Selecting Coatings Under Insulation

1
Selecting Coatings Under Insulation

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

2
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

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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

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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

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Basic Corrosion Control

• Metal corrosion requires 4 elements
• Anode
• Cathode
• Electrolyte
• Electrical Path

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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

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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

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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.

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Electrical Path

• A connection between the anode and cathode where
  current in the form of electrons can flow

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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

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Basic Corrosion Control

• One of the most effective ways to control
  corrosion is to use a properly selected and
  applied corrosion coating

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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

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System Operating Temperatures

• A coating has to be flexible enough to withstand
  the expansion and contraction of the piping
  system when temperatures cycle

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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

15
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

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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

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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

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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

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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

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Compatibility with Insulating Material

• Coating selection and insulation characteristics
  should be considered jointly when specifying a
  system

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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

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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

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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

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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

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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.

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Powder Coatings

• Applied to a hot surface (normally 450- 488 F)
• Applied in a specialized pipe coating plant with
  temperature and humidity control

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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

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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

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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
  pipes surface and remain there without corrosion
  taking place

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Mineralization Conversion Compounds

• The excess coating from the installation process
  chemically binds the water (buffering it) so that
  it cannot corrode the pipe

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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

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Insulation

• The insulations used for above freezing yet below
  ambient piping are quite broad including
• Fiberglass
• Elastomeric plastics
• Elastomeric rubber
• Mineral wool

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Insulation

• Insulation for subzero applications are
• Polyisocyanurates
• Polystyrenes
• Cellular glass
• Phenolics

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Insulation Thickness

• Worst-case atmospheric job conditions should be
  used when calculating insulation thickness

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Vapor Retarders and Protective Jackets

• Protect vapor barrier from physical abuse
• They include products such as
• ASJ paper
• FSK paper
• Vapor barrier mastic
• Mylars
• Proprietary polymers
• Laminated self-adhesive membranes
• Low perm, peel-and-stick, self-healing vapor
  barrier membranes

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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.

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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