SS linings and PWHT

[KevinNZ]

ASME VIII 6.5.5.2 requires all vessels with SS linings to have PWHT why?
And why do 405 and 410S linings not require PWHT?

 

[metengr]

If you review ASME Section VIII, Div 2 the reference you cited below is for 4XX martensitic stainless steel which is hardenable, thus PWHT is necessary. The Type 405 or 410S are ferritic stainless steel which are not hardenable by heat treatment.

6.5.5.2 Requirements When Base Metal or Lining Is Chromium Alloy Steel. Vessels or parts of vessels constructed
of chromium alloy stainless steel clad base material and those lined with chromium alloy stainless steel applied linings
shall be postweld heat treated in all thicknesses, except that vessels clad or lined with Type 405 or Type 410S and
welded with an austenitic electrode or non-air-hardening nickel-chromium-iron electrode need not be postweld heat
treated unless required by 6.5.5.1.

 

[NBrink]

Like metengr says. Please don't mistake this to mean all stainless cladding besides 405 and 410 need PWHT. You'll really muck up the corrosion resistance of a lot of austenitic stainless steel with PWHT.

Nathan Brink

 

[moltenmetal]

You'll not just muck up the corrosion resistance- if you do it wrong, you'll destroy the cladding entirely.