Requirement of the PWHT for SS material

[PK M]

Dear Experts,

I am looking forward for the clarification on the non requirement of the PWHT for SS material. Kindly let me know in the reference standard where it has been mentioned that SS material does not need PWHT.

thanks,

Pkm

[Octane Mac]

What codes are you dealing with?

Construction codes including ASME VIII Div. 1 & 2, ASME B31.3, ASME B31.1 and ASME Sec. 1 doesn't call for any PWHT of stainless steel welds however in case of duplex stainless steels, some codes mention PWHT as "Neither required nor prohibited"

In addition to this, here goes a para from ASME Sec. II Part D:

"HEAT TREATMENT OF AUSTENITIC CHROMIUM–NICKEL STEELS"

In recognition of controversial opinion relative to the effects of postweld heat treatment of austenitic stainless steels, mandatory requirements for such have been omitted. Service experience is too limited to permit comparison between the relative safety of as-welded and postweld heat treated austenitic steel weldments, particularly in thick sections. It is recognized that the stability of austenitic steels and their optimum behavior in service are influenced by the mechanical and thermal treatment they have received; however, it is a basic principle that the Code rules are intended to provide minimum safety requirements for new construction, not to cover deterioration which may occur in service as a result of corrosion, instability of the material, or unusual operating conditions such as fatigue or shock loading. Where maximum corrosion resistance is required, it is advisable to heat treat in such a fashion as to place all chromium carbides in solution. For such service it is recommended that the following procedure be followed: hold the vessel within the solution temperature range prescribed by the governing material specifications for not less than 1 hr/in. of thickness. Quench all parts of the vessel uniformly and as rapidly as possible. Material not stabilized with columbium or titanium should be cooled through the range from 1700°F to 1000°F in not more than 3 min. The rapid cooling should be continued to below 800°F. Slower cooling rates may be just as satisfactory for some compositions of the material and conditions of service.

Octane

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