Pressure vessel attachments

[markzu3]

I would like to know if it is acceptable for a pressure vessel, designed and built according to ASME VIII div 1 to be directly welded to the incoming & outgoing piping instead of flanged connection. I am discussing with a contractor who suggets to weld the piping directly to the vessel nozzles. The system is designed for power piping carrying steam at around 90psig - piping design is to B31.1. Comments appreciated. Thanks

 

[DSB123]

markzu3,
There is no problem connecting the pipe to the pressure vessel using a welded connection. Obviously the materials of the pipe and branch need to be comparable for welding process.

 

[metengr]

Agree with DSB123. Also you need to evaluate piping loads on the nozzles to assure adequate design with Code requirements.

 

[jte]

markzu3-

No problem at all. Not frequently done, but often enough. For Code references, see VIII-1 U-1(e)(1)(c) and UW-13(g) and Fig. UW-13.4.

The VIII-1 scope ends at the weld prep of the nozzle. The weld metal is piping code (in your case B31.1) territory. This makes sense, as it makes shop fabrication and stamping of the vessel possible. If the weld metal was in VIII-1's scope then the field weld to attach the piping to the vessel would have to be completed prior to putting the U stamp on the nameplate etc.

jt

 

[MJCronin]

mark,

I agree with those above

Not a problem.....the specification of vessels with butt weld ends is common.

However, the possible removal/replacement of that tank or vessel may be a problem in the future....

MJC

 

[GenB]

I see a problem with the practic,
of who will take responsability for the vessel and who will for the piping,
the piping contractor can verywell do the weld directly to the vessel,
the vessel stamp ends at the first flange or last welded connection and that one can be a nozzle, pipe stub end but not a direct vessel component as SE head or shell.
I like to hear other coments. If the vessel mfr takes responsability, then that Co. will have to weld the pipe whether at the shop or field if the stamp covers both.
I believe the piping contractor is not authorzed to touch the vessel in that regard.
er

 

[PEHasan]

In my opinion, pressure vessel should be provided with flanged ends. What about the hydrotest of vessel? How we will carry out the hydrotest of vessel.

 

[jte]

GenB-

I think we're violently agreeing here. I don't think anyone has advocated welding pipe directly to the shell or heads. The vessel fabricator provides a nozzle neck with ends beveled/prepped for welding, as though the fabricator was going to weld a weld neck flange on. Except the flange is not installed; the piping contractor in the field simply does a field weld of the nozzle stub to the piping.

PEHasan-

It's done often enough and fully complies with the code. Hydrotesting is simple: If I ask for a 12" stub, you install a 14" with a 2:1 head (chances are that we're talking about a large pipe here). After the hydro you cut the nozzle to length and prep the edges for me. Simple.

jt

 

[weldtek]

Apparently some states charge a penalty for each flanged connection in a plant. Presumably because it's a potential leak source.

 

[alexander123]

I believe this would require an "R" stamp, as you are welding directly to the vessel.

 

[GenB]

jt,
violent enough, you are right I did not see the stub in the orig posting,
it is a standard procedure to buttweld piping to an incoming nozzle,.
bye, er