Post Weld Heat Treatment (PWHT)
Post Weld Heat Treatment (PWHT)
(OP)
Currently I am designing on ASME section-VIII Div-1 (Code)drum with 'U' stamp. Drum is SA 516 Gr 70N and the shell and head thickness approximately 80 mm. Stainless steel SS 316L internals are placed inside drum. The fabricated drum shall be PWHT as per the Code. The SS 316L internals are welded inside the SA 516 Gr 70N Shell. How to perform post weld heat treatment (PWHT) for the vesel. Is there any pre-caution or notes, I have to include in the data sheets for the fabricatot to observe?





RE: Post Weld Heat Treatment (PWHT)
I would think, and you have to confirm this with your design, that the attachment welds joining the stainless (P8) internals to the carbon steel vessel wall (P1) would be exempt from PWHT, based on the nominal thickness of the weld deposit.
Second comment concerns the selection of filler metal for attaching the stainless internals to the carbon steel drum. I would give serious consideration to using a nickel-base filler metal like Inconel for these attachment welds. Two reasons; the linear coefficient of expansion for the nickel-base filler metal is between the linear coefficient of expansion for 316L SS and carbon steel reducing thermal stresses across the weld fusion zones. Second reason is the potential for carbon migration resulting in premature failure of the weld fusion zone on the carbon steel side of the attachment weld should the operating temperature of the vessel exceed 650 deg F. A 309SS filler metal is common for dissimilar metal welds. However, over time the carbon will diffuse from the carbon steel side of the fusion zone to the higher chromium weld deposit. To reduce carbon diffusion, a nickel-base filler metal is used.
RE: Post Weld Heat Treatment (PWHT)
SS to CS with temperature doesn't give me that warm fuzzy feeling. Mainly due to all the reasons stated above and some.
RE: Post Weld Heat Treatment (PWHT)
Thanks for both the inputs. However the internals shall be placed through the dished end opening and after the internals are welded, dished end also welded. The whole vessel shall be PWHT. The internals are welded inside of the shell and not bolted. Based on the size of the internals, it not possible to install or remove through the man-hole opening.
RE: Post Weld Heat Treatment (PWHT)
RE: Post Weld Heat Treatment (PWHT)
we usta call them "Poison Pads" - they keep the metallurgically/thermally bad stuff out of the pressure retaining wall of the vessel.