"PWHT on SS321"

Question:

"In our project spec of our refinery, there was PWHT on SS321, with spec :
- Heating : 850-950 C
- Holding Time : 10 min/10mm, 20 min(MIN)
- Heating Rate : 200x25/T C/hr (MAX)
- Cooling Rate : (150 - 200 ) x25/T c/hr(max)
My question :
Is that PWHT avoid SSC (from Chloride in service) completely ?"

Answer:

From your stated temperature range, the heat treatment is most likely a carbide stabilization heat treatment, designed to prevent "knife-line" corrosion resulting from sensitization in the heat affected zone (HAZ) of welded components.

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