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Re: [MW:23928] Bulge P-91 Pipe after PWHT

By Materials & Welding
Dear Sir,
I already discussed with heat Treater regarding this matter & found thermocouple is placed in the middle so there is no overheating Chances.  Thermocouple Photo Attached.
We have Thermocouple & recorder calibration certificate.
Regarding the question of overheating/Overlapped the Heating band...... the joint is painted there is no color difference of the particular area of the heating band/ Bulge Area. Although machine will show that if it is overheated.

My question is all spool ( Eight Nos & each spool has two nos of joint ) is a common header ( Header weight is 6,3 Ton) downside is locked in the another header. Is it possible there is no expansion area of the joint & so the pipe is expanded at side ? 
Regards,
Pradip

On Thu, Nov 26, 2015 at 9:48 AM, pgoswami <pgoswami@quickclic.net> wrote:

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

pgoswami@quickclic.net

pradip.goswami@gmail.com

All provided answer are personal opinions or personal judgements only. It's not connected with any employers by any means. 

 

 

*******************************************************************************************************************************************************************************************************************************************************

 

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

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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