04 Pretreatment_grade1

7/28/2019 04 Pretreatment_grade1

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Paint School1

Pre-treatment


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Paint School2

Good pre-treatment of the substrate

is a requirement to obtain

good performance of the paint system

Performance of a paint system


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Paint School3

Salt and soil: Clean water

Oil - grease: Solvent with emulsifying agentor alkaline cleaner

Work to be carried out

in the cleaning shop

Remove prior to pre-treatment:


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Paint School4

Salts

Contaminations

Particles

Potential sources Potential paint failures

Osmotic

blistering

Dust after dryingLoss of adhesion

Water quality:

Potential sources and risks


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Paint School5

The mechanism behind

Osmotic blistering

Fresh water will try to dilute the salt water Migration through a semi-permeable membrane

The pressure will increase

Fresh water and salt

water separated by a

membrane

Steel structure

contaminated with salt.

Paint applied without

proper cleaning


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Paint School6

Different types of salt have different

affinity to water / humidity

Laboratory test. Different types of salt are applied to the steel plates

Several month of exposure

At similar levels: Chlorides more severe than Sulphates

CD 4932 no. 99

Sodium Iron No

Chloride Sulphate salt


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Paint School7

Equipment contaminating the surface

Oil contamination from grinder

Reasons may be:

Oil leaking out ofequipment

Equipment has beenstored with oil

Lack of oil trap.

(Air from compressor

contains oil) CD 4932 no. 22

Must be removed prior

to surface preparation


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Paint School8

Flaking of Tar Epoxy

Tar Epoxy system

Flaking down to shop

primer Flaking due to poor

pre -treatment

Remains of oil found

underneath the paint CD 4934 no. 57


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Paint School9

Welding smoke is water soluble

and can only be removed by water

Solvents will not

remove the weldingsmoke completely

If not removed,osmotic blistering

may occur.

Welding smoke

Area washed

with water

CD 0589 no. 11


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Paint School10

Blisters close to weld, probably due to

welding smoke remaining on the the steel

Welding smoke is resoluble in water and willcreate osmotic blistering

Galvanic difference between steel plate and weldmay aggravate the attack

CD 4934 no. 79


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Paint School11

Portable blast-cleaning unit

Vacuum blasting equipment

Air-powered grinding equipment

(Available with and without vacuum unit)

Air-powered wire-brush

Needle gun

(Available with and without vacuum unit) Air-powered chisel

Scraper with interchangeable hard metal shears

Pre-treatment.

Recommended equipment


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Paint School12

Pre-treatment

Evaluation of methods

Blast cleaning

Power grinding

Power wire-brushingManual wire- brushing.

Needle hammer

Power chiselling

Manual scraping

Ideal

Not as good as blast cleaning, but

best alternative.

Great risk of unwanted polishing.

Not recommended. Very poor.

Usable, but risk of unwanted rough

surface,

Good in combination with othermethods

Usable in combination with other

methods.


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Paint School13

Reciprocating impact tools

Needle scalars or guns

Chipping guns (chisels)

Scabblers.

Small hand-held and walk-behind models.

To break up heavy rust, mill scale and coatings.

Example: Rustibus


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Paint School14

Equipment.

Hand and power tool cleaning

Mechanical rotating wire brush Needle gun

Hand Wire brush

CD 4932 no. 39


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Paint School15

Pre-treatment of a tank.

Disc sanding of substrate

Part of a tank

Nice St 2 standard, almost St 3

CD 0589 no. 99


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Paint School16

Hand wire brushed surfaces

Surfaces treated approximately to thegiven standards according to ISO 8501

St 2 St 3

CD 4932 no. 41 CD 4932 no. 42


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Paint School17

Needle-hammer makes a rough

surface and deep indentations

Rotating wire brushes and disc-sanders

may give a polished surface

Mechanical cleaning may

give unfavourable surfaces


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Paint School18

Pre-treatment

Illustration of various blasting methods


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Paint School19

Dry blasting

Benefits and limitations

Advantages

Surface remains dry

Good anchor patternfor paint

No pre-rusting profile

Disadvantages

Does not remove salt

Does not remove oil

Creates dust


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Paint School20

Introduction to blast-cleaning

Gives a good surfaceprofile

Several blastingstandards can be

achieved

Does not remove saltsfrom the substrate

Pre-treatment: Blast-cleaning1


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Paint School21

Blast cleaning with Metallic or

Non-metallic abrasives to specified:

Cleanliness acc. to ISO 8501 - 1 or 2

Roughness acc. to ISO 8503

Surface preparation

Metallic or non-metallic abrasives.

