Dear Mr. Rao
The sentence is not fully correct. PWHT is sometimes required on Austenitic Stainless steel.
Simple rule, any material subjected to lethal sevice designated by ASME Sec viii div-01 UW-02, will undergo PWHT.
PWHT is not required because , Cr will form Cr carbide which will cause sensitisation & reduce corrosion resistance. High temp can cause this problem, so PWHT is recommende with less temp.
PWHT is seldom required to avoid stress corrosion cracking.
Thermo-mechanical properties of welds in stainless steel is substantially improved by the implementation of a post weld heat treatment that iliminates sigma phase in the heat treated zone and favors niobium carbonitride precipitate formation in a desirable size range. In most cases, post weld heat treated material can be employed in pressurized devices at temperatures exceeding 550° C., which is currently regarded the upper safe temperature limit, and material according to the inventive subject matter was tested at temperature of up to 850° C. without reheat cracking.
if u could specify the material with conditions, i will be able to elaborate more on this topic.
Regards
Manpreet Singh
Welding Engineer
Spiecapag
On Fri, 30 Jul 2010 09:05:44 +0530 wrote
>dear sir
why we are not doing pwht in ss materials
please explain the reason
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