ASTM A335 GR. P-91, P5B material

By RonG

Date 10-17-2001 16:53

You got the Welding and PWHT completed with out problems, so deviations in the preheat are a moot point.

By roybuck (*)

Date 10-17-2001 18:40

Please elaborate.... Where do we find this in writing?
Roy

By CHGuilford (****)

Date 10-17-2001 20:39

I don't believe you will find it in writing. I tend to agree with Ron though. Preheat is intended to slow the cooling rate and prevent problems in the weldment. So, okay, yours was lower than it should have been but you experienced no problems. The PWHT was done which would tend to eliminate stresses that might lead to cracking. The weld passed NDE and apparently showed no indications. No one can ever be sure that a weld will not a fail, it depends on fatigue, loading, stress corrosion cracking and other neat sounding conditions. But it seems your weld probably wont cause problems in view treatment and testing.
I would say that if your weldment serves a critical function where you cannot tolerate a failure, then reject it. (Keep in mind that a weldment welded per specs can fail too) If the function is not so critical I would use it. However, you know the conditions best.
CHGuilford

By M-Squared (**)

Date 10-18-2001 14:08

One thing to keep in mind is PWHT of this material is performed to temper the Martensite that has formed in the weld. Proper tempering of the martensitic microstructure is essential for obtaining reasonable levels of toughness. I would suggest that you perform hardness checks on the welds. I would take 5 readings throw out the low and the high readings, then average the rest. You should see hardness readings in the range of 225-280 HB. These hardness values will give you toughness values of 20 ft-lbs or better. Another important point is that the time specified in B31.1 for PWHT is inadequate. A minimum of 2-3h in the range of 750-760C (1382-1418 F) is required, or longer for thicker sections to provide sufficient tempering.

Also, your welding rod should have a Ni+Mn content of <1.5%. This will ensure that the Ac1(Transformation Temperature) Will be high enough so that your PWHT temperature will not exceed it. It has been shown that when the Ni+Mn is = 1.5% the Ac1 temperature is 1436 F. This is extremely close to the PWHT of 1400 F, and exceeding the 1436 F temperature would not be uncommon, it is very possible that the AC1 could or would be exceeded! If the Ac1 temperature were exceeded, some austenite would form which in turn transforms to fresh untempered martensite on cooling.

By RonG

Date 10-24-2001 18:35

I am curious!

The welding has been done. The PWHT and NDE is completed.

What will that change?

1418 F vs 1436 F

Are you suggesting that the situation can be reversed?

I still say the biggest concern is how fast the weld cools unless there is a problem with Hydrogen and if there was I am sure they would have reared there ugly little heads by now.

By chall

Date 10-24-2001 13:24

I suggest you call Roger Swain or Bill Newell at Euroweld (704) 662-3993. Both gents are very nice and willing to share info about P-91 issues. They are responsible for much of the research data available regarding these materials. I have discussed many issues with them and always receive info that I hadn't thought of. Charles Hall.