Interpass Temperature 1

[powerplantcwi]

I am working on a SA335-P22 header that is 4" thick. We are welding with E9018-B3 and are going to perform post weld heat treatment, my client is requesting the use of a 550 deg F preheat, the interpass temperature on my welding procedure is also 550 deg F. My question is where can I find, or how to find acceptable interpass temperature for this material.

 

[metengr]

The interpass temperature is an arbituary value based on how much heat input you can tolerate in the weld region. Too high of interpass temperature can result in lower notch toughness (if impact qualification is required). For your application, I would agree that preheat should be at above 500 deg F because of the material thickness (I also ran into a similar situation when we replaced some heavy wall P22 pipe where I needed 500 deg F).

Since the interpass temperature is probably not an essential or supplementary essential variable (unless impacts are required) you can revise the WPS to increase the interpass temperature to 150 deg F above the preheat maintenance temperature of 550 deg F.

 

[Duwe6]

Second *all* of metengr's recommendations.

I hope that you are planning on using PWHT electric pads to maintain the preheat, and that you will be continously welding these items. No lunch breaks, no time off for shift turnover - use 2ea. 13-hr overlapping shifts. With something like this 4-inch weld, once you start, you CANNOT stop before there is 1-inch of weld deposited [that is only 25%] and should not stop until it is welded out.

If you are forced to stop by uncontrollable issues after the first inch, give the incomplete weld a 1-hr(+) per inch of completed weld, a Hydrogen bake-out at 700-800°F, then hold the incomplete weld at 500°(+) until welding can restart.