PFHT of nozzle already welded 1

[ElCidCampeador]

Hi,
a friend of mine, who works in a workshop, is asking me if he can do something for this issue.

He is building a pressure vessel acc.to EN 13445, Gr.1.2 (c.steel).
This vessel has a shell with a nozzle bended from plate; this nozzle is welded to the vessel with a set-in weld and has a reinforced pad. At the end of the nozzle it is welded a WN flange with butt weld.

My friend told me that he forgot to PFHT the nozzle (since nozzle is cold formed by bending and F>5%), but now all welds has been done and the nozzle is already welded to shell and to welding neck flange.

He suggests, in order to "save" the situation, to PFHT locally "only" the nozzle (not pad or WN flange, just the rolled part), taking care to stay at an appropriate distance from welds in order to not create thermal stress.

I told him that the correct procedure would be cutting all welds and PFHT the nozzle separately (with test coupon) and then re-weld.

I don't know what he will do, but if the final purpose is to "save" material in the best way as possible (without cutting anything), do you really think that it's better PFHT the portion of nozzle bended (without welds) than leaving the nozzle as welded now (so with deformation due to bending)? My fear is that new local heat treatment would add more stress, expecially close to welds, instead of "reset" material behaviour...what do you think is the least worst solution?

Thanks

 

[XL83NL]

I'm asking for a friend ;-)

Huub
- You never get what you expect, you only get what you inspect.

 

[Geoff13]

For PWHT in place, I would heat a full circumferential band on the shell. I would then call for about 3+ feet (1+ m) each side to also be insulated to provide a gradual cool-down length.

If you only PWHT the nozzle, it will dimple out under heat, and most likely only partially return when cooled. I won't guess the resulting stresses. I would never do this on my vessel.

I do not know EN steel designations, so I can't guess if your steel can take PWHT without altering it's properties. I'm primarily thinking of Q&T steels where the PWHT might be hotter than the temper.

Then it's a cost / schedule comparison between a full PWHT, and cutting everything apart to just PWHT the neck plate.