Welding ball valves 1

[willyc57]

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

 

[RXH]

I have come across several cases of seat problems with small ball valves when welding too close. The basic problem is that the soft seat material (PTFE, Nylon, Delrin, etc) degrades under high heat input.

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 &quot;Tempilstiks&quot; to monitor and stay below the this temperature during welding.

 

[Scipio]

I've seen it a couple times on small 1&quot; and 1.5&quot; socket weld two-piece, end-entry ball valves, where teflon seats warp. Usually if it's built as a socket weld valve, you're safe assuming it can be welded without removing the trim unless the vendor specifically states otherwise. It's that &quot;usually&quot; part that causes problems. Like RXH said, it's best to check with the manufacturer.

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.

 

[enggeorge]

Can you tell me more about templisticks?

 

[unclesyd]

These are crayons, tablets, or paints that indicate a temperature by melting at specific the specific temperature indicated on the crayon. Templestick is one brand name and had been around a long time. You can get a very good indication of temperature with them.
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&quot; 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.

 

[sterl]

Socket weld valves notorious for this...High penetration requirement and large land on valve leads to welder running high current with much of heat input to valve body.

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...