Download - Selecting Coatings Under Insulation Presented by: Brent W. Griffin, SME On behalf of SSPC
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