochets and eventually, its kinetic energy spent, drops. The floor of the unit is open grating over a ‘V’ shaped pit, in the bottom of which is a rotating screw which carries the spent abrasive plus detritus into a hopper. A conveyer system then carries the abrasives to the top of the machine, dispenses it, to start a gravity fed path back to be re-used. As an integral part of the system the abrasive passes aver a tilted plated, known as a weir plate. As the abrasive and detritus cascades over the edge of the weir plate, a current of air is drawn through it. This draws out low density materials such as rust, millscale, flakes of paint etc., and finings, abrasive worn so small that it is no longer useful. This is known as an Air Wash Separator, the same principle is used in enclosed grit blasting pens. Meanwhile the cleansed abrasive is fed back into a common hopper with feed lined to all the wheels, to be re-used. As mentioned previously new abrasives need to be added periodically to maintain an adequate working mix. Considerations The quality can be controlled by adjusting the feed roller speeds and therefore is more consistent. Because the system is totally enclosed there is efficient use of abrasives. More operator safety because the operator is not involved. The systems can be far more productive (dependent on supply of components) than open blasting. One major problem is access to bolt pockets, gussets and stiffeners etc. Because the wheels are fixed, there is no manoeuvrability, and thus shadow areas arise. One way to avoid this is manually blast difficult areas prior to machine blasting. Air Blasting Site blasting is normally carried out using expendable abrasives and open blasting systems. Open blasting systems operate using. a) A compressor. b) A pot containing the abrasives. c) Vapour Traps for oil and water (knock out pots). d) A hose, usually carbon impregnated. e) A nozzle f) A dead mans handle for operator safety.



a) Compressor Compressors are rated by two factors. i Air pressure – measured in psi, pounds per square inch. ii Capacity, the amount of air it can deliver at the pressure required, in cubic feet per min

cfm, or litres/min. It is normal in the UK for portable compressors to be set at 100 psi, which is considered to be the ultimate pressure for open blasting. Air abrasive mix and stand off being constant it is considered that blasting at 100 psi gives 100% efficiency. Using pressures over the 100 psi uses more abrasives, more fuel, more effort from the operator, more work by the compressor, without a proportionate increase in area blasted, where as every 1 psi drop in pressure results in an efficiency drop of 11/2%. 80 psi blasting pressure results in 70% efficiency. Although this is not a responsibility of the inspector it is required information. It is far better to have a large capacity compressor working below its capacity than to have a smaller rated compressor working to full capacity. b) Blast Pot For site work the most common is the pressurised blasting pot. These are supplied in various sizes and are selected according to purpose. E.g. it would not be economical to recharge the pot every 5 minutes when blasting a large crude oil tank. The pots are charged with abrasives and when pressurised, seal, rubber to rubber, by means of a mushroom shaped cap. The abrasive is blown by air pressure into the air stream feeding the nozzle. The abrasive flow can be adjusted by means of a metering valve on the conical base of the pot. This is sometimes called a ‘miser’ valve. c) Vapour Traps Air contains water vapour and when air is compressed the water vapour in the air is compressed. Compression produces heat and as the air heats up its capacity to hold water increases, every 110C rise in temperature the airs capacity to hold water doubles. Conversely when the air cools rapidly on expansion, exiting the nozzle, water droplets are formed. Should this water contact the substrate, corrosion would result. Also atomised oil (from the cylinder lubricants) needs to be extracted, otherwise low surface energy material, oil, on the substrate will adversely affect adhesion. The knockout pots are on the main airline and are inverted transparent glass domes. A small cock on the bottom allows them to be emptied, and usually are kept slightly open. In the UK climate it is not unusual to blow downstream 20 gallons of water in an eight-hour working day.



d) Carbon impregnated Hose Because pressure drops along the length of the hose, line lengths are better restricted to around seven to eight metres. Internal couplings reduce the hose diameter and act as pressure reducers, cause turbulence and wear, so external couplings should be used. Hose diameter is related to nozzle size and should have an internal diameter at least three to four times the nozzle diameter. Any specified blasting pressure refers to pressure as taken at the nozzle. This can be measured using a hypodermic needle gauge. The needle is placed through the hose near the nozzle with the needle facing towards the nozzle. e) Nozzles The air consumption and air speed are directly related to the nozzle aperture size. The larger the nozzle size the more air will be needed to maintain pressure. Typically a ¼" nozzle will need 103 cfm to maintain 100 psi, where as a ½" nozzle needs 413 cfm. Therefore big nozzle, large bore hose, needs high capacity compressor. Sometimes the nozzles are lined with tungsten carbide or ceramics to reduce wear. Various types of nozzles exist including angled nozzles straight bore and venturi. The venturi shaped nozzle give a larger blast pattern with a more even spread of abrasives and higher velocity of the particles at approximately 450 mph. The straight bore nozzle gives a small concentrated area of abrasive contact with a fringe area of lower concentration and particle speed of around 200 mph. The stand off distance for both types varies according to hose size and nozzle aperture size, but an average figure is around 450mm. f) Safety to 1GE SR 21 With enclosed systems like wheel abrators, personnel passing the equipment are far safer than in site situations, abrasives are confined in a small area. When abrasive blasting is taking place on a construction site or pipeline, access is not restricted and vehicles and personnel can be within close proximity of the equipment. It is therefore necessary to have warning signs advising that abrasive blasting is in progress, along with warning buntings segregating the area. Other safety considerations are. i The hose should be carbon impregnated to reduce the chance of the operator getting

electric shock from static. ii A dead mans handle should be under direct operator control for his/her own safety. iii Hoses should be kept as straight and as short as possible to avoid kinks, and blowouts and

to maintain pressure at the nozzle. iv Use reinforced hoses if possible. v Use external bayonet type couplings, continually bonded. vi Maintain operating pressure at 100 psi. vii Correct protective clothing should be worn by the operator, including direct air fed helmet,

with adequate visors, leather aprons and gloves, boots and ear protectors.



Water Blasting Surface preparation methods using water are more environmentally friendly than open blasting and also, from the safety aspect, spark free. They are ideal for removal of soluble salts, sulphates and chlorides, (the hygroscopics) although complete removal needs high pressure ranges. Wet blasting methods are also ideal for removing layers of toxic materials, e.g. red lead, calcium plumbate, and zinc chromate primers. These materials are safe during application but removal by abrasion results in fine particulate matter passing into the air, which can then be inhaled and passed into the bloodstream. There are certain disadvantages related to wet blasting e.g. supply of large amounts of water and disposal of the resulting slurry (water and detritus as an entity) and also mixing substrate inhibitors if the specification demands it. (Substrate inhibitors are substances usually sodium compounds, added to the water, to retard the formation of corrosion products) Some organisations, including B G do not allow the use of inhibitors, in which case wet blasting is followed by dry blasting, to remove light oxidation. High pressure water blasting up to 30 000 psi (water jetting) Using pure water, usually out of a rotating head giving alternating pencil and fan jets. Water usage is about 60 litres per minute. To work efficiently the head must be near to the surface, within 25 to 35 mm, and as the distance increases the efficiency reduces, until at approximately 250 mm only loose and flaking material will be removed.. The principle of operation is simple and flexible, but operator fatigue is a problem. This system will remove soluble contamination and millscale at the higher pressure ranges but will not cut a profile. It will only clean up the original profile on rework areas. High pressure water plus abrasive injection This system operates at about 20,000 psi. and uses abrasives, either gravity fed into the system, suction fed or mixed as a slurry. Marine growths e.g. barnacles, are easily removed with this system and it us often used in dry-docks on ship hulls. Because of the abrasives a profile is cut using this method. Low pressure water plus abrasive injection Uses normal blasting pressures of 100 psi. but with water as a propellant rather than air. The abrasive content is semi-soluble e.g. Sodium Bicarbonate crystals, talc, chalk, and ideal for use on non-ferrous metals and G. R. P. Sodium Bicarbonate is excellent for acidic or greasy situations. This method is very slow and controllable and can if needed, remove one coat of paint. The abrasives have a very gentle action but leave masses of problematic slurry.



Steam Cleaning Ideal for oily and greasy situations, but steam production requires a heat source, which is not conducive with the oil and gas industry.

Air blasting with water injection Water is injected, with or without an inhibitor into the air/abrasive stream, either immediately after it exits the nozzle or immediately before it enters the nozzle. Water usage with this method is approximately one to one and a half litres per minute, which is sufficient to control dust.

Hand and power tool cleaning. 7079 Pt A, ISO 8501, SS 05 59 00 Any hand operated or power tools, including needle guns, wire brushes, emery cloth and grinders can be used to achieve these standards. Hand and power tool cleaning methods are tried and tested over many years, but are now considered to be far less efficient than other modern methods. Limited access or environmental considerations may be factors which influence the choice of methods. Hand and power tool cleaning is often specified for short term maintenance programmes. One major disadvantage of this method is the lack of surface profile. Wire brushing will not produce a profile and in most cases will actually reduce an existing profile, sometimes resulting in burnishing, which is polishing, and a smooth shiny area does not provide good adhesion. Burnishing needs to be treated by abrading with coarse emery. As with abrasive blasting heavy rust, oil and grease need to be removed prior to preparation of the substrate. St2 – Thorough hand and power tool cleaning. When viewed without magnification the surface shall be free from visible oil, grease and dirt and from poorly adhering millscale rust, paint coating and foreign matter. St3 – Very thorough hand and power tool cleaning. As for St2 but the surface shall be treated much more thoroughly to give a metallic sheen arising from the metallic substrate. There are no wire brushing grades for Rust Grade A as the millscale is much harder than the bristles on the brushes, which are of non sparking alloys such as phosphor bronze and beryllium bronze. If needle guns, jasons hammers, are used they tend to leave a very coarse profile which invariably needs to be reduced by abrading with emery, or grinding.



Flame cleaning Not likely to be used on oil and gas plants, but it is an approved method of surface preparation, with photographic standards. The BS 7079, ISO 8501 (SS 05 5900) contains four photographs showing flame cleaning standards from the original rust grades A, B, C, D. The designation given is AFl, BFl, CFl, and DFl. There is only one flame cleaning standard for each rust grade. Three factors contribute to how flame cleaning works. 1. Expansion All materials have different co-efficient of expansion. I.e. all expand and contract at different rates per degree centigrade rise or fall in temperature. Millscale is chemically bonded to the steel and applied heat causes the materials to expand at different rates, thus breaking the chemical bond. 2. Dehydration Water in the corrosion products and in the fissures etc. is evaporated away, facilitating the removal of the corrosion products. 3. Heat penetration The heat is conducted efficiently into the substrate aiding the drying of the steel and removal of penetrated oil or grease. It is not wise to use this method of surface preparation on any fasteners relying on tension, e.g. rivets, screws, nuts and bolts. Method The operator slowly passes an oxygen/HC gas flame (Butane, Propane, Acetylene) over the area to be cleaned, (weld preheat torches or specially adapted lances) to burn and de oxidise the corrosion products and other contaminants. This leaves a grey coloured ash deposit. A second operator follows on with a power brush to remove the now loose, ash deposits. The primer can now be applied over the warm steel, reducing the need for addition of thinners. Other benefits are that the heat reduces the viscosity of the paint and gives better flow properties. The paint can then 'wet out' better and pass into tiny cavities and irregularities on the surface. The heat also accelerates the drying process and keeps the steel above dew point temperature.



Pickling Pickling is a general term relating to the chemical removal of oxides (rust), from a metal substrate. The metals can be either dipped (totally immersed) in the pickling fluid or sprayed with it. Usually aqueous solutions of acids are used for steel, they convert the oxides into soluble salts e.g. Sulphuric Acid produces Iron Sulphate salts. Sulphuric is the most common acid used for economic and safety reasons. Footners Duplex System involves the pickling process followed by a passivation process using Phosphoric or Chromic acid along with a small percentage of iron filings, which produces Iron Chromate or Iron Phosphate salts, which are not soluble. These form a rust inhibitive layer, which passivates the surface and increases the adhesion properties. They are also extremely resistant to cathodic disbondment. A typical process would be: - 1. Any oil or grease needs to be removed by using a suitable solvent e.g. xylene or as

specified. Oil and grease show up as fluorescent yellow/green under an ultra violet light. 2. Totally immerse in a bath of Sulphuric Acid, 5 – 10% concentration at a temperature of 65

– 70oc. Time can vary from 5 to 25 minutes depending on degree of contamination but is invariably at the lower end.

3. Rinse using clean warm water to remove the layer of soluble salts formed. If required the component could be coated after pickling. Likewise components can be blast cleaned and sent on for phosphating/chromating, but the patented process is only called “Footners” when pickled then phosphated/chromated.

4. Immerse in a bath of phosphoric/chromic acid, 2% solution at 80oc for approximately one to two minutes with iron filing (0.5%) (and an inhibitor to prevent embrittlement). This leaves a very thin layer of iron phosphate/chromate, which acts as a rust preventative for a limited time.

5. Rinse in clean water, and check for pH values. pH is a measure of acidity or alkalinity of a substance and is measured using pH indicator strips. An indicator such as litmus will only tell if a substance is an acid or an alkali. Indicator strips give a measure of acidity or alkalinity, based upon the scale below. Figure 2.8 pH scale This is a logarithmic scale and seven is neutral, the pH value of distilled water. From 7 to 0 the acidity increases, and from 7 to 14 the alkalinity increases. A typical requirement after rinsing will be in the region of pH 4.5 to 7.0, slightly less acidic than household vinegar.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Alkaline Acid



Vapour degreasing Fumes from a solvent bath condense on a component suspended over the bath and dissolve any oil or grease, which then drips back into the bath. Very rarely used because of modern regulations regarding strong hydrocarbon solvents. Weathering Weathering relies on co-efficient of expansion properties as mentioned in Flame Cleaning. When left in a stockyard, open to temperature changes, day and night, the millscale sheds. This can now leave the steel open to atmospheric corrosion, which produces such as Sulphate salts.



Painting Inspection Grade 3/2. Rev 1 April 2004 Surface Contaminants 3.1 Copyright © 2003, TWI Ltd


SURFACE CONTAMINANTS AND TESTS FOR DETECTION Any contaminants left on a prepared substrate will effect the adhesion of a coating to that substrate, and therefore specifications often request that certain tests are done to ensure that contamination is within set criteria. Some tests are qualitative and some are quantitative. A qualitative test is one, which give a result as accept/reject, pass/fail, go/no go, whereas a quantitative test is one, which gives a result in known units e.g. milligrams/m2.

Test for soluble iron salts This is a qualitative test, it will not even differentiate between the salts. It will detect the presence of either Sulphates or Chlorides. This test is known as the Potassium Ferricyanide test, although it is now under a new universal naming system, known as Potassium Hexa-cyanoferrate, a name more descriptive of its formula. Test papers, usually Whatman No3 laboratory filter papers are soaked in a 5 – 10% solution of potassium ferricyanide and distilled water, and left to dry. The result is a lime green paper, fringed with an orange brim. The area of blast to be tested is sprayed with a fine mist of distilled water, (any other water is likely to contain dissolved salts), and left a few seconds to allow the salts, if present, to dissolve and form a solution. A potassium ferricyanide test paper is then applied to the area and by capillary action draws up the solution like blotting paper. If there are any dissolved salts they react with the potassium ferricyanide to form potassium ferrocyanide. The ferrocyanide is prussian blue and shows as blue spots on a lime green background.

Test to detect soluble chlorides The test for detecting chloride salts is known as the Silver Nitrate Test. As with the previous test a solution of silver nitrate, 2% with distilled water, is made and the Whatman papers cut into strips. The strips are then soaked in the solution and pressed onto the area under test for about 20 seconds, then washed in distilled water.



The reaction between silver nitrate and any chloride salts present produces silver chloride, which remains on the strip after washing. If the strip is then dipped into photographic developer the chlorides show up as black/brown.

Other tests for salts 1 Merkoquant A salts/water solution is made by swabbing an area of 150 mm x 150 mm with distilled water, 22.5 ml. Merkoquant strips are then dipped into the solution and the resulting colour change is compared to a master chart on the container. The concentration is read off from the chart. 2 Bresle sample patch Reported as being 95% accurate. An adhesive patch with a rubber diaphragm is stuck onto the surface and distilled water injected and extracted several times to produce a solution of any salts present. By a process of Mercuric Nitrate Titration concentrations of 15 mg/m2 can be detected. A quantitative test. 3 Salt contamination meters Salt contamination meters measure the resistivity or conductivity of a given sample and convert this value into a concentration (mg/m2). With any of the above tests, if the amount of salts present is greater than specified, the area should be washed down with copious amounts of clean water, reblasted and retested.

Test to detect the presence of millscale Millscale being cathodic in relation to steel can cause corrosion cells under a paint film and subsequent early disbondment. Millscale in small quantities is permitted on a SA 2½ blast standard, but not on an SA3. Therefore the test needs to be carried out only if the specification requires an SA3. Blasted steel is dark grey in colour and millscale is dark blue, so by naked eye the contrast is difficult. However, if the surface is sprayed with a fine mist of slightly acidic copper sulphate solution, the solution ionises and tints the steel copper colour and blackens the millscale, if present, thus providing a better contrast. If this test indicates millscale presence then it should be reblasted and then retested.



Test to detect the presence of dust on a substrate Any dust on a blasted substrate will adversely effect the adhesion of a paint film. In conditions of low relative humidity, dust and finings passing down a blast hose become electro statically charged and stick onto the substrate. Brushing or air blowing the surface will not remove them, self adhesive tape however, will. If a piece of self adhesive tape is stuck onto the surface and snatched off, the dust/finings sticks to the tape. By then sticking the tape onto white paper the dust can easily be seen.

Test to detect the presence of moisture on a substrate Presence of moisture, even in the teeniest amount, can affect the choice of paints and if work can be done or otherwise. A very simple test for the presence of moisture is to sprinkle with talc or powdered chalk and then lightly blow away. The powder will stick to areas where moisture is.

Test to detect the presence of oil or grease Other than ultra violet light, oil and grease can be detected by dropping solvent onto the suspect area, and absorbing the solution on Whatman or blotting paper. The solvent will evaporate and oil or grease will give a darker appearance.



Painting Inspection Grade 3/2. Rev 1 April 2004 Paint Constituents 4.1 Copyright © 2003, TWI Ltd


PAINT CONSTITUENTS AND BASIC TECHNOLOGY Paint is a material, which will change the texture colour or appearance of a surface and give some form of protection to the underlying surface. Paint has been classified in many ways e.g. by principle involved. 1. Barrier The material forms a thick impermeable layer of a high electrical resistance e.g. urethane. 2. Passivation Causing a chemical reaction between the paint constituents and the substrate e.g. rust inhibitive primers. 3. Cathodic protection Employs the bi-metallic principles by using a less noble metal as pigmentation e.g. zinc in zinc rich primers. By function e.g. Anti Fouling - To inhibit marine growth on ship hulls Road Marking - To give white or yellow lines on roads Fire Proofing - To provide resistance to fire Heat Resistant - For surfaces working at high temperatures Anti-corrosive, and many more. Paints can be classified by binder type (the main constituent) or by colour, and in some cases even by the pigment type. No matter which identification system is used, all the paints contain the same basic ingredients. 1. Binder 2. Pigments and other additives 3. Solvent (where applicable) It is the chemical structure and composition of these constituents, which gives the paints their own individual properties. Paints are supplied as either liquids or solids in powder form and can be subdivided into groups.



a) Liquid paints containing solvent This group is still the largest in terms of sales. It is important to realise that solvent does not relate solely to Hydrocarbon solvents, but also includes water. Due to the modern EPA (Environmental Protection Act) requirements, manufacturers are researching into new paint technology involving vastly reduced amounts of volatile organic compounds. Some are using water based technology, some are concentrating on the solvent free materials. b) Solvent free As the name implies these materials contain no (or in some cases a minute amount of) solvent. These are generally chemical curing materials which require the mixing of two or more components and usually go under the name of MCLs (Multi Component Liquids). Some MCLs are made using solvent borne materials. c) Powders Virtually solvent free MCLs, which are solid at, room temperatures. The base resin and the chemical activator, along with the other constituents required to complete the formulation are heated up to the resins melting point, mixed into an homogeneous liquid, cooled and ground into powder form. In theory every particle contains all necessary ingredients to effect a cure into a protective film. The powder can be applied onto a preheated substrate (in the case of substantial steel thicknesses) at about 240oc, or onto thin plate electro statically and post heated. In either case the powder melts, undergoes a chemical reaction and in approximately three minutes the reaction is complete. The three subdivisions are all made up from the basic ingredients mentioned earlier, Binder, Solvent, Pigment and other additives.

Binder The binder is the main constituent of a paint and is often referred to as a film former. Other terms are vehicle and non volatile. A paint binder is selected according to the function the paint has to perform within vastly different environments. Some major considerations of a binder are: - 1. Ease of application (flow properties or viscosity). 2. Adhesion to the substrate for the expected life of coating. 3. Resistance to abrasion. 4. Resistance to chemical attack according to environment. 5. Cohesive strength, its ability to hold together as a film. 6. Dialectric strength. 7. Ability to resist the passage of water. 8. Ability to change from a liquid as applied, into a solid to provide the above properties, and

others, for the expected life of the coating.



Several materials satisfy the criteria above for different environmental conditions, among them are: - a) Acrylic Synthetic resins, can be used in H C solvents or water. Good colour retention, good film properties can be hybridised with other binder’s e.g. Urethane modified Acrylic as used by BG b) Alkyd A term derived from alcohol – acid reaction, usually associated more with the domestic market, they have a low resistance to alkalies. In common with most resins they are brittle and need modification with oils. c) Ashphaltic Bitumens Petroleum based materials, thermoplastic, relatively inexpensive, known for water proof properties, poor resistance to sunlight, very low resistance to solvents. d) Cellulose Resins Synthetic material, not extensively used for industrial coating but a good example of reversible materials. e) Chlorinated Rubber Organic resins derived from reaction of rubber with Chlorine. Widely used years ago until strict VOC regulations came into force. Especially resistant to alkalies and acids and were used on chemical plants, water treatment etc. Very poor resistance to HC solvents. Still found on some structures. f) Emulsions Obviously not used for anti corrosive systems but are included for other factors e.g. Drying mechanisms. g) Epoxies Synthetic organic resins, generally provide good chemical, solvent and water resistance. Good exterior durability but are prone to chalking (discussed later). Epoxies come as two pack, single pack, solvent free and solvent borne. h) Ethyl and Methyl Silicates Inorganic materials with excellent weathering, solvent and heat resistance. When cured the binder is a silicate, which contains a high percentage of zinc dust, thus protecting by galvanic action.



i) Natural oils Many natural oils can be used in the paints industry but because of their slow drying properties, cannot be used on their own as binders. They are mixed with resins to modify the film properties. Some natural oils used in the paint industry are Linseed Oil, Tung Oil (also known as China Wood Oil), Soya Oil, Tall Oil and Safflower Oil. j) Natural resins Natural resins are brittle by nature and fast drying. As mentioned above they need to be mixed with oils to modify some properties. A mixture of oil and resin is known as “oleoresinous”. Examples of natural resins are copals, dammars and coumarones. Natural resins are not soluble in water. k) Phenolic resins Made from phenol and formaldehyde, coal derivatives, characterised by excellent adhesion properties and resistance to heat and chemicals. Were used in temperature ranges where Chlorinated Rubber couldn’t be used e.g. greater than 65oc. Commonly called hot drying oils. l) Polyurethane’s Can come in several forms, Moisture Curing, two pack polyurethane’s, chemically curing and single pack. Industrial coatings are mainly the first two. They produce an excellent synthetic coating, with outstanding abrasion resistance, chemical resistance, and good exterior gloss and colour retention with a minimum of chalking. m) Silicones Designed as high temperature service materials for temperatures ideally above 150oc service temperature. Usually carbon or aluminium pigmented, they are used to seal inorganic zinc silicates or metal sprayed surfaces. n) Styrene Styrene is sometimes referred to as a binder and is used to modify other properties. Styrene is referred to as a vinyl type monomer and is used to cross-link the film. o) Vinyl The actual composition of the vinyl depends upon the designed end use, but in general has slightly better properties than a similar material, chlorinated rubber. However vinyls use a different solvent group, and water. CR is limited to one solvent group.



Binder – solvent groups and compatibility A solvent free binder, or a binder using a very weak solvent, will cause very few problems when over coating another product. Usually in this situation the problem would be limited to different expansion and contraction ratios. Providing a key by abrading can mostly rectify or at least minimise this. However, a very strong chemically curing binder like epoxy, needs a strong solvent and can cause problems over coating other materials, even when they are fully cured. Guide to binder solvent combinations Solvent strength in descending order

Common Names Binders

Water Emulsions PVC/PVA Vinyl’s Acrylics – other materials e.g. epoxy Bitumins, Polyurethanes, Alkyds, Acrylated Rubbers

Aliphatic Hydrocarbons White Spirit Turpentine Turpentine substitute Solvent naphtha’s Hexanes upwards

Natural oils Natural resins Alkyds Phenolics

Aromatic Hydrocarbons Xylene Toluene Benzene

Chlorinated Rubber

Ketones Acetone Methyl Ethyl Ketone Methyl ISO Butyl Ketone

Epoxy

Embolden name is the main one used. Polyurethanes use ketones and esters with aromatic diluents. In descending order down the table the solvent groups increase in strength. It is not advisable to use a binder with a strong solvent over an existing coating, which uses a weak solvent. For example Chlorinated Rubber coated over an Alkyd would result in lifting, and wrinkling, but Alkyd over Chlorinated Rubber would have no ill effect. Because an epoxy is chemically cured, there is no problem over coating with polyurethane two pack, chemically cured, but a hydrocarbon solvent borne epoxy coating applied over Chlorinated Rubber would not be advisable.



Ethyl and Methyl Silicates do not appear on the list because they are high (or low) temperature performance coatings, the criteria for compatibility with these materials for over coating is working temperatures. I.e. will the over coating material withstand the operating temperature? Usually the only material suitable is silicone. Ethyl and Methyl Silicates will not adhere over any substrate other than bare, clean steel. Any binder which can be converted into a polymeric salt can be modified to be water based and many of the binders mentioned above fall into that category. Chlorinated rubber doesn’t, neither can it be made using reduced amounts of solvents, and therefore to comply with modern EPA requirements its usage now is limited, although many structures, both on and off shore are still coated in this material. It used to be the main material for ambient temperature usage for BG The advantages of using this material were: - 1. Because of the chlorine content, high resistance to mould growth. 2. Again because of the chlorine, non-flammable after solvent release. 3. Very resistant to chemical attack e.g. Acids and Alkalis. 4. Very high resistance to water vapour transmission. 5. Material is non toxic and provides a very durable film. 6. Very easily maintained, no abrasion needed, clean surface only. Disadvantages were: - 1. Its position on solvent compatibility list shows low resistance to solvents i.e. only resistant

to Aliphatics and Water. 2. Low temperature tolerance, 65oc maximum. 3. Spray application resulted in ‘cobwebs’. Polymers One of the properties expected of a binder is to change from a liquid into a solid to form a film. To perform this function all binders form polymers or use polymers already partially formed. The word polymer means literally many parts, poly = many, mer = single unit or part. Mer (meras GK) can be a single atom, or a molecule, (a group of atoms) and can be described as being “a string or structure of repeated units”, and polymerisation is the “joining together of a string or structure of repeated units”. In the case of most paints the main constituents of the polymers are: - H - Hydrogen C - Carbon N - Nitrogen O - Oxygen Cl - Chlorine Although there are variation the main three polymer types are Linear, Branched and Cross-linked



1 Linear Polymers As the name implies the atoms or molecules which form the polymer, join on at the end of the structure, and in so doing saturate the structure. This type of polymer is also referred to as, solution polymer. Figure 4.1 Linear polymer Each shape represents a molecule (mer) joined to the next by a single line, an ionic bond, an electron joining to the next molecule. The process depends upon the properties of carbon, which forms the backbone of the structure. Carbon can give away electrons, take in electrons, share electrons, or join with itself in many ways.

H |

H – C – H |

H

H H | |

H – C – C – H | | H H

H H | |

C = C | | H H

METHANE

SATURATED

ETHANE

SATURATED

ETHYLENE OR ETHYNE

UNSATURATED The Ethylene or Ethyne molecule is defined as being unsaturated, the two carbons are sharing electrons, hence leaving potential for the spare electrons to combine with another molecule or radicle. Figure 4.2 Ethylene molecules close together The above figure represents ethylene molecules close together. The dotted line being the weaker bond (the secondary valency bond). This being the one that joins to the next molecule giving: -

H H | | C...... C | | H H

H H | | C...... C | | H H

H H | | C...... C | | H H

H H | | C......C | | H H



Figure 4.3 Ethylene molecules polymerise This gives saturation throughout the polymer, no activity points (polyethylene polymers, depending upon density vary from 25 to 35000 molecules) as both ends are closed off with a Hydrogen atom. It can be seen that linear polymers, once formed, cannot react with anything to chemically produce another compound, and until destruction will maintain the same structure and properties. A linear polymer is a non-convertible or reversible material and also thermoplastic. From the binder types the linear polymers are Acrylics, Vinyls, Chlorinated Rubber, Asphalt and Coal Tars and Cellulosic Resins. 2 Branched polymers Branched polymers are formed by combining oxygen with the double bonds available. Oxygen, from the atmosphere, a very reactive element, combines with a constituent of natural oils and resins called fatty acid esters. The double bonds in these fatty acid chains are not at the end of the structure, but in the middle. So any combination doesn’t occur lengthways to elongate the chain, but forms a branch from the main carbon backbone. Because of the abundance of reactive oxygen in the atmosphere, the branching carries on and on over several years until eventually the matrix becomes cross linked and very brittle, and cracks and flakes off. Binders, which fall under this category, are Natural Oils and Natural Resins, and isomers such as Alkyds and Phenolics. By combining with another element and chemically reacting to form another compound, these materials become non-reversible or convertible coatings, thermosetting. Figure 4.4 Branched polymer

H H | | C C | | H H

H H | | C C | | H H

H H | | C C | | H H

H H | | C C | | H H

| C H | H C H | H C H H

| C = C - C = C - C | | | | | H H H H H

OH

O

Oxygen Another chain



3 Cross linked polymers Cross linking, or chemical curing is a three dimensional polymerisation process which occurs fairly rapidly using only components provided in the cans. Because the components are in calculated amounts the cross linking stops when all the available bonds are occupied. Some urethanes fully cure in 16 hours, some epoxies in three days, and others in seven days, dependant on temperature. Figure 4.5 Cross linked polymer



Oils Natural oils (vegetable oils) are produced from seeds of a plant, well known examples being linseed, castor, olive, coconut, soya and tung oil. In order to be usable as a paint binder the oil must be of a type that will combine with oxygen, i.e. it must be “unsaturated”. A saturated oil cannot be used as a binder because it will not solidify by polymerisation to form a film. Therefore, oils can be divided into three groups. Drying oils Semi drying oils Non drying oils 1 Drying oils Drying oils are oils which have three sets of double bonds along the carbon backbone, and react with oxygen readily at ambient temperature. 2 Semi drying oils Semi drying oils have one or two sets of double bonds, and may need heat addition, or some other catalyst to promote oxidation. 3 Non drying oils Non drying oils will not oxidise and therefore cannot be used as binders. Instead these are used as plasticisers in paint formulation, to modify properties of a resin. Although linseed oil and tung oil used to be referred to as rapid drying oils, the term rapid was compared to some other oils, and in fact it could be many weeks before a reasonably resilient film was formed. Treated natural resins have the exact opposite properties, i.e. fast drying and very brittle. Oils and resins are mixed to give a binder with modified properties. Long oil paint – more than 60% oil to resin, elastic, slower drying properties suitable for domestic applications, decorative materials. Medium oil paint – between 45 – 60% oil to resin. Short oil paints – less than 45% oil to resin, faster drying material, suitable for steelwork. More brittle with shorter over coating time.