Ab i


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Paint School22

Chilled iron grit (angular)

High-carbon cast steel grit and shot (angular or round)

Low-cast cast steel snot (round)

Cut steel wire (cylindrical)

Natural abrasives: Garnet, Olivine, Staurolite

Slags: Copper refinery Nickel refinery

Coal furnace Fused aluminium oxide

Iron furnace

Abrasives

There are two main groups

1. Metallic abrasives

2. Mineral and slag abrasives


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Paint School23

Metallic abrasives and Carborundum

(Al.oxide) can be recycled and are usually used

more than once.

For stationary plants

Mineral and slag abrasives are generally

used only once.For open blast-cleaning

Metallic / mineral abrasives

Re-use


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Paint School24

Shape of abrasives

Grit (Angular)

Shot (round)

Wire cut (cylindrical)

Three main types of abrasives

R d ti


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Paint School25

Loose paint and rust to be removed prior to blast-cleaning

Use correct ratio between air and abrasive

Always use good quality abrasive

Correct air-pressure 7 kg/cm (100 psi) at the nozzle

4 - 4,5 kg/cm is a waste of time

Remove dust and spent abrasive residue with vacuum cleaneror eventually dry, oil-free compressed air

Recommendations

regarding blast cleaning


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Paint School26

Productivity is directly proportional to:

Pressure at Nozzle

Capacity of the air compressor

Pressure at Nozzle 7 kg/cm = 100% productivity

Pressure at Nozzle 5,6 kg/cm = 66% productivity

Pressure at Nozzle 4,2 kg/cm = 50% productivity

Blast cleaning

Factors influencing the production rate


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Paint School27

Nozzle Nozzleholder

Air

Blast - cleaning

Measure the air pressure at the nozzle

Rubber hose

Pressure

gauge

Bl t l i


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Paint School28

7 bar : Recommended

< 4 bar : Waste of time

0 50 100 150 200 250

2

4

6

8

10

Hose length, m

Air pressure, bar

Hose diameter 3/4" 1" 1 1/4" 3/4" 1" 1 1/4"

Blast cleaning

Loss of pressure

S f bl t l d


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Paint School29

Surfaces blast - cleaned

to various standards

Plate was originally partly rusty and partly painted.Blast-cleaned approximately to the given standards

Sa 1 Sa 2 Sa 2

CD 4932 no. 61

CD 4932 no. 62 CD 4932 no. 63


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Paint School30

Water-jetting is an alternative

to blast cleaning.

Water-jetting has:

- Environmental

- Technical

- Practical

.benefits and drawbacks

Water jetting

A i t d ti t Ult Hi h


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Paint School31

An introduction to Ultra High

Pressure Water Jetting (UHPWJ)

High water pressures(up to 2500 bar)

Manual equipment:Heavy work

Different types ofnozzles can be included

in one rotating nozzle

unit

Removes water solublesalts

Pre-treatment: Wj_equipment1


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Paint School32

Water Cleaning is classified according

to the pressure (NACE / SSPC)

Pressure, bar Classification

Below 340 LPWC

340 - 680 HPWC

680 - 1700 HPWJ

Above 1700 UHPWJ

NB - Pressure at nozzle !


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Paint School33

The Environment is affected (tosome degree) by all types of surface

preparation.

Water jetting has many technical andenvironmental advantages, but also

some drawbacks.

Why Water-jetting ?


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Paint School34

CD-1183 no.90CD-1183 no.89

Formation of blisters as a function of salt

concentration on substrate (1 of 2)

Salt: 0 mg/ m

Film: 150 microns

Salt: 60 mg/ m

Film: 150 microns



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Paint School

CD-1183 no.92CD-1183 no.91


concentration on substrate (2 of 2)

Salt: 100 mg/ m

Film: 150 microns

Salt: 200 mg/m

Film: 150 microns

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04 Pretreatment_grade1