Pradip,
Something definitely had gone wrong with the PWHT process causing the headers to bulge. I’ve tried to put all of your back and forth correspondence in one place. The root cause analysis looks to me are as follows:-
- The PWHT temperature is not very clear, but something in the vicinity of 760-780 Deg C and of 2hrs of soaking time for ½” wall thickness is high.
- Please follow Sec-I guidelines (as below)
- The PWHT chart should be very clear. It’s not clear from the PWHT chart what was the temperature adopted vs the soaking time .Needs to be specified in the chart
- I’m not sure, but from the hand drawn sketch, it looks two heating pads were overlapped. If so it definitely would add to overheating .
- It’s not a mandatory requirement. However as per D-10.10 it’s advisable to place additional thermocouples in the soaking and heating zone to monitor PWHT temperature accurately. This is required for CSEF steels such as Grade -91 Or else over tempering would destroy the Creep Resistance of this steel.
- I would think one needs to discuss these issues upfront with the heat treaters, then approve the PWHT procedure and monitor well in the field.
I hope the attached information would help you.
Thanks.
Pradip Goswami, P.Eng,IWE
Welding & Metallurgical Engineering Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299
All provided answer are personal opinions or personal judgements only. It's not connected with any employers by any means.
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Subject: Re: [MW:23914] Bulge P-91 Pipe after PWHT
Dear Dennis,
Pls find the PWHT chart & in 10" we used two nos of thermocouple with equal distance i.e 180 degree. We checked the hardness in the weldment as well as HAZ zone & found 210 to 238 HB (This is fine) but in bulge zone ( Parent Material ) which is 140 mm away from weldment is coming 155 to 175 HB.—Over tempered, Poor Creep Strength
Thanks in advance.
Regards,
Pradip
| Dear Mr. Rems, Bulge happened just outside PWHT heat band. Pipe thickness is 12.70mm & did soaking 2 hrs. I already attached Time temp. chart. Header has eight nos of pipe but during PWHT only two pipes are bulge. Thanks & Regards, Pradip From: pradip kumar Sil Sent: Τρίτη, 24 Νοεμβρίου 2015 - 12:42 To: materials-welding Reply To: materials-welding@googlegroups.com Subject: Re: [MW:23914] Bulge P-91 Pipe after PWHT |
It is not possible to do PWHT horizontally because spool piece is welded at location
On Tue, Nov 24, 2015 at 12:26 PM, pradip kumar Sil <pradipsil@gmail.com> wrote:
Dear Expert,
In P91 Material ( HRSG header Joint ) after pwht one joint is bulge.We did Preheating ,Welding , Post Heating,& PWHT in proper way.
Can anybody explain why this bulge occurs & remedy.
During fit-up inspection & weld visual inspection all round the joint is perfect but after PWHT pipe is bulge 140 mm away from the weld ment
Pic Attached
Regards,
Pradip
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