Pigments Pigments have many properties and characteristics. They are derived from many sources, animal, vegetable, mineral and synthetically produced, and can be in a wide variety of particle sizes and shapes. Pigments used in paints must remain as solid particles within the vehicle (the binder plus the solvent if a solvent is used), and not dissolve. If it dissolves it is known as a dye, not a pigment.



Pigment particles contribute to the paint films strength cohesively, its abrasion resistance, durability, opacity, in some cases impermeability and resistance to ultra violet rays. Some pigment particles are as small as 1/10

th micron. Pigments can be subdivided into groups according to the main function they perform in paint. Rust inhibitive pigments. Anticorrosive Rust inhibitive pigments are added into primers to protect the steel substrate by passivation. Typical materials in the category are: - a) Red lead * b) Calcium plumbate * c) Coal tar * d) Zinc chromate * e) Zinc phosphate f) Barium metaborate g) Zinc phosphosilicate Zinc phosphate is the most commonly used material from the list. The four marked with an asterisk are toxic and restricted in use. Red lead is a basic inhibitor and works in the presence of fatty acid esters in natural oils and resins only. These systems provide lead soaps, which give the actual inhibition. Metallic Pigments Metallic pigments are also used on a steel substrate to protect the steel, but this time by cathodic protection. If a metal which is less noble than steel, (more electronegative) is included in the film, and an electrolyte e.g. water, passes through the film, contacting substrate and pigment particles, then a circuit can be engaged whereby the pigment particles will receive the hydroxyl ions and thus suffer corrosion in preference to the steel substrate. In order to satisfy this requirement the metal pigment must be below the position of steel on the galvanic list. The two most amenable metals to satisfy this are: - 1 Zinc 2 Aluminium Zinc is the better of the two for galvanic protection but Aluminium is excellent for solar protection, reflecting the ultra violet A and B. For every other layer of paint other than the metallic primers, colouring pigments are used, usually know as Opaque pigments.



Opaque pigments Opaque pigments are inert particles with excellent light scattering properties in order to give covering power, (opacity) and colour. 1. Carbon Black 2. Compound of Cobalt Blue 3. Compound of Chromium Greens, Yellows and Oranges 4. Compound of Iron Browns, Reds and Yellows 5. Compound of Calcium Reds and Yellows 6. Titanium Dioxide White Extender pigments Sometimes known simply as extenders or fillers, these materials provide some of the main properties expected of the film, such as adhesion, cohesion, film strength and durability. They also have a role in application and flow, levelling, and other mechanical properties of the film, and are an aid to inter coat adhesion and can reduce gloss. Materials used as extenders are usually low priced readily available materials such as: - Clays e.g. Kaolin, China clay Chalk Calcium carbonate Talcum Magnesium silicate Slate flour Aluminium silicate Laminar pigments Plate like pigments such as MIO (Micaceous Iron Oxide), Aluminium Flake, Glass Flake, Mica and Graphite, provide excellent barriers. These pigments have a leafing effect and in theory overlap when the coating dries. MIO sometimes known as specular haematite is widely specified, and to be regarded as pigment quality material quite often has to meet quite stringent requirements e.g. 85% of the total mineral compound has to be Fe2 O3, haematite, of this 85% less than 1% should be permeable to moisture, thus giving a paint film with high resistance to water permeation. Figure 4.6 Theoretical leafing layers and practical de-lamination In theory when moisture passes into the film, on contact with the MIO platelet, it has to pass around it, thus almost doubling the distance to reach the substrate. Glass Flake as a laminar pigment is usually for abrasion resistance, but in common with the others, improves the tensile strength of the film. Aluminium Flake and MIO have good ultra violet A and ultra violet B reflectance properties, protecting the underlying binder from attack and subsequent degradation. PVC

Theoretical Leafing layers

/ __ __ / ____ \ ___ _____ \ \ / / ___ / __ \ ___ ___ \ / ___

Practical De-lamination



The pigment to binder ratio is a very important factor in the design and manufacture of paint and is known as the Pigment Volume Concentration. There is an ideal pigment binder ratio, which varies from paint to paint, pigment to pigment, and this is known as CPVC, Critical Pigment Volume Concentration. CPVC is defined in BS 2015 as “The particular value of the pigment volume concentration at which the voids between the solid particles that are nominally touching are just filled with binder and in the region of which certain properties are changed markedly. Figure 4.7 Below CPVC Figure 4.8 Near CPVC Figure 4.9 Above CPVC Figure 4.7 – Too much binder to solids ratio, would give a film of good gloss properties, but poor covering power (opacity) and with a tendency to blister (low cohesive strength). Figure 4.8 – A film with lower gloss properties but greater cohesive strength and just enough resin to encapsulate each particle, giving good resistance to water permeation. Figure 4.9 – The CPVC is exceeded and all particles are not wetted, the film would be porous, low in cohesive strength and adhesion.

Solvents Solvents are added to paints to reduce the viscosity and ease application properties. The solvents used in paints have to fulfil various other requirements, for example if a solvent evaporates away too quickly the film will not dry evenly, if it evaporates too slowly drying will be protracted and on vertical surfaces the paint is likely to sag. The four important properties of a solvent are: - 1 Solvent Strength Low molecular weight solvents are stronger than high molecular weight solvents and, strong binders such as epoxies and polyurethanes, need strong solvents to ‘cut’ or separate the molecules. Hence Ketones and Aromatics are used for these materials. Natural resins don’t have the same attraction between the molecules and therefore need weaker solvents, higher molecular weight, such as Aliphatics. 2 Evaporation Rate



The evaporation rate governs at what point the polymerisation starts. For decorative materials a long wet edge time is needed, so a long slow evaporation rate is needed, otherwise dragging and ropiness would occur when joining area to area. Industrial coatings need to dry quickly for protection and so that further coat can be applied. 3 Flash Point The flash point of a solvent is a safety consideration. Roughly defined as “The minimum temperature of the solvent at which the vapours given off are flammable if a source of ignition is introduced.” The higher the flash point, the safer the solvent. 4 Toxicity Solvents, especially modern solvents, are substances hazardous to health, and therefore have predetermined concentrations to which humans can be safely exposed. These limits are expressed in parts per million, ppm.

Other Additives Other than the main constituents of a paint viz, binder, solvent, pigment and extenders, there are approximately fifty other materials which can be added to give other, or alter existing properties. These can be grouped into Aids to Manufacture, Aids to Storage, Aids to Application, Aids to Film Formation, Aids to Film Curing, and others. Some are used more than others, among them being. Anti settling agents An anti settling agent is an aid to shelf life. It is a thixotrope, a thickener, which also allows a higher film thickness. Thixotropic paints are jelly paints, non-drip, and if stirred change to normal liquid consistency. When left they slowly revert to thixotropic consistency. Thixotropic agents are bentones and waxes, and help keep solid particulate constituents in dispersion within the paint. I.e. stop settlement. Plasticisers A plasticiser basically gives paint flexibility and reduces brittleness and therefore needs to be compatible with the binder and have a very low volatility in order to stay in the film for a long time. Alkyd resin was used extensively in Chlorinated rubber binders, but for natural resins and their isomers Non Drying Oils are used, saturated oils, which will not polymerise. Castor Oil, Coconut Oil and some Palm Oils fall into this category.



Driers Also known as oxidants, used in oxidising oils and resins. These are heavy metal salts, rich in oxygen, which are added to the paint during manufacture. Instead of relying on atmospheric Oxygen penetrating the paint layer, the oxygen is already there, to allow even through drying of the film. Common salts are octoates or naphthanates of cobalt, manganese and zirconium e.g. cobalt naphthanate. (The acids producing the salts from the heavy metals are Octoic Acid and Naphthanic Acid) Anti skinning Anti skinning agents are also known as anti oxidants. These are added to oxidising paints to retard the formation of a skin on the surface of the paint. If a skin forms it cannot be stirred back into a solution, and must be removed. Because the anti oxidant works against the oxidant they are added in very small controlled amounts and are liquids usually. E.g. Methyl Ethyl Ketoxime.



Painting Inspection Grade 3/2. Rev 1 April 2004 Solutions & Dispersions 5.1 Copyright © 2003, TWI Ltd


SOLUTIONS AND DISPERSIONS

Solutions A solvent is a liquid, which will dissolve another material, liquid or solid. A solute is the material dissolved by the solvent. A solution is the resulting liquid. Salt and water, sugar and water are solutions, a binder and solvent are also a solution.

Dispersions A paint consists of solid particles suspended in the vehicle, where there is no solubility, so a paint is a dispersion. A dispersion can be either a solid or liquid dispersed within another liquid, where there is no solubility.

A suspension A suspension is when fine particulate solids, e.g. pigment and extenders are dispersed within a liquid, the vehicle. Ideally after the manufacturing process, each particle should be completely wetted by the vehicle. However because the pigment particles are so small, they cluster together to form agglomerates or aggregates. In some paints, especially gloss, the size of these aggregates is a very important factor and so has to be checked. The aggregate size is known as Degree of Dispersion of Fineness of Grind.

An emulsion An emulsion is a liquid dispersed in another liquid when there is no solubility. In vinyl or acrylic emulsion, very tiny droplets of resin are suspended within water, which can now be seen to be a non solvent. In an emulsion water is a carrier, not a solvent. Water is called the continuous phase, and oil/resin is called the dispersed phase.

Painting Inspection Grade 3/2. Rev 1 April 2004 Solutions & Dispersions 5.2 Copyright © 2003, TWI Ltd


Painting Inspection Grade 3/2. Rev 1 April 2004 Drying & Curing 6.1 Copyright © 2003, TWI Ltd


DRYING AND CURING OF PAINT FILMS During the drying/curing process a paint changes from a liquid into a solid. It does this by various mechanisms and combinations of mechanisms. The time it takes to undergo this physical change is governed by several factors including temperature. Generally three terms are used to refer to drying/curing temperatures. a) Air Drying This refers to normal ambient temperatures. b) Forced Drying When heat is needed to effect a cure or accelerate the reaction it is called forced drying, but the temperature range for forced drying is ambient to 65oc. c) Stoving When temperatures above 65oc are used, using ovens or infra red, the term used is stoving. Industrial paints, with a few exceptions e.g. intumescents, are generally in the air Drying category, and the liquid to solid transition is dependant on one of the four drying mechanisms as follows. 1 Solvent Evaporation Paints employing this drying mechanism are linear polymer materials, sometimes referred to as solution polymers. Solution polymers dissolve in the solvent, when the paint is applied the solvent evaporates away allowing the fully formed linear polymers, saturated, with no activity points, to come out of solution and form a film on the substrate. The polymers lie in a random interlocking pattern, similar to cooked spaghetti or noodles and loosely bond together by “ secondary Hydrogen bonds”. The solvents used by these materials are strong solvents and, when reapplied onto the paints, easily penetrate between the polymers and split the secondary bond, allowing the polymer to go back into solution. Materials, which can do this are, called reversible or non-convertible. Chlorinated rubber, vinyl’s, acrylics, cellulosic materials and laquers fall into this category.



2 Oxidation Paints using this mechanism form a film by “oxidative cross linking” (polymerisation) using atmospheric oxygen, and in some cases, the oxygen contained in the driers. First of all if a solvent is present, the solvent evaporates away, allowing the oxidation to begin. Oxygen then combines with the unsaturated bonds on the fatty acid esters, progressively linking them together, to form the film. Once the oxygen has reacted with the binder, it has changed the chemical structure of the binder and cannot be removed. These materials are therefore convertible or non-reversible. Because oxygen is in abundance in the atmosphere the reactions continue, ad infinitum, until the materials crack and peel, having formed a very complex cross-linked matrix. Alkyds, Phenolics, natural oils and resins are materials from this category. 3 Chemical Curing Chemical curing paints need addition of a second material, (in some cases as in moisture curing, water from the atmosphere) but generally the second material, the activator, is supplied in a can, hence the term 2 pack or Multi Component Liquid. In order to obtain the desired film the whole of the contents of both cans should be thoroughly mixed together and instructions on the materials data sheet should be strictly observed. Some materials will require an induction period and most data sheets will state the 'pot life'. An induction period is “The length of time after mixing which the paint should stand before use”. Induction time is also called stand time or lead time, and is recommended to allow thorough wetting of the solids. During the induction period the chemical reaction will commence and will be either: - a) An exothermic reaction. Giving off heat, the container will warm up b) An endothermic reaction. Taking in heat, the container will cool forming condensation. A typical induction period is 20 – 30 minutes. Pot life is the period of time after mixing in which the paint must be used, and with industrial paints, dependant on temperature is usually 6 – 8 hours. After the recommended pot life the material becomes very user unfriendly and if in bulk, is quite often subject to spontaneous combustion. 2 pack materials curing agents Amides – Epoxy curing agents, usually quote seven days to full cross linking at 20 oC. Amines – Epoxy curing agents, three days to full cross linking at 20oc. Isocyanates – Mainly used for urethanes but also for some epoxies where low temperature application is unavoidable, -10oc being typical. Ambient temperature urethanes, especially for pipeline use quote 16 hours to full cure. NB. Isocyanates are very toxic and need great care during use.



Chemically curing materials are convertible or non-reversible. 4 Coalescence Coalescence means to physically join together. In an emulsion the resin droplets are dispersed in the continuous phase, water. Upon application the water evaporates away allowing the resin droplets to come close together until they are touching. At this stage small amounts of high boiling point solvents are concentrated in the voids between the spheres, from where they migrate into the spheres, plasticise them and allow them to fuse together. In so doing they also reduce the Tg of the material (Tg = Gloss Transition and is the temperature at which the material changes from a rubbery to a glossy solid and vice versa). If the Tg wasn’t changed, the resulting film would stay as a liquid and be easily wiped away. These materials e.g. acrylics and vinyl’s are reversible. It is important to remember in this case that water is not a solvent, but if the true hydrocarbon solvent was used the material would form a solution.



Painting Inspection Grade 3/2. Rev 1 April 2004 Paint Systems 7.1 Copyright © 2003, TWI Ltd


PAINT SYSTEMS A paint system is one or more layers of paint, which will give corrosion protection by one of, or a combination of corrosion protection methods. For example, a single layer of Fusion Bonded Epoxy or Urethane would give excellent protection employing the Barrier Principle. A zinc phosphate pigmented primer would be a Passivation system but would need further protection in the form of a barrier system to protect it. An organic zinc rich epoxy would provide galvanic protection through bimetallic principles but would last longer with a barrier system to protect the zinc. Each layer within a system has a function to perform as follows.

Primer A primer will not work as designed anywhere else other than in contact with the substrate. A primer, normally low volume solid materials, wets out the substrate and provides excellent adhesion and also provides a key for any subsequent layer. The binders usually have a relatively low resistance to vapour transmission, and allow water into the film to carry tiny amounts of the rust inhibitive pigmentation onto the substrate to form a passivating layer. Older versions of BG specifications required that all primers should be brush applied. This was to ensure that any dust or detritus left on a substrate was ‘worked’ into the film, and not left lying where air could be entrapped, forming pinholes. Other primers exist for non-ferrous substrates such as Wash or Mordant primers, and PVB etch primers. Mordant means ‘of a corrosive nature, or will bite into”, and as suggested contains an acid, Phosphoric acid. Their use is limited nowadays, mainly through the EPA requirements to reduce VOC emissions. These materials contain approximately 96% VOCs in the form of Ketones, and approximately 4% phosphoric acid, tinted with copper phosphate (blue). Their primary use was for etching new galvanising. The reaction turns the surface black (zinc phosphate salts). Some specifications allowed painting as soon as dry, but others required a water wash. Etchants do not leave a measurable thickness. PVB Etch primers, Polyvinyl Butyrol are principally used on Aluminium, but were used on virtually every non ferrous metal. PVBs are 2 pack materials, low volume solids with a dry film thickness of 15 to 25 um. This material also contains phosphoric acid. The acid etches the Aluminium (Aluminium Phosphate) provided a key for the vinyl binder. The general appearance when dry, is a matt yellow translucent film, with an underlying black or darkened substrate. Some specifications require coating before 16 hours. Because of the acid content if is not wise to spray apply these materials without extraction facilities.



Mid-coats Mid-coats are mainly barrier coats. They are applied over the primers to prevent further water passing into the film and leaching out the inhibitive pigmentation, without which there would be no passivation. Mid-coats also build up the film thickness and even out any irregularities. They also provide a key for any subsequent layer to adhere to. This is done by aggregates and extenders. Some extender materials have particle sizes of 40 um, if there is a high concentration of extenders in the coating then many of these large particles will protrude through the surface, increasing the area available for adhesion.

Finishing coats Finishing coats of a system are mainly aesthetic, but also need certain properties. Colour and appearance are important e.g. gloss. To have a gloss finish the surface must be perfectly smooth, and this also helps in the removal of dust and dirt, and natural drainage or shedding of water. The storage facilities of volatile materials need to have solar reflective properties to reduce boil off and materials needing distillation require heat input and are very often black, to absorb heat.

Moisture tolerant systems Pipelines transport many different products at different temperatures and pressures. Gas is transported in non-insulated pipes, over huge distances subsea and subterranean. Therefore the gas is cool. Where a pipeline comes above ground (an AGI, Above Ground Installation) the gas in the pipes is much cooler than the ambient temperature and condensation forms on the pipes, posing a problem for repainting and maintenance. Either the gas stream can be diverted along another route, or special materials can be used, tolerant of the situation. The BG Transco specifications include a clause permitting the latter alternative, the use of moisture curing polyurethane or a high sold epoxy. (Section SPA4 in paragraph 10). Three definitions apply when referring to quantity of water present. Damp, Moist, and Wet (Paragraph 10). Damp and moist conditions will allow the use of the materials specified, but wet conditions require excess water to be removed. Single pack moisture curing polyurethane’s are materials which use moisture from the atmosphere to cure, not standing water on the substrate. Surface preparation as per the specification, then any excess water should be swabbed off, before brush application of the material. Because the material cures by using air borne moisture, as soon as the lid is removed from the can the cure reaction starts. The more moisture there is present in the atmosphere, the faster the cure. The criteria with this type of material is not high RH, 100% is no problem, but low humidity. Some manufacturers state 35% as minimum RH criteria.



Powder coating materials As mentioned earlier, powder coatings are solvent free materials, which are solid at room temperature.

Thermosetting Thermosetting means the material will cure with the application of heat and therefore are convertible or non-reversible materials like epoxy and urethane. With thick steel sections like underground pipes the powders are electrostatically sprayed onto a preheated substrate, approximately 245oc, as soon as the powder hits the heated steel, it melts, undergoes a chemical cure and is fully cross linked in approximately three minutes. This group of materials is used extensively on subsea and subterranean pipes, office furniture and kitchen white goods. Thinner plate sections are post heated, after electrostatic application of powder.

Thermoplastic Thermoplastic materials soften with the application of heat, are linear polymer and therefore reversible or non-convertible. Polyethylene and Polypropalene being examples of these materials. Usually flame sprayed as repair systems on existing thermoplastic coatings.

Sacrificial coatings As the name implies, this classification of materials sacrifices itself to protect the underlying substrate. In order to work in this way the sacrificial component must be less noble (more electronegative) than the substrate which it is protecting. Zinc and Aluminium are the most common materials used to protect ferrous substrates. Zinc and Aluminium have relatively low melting points and so are commonly used in the form of metal spray, applied by flame onto structural steel e.g. bridges, as an added form of protection which purportedly can extend the major maintenance free life of steel work by as much as 20 years. Zinc is used in hot dip galvanising of steel, to totally encapsulate a section. In this situation the zinc works as a barrier coat initially and undergoes atmospheric corrosion itself forming corrosion products such as Zinc Sulphates and Zinc Carbonates. To stop this natural process on the zinc it is usual to paint over the galvanising. However, if the galvanising is damaged, exposing the steel underneath so that both metals are in contact with electrolyte, the zinc then starts working sacrificially, corroding in preference to the steel, producing Zinc Oxides on the damages faces until the damage is filled to exclude electrolyte contact. The zinc then works as a barrier again.



If the galvanising suffered damage of more than a scratch or gouge repair might be a better option. In this instance a zinc rich epoxy might be used. These materials contain a very high percentage content of zinc pigment. Specifications vary but 90% by weight of the dry film is a typical requirement. If moisture, an electrolyte, passes into a film of this nature, each particle of zinc needs to be in contact with at least one other, in order to form the metallic circuit through to the steel for the electrons. These electrons, in the form of Hydroxyl ions will then return through the electrolyte to the zinc and the zinc will corrode, sacrificially. In order to hold the high concentration of zinc particles together, a very strong binder is required. This is usually an organic epoxy. Inorganic binders such as Ethyl or Methyl Silicates are zinc pigmented but are primarily designed for high temperature service and need sealers such as aluminium or carbon pigmented silicones.

Painting Inspection Grade 3/2. Rev 1 April 2004 Water Borne Coatings 8.1 Copyright © 2003, TWI Ltd


WATER BORNE COATINGS ‘Compliant’ is a term often used nowadays and refers to a material, which complies with COSHH Regulations and EPA requirements. Progressively, year by year, stricter regulations are brought into force regarding solvent emissions into the atmosphere. For example a 60% vs paint using a hydrocarbon solvent will release 400 cc of solvent into the atmosphere for every one litre of paint applied irrespective of thinners added and cleaning solvents used. Hydrocarbon compounds are known to be harmful to the environment, the ozone layer, and human life. Paint manufacturers have therefore taken steps to comply with these requirements by using alternatives, in the form of Solvent Free, High Volume Solids, and Water Borne. Many binder types can now be modified to use water among them being. a) Alkyds b) Epoxies c) Polyesters d) Polyurethane e) Vinyl’s f) Acrylics g) Silicones Every material has advantages and disadvantages. Water as a solvent, poses no problems with compatibility over any other material but may prove problematic for adhesion. Abrasion will almost certainly be required, but generally the following will appertain. Advantages 1 Water is of a suitably low viscosity for any application method, brush, roller or spray. 2 Water is recyclable cheap, abundant, non-toxic and non flammable. 3 Water is not harmful to environment, the ozone layer or to mankind. 4 Water can be applied over any existing binder type with impunity. 5 In good conditions several coats can be applied in one working day. Disadvantages 1 Water usually needs a small amount of a co-solvent for modification. 2 In periods of high humidity drying will be retarded. 3 Needs controlled storage conditions, in low temperatures certain components may come

out of solution. 4 Not as versatile as HC’s for application windows.

Painting Inspection Grade 3/2. Rev 1 April 2004 Water Borne Coatings 8.2 Copyright © 2003, TWI Ltd


Painting Inspection Grade 3/2. Rev 1 April 2004 Paint Manufacture 9.1 Copyright © 2003, TWI Ltd


PAINT MANUFACTURE Paint manufacturers buy ingredients from many sources, mix them and process them into their own formulations, which they then sell on as their paint. Part of this manufacturing process is grinding aggregates and agglomerates down to a suitable size for the paint type being processed. For example a gloss paint with a dry film thickness of 30 um would need an aggregate size of far less than 30 um, typically 20 um or in some instances 10 um, because an aggregate of larger size than the nominal film thickness would protrude and deflect light. Where as an undercoat or mid coat would require a larger degree of grind (some extender have 40 um particle size to aid with cohesion and inter coat adhesion). Paint manufacture basically involves three main stages, once all constituents are available. 1 Premixing Pigment/binder/solvent are mixed in proportions suitable to give a consistency of premix or mill base, suitable for the machinery to be used in the next part of the operation. 2 Dispersion or grinding or milling The actual dispersion or grinding or milling of the paste from the above. 3 The letdown process Where the remaining amounts of binder/solvent and any other additives are finally and thoroughly mixed prior to quality checks and canning.

Direct charge dispersing mills 1 Ball mill A ball mill in a horizontal steel drum, typical dimension 1m diameter x 1½m long, which is approximately half, filled with various types of balls. Steel balls for darker colours and porcelain or selected flint for lighter colours. The balls are 1" to 1½" diameter. Mill base is added to the drum until the balls are covered, about 50% capacity of the drum. The hatch is then sealed off and the drum started rotating at such a speed so that the balls cascade down and do not stick on the drum due to centrifugal forces. Shear forces are applied to the mill base as the balls cascade both between the balls and balls and vessel walls. A typical dispersion time would be overnight for a 50-60 gallon batch.



Figure 9.1 Ball mill 2 Attritor mill The attritor mill is a vertical version of the ball mill, but more efficient and also static. The balls are driven by paddles. The mill base is continually circulated by pump from bottom to top and gives adequate dispersion in less time. Used to be regarded as a fixed charge M/C but largely modified now for continuous use.

( )

)

Feed hatch

Cascade angle

Support frame

Balls and mill base



3 High speed disperser Sometimes called a high speed dissolver, this piece of equipment can be used for mill base production or complete batch production, but mainly for the former. It is analogous to a large food mixer with a flat toothed impeller blade at the end of a shaft. Dispersion is achieved because of the extreme turbulence that occurs at very high shaft rotation speeds near the impeller blade. The mill base produced then undergoes a further process in a Bead Mill (Sand Mill or Pearl Mill are alternate names). Figure 9.2 High speed disperser



4 Kady and Silverson mills Both the Kady and the Silverson mills are suitable for rapid dispersion of aggregates in aqueous emulsions and other water borne material. 5 The sand mill Also known as a bead or pearl mill, the sand mill is particularly suited to long production runs on popular paint colours. The mill base is pumped under pressure up through the vessel which is partially filled with sand or other grinding mediums. Through the centre of the vessel runs a shaft with fixed discs, which causes the abrasives to be moving constantly. As the mill base passes through this moving abrasive, it is subject to shear dispersion. As the paint exits at the top it passes through a fine screen, which retains the abrasive in the vessel. A cold water cooling jacket is needed because of the heat generated by friction. Figure 9.3 Sand mill 6 Colloid mill Also known as high speed stone mills, usually fairly small, using stone grinding discs containing carborundum, approximately 10" in diameter. The top stone is stationary and the lower stone is rotating fast at speeds up to 3600 revs per minute. Gravity fed low viscosity slurry enters the centre of the static top stone and is passed between the two stones by centrifugal force, where it is subjected to extreme turbulence and shear forces to affect the dispersion.

Dispersion out

Filter Screen

Sand slurry

Slurry in

Typical disc



7 Triple roll mills Three rollers made from chilled steel or granite, run parallel to each other, and each one rotates at a different speed, and each contact face passes in the opposite direction to the adjacent roller. The gap between them, the nip, can be adjusted. These machines need a thick paste like mill base to operate efficiently. The mill base is fed into the nip between rollers one and two and the final product is taken from roller three by means of a scraper bar. Figure 9.4 Triple roll mill 8 Single roll mills This system utilises a single chilled steel roller. Mill base is gravity fed from a hopper into a small gap between a longitudinal bar and the rotating oscillating roller. The material is thus subjected to shear and dispersion. The bar can be adjusted to control the gap by screws or hydraulic pressure along the length of the bar. There are two types of bars which can be operated, a single roll refining bar and a recessed bar. The final product is removed by scraper bar. Figure 9.5 Single roll refiner

Paste Scraper Apron

Feed hopper

Pressure adjustable bar

Refining bar

Recessed bar



Painting Inspection Grade 3/2. Rev 1 April 2004 Testing of Paints 10.1 Copyright © 2003, TWI Ltd


TESTING OF PAINTS FOR PROPERTIES AND PERFORMANCE BG Transco Specification No PA9, lists a number of tests, (and required results), which a paint must be subjected to and comply with before acceptance as a material suitable for use on a BG Transco site. BS 3900, Methods of test for paints, is the British standard which details these tests, for method of test and equipment. It is subdivided into groups of tests from group A, tests on liquid paints (excluding chemical tests), through to group H, which covers defects and rating of. The following tests are to PA9 requirements.

Tests done on paint Determination of volatile, non volatile This test, done to BS 3900 part B2, can only be a guide and not 100% accurate, as it relies on solvent evaporation from a test sample. As soon as the can is opened the evaporation will start. A typical procedure would be. • Select a clean, thoroughly dry glass stirring rod and watchglass, and weigh on a sensitive

balance to the nearest milligram. • Place onto the watchglass approximately 2gm of paint and weigh again. • Place the watchglass with paint into a hot air oven, no naked flame or element, repeatedly

stir to drive away the volatile content. • Take a final weight of the glass, rod, and dry paint and simple calculations will give

volatile/non volatile ratio by weight. Flash point determination As per BS 3900 part A9, using a closed Abel cup (as opposed to the open cup). Flash point is defined as being “the lowest temperature at which solvent vapour from the product under test in a closed cup, gives rise to an air/vapour mixture capable of being ignited by an external source of ignition” and is a safety factor. A high flashpoint material is safer than a low flash point material and would be determined as follows. • Add solvent to the Abel cup, replace lid with thermometer and agitator in place. • Clamp the Abel cup onto a retort and lower into a water bath. • Gently heat the water bath, which will in turn heat the solvent under test. • Every ½oc rise in temperature activate the high frequency spark.



• The flash point temperature is reached when a blue flame flashes over the solvent.

An orange flame signifies that the flashpoint temperature has been exceeded and the test should be redone.

