is PWHT the "fabrication heat treatment" ?

[YuJie_PV]

hi all,

i am reading UCS-85 of ASME VIII-1, and confused with the terms " fabrication heat treatment".

i also find the term "post-fabrication heat treatment" in the Companion Guide book of ASME.
it seems not a formal terminology specifically defined in ASME code.
my enquiry:
which does "fabrication heat treatment" refer to?
is PWHT included?
where is the border between "fabrication heat treatment" and "post-fabrication heat treatment"?

thanks in advance?

 

[TGS4]

That paragraph is the only location where the phrase "fabrication heat treatment" is used in the entire book.

I strongly encourage you to submit this as a Request for Interpretation of the Section VIII Committee - https://cstools.asme.org/Interpretation/InterpretationForm.cfm

This needs some (official) clarification.

 

[DekDee]

Hot forming during fabrication at temperatures exceeding 900 F (480 C) will require mechanical testing. ???

 

[YuJie_PV]

@TGS4, thanks. i may try.
@DekDee, i am not quite sure with your question, but the forming exceeding 900 F (480 C) is not hot forming if it's still below lower critical temperature.
let me find basis for your question.

 

[Geoff13]

I wonder if they are trying to refer to the heat treatment that might be done as a result of UCS-79(d)?

If the welds are not thick enough to require PWHT this fabrication heat treatment could be done on the unwelded formed plates, but UCS-85(b) would still apply.

 

[DekDee]

Cold formed heads may be stress relieved separately to the vessel (prior to installation) if the completed vessel does not require PWHT.
Would this then be classed as fabrication heat treatment ?

 

[YuJie_PV]

i've read so many interpretations regarding UCS-85, i think i could conclude that both PFHT （post-forming HT and PWHT are fabrication heat treatment.

Hot forming during fabrication at temperatures exceeding 900 F (480 C) will require mechanical testing. ???

@DekDee， typically, a pressure vessel component subjected to hot forming shall be followed by a heat treatment above the lower transformation temperature (such as normalization) upon completion of forming, thus, the exemptions in UCS-85(c), (d), (e), (f), and (g) may not be applicable, hence the mechanical testing is required.

 

[DekDee]

YuJie - I am not an engineer.
Nor am I greatly experienced with pressure vessels - I am heavily involved with piping.
I was just giving suggestions as to your question of what is "fabrication heat treatment" ?