Welding and PWHT Valves into Pipe Lines

[Davidiow]

What is the prefered position the valve should be in, when welding and PWHT of the butt welds to piping, should it be open, closed or somwhere between? my main concern is for Alloy like P5A & P5B.
Is there any backup information, and where can I find it.

 

[RXH]

The valve manufacturer is the best one to ask.

In general, I can think of two concerns during welding and PWHT: (1) Weld splatter could cause damage. This is to be avoided by putting the valve in the position where the least damage can occur e.g. if it is a ball valve, keep it in the open position, and mask off the exposed portion of the seating area. (2) Heat could damage the soft seals and inserts, if any. Normally the manufacturer will provide a sufficient length for the BW ends to avoid this problem. Please see other threads in this forum for discussions on this topic.

However, I could not think of a possible relationship between the type of material (P5A, P5B) with the position of the valve. Can you clarify?

 

[MikeONeill]

The short-version answer is 'fully open'. For gate and globe valves you want to fully backseat the valve.

 

[JNieuwsma]

Rule of thumb from my experience is "partially" open. Check manufacturer's installation and maintenance manual for specifics.

JN