Figure 10.1 Abel cup Paint density Defined as being weight per unit of volume, density is calculated by weighing a know volume of material and using the formula: - Density = Weight Volume When imperial units were used density could be expressed as being pounds (lbs) per gallon. However metric units are now standard and the units for density are grams per cc. 1cc (cubic centimetre (cm3)) weighs 1 gram 1 litre (1000 cc) weighs 1 kilogram A density cup with a capacity of 100 cc is used for measuring density of paint. Other names referring to the same cup are: - 1 Relative density cup 2 Specific gravity cup 3 Weight per litre cup 4 Weight per gallon cup 5 Pyknometer

Agitator

Spark electrode

Retort

Water bath

Thermometer



Figure 10.2 Density cup with lid chamfered to centre vent on underside Procedure for use • Weigh the clean, empty cup and the lid on a metric scale, sensitivity ± 0.1gm. • Fill the density cup with the paint, to within approximately 2mm of the brim. • Allow any entrapped air bubbles to burst and replace the lid slowly and firmly until it seats

firmly on the shoulder of the brim. • The chamfer in the lid allows air to be expelled as, the lid is replaced, followed by paint

over the required 100cc volume. If no paint is expelled remove the lid and add more. • Wipe off any excess paint from the vent and weigh the filled cup. • Deduct the weight of the empty cup from the final weight and divide by 100. • The answer is the density in grms/cc. From information given on the materials data sheet and calculated density of the solvent it is possible, but difficult, to calculate the percentage of any added solvent, although better and easier ways exist. This piece of equipment however can be used in calculating if a 2 pack material has been mixed in the correct proportions. Relative density or specific gravity The density of distilled water is known to be 1gm/cc and the density of any other material can be calculated as above. Relative Density or Specific Gravity is in effect comparing the density of another material with that of water using the formula: - SG or RD = Density of x Density of water

100cc



Because Relative Density is comparing, and giving a value of “times heavier than”, there are no units of value, but the digits will be exactly the same as density. Example If five litres of paint weight 7.2Kg, what would be the density? Step 1 Convert units to gms and cc’s

5L x 1000 = 5000 cc 7.2Kg = 7200gms Step 2 Density = WT = 7200 gms Vol 5000 cc’s Step 3 Perform calculation = 1.44 grms/cc Therefore SG or Relative Density would be 1.44 Example for 2 pack ratio calculation A two pack epoxy is mixed at a ratio of five parts base to two parts activator, the given densities of which are pack A 1.25 gm/cc and pack B 0.97 gm/cc. What is the density of the mixed paint? Five parts base at 1.25 gm/cc = 6.25 gms Two parts activator at 0.97 gm/cc = 1.94 gms Therefore total weight = 8.19 gm Total volume for weight = 7 cc Density of mix = 8.19 = 1.17 gms/cc 7 Hegman grind gauge The Hegman grind gauge, also called a fineness of grind gauge, is used to measure the degree of dispersion of paint. Aggregates are going to be present in all pigmented paints, but only the largest aggregates are of any concern. With gloss paint a perfectly smooth surface is required, so any aggregates within the paint should be substantially below the dimension of the film thickness. The Hegman Grind Gauge is a stainless steel block approximately 17.5cm x 6.5cm x 1.4cm and is highly polished on the sop surface. Two grooves, or on some gauges one groove, are precision ground tapering from 100 um deep to zero along almost the total length of the gauge. A 10um increment scale is engraved along the length of the groove, representing the depth at that point. Paint is added to the deepest point of the scale and drawn along to totally fill the groove using a specially profiled scraper bar. The specification BS 3900 requires that within three seconds of this operation the scale should be placed so that the eye looks almost parallel along the groove, very obliquely, to observe a point along the groove where, within a 3mm band, five to ten aggregates break through the surface of the paint. This actually, looking at the stated angle is the point where the surface will change from gloss, at the deep end, to matt at the shallow end.



Figure 10.3 Hegman grind gauge Figure 10.4 Cross-section of a Hegman grind gauge AA Along the groove, at some point, the aggregates will rest along the bottom and protrude through the surface giving a result as below. Figure 10.5 Aggregates protruding and resting on the bottom Viscosity Viscosity is a very important property for paint, it affects the manufacturing process and application and levelling properties. Viscosity is defined as being a fluid resistance to flow. Therefore a liquid described as being of a high viscosity is one which as a high resistance to flow, it will not run easily, and conversely, a low viscosity fluid runs very easily.

3mm band

Gloss Matt

Aggregates protruding

Aggregates on the bottom

0 20 40 60 80 100

10 8 6 4 2 0

Cross-section below

A A

Gloss Matt



An increase in temperature (or decrease) can have a severe effect on a fluid’s viscosity and therefore comparative tests should be done at the same temperature. As the temperature increases the molecules within the paint gain more molecular freedom, move more easily and thus reduce viscosity. A typical recommended temperature is standard laboratory temperature of 20oc ± 0.5oc. There are several types of equipment available for measuring viscosity but they mainly fall into two categories. 1 Rotational Viscometers 2 Flow Viscometers 1 Rotational viscometers Rotational viscometers rely on a paddle, disc or ball rotating in a liquid to measure the viscosity. The rotation can be driven by an electric motor, which gives Dynamic Viscosity measurements, or by falling weights which gives Kinematic Viscosity measurements. a) Dynamic viscosity For dynamic viscosity measurements a rotothinner can be used Figure 10.6 Rotothinner The rotothinner, a flat circular disc with four holes drilled transversely through it, is fixed into the chuck of the rotational viscometer (not unlike a pillar drill) and lowered into a 250 millilitre can containing the fluid under test. The can is magnetically attached to a spring loaded conical shaped base. When the disc enters the can, a micro-switch engages the motor and starts the disc rotating. When the rotating disc enters into the paint the frictional forces between the disc and the paint molecules and the can cause the can to rotate, which in turn tensions a spring in the base. When the two equalise the can will stop rotating and a reading can be taken from the pointer on the scale on the conical base.

Poises



The systems international (SI) units for dynamic viscosity are, newton-second per square metre (N.s/m2) although on many machines the poise is still used (cgs. unit). A poise has ten subdivision called centi-poise. Water has a viscosity of approximately one centi-poise. One poise is equal to one dyne second per cm2.

Kinematic viscosity Figure 10.7 Krebs stormer viscometer Kinematic viscosity is measured using a Krebs Stormer Viscometer. The weight is allowed to fall, which in turn causes the paddle to rotate in the paint. More weight added results in a higher rotation speed. Weights are added until the rotation speed is 200 rpm as measured either with a stroboscope or digital display counter. A viscosity unit frequently used for kinematic viscosity is the stoke and centi stoke. A fluid having a viscosity of one poise and a density of 1 gm/cc has a viscosity density ratio of one stoke. (Krebs units or poise can also be used.) Flow viscometers (Flow cups) There are various types of flow cups e.g. Zahn and Frikmar, used for hot fluids, Ford, ISO and DIN used for ambient temperature materials. The ford cup being the most widely used for industrial paints. The flow cup is machined from Aluminium, has a capacity of 100cc, and is fitted with a stainless steel nozzle at the bottom with various orifice sizes, in millimetres. For use with industrial paints a 4mm hole size is standard, and known as A Ford Flow Cup No4. The cup is mounted on a special stand, and has a lid with a bubble spirit level. The triangular base of the

Weight



stand has one fixed foot and two screw adjustable feet, to facilitate the levelling of the stand and cup. A typical procedure for use would be: - 1 Ensure that the equipment and paint temperatures are at 20oc ± 0.5oc. 2 Level off the equipment using the bubble level and adjustable screw legs. 3 Put the lid to one side when levelling is complete. 4 Place a suitably sized receptacle under the orifice (greater than 100cc). 5 Place a finger over the nozzle orifice and fill with the paint to be tested, up to the brim,

leaving a convex meniscus. 6 Using a straight edge (a ruler) quickly scrape excess material into the overflow rim on the

top of the cup. 7 Simultaneously start a stopwatch (or use sweep second hand) and remove finger from the

nozzle. 8 The paint will run from the orifice in a continual stream. At the first distinctive break in

the stream i.e. when it drips, stop the watch. The time in seconds is recorded as the viscosity, at the measured temperature.

Thinners added to paint over and above recommended quantities could also be determined by viscosity. To do this a sample containing maximum amount permitted (by manufacturers TDS) is prepared, and compared to samples taken from the operators at the point of application. Using the flow cup, if the operators sample runs through the cup faster than the reference sample, then more thinners than allowed has been added. To find the exact percentage added, small amounts can be added to the reference sample until operator’s sample and reference sample run through in the same time. Should the operator’s sample take longer than the reference sample, then there is no problem. Thixotropic paints cannot be measured using a flow cup.

Painting Inspection Grade 3/2. Rev 1 April 2004 Film Thicknesses 11.1 Copyright © 2003, TWI Ltd


FILM THICKNESSES

Wet film thickness measurement From information given on a specification and the technical data sheets (TDS) correct application thickness can be calculated. If regular checks of wet film thickness (WFT) are carried out, and found to be adequate, it gives added confidence that upon checking the following day, the dry film thickness (DFT) should meet specification requirements and hopefully eliminate major rectification. Wet film readings should be taken immediately after application, in order to obtain true readings (solvent starts to evaporate away as it exits the spray tip). WFTs can be measured by using either an eccentric wheel, or comb gauges. 1 Eccentric wheel An eccentric wheel is a steel disc, machined to cut two grooves leaving three rims. The centre rim is machined smaller than and eccentric to the two outer rims. The inner rim is called the Eccentric Rim and the two outer, the Concentric Rims. Figure 10.8 Eccentric wheel A scale is engraved on the outer surface of one side of the wheel giving degree of eccentricity at any point. To use the wheel it should be placed on the surface with the zero at the six o’clock position, rolled through 180o in one direction, back to the zero and then 180o in the opposite direction, back to zero. The concentric outer rims will be wet for the full circumference, but the inner rim,

Degree of eccentricity, 250 um normal

0

125

250

125



the eccentric rim, will only be wet for part of the circumference, having left and re-entered the film on two occasions. The wet film thickness value is taken by transferring (mentally) the interface between wet and dry on both sides of the eccentric rim into a value from the scale. The average of the two values is the WFT of the paint film. It should be noted that the eccentric wheel can only be used on flat plate. On a pipe, for example it would be used circumferentially. 2 Comb gauges Comb gauges are supplied in many forms, square, rectangular, and triangular, in metal and in plastic. Disposable plastic gauges will be supplied in small boxes containing several hundred. Stainless Steel gauges are supplied in sets of four in a leather wallet. However all comb gauges are used in a similar manner. Assuming use of the SS gauges, four gauges will each have two working ends covering eight different WFT ranges. Above each tooth is engraved a value ‘thou’ on one side and its equivalent in microns on the other side. This represents the value of the gap from tooth end to substrate when the gauge is place firmly, perpendicularly onto the substrate. When the gap under the tooth is full of paint it will wet the tooth. When not full it will not wet the tooth. A procedure for this operation would be: - a) Select the appropriate gauge with the smallest increment rise tooth to tooth. b) Apply the gauge firmly, perpendicular to the substrate into the paint film ensuring that the

two end lands are firmly on the substrate. c) Withdraw the comb gauge and look at the teeth. d) Two values should be recorded. The number above the last tooth wetted by the paint and

the value of the next highest not wetted. The WFT is not an absolute value but ‘in between’. NB Comb gauges should be used longitudinally on curved surfaces e.g. pipes. Figure 10.9 Comb gauge

Paint

Substrate

25 50 75 Wet

Wet

Not wet Recorded as 50/75

Wet



WFTs can be calculated by using the following formulae, according to information given. WFT = 100 x DFT VS WFT = V = Volume A Area Figure 10.10 Contraction from evaporation

Tests done on dry paint films Dry film thickness The specification for a painting contract will state a DFT criteria for each coat of paint applied. As it is the inspector’s main function to ensure that work is carried out to specification, he/she should perform as many checks as needed to ensure that the specification criteria is met. The DFT value can be determined by one of four methods. 1 Test panels 2 Calculations 3 Destructive test gauges 4 Non destructive test gauges Test panels Test panels are usually 150mm square plates of the same material as the component being processed. The plates undergo the same operations at the same time as the main components. Mainly used for destructive tests e.g. adhesion, they can also be used for DF. T checks.

Solvent WFT Solvent

Binder

Pigment, Extenders and others

DFT Volume Solids %

Solvent %



Calculations Using certain formulae and information given on a materials data sheet, in conjunction with values determined from WFTs for example, calculations can give us the ‘unknown’ values. Four formulae can be used according to information provided. 1 WFT = V A

3 DFT = WFT x VS 1 100

2 WFT = 100 x DFT VS 1

4 VS% = DFT x 100 WFT 1

Examples of which are as follows: - 1 WFT = V A Question: If 12 litres of paint was used to cover an area of 10m x 10m what would be the average WFT? Answer: Step 1 WFT = Volume = 12 Litres = 12 L Area 10 x 10 100 m2 Step 2 Change to units common to volume and area = cm2 cm3

12 L x 1,000 = 12000 cm3 = 0.012 cm 100 m2 x 10,000 1,000,000 cm2

Step 3 Multiply x 10,000 (um/cm) = 120 um 2 WFT = 100 x DFT VS 1 Question: What WFT would be needed to give 50 um DFT using a paint with a VS% of 65%? Answer: WFT = 100 x DFT = 100 x 50 = 5000 = 76.92 um VS 1 65 1 65 3 DFT = WFT x VS 1 100 Question: What would be the DF. T if a paint with a VS content of 45% was applied at 120 um WFT? Answer: DFT = WFT x VS = 120 x 45 = 5400 = 54 um 1 100 1 100 100



4 VS% = DFT x 100 WFT 1 Question: What would be the VS% of a paint if it was applied at a WFT of 110 um and the DFT was 63 um Answer: VS% = DFT x 100 = 63 x 100 = 57.27% WFT 1 110 1 Destructive test gauges As the name implies these types of gauges cause damage to the film which then needs to be repaired. If a specification required a magnetic gauge to be used to measure a coating including MIO (Micaceous Iron Oxide), in theory it can't be done, MIO is magnetic and would cause error in the reading. In this instance a destructive test gauge might be specified or it may be required to monitor closely the WFT and calculate (as above) the DFT. A PIG, paint inspectors gauge is a type of destructive gauge. A reference line of a contrasting colour is drawn on the painted surface to be tested. A blade is tightened into a special slot in the PIG, pressure applied to force the blade through the paint to the substrate and then cut across the reference line, leaving a damage about ⅜" it is then possible to examine the damage through a focusable microscope. Measurements can be taken by means of a graticule scale engraved on one of the lenses. Figure 10.11 Destructive test gauge

Blade

View

Damage

Reference line

View through lens with graticule scale



The dimensions taken from the graticule scale at this point are not in any units, as the angle of the cutter used alters, so will the representations of the graticule. A chart is supplied with each gauge, and blades of different angles. If for example the chart indicates Blade No3 will be ground to x angle, can be used on thickness less than 500 um, multiply graticule reading by 1.8, 20 unit of graticule scale would then convert to 20 x 1.8 = 36 um. Other commonly used destructive gauges are the Ericson Test Drill and Saberg Thickness Drill. The damage caused with this is circular.

Non destructive test gauges This category of gauges is the most widely used and can be subdivided into Electronic and Magnetic. a) Electronic The electronic gauges work mainly on two principles. Electro Magnetic Induction and Eddy Current. The Electro Magnetic Induction is suitable for ferro-magnetic substrates and the Eddy Current is suitable for non ferro-magnetic substrates. Modern electronic gauges are sometimes supplied with probes suitable for both situations, and the gauges automatically change function according to the fitted probe. Both types are for measuring non-ferro magnetic coatings. Accuracy ± ½ %. b) Magnetic This classification of gauges works with permanent magnets, no batteries. The simplest of these is: - The Tinsley Pencil or Pull of Gauge. Sometimes called a foreman's gauge is suitable for spot checks and is not very accurate, even on modern gauges of this type ±15 % accuracy is quoted. It looks very much like a pen and indeed is sometimes fitted with a pocket clip. It has a permanent magnet attached to a spring. The tension of the spring can be adjusted so that the gauge can be calibrated to work over a variety of thicknesses.



Figure 10.12 Cross section of Tinsley pencil Figure 10.13 Magnetic horseshoe gauge

Screw to adjust tension

Spring

Cursor line

Permanent magnet

Scale

Lock/unlock

Knurled wheel for calibration



The Magnetic Horseshoe gauge is a very old type of gauge still favoured for measuring hot surfaces such as metal spray. Accuracy often quoted as better than ± 10% and as for all magnetic gauges, it is suitable for use in hazardous areas. This gauge works by measuring the change in magnetic flux between two magnetic poles at the bottom of the gauge. The flux change is brought about by the thickness of the non-magnetic coating. The gauges are supplied in a wide variety of scales and are calibrated like all magnetic gauges. The Magnetic Coating Thickness gauge, known colloquially as the 'banana gauge', measures non-ferromagnetic coatings over ferromagnetic substrates and can, according to the manufacturer even be used under water. This type of gauge relies on spring tension to break the magnetic attraction of a permanent magnet to a ferromagnetic substrate. Because spring tension doesn't have a linear function the scales on the gauges are in logarithmic increments. When calibrating for use it is therefore of paramount importance to calibrate using a shim as near as possible to the paint thickness. Modern gauges of this type often quote ±5 % accuracy. Procedure for calibration to BS 3900 PT C5 (now ISO 2808) (BG Transco specify calibration on a prepared surface, therefore a plate with the same substrate surface finish as that to which the paint is applied, should be used). It is extremely important to remember that should the gauge be calibrated on a flat plate, the reading on a blasted surface would take from approximately ⅔ of the depth of the profile, giving values of up to 50 um more than the actual 'over the peak' value. 1. Select a plastic shim (magnetically insulated) as near as possible in thickness to that of the

paint to be measured. 2. Place the shim centrally on the calibration plate, as detailed above. 3. Locate the magnet in the gauge onto the shim, apply a light pressure to ensure that the heel

doesn't wobble or rock, and wind the scale wheel on the gauge fully forward to release all tension on the spring allowing the magnet to attach to the substrate.

4. Wind the wheel slowly back, clockwise, tensioning the spring until the magnet detaches. At this point the movable cursor on the gauge is adjusted so that the red line on top of the cursor is in line with the thickness value of the shim as shown on the scale wheel.

The gauge is now ready to use. Some 'banana' gauges do not have a movable cursor. Instead these have a fixed cursor, moulded into the case, and a movable scale, and to calibrate these gauges, the value of the shim on the scale wheel has to be moved to the cursor.

Tests for mechanical properties on paint films Abrasion resistance Ericson, Taber and Gardner are just three of many companies who manufacture specialist equipment for testing paint films.



A materials resistance to abrasion can be tested using a Taber Rotary Abraser. Discs painted with the material to be tested are rotated under special abrading wheels. The abrading wheels can be of various compositions, depending upon the degree of abrasion required. For example, sand paper or carborundum. Periodically the samples can be checked for thickness or damage inflicted. Hardness The hardness of a film can be tested by many methods including the Buchholz Indentor and the Sward Hardness Rocker, but one of the most frequently used for hard coatings is the Koenig Albert. A pendulum with two spherical fulcra is free to swing on a plate painted with the material under test. The number of swings is counted electronically. (If the fulcra penetrate the surface, more resistance will reduce the number of swings). Flexibility BS 3900 E1 Standard panels are coated with material to be tested and bent around cylindrical mandrels of various diameters. The flexibility of a coating is expressed as the smallest diameter mandrel over which the paint will not crack when bent. A conical mandrel with a uniform taper from 3 mm diameter to 37 mm diameter is frequently used now. The conical type needs only one sample to achieve a result whereas the straight mandrels need a plate for each mandrel. Impact resistance Each generic type of coating material used has it's own impact resistance requirements, as measured, in joules. Tubular impact testers are commonly used for this test. A weight, typically 1 Kg. is lifted up the tube to the height required and held in place by a retaining collar. A painted sample is fixed under the tube. By rotating a ring within the collar the weight is released and falls onto the sample, which is then assessed for damage. Two types of test can be done, direct impact and indirect impact. Direct being onto the painted side of the sample and indirect on the non-painted side. Accelerated testing Normal weathering tests are a simple process of hanging out painted panels, facing South, on an ' A' frame and periodically testing for colour retention, chalking, water absorption etc. over a period of years. However new products ready to go on the market, cannot wait years for test results. The manufacturers may have spent many thousands of pounds on Research and Development of the product, and will want some return. Accelerated tests can be done which reduce testing time to months by accelerating or intensifying the conditions to which the paint will be exposed.



Some typical test cabinets used for testing specific conditions are: - • Humidity cabinets For testing tropical conditions. Humidity is very high at 95% and elevated temperatures up to 55oc. • Salt spray cabinets For checking paint ability to withstand salt laden environments. • Water soak tests Allowing painted panels to be submerged to test for water absorption, by weighing before and after submersion. • Temperature cycling Painted samples are subjected to constant temperature cycles from hot to cold. Paints in common with most materials expand and contract according to temperature. Constant expansion and contraction can result in cracking. Maximum and minimum temperature can be set and cycle time, over a running period of 1000 hours, as an example. • Prohesion testing Painted sample plates are cut with a pre-damage in the form of an X, 50 mm each incision length. A 3% saltwater solution is sprayed onto the plate for 60 minutes and stopped for 60 minutes, at a constant 35oc. The cycle continues for 1000 hours. On examination after the 1000 hours, there shall be no blistering or undercut outside of a 3 mm boundary on each side of the pre-damage.

Drying and curing tests On the manufacturers data sheet for a paint it will invariably state a recommended over coating time, at a specific temperature, as a guide. The reason being that tests done to determine the drying/over coating time will have been done in a laboratory to that specified temperature. Higher ambient temperatures will shorten the stated time and conversely lower temperatures will need longer over coating time. Two tests to determine the drying time are: - • Ballotini test • Beck Koller Stylus test (BK trying time recorder)



Ballotini test Ballotini, tiny spheres of glass, or sometimes sand is trickled onto a newly painted block graduated in hour of traverse, e.g. 24 hours for the block to traverse full length under the funnel. After a specified time the block is removed, tipped onto its side, tapped lightly, and examined. The position of the last grain of sand or ballotini sticking to the surface is recorded as the drying time at that temperature e.g. 20oc ± 0.5oc. Figure 10.14 Ballotini test BK drying recorders The BK gives more information than the Ballotini, which purely indicates drying time. The BK defines also the stages of drying. E.g. Solvent Evaporation Time, The SolGel Transition, Surface Drying Time and Final Dry Time. Needles (stylus) are fixed to motor driven wires which then traverse over the full length of painted glass strips 300 mm x 25 mm, in pre set times of 6, 12, 24 hours. The needles can also be weighted if required. When the paint is wet the needle will penetrate through to the glass. As the solvent evaporates the needle will start to cut a continuous track in the film, as drying progresses it will cut an interrupted track, until finally dry when no scratch is visible. Other tests Mechanical thumb test This is a test for even through drying of paint. It simulates pressing a thumb onto a surface and applying a twisting motion. A cam drives a weighted shaft with a semi spherical rubber end cap, allows it to drop onto the painted plate, rotate through 270o, then lifts it off again. The plate is then visually inspected for tearing, pulling, wrinkling etc.

2 4 6 8 10 12 14 16 18 20 22 24



Pencil scratch test (Wolff-Wilborn) Pencils are graded in degree of Blackness B and degree of Hardness H. HB being the middle of the range. Higher the number and harder or blacker the lead is. A sharpened pencil is fitted into a special steel block and pushed along the surface, starting with e.g. 3H and working up 4H, 5H etc. The first pencil to scratch the paint lends its hardness value to the paint e.g. 5H.

Mechanical scratch test A stylus with various added weights is drawn across the painted surface. The weight that causes the surface to be scratched gives its value to the hardness e.g. 500 gm. Gold leaf test A test for residual tack. A small square of gold leaf is lightly pressed onto the surface of the paint. The gold leaf is then pealed off and the area examined with a magnifying glass. No residual gold leaf should remain. Thumbnail test A quick test for hardness is to try to penetrate the paint film with the thumbnail. If the thumbnail penetrates, the film is “cheesy”. Opacity The opposite of transparency, a test to determine the ability to hide (cover) the substrate. The following are methods to determine the wet film opacity, a combined function of pigment concentration and refractive index, using cryptometers. Commonly used cryptometers are Pfund Cryptometers and there are two types.



1 Trough type A wooden block with a tapered sunken trough in the middle, the bottom of which is formed by chequered black and white glass squares. Paint is added at the deep end and scraped along to fill the trough. Looking perpendicular onto the trough, find the point where the underlying square can just no longer be seen. (Look at the squares offering the biggest contrast to the paint colour). A scale running along the groove will indicate the depth of the groove at that point, and is recorded as a wet film thickness.

Figure 10.15 Pfund cryptometer, trough type 2 Black and white fused plates The second type is a black and a white glass square, fused together. On each square is an engraved scale starting at zero on the joint. Paint is applied onto the square with the most contrast and a “top plate” of clear glass placed in position with the tapered contact edge exactly on the fusion line. Small “feet” at the end of the top plate allow a tapered film of paint to form under the glass top plate. Look for a point along the film where the underlying black or white plate can just no longer be seen. Note the value on the scale and multiply by the constant on the top plate. Figure 10.16 Black and white fused plates

A A

Section on A - A

70 60 50 40 30 20 10

10 20 30 40 50 60 70

Black Square White

Square Glass plate in position



Hiding power charts and micrometer adjustable film applicator Various designs of black and white A4 signed cards are used for this method. Chequered, striped, zigzag, half and half and cards of ones own design can be used. The surface is coated with a solvent resistant lacquer to prevent immediate absorption. The applicator is a frame with an adjustable gate, which can be controlled by two micrometers for vertical movement. After zeroing on a flat surface the reading on the micrometers represents the gap under the gate. Paint is applied onto one chart and the bar applicator immediately drawn over it. If opacity is not achieved (as previous) the gate is adjusted 5 um higher and the operation repeated on another card until the film thickness required for opacity has been attained. Degree of Gloss Gloss is a measure of reflectivity. Light follows general rules and travels in a straight line. When light hits a surface it reflects off at the same angle as it strikes the surface. A modern gloss meter works on exactly this principle, a light source directs a beam of light onto the surface under test, and a photo electric cell, set at the same angle, collects the reflected light and quantifies it and converts it digitally into a percentage of the incident light. On a perfectly smooth surface it would give almost 100%. On an uneven surface some of the light is deflected and so the percentage reading would be lower. A high percentage of reflection will be gloss and a low percentage will be matt. Gloss meters for general use have two common angles, typically 60% and 20% both taken from the perpendicular, the 60% angle being the most common usage. Figure 10.17 Degree of gloss

Incident light

Light scattered

Uneven surface

Incident light

Smooth surface

Photo electric cell

Reflected light



Any property, which can affect the paint surface formation, can affect the gloss factor. Main contributors are PVC Degree of Dispersion Particle size, Resin type (for polymer formation and RI, refractive index) and Solvent type.

Adhesion Inspection is defined as “Examining, testing, gauging, one or more characteristics etc.” One of the properties required of a paint film is to ‘provide adhesion to the substrate’, therefore an inspector is expected to test to ensure the paint is performing this function. There are three main areas for adhesive failure within a paint system. a) Primer to substrate failure b) Inter-coat adhesion (between films) c) Cohesive failure (within a paint film) a) Primer to substrate failure Primer to substrate failure is the most serious. Failure here means no protection at all. This is a surface contamination problem mainly. Lack of adequate surface preparation, grease, oil, dirt, dust are the usual causes. b) Inter-coat adhesion Caused by the problems above and others. Lack of observance of recommended over-coating limits and expansion/contraction differences between materials. c) Cohesive failure Over thickness of a layer can entrap solvent during the drying process and thus stop polymerisation and the correct formation of the film, reducing cohesive strength. The main reason for cohesive failure is solvent entrapment but incorrect ratio mix of a two pack can have exactly the same effect. These failure points can be detected in several ways, some costly, requiring equipment costing several hundred pounds and some requiring an outlay of a few pounds only. ‘V’ cut test A craft knife is all that is required to perform this test. Cut through the paint, to the steel substrate, with two cuts forming an inclusive angle of approximately 30o, with leg length of approximately 13 mm. Insert the tip of the blade into the tip of the ‘V’ and try to lever off. The paint should chip across the tip of the ‘V’ clearly and cohesive without following the line of any of the faults described. It should not expose any of the substrate.



Cross cut (cross hatch test) Cut through the paint using six horizontal and six vertical cuts approximately 2 mm spaces giving a 25 squared grid. Special profile cutters can be purchased for this, or a craft knife can be used. Apply an agreed tape to the area (different tapes have different degrees of stickiness and would give different results), rub smoothly onto the hatched area and then snatch off. The resulting areas of disbondment are then compared to diagrams shown in BS 3900 Pt E6 and classified according to percentage area of disbondment. Dolly test The dolly test is more expensive to use, but unlike the above gives an answer in units of psi or newtons/um square, etc and so is classed as a quantitative test. A typical procedure for the test would be: - Ensure the test area is clean and oil/grease free, lightly abrade the area and apply mixed two pack heavy duty adhesive. Firmly place the aluminium alloy dolly in position onto the adhesive ensuring that the skirted flange is to the adhesive. Leave for manufacturers recommended cure time. Place the core drill supplied around the dolly and cut through the coating to the substrate (this ensures that only the area of the dolly flange receives the pull off forces). Apply the pull off gauge and apply pull off force, (some models use a ratcheted lever, others a knurled wheel) until failure occurs. This will usually involve a loud bang and the instrument will ‘jump’ from the substrate. Examine the face of the dolly and apportion adhesive failure according to areas exposed, at the pull off force indicated on the scale. For example with an aluminium metal spray, single coat, there could be: - 1. Adhesive to dolly failure. 2. Adhesive to aluminium failure. 3. Cohesive failure within the aluminium. 4. Aluminium to substrate failure. Hydraulic adhesion test equipment This is a much quicker test with a higher degree of accuracy. The HATE use cyano-acrylic impact adhesives and can usually be done approximately two hours after dolly/adhesive application, the dolly’s are mild steel and reusable because they are heated up to destroy the adhesive after use. Big downside for this test is initial cost and usually high maintenance.

Painting Inspection Grade 3/2. Rev 1 April 2004 Cathodic Protection 13.1 Copyright © 2003, TWI Ltd


SPECIFIED COATING CONDITIONS A manufacturers product data sheet will indicate under which ambient conditions a paint/coating can or cannot be applied. The clients specification may sometimes be a little stricter. However, in all cases, it is the specification which takes precedence, (it is common practice nowadays to include a phrase such as “when these conditions do not prevail” or similar, to allow coating to continue using special products). A typical specification used to be: - “It is not permissible to apply paints 1. During rain, snow, or high winds”. This clause would be sensible even in modern

specifications. 2. When the air or metal temperature is down to within 3oc above the dew point temperature”.

Still common in specification now, but can be overridden by giving alternate systems. 3. When the air or metal temperature is below 5oc”. Solvent evaporates very slowly at low

temperatures and chemical cure rates used to be static. 4. When the relative humidity is more than 90%”. Still a very common restraint, and

sometimes the benchmark for using moisture curing polyurethane’s. From the above, two very important phrases arise, Relative Humidity and Dew Point.

