Welding in-line valves

[Jackson306]

I understand that manufacturer recommendations should be followed when welding in valves of all types but my question is, "what is the reasoning why some would recommend, say gates, to be in the closed position when others say to have them open". My question also relates to PWHT, which seems to usually be the same as how the valve is welded in. My opinion is to have valves closed during welding and PWHT but bearing in mind the welding lead is on the same side of the valve as the welding is taking place. Also unless recommended by manufacturer the valve is not disassembled.

 

[metengr]

Never seen instructions on industrial valves to have the valve fully closed during welding and PWHT. The instructions are to have the valve open and keep the gate material away from heat exposure. In some cases if the valve can be disassembled, so be it, to protect the packing material from PWHT. The last thing you want is for the stem and gate material to soften from PWHT.

The end of the day, you should follow the manufacturer's specific instructions because if something goes wrong warranty issues come into play.

 

[btrueblood]

The issue may be, for metal gate valves, to prevent spatter from the weld from entering the gate pocket and preventing the gate from seating. Also, they may be thinking the gate in contact with with the seat forms a better heat sink.

 

[rconner]

Am curious where you saw advice that valves are to be welded in the "closed" position?

 

[Jackson306]

Velan bolted bonnet gate valve installation manual.

 

[rconner]

Thanks

 

[metengr]

If this is a bolted bonnet, why not take the bonnet off, remove the internals, PWHT and re-assemble? You could destroy the packing if the valve is closed and subject to PWHT.