PWHT at valve 1

[PAN]

In some service, PWHT is required in piping system. I use small size of valve with socket ends. How I ensure that the heat does not damage some internal parts such as packing or gasket of valve? Please advise.

 

[MJCronin]

PAM,

I wonder why you have a PWHT requirement in small diameter piping systems ?? Socket weled connections for valves are ususally for 3 inch NPS piping and smaller.

Typically, these small diameter systems have piping wall thicknesses that are less than the minimum that requires PWHT. (this is the way I have always undrestood the requirements of ASME B31.1)

Is there some strange piping material or some super high pressure that this system will see ? PWHT would never be required for a "small bore" carbon steel system built to ASME B31.1/B31.3 in the good old US of A.....

More details please.....


MJC

 

[PAN]

MJCronin,

I agree with you that it is not a requirement in ASME/ANSI B31.1 (or B31.3). However, I found this requirement in a project specification for wet H2S service. It indicates that carbon steel valves of welded fabrication are not permitted, except where PWHT. Please comment.

 

[kstaylor]

What you do depends on whether the valves are welded or bolted bonnet:

1. For bolted bonnet valves we disassemble the valves, match all parts so they can be reassembled correctly (proper orientation and all...), heat treat the piping including the valve bodies (either in an oven or with local stress relief heating), and reassemble the valves after cool down. Use new bonnet gaskets and hydrotest for leak tightness.

2. For welded bonnet valves, bonnet disassembly is not an option without destroying the valve. Therefore, remove the packing from the valve's stuffing box (it will be destroyed during the PWHT operation) and back the gate or plug off of the seat so the valve is about 1/4 to 1/3 open. Run through the PWHT cycle, cool down, repack the valve, and hydrotest.

We have used these procedures successfully for many years in wet H2S or other sulfide service. Good luck.

 

same procedure as outlined by kstaylor we followed here with little mods on item 2. if its graphite packing, we dont pull em out. sure u run a pwht on small bore piping if the service is caustic on certain temp range and concentration.

 

You can also solve that problem using valve with niple, so the joint will be far from the valve internals. If there is no space enought you will have to take out the internals.