Relative Humidity Defined as being “The amount of water vapour in the air expressed as a percentage of the amount of water vapour which could be in the air at that same temperature”. 100% humidity, saturation, is measured as being taken within 1" of the surface of a fast flowing river.

Dew Point This is the temperature at which water vapour in the air will condense. Condensation cannot occur unless the relative humidity is 100%. Recalling that every 11oc drop in temperature results in the airs capacity to hold water halving, even the smallest drop in temperature results in water being released from the air, in the form of condensation. So at 100% humidity the air temperature and dew point temperature, and wet bulb temperature on the whirling hygrometer are all the same value.



The Whirling Hygrometer, Aspirated Hygrometer or Psychrometer Commonly called the whirling hygrometer, this piece of equipment is widely used by coating inspectors to determine wet and dry bulb temperature readings, from which, using calculators or hygrometric tables, relative humidities and dew points can be calculated. Two thermometers are mounted in a plastic frame, fitted with a handle so that the frame can be rotated through the air. One of the thermometers is fitted with a wick around the bulb. The wick passes through a hole in the end of the frame and into a small container with a screw lid, into which is put distilled water or clean rainwater i.e. de-ionised water. The water is drawn by capillary action all along the wick out the area enveloping the thermometer bulb. This is referred to as the wet bulb and the second thermometer is the dry bulb. The frame with the thermometers mounted should be rotated quickly about a horizontal axis. (The BS 2482 states in front of and to windward of the operator) so that the bulbs pass through the air at 4m/sec. If there is a wind the operator should face into the wind, if no wind then walk slowly into a clean air current. The frame should be rotated for 30 – 40 seconds, or as otherwise specified, as fast as possible (to meet requirement as above) and then read the values on the thermometer, always the wet bulb first, immediately on ceasing rotation. The water on the wet bulb uses heat energy from the air to change into water vapour, so the wet bulb will give a lower temperature reading than the dry bulb. When rotation stops, the aspiration rate slows and so the wet bulb temperature will slowly start to rise towards that of the dry bulb. This operation should be repeated as many times as is necessary until the following criteria is met. On two consecutive spins the readings should be within 0.2oc, wet bulb to wet bulb and dry bulb to dry bulb. The wet bulb and dry bulb temperatures recorded can then be used to determine the RH and DP from scales or tables. This operation should be carried out as near as possible to where the work is being done. Big difference in temperature can occur from N side to S side of a tank or down a trench and topside.

Steel temperature measurement The air temperature (ambient) is the temperature recorded from the dry bulb thermometer. To measure the steel substrate temperature a magnetic gauge, known commonly as a limpet gauge is used, or a digital thermometer, thermocouple, sometimes called a touch pyrometer.



CATHODIC PROTECTION Cathodic protection is a secondary line of defence against corrosion, the primary defence being the coating. When damage to the coating occurs e.g. through impact on the coating during back filling on a pipeline, sling damage during the lowering in operation, or flotsam impact on an offshore platform leg, the underlying steel can then be in contact with electrolyte and corrosion can occur. But if these areas can become cathodic i.e. receive current, corrosion can be avoided. In order for cathodic protection to be applied, an electrolyte must be present. For example the external surface of a tank cannot have cathodic protection, but internal surfaces can if the tank is holding an electrolytic medium, but only up to the level of medium, not above. Underground and subsea pipelines can be protected, but steelwork above ground in an AGI needs painting. Cathodic protection can be applied in one of two ways. a) Sacrificial Anodes Systems. b) Impressed Current Systems.

Sacrificial anode systems This system sometimes called, Galvanic Anode System, works on the principle of bimetallic corrosion, the natural potential between metals. Any metal which is more electronegative (less noble) or below steel on the galvanic list can be used as an anode. The choice of metal used would depend upon the potential required to protect the prescribed area. Sacrificial systems only protect small areas and the anodes need changing regularly as they corrode away. Figure 11.1 Sacrificial system

Approximately 50 m maximum Connecting wire of

copper. Minimum resistance

+

Aluminium zinc or magnesium or alloys of these



Impressed current system The impressed current system is used to protect long lengths of pipeline from one installation, a distance of approximately 10 miles. The current needed to run the system comes from the national grid and is connected through a transformer rectifier (TR). The national grid is very high voltage and very high amperage and also AC. Anti-corrosion currents need to be DC. The TR rectifies the current to DC and transforms it to low voltage and amperage. The positive side of the TR is connected to a ground bed (anode system) and the negative to the pipe, making the pipe the cathode. The current is released into the electrolyte at the ground bed, passes through the electrolyte and is received at areas of coating damage on the pipe. A typical ground bed will be approximately 50 m in length, at the same depth as, and running parallel to the pipe. The cables carrying the current are of a substantial diameter and pure copper to produce a circuit of little or no resistance at the anode. The resistance encountered comes in the soil/clay/rock bearing the electrolyte and this will govern the driving voltage required, and the number of anodes required to maintain negative potential on the buried pipe. The voltage required varies but is usually within the range of 10v to 50v at an amperage of around 0.15 amps. A CP system does not eliminate corrosion, it controls where corrosion occurs. Figure 11.2 Impressed current system

Ground bed releases current into electrolyte

To national grid supply

Current received at cathode. Protected.

TR. Transformer rectifier



Interference When a buried steel structure is near to, or in the case of another pipeline, passes over or below a pipeline which is cathodically protected, problems can occur. This is “interference” but the term can be misleading. The offending structure does not adversely affect the CP system, but instead is affected by it. The “interference” structure picks up current released from the anode bed and conducts the current through a circuit of minimal resistance and releases the current again into the electrolyte near to the protected line. The interference therefore becomes a secondary anode and can suffer severe corrosion. If there is a possibility of a structure becoming interference then precautions need to be taken to avoid this eventuality. With the permission of the owner of the offending structure, three main methods can be employed. 1 Attach isolation joints one pipe length either side of the nearest point of the offending line

to the protected line. Join the two pipe lengths to the protected line with insulated wire and doubler plates, thus making them the same potential.

2 Attach isolation joints to both lines, one pipe length either side of the nearest point. Join

the two isolated sections together and install a sacrificial anode to protect both sections. 3 Double wrap and contra-wrap the protected line giving four tape thicknesses with Cold

Applied Laminate Tape for one pipe length either side of the nearest point. The method chosen would be at the discretion of the engineer.

Monitoring CP It is considered that –850 mv will maintain a pipeline in a passive state but most CP engineers will require a more negative value, -1 to –2v being typical. To ensure that the required potential is being maintained, checks need to be carried out at regular intervals. One method of monitoring is known as half-cell reference electrode. The most commonly used half-cell electrode is the copper/copper sulphate half-cell electrode. It is used for measuring the pipe to earth potential, i.e. cathode to earth, the other half of the circuit being anode to earth. Periodically along the line, CP monitoring posts are installed, with a direct wire connection to the pipe, accessed from a stud on the CP post panel. A voltmeter is connected to the stud and to the copper/copper sulphate half-cell, which is then pushed into the earth directly above the pipe. This provides a circuit for electrons from the pipe, into the electrolyte, back to the anode bed.



Figure 11.3 Monitoring CP Cathodic disbondment Part of the electrical circuit of the corrosion reaction is the evolvement of Hydrogen gas from the cathode. Hydrogen is a very powerful gas and can cause cracking in steel, (HICC). If Hydrogen gas can penetrate underneath a coating it can easily disbond it. This is known as Cathodic or Hydrogen Disbondment. Over protection of damaged areas on a pipe, results in over production of Hydrogen and subsequent disbondment of more of the coating, resulting in a bigger area to protect, needing more current. All material used on a pipeline have to undergo tests to determine their resistance to cathodic disbondment. The test is done in the following manner. A 6 mm diameter hole is drilled into a plate coated with the material to be tested, through the coating and into but not through the underlying steel. A short length, approximately 50 mm of plastic tube approximately 50 mm diameter is fixed in position, using typically araldite epoxy or elastomeric sealant with the drilled hole central to the tube. This is then part filled with 3% solution of common salt, sodium chloride, and a lid fitted. The lid can be machined from a block of polyethylene with a suitable diameter hole drilled through. The plate is connected to the negative pole of a battery, an anode is connected to the positive pole and inserted through the hole in the lid into the salt solution. When the circuit is switched on the plate is the cathode and Hydrogen (and Chlorine) will be evolved from the steel, and also at the interface of steel/coating. This enables Hydrogen to penetrate under the coating, simulating areas of coating damage.

Pipe

CP post Voltmeter

Half cell reference electrode filled with copper sulphate solution

Porous plug Ground level



The circuit is stopped after 28 days stripped down, dried off, and using a craft knife, two cuts are made at an inclusive angle of approximately 30o radiating from the centre of the hole, through the coating to the substrate. Where disbondment has occurred the coating will chip of as the cuts are being made. The distance from the edge of the hole to the extent of the disbondment is measured and should not exceed the stated requirements. For example FBE maximum 5mm after 28 days. Figure 11.4 Cathodic disbondment

Plate

6 mm diameter hole

Elastomeric sealant

Coating

Lid Plastic ring

Salt solution

Battery



Painting Inspection Grade 3/2. Rev 1 April 2004 Holiday/Pinhole Detection 14.1 Copyright © 2003, TWI Ltd


HOLIDAY/PINHOLE DETECTION Holidays and pinholes in a paint film are defects which allow ingress of an electrolyte, and therefore are detrimental to an anti corrosion system and need repair. Not all defects of this nature are visible to the naked eye and we therefore need equipment to facilitate the detection. For coatings of thicknesses above 500 um it would be necessary to use a high voltage holiday detector, but for coatings of less than 500 um it is normal to use a wet sponge pinhole detector. Most paint systems on new steel fall into the latter. The wet sponge pinhole detector is a very simple piece of equipment and consists of a small control box, usually pocket size, with two terminals, positive and negative. The negative terminal is connected to bare steel on the structure to be tested. The positive terminal is connected to a hand stick with a sponge on the end. The operating power is provided by two, 1½v batteries in the control box. To use the detector the sponge electrode is wetted in water with a tiny amount of detergent/washing up liquid added, and squeezed out to remove excess water. After switching on and selection of operating voltage, the sponge is traversed methodically over the area. On a vertical surface it is better to work upwards. On contact with a pinhole, the wetting agent (detergent) allows immediate penetration of the water, so providing a very low resistance circuit back to the control box. A high pitched bleep indicates the presence of a pinhole, the exact position of which is located by using a corner of the sponge. The position is then marked ready for repair.

Voltage setting Basic models have two options for setting, 9v and 90v. More sophisticated models have an intermediate setting. For DFTs of less than or equal to 300 um the 9v setting is normal. For DFTs of 300 – 500 um 90v or 67½v intermediate sensitivity would be preferred.

Painting Inspection Grade 3/2. Rev 1 April 2004 Holiday/Pinhole Detection 14.2 Copyright © 2003, TWI Ltd


Painting Inspection Grade 3/2. Rev 1 April 2004 Paint Application 15.1 Copyright © 2003, TWI Ltd


PAINT APPLICATION Paint technology is advancing rapidly and specialised equipment and materials are being introduced into the industry on a regular bases. However, conventional paint application methods still apply. The three main basic methods are: - • Brush • Roller • Spray Brush application Brushing is relatively slow, labour intensive, produces coating of uneven thicknesses, but is more environmentally friendly, results in less waste material and virtually no spotting or over spray damage to adjacent areas. Various types and quality of brushes are used, the most common being the “flat” brush, as opposed to the round headed variety called tar brushes, (and a variety of other names dependant upon geographical areas). The quality of the brush depends mainly upon the type of bristle, or filling used. Natural bristles have a scaly surface, taper along the length, and split at the end. These factors allow the brush to hold more paint and spread it more evenly for a better finish. Synthetic fibres have smooth surfaces and are of uniform thickness for the full length. It was considered that brush application had a more personal shearing action and “worked” paint into the profile, and any dust or other fine detritus present on the substrate worked into the film. Spray application deposits atomised droplets over the particles, entrapping air, which results in pinholes and loss of adhesion. Modern specifications usually state, “as per manufacturers recommendations”. Roller application Rollers are available in several materials e.g. mohair, lambs wool and sponge, and in several different designs, jumbo rollers for large areas, radiator rollers for confined spaced, pressure fed rollers to avoid recharging, and extension rollers which increase access. Curved rollers are supplied for pipe work and roller pile material is even made in glove form for areas of difficult access. However no matter what, they all have the same advantages and disadvantages. They enable paint to be applied quickly but do not give a uniform coating thickness and leave a distinct pattern known as roller stiple. Roller application doesn’t work the paint into the substrate and invariably is not mentioned as an approved application method on specifications. It is a method used “at the discretion of the engineer”, and is certainly not suitable on internal corners, welds, toes, bolts, rivets and plate over laps. In areas of this nature a stripe coat must be applied.



Spray application Paint spray equipment can be divided into two distinctly different types. • Conventional spray. • Airless spray. Conventional spray Conventional spray systems can be subdivided into three different types of equipment which all have the same atomisation mechanism. 1 Suction feed The paint container is underneath the gun, usually aluminium about one litre capacity, and the paint is drawn up by venturi principle to the gun. 2 Gravity feed The paint container is above the gun and paint feeds to the gun by gravity. 3 Remote pressure pot Figure 13.1 Remote pressure pot Remote pots are supplied in several sizes and have the advantage of having a much greater capacity than the above and much bigger areas can be painted before refilling is required. A container (pot) is charged with paint and then sealed with a lid. Air from a compressor is fed into the top of the pot and the paint is forced out through a line to the gun.

Paint

Air in Pressurised air volume

Paint out to gun



At the gun, when the trigger is operated, a tapered needle is drawn back opening the aperture, out of which the paint exits in a continual stream. Approximately 25 mm in front of the aperture, two air channels, from lugs on the cap, diametrically opposed, blow air to converge at the paint stream. At this convergeance the paint is atomised into very minute droplets, and conducted onto the workpiece. Figure 13.2 Conventional gun Airless spray With an airless spray the fluid (paint), is pressurised by means of a pump. Electric motor pumps and hydraulic pumps are sometimes used but the most common is the pump operated by compressed air. These units operate by increasing the compressed air inlet pressure by a stated ratio, e.g. 35:1, by means of two pistons on a common shaft. For instance, if an air driven piston has a surface area of 35 Square inches and is exposed to a pressure of 100 psi, a piston at the other end of the shaft with a surface area of one square inch will exert a pressure of 3500 psi. As the piston is driven down to pressurise the paint, the one way valve at the paint inlet is forced to close position and the paint out port is opened. When the piston reached the bottom of its stroke, the air circuit reverses and forces the piston back upwards. As this happens the outlet port is closed and the inlet port opens to refill the cylinder with paint. At the top of the stroke the air circuit reverses again and drives the piston down again.

Air

Air Needle

Trigger



The outlet pressure can be adjusted by reducing the inlet pressure from the compressor. Figure 13.3 Airless spray These systems are called airless because air is not used for atomisation. Atomisation occurs by forcing the paint at extremely high pressure, usually 2000 to 2500 psi through a very small aperture, 12 to 23 thou diameter, into a volume of air offering a resistance to the paint flow. As the air and paint meet, the paint atomises. Most tips used on airless spray equipment have a facility for reversing the flow of paint through the tip. Blockages can then be cleared by turning the tip through 180o, triggering to ground or a container to clear the blockage, then reverse the tip again to its original position. A type of airless spray tip exists with an adjustable aperture size, called a Titan Tip. The aperture can be closed up or opened by turning a small knurled protrusion, which positions a small steel pin into the aperture to control the size. Pigments and extenders, especially MIO and metallic pigments can be quite abrasive and the tips are subject to wear. Some are sleeved with tungsten carbide to give a loner life.

Lubricant packing

Paint pressurising piston

Paint inlet

One way ball valves

Paint to gun

Compressed air in

Air driven piston



Data sheets for a product will recommend spraying pressure and tip sizes although each sprayer will have his/her own preference. Typical recommendations would be: -

Paint Type Tip Size Pressure PSI Chlorinated Rubber 13 – 21 thou" 2400 High Build Epoxy 17 – 23 thou" 3000 Zinc Rich Epoxy 17 – 23 thou" 2800

Orifice sizes for conventional guns are quoted in metric. Airless spray application is much faster than conventional and more than one gun can be operated from a single pump. The manufacturers container can be used to supply the “wet end”, the inlet pipe, as there is no need for a pressurised container. Notable differences

Conventional Airless Slow application due to fluid delivery.

Excellent application rates.

Low air pressure 40 – 75 PSI

Can need 100 PSI to operate the pump.

Delivery pressure greater than 20 PSI Delivery pressures greater than 6000 PSI, dependant on pump ratio.

Need special paint containers.

Uses manufacturer’s containers.

Guns can be unwieldy, two lines to supply the gun.

Single line supplies pressurised paint.

Basic equipment needs very little maintenance.

Needs more maintenance due to high pressure and moving parts.

Easier to clean after use. Equipment needs flushing well to remove all traces of paint. Expensive replacement.

Safety considerations • Always observe manufacturers recommendations. • Wear recommended safety equipment. • Always depressurise the system before even minor maintenance. • Regularly check fluid lines for wear and leaks. • Ensure that swivels and couplings are properly tightened. • Always engage the safety catch when the gun is not in use. • Never point the spray gun at yourself or other people.



Electro-static spray Both liquid and powder paints can be electro-statically applied. For liquid paints a small air driven turbine is mounted on the gun and supplies a current to the tip. The current is usually on a thumb control for adjustment and operates in the region of 85 kv. Powder paints in general are charged electro-statically by spraying the powder through an area of ionised air. In either case the component to be coated is earthed into the same circuit and thus becomes negatively charged. The coating material is positively charged and is attracted to the component. As the coating thickness increases it has an insulation effect and the coating material is then drawn to other charged areas. The voltage can control the thickness, especially when using powder coatings. Wastage is significantly reduced and it produces a more uniform coating. Electro-static application is widely used in industry for components such as kitchen white goods, office cabinets and line pipe. (When powers are used the components are either pre heated or post heated. Line pipe and other substantial section components can be pre heated, but thin steel plate components will not maintain sufficient heat and so are electro-statically coated and then post heated).

Other paint application methods Industrial anti-corrosion systems are generally applied by the systems discussed previously, however various other accepted methods exist. Viz. Dip coating - A component is dipped into paint and hung to dry. Padding - Mainly DIY Pads of mohair or foam are used to apply paint. Large

pads like plaster hawks for large areas and small ones (about 25 mm square) for cutting in around door furniture and putty lines on windows.

Hot spraying - When paint is heated it reduces in viscosity (flows easier) and the cure or drying starts quicker. It is therefore easier to apply and wets out better, and reduces the need for solvent addition.

Spin rotating - Usually called a spinner, the equipment, consisting of a three-legged frame, each with a wheel at the end and a centrally mounted spinner is drawn along dispensing paint from the spinner. Ideal for internal coatings on line pipe sections.

Flow coating/ curtain coating

- Bitumen and Coal Tar enamel pipeline coatings, when used, are applied hot, about 200oc, to the 12 o’clock position of a pipe, the material flows down both sides to meet at 6 o’clock. The material being thermoplastic hardens as it cools and coats the pipe.

Aerosols - Pressurised cans operated by push buttons, car paint touch up kits among other used.

Painting Inspection Grade 3/2. Rev 1 April 2004 Metal Coatings 16.1 Copyright © 2003, TWI Ltd


METAL COATINGS Galvanising The coating of components with zinc. Many components both for offshore and onshore use, are galvanised. Galvanising can give protection to steelwork for periods of up to 60 years dependant on exposure conditions. The components are chemically cleaned (acid), washed and fluxed, then totally immersed in a vessel containing molten zinc at approximately 450oc. When drawn out, the zinc solidifies at an average thickness of approximately 100 um.

Sheradising Nuts and bolts and other similar components are coated with this method. Galvanising threads would make a significant difference to the dimensions and workings of fixings and fasteners, so zinc powder, just below the melting point, is used instead. After cleaning the components are tumbled in the powdered zinc, impact fuses the zinc onto the components and in effect, “cold welds” the powder onto the metal.

Calorising Calorising is coating with aluminium. Aluminium has a melting point of 625oc as apposed to 425oc of zinc so it is not really practical to tumble. One way of calorising a component is to dip it into molten aluminium. The resulting exothermic reaction is so severe that is alloys the aluminium with the steel. Calorising can also be done by immersing a component in a mix of fine sand and aluminium powder and heating.

Anodising A treatment for aluminium, anodising is an electrolytic method of coating which results in the formation of a dense oxide. The component is immersed in a weak acid bath and oxidation is induced electrically.

Electro-plating This is done by electrolytic deposition. If a current is released from an item into a metal salt solution through to a cathode, the metal salts ionise and deposit the metal ions on the cathode bar.



Hot metal spraying Any metal, which can be easily melted, can be sprayed. Zinc and aluminium are the most commonly used metals for spraying. They are both below steel on the galvanic list and so will provide cathodic protection to the steel, and both metals have a reasonable low melting point. Both metals have advantages and disadvantages, for instance zinc performs far better than aluminium in rural areas and alkaline environments. Aluminium is considered to be superior to zinc in slightly acidic environments and because of its higher melting point is more widely used on high temperature surfaces such as exhaust stacks, compressor exhausts etc. where extremely high temperatures are encountered. It is specified for use on surfaces with working temperatures of up to 540oc. Application of metal sprayed coatings can be carried out by any of the following methods. Powder system Powdered metal is fed into a heat source (usually butane or propane and pure oxygen burning) and propelled onto the substrate. Using this method a relatively low proportion of the metal powder is actually deposited on the substrate. Electric arc system This method is ideal for production line type facilities such as gas bottle production and lamp standards etc. where components are of a uniform shape and the process can be mechanised. As in a welding process the metal (to be sprayed) acts as an electrode in a circuit and the electrode melts. The molten metal is atomised and blown onto the component by means of a heated air jet. This system gives a superb fine grain finish.

Wire and pistol system By far the most common and widely used method for site application of metal spray. The metal wire, of a very high degree of purity, greater than 99.5%, is driven through a gun by means of two knurled wheels powered by compressed air. As the wire, 3mm – 5mm passes through to the front of the gun it passes through a ring of burners, with the flames focused about 35mm from the exit point. The fuel gases used are butane/propane and pure oxygen. The flames melt the wire and droplets of metal are propelled to the steel by the combustion gasses and compressed air. The coating is usually applied at a thickness of 100 – 125mm and is about 85% to 95% density of the original wire. This is because the resulting film is in an open cell structure due to individual particles forming a “fish scale” like structure, the interstices between the particles are not all filled.



If the coating is to be subjected to high temperature services it will need sealing with a silicone sealer, aluminium or carbon pigmented. If however the metal spray is applied to give an extended major maintenance free life to an anti-corrosion system, then either an epoxy sealer or etch primer would be applied prior to the specified system.



Painting Inspection Grade 3/2. Rev 1 April 2004 Coating Faults 17.1 Copyright © 2003, TWI Ltd


COATING FAULTS As defined in BS 2015, Glossary of Paint and Related Terms. Bittiness The presence of particles of gel, flocculated material or foreign matter in a coating material, or projecting from the surface of a film. Note 1 The term seedy specifically denotes the presence of bits that have developed in a

coating material during storage. Note 2 The term peppery is sometimes used when the bits are small and uniformly

distributed. Bleeding The process of diffusion of a soluble coloured substance from, into, or through a coating material from beneath, thus providing an undesirable staining or discolouration. NB. Examples of materials, which may give rise to this defect, are certain types of the following materials: - bituminous paints, wood preservatives, oleoresins from wood knots, organic pigments and stains and coal tar. Bitumen and Coat Tar Enamels also. Blistering The formation of dome shaped projections or blisters in the dry film of a coating material by local loss of adhesion and lifting of the film from the underlying surface. Note 1 Such blisters may contain liquid, vapour, gas or crystals. Bloom A deposit resembling the bloom on a grape that sometimes forms on the floss film of a coating causing loss of gloss and dulling of colour. Chalking The formation of a friable, powdery layer on the surface of the film of a coating material caused by disintegration of the binding medium due to disruptive factors during weathering. Note 1 Chalking can be considerably affected by the choice and concentration of pigment.



Cissing The formation of small areas of the wet film of a coating material where the coating material has receded leaving holidays in the film. Cracking Generally the splitting of the dry film of the coating material usually as a result of ageing. Specifically a break down in which the cracks penetrate at least one coat and which may be expected to result ultimately in complete failure. a) Hair cracking Cracking that comprises of fine cracks, which may not penetrate the top coat, they occur erratically and at random. b) Checking Cracking that comprises of fine cracks, which do not penetrate the top coat and are distributed over the surface giving the semblance of a small pattern. c) Crazing Cracking that resembles checking but the cracks are deeper and broader. d) Crocodiling/alligatoring A drastic type of crazing producing a pattern resembling the hide of a crocodile or alligator. e) Mud cracking A network of deep cracks that form as the film of a coating material dries, especially when it has been applied to an absorbent substrate. Mud cracking is associated primarily with highly pigmented water borne paints. Cratering The formation of small bowl shaped depressions in the film of a coating material. Curtaining/sagging A downward movement of a coat between application and setting that results in an uneven area of coat having a thick lower edge. The resulting sag is usually restricted to a local area of a vertical surface and may have the characteristic appearance of a draped curtain.



a) Run A narrow downward movement of a coat that may be caused by the collection of excess quantities of paint at irregularities in the surface e.g. cracks and holes, the excess material continuing to flow after the surrounding material has set. b) Tear A small run resembling a teardrop. Dry spray The production of a rough or slightly bitty film from sprayed coating materials where the particles are insufficiently fluid to flow together to form a uniform coat. Efflorescence A whitish crystalline formation on bricks, mortar, plaster etc. Usually forms under paint films on the above substrates, and is not a paint defect. Caused by soluble salts crystallising on the surface. Flaking Lifting of the coating materials from the substrate in the form of flakes or scales. Flocculation The development of loosely cohesive pigment agglomerates in a coating material Grinning through The showing through of the substrate due to the inadequate hiding power of the coating material. Holidays A defect due to faulty application techniques seen as areas where the film of a coating material is of insufficient thickness or where there is a complete absence of coating materials on random areas of the substrate. Lifting Softening, swelling or separation from the substrate of a dry coat as a result of the application of a subsequent coat.



Orange peel The uniform pock marked appearance, in particular of a sprayed film, resembling the peel of an orange due to the failure of the film to flow out to a level surface. Pinholing The formation of minute holes in the wet film of a coating material that forms during application and drying, due to air or gas bubbles in the wet film which burst, giving rise to small craters that fail to coalesce before the film has set. Residual tack The degree of stickiness remaining in the film of a coating material which, although set, does not reach the true tack free stage. Ropiness Pronounced brush marks that have not flowed out because of the poor levelling properties of the coating material. Saponification The formation of a soap by the reaction of a fatty acid ester and an alkali. Note 1 In painting practice, saponification refers to the decomposition of the medium of a

film by alkali and moisture in the substrate, e.g. new concrete or rendering based on cement, sand and lime. Saponified films may become sticky and discoloured. In very severe cases the film may be completely liquefied by saponification.

Wrinkling/rivelling The development of wrinkles in the film of a coating material during drying. Usually due to the initial formation of a surface skin.

Painting Inspection Grade 3/2. Rev 1 April 2004 Colour 18.1 Copyright © 2003, TWI Ltd


COLOUR When considering the aesthetics of a final coat of a paint system, colour is an important property, as gloss and opacity. Colour can affect mood and perception, and can create illusions. White light, light emitted from the noonday sun is a combination of electromagnetic wavelengths from 400 nanometers to 700 nanometers, blue through to red. When white light strikes an object, certain frequencies are absorbed and others reflected. It is the reflected frequencies that the human eye translates into colour. Colour has three attributes, which are: - 1 Hue Refers to the basic colour e.g. red, yellow, green and blue. Can be represented in circle form, clockwise, red yellow green blue red. 2 Brightness Sometime called lightness, it refers to the amount of lightness or darkness of the colour. The degree of reflectivity of the surface receiving the light governs this property and is sometimes called value or reflectance value. 3 Saturation How vivid colour appears. It is measured in terms of the difference of a colour from the neutral grey with the same degree of brightness. Lower saturation, greyer the colour. The terms chroma and intensity, and sometimes weight, are also used. Black and white and the greys in between are called “achromatic” colours, they lack hue and saturation. Anything perceived as having colour is “chromatic”.



The three attributes can be related to a three dimensional model of a helix. Figure 16.1 Three dimensional helix

The Munsell colour system An American system, which identifies colour by its three attributes, Hue Chroma and value (Reflectance value). In the Munsell system, Hue is divided into five basic colours Red, Yellow, Green, Blue and Purple each identified by its initial letter, with a second dimension between each, giving ten basic colours. Value is defined in eleven steps from white to black and chroma has fifteen steps.

The BS 4800 colour system This BS specifies 100 colours selected from 237 used in the BS 5252. The BS 4800 uses the same basic colours but expands to thirteen, including a neutral. The colours are numbered from 02 to 24, 00 being neutral, achromatic, using even numbers only.

Red

Red purple Purple Purple blue

Blue

Blue green

Green

Green yellow Yellow

Yellow red

White

Black

Saturation

Brightness

Hue



Lightness is identified by capital letters A to E, where A is maximum lightness and E is minimum lightness. The chroma is given by number, the third part of the coding, from 01, in single digit rises to 56. The higher the number, the stronger the colour.

The BS 5252, framework for colour co-ordination for building purposes The BS 5252, framework for colour co-ordination for building purposes, selects a framework of 237 colours as a source for all building colour standards and a means of co-ordinating them. It is not itself a rang of colours.



Painting Inspection Grade 3/2. Rev 1 April 2004 Health & Safety 19.1 Copyright © 2003, TWI Ltd


HEALTH AND SAFETY Control of substance hazardous to health regulations 1988 generally abbreviated to COSHH regulations. These regulations provide a framework to help to protect personnel at the workplace against health risks from substances, which are hazardous. For the purpose of COSHH regulations, substances hazardous to health include. a) Substances or preparations listed as being toxic, very toxic, harmful, corrosive or irritant in

part 1A of Chemicals (Hazard Information for Packaging) Supply. b) Substances with MEL or OES as detailed in schedule one of COSHH or if Health and

Safety Commission has approved an OEL. c) Harmful micro-organisms. d) Dust of any kind in substantial concentrations. e) Any other substance creating comparable hazards to peoples health such as pesticides and

other chemicals used on farms.

Hazard warning symbols

- Black symbol of skull and crossbones on an orange square with the words Toxic or Very Toxic printed below

- Black diagonal cross on an orange square with the words Harmful or Irritant printed below.

- Black symbol showing a tilted test-tube dripping onto a hand with a chunk out, adjacent to a test tube dripping onto a stone flag. Orange background with the word corrosive printed below.

