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March 11 - March 15, 2019

Should 304 stainless steel pipework be coated prior to insulation?

Selected Answers

From Tony Rangus of Bechtel on March 18, 2019:
For SCC to be an issue, you need a susceptible material, a corrodent and a stress that is pretty close to the yield stress of the material being considered. I doubt the operating stresses are anywhere near the yield stress, so the only areas susceptible are weld joints and possibly cold bends/cold-worked areas. If low carbon grade Type 304 (304L) material was used, there will not be IGSCC in the weld HAZ. The bigger issue is rapid pitting and/or crevice corrosion due to chlorides. Go to the Nickel Institute website and pull up publication #10066.

From William Gusnard of Southern Company Services on March 15, 2019:
I would coat the stainless steel underneath insulation in any conditions per NACE. If you are using calcium silicate, there is a very good likelihood that it will contain chlorides - which will speed up stress corrosion cracking of the stainless. My plants wash down indoors, so there is always a chance of the insulation becoming wet. I have pulled out 5-year-old stainless that has failed due to no coating underneath the insulation.

From Chad Laubenthal of Titan Process Services on March 13, 2019:
Indoors and if it stays dry, I would say no. Outdoors where it could get wet from jacketing failures I would coat it. I have seen failures after 20 years on stainless where the outer insulation jacketing leaked and water migrated onto the steel. Trace amounts of chlorides from area conditions then promoted cracking.

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Tagged categories: Coating Application; Pipeline; Stainless steel

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