PWHT time for P91
PWHT time for P91
(OP)
I'm sure the question has been asked before, but what is the minimum hold time for PWHT on P91? The question is pertinent to thin sections (1/2" and lower say).
I believe ASME VIII (UCS-56) suggests it is possible to do as little as 15 mins on thin sections (<1/4"). However, I've seen some guidance, including:
http://preview.tinyurl.com/ok7ek38
and
http://www.sperkoengineering.com/html/Grade%2091%2...
Suggesting 2 hr min on the basis to ensure complete tempering.
Is anyone able to advise?
Regards
kclim
I believe ASME VIII (UCS-56) suggests it is possible to do as little as 15 mins on thin sections (<1/4"). However, I've seen some guidance, including:
http://preview.tinyurl.com/ok7ek38
and
http://www.sperkoengineering.com/html/Grade%2091%2...
Suggesting 2 hr min on the basis to ensure complete tempering.
Is anyone able to advise?
Regards
kclim





RE: PWHT time for P91
RE: PWHT time for P91
NEM has published recommendations for PWHT time vs temperature in the magazine"Combined cycle quarterly" 3rd quarter 2005. There can be plotted a relationship of LMP vs weld hardness, where if the objective is a final weld hardness of Hv=270, then the correlation is
LMP=21= T*(20+Log(t))/1000 for hardness = 270Hv. For a lower hardness , set LMP=21.5 . For LMP=21 I get:
For T= 1425 F = 1047 K, t= 66 minutes = 1.1 hrs, but code requires 2 hrs min
T=1400F , t=2.1 hrs
T=1375 F, t= 4.0 hrs
T=1350F, t= 7.6 hrs
If you have in hand the material certs for the weld consumables, you can calculate the max permitted T AC1, and you would set the PWHT temp at least 50 F below that T Ac1. If you overshoot T Ac1, then you will need to recycle that section of pipe or submit it to a N+T.
This correlation is independent of wall thickness.
"Nobody expects the Spanish Inquisition! "
RE: PWHT time for P91
http://www.epri.com/abstracts/Pages/ProductAbstrac...
RE: PWHT time for P91
RE: PWHT time for P91
http://files.aws.org/wj/2006/06/wj200606/wj0606-42...
luis marques
RE: PWHT time for P91
http://www.weldinguide.com/viewtopic.php?f=2&t...
RE: PWHT time for P91
Ultimately we are going to be OK with 0.5 hr PWHT for thin wall tube:
- Qualification testing will show suitable properties are obtained
- Industry experience - 0.5 hr for thin wall tube is OK
- Metengr link to the EPRI document suggests oxide scaling can be an issue at long hold times, which is an issue with thin wall tube where scaling will consume a proportionally larger amount of material.
Cheers
RE: PWHT time for P91
http://www.weldinguide.com/gdanastasiadis/viewtopi...