Toxic or Very Toxic

Corrosive

Harmful or Irritant



Responsibilities It is the employer’s duty to assess the risk to employees on his/her premises and any other premises, which might be visited during the execution of duties. Training establishments are responsible for trainees. It is an employers duty to prevent, where ever possible, exposure to hazardous substances, but if it is not reasonably practical to totally prevent exposure then protective clothing, masks etc. should be issued to minimise exposure. COSHH regulations require that regular monitoring should be carried out and records kept, particularly in situations where there could be serious risk to health if control measures were to fail or deteriorate. Guidance note EH 40 (occupational exposure limits), is a document published by the HSE, which lists all substances known to be hazardous to mankind. It gives details in table form of common names, chemical formulae and chemical names of hazardous substances. The Hydrocarbon solvents used in modern paint formulations are hazardous to health and are listed in EH 40. Xylene is one such solvent and has an Occupational Exposure Limit (OEL) of 100 ppm (parts per million). This means that air containing more than 100 ppm would be considered to be a hazard to the health of personnel exposed to it. There are two categories of OEL. 1 Maximum Exposure Limit (MEL). “The maximum concentration of an airborne substance, averaged over a reference period, to which employees may be exposed by inhalation under any circumstances and is specified, together with the appropriate reference period, in Schedule one of COSHH.” 2 Occupations Exposure Standard (OES). “The concentration of an airborne substance, averaged over a reference period, at which, according to current knowledge, there is no evidence that it is likely to be injurious to employees if they are exposed to inhalation, day after day, to that concentration, and which is specified in a list approved by HSE.” When referring to reference periods above, long term exposure limits are averaged over an eight hour reference period and short term exposures over ten minute reference periods. If the EH 40 specifies that a substance has an MEL then the quoted figure must not be exceeded at any time, but kept as low as is reasonably practical.



With an OES it is permissible to exceed the stated figure provided that the average over a reference period is below the stated figure. Exposures

OEL examples of some solvents Solvent Name OEL in ppm Alcohol’s Methanol

Ethanol 200 1000

Ethers Ethyl Ether Isopropyl Ether

400 250

Esters Methyl Acetate Ethyl Acetate

200 400

Ketones Acetone Methyl Ethyl Ketone

750 200

Aromatics Xylene Toluene

100 50

Aliphatics White Spirit Hexane

100 500

Chlorinated Hydrocarbons 1.1.1 Trichloroethane Trichloroethylene

350 ab 100 ac

Dräger tube and Dräger bellows Figure 17.1 Dräger tube One way of monitoring the toxicity of the air is by dräger tube and dräger bellows. The dräger tube is a glass tube about 110 mm long with moulded nipples at each end. One half of the tube is filled with chemical crystals (sensitive to the material testing for) and are held in position by fine wire mesh plugs. A cellophane sleeve, incorporating a scale in ppm is wrapped around the tube. There is also an arrow on the sleeve indicating the way in which the tube is to be inserted into the bellows.

a = MEL b = Maximum short term exposure 450. c = Maximum short term exposure 150.

N =

5

Dräger



The bellows are hand operated and are a one way air system, as the bellows are depressed, air is expelled from a slot at the back, when released, air is drawn in through a small rubber grommet like aperture at the front. The bellows incorporate two compression springs and stops, and two retaining chains, so that every depression and release exchanges an air volume of 100 cc exactly. Figure 17.2 Cross-section of dräger bellows

Using the tubes and bellows Using a special fitting situated on the bellows, the nipples are snapped off both ends of the tube, which is then inserted into the aperture on the bellows in the direction indicated by the arrow. The crystals should be adjacent to the bellows. The bellows are then depressed and released according to the number expressed as n =, as written circumferentially around the centre of the tube. Each depression and release slowly draws 100 cc of air through the open end of the tube, through the crystals and into the bellows. As the air containing the hazardous material passes into the crystals, a chemical reaction takes place, resulting in a colour change in the crystals. The extent of the colour change along the scale is recorded in ppm. NB. Many variation of crystal combinations exist for monitoring a variety of different toxicants, all have a different requirement for number of depressions and different colour changes. The tube for monitoring the concentrations of Xylene needs five depressions and the colour change is from white to reddish brown.

Limiting chain

Discharge valve

Front plate

Break-off husk

Pump head

Sieve



Some materials in common use in the coatings industry do not evaporate into gas or fumes, they remain instead as tiny particles of solids suspended in the atmosphere. Materials of this nature cannot therefore be detected by Dräger Tube. They are quantified by the units milligrams per cubic metre rather than ppm. Three materials, which fall into this category, are Asphalt, Coal Tar and Isocyanates. Asphalt is considered to be fairly safe with an OEL of 5 m/gm per m3. Isocyanates are very toxic with an MEL of 0.02 m gm/m3.



Painting Inspection Grade 3/2. Rev 1 April 2004 Duties of an Inspector 20.1 Copyright © 2003, TWI Ltd


DUTIES OF AN INSPECTOR BS 4778 Pt1 (EN 28402, ISO 8402) Quality Vocabulary – International Terms, defines inspection as “Activities such as measuring, examining, testing, gauging, one or more characteristics of a product or service and comparing these with specified requirements, to determine conformity”. Documents available to an inspector could include, but not be limited to. a) Job Specification. b) Data Sheets for the paints/coatings. c) Procedures. d) Quality Plans. e) Plant Drawings. f) Site Plans. g) BS’s e.g. 7079 Pt A. h) Waste Management, Duty of Care Document. i) Relevant Local Regulations. The job specification is the main tool of the inspector and should be observed at all times. It is not the inspector’s responsibility to rewrite the specification and permission for any deviation should be given in writing and retained by the inspector. An inspector should keep adequate and accurate records of all stages of the work being carried out, materials used, ambient conditions etc. so that in the event of illness or any other situation requiring a replacement, the new inspector will be in full possession of all relevant information. Paint/Coatings Inspectors Daily Report Sheets need to be completed, and passed on to the engineer, containing all information requested, and a copy retained by the inspector. The format of Daily Report Sheets varies but in general will require the following information. 1 Details about the contract and contractor, including plant on site and number of personnel. 2 Ambient conditions applicable during the work period, to be monitored as near as possible

to the task location. 3 For surface preparation activities the information required will include, method used,

original substrate condition, abrasive type, degree of cleanliness achieved, profile achieved, identity of plant and times of starting and completion.

4 For materials, the information required will include manufacturer, product reference number, expiry date, batch number, colour, reference number of thinners, WFT and resulting DFT, time of application and identity of plant. In the case of labour only contracts it will be required to record quantity used.

5 The comment part is a space left for the inspector to report on any irregularities, non-conformance or deviation from specification.



In addition to the daily reports it may also be a requirement to complete a weekly summary, detailing progress and any other information, such as repeated deviation from specification, for the engineer. Typical examples of situations to report would be. 1 Substituting approved products with unapproved products. 2 Substituting new materials with out of date materials. 3 Using solvents other than those approved by the manufacturer. 4 Not observing induction times when specified. 5 Using untrained personnel. 6 Re-using expendable abrasives. 7 Not observing recommended over coating times. 8 Continuing with the next stage of operations without inspection of the substrate and

approval. 9 Painting/coating over areas of inadequate surface preparation. 10 Working in conditions outside of specified requirements.



Job: Report No. Contractor: Date: Location: Specification: No. of men: Start time: Finish time:

Weather a.m. p.m.

Time Ambient temp.oC

Relative humidity%

Dew point oC

Steel temp oC

Time Ambient temp.oC

Relative humidity%

Dew point oC

Steel temp oC

Surface preparation: Initial condition: Blast clean Abrasive: Type: Profile Sa2 Sa2½ Sa3 Hand clean Method St2 St3

Paint application: Manufacturer’s name: Coat No. Manufacturer’s description Ref. No. Colour Wft Dft Quantity

used-ltrs.

Item coated Coat No. Ref. No. Batch No. Time interval Wft Total Dft Comments: Signature:

Transmission Department PAINTING INSPECTION FORM

WALES GAS NWY CYMRU



EXAMPLE

PAINTING CONTRACTOR

PAINT SUPPLIER

ABRASIVE SUPPLIER

AREAS TREATED SURFACE PREPARATION

PAINTS APPLIED

METHOD OF APPLICATION

WFT DFT

TIME DRY

BULB TEMP

WET BULB TEMP

REL HUM

DEW POINT

STEEL TEMP

TYPE OF

WORK TIME

DRY BULB TEMP

WET BULB TEMP

REL HUM

DEW POINT

STEEL TEMP

TYPE OF

WORK

WEATHER No OF MEN ON SITE

COMMENTS INSPECTOR PRINT SIGNED INSPECTOR SIGNED ENGINEER

PAINTING INSPECTION REPORT

CUSTOMER REF NO CONTRACT REF No

CLIENT LOCATION

REPORT No DATE

Painting Inspection Grade 3/2. Rev 1 April 2004 Specification & BS Numbers 21.1 Copyright © 2003, TWI Ltd


LIST OF SPECIFICATION AND BS NUMBERS BS 410 - Specification for test sieves. BS 2015 - Glossary of paints and related terms. BS 2569 Pt 2 - Specification for sprayed metal coatings. BS 3900 - Methods of test for paints. BS 4800 - Schedule of paint colour’s for building purposes. BS 5252 - Framework for colour co-ordination for building purposes. BS 5493 - Code of practice for protective coating of iron and steel structures. BS 7079 - Preparation of steel substrates before application of paints and

related products. BS 7079 Group A - Visual assessment of surface cleanliness. BS 7079 Group B - Methods of assessment of surface cleanliness. BS 7079 Group C - Surface roughness characteristics of blast cleaned steel substrates. BS 7079 Group D - Methods for surface preparation. ISO 8501 - Group “A” as above. ISO 8502 - Group “B” as above. ISO 8503 - Group “C” as above. ISO 8504 - Group “D” as above. SIS 055900 - Pictorial surface preparation standards for painting steel surfaces. B6C PS PA 5 - Notes for guidance, painting inspection. B6C PS PA 7 - Stoved paint finishing. B6C PS PA 8 - Internal coating for steel small bore pipe. B6C PS PA 9 - Paint properties and performance requirements. B6C PS PA 10 - New and maintenance painting at works and site for above ground

pipeline and plant installations. 1GE SR 21 - Code of practice for safety during blast cleaning operations. B6C PS PWC1 - Acoustic cladding B6C PS PWC2 - Thermal insulation of above ground pipe work and equipment.

Painting Inspection Grade 3/2. Rev 1 April 2004 Specification & BS Numbers 21.2 Copyright © 2003, TWI Ltd


Painting Inspection Grade 3/2. Rev 1 April 2004 Quality 22.1 Copyright © 2003, TWI Ltd


QUALITY

Quality assurance The definition of quality assurance in BS 4778 Pt1, Quality Vocabulary is “All those planned and systematic actions necessary to provide adequate confidence that a product or service will satisfy given requirements for quality”. Quality assurance is regarded as being a management tool, a method of maintaining and improving quality whilst controlling costs. A quality system operates on the theory that if there is time and budget allocation to rectify mistakes within a process, then it is preferable to allow a little time to “get it right first time” at reasonable cost. (By using mathematical tools like Pareto Analysis on a production line, eliminate the most frequent fault and reparation is often halved, then eliminate the next most frequent.) Companies employing quality systems produce procedures for every task performed, if everyone works in a formalised way to achieve the requirements of the specification, then consistency of quality should automatically follow. If quality is improved and costs reduced than a company can be more competitive and consequently improve its position in the market place. Quality assurance is not solely operated by production, but is throughout an organisation, and deals with every aspect of a companies operations from planning and design and training through to packing the final product, transport and marketing.

Quality control BS 4778 Pt1 definition “Operation techniques and activities that are used to fulfil requirements for quality”. The inspection function provides information in order that quality control can be maintained by adjusting the process to eliminate any deficiency.

Quality related standards BS EN ISO 9000 series Quality systems. BS 4778 Quality vocabulary (EN 28402 ISO 8402). BS 7229 Quality systems auditing. BS EN 30011 Guidelines for auditing quality systems.

Painting Inspection Grade 3/2. Rev 1 April 2004 Quality 22.2 Copyright © 2003, TWI Ltd


Quality related definitions (from the above) 1 Code of practice - Document that recommends practices or procedures

for the design, manufacture, installation maintenance or utilisation of equipment, structures or products.

2 Instruction - Provision that conveys an action to be performed.

3 Normative document - A document that provides rules guidelines or characteristics for activities or their results.

4 Procedure - A specified way to perform an activity.

5 Regulation - A document providing binding legislative rules that is adopted by an authority.

6 Specification - The document that prescribes the requirements with which the product or service has to conform. NB. A specification should refer to or include drawings, patterns or other relevant documents and should also indicate the means and the criteria where by conformity can be checked.

7 Standard - Document, established by consensus, and approved by a recognised body, that provides, for common and repeated use, rules, guidelines or characteristics for activities or their results, aimed at the achievement of the optimum degree of order in a given content.

8 Technical specification - A document that prescribes technical requirements to be fulfilled by a product, process or service. NB. A technical specification should indicate, where ever appropriate, the procedure(s) by means of which it may be determined whether the requirements given are fulfilled. A technical specification may be a standard, a part of a standard or independent of a standard.

Painting Inspection Grade 3/2. Rev 1 April 2004 Revision Questions 23.1 Copyright © 2003, TWI Ltd


REVISION QUESTIONS

Corrosion OP – Monday 1 Is the electrical circuit in a corrosion reaction AC or DC? 2 Does corrosion occur at the cathode or at the anode? 3 Name the three factors needed for corrosion to occur. 4 What is meant by the term electrolyte? 5 What is corrosion? 6 In the corrosion circuit do electrons flow from anode to cathode? 7 Which gas is released at the cathode when the electrolyte is water? 8 Which is the more noble metal, steel or Aluminium? 9 Which is more electronegative, steel or Aluminium? 10 If steel and copper were in contact in an electrolyte which would corrode? 11 Name two common Hygroscopic salts. 12 Name three metals used as sacrificial anodes on a steel pipeline. 13 What is the approximate thickness of millscale? 14 Which of the two metals would corrode if steel and zinc were coupled? 15 Which other names relate to the Galvanic List? 16 In which environment are you likely to encounter chloride salts? 17 Which three compounds together form millscale? 18 If magnesium was coupled with zinc, which would corrode? 19 In which environment would sulphate salts be found? 20 What is an osmotic blister? 21 What is an ion? 22 What is meant by polarisation? 23 Is an anode positive or negative? 24 Can corrosion occur without an electrolyte? 25 Name a sub atomic particle. 26 What is millscale and when and where does it occur? 27 Name three factors, which can accelerate corrosion reactions. 28 Why is it considered essential to remove millscale prior to painting? 29 Why does an un-coated steel plate corrode? 30 If corrosion occurs at anodic areas, why does steel corrode evenly all over the surface?



Surface preparation - Monday 1 Which British standard would be used in determining the size of copper slag abrasive? 2 Which British standard would be used in determining the size of metallic abrasives? 3 Which regulations prohibit the use of sand for blasting steel? 4 What is meant by the term ‘key’? 5 Why is it important to have good surface preparation? 6 What is meant by the term sliver? 7 What is a hackle? 8 Name two other terms that could be used for ‘anchor pattern’? 9 What are the main advantages of using ‘Testex papers’ for measuring profiles? 10 What is meant by the term grade, relating to a blast finish? 11 What are the main factors governing the grade of a blast finish? 12 Can the grade of a blast finish be determined by using the surface comparators to BS 7079

Pt C3? 13 What profile range can be measured using X coarse Testex? 14 What profile range can be measured using coarse grade Testex? 15 What are the two theories of adhesion? 16 Briefly describe the mechanisms of the two theories of adhesion. 17 How many microns are in 1thou? 18 Give three different names for the cross section of a blast. 19 What is the approximate speed of abrasives leaving a venturi nozzle? 20 What is the most common cause of flash rusting on a blasted substrate? 21 What would be considered to be an ideal shot grit mix? 22 What is the purpose of mixing shot and grit? 23 Which abrasive would have the effect of work hardening a substrate? 24 Name three methods of measuring or assessing a profile. 25 What is the most common cause of rogue peaks on a substrate? 26 In what situation would it be better to use steel grit in preference to copper slag abrasives? 27 If cracks or laminations are found on a substrate after blasting what steps should be taken? 28 Using comparators to ISO 8503, what are the three main profile assessments? 29 What are the other two assessments when the above three are not appropriate? 30 What would be size of copper slag needed to give a profile of 50 to 75 um?



Surface preparation – Tuesday 1 What is the title of the BS 7079? 2 What are the four characteristics of an abrasive? 3 Why are blast hoses carbon impregnated? 4 Name the gauge used for measuring pressure at the blast nozzle? 5 Name four advantages of centrifugal blasting over open blasting. 6 According to BS 7079 is it possible to blast clean to an A Sa1? 7 Is there any difference between an A Sa1 and B Sa1? 8 Could you tell the difference between rust grades A and B blasted to Sa3? 9 Could you tell the difference between rust grades C and D blasted to Sa3? 10 What would be a typical speed of abrasives leaving a wheel abrator? 11 What is considered to be the most efficient blasting pressure? 12 What is meant by the term “burnishing”? 13 What would be the equivalent to St2 in the Sa grades? 14 What is the neutral figure on the pH scale? 15 How is pH measured? 16 Why are inhibitors sometimes added to water in wet blasting? 17 Name two typical areas where needle guns might be used? 18 What is the Duplex Process of surface preparation? 19 Which pH range covers acids? 20 Which pH range covers alkalies? 21 What is the meaning of pH? 22 Name three disadvantages of wet blasting. 23 Name two areas on a structure where flame cleaning cannot be done. 24 Which three basic operations are performed during flame cleaning? 25 How does BS 7079 define Flame Cleaning standards? 26 What is a ‘Jasons Hammer’? 27 What is meant by St2 and St3? 28 Two alloys are used to render wire brushes spark free, what are they? 29 Why should ‘Burnishing’ be avoided? 30 Name two major disadvantages of using a needle gun. 31 After phosphating, what would be a typical pH requirement prior to coating? 32 What is understood by the term ‘knock out pot’? 33 If an operator was blasting with a nozzle pressure of 80 psi. What would be his

approximate efficiency? 34 Which solvents are commonly used for degreasing? 35 What is a ‘dead mans handle’? 36 Why is carbon impregnated into blast hoses? 37 How is abrasive cleansed in a wheel abrator system? 38 What is the main disadvantage of high pressure jetting compared to other systems? 39 Name five methods of wet blasting. 40 What would be the typical temperature and concentration of Sulphuric Acid in the pickling

process? 41 Describe the ‘Duplex Process’. 42 What would be a maximum pressure for high pressure water jetting? 43 What are the disadvantages of wet blasting over dry blasting? 44 Describe the phosphating process.



45 What would be considered to be advantages of wet blasting over dry blasting? 46 Why is the phosphating or chromating of steel done? 47 What would be an acceptable remedy for burnished areas? 48 Would burnishing be expected on areas of St2 preparation? 49 How many photographs of blast cleaning standards are shown in BS 7079 Pt A? 50 Do the plates shown in Bs 7079 Pt A relate to grit blasting or shot blasting?



Paint technology (1) - Wednesday 1 Name a third type of paint other than solvent free and solvent borne. 2 An epoxy resin would use which solvent? 3 Name four or more advantages of Chlorinated Rubber paints. 4 What are the three main disadvantages of Chlorinated Rubber paint? 5 Which solvent could be used with a Phenolic Resin? 6 Chlorinated Rubber paint would contain which solvent? 7 Would it be good practice to apply Chlorinated Rubber over Alkyd resin? 8 Which solvent would be used with an Alkyd Resin? 9 How was the word Alkyd derived? 10 What is meant by opaque? 11 What is meant by vehicle? 12 Would it be acceptable practice to apply an Alkyd over Chlorinated Rubber? 13 Would it be acceptable practice to apply Chlorinated Rubber over Phenolic? 14 Would it be acceptable practice to apply Phenolic Resin over Chlorinated Rubber? 15 Would it be acceptable practice to apply Epoxy over linseed oil base? 16 Would it be acceptable practice to apply Chlorinated Rubber over Epoxy? 17 Would it be acceptable practice to apply Epoxy Resin over Alkyd Resin? 18 What is another name for an un-pigmented paint? 19 What are the natural properties of a Resin? 20 What are the natural properties of an Oil? 21 How does paint using the barrier principle work? 22 How does paint using the passivation principle work? 23 How does paint using cathodic protection principle work? 24 Give another name for solvent free two packs. 25 Name six properties of a binder. 26 Name three natural resins used in paints. 27 Name five natural oils used in paints. 28 What does oleoresinous mean? 29 Name an Inorganic high temperature service binder. 30 Name two pigments likely to be used for high temperature service.



Paint technology (2) - Wednesday 1 By what name would you call the basic unit of a polymer? 2 What is polymerisation? 3 Name three types of polymers. 4 What would be the characteristics of a short oil paint? 5 What would be the characteristics of a long oil paint? 6 What is meant by the term “opaque pigment”? 7 What is a typical size of a pigment particle? 8 Briefly describe the difference between “saturated” and “unsaturated” when referring to

oils or polymers. 9 Name two drying oils, which are unsaturated. 10 What is the main difference between a dye and a pigment? 11 What are the sources of pigments? 12 If Titanium Dioxide was used in paint, what would be the colour? 13 Name three rust inhibitive pigments considered to be toxic. 14 Name four commonly occurring minerals used as extender pigments. 15 Name three laminar pigments. 16 If pigment was added way below the CPVC, how would it affect the film? 17 The abbreviation CPVC means what? 18 Why are thixotropes added to a paint formulation? 19 If carbon was used as a pigment what would be the paint colour? 20 Name four properties that a binder contributes to a paint film. 21 Describe how a basic inhibitor works. 22 Which of the common extenders could not be used in whites and pastels? 23 How would the film be affected if pigment was added above the CPVC? 24 Which of the rust inhibitive pigments is the most common? 25 Why are extenders used in paint formulation? 26 If chromium was used as a pigment, what colour would the paint be? 27 Why are plasticisers added to paint? 28 Two metals are commonly used as galvanic pigmentation, name them. 29 Why are driers added to oil based paint? 30 What is meant by the term ‘thixotropic’? 31 What is meant by the term ‘aggregate’ when referring to paint? 32 If an antioxidant was added to paint, what would it do? 33 Give the names of two plasticisers. 34 What is meant by the term solution? 35 Give two examples of a solution. 36 What is meant by the term dispersion? 37 There are two types of dispersion, what are they? 38 If paint cures by chemical reaction is it reversible or convertible? 39 What type of polymerisation occurs in chemically curing paint? 40 Name a paint, which dries solely by solvent evaporation. 41 What is meant by ‘non convertible’? 42 What is meant by ‘non reversible’? 43 Name four drying mechanisms. 44 In a coating, which dries by solvent evaporation, what type of polymerisation occurs? 45 What is another term for Fineness of Grind? 46 Which generic types of paint dry by solvent evaporation followed by oxidation?



47 What type of polymer forms during oxidation? 48 What term applies to paint drying at ambient temperatures? 49 What is meant by the term ‘co-alescence’? 50 What is meant by the term ‘pot life’? 51 Name three curing agents used in epoxies? 52 Is paint a solution or dispersion, qualify? 53 What is an exothermic reaction? 54 What is meant by the term ‘induction period’? 55 What is the difference between ‘thermoplastic’ and ‘thermosetting’? 56 With a chemically curing paint, what type of polymerisation occurs? 57 Two other terms relate to induction period, what are they? 58 Does a phenolic resin have an induction period? 59 Which of the following binders are reversible?

a) Epoxy b) Phenolic c) Vinyl

d) Urethane e) Chlorinated Rubber f) Alkyd

g) Cellulose h) Silicone

60 Is an epoxy powder paint thermoplastic or thermosetting? 61 If a coating is permeable, what does it mean? 62 What is meant by cross-linking, give two binders as an example. 63 What is the opposite to exothermic? 64 What is the term used for paints needing temperatures in excess of 65oc to cure? 65 What would be a typical induction period for Chlorinated Rubber paint? 66 Name a material used as a dryer in paint formulation. 67 Why would bentonite or wax be used in paint formulation? 68 Name two materials used as plasticisers. 69 What generic type of paints would use anti-oxidants? 70 How does a single pack, epoxy ester paint dry? 71 How is Dewpoint defined? 72 How is Relative Humidity defined? 73 When using a whirling hygrometer which bulb should be read first and why? 74 At what speed should the thermometer bulbs pass through the air? 75 What should be used when wetting the wick on whirling hygrometer? 76 By what other name can we refer to a whirling hygrometer? 77 When the air temperature rises does the air’s capacity to hold water increase or decrease? 78 What is the stated criterion for acceptance, prior to calculations, on a whirling

hygrometer? 79 Name two pieces of equipment used for taking steel temperature. 80 Is it possible for a wet bulb temperature to be higher than the dry bulb?



Paint testing – Thursday 1 Define viscosity. 2 What is meant by high viscosity? 3 Approximately, what is the viscosity of water? 4 Name the cgs and SI units of dynamic viscosity. 5 Name three different flow cups. 6 When using a flow cup which unit of viscosity would be used? 7 In ‘Ford Flow Cup No 4’ what does ‘4’ relate to? 8 Give the names of three different rotational viscometers. 9 Give a reason for performing a viscosity test on site. 10 Which viscometer would not be used on thixotropic paint? 11 Why is temperature very important when doing viscosity tests? 12 What is the main difference between the rotathinner and Krebs Stomer? 13 Describe how to use a Ford Flow Cup. 14 Give another name for a Fineness of grind gauge. 15 Is a low flash point safer than a high flash point? 16 How and for what is a Hegman grind gauge used? 17 Briefly describe how to do the volatile, non-volatile test to BS 3900 Pt B2. 18 Name the equipment used to determine the flash point of a solvent. 19 What colour should the flame be at the flash point? 20 What formula is used to calculate the density? 21 What formula is used to calculate specific gravity? 22 What is relative density? 23 What are the other names for a density cup? 24 What is a stoke, the unit for? 25 Which test is used to determine Abrasion Resistance? 26 Which equipment would be used to determine flexibility? 27 Which equipment would be used to measure Impact Resistance? 28 For what reason would the Koenig Albert Apparatus be used.? 29 For which two reasons could a density cup be used on site? 30 Name four accelerated test boxes. 31 Why would a tropical box be used? 32 Would a paint be higher or lower density than water? 33 How would the density be affected if solvent was added to paint? 34 What is the capacity of a density cup? 35 What difference is there between SG and Density? 36 What information could be obtained from a water soak test? 37 What information could be obtained from a temperature cycling test? 38 What information could be obtained from a cold check test? 39 Name four drying and curing tests. 40 What stage of the BK test would be recorded as the drying time? 41 Name three methods of determining opacity. 42 What effects the opacity of a paint film? 43 Why would a Pfund cryptometer be used? 44 Give one reason why an inspector would use a PIG gauge? 45 Why are wet paint film thicknesses needed?



46 Name two methods of measuring WFTs 47 What is the reason for taking WFTs immediately after application? 48 Where could an inspector find information to determine if a 2 pack paint was mixed in the

correct proportions, using a density cup? 49 Can a banana gauge be used on non-ferromagnetic substrate? 50 Could an eddy-current gauge be used on ferromagnetic substrates? 51 Can a horseshoe gauge be used on non-ferromagnetic substrates? 52 As part of which test would a bar applicator be used? 53 Which instruments would be used to measure reflectivity? 54 How does a gloss meter work? 55 Which factors in paint govern the degree of gloss? 56 In a primer/mid coat what would be the expected degree of grind? 57 In a gloss paint what would be a typical degree of grind? 58 What percent reading would be expected when measuring gloss on a glass panel? 59 Using a gloss meter a reading of 25% would signify what? 60 If an aggregate size of 35 um was present in a paint of 30 um DFT what would be a likely

result when using a gloss meter? 61 Name three common tests for determining adhesion of a paint film? 62 Which adhesion tests are quantitative? 63 Inter coat adhesion and primer to substrate adhesion are two adhesion faults name the

third? 64 What chemical solution is used to conduct a Cathodic Disbondment test? 65 Which gas evolved at the cathode causes disbondment? 66 What criterion is used when assessing a Cathodic Disbondment test panel? 67 Name the two methods of applying Cathodic Protection. 68 What is used to determine the potential of a pipeline? 69 Would it be advisable to refill a pipe trench with carbonaceous backfill? 70 Does a Cathodic Protection System eliminate corrosion? 71 Can the external surface of a tank be protected? 72 Could a crude oil tank be fully protected internally? 73 What voltage would be used on a 250 um thick paint using a sponge type pinhole detector? 74 What voltage would be used on a 450 um thick coating with a sponge type pinhole

detector? 75 When using a wet sponge, what other liquid is added to the water? 76 What function does the above additive perform? 77 Would it be advisable to do wet sponge detection on galvanising? 78 Why work upwards on a vertical surface with a wet sponge? 79 Does a sponge detector work on AC or DC current? 80 Other than the wet sponge, which other equipment could be used to determine the

presence of pinholes/holidays?



Revision questions general – Friday 1 Name two categories of paint mill. 2 What is the main reason for processing paint in a mill? 3 Briefly describe how a ball mill works. 4 Briefly describe how an attritor mill works. 5 When would steel balls not be used in a ball mill? 6 A bead mill is sometimes called by which other names? 7 How does a colloid mill work? 8 Name eight items of information listed on a materials data sheet. 9 What do you understand from the term Halogenated Hydrocarbon? 10 How can we determine the viscosity of a high viscosity paint? 11 Briefly describe the principles of CP. 12 What function does a primer have in a paint system? 13 In a mordant primer what is the main working constituent? 14 What advantages do electrostatic application methods provide? 15 Which is the most expensive type of brush filling? 16 What is cohesive failure in paint, give the main cause? 17 Why does a zinc rich paint need a strong binder? 18 Why are etch primers not spray applied? 19 What do you understand by the term over spray? 20 Name four methods of determining DFTs. 21 What is a psychrometer used for? 22 What colour should a galvanised surface be after application of ‘T’ wash? 23 How soon can a ‘T’ washed substrate be coated? 24 Other than pigment, base and curing agent name two other constituents of FBE powder

paint. 25 Give the main differences between airless and conventional spray. 26 Brush application has advantages over spray application, what are they? 27 What is the main consideration when selecting a metallic pigment for a sacrificial paint? 28 What is meant by shererdizing? 29 Name three types of paint feed for a conventional spray. 30 What is the calorising process? 31 Why would a sealer be applied to Aluminium metal spray? 32 What is the BS 2015 term for skipped or missed areas? 33 A colour has three properties, what are they? 34 Why would paint be applied by ‘hot spray’? 35 On an airless spray tip how are blockages cleared? 36 How is atomisation achieved using conventional sprays? 37 How is atomisation achieved using airless sprays? 38 What is dip coating? 39 What do you understand from the term ropiness? 40 What is efflorescence and how does it occur? 41 Name two ways of melting aluminium to enable it to be sprayed. 42 What is flocculation? 43 What could be the cause of bittiness in a paint film? 44 What is a tie coat? 45 How many depressions of the bellows are needed for the Dräger test?



