Corrosion under insulation: a materials and specification problem
CUI is one of the largest maintenance costs in process plant, and most of it is designed in at specification stage rather than caused in service.
The mechanism
Water enters the insulation system, reaches the pipe surface, and cannot dry. In the 60 °C to 175 °C band on carbon steel. Around chloride exposure on austenitic stainless, that wet metal surface corrodes steadily and invisibly under the cladding until something fails. The insulation is not the cause; the water is. The insulation just hides it.
Specify low-chloride material near stainless steel
ASTM C795 exists for exactly this reason. Insulation in contact with austenitic stainless steel must be tested for leachable chloride, fluoride, silicate and sodium content per ASTM C871, because chlorides leaching out of an otherwise perfectly good insulation material cause stress corrosion cracking. Always ask for the C795 certificate on stainless service, and read it rather than filing it.
The jacketing is the system
Most CUI is a water ingress problem at terminations, valves, supports and penetrations, the places the standard detail drawings gloss over. Overlaps facing the wrong way, unsealed banding, missing fitting covers and cut-outs left open at supports do more damage than any core material choice.
Closed-cell materials change the risk profile
Cellular glass and closed-cell foams do not absorb or hold water in the same way as fibrous insulation, which is why they are specified on cyclic and cold service where CUI risk is highest. They cost more per cubic metre and considerably less over a twenty-year maintenance horizon.
What to ask your supplier for
Chloride content certification, a vapour barrier detail for terminations and penetrations, correct fitting covers rather than site-fabricated ones, and a jacketing overlap orientation stated on the drawing. If a supplier cannot produce these, they are selling insulation material, not an insulation system.
Next step
Send us a specification. Get a real quotation.
Drawings, a bill of quantities, a line list or a written brief, whatever you have. We come back with a costed, line-by-line offer, and tell you plainly if anything in it will not work.