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P91 preheat to 899F.

P91 preheat to 899F.

P91 preheat to 899F.

We have a customer that has come back on our ASME P91 GTAW procedures that 400deg preheat is insufficient. They require us to maintain a MINIMUM preheat of 899F!!! No, that's not a typo.

Here's the real kicker....they ALSO require a MAX heat input of 1.2 kJ/mm.

Yes, I know it's impractical but they are adamant that we meet their requirements.

I am curious of the community's collective thought. We are a bit curious here and treating it like a brain-teaser...what would happen if we ACTUALLY tried to weld it with those req.

RE: P91 preheat to 899F.

Maybe they are confused on the different between C and F or how to convert C to F?

Or maybe they need a consultant's help in understanding the need for preheat.

Best regards - Al

RE: P91 preheat to 899F.

When the laughter stops, ask them......1. Is it correct? 2. Why is it needed? 3. What is the history of this requirement?

RE: P91 preheat to 899F.

Confusion. Point your customer back to a code or standard, say ASME B&PV Code, Section I or even B31.1 Power Piping. The minimum preheat is indeed 400 deg F. Perhaps they are confusing interpass temperature with preheat.

RE: P91 preheat to 899F.

A very confused or ignorant client. Agree with all the above comments. No max interpass temp.!!?? If one wanted to ruin a P91 weldment, this would be a great requirement.

RE: P91 preheat to 899F.

Hi Viper 3982,
Forget about C or F. The client is totally at loss and has ill-knowledge about grade 91 steel.
Some education from the vendors end might help to speed up the work without undue interference and hindrance.
Ask them to refer any EPRI Grade-91 document or API-TR-938B as a good educative document on grade 91 steel.
That's my advice.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist

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