46 What are the hazard signs for Toxic, Very Toxic, Harmful and corrosive? 47 What is saponification? 48 What units are used for measuring toxicity? 49 Which material would have to be used on a perpetually damp surface? 50 What is padding? 51 What air inlet pressure is needed to give 2500 psi delivery with 35:1 pump? 52 What causes lifting of a paint film? 53 What is cissing and how is it caused? 54 What is meant by the abbreviations: OES, OEL, MEL, UEL, LEL and RAQ? 55 Why would a paint inspector use potassium hexacyonoferrate? 56 What would be an average thickness for galvanising? 57 How can you tell the difference between blooming and chalking? 58 What could be the reasons for inter coat adhesive failure? 59 How would you determine quality of added thinners in thixotropic paint? 60 Why are manufacturers developing solvent free, water borne and powders? 61 What would be the cause of grinning on a paint film? 62 How can ‘bleeding’ be avoided? 63 In less than 30 words, explain the duties of a painting inspector. 64 Name five documents, which a painting inspector might need on a contract. 65 What information should be given on a daily report sheet? 66 Curtains, Sags, Runs and Tears are a result of what? 67 Some binders can be modified to use water as a solvent, name four. 68 What is meant by the term stripe coat? 69 How many cm3 are there in 4.5 litres? 70 A paint data sheet provides a wealth of information, name eight items.



Revision questions PA 10 specific 1 What is the specified course of action for grit inclusions? 2 The term ‘long term protection’ refers to what? 3 What is the difference between new and weathered galvanising? 4 What criterion determines which paint system should be used? 5 What is the total DFT of the compliant epoxy system? 6 What is the total DFT of the water borne system? 7 When can ladders and other means of access be removed? 8 Two materials are specified for used on damp surfaces, what are they? 9 After removal of a non-drying paint, which type of primer is recommended? 10 Some non-ferrous substrates are painted for aesthetics only, name four. 11 Which three non-ferrous substrates are painted for anti corrosion purposes? 12 According to PA 10 in which situations would ‘T’ wash be used? 13 How many coats of primer are specified on surfaces at 100 – 149oc? 14 Give preferential order of coating systems for surfaces 150 – 340oc. 15 Is it mandatory for a contractor to produce a test area? 16 List four items needing masking off prior to blasting and painting. 17 Which Aluminium substrate would not be sweep blasted? 18 Which three paint systems are specified for use on Aluminium? 19 What differences are there in new and maintenance painting specifications for substrates

below 100oc? 20 Toxic coatings need special considerations for removal from substrates, name two

methods which comply. 21 In which situations is a Permit to Work required? 22 Which primers are specified for non-weathered galvanising? 23 Which primers are specified for weathered galvanising? 24 According to PA 10 is flame cleaning allowed? 25 According to PA 10 is thinning of paint allowed? 26 What temperature range is covered by ‘hot duty service’? 27 Does PA 10 cover internal coatings on pipes? 28 What is the specified overlap on repair areas? 29 What would be the specified surface preparation and coating system for Aluminium

cladding? 30 What would be the procedure for removal of algae and mould? 31 What would be the procedure for degreasing prior to surface preparation? 32 What would be the procedure for degreasing after to surface preparation? 33 When blast cleaning on an AGI what precautions are taken? 34 Is it permissible to prepare paint by stirring? 35 What would be the surface preparation method for new galvanising? 36 When would it be necessary to apply a sealer to inorganic zinc silicate? 37 How could areas of a paint breakdown be prepared for repainting? 38 What information should be on a paint can label for BG? 39 When measuring DFTs over galvanising what allowances are made? 40 What is the first coat applied to galvanised substrates and why? 41 Properties and Performances of paint are covered in which BG specification? 42 What are the considerations when selecting a paint system? 43 According to PA 10 which two coats are applied ‘at works’?



44 Give the criterion for when and when not, painting can take place. 45 What should be the substrate reaction when ‘T’ wash is applied to a newly galvanised

substrate? 46 Which two materials are specified for use on damp surfaces? 47 What is the maximum time lapse from surface preparation to coating? 48 Which is the most common pigment used in high temperature paints? 49 What would be the result of over thick application of zinc silicate? 50 According to PA 10 is roller application permissible?



B. Gas 3.2 Maths Exercises WFT calculations 1 What WFT would need to be applied to give a DFT of 45 um using a paint of 56% vs? 2 What WFT would need to be applied to give a DFT of 60 um using a paint of 40% vs? 3 A paint of 38% vs was used to give a DFT of 45 um what wad the WFT? 4 A DFT of 55 um was obtained from a paint of 55% vs, what was the WFT applied? 5 What WFT would be applied to leave a DFT of 65 um using a paint of 49% vs? DFT calculations 1 What would be the DFT if 20 litres of paint, vs. 45% covered an area of 9m x 12m? 2 25 litres of paint, vs. 65% was used to cover a circular area of 10m diameter. What would

be the resulting DFT? 3 What DFT would be obtained if a paint vs content 42% was applied at a WFT of 84 um? 4 What would be the resulting DFT if a WFT of 130 um, what would be the resulting DFT? 5 A paint, vs 65% was applied at a WFT of 130 um, what would be the resulting DFT? VS calculations 1 A DFT of 53 um was obtained from a WFT of 110 um, what was the vs% of the paint? 2 A paint was applied at 120 um WFT. The resulting DFT was 65 um, what was the vs%? 3 What would be the vs% of a paint if it was applied with a WFT of 120 um and a DFT of

68 um was obtained? 4 What was the vs% of a paint with a DFT of 36 um, when the WFT was 108 um? 5 A DFT of 62 um was measured, from a WFT application of 100 um, what would be the

vs% of the paint used? Volume calculations 1 What volume of paint would be required to cover an area of 300 square metres, to a

specified DFT of 65 um, using a paint of 45% vs? 2 How much paint would be required to coat a tank, roof and side sheets to a DFT of 100

um? The tank is 5 metres diameter and 6 metres high. The paint to be used is solvent free. 3 How much paint would be needed to cover a circular area of 10 metres diameter, using a

paint 65% vs to a DFT of 60 um? 4 A circular area of 7 metres radius is to be coated to a DFT of 45 um. What volume of

paint would be required if the vs content was 48%? 5 How much paint would be needed, at 55% vs, to coat an area of 250 square metres to a

DFT of 60 um?



Density and SG exercise 1 What would be the weight of 16.5 litres of paint with a SG of 1.45? 2 What is the density of a paint if 7.5 litres weighs 9.75 kg? 3 What would be the relative density of paint in question two? 4 If the weight of 25 litres of paint is 37.5 kg, what would be the SG? 5 A 2 pack epoxy should be mixed at one part base to one part activator, the base has a

density of 1.4gm/cc and the activator 0.9 gm/cc. What would be the density of the mixed components?

6 A 2 pack paint is mixed at a ratio of six parts pack A (density 1.3gm/cc) to one part pack B (density 0.9gm/cc). What would be the density of the combined parts?

7 A mixed 2 pack paint has a density of 1.35gm/cc. The density of the base was 1.5gm/cc and the activator 0.9gm/cc. The mixing ratio was 3:1. Has the paint been mixed correctly?

8 A mixed 2 pack paint has a density of 1.35gm/cc. Mixed at a ratio of 6:1, base density 1.45gm/cc, activator density 0.95gm/cc. Has the paint been mixed correctly?



RH and DP exercise WB DB DP RH Steel Temp. Y/N 1 10 12 13 2 9 10 11 3 4 6 6 4 5 7 6.5 5 11 12 12 6 14.5 15.5 16 7 9.5 10.5 11 8 12 16 17 9 12 13 13 10 13 13.5 14 11 17.5 21 23 12 14 17.5 17 13 11 11 11.5 14 7.5 8.5 8 15 7 6 7 16 6.5 8 11 17 2 3 3 18 13 15 16 19 8 8 8 20 16 18.5 19 21 17 18 18 22 8 9.5 10 23 22 24.5 24.5 24 16 16.5 19 25 3 4 5 26 7 8 9 27 19 18 20 28 12 12.5 13 29 14 16.5 16.5 30 8.5 11 11

Painting Inspection Grade 3/2 1 Appendix A

Appendix A

PA10 TECHNICAL SPECIFICATION FOR NEW AND MAINTENANCE PAINTING AT WORKS AND SITE FOR ABOVE GROUND PIPELINE AND PLANT INSTALLATIONS

AUGUST 1995

J020 ( Rev 08/98 )



PA10

CONTENTS

Page

FOREWORD v

BRIEF HISTORY vii

SECTION 1 - PRELIMINARY INFORMATION 1

1. SCOPE 1

2. REFERENCES 1

3. DEFINITIONS 1

3.1 General 1

3.2 Miscellaneous 1

3.3 Mandatory and non-mandatory requirements 2

SECTION 2 - GENERAL PAINTING INFORMATION 3

4. SELECTION OF PAINT SYSTEM 3

5. CONDITIONS TO BE MET BY THE CONTRACTOR 3

5.1 General 3

5.2 Local site regulations 4

5.3 Inspection 4

5.4 Test areas 4

5.5 Access equipment 4

5.6 General cleanliness 4

5.7 Equipment to be protected and masked before preparation and painting 4

5.8 Paints containing metallic zinc 4

5.9 Preparation of surfaces 5

5.10 Disposable cleaning materials 7

6. MATERIALS 7

6.1 Paints 7

6.2 Grades of paint 7

6.3 Supply of paints 7

6.4 Storage of paints 7

6.5 Preparation of paint for use 7

J020 ( Rev 08/98 ) - i -

PA10


Page

6.6 Pot life of paint (after mixing) 8

6.7 Paint samples 8

7. APPLICATION OF PAINT 8

8. MEASUREMENT OF PAINT THICKNESS 8

9. SITE SAFETY REQUIREMENTS 9

10. ENVIRONMENTAL REQUIREMENTS 9

11. VARIANTS 9

SECTION 3 - SPECIFIC PAINTING APPLICATIONS (SPAs) 10

SPA1 - NEW AND MAINTENANCE PAINTING FOR LONG TERM

PROTECTION OF INSTALLATIONS AND COMPONENTS 10

12. GENERAL 10 13. PREPARATION FOR PAINTING OF UNCOATED OR UNSUITABLY COATEDSURFACES AT WORKS OR SITE 10

14. PREPARATION OF PAINTED SURFACES WITH LIMITED COATING DAMAGE 10

15. APPLICATION OF PAINT TO PREPARED SURFACES 11

16. FINAL COATING 11

17. MAINTENANCE PAINTING 11

17.1 General 11

17.2 Preparation of surfaces 12

17.3 Application of paint 12

SPA2 - NEW AND MAINTENANCE PAINTING FOR INDOOR USE OR

SHORT TERM PROTECTION 15

18. GENERAL 15

19. PREPARATION OF SURFACES 15

20. NEW PAINTING FOR INDOOR USE AND FOR SHORT TERM PROTECTION (TABLE SPA2a) 15

21. MAINTENANCE PAINTING OF SYSTEMS FOR INDOOR USE AND FOR SHORT TERM PROTECTION (TABLE SPA2b) 15

SPA3 - PAINTING OF METAL SURFACES FOR HOT DUTIES 17

22. GENERAL 17

23. FOR DUTIES AT TEMPERATURES FROM 100 0C TO 149 0C (TABLE SPA3a) 17

23.1 Preparation for painting of new installations and maintenance painting 17

- ii - J020 ( Rev 08/98 )


PA10

Page

23.2 Application of paint to prepared areas 17

24. FOR DUTIES AT TEMPERATURES FROM 150 0C TO 340 0C (TABLE SPA3b) 17


24.2 Application of coating material 17

25. FOR DUTIES AT TEMPERATURES ABOVE 340 0C (TABLE SPA3c) 18


25.2 Application of coating material 18

SPA4 - PAINTING OF DAMP FERROUS SURFACES 21

26. GENERAL 21

27. PREPARATION OF SURFACES 21

28. APPLICATION OF PAINTS 21

SPA5 - MAINTENANCE PAINTING OF LOW PRESSURE GASHOLDERS 23

29. GENERAL 23

30. PRELIMINARY CONSIDERATIONS (PRIOR TO PREPARATION OF SURFACE FOR PAINTING) 23

31. SURFACE PREPARATION FOR PAINTING 24


33. HOLDER CUP WATER MANAGEMENT 27

34. GUIDANCE NOTES 28

SPA6 - PAINTING OF NON-FERROUS SURFACES 31

35. GENERAL 31

36. PREPARATION OF SURFACES FOR PAINTING 31


TABLES

1 Treatment of contaminated paint film 9

APPENDICES

A LIST OF REFERENCES 35

B SAFETY 39 J020 ( Rev 08/98 ) - iii -


- iv - J020 ( Rev 08/98 )


PA10 FOREWORD This specification has been adopted by Transco and is an editorial revision of the former British Gas Transco specification PA10. It reflects the identity and organisational structure of Transco - a part of BG plc. This Transco specification has been approved for use throughout Transco. Comments and queries regarding the technical content of this Transco specification should be directed to: Lead Engineer Transco Norgas House PO Box 1GB Killingworth Newcastle upon Tyne NE99 1GB Further copies of this Transco specification can be obtained from Dataform Print Management using the print requisition form G004 quoting the Form Number of this Transco engineering document (not the designation) and your cost code. Transco engineering documents are revised, when necessary, by the issue of new editions. Users should ensure that they are in possession of the latest edition by referring to the Transco Register of Engineering Documents available on the Transco Information Library. Compliance with this engineering document does not confer immunity from prosecution for breach of statutory or other legal obligations. Contractors and other users external to Transco should direct their requests for further copies of Transco engineering documents to the department or group responsible for the initial issue of their contract documentation. DISCLAIMER This engineering document is provided for use by Transco and such of its contractors as are obliged by the terms of their contracts to comply with this engineering document. Where this engineering document is used by any other party, it is the responsibility of that party to ensure that the engineering document is correctly applied. J020 ( Rev 08/98 ) - v -


- vi - J020 ( Rev 08/98 )


PA10 BRIEF HISTORY

First published as BG/PS/PA10: Parts 1 and 2 and Supplements CS1 to CS17 inclusive Revision published as PA10

June 1987 August 1995

© BG plc 1995 This Transco specification is copyright and must not be reproduced in whole or in part by any means without the approval in writing of BG plc. J020 ( Rev 08/98 ) - vii -


- viii - J020 ( Rev 08/98 )


PA10: SECTION 1 TECHNICAL SPECIFICATION FOR NEW AND MAINTENANCE PAINTING AT WORKS AND SITE FOR ABOVE GROUND PIPELINE AND PLANT INSTALLATIONS SECTION 1 - PRELIMINARY INFORMATION 1. SCOPE 1.1 This Specification specifies procedures for painting the surfaces of all types of ferrous and non-ferrous metal engineering components. 1.2 This specification is not suitable for use in the following areas: a) below ground (buried); b) offshore installations; c) internal coatings of pipes; d) stove enamel coatings. 1.3 An appropriate specific painting application (SPA) in Section 3 of this specification, specifies in detail the materials, surface preparations and methods of application to be used in the particular applications. Only the relevant SPAs need to be taken into account for a particular painting system. 1.4 Site safety requirements are given in clause 9 and Appendix B. 1.5 Environmental requirements are given in clause 10 and Appendix B. 2. REFERENCES This specification makes reference to the documents listed in Appendix A. Unless otherwise specified, the latest editions of the documents apply, including all addenda and revisions. 3. DEFINITIONS 3.1 General For the purposes of this specification, the definitions given in 3.2 and 3.3 apply. 3.2 Miscellaneous compliant coating: a coating which complies with the requirements of the Environmental Protection Act 1990. Contractor: the person, firm or company with whom Transco enters into a contract to which this specification applies, including the Contractor's personal representatives, successors and permitted assigns. damp surfaces: surfaces on which water is not readily detectable but of which the temperature is below the dew point. dew point: the temperature at which the vapour pressure of the water vapour in the air is equal to the saturation vapour pressure over water. Engineer: the Engineer appointed from time to time by Transco and notified in writing to the Contractor to act as Engineer for the purpose of the contract, or their permitted assign. J020 ( Rev 08/98 ) - 1 -


PA10: SECTION 1 fully weathered galvanizing: a galvanized steel surface on which a cohesive oxide layer has formed by natural weathering. The surface will normally be dull and lacking in metallic sheen. hot duty surfaces: metal surfaces on the assembly that will attain a temperature of 100 0 C or above during use. long term protection: protection typically lasting ten years. medium term protection: protection typically lasting five years. moist surfaces: surfaces from which standing water and droplets have been removed but on which there is a noticeable film of water. multi-component paint: a paint supplied as separate components. new galvanizing: a galvanized steel surface on which a cohesive oxide layer has not yet formed. It will normally have a bright unweathered zinc surface. Some steels (e.g. silicon killed steels) may exhibit a dark surface. paint technologist: a person suitably qualified to act as a technical adviser to Transco for the purpose of the contract. pot-life: the maximum time during which a coating material supplied as separate components should be used after they have been mixed together. relative humidity: the ratio of the actual vapour pressure to the saturation vapour pressure over a plane liquid water surface at the same (dry bulb) temperature, expressed as a percentage. short term protection: typically two years to three years life. Transco: Transco - a part of BG plc T-wash: a non-proprietary material used as a primer or pretreatment for zinc metal surfaces. (see BS 5493, clause 11.3.2c). wet surfaces: surfaces on which droplets or standing water are present. 3.3 Mandatory and non-mandatory requirements can: indicates a physical possibility. may: indicates an option which is not mandatory. must: indicates a requirement in law and in matters of health and safety. shall: indicates a Transco requirement. should: indicates a strong preference, but allows deviation exceptionally. will: indicates an intention by Transco to do something. - 2 - J020 ( Rev 08/98 )


PA10: SECTION 2

SECTION 2 GENERAL PAINTING INFORMATION 4. SELECTION OF PAINT SYSTEM 4.1 Each painting job is unique, therefore it is essential to be selective and to specify unequivocally. 4.2 For new painting projects, the design of painting is very important because the type of system chosen can have a significant effect on the cost of painting. 4.3 For maintenance painting, special treatment may be required in certain cases involving modification or amendment of the original design for painting. 4.4 The advice of a corrosion engineer and/or paint technologist should be obtained at the earliest stage possible when painting or re-painting is to be carried out. This will assist in making a decision on the following: a) The most appropriate cost effective method(s) of surface preparation. b) The most appropriate cost effective paint system(s) to give the required service life. 4.5 For painting of new items or plant, this advice (see 4.4) should be sought at the conceptual design stage to ensure that the paint systems are cost effective. 4.6 For maintenance/re-painting, the extent and methods of painting should be based on a survey of the item or plant which would determine:

a) The existing paint system.

b) The extent of breakdown and corrosion.

c) The in-service environmental conditions.

d) The nature and extent of any surface contamination. 5. CONDITIONS TO BE MET BY THE CONTRACTOR 5.1 General The Contractor shall take into consideration the following general conditions:

a) In order that the Contractor be clearly informed of Transco requirements, the contract or specification for a particular job shall be drawn up after taking into account the appropriate clauses, Appendices and SPA(s) in Section 3.

All parts to be painted shall be as specified by Transco with reference to the appropriate SPA(s) in Section 3.

b) The method of surface preparation for each part shall be as specified by Transco with reference to

the appropriate SPA(s) in Section 3.

c) The painting system to be applied to each part shall be as specified by Transco with reference to the appropriate SPA(s) in Section 3.

d) All painting shall be carried out in accordance with a programme of work which shall be

prepared by the Contractor and agreed by the Engineer.

e) Paints shall be listed as separate items on the contract document and should be ordered to comply with PA9.

J020 ( Rev 08/98 ) - 3 -


PA10: SECTION 2 5.2 Local site regulations Relevant local site regulations will be detailed in writing by the Engineer. 5.3 Inspection All painting shall be subject to inspection and no deviation from the requirements of this specification will be permitted, unless previously agreed with the Engineer. Independent inspection shall not in any way relieve the Contractor of his responsibilities under the terms or conditions of the contract. Detailed records of the surface preparation and paint system applied to any given structure shall be kept together with the results of the inspection and testing carried out. 5.4 Test areas 5.4.1 The Contractor may be asked to prepare and paint test areas to demonstrate that a correct quality of surface preparation with a satisfactory film thickness and finish to the paint film is obtained. 5.4.2 The equipment and techniques used for the accepted surface preparation and application of paint to the test areas shall be representative of those to be used for the main painting work. 5.5 Access equipment 5.5.1 It is of particular importance that reference is made to Appendix B and that all relevant requirements are carried out. 5.5.2 Until approval has been given by the Engineer, fixed access equipment shall be left in position and any movable equipment required (ladders, towers, etc.) shall remain on site and be readily available for use. 5.6 General cleanliness 5.6.1 When cleaning, surface preparation or painting operations are being carried out on site, the Contractor shall ensure that adequate protection is given to surrounding areas and adjacent structures to avoid spotting, over-spray, or contamination produced by these operations. 5.6.2 The Contractor shall be responsible for the removal of all paint and corrosion products, spent abrasive, empty containers, brushes, tissues, etc., from the site and shall ensure that the disposal of waste products complies with the appropriate statutory requirements. 5.6.3 In all cases, the operation shall be carried out in compliance with the current environmental requirements (see Appendix B). 5.7 Equipment to be protected and masked before preparation and painting 5.7.1 Prior to any cleaning, surface preparation or painting, the Contractor shall protect and mask equipment and areas in need of protection. Care should be taken with the use of masking materials to prevent possible malfunction of the plant. Typical items to be masked are fire protection equipment, weld end preparations, atmosphere sensing heads, spray heads, vents on control equipment, flame traps, lubrication points and nameplates. 5.7.2 The Contractor shall be responsible for removing all masking materials. 5.8 Paints containing metallic zinc Special care shall be taken to ensure that paints containing metallic zinc (zinc-rich paints) are not allowed to contaminate stainless steel. These paints shall not be applied within 75 mm of weld end preparation. - 4 - J020 ( Rev 08/98 )


PA10: SECTION 2 5.9 Preparation of surfaces 5.9.1 Conditions for final surface preparation 5.9.1.1 When the conditions in the working zone are such that the metal surfaces are moist or damp, final surface preparation shall not normally be carried out. 5.9.1.2 The operation of any surface preparation or cleaning method shall not be allowed to contaminate wet paint films. 5.9.1.3 Equipment used on site for surface preparation shall be of the type which does not cause sparks. 5.9.1.4 Electrically operated tools shall not normally be permitted on site. 5.9.1.5 Power tools operated by compressed air shall have oil and vapour traps fitted to the compressed air lines. 5.9.1.6 Before surface preparation operations commence, all contaminants including oil or grease and water soluble salts on the working surfaces, shall be removed by washing with an appropriate solvent. 5.9.1.7 All algae and mould growth shall be treated with a biocidal agent and left for a minimum of 24 h. It shall then be removed by scrubbing with stiff bristle brushes and clean water or by use of high pressure water washing. 5.9.1.8 All surfaces shall normally be thoroughly dry before painting commences. 5.9.2 Abrasive blast cleaning methods 5.9.2.1 Safety requirements associated with abrasive blast cleaning shall comply with IGE/SR/21. 5.9.2.2 The type of abrasive used shall be capable of providing a blast cleaned profile (peak-to-trough height) of not less than 30 μm and not greater than 75 μm , unless otherwise required by the appropriate SPA in Section 3. The profile shall be measured using Testex replica tape or by an alternative device approved by the Engineer. 5.9.2.3 Non-metallic abrasives shall be of a silica free type. Air for blasting shall be clean, dry and oil free. Other blasting media may be used with the agreement of the Engineer. 5.9.2.4 Abrasive used in an open blast system shall be of the expendable type. The re-use of expendable abrasive shall not be permitted. A closed blasting system (e.g. vacuum blasting) may also be used. For closed vacuum blasting systems, the re-use of abrasives shall be permitted provided that such systems efficiently clean and monitor the size of the abrasive. 5.9.2.5 Wet blast systems or enclosed recovery blast systems, shall be used for the removal of lead-based paint, and also may be proposed as a variant for consideration by Transco in other cases (e.g. for removal of water soluble salts). Following wet blasting, dry blasting shall be carried out to remove any subsequent flash rusting. 5.9.2.6 All traces of corrosion, chemical contamination, existing paint or other coating shall be removed from the surface. 5.9.2.7 All surfaces prepared by blast cleaning shall comply with the requirements of BS 7079 (see also ISO 7167) as specified, immediately prior to painting. The profile and degree of cleanliness shall be in accordance with the requirements of the appropriate SPA in Section 3. J020 ( Rev 08/98 ) - 5 -


PA10: SECTION 2 5.9.2.8 All surface defects, such as surface laminations or inclusions, shall be referred to the Engineer before any dressing is undertaken. All fins at saw cuts, burrs and sharp edges shall be removed by dressing, with the agreement of the Engineer. 5.9.2.9 Where dressing has been necessary, these areas shall be re-blasted to remove all rust and to provide an adequate paint key. 5.9.3 Water jetting High pressure and ultra-high pressure water jetting can be usefully employed for removal of paint, scale and corrosion products. Since high pressures are involved, care shall be taken to ensure that appropriate safety measures are taken and that equipment is not damaged (see IGE/SR/21). 5.9.4 Manual mechanical methods 5.9.4.1 General The methods of surface preparation, specified in 5.9.4.2 to 5.9.4.5 inclusive, may only be used when blast cleaning is considered to be unsuitable and with the prior approval of the Engineer. As these methods generally achieve lower standards, additional care shall be taken to ensure an agreed standard of surface preparation is reached. These methods of surface preparation shall provide a surface of equivalent cleanliness to BS 7079, St 2 or St 3 quality which is considerably inferior to Sa 2 ½ and may reduce the expected life of the paint system. 5.9.4.2 Surface preparation by hand tools Ferrous impact tools shall not normally be used. In some areas, manual scraping may be adopted and may be followed by further surface preparation, such as wire brushing. The scrapers shall be of the type having a carbide tip. 5.9.4.3 Needle gunning The guns shall have needles of small cross-section. Care shall be exercised when using a needle gun to ensure that the profile of the surface shall not exceed 100 μm and that no sharp-edged craters are left on the metal surface. All rogue peaks shall be removed. 5.9.4.4 Abrasive discs The use of abrasive discs may be permitted in certain circumstances and shall only be carried out with the prior approval and under the control of the Engineer. Particular care shall be taken when using these methods on pressure containing parts, because of the danger of creating notches. 5.9.4.5 Grinding Grinding shall only be carried out under the direct supervision of the Engineer (see 5.9.4.4). 5.9.5 Surface preparation of weld areas 5.9.5.1 All weld areas including primed surfaces damaged by heat shall be prepared by blast cleaning to comply with the requirements of BS 7079 (see also ISO 7167) as specified, immediately prior to painting. 5.9.5.2 All weld flux and spatter shall be removed prior to painting operations. 5.9.5.3 Any painted areas next to the weld area shall be suitably protected when the operations specified in 5.9.5.1 and 5.9.5.2 are carried out. 5.9.6 Cleaning down 5.9.6.1 The standard of surface cleanliness shall be such that all dust, chemical contaminants, oil and moisture are removed prior to paint application. - 6 - J020 ( Rev 08/98 )


PA10: SECTION 2

5.9.6.2 For existing sound paint surfaces, all grease and surface contamination shall be removed. For large areas, consideration shall be given to the use of low pressure water detergent washing prior to painting. These surfaces shall then be washed with clean water and allowed to dry prior to painting. 5.9.6.3 All surfaces, after completion of the surface preparation and immediately prior to painting, shall be cleaned by air blasting using clean, dry, oil-free air or vacuum cleaned to ensure that all traces of abrasive and corrosion products are removed. 5.9.6.4 Any oil or grease on the prepared surface of the steel shall be removed by swabbing with an appropriate solvent followed by washing with a 2% solution of detergent. The surface shall then be washed with clean water and thoroughly dried. Abrasive cleaning shall then be repeated. 5.10 Disposable cleaning materials 5.10.1 Where cleaning and swabbing of steel and paint film surfaces are required, disposable lint-free swabs shall be used. Cloth rags shall not be used. Swabs shall be used once only. 5.10.2 Areas below surfaces being prepared as specified in 5.9.6.4 shall be protected from drips, spillage, etc., to prevent permanent scarring. 6. MATERIALS 6.1 Paints Unless otherwise specified, all paints used on any one contract shall be supplied by one manufacturer only. All paints shall be ordered against PA9 which shall be quoted on all relevant documentation. Attention shall be drawn to the Environmental Protection Act 1990, prior to selection of paints. 6.2 Grades of paint Paints are obtainable in both brushing and spraying grades. When ordering paints, the grade required shall be specified. 6.3 Supply of paints All paints shall be provided by the Contractor. 6.4 Storage of paints All paints shall be stored under cover and in conditions recommended by the paint manufacturer and in accordance with the appropriate fire regulations. On operational sites, the storage method and area shall be approved by the Engineer. 6.5 Preparation of paint for use 6.5.1 No paint shall be used beyond the manufacturer's stated shelf life. 6.5.2 All paints shall be prepared adjacent to the location where the painting work is to be carried out. 6.5.3 The condition of the paint shall be checked before preparation begins and any unsatisfactory painting materials shall be discarded. 6.5.4 All paints shall be thoroughly prepared by mechanically mixing to ensure that no sediment is left. For 5-litre containers or less, hand mixing can be considered. In all cases, the manufacturer's instructions shall be followed. J020 ( Rev 08/98 ) - 7 -


PA10: SECTION 2 6.6 Pot life of paint (after mixing) Multi-component paints have a limited pot life. This information shall be obtained from the manufacturer and also be stated on the container. Paints of this type shall not be used after the stated pot life. When a multi-component paint is being used, new material shall not be added to any of the old material left in the pot. 6.7 Paint samples Representative samples of each batch or grade of paint may be requested by the Engineer. 7. APPLICATION OF PAINT 7.1 Paint shall normally be applied when the relative humidity in the work zone is less than 90% or when the air and metal temperatures are at least 3 0 C above the dew point. Measurement of relative humidity and dew point shall be carried out using a whirling hygrometer complying with and used in accordance with BS 2842. Ambient and substrate temperatures should not be below the minimum application temperature for the paint, as stated in the manufacturer's instructions being used, as advised by the manufacturer or as stipulated by Transco. 7.2 Paint shall not normally be applied when conditions in the working zone are such that the prepared surface is likely to become moist or damp during the painting operation. When this condition prevails, and cannot be overcome by altering the normal operating conditions (e.g. regulator stream selection) painting shall be carried out in accordance with SPA4 in Section 3. 7.3 After completion of the specified cleaning process, metal surfaces shall be painted as specified in the appropriate SPA in Section 3 (by brushing or spraying). 7.4 Painting equipment used shall be of a type complying with the paint manufacturers recommendations. 7.5 All paint shall be applied in such a manner as to ensure a firmly adherent film, free from misses, tears, runs, sags, etc. 7.6 Stripe coating shall be necessary to achieve the required dry film thickness (DFT) at edges and to ensure coverage of weld profiles. 7.7 In the course of painting operations, all painted areas shall be thoroughly dried before being overcoated and any contamination of the paint film shall be dealt with as specified in Table 1 before further coats of paint are applied. 7.8 The final coating shall be free from significant visible imperfections. 7.9 Contaminated paint films shall be treated in accordance with Table 1 prior to over painting. 8. MEASUREMENT OF PAINT THICKNESS 8.1 The measurement of both wet and dry paint thickness shall be carried out during application on each coat and shall be in accordance with procedures in BS 3900: Part C5, except that the DFT gauge should be calibrated using the prepared surface. 8.2 Quality control thickness measurements of paint films containing micaceous iron oxide (MIO) pigment, and all layers of paint applied over such films, shall be carried out using a wet film thickness gauge (e.g. comb gauge). The wet film thickness needed to achieve the specified DFT differs from paint to paint and for each manufacturer. The manufacturer's literature shall be consulted for each application. - 8 - J020 ( Rev 08/98 )


PA10: SECTION 2

9. SITE SAFETY REQUIREMENTS All work carried out on the site shall comply with good safe working practice and the specific conditions of a Permit to Work where issued on an operational site. The following list of conditions or activities does not purport to include all requirements for safety but it summarizes the more important warnings included in this specification and presents them here for easy reference:

a) Safe working areas - proper use and erection of scaffolding, ladders, etc. (see 5.5.1).

b) Safety requirements associated with abrasive blast cleaning (see 5.9.2).

c) Identification of coating materials - with reference to any associated hazards such as toxicity, flammability, etc. (see PA9, 8.2).

d) Compliance with fire regulations - storing of combustible materials (see 6.4).

e) Safe handling of coating materials and safety precautions on site (see Appendix B, B.1 and B.2).

