You will need to PWHT again. From experience with test welds, PWHT < 1350F (730C) will have no effect on hardness of the weld metal or heat affected zone. Water initiated SCC is a problem with 91 in the as welded condition and I would expect it to be a problem with a material experiencing a severely slack PWHT as well. You will also have issues due to the difference in strength of the WM & HAZ vs. base metal.
John
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of GOSWAMI Pradip -THERMAL
Sent: Tuesday, October 12, 2010 11:42 AM
To: materials-welding@googlegroups.com
Subject: [MW:7516] RE: 7505] PWHT
Hi Ganesh,
What’s the design/construction code ?, B-31.1 or Sec-I.
For Grade -91(Sec-IX-P-15E) material you do not have the choice of performing PWHT at a lower temperature than what’s specified the design code. The recommended PWHT temperature range for P-91 materials for electric utility applications are as follows:-
· Section-I, Code- 730 Deg C minimum, 775 Deg C maximum
· B-31.1 Piping Code- 730 Deg C minimum, 775 Deg C maximum
I would say the recommendation would be to perform the PWHT again at the above specified range. This should be in line PWHT temperature followed for WPS/PQR qualification. If the PQR was qualified with maximum time , any amount of time upwards of 90 minutes, there should not be any issues with meeting the nominal mechanical properties,following Re-Stress Relieving.
Otherwise it would be wise to verify the tempering condition of the base metal in the mill and then to select the best PWHT cycle (time and temperature).
I do not want to be prejudiced or throw a smoke screen, if you do a goggle search on “failures of P-91 steel” you’d come across some recent incidents. The following article from welding journal gives some food for thoughts. P-91 steel works under extremely demanding conditions, improper welding could be dangerous.
Thanks.
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Ranjith Kumar .B
Sent: Tuesday, October 12, 2010 9:08 AM
To: materials-welding@googlegroups.com
Cc: 'Ganesan'
Subject: [MW:7505] PWHT
Dear Sirs,
We have Planned to Stress relive the Pipe butt joint of SA 335 Gr P91and Dia.323.9X33.3 at Soaking Temp:745°C ±10°C and soaking time:90mints. But by mistake while in process the operator has completed the Stress reliving at Soaking Temp:695°C ±10°C and soaking time:90mints.
For this can go to Re- stress reliving or can I accept as in condition(Request to guide me by mentioning the related standard) . I request any of us to guide me in this case to proceed further.
Thanks and Warm Regard’s,
K.GANESAN/QA&C,
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