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PWHT in Caustic Service

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

lcmechengr;
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.

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