10. ENVIRONMENTAL REQUIREMENTS All works carried out on the site including storage and disposal of paint and all waste materials shall be in accordance with the current environmental requirements (see Appendix B, B.1 and B.3). The Contractor shall be alerted of the possible toxic nature of the deposits and paint debris, and the appropriate action and Certification required for their disposal (see Appendix B, clause B.3.l). 11. VARIANTS A contractor shall only propose variants to this specification where the text indicates that variants would be considered by Transco. TABLE 1 - Treatment of contaminated paint film

Type of contamination

Treatment

Loose paint particles, rust, debris and other atmospheric contamination or salt deposition

Wash down using soft nylon brushes and clean water. Dry thoroughly

Oil or grease

Brush and wash with an appropriate solvent then scrub with a 2% solution of detergent in clean water. Wash with clean water and dry thoroughly

Foreign materials (e.g. shot or grit) embedded in the paint film

Re-prepare the affected areas and re-apply the complete painting system

J020 ( Rev 08/98 ) - 9 -


PA10: SECTION 3 SECTION 3 SPECIFIC PAINTING APPLICATIONS (SPAs) SPA1 - NEW AND MAINTENANCE PAINTING FOR LONG TERM PROTECTION OF INSTALLATIONS AND COMPONENTS 12. GENERAL 12.1 This SPA1 applies to the painting at works or site of new installations and components and to site maintenance painting of carbon steel surfaces operating below 100 0 C. It is normal practice for new components to be prepared and part painted at works for subsequent completion at site. This SPA1 shall apply to:

a) Part painting of new components at works (see Table SPA1a).

b) Completion at works or site of components part painted at works (see Table SPA1c).

c) Site painting of uncoated and unsuitably coated surfaces (see Tables SPA1a, SPA1b and SPA1c).

d) Site maintenance painting (see Table SPA1d). 12.2 Before preparation and painting commences, those surfaces not to be painted shall be masked as specified in 5.7. 12.3 Each coat of paint shall be of a contrasting colour to the previous coat. 12.4 The operations for preparation are specified in clauses 13 and 14 and for painting in clauses 15 and 16. 12.5 Site maintenance painting is described in clause 17. 13. PREPARATION FOR PAINTING OF UNCOATED OR UNSUITABLY COATED SURFACES AT WORKS OR SITE 13.1 The procedure in 13.2 is also described in Table SPA1a. 13.2 All mill scale, corrosion products and, where applicable, unsuitable existing paint and coatings shall be removed from the surface. The surface finish at the time of painting shall be equivalent to BS 7079 Sa 2 ½ quality and have a profile within the range of 30 μm and 75 μm . This shall normally be achieved by blast cleaning as specified in 5.9.2. 14. PREPARATION OF PAINTED SURFACES WITH LIMITED COATING DAMAGE 14.1 The following procedure (see also Table SPA1b) shall be applied where slight damage to the factory coating has occurred during transport and/or storage. 14.2 The affected surfaces shall be prepared as specified in 5.9.4 to comply with the requirements of BS 7079 St 3 as a minimum quality. The method of cleaning shall normally be by means of mechanical wire brushing but other methods of preparation may be proposed to Transco for consideration as variants. 14.3 The edges of the existing remaining coating shall be feathered. 14.4 Areas of extensive coating damage shall be prepared in accordance with 17.2.2. - 10 - J020 ( Rev 08/98 )


PA10: SECTION 3 15. APPLICATION OF PAINT TO PREPARED SURFACES 15.1 All paint shall be applied as specified in clause 7. 15.2 For paint applied at works the preferred system is a high solids solvent based epoxy primer and epoxy MIO coat. Alternative equivalent compliant systems are available, such as water-borne paints and may be proposed to Transco for consideration as variants. 15.3 For painting at site the preferred systems are given in Table SPA1e. 15.4 One coat of primer shall be applied, by brushing or spraying as appropriate, to all prepared exposed metal within 4 h of metal preparation and before any rust blooming or contamination of the surface occurs. The DFT shall be as specified in Table SPA1e (measured as specified in clause 8). All welds and edges shall be stripe coated to assist in achieving the minimum DFT in these areas. The paint shall overlap onto any existing coating by at least 100 mm. The manufacturers' recommended overcoating times shall be followed. 15.5 One coat of MIO shall be applied to all primed surfaces, by brushing or spraying, to a DFT as given in Table SPA1e (determined by means of a wet film thickness gauge as specified in clause 8). 15.6 Overcoating is normally carried out within three months of the application of the MIO coat and in accordance with Table SPA1c. 16. FINAL COATING 16.1 On completion of painting in accordance with the requirements of clause 15, the final coating shall be carried out as specified in 16.2 to 16.5 inclusive (see also Table SPA1c). 16.2 All areas to be painted shall be free of all surface contamination immediately prior to painting as specified in 5.9.6. 16.3 One coat of high build undercoat shall be applied overall, by brushing or spraying, to a DFT as specified in Table SPA1e (determined by means of a wet film thickness gauge as specified in clause 8). The manufacturers' recommended overcoating times shall be followed. 16.4 One coat of finish shall be applied, by brushing or spraying, to a DFT as specified in Table SPA1e (determined by means of wet film thickness gauge as specified in clause 8). 16.5 The final coating shall have an acceptable uniform appearance and shall be free from cosmetic defects. 17. MAINTENANCE PAINTING 17.1 General 17.1.1 The Engineer shall specify the areas to be painted, the appropriate method of surface preparation and the paint systems to be applied. The number of coats applied will be dictated by the degree of breakdown of the existing paint system and its required life. 17.1.2 For installations previously painted with drying oil or chlorinated rubber paint systems, maintenance painting can generally be carried out with either of the systems detailed in Table SPA1e. 17.1.3 Installations previously painted in accordance with Table SPA1e should generally be repainted with the same system. J020 ( Rev 08/98 ) - 11 -


PA10: SECTION 3 17.2 Preparation of surfaces 17.2.1 Prior to repainting, some existing paint systems may need a key to ensure adhesion for the new paint. This can be produced by abrading for small areas but sweep blasting is recommended for large areas. 17.2.2 For areas where the existing paint system is to be completely removed or where the substrate is exposed, the surface preparation shall be by blast cleaning or wire brushing in accordance with clauses 13 and/or 14, as specified by the Engineer. 17.3 Application of paint 17.3.1 The primer shall be applied to the prepared surfaces in accordance with 15.4 followed by the MIO in accordance with 15.5. 17.3.2 The final coats shall be applied in accordance with clause 16 either to the areas prepared and painted above, or to the overall installation as specified by the Engineer. TABLE SPA1a - Operations chart for use with clauses 13 and 15 for uncoated or unsuitably coated surfaces Operation

number Subject of operation Comments Relevant clauses in PA10

Section 2 Section 3 1 Mask areas 5.7

2 Blast clean BS 7079 Sa 2½ quality; maximum profile 75 um

5.9.2 13.2

3 Clean all surfaces Immediately prior to primer application

5.9.6

4 Apply primer Dry film thickness dependent upon system (see Table SPA1e)

7 and 8 15.4

5 Apply micaceous iron oxide

Dry film thickness 75 um minimum 7 and 8 15.5 15.6

TABLE SPA1b - Operations chart for use with clauses 14 and 15 surfaces with limited coating damage Operation



2 Mechanically wire brush and feather edges

BS 7079 St3 quality as minimum 5.9.4 14.2 14.3


5.9.6

4 Apply primer Dry film thickness dependent upon system (see Table SPA1e)

7 and 8 15.4

5 Apply micaceous iron oxide

Dry film thickness 75 um minimum 7 and 8 15.5 15.6

- 12 - J020 ( Rev 08/98 )


PA10: SECTION 3 TABLE SPA1c - Operations chart for final coatings Operation


Section 2 Section 3 1 Clean all surfaces 5.9.6 16.1

16.2

2 Apply undercoat Dry film thickness dependent upon system (see Table SPA1e)

7 and 8 16.3

3 Apply finish Dry film thickness dependent upon system (see Table SPA1e)

7 and 8 16.4

TABLE SPA1d - Operations chart for maintenance painting Operation



2 Surface preparation of existing paint system

Key existing paint system if required

17.2.1

3 Surface preparation of areas of exposed substrate or where paint is to be removed

Blast cleaning or wire brushing as specified

5.9 17.2.2

4 Clean all surfaces Immediately prior to painting 5.9.6

5 Spot primer

6 Spot micaceous iron oxide

Overlapping existing paint at least 100 mm 7 17.3.1

7 Apply undercoat

8 Apply finish Overall or to areas spot painted above, as specified 7 17.3.2

J020 ( Rev 08/98 ) - 13 -


PA10: SECTION 3 TABLE SPA1e - Preferred systems - 14 - J020 ( Rev 08/98 )

Stage Compliant solvent-based Minimum dry film thickness (um)

1 High build epoxy aluminium primer 75

2 Epoxy Micaceous iron oxide 75

3 High build epoxy undercoat 75

4 Epoxy or polyester acrylic finish 40

Stage Water-borne acrylic Minimum dry film thickness

(um)

1 Primer 50

2 Micaceous iron oxide 75

3 Undercoat 50

4 Finish coat 50

NOTE – Other compliant systems which meet the requirements of PA9 and which give equivalent long term performance to the systems specified above may be proposed as variant for consideration by TransCo.


PA10: SECTION 3 SPECIFIC PAINTING APPLICATION (SPA) SPA2 - NEW AND MAINTENANCE PAINTING FOR INDOOR USE OR SHORT TERM PROTECTION 18. GENERAL 18.1 This SPA2 applies to new and maintenance painting for indoor use or short term protection of carbon steel surfaces operating below 100 0 C. The operations chart shown in Table SPA2a relates to new painting and Table SPA2b to maintenance painting. 19. PREPARATION OF SURFACES 19.1 All surfaces not to be painted shall be masked in accordance with 5.7. 19.2 Before cleaning operations commence, all surface contaminants shall be removed by washing with an appropriate medium. 19.3 Surfaces shall be prepared as specified in 5.9.4 to comply with the requirements of BS 7079 St 3 quality as a minimum. The method of cleaning shall normally be by mechanical wire brushing but other methods of preparation may be proposed to Transco for consideration as a variant. 19.4 The edges of existing sound coating shall be feathered. 20. NEW PAINTING FOR INDOOR USE AND FOR SHORT TERM PROTECTION (TABLE SPA2a) 20.1 Compliant materials normally based on drying oil or water borne acrylic paints shall be specified and applied in accordance with clause 7. 20.2 One coat of primer shall be applied, normally by brushing. The paint shall overlap onto any existing coating by at least 100 mm. The manufacturers' recommended overcoating times shall be adhered to. 20.3 One coat of MIO build coat shall be applied to all primed surfaces normally by brushing. 20.4 If a decorative appearance is required, one coat of undercoat and finish shall be applied. The undercoat should be of a complementary colour to the finish coat. 21. MAINTENANCE PAINTING OF SYSTEMS FOR INDOOR USE AND FOR SHORT TERM

PROTECTION (TABLE SPA2b) 21.1 Areas requiring maintenance painting shall be prepared in accordance with 19.1 and 19.2. 21.2 Damaged areas shall be prepared in accordance with 19.3 and 19.4 and spot repaired in accordance with 20.1 to 20.3 using primer and MIO. The coating shall overlap 100 mm onto the existing sound coating. 21.3 Depending on the required finish, either one full coat of MIO or alternatively one full coat of undercoat and finish to the required colour shall be applied. J020 ( Rev 08/98 ) - 15 -


PA10: SECTION 3 TABLE SPA2a - Operation chart for new painting Operation


Section 2 Section 3 1 2 3 4 5 6

Mask off Remove all deposits Wire brush Clean areas Apply primer Apply micaceous iron oxide

BS 7079,St3 as a minimum Minimum dry film thickness 45 um Minimum dry film thickness 50 um*

5.7

5.9.4 5.9.6

7 7

19.1 19.2 19.3

20.2 20.3

7** 8**

Apply undercoat Apply finish

Minimum dry film thickness 45 um* Minimum dry film thickness 25 um*

7 7

20.4 20.4

* These values to be determined by means of a wet film thickness gauge as specified in clause 8. ** Operations 7 and8 are to be carried out if a decorative finish is required. TABLE SPA2b - Operation chart for maintenance painting Operation


Section 2 Section 3 1 2 3 4 5 6*

Mask off Remove all deposits Wire brush Clean areas Spot prime Spot micaceous iron oxide

BS 7079,St3 as a minimum Minimum dry film thickness 45 um Minimum dry film thickness 50 um**

5.7

5.9.4 5.9.6

7 7

19.1 19.2 19.3

20.2 20.3

7 8

Apply undercoat Apply finish

Minimum dry film thickness 45 um** Minimum dry film thickness 25 um**

7 7

21.3 21.3

9 Apply full coat of micaceous iron oxide

Minimum dry film thickness 50 um**

7

21.3

* On completion of operation 6, if decorative finish is required, operations 7 and 8 only are to be carried out. Alternatively, operation 9 may be carried out on completion of operation 6, if a decorative finish is not required. ** These values to be determined by means of a wet film thickness gauge as specified in clause 8.. - 16 - J020 ( Rev 08/98 )


PA10: SECTION 3 SPECIFIC PAINTING APPLICATION (SPA) SPA3 - PAINTING OF METAL SURFACES FOR HOT DUTIES 22. GENERAL 22.1 This SPA3 applies to the painting of surfaces which are likely to operate at 100 0 C or above. 22.2 Areas where the operating temperature of the metal surface is likely to reach, but not exceed, 149 0 C shall be painted as specified in clause 23. 22.3 Areas where the operating temperature of the metal surface is likely to exceed 149 0 C and 340 0 C shall be protected as specified in clauses 24 and 25 respectively. 23. FOR DUTIES AT TEMPERATURES FROM 100 0 C TO 149 0 C (TABLE SPA3a) 23.1 Preparation for painting of new installations and maintenance painting 23.1.1 All surfaces not to be painted shall be masked as specified in 5.7. 23.1.2 Before cleaning operations commence, all surface contaminants shall be removed by washing with an appropriate medium. 23.1.3 All areas shall be prepared for painting as specified in 5.9.2. 23.1.4 Mechanical cleaning in accordance with 5.9.4 may be allowed in small areas at the discretion of the Engineer. 23.2 Application of paint to prepared areas 23.2.1 A heat resistant, aluminium pigmented epoxy or urethane primer shall be applied in accordance with the manufacturers' recommendations to all areas of exposed metal. Paint shall be applied within four hours of blast cleaning but before any rust blooming or contamination occurs. 23.2.2 Within the manufacturers' recommended overcoating times, further coats of primer shall be applied to achieve a total minimum DFT of 100 μm for urethane or 250 μm for the epoxy coating, as appropriate. 23.2.3 Heat resistant paints are normally pigmented with aluminium flake, therefore a finish to a designated colour may not be possible. 24. FOR DUTIES AT TEMPERATURES FROM150 0 C TO 340 0 C (TABLE SPA3b) 24.1 Preparation for painting of new installations and maintenance painting 24.1.1 All surfaces not to be painted shall be masked as specified in 5.7. 24.1.2 Before cleaning operations commence, all surface contaminants shall be removed by washing with an appropriate medium. 24.1.3 All areas shall be prepared for painting as specified in 5.9.2. 24.2 Application of coating material 24.2.1 Thermally sprayed aluminium (TSA) shall be applied to prepared surfaces in accordance with BS EN 22063 and/or BS 2569: Part 2. 24.2.2 Where TSA is deemed to be impractical due to operational restraints, or judged to be too high a standard of coating for this temperature range, consideration shall be given to the use of paint systems based on inorganic zinc silicate or polysiloxane primers. Paints shall be applied in accordance with the manufacturers' recommendations. J020 ( Rev 08/98 ) - 17 –


PA10: SECTION 3 24.2.3 With the use of inorganic zinc silicate, mud cracking of the coating may result if the manufacturers, recommended film thickness is exceeded. 25. FOR DUTIES AT TEMPERATURES ABOVE 340 0 C (TABLE SPA3c) 25.1 Preparation for painting of new installations and maintenance painting All preparations shall be carried out in accordance with 23.1. 25.2 Application of coating material 25.2.1 TSA, which is the preferred coating choice, shall be applied in accordance with BS EN 22063 and/or BS 2569: Part 2. 25.2.2 Where TSA is deemed to be impractical due to operational restraints, consideration shall be given to the use of paint systems based on inorganic zinc silicate or polysiloxane primers. Paints shall be applied in accordance with the manufacturers' recommendations. 25.2.3 With the use of inorganic zinc silicate, mud cracking of the coating may result if the manufacturers' recommended film thickness is exceeded. 25.2.4 Where TSA and inorganic zinc silicate primers are used, they shall be sealed with a high temperature sealer. Sealers shall be applied and cured in accordance with the manufacturers' recommendations. - 18 - J020 ( Rev 08/98 )


PA10: SECTION 3 TABLE SPA3a - Operations chart for hot duty surfaces from 100 0 C to 149 0 C Operation


Section 2 Section 3 1 Mask 5.7 23.1.1

2 Remove surface contamination

23.1.2

3 Blast clean BS7079 Sa 2½ quality; maximum profile 75 um

5.9.2 23.1.3

4 Apply primer Dry film thickness depends upon primer used

23.2.1

5 Apply additional coats of primer

Dry film thickness depends upon primer used

23.2.2

TABLE SPA3b - Operations chart for hot duty surfaces from 150 0 C to 340 0 C J020 ( Rev 08/98 ) - 19 -

Operation number

Subject of operation Comments Relevant clauses in PA10



24.1.2

3 Blast clean BS7079 Sa 3 quality; maximum profile 75 um

5.9.2 24.1.3

4 Apply system System to be chosen from the list of options below

24.2.2

Operation


Section 2 Section 3 a Thermally sprayed

aluminium In accordance with BS 2569: Part 2 and/or BS EN 22063

24.2.1

b Inorganic zinc silicate Apply in accordance with manufacturers’ instructions

24.2.2

c Polysiloxane inorganic coating

Apply in accordance with manufacturers’ instructions

24.2.2


PA10: SECTION 3 TABLE SPA3c - Operations chart for hot duty surfaces operating above 340 0 C Operation




24.1.2

3 Blast clean BS7079 Sa 3 quality; maximum profile 75 um

5.9.2 24.1.3

4 Apply thermally sprayed aluminium

In accordance with BS 2569: Part 2 and/or BS EN 22063

25.2.1

NOTE – Thermally sprayed aluminium is the preferred system and will provide the longest service life.

Alternative coating systems to thermally sprayed aluminium are:

4a i) Inorganic zinc silicate Apply in accordance with manufacturers’ instructions

25.2.2

ii) Apply sealer Apply in accordance with manufacturers’ instructions.

Not required for polysiloxane coatings

25.2.4

iii) Apply heat to cure sealer

In accordance with manufacturers’ instructions. Check plant operating conditions

25.2.4

4b Polysiloxane inorganic coating

Apply in accordance with manufacturers’ instructions

25.2.2

- 20 - J020 ( Rev 08/98 )


PA10: SECTION 3 SPECIFIC PAINTING APPLICATION (SPA) SPA4 - PAINTING OF DAMP FERROUS SURFACES 26. GENERAL 26.1 This SPA4 applies to the painting of ferrous surfaces on which the presence of condensation during painting cannot be operationally prevented. A number of paint systems are available which are tolerant to damp surfaces but, in general, cannot be used on wet surfaces (see clause 3). They shall not be used when ice is present, or where the surface temperature is likely to be below 3 0 C. 26.2 Types of materials which are known to perform satisfactorily on damp metal surfaces are:

a) Moisture curing polyurethanes.

b) High solids multi-component epoxy paints. 27. PREPARATION OF SURFACES 27.1 Any oil or grease shall be removed by swabbing with grease removing solvents. The surface shall subsequently be washed with a 2% detergent solution. 27.2 All surfaces shall be blast cleaned as specified in 5.9.2 to achieve BS 7079 Sa 2 ½ quality immediately prior to paint application. In general, a degree of rust blooming is acceptable, but in all cases, the manufacturers' instructions shall be followed. 27.3 All grit and dust shall be removed from the blast-cleaned surface by washing with clean water. 27.4 Immediately prior to painting, all droplets and standing water shall be removed from the surfaces to be painted by mopping or using a squeegee. Cloths or rags shall only be used if they are lint-free. 28. APPLICATION OF PAINTS 28.1 All paints shall be applied in strict accordance with the manufacturers' instructions. 28.2 All paints shall be brush applied. 28.3 An operations chart for painting in accordance with the above procedure is given in Table SPA4a. J020 ( Rev 08/98 ) - 21 -


PA10: SECTION 3 TABLE SPA4a - Operation chart for painting damp metal surfaces Operation

number Subject of operation

Period before next operation

Comments Relevant clauses in PA10

Minimum Maximum Section 2 Section 3

1 Remove all surface contamination, etc.

5.9.6 27.1

2 Blast clean 4 h BS 7079 Sa 2½ quality

5.9.2 27.2

3 Wash To remove all grit and dust

27.3

4 Remove droplets and standing water

Surface shall not be wet

27.4

5 Apply system In accordance with manufacturers’ instructions

To be applied by brushing

7 28.2

- 22 - J020 ( Rev 08/98 )


PA10: SECTION 3 SPECIFIC PAINTING APPLICATION (SPA) SPA5 - MAINTENANCE PAINTING OF LOW PRESSURE GASHOLDERS 29. GENERAL 29.1 This SPA5 details procedures for the planning, surface preparation, cleaning and painting of external surfaces of low pressure water sealed gasholders (see clauses 30, 31 and 32). Holder cup water management during preparation and painting operations of cup, grip and the wind and water lines is described in clause 33. Guidance Notes relating to safety during preparation and painting operations are described in clause 34. Waterless gasholders of the Wiggins, Hammond, Klonne and MAN. types and the above ground frame work and water tank associated with water sealed gasholders shall be painted in accordance with SPA1. The painting of damp ferrous surfaces, such as tank bottom plates and gas mains in pits which extend into the gasholder foundation is covered by SPA4. 29.2 Tender documents for all gasholder painting contracts shall clearly identify the following:

a) Surfaces to be painted.

b) The method of surface preparation.

c) The painting systems to be applied and the finished colour(s) defined to BS 4800.

d) Surfaces and items not to be painted.

e) Sections of the structure and attachments which need to be protected by the Contractor during the preparation and painting operations.

29.2.1 The selection of paint systems to be applied should be determined by the following:

a) Environmental in-service conditions.

b) Existing paint system.

c) Extent of paint breakdown and corrosion.

d) Method and extent of preparation.

e) Standard of cleanliness achievable.

f) Service life requirement. A range of paints which give acceptable performance is available and specialist advice should be sought when selecting the paint system. Water-borne acrylics, compliant alkyds and moisture cured urethanes may be used satisfactorily in most cases. 29.3 Reference shall be made to the Guidance Notes in clause 34 and, where applicable, relevant sub-clauses shall be included in the tender documents. J020 ( Rev 08/98 ) - 23 -


PA10: SECTION 3 30. PRELIMINARY CONSIDERATIONS (PRIOR TO PREPARATION OF SURFACES FOR PAINTING)30.1 Extensive rust staining alone will not necessarily warrant repainting as this can be removed by means of chemical treatment. 30.2 The pH of the holder water should be determined prior to any major painting proposal and adjusted to ensure that an acceptable value (within the rang pH9 to pHl0) is achieved at least six months prior to painting. No further dosing should be carried out until six months after completion of painting. 30.3 Consideration should be given to the need for the isolation of all electrical equipment fitted to the gasholder, particularly in respect of electrical anti-freeze systems. 30.4 The Engineer shall ensure that Grid Control is notified and local procedures are complied with to prevent accidental movement of the gasholder during the painting contract. 30.5 All surfaces not to be painted or areas which may be adversely affected by preparation and painting operations shall be identified by the Engineer and suitable protection agreed and carried out by the Contractor. Typical areas and items of equipment to be protected are:

a) Water seals.

b) Guide carriages.

c) Lubrication facilities.

d) Steam, water or anti-freeze injection facilities (including nozzles).

e) Anti-siphon vents.

f) Flexible hoses.

g) Electrical antifreeze facilities (including cables).

h) Junction boxes.

i) Instrumentation.

j) Control equipment and associated services and any other operational equipment suspended in the cups or tank.

30.6 The Contractor shall be alerted of the possible toxic nature of the deposits and paint debris and the appropriate action and certification required for their disposal (see B.3.1). 30.7 Where necessary, the Engineer shall arrange for the oil to be removed from the surface of the water seals before cleaning and surface preparation commence. Examination of the cups shall also be carried out prior to the cupping up of each lift. 30.8 The Contractor shall not attempt to lower water levels unless specifically directed to do so by the Engineer. In all cases, the removal of water shall be carried out under the direct supervision of the Engineer or his nominated representative. 30.9 The Engineer shall arrange for the gasholder lifts to be positioned as necessary, to facilitate preparation and painting. The area on which work is taking place should normally be at the tank balcony/cupping level. - 24 - J020 ( Rev 08/98 )


PA10: SECTION 3 31. SURFACE PREPARATION FOR PAINTING 31.1 A number of preparation techniques may be used on a project (e.g. blast cleaning, water jet cleaning, mechanical cleaning, manual cleaning, etc.). Precautions shall be taken to prevent debris from the work entering the cups, the tank, and any other vulnerable work areas. 31.2 Before preparation and painting commence, surfaces for which a particular method of preparation has been specified shall be clearly defined by the Engineer. Non-drying paint has been found to mask severe corrosion and should be removed prior to painting. Methods such as scraping, the application of an approved heavy duty solvent, detergent, hot water or steam cleaning may be employed for this purpose (also see 32.6, Note 5). 31.3 All surfaces shall be prepared for painting in accordance with 5.9). Where surfaces are blast cleaned, the surface finish immediately prior to painting shall be equivalent to BS 7079 Sa 2 ½ quality and have a profile within the range of 30 μm to 75 μm . Particular reference is drawn to 5.9.2.5 if lead based paints are present. Where surfaces are to be prepared by mechanical or hand tools, or high pressure water jetting, the method of surface preparation shall provide a surface of equivalent cleanliness to BS 7079 St 3 as a minimum quality. The surface shall also be free of significant areas of mill scale. 31.4 The existing remaining coating will be feathered at the edges. 32. APPLICATION OF PAINT TO PREPARED SURFACES 32.1 All paint shall be applied as specified in clause 7. Brush application of the primer is essential when the surface has not been totally blast cleaned or where areas of the previous coating remain. Primer coats may be applied by spraying only when the metal surface has been fully blast cleaned. Subsequent coating should be applied by brushing or spraying as appropriate. Application of paint by roller is not recommended. Prior to each application of paint, all surfaces shall be free of contamination as specified in 5.9.6. For the application of paint onto surfaces predominantly immersed in water (i.e. cups, grips, wind and water lines), 32.7 applies. For all other areas 32.2 to 32.6 may apply. 32.2 The primer shall be applied to all prepared exposed metal to a DFT as specified in the manufacturers' instructions. This may range from minimum spot preparation to the application of a full primer coat as specified in the manufacturers' instructions. Stripe coating may be necessary to achieve the required DFT at edges, rivets and weld areas. Where applicable, spot priming shall overlap onto any existing sound coating by at least 100 mm. The manufacturers' recommended overcoating times shall be followed, although not more than seven days shall have elapsed before overcoating. J020 ( Rev 08/98 ) - 25 -


PA10: SECTION 3 32.3 One coat of MIO high build paint shall be applied to all newly primed surfaces, overlapping onto existing sound coating by at least 100 mm. The DFT shall be as specified in the manufacturers' instructions (determined by means of a wet film thickness gauge as specified in clause 8). The manufacturers' recommended overcoating times shall be followed although not more than seven days shall have elapsed before overcoating. 32.4 One further coat of MIO paint may then be considered in the following situations:

a) Where there has been minimal breakdown of the existing paint system, the additional coat shall be applied only as a spot coat, (the total system will then comprise of spot primer, spot MIO, spot MIO, finish coat).

b) If justified, or where additional protection is required, the additional coat shall be applied as full

coat (the total system will then comprise of primer and MIO to prepared areas, followed by full MIO, full finish).

