Can Large size but welded valves be welded together without a pup piece in-between them
Can Large size but welded valves be welded together without a pup piece in-between them
(OP)
There is a case of two isolation valves in a control valve station and the end connection of valves are butt weld. Is it mandatory to have a pup piece between them or can the valves be welded together direclty. Please share your experience in this case.





RE: Can Large size but welded valves be welded together without a pup piece in-between them
Pipe pup pieces are added for various reasons - the main one is the properties of the valves may be different to the run pipe so a compatible pup piece is added so when the purchaser receives a valve it is easier to be welded into the line with existing WPS's.
The other reason may be clashes between valve handles - if they are too close you may not be able to open/close one of them.
IMHO if they are both of compatible materials and you have a qualified WPS then no problem with welding them to each other,
Cheers,
DD
RE: Can Large size but welded valves be welded together without a pup piece in-between them
RE: Can Large size but welded valves be welded together without a pup piece in-between them
If you are worried about heat input what is the difference between welding a pup piece to the valve and welding a valve to another valve ?
Surely the valve will provide a better "heat sink" and absorb heat better than a short pup piece.
Cheers,
DD
RE: Can Large size but welded valves be welded together without a pup piece in-between them
"Can Large size but welded valves be welded together without a pup piece in-between them?"
The answer:
Yes
Sometimes its possible to do all the right things and still get bad results
RE: Can Large size but welded valves be welded together without a pup piece in-between them
As I seem to say here quite a lot, just because you can do it, doesn't mean it's a good idea.
RE: Can Large size but welded valves be welded together without a pup piece in-between them
As the connection won't be the weld under pressure, you could always weld a WN flange onto both valves.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Can Large size but welded valves be welded together without a pup piece in-between them
Thus, since each end of each single valve will be equal in weight and wall thickness of its matching pipe, the two valves should logically be able to be welded together. Weld pre-heat and weld PWHT and metal heatup rates should be calculated by the valve bodies, just like the weld of valve to pipe is calculated.
But, unless space constraints make it absolutely necessary, my instincts and observations say "Don't do it. Unless you have to."
RE: Can Large size but welded valves be welded together without a pup piece in-between them