Welding ball valves
Welding ball valves
(OP)
Has anybody ever experienced warpage of a ball valve seat when welding very close to a small diameter (< 4")valve? Tribal knowledge here says to keep the valve open when welding close (within 6") but we need the valve closed for isolation. I'd appreciate any insights.





RE: Welding ball valves
The traditional way to avoid the problem is to remove the internals, weld, and then re-assemble the valve. Some manufacturers keep enough distance between the seats and the ends so that the seats are unaffected.
It sounds like you have a socketweld or buttweld end isolation valve that is installed in a line that cannot be taken out of service.
I suggest that you call the valve manufacturer and find out if welding is a problem. If so,, find out what is the maximum allowable temperature at the seat, and discuss the possibilty of using "Tempilstiks" to monitor and stay below the this temperature during welding.
RE: Welding ball valves
After that, you should also make sure your welders know what they're doing. If they run too hot, or try to take a shortcut by laying heavier passes, they can screw up a valve even when it's designed to be welded with the internals in place by letting the interpass temperatures get too high.
RE: Welding ball valves
RE: Welding ball valves
You buy the sticks, looks like a chalk marker, at or near the temperature you are want to achieve or maintain. Say you want to get a preheat of 400°F you have a Templestick that would indicate this temperature. As you heat the part you continue to mark the part with the stick and when it melts, very noticeable, you have achieved your desired temperature. Normally one would have 1 or 2 sticks on the approach and one over.
They are available in very wide range of temperatures and available at welding supply houses or scientific supply houses.
In welding they are often used to indicate preheat and monitor inter pass temperature. Some times a procedure will call-out the location needed for the temperature indication, 4" from the center of the weld is quite common.
All welders on site had a sticks for our required preheats and were required to use them.
We used them for a lot of other temperature measurements around the plant.
RE: Welding ball valves
WN valve and TIG the first pass will eliminate most of the heat concentration to body. Adminster the second pass application as suggested by unclesyd and the topic dies...