The DFT shall be as specified in the manufacturers instructions (determined by means of a wet film thickness gauge as specified in clause 8 The manufacturers' recommended drying times shall be followed before any operation of the gasholder is undertaken or before overcoating as described in 32.5. Overcoating is normally carried out within three months of the application of the build coat. 32.5 If required, one high build finish coat shall be applied (see Notes 2 and 3) to a DFT as specified in the manufacturers' instructions (determined by means of a wet film thickness gauge as specified in clause 8). The coating shall be allowed to dry for as long as possible and, in any case, for a minimum period of two weeks prior to any operation of the gasholder. 32.6 Table SPA5a gives details of the relevant preparation and painting operations. NOTES:

1. Each coat of paint shall be of a contrasting colour.

2. The finish coat on any one lift or on the above ground tank shall be from the same manufactured batch.

3. On the crown of a gasholder, the number of coats in the paint system should be kept to a

minimum. Where the crown is prepared by grit blasting, only a two-coat system of a primer and an MIO need be applied with the MIO acting as the finish coat. This MIO should be of a light/silver grey colour to provide a reflective surface to minimise the crown temperature. Reduced coating thickness will also improve flexibility and resistance to cracking.

4. Non-slip paint, made by mixing dry soft-wood coarse grade sawdust to the top coat paint, should

be applied as an additional coat to access areas such as walkways, stairs and a one metre band across the crown and around the inside of the crown perimeter.

5. Where non-drying paint is to be removed prior to painting, the additional cost to remove the final

traces can be prohibitive. Under this circumstance, a white spirit-based primer should be used: water-based primer is not recommended.

6. Water-based paints require the movement of air to dry quickly, otherwise localised rust spotting

will occur. This problem can be overcome by replacing the primer coat of the water-based system by a quick drying solvent-based primer.

- 26 - J020 ( Rev 08/98 )


PA10: SECTION 3 32.7 For surfaces which are predominantly immersed in water, one coat of moisture tolerant epoxy shall be applied by brushing to a minimum DFT of 100 μm (determined by means of a wet film thickness gauge as specified in clause 8). Where applicable, newly applied paint shall overlap onto the existing coating by 100 mm. The manufacturers' recommendation in respect of drying times should be followed, but typically a minimum period of two hours at 15 0 C should elapse before immersion into water. Since it is necessary to restore adequate water seals at the end of each day, the paint system used should meet this specific application requirement. The area to be prepared and painted on cups and grips shall extend from the lowered water level to a point at least 150 mm above the highest cup water working level around the full circumference of the gasholder. The area for tank wind and water lines shall extend from the lowered water level to the tank top curb around the full circumference of the tank. Table SPA5b gives details of the operations applicable to painting cups, grips and tank wind and water lines. 33. HOLDER CUP WATER MANAGEMENT 33.1 Preparation and painting of cup and grip areas necessitates the removal of water from the cup. Reduced water levels shall not remain during periods when the site is unattended and, in particular, overnight. The operations associated with the preparation and painting of cup and grip wind and water lines shall be planned to ensure that an adequate seal can be restored before leaving site each day. 33.1.1 During preparation and painting of cups and grips, water levels shall not be lowered to the point at which gas can escape beneath the grip plate and lead to potentially serious results. A gas/air mixture may also be trapped in the grip in which case a purging operation may be necessary before the gasholder is re-inflated. 33.2 The Engineer or the Engineer's nominated representative shall be present at all times to maintain observation of water levels during painting operations and until adequate seals are restored. 33.3 To facilitate painting operations, special arrangements may need to be made in respect of the disposal of water removed from the seals or tanks. 33.4 The Engineer may decide that tank water levels on multi-lift gasholders can be lowered sufficiently to protect the wind and water line by inflating the gasholder into the outer lift, allowing surplus water to drain from the tank to the tank overflow pipe level, and then lowering the gasholder into the inner lift. 33.4.1 If tank wind and water lines are to be protected on a single lift gasholder, water levels will need to be lowered by controlled syphoning or pumping. 33.5 When the gasholder is in the required position, the Engineer shall arrange for the Contractor to remove all sediment from the base of the cup. 33.6 If, after the removal of sediment from the base of the cup, the water level has not reduced sufficiently to enable the preparation and painting of the cup and grip wind and water line, the Engineer shall arrange for further water to be removed to a safe minimum level. 33.7 Each cup shall be cleaned before commencement of painting of the next lift. This does not preclude the possibility of additional cleaning being required during the progress of the painting operations. 33.8 If water blast cleaning is applied, it may be necessary to remove a further quantity of water from the cup before proceeding with the next operation. J020 ( Rev 08/98 ) - 27 -


PA10: SECTION 3 33.8.1 Materials/debris arising from this operation shall be removed from the cup before proceeding with the next operation. 33.8.2 Materials arising from cup cleaning operations shall be prevented from falling into the tank. If materials do fall into the tank, attempts shall be made to remove them before proceeding with the next operation. 33.9 On completion of the full protection of any cup and grip, the water seal shall be restored either by lowering the cup fully into the tank, re-cupping and checking that a correct seal has been obtained, or by pumping the water back into the cup to the required level. 33.10 If for any reason work relating to the preparation or the application of paint is suspended and it is necessary to temporarily restore adequate water seals, those operations relating to the removal of sediment and preparation for painting shall be repeated before proceeding with subsequent painting operations. 33.11 Circumstances which may give rise to the immersion of partially painted areas are:

a) Operational requirements during the Contract period.

b) Variations in atmospheric temperature which cause expansion and contraction of stored gas. Account should be taken of the effects of b) above when arranging for cups and grips to be prepared and painted. 33.11.1 Attention is drawn to the fact that rainfall can very quickly refill cups in which water levels have been lowered for preparation and painting. If this should occur, the relevant operations relating to the total preparation in readiness for the application of paint may need to be repeated. 33.12 Care should be taken to ensure that the cup water levels are sufficient to accommodate changes in gas pressures due to the effect of sun gas. 34. GUIDANCE NOTES 34.1 In addition to the reference to safety in other parts of this Specification, the following requirements shall apply to maintenance painting of low pressure gasholders:

a) Reference shall be made to:

1) Safety recommendations IGE/SR/3.



4) Any company or other safety standards applicable to work carried out on low pressure gasholders.

b) Leakage of gas observed during the course of the work must be reported to the Engineer immediately and operations suspended until the leakage has been sealed.

c) Any damage arising from painting operations shall be reported to the Engineer immediately.

d) There shall be no interference with auxiliary equipment fitted to or associated with gasholders. If

equipment is inadvertently moved, the occurrence shall be reported to the Engineer immediately. The Contractor shall not attempt to re-set equipment unless directed to do so by the Engineer or the Engineer's nominated representative.

- 28 - J020 ( Rev 08/98 )


PA10: SECTION 3

e) The painting shall be carried out in such a manner as to preclude paint being splashed or air borne particles being carried to adjacent Transco property or on to the property of adjacent occupiers.

f) Deposits resulting from cleaning and surface preparation shall be removed, bagged and disposed of in the manner prescribed by current legislation and local procedures. Attention is drawn to the requirements of the Environmental Protection Act - Duty of Care.

g) Access to the roof, crown, walkways and staircases of the gasholder shall be restricted after

painting, for a period of time to be determined by the Engineer. TABLE SPA5a - Operations chart for maintenance painting of low pressure gasholders Operation





1 Protect defined areas against effect of preparation and painting operations

5.7 30.5

2 Remove all surface contamination particularly non-drying paints and oil films

5.9 31.1 31.2

3 Surface preparation for painting

4 h Blast cleaning or mechanical/hand cleaning, as specified

5.9 31.3


5.9.6 32

5 Apply primer 7 days Spot or full coat, as appropriate. Stripe coat welds and edges

7. 8.

32.1 32.2

6 Apply micaceous iron oxide (build coat)

7 days Spot or full coat, as appropriate

7. 8.

32.3

7 Apply micaceous iron oxide (if required)

3 months Spot or optional full coat, as appropriate

7. 8.

32.4

8 Apply finish (if required)

2 weeks Overall or to areas spot painted above, as specified

7. 8.

32.5

J020 ( Rev 08/98 ) - 29 -


PA10: SECTION 3 TABLE SPA5b - Operations chart for maintenance painting of low pressure gasholders (cups, grips, and steel tank wind and water lines) Operation





1 Position gasholder Preliminary considerations

30.9 33.5

2 Protect defined areas

Preliminary considerations

5.7 30.5 33.9

3 Remove sediment from cups

Preliminary considerations

33. 33.5

4 Lower water levels Preliminary considerations

33. 33.4.1

5 Surface preparation for painting

BS 7079 St3 as minimum quality

5.9 31.3

6 Clean all surfaces Immediately prior to paint application

5.9.6 32

7 Apply epoxy paint (moisture tolerant grade)

2 h Full coat dry film thickness 100 um minimum

32.7

8 Restore water levels Before leaving site

33

- 30 - J020 ( Rev 08/98 )


PA10: SECTION 3 SPECIFIC PAINTING APPLICATION (SPA) SPA6 - PAINTING OF NON-FERROUS SURFACES 35. GENERAL 35.1 This SPA6 applies to the painting at site of the non-ferrous surfaces specified below:

a) New galvanized surfaces.

b) Weathered galvanized surfaces.

c) Previously painted galvanized surfaces.

d) Aluminium surfaces.

e) Stainless steel.

f) Pre-painted cladding ('Plastisol' cladding or equivalent).

g) Glass reinforced plastics (GRP).

h) Fusion bonded epoxy (FBE).

i) Multi component liquids (MCL).

j) Concrete. 35.2 All these surfaces, especially aluminium and stainless steel shall be thoroughly cleaned in accordance with 5.9.6 and then lightly abraded to provide an adequate key for the new paint system (see Table SPA6a). 35.3 It should be noted that items a) to d) are painted primarily to provide corrosion protection. The remainder are painted for cosmetic purposes only. 36. PREPARATION OF SURFACES FOR PAINTING All forms of surface contamination and disbonded paint shall be removed, especially oil, grease, salts, dirt and dust. This should be achieved by the use of detergent cleaners or emulsifying agents followed by a clean water rinse. 36.2 The surface shall then be prepared as detailed in the requirements in Table SPA6a. 37. APPLICATION OF PAINT TO PREPARED SURFACES 37.1 Compliant materials of the type listed in Table SPA6b shall be specified by the Engineer and applied in accordance with clause 7. 37.2 The choice of the generic paint system will determine the initial coat required and this is shown in Table SPA6c. 37.3 For items a) to d), the minimum dry film thickness of the full paint system shall be 120 μm and shall include a MIO build coat. Water borne acrylic paint systems do not require a separate primer as the MIO will fulfil this function. 37.4 Items e) to i) do not require a MIO coat. 37.5 Coating systems shall normally be terminated with a full gloss finish of the same generic type as the preceding coats. Where an epoxy primer and intermediate coat have been applied, an epoxy acrylic or epoxy polyester topcoat shall be specified. In some situations, it may be required to terminate the paint system at the MIO coat. J020 ( Rev 08/98 ) - 31 -


PA10: SECTION 3 TABLE SPA6a - Non-ferrous surfaces - surface preparation

Non-ferrous surfaces Surface preparation Comments

Preferred option First option

a) New galvanizing Sweep abrasive blast

Hand abrading The preferred and first options eliminate the need for an ‘Etch’ primer. An ‘Etch’ primer (T-wash) shall be used where these options are impractical

b) Weathered galvanizing Stiff bristle brushing

- Weathered surface provides its own key

c) Previously painted galvanizing

Sweep abrasive blast

Hand abrading -

d) Aluminium Sweep abrasive blast

Hand abrading Thin gauge aluminium should not be blast cleaned and should be treated with an etch primer prior to the application of intermediate and finish coats.

Chlorinated hydrocarbon solvent shall not be used

e) Stainless steel Sweep abrasive blast

- Only aluminium oxide should be used as the blasting medium

f) Pre-painted cladding (‘Plastisol’ cladding or equivalent)

Sweep abrasive blast

Hand abrading -

g) Glass reinforced plastics Sweep abrasive blast

Hand abrading -

h) Fusion bonded epoxy Sweep abrasive blast

Hand abrading -

i) Multi component liquids Sweep abrasive blast

Hand abrading -

j) Concrete In accordance with the Manufacturers’ recommendations

- Surface abrasion may not be required for new concrete. Old paint should be removed if required using scrabblers

- 32 - J020 ( Rev 08/98 )


PA10: SECTION 3 TABLE SPA6b - Non-ferrous surfaces - Paint systems

Non-ferrous surfaces Groups of paint systems Comments

G1 G2 G3

a) New galvanizing Water-borne acrylic

Epoxy high build

Alkyd or modified alkyd

-

b) Weathered galvanizing Water-borne acrylic

Epoxy high build


Any damaged galvanizing shall be repaired with zinc rich epoxy


Water-borne acrylic

Epoxy high build


-

d) Aluminium Water-borne acrylic

Epoxy high build


-

e) Stainless steel Water-borne acrylic

Epoxy high build

- -

f) Pre-painted cladding (‘Plastisol’ cladding or equivalent)

Water-borne acrylic

Moisture cured urethane


Any damaged areas where the steel substrate is exposed, should be repaired in accordance with SPA1

g) Glass reinforced plastics Water-borne acrylic



-

h) Fusion bonded epoxy Water-borne acrylic



-

i) Multi component liquids Water-borne acrylic



-

j) Concrete Water-borne acrylic



For new concrete a sealer coat may be required

NOTE Other compliant systems which meet the requirements of PA9 may be proposed as a variant for consideration by Transco. J020 ( Rev 08/98 ) - 33 -


PA10: SECTION 3 TABLE SPA6c - Non-ferrous surfaces - Paint systems - Initial coat

Non-ferrous surfaces Options

G1 G2 G3

a) New galvanizing Water-borne acrylic micaceous iron oxide

(65 um minimum)

Pigmented high build epoxy (65 um

minimum)

Alkyd or modified alkyd (40 um

minimum)

b) Weathered galvanizing Water-borne acrylic micaceous iron oxide

(65 um minimum)


minimum)


minimum)


Water-borne acrylic micaceous iron oxide

(65 um minimum)


minimum)


minimum)

d) Aluminium Water-borne acrylic micaceous iron oxide

(65 um minimum)


minimum)


minimum)

e) Stainless steel Water-borne acrylic micaceous iron oxide

(45 um minimum)

Chloride free epoxy high build (65 um

minimum)

-

f) Pre-painted cladding (plastisol cladding)

Water-borne acrylic micaceous iron oxide

(45 um minimum)

Compatible moisture cured urethane (25 um

minimum)

Compatible alkyd or modified alkyd (40 um

minimum)

g) Glass reinforced plastics Water-borne acrylic micaceous iron oxide

(45 um minimum)


minimum)


minimum)

h) Fusion bonded epoxy Water-borne acrylic micaceous iron oxide

(45 um minimum)


minimum)


minimum)

i) Multi component liquids Water-borne acrylic micaceous iron oxide

(45 um minimum)


minimum)


minimum)

Walls j) Concrete Floors

{Single pack } {water-borne acrylic} {primer (30 um } {minimum) }

Moisture cured urethane sealer


minimum)

- 34 - J020 ( Rev 08/98 )


PA10 APPENDIX A LIST OF REFERENCES This specification makes reference to the documents listed below (see clause 2). It shall be the Contractor's responsibility to acquire all relevant standards applicable to the particular work involved. Copies of the relevant Transco specifications will normally be supplied by Transco at the tender stage. Statutes and Regulations No. 1145 1948 - The Building (Safety, Health and Welfare) Regulations No. 1580 1961 - The Construction (General Provisions) Regulations No. 1581 1961 - The Construction (Lifting Operations) Regulations 1989 - The Construction (Head Protection) Regulations No.1248 1980 - Control of Lead at Work Regulations 1963 - The Contracts of Employment Act 1961 - The Factories Act 1947 - The Fire Services Act 1963 - The Offices, Shops and Railway Premises Act 1974 - Health and Safety at Work etc. Act 1990 - Environmental Protection Act 1991 - Environmental Protection Act - EPA - (Duty of Care Regulations) 1974 - Control of Pollution Act (1974) & Amendment (1989) 1980 - Control of Pollution Special Waste Regulations (Amendment 1988) 1988 - Collection and Disposal of Waste Regulations 1988 - Control of Substances Hazardous to Health Regulations 1989 - Noise at Work Regulations

- Management of Health & Safety at Work Regulations - Manhandling Operations Regulations

1992 - Provision and Use of Work Equipment Regulations 1992 - Personal Protective Equipment at Work Regulations 1992 - Workplace (Health, Safety & Welfare) Regulations

1994 - Certification, Packaging and Labelling (CPL) Regulations (for Carriage of Dangerous Goods by Road and Rail)

J020 ( Rev 08/98 ) - 35 -


PA10 1993 - Chemicals Hazard Information and Packaging (CHIP) Regulations

- Water Resources Act International Organisation for Standardisation (ISO) standard ISO 7167 - Preparation of steel substances before application of paint and related Products European Standards BS EN 345, 355, 358/361 – 365 - Specifications for industrial safety belts, harnesses and safety lanyards BS EN 22063 - Metallic and other inorganic coatings. Thermal spraying. Zinc, aluminium and their alloys British Standards BS 1129 - Specification for portable timber ladders, steps, trestles and lightweight stagings BS 1139 - Metal scaffolding BS 2569 - Specification for sprayed metal coatings: Part 2 - Protection of iron and steel against corrosion and oxidation at elevated temperatures BS 2830 - Specification for suspended safety chairs and cradles for use in the construction industry BS 2842 - Specification for whirling hygrometer BS 3900 - Methods of test for paints: Part C5 - Determination of film thickness BS 4800 - Schedule of paint colours for building purposes BS 5493 - Code of practice for protective coating or iron and steel structures against corrosion BS 5973 - Code of practice for access and working scaffolds and special scaffold structures in steel BS 7079 - Preparation of steel substrates before application of paints and related products: Part 0 - Introduction Part A - Visual assessment of surface cleanliness Part A1 - Specification for rust grades and preparation grades of uncoated steel substrates and of steel substrates after overall removal of previous coatings Part Al: - Supplement 1 - Representative photographic examples of the change of appearance imparted to steel when blast-cleaned with different abrasives - 36 - J020 ( Rev 08/98 )


PA10 Institution of Gas Engineers (IGE) Recommendations* *These Recommendations are available from 21 Portland Place, London WIN 3AF. IGE/SR/3 - Electrical equipment in gas production, transmission, storage and distribution IGE/SR/4 - Low pressure gasholders storing lighter-than-air gases IGE/SR/5 - Opening of gas works plant and working in confined spaces IGE/SR/12 - Handling of methanol IGE/SR/21 - Blast cleaning operations IGE/TD/6 - Handling, transport and storage of steel pipes, bends, tees, valves and fittings Transco specifications G11 - Notes for guidance on the issue of Permits to Work CW5 - Code of Practice for the selection and application of field applied external pipework coatings PA9 - Technical specification for paint properties and performances requirements DIS 3.1 - Engineering Procedures - Safety - Health and Safety at Works DIS 3.5 - Engineering Procedures - Health, Safety and Environmental Protection Other Transco publications - Handbook on Safe Handling of Substances in Use within the Gas Industry - Computerised Information System for Substances in Use in Transco (CISSUB). J020 ( Rev 08/98 ) - 37 -


- 38 - J020 ( Rev 08/98 )

Painting Inspection Grade 3/2 1 Appendix B

PA10 APPENDIX B SAFETY B.1 GENERAL Personnel shall comply with all relevant regulations when cleaning, painting and disposal procedures are being carried out (see Statutes and Regulations, Appendix A). Attention is drawn to the safety section of paint manufacturer's data sheets, to IGE/SR/21, BS EN 345, 355, 358/361 to 365, to DIS 3.1 and DIS 3.5. B.2 SAFETY PRECAUTIONS ON SITE B.2.l All site work is normally subject to a Permit to Work system, (see G11). The Contractor shall comply with the requirements of this system at all times. No work shall be allowed to take place until a Permit to Work or form of authority has been issued. A representative shall be nominated by the Contractor to act on his behalf; his duties shall include obtaining Permits to Work or forms of authority. This representative shall agree with the Engineer at the beginning of each day, or by alternative arrangement, the extent of the work to be undertaken and the precautions needed. Once agreed, this programme shall not be modified unless further permission is obtained. The Contractor's nominated representative shall be responsible for ensuring that the Permit to Work or form of authority in force is always appropriate to the work being undertaken. B.2.2 Delay in the provision of Permits to Work or forms of authority will be avoided if prior warning is given to the Engineer. This shall ideally be two days' advance notice in order that prior arrangements can be initiated and completed. Proper planning of the work programme is required as no additional payments shall be permitted for delays in obtaining the necessary permits or authorities. B.2.3 If the contract is scheduled to last for more than six weeks, the Contractor shall notify the Factory Inspector. B.2.4 All pressurised equipment, associated nozzles, etc., and electrically or pneumatically operated power tool equipment shall be earthed. 'No Smoking' regulations shall be observed, and Transco reserves the right to demand the removal from site of any person who disregards this instruction. Fires or flames shall not be used for the cleaning out of paint kettles, etc., or for disposal of rubbish. B.2.5 The Contractor shall not operate any Transco valves or plant on site. B.2.6 The Contractor shall note that certain areas on the installation are termed 'hazardous'. When working in such areas, the use of non-spark tools for cleaning purposes and flameproof equipment shall be compulsory. B.2.7 Where sheeting is used (e.g. for protection against accidental paint spillage), it is essential that the material be non-flammable. Tarpaulin sheets shall not be permitted on the site. B.2.8 During the work, the site shall be kept in an orderly manner and no materials or plant shall be placed in any buildings or positions where they could present a hazard to persons passing by on their normal duties. B.2.9 Vehicles shall only be allowed on site at the discretion of the Engineer. Vehicles so admitted shall keep to the roadways. They shall proceed as directed by Transco staff and be accompanied by a Contractor's representative from and to the main gate of the site. J020 ( Rev 08/98 ) - 39 -


PA10 B.2.10 If doubt exists regarding the demarcation of hazardous areas, working areas, or the requirement of any form of authority or Permit to Work, the Engineer shall provide an interpretation. B.2.11 The Contractor shall acquaint himself with all installation safety and security restrictions. B.2.12 In the event of an accident on site, the Contractor shall notify the Engineer and details shall be entered in the installation's Accident Record Book. This does not relieve the Contractor of his own responsibilities in this respect. B.2.13 The method of work and the equipment used by the Contractor may be inspected by the Engineer at any time without prior notice. No inspection shall in any way relieve the Contractor of any responsibility, under the Factories Acts 1961, or otherwise, in the method of work or use of equipment. B.3 ENVIRONMENTAL REQUIREMENTS B.3.1 Environmental protection B.3.1.l All waste materials resulting from surface preparation and painting operations covered in this Specification shall be properly disposed of in accordance with the requirements of the Environmental Protection Act - EPA - (Duty of Care). B.3.1.2 When surface preparation and painting operations covered in this specification are carried out in the vicinity of rivers, lakes or other water courses, special precautions may be necessary to prevent the possibility of pollution. Care shall be taken to ensure operations are carried out in accordance with the requirements of the Water Resources Act. B.4 STATUTORY REGULATIONS B.4.1 All operations covered in this specification shall be subject to the Health and Safety at Work etc. Act 1974 and other relevant legislations, such as European Union (EU), and regulations as listed in IGE/SR/12, Appendix 1. B.4.2 Due regard shall be taken in respect of the legislation regarding the use and care of protective clothing and other safety aids. B.4.3 It is an obligation that Transco will ensure that all personnel involved in the activities covered in this specification, be made fully aware of the relevant safety aspects, including the dangers of toxic materials. B.4.4 Attention is drawn to the Transco publication entitled Handbook on the Safe Handling of Substances in Use within the Gas Industry, or, alternatively, the Computerised Information System for Substances in Use in Transco (CISSUB) database. All activities concerning these substances shall have been subjected to an assessment under the Control of Substances Hazardous to Health (COSHH) Regulations. B.4.5 Containers and any associated packaging shall, where appropriate, be marked in accordance with the Certification, Packaging and Labelling (CPL) Regulations for Carriage of Dangerous Goods by Road and Rail 1994 and Chemicals Hazard Information and Packing (CHIP) Regulations. - 40 - J020 ( Rev 08/98 )


Appendix B

INSULATION

General The following text deals with acoustic cladding and thermal insulation. The materials used for both applications may be split into three separate types: 1 Insulating materials. 2 Protective coverings. 3 Fixing materials. All insulating materials must be stored in dry conditions under cover. During installation, weatherproof sheeting must be used during inclement weather and after each day’s application. Installation must be performed generally to standards normally accepted as first class workmanship. The finished cladding must be of good appearance and free from dents and sharp edges. Nameplates, code inspection plates and stampings on equipment must be left permanently visible and the cladding must be properly sealed around them. If the above requirement is impracticable, a second plate supplied by British Gas and permanently marked with the same information and with the work ‘DUPLICATE’ must be fixed on the outside of the cladding in the most convenient, adjacent position.

Acoustic cladding General The relevant British Gas standards are: BGC PC PWC1 - Acoustic cladding. Part 1 - Cladding of gas pipe and equipment. Part 2 - Notes for guidance. Cladding is defined as ‘an assembly comprising porous insulation material with a metal outer jacket’. The purpose of the cladding in this application is to cut down noise, typically by 10 – 20 dB.


Materials The insulation is usually in the form if semi-rigid sections. For small bore pipework, 25 mm diameter and below, flexible wool or fibrous materials may be used. The insulation is typically 50 – 100 mm thick and must comprise of non-toxic materials including materials which release non-toxic fumes during a fire. The metal jacket must be aluminium alloy, or galvanized mild steel sheet where greater rigidity is required. The thickness of the jacket must be related to the durability and strength required, ease of fitting and costs but will normally be between 0.71mm and 1.6 mm thick. Galvanized materials, or any materials which contain zinc, must not be used on stainless steel due to the danger of causing zinc embrittlement. Insulation banding may be metallic or non-metallic. If metallic, it must be of the same material as the jacket. Mastic sealants and rubber or neoprene bedding strips used must be suitable for use at temperatures between –200C to 500C with occasional increases up to 800C. Nuts, bolts, screws and washers must be either stainless steel or zinc metal coated mild steel Application of materials The basic sequence for the application of acoustic cladding: 1 Preparation. 2 Insulation plus fixing. 3 Repeat insulation and fixing if required. 4 Metal cladding plus fixing. All surfaces to be clad must be clean and dry. For pipework up to approximately 300 mm, preformed section of insulation must be cut and profiled to fit, and secured at 450 mm intervals with banding strip. For greater diameters, flexible flat forms of insulation, e.g. mattresses, must be used. The jacket should not be allowed to come into direct contact with the noise radiating structure or with its supports, but should cover the whole noise radiating area without gaps or voids. The finished insulation must be even, solid, tightly joined and well secured. Where two layers of insulation are specified, then both the longitudinal and circumferential seams must be staggered.


The insulation must be completely covered by a metal jacket. All overlapped joints must be at least 25 mm, bonded with mastic sealant, and must be arranged to shed water. The metal jacket must never touch the pipe or equipment. Clearance between the metal jacket and branches should be approximately 6 mm and filled with mastic. Potential metallic contact at other similar locations is also important to consider. The metal jackets of all acoustic cladding must be continuously bonded together by a strip of jacketing metal and connected to the pipe, however, cladding must not act as an electrical bridge over isolation joints.

Thermal insulation General The relevant British Gas standard is: BGC PS PWC2 - Thermal insulation of above ground pipework and equipment. The insulation in this application is used for heat conservation, cold conservation, personnel protection, anti-condensation, frost protection and for the maintenance of operating temperatures. Temperatures applicable are from –2000C to 10000C depending on the application. Materials

Insulating materials The insulating materials proposed for any application must be selected from the following types: a) Glass fibre. b) Foamed glass. c) Rock wool. d) Modified slay wool. e) Expanded perlite. f) Vermiculite (loose granular fill). g) Calcium silicate. h) Phenolic foam (not within buildings – toxic during combustion). i) Polyisocyanurate (not within buildings – toxic during combustion). The insulating materials used must not contain substances which support pests or encourage the growth of fungi. They must not cause a known hazard to health from particles or toxic fumes, during application, whilst in use or on removal. The insulating materials used may be applied in layers depending on the total thickness required; in some cases up to approximately 400 mm total thickness may be specified.


Protective coverings Protective coverings include: Vapour seals – vapour sealing compound, preferably trowelling grade, which has an interposed scrim cloth made of woven glass cloth. Vapour sealing tape may also be used. Vapour seals are used for cryogenic applications. Metal cladding – galvanized mild steel must be used, unless stainless steel is being insulated, in which case aluminium alloy sheet is used. Hard-setting composition/self-setting cement and glass cloth may also be used as protective coverings as an alternative to metal cladding in certain circumstances. Fixing materials To hold down insulating materials and protective coverings, the following may be used: a) Wire netting – used to hold down insulation but only used with hard-setting or self-setting

cement as a protective covering. b) Binding wire. c) Binding tape. d) Fixing bands. e) Self-tapping screws. f) Nuts, bolts and other fastenings. g) Adhesives. h) Anti-abrasion compound. i) Joint sealant Application of materials The basic sequence for application for general heat conservation and protection: 1 Preparation. 2 Insulation plus fixing. 3 Repeat insulation and fixing if required. 4 Metal cladding plus fixing, or self-setting or hard setting cement. The basic sequence for application for general cold conservation and cryogenic service: 1 Preparation. 2 Insulation plus fixing. 3 Repeat insulation and fixing if required. 4 Vapour seal. 5 Metal cladding.


As far as possible, insulation of pipework must be performed with preformed sections of insulating materials not exceeding 1 m in length. Each layer of insulation is secured with binding wire every 150 mm on pipework; the wire must not be allowed to cut into the insulation. If insulating equipment, fixing bands are used every 300 mm. Metal cladding must be applied so that all overlapped joints must be at least 75 mm (40 mm on 40 mm diameter pipe and below). The overlapped joints must be arranged to shed water. The metal cladding must never touch the pipe or equipment. Fixing bands must be used every 450 mm.


Painting Inspection Grade 3/2 1 Appendix C

Appendix C

DATA SHEET EXAMPLES





Contact us for information on our wide range of courses at: Training and Examination Services TWI Training & Certification (SE Asia) TWI Ltd No. 8 Jalan TSB 10 Granta Park SG Buloh Ind. Park Gt Abington SG Buloh Cambridge Selangor Darel Ehsan CB1 6AL, UK Malaysia Tel: +44 (0)1223 891162 Tel. : 603-61573528/6 Fax: +44 (0)1223 891630 Fax : 603-61572378 Email: [email protected] E-Mail : [email protected] TWI Technology Centre (N East) TWI Training and Examination Services Aurora Court PO Box 52721 Barton Rd Abu Dhabi Riverside Park Middlesbrough TS2 1RY, UK Tel: +44 (0)1642 210512 Tel: +971-2-6270750 Fax: +44 (0)1642 252218 Fax: +971-2-6270424 Email: [email protected] E-mail: [email protected]