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Home > Forums > Engineering Codes, Standards & Certifications > Engineering Codes, Standards & Certifications > AWS (welding) Code Issues Forum

PWHT of Butt Welds

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pipeneer (Petroleum)

16 Feb 10 15:34

Hi,
I am installing a 6"-900#,BW,FLEXIBLE paralell wedge GATE valve, my questions is while PWH treating of the two BW at the ends of the valve, should we close the wedge completely or let them stay open, my guess is fully closed but any secound opinion would be greatly appreciated.
For what it's worth, valve's material is A182 F11,DP 130 bar and DT 160 Deg.C.

metengr (Materials)

19 Feb 10 20:59

Check with the valve supplier first. If they cannot supply an answer, I would leave the wedge open. The wedge and valve body are different masses and thus will heat up at different rates from externally applied heat. The wedge being a smaller mass will heat up faster and could put increased thermal stress on the valve body in a fully closed position and crack the seat if it has hard facing. How do I know this? I learned it the hard way years ago.

pipeneer (Petroleum)

21 Feb 10 12:43

Thnxs metengr, I'll contact the manufacturer, and believe even your point is valid, if they have componsated for the forces that you mentioned,then keeping the gate closed ! at least mitigates distorsions alot.

Mr168 (Materials)

22 Feb 10 11:13

More often than not, these requirements will be right there in the O&M manual. Typically when I see them specified in the closed condition, it's a combination of preventing weld spatter from damaging the seat (never an issue, as we use GTAW on all root passes) and distortion control.

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