Interpass Temperatures on P91 Piping 2

[jdfife]

Hello,

I have a question about interpass temperature requirements for P91 piping. We are attempting to qualify a robotic welder to perform continuous girth welds and branch connections to 6" pipe. We are concerned that the base metal temp will exceed the typically recommended 550-600°F interpass maximum. What sort of detrimental effects will this have on this particular grade of pipe? Can they be eliminated with a normalize and temper process? We are fabricating small pressure vessels, so heat treating of the entire assembly is possible. Any advice would be appreciated.

Thanks,
jdfife

 

[metengr]

The interpass temperature requirement has more to do with keeping the heat input in the surrounding base material localized and broadening the intercritical heat affected zone away from the weld region. This region is where the Type IV cracking develops.

This is very important for field welds that will be subcritically post weld heat treated. If you intend to re-heat treat the welded component, I see no problem.

So,

Can they be eliminated with a normalize and temper process?

Yes. The entire component should be subjected to a normalize and temper heat treatment.

 

[EdStainless]

If you plan on N&T for the entire assembly then the only possible problem that I see has to do with the uniformity of the welds. If you preheat and then have the IP temp rising you may have issues with controlling the weld and keeping it uniform.

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[jdfife]

Thank you both for the assistance! I am aware of the difficulty of controlling the weld pool, but I wanted to make sure that we could eliminate other problems with exceeding the typically recommended interpass temperature.

Thanks again,
jdfife