Selecting Coatings Under Insulation

Presented by: Brent W. Griffin, SME On behalf of SSPC.

Learning Outcomes• This webinar will discuss:– Basic Control of Corrosion Under

Insulation– Coating Selection Considerations for

Metals Under Insulation– Types of Coatings Applied to Metals

Under Insulation

Introduction• Corrosion under insulation is a major

problem. When insulation becomes wet it creates the potential for corrosive failure of the structure. Whether the structure is above ground or buried, proper design and installation technique can control corrosion

Introduction• For a corrosion under insulation

system to be successful and not contribute to the corrosion process, it must be specified in the following manner:– Use a corrosion control coating– Taylor the insulation to the application

and environment– Calculate adequate insulation thickness– Apply a superior vapor barrier– If necessary, install a mechanical jacket

Basic Corrosion Control• Metal corrosion requires 4 elements:– Anode– Cathode– Electrolyte– Electrical Path

Anode• The electrode of an electrolytic cell

at which oxidation occurs • Electrons flow away from the anode

in the external circuit• It is usually at the anode that

corrosion occurs and metal ions enter solution

Cathode• The electrode of an electrolytic cell

at which reduction is the principal reaction

• Typical cathodic processes are cations taking up electrons and being discharged, oxygen being reduced, and the reduction of an element or group of elements from a higher to a lower valence state

Electrolyte• A chemical substance or mixture,

usually liquid, containing ions that migrate in an electric field

• A chemical compound or mixture of compounds which when in solution will conduct an electric current.

Electrical Path• A connection between the anode

and cathode where current in the form of electrons can flow

Basic Corrosion Control• The corrosion of metals requires the

following conditions:– An anode, a cathode, an electrical path

and an electrolyte must all be present– The anode and cathode must be in contact

with the same electrolyte– The metal must electrically connect the

anode and cathode for electrons to flow– The anodic (oxidation) and cathodic

(reduction) reactions must be equivalent and simultaneous

Basic Corrosion Control• One of the most effective ways to

control corrosion is to use a properly selected and applied corrosion coating

Coating Selection Considerations• The proper selection of coating

materials is important. When selecting coatings for metals under insulation, consider:– System operating temperatures– Application and site requirements– Surface preparation requirements– Compatibility with insulating materials

System Operating Temperatures• A coating has to be flexible enough

to withstand the expansion and contraction of the piping system when temperatures cycle

Temperature Fluctuations• Can cause a loss of adhesion

between the coating and metal, which allows water to reach the pipe– High temperatures can cause coatings

to flow, crack or sag– Low temperature can cause coatings to

become less flexible or brittle

Application Requirements• Liquid coatings can be applied by:– Brush– Glove– Spray Method (Airless or Plural

component)

• Tape coatings can be applied in a “cigarette wrap” or by spiral wrapping

Surface Preparation• Most critical part

of any coating process

• The type of surface to be coated dictates the type of surface preparation and coating to be used– Carbon Steel– Stainless Steel

Carbon Steel• New carbon steel can be cleaned

and blasted easily, compared with corroded or pitted steel in used systems

• Corroded or used metal systems may have surface contaminants such as chlorides or salts that must be properly removed before blasting

Stainless Steel• Very hard, making it difficult to

create a profile• Should not be blasted with steel grit

or shot– Causes corrosion problems– Non-carbon blast materials, brushes or

grinding disks should be used

Removal of Contaminants• Before surface preparation any oil, grease

or other debris must be properly removed– SSPC-SP 1, Solvent Cleaning

• Chlorides and other salts must be removed by proper washing and rinsing techniques– SSPC Guide 15, Field Methods for

Retrieval and Analysis of Soluble Salts on Steel and Other Nonporous Substrates

Compatibility with Insulating Material• Coating selection and insulation

characteristics should be considered jointly when specifying a system

Types of Coatings• Types of coating choices on the market

include:– Epoxies– Urethanes and Polyureas– Tape and Shrink Sleeves– Powder Coatings– Brushable Coal Tar or Asphalt Based

Corrosion Coatings– Mineralization Coatings– Thermal Sprayed Metallic's -TSA

Epoxies• Epoxies are two component and applied

by spray or brush• Must be mixed at proper ratio!• Phenolic epoxies are excellent for higher

temperature applications (up to 450F)– Applied by plural component using

heated hoses, Airless & Conventional–Modified epoxy phenolics offer good

abrasion resistance and are more flexible, Novolac or immersion grade are excellent

Urethanes and Polyureas• Excellent coatings for cold process

piping and vessels• Limited use for higher temperature

operations at greater than 150F• Flexible and can be applied in one

thick coat with plural component equipment

• Moisture-cure urethanes perform well for applications where moisture is a problem

Tape and Shrink Sleeves• Provide excellent corrosion

protection for pipes on systems that operate at temperatures of 150F or less

• Require a primer in order to adhere properly –Surface prep is key

• Vary from 25-100 mils in thickness– Insulation material must have the

proper ID to enable that insulation fits over the tape

Tape Coatings• Will affect the

inner diameter (ID) and the fit of the insulation

• Some tapes are applied using heat (propane torch)

• There is skill and proper technique required for appl.

Powder Coatings• Applied to a hot surface (normally

450- 488 F)• Applied in a specialized pipe coating

plant with temperature and humidity control

Asphalt or Coal-Tar Based Materials• Applied by brush or paint glove • Surface preparation requirements are not

as stringent• Good for irregular shapes• Are flexible, adhere well, resistant to most

chemicals, can be repaired easily, has fair abrasion and impact resistance

• At low temperatures (below 0F) coating may be less flexible

• At high temperatures (above 120F) coating may become soft or tend to run

Mineralization Conversion Compounds• The ability to grow very thin minerals on

metal surfaces for useful purposes• Developed to deliver the mineral forming

reactants in a variety of formulations– Paints, coatings, synthetic gels,

greases, thread dressing, sealants, adhesives and water gels

• Reduces the amount of surface preparation required before installing the coating

Mineralization Conversion Compounds• Effective on systems at temperature

ranges from -50F to 250F • If vapor barrier is compromised and

moisture enters the system, it can travel directly to the pipe’s surface and remain there without corrosion taking place

Mineralization Conversion Compounds• The excess coating from the

installation process chemically binds the water (buffering it) so that it cannot corrode the pipe

Compatibility with Insulating Material• Some types of insulating materials

may be:– Abrasive– Cause the coating to deteriorate

(become soft or brittle)– React with the corrosion coating prior to

the coating curing• Typically coating is cured prior to installing

the insulation

Insulation• The insulations used for above

freezing yet below ambient piping are quite broad including:– Fiberglass– Elastomeric plastics– Elastomeric rubber–Mineral wool

Insulation• Insulation for subzero applications

are:– Polyisocyanurates– Polystyrenes– Cellular glass– Phenolics

Insulation Thickness• Worst-case atmospheric job

conditions should be used when calculating insulation thickness

Vapor Retarders and Protective Jackets• Protect vapor barrier from physical

abuse• They include products such as:– ASJ paper– FSK paper– Vapor barrier mastic– Mylar’s– Proprietary polymers– Laminated self-adhesive membranes– Low perm, peel-and-stick, self-healing

vapor barrier membranes

Conclusion• Through testing, proper selection of

materials and methods and well-written and detailed specifications, tremendous improvements can be made in controlling corrosion under insulation.

Conclusion• The following suggestions are recommended for

industry:– The industry must be committed to

preventing corrosion – Testing and insulation specifications must be

developed and must outline specific coating systems for each application

– Inspection and testing must be performed– Appropriate vapor barriers, waterproofing

materials and insulations should be used