PWHT in Caustic Service
PWHT in Caustic Service
(OP)
I have a caustic system that will typically operate at 90 deg F with a max of 20% caustic solution. The piping and equipment is constructed of carbon steel and has not been post weld heat treated. I have located several references that specifies that PWHT is only necessary for CS in 20% caustic solution at temps of 140 - 160 deg F. However, I do have a potential for upset temperatures in excess of 160 deg F that could last for a few hours. Are the mechanics of caustic corrsion so that any exposure to 20% caustic solution above the treshhold temperatures will compromise the integrity of the metal? Thanks for any input.





RE: PWHT in Caustic Service
What you reported is indeed correct for exposure of CS to caustic solutions and resultant SCC (stress corrosion cracking) along weld regions. If you anticipate over temperature excursions, I would perform local PWHT of the girth welds for added resistance to SCC. The cost of PWHT is small in comparison to leaks and repairs in service.
RE: PWHT in Caustic Service
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