PWHT of Carbon Steel Vessel Materials
PWHT of Carbon Steel Vessel Materials
(OP)
A client specification states that "Materails with properties enhanced by heat treatment cycles such as Tempering, Intermediate Stress Relief and the final post weld heat treatment shall be tested to verify that their mechanical properties have been retained after all heat treatment cycles."
I had considered that this clause relates to materials covered by ASME VIII Part UHT “Requirements for Pressure Vessels Constructed of Ferritic Materials with Tensile Properties Enhanced by Heat Treatment” but am now not so sure.
We are using A516-Gr.70N plate, A106-Gr.B pipe and A105N forgings which do not come under the requirments of Part UHT. Maximum shell thickness is 20mm and the vessel is subject to post weld heat treatment to reduce hardness in DGA duty.
For these materials, what material properties are likely to change during PWHT?
I had considered that this clause relates to materials covered by ASME VIII Part UHT “Requirements for Pressure Vessels Constructed of Ferritic Materials with Tensile Properties Enhanced by Heat Treatment” but am now not so sure.
We are using A516-Gr.70N plate, A106-Gr.B pipe and A105N forgings which do not come under the requirments of Part UHT. Maximum shell thickness is 20mm and the vessel is subject to post weld heat treatment to reduce hardness in DGA duty.
For these materials, what material properties are likely to change during PWHT?





RE: PWHT of Carbon Steel Vessel Materials
What is the requirement of test in your client specification? In general, I will perform only hardness test after PWHT.
What is the operating and design temperature of your DGA service?
RE: PWHT of Carbon Steel Vessel Materials
The tests have to included to additional PWHT cycles to account for future repairs or alterations.
Final welds and material will be subject to hardness testing.
RE: PWHT of Carbon Steel Vessel Materials
Operating Temp = 140°F
RE: PWHT of Carbon Steel Vessel Materials
RE: PWHT of Carbon Steel Vessel Materials
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RE: PWHT of Carbon Steel Vessel Materials
Accordingly, PWHT will increase to the resistance to brittle fracture due to hardness reduction and relaxing residual stresss on weldmetal.
For your reference PWHT is not necessary most applications.
The need of PWHT assumes a potential hydrogen cracking problem exists in due to a sensitive base metal microstructure, high level of hydrogen, and/or high stresses.
Neverthless, as PWHT may be a code requirement, so it has to be carried out as per governing code.
For SA-516-Gr.70N notch toughness could be affected depending on plate thickness.
RE: PWHT of Carbon Steel Vessel Materials
How many PWHT cycles in your concern? This should be a factor in your consideration during PQR preparation.