PWHT time for P91 2

[kclim]

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 91 R 10-05.pdf

Suggesting 2 hr min on the basis to ensure complete tempering.

Is anyone able to advise?

Regards

kclim

 

[racookpe1978]

I have never heard of a 15 minute soak time. 2 hr is minimum for even a .216 thick alloy pipe wall.

 

[davefitz]

You have to meet the requirements of the code . ASME sect I requires a min 2 hr soak.

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! "

 

[metengr]

Review the free EPRI publication below for handling Grade 91 steels;

http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000000001023199

 

[metengr]

If you are going to use the 2011 Edition of ASME B&PV Code, for P-No 15E Group 1 material, the minimum PWHT time is 30 min at temperature, with 1 hour/inch of thickness up to 5" of nominal weld thickness per Section I, Table PW 39-5.

 

[0707]

Go to the site below maybe it helps

http://files.aws.org/wj/2006/06/wj200606/wj0606-42.pdf

luis marques

 

[wegm]

you could also have a look at this link:

http://www.weldinguide.com/viewtopic.php?f=2&t=10

 

[kclim]

Thanks to everyone for their feedback.

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

 

[wegm]

Sorry, the above link doesn't work, you could have a look at this link:

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=2&t=10