PWHT
PWHT
(OP)
Hi,
Is it possible to weld a attachment in a PWHT completed vessel. If it is, guide how to do.
Is it possible to weld a attachment in a PWHT completed vessel. If it is, guide how to do.
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RE: PWHT
RE: PWHT
RE: PWHT
Regards,
Mike
RE: PWHT
RE: PWHT
Let us know if thread794-264274: Non-pressure Welds to Section VIII Div I Vessel does not answer your questions. If you need further info, please first let us know why the vessel is being PWHT. There may be a substantial difference if the heat treat is required for process vs required for Code reasons.
jt
RE: PWHT
Let me brief my current situation. I am handling more than 80 vessels out of many Post weld heat treated vessels (Some have process reasons and some have mechanical reasons)
have the requirement of steam tracing coils.
Now vendor cannot proceed with vessel PWHT with steam tracing coils. Hence we are planned to completed PWHT first. Then complete the steam tracing.
Locating the steam tracing coil need a clip need to be welded.
Hope u understood.
RE: PWHT
All welding shall be done before hydrotest.
RE: PWHT
When pwht is required for service, normally you write up a procedure saying preheat, WPS, Temper bead, etc and submit it to the user and let him decide
RE: PWHT
If the PWHT was for service reasons (e.g., sour service) then any welding following PWHT would require local PWHT, or would need to follow a strict welding procedure as described by vesselfab, and should be submitted to the end user for approval.
Most end user's have specifications that say there shall be no welding on the vessel following PWHT if the PWHT is for service reasons.
RE: PWHT
If you have 80 vessels, you'll need to make 80 decisions.
jt
RE: PWHT
UCS-56 (a): PWHT is required when the nominal thickness, as defined in UW-40(f), exceeds the limits in Table UCS-56. (This means that not all welds require PWHT).
UW-40 (a) (5): heating a circumferential band containing nozzles or other welded attachments that require postweld heat treatment... (see: not all attachments require PWHT).
My opinion: if your attachment fillet weld has the throat dimension less than specified in the Table UCS-56 you do not need to do PWHT for those welds. Nevertheless, I would recommend to research Code interpretations.
Another option: to avoid potential problems with a Customer just do a local PWHT of your attachments welds.
RE: PWHT
RE: PWHT
RE: PWHT
Assuming that the vessel is not in Lethal Service or subject to PWHT due to process service, per ASME VIII, Div. 1, UW-40 (f) "the nominal thickness is the welded joint as defined below.
(f)(3) For fillet welds, the nominal thickness is the throat dimension.
(f)(5)(f) the thickness of the weld at the point of attachment when a nonpressure part is welded to a pressure part..."
Per Table UCS-56, Note 2 "Postweld heat treatment [for P-No.1] is mandatory under the following conditions:
(a) for welded joints over 1 1/2in. (38 mm) nominal thickness.
(b) for welded joints over 1 1/4-in..."
Therefore, assuming that the throat of the fillet weld is less than 1 1/4 inch, you may make the welds without subsequent PWHT.
RE: PWHT
RE: PWHT
I do not think that is a correct statement
RE: PWHT
Per UCS-56 (a)"Except as otherwise specifically prvided in the notes to Table UCS-56 and Table UCS-56.1, all welds in pressure vessels or pressure vessel parts shall be given a postweld heat treatment at a temperature not less than specifed in those Tables when the nominal thickness, as defined in UW-40(f), including corrosion allowance exceeds the limits in those Tables. The exemptions provded in Table UCS-56 or Table UCS-56.1 when postweld heat treatment is a sevice requirement as set foth in UCS-68..."
I stand by the definitions of nominal thickness as previously quoted from UW-40(f)(3)and (f)(5).
RE: PWHT
ucs-56 has rules set up for size of welds allowed to be welded after PWHT.
If memory serves me, it lists a small throat, maybe 3/8" if preheat is done at like 200-300*F
the rules you are speaking of is exemption from pwht, not welding after pwht.
OR maybe i misunderstood the whole basis of the original poster's statements.
RE: PWHT
jt