RE: [MW:14021] PWHT OF P91 BY INDUCTION HEATING

Sandeep,

 

AWS D-10.10 is written to facilitate local PWHT for all types of C-Mn and low alloy steels. Grade-91 requires special considerations. Attached is the specification for P-91 and P-92 steels written by one of the well reputed EPC organization in North America. This specification,though a bit generic is downloadable form the link below.

 

I ve highlighted the clauses very relevant to local PWHT on P-91 . You may read and use these recommendations at your discretion.

 

To answer to your point, P-91 requires a complete soak at the suggested PWHT cycle. For guidance in the  attached spec  if the O.D is @ 760 Deg then the ID should be 730 Deg.If induction heating of up to 139 mm thickness could attain this temperature range, then this technique would be acceptable otherwise do not use it subject to your client and your management's discretion.

 

As I mentioned before P-91 is a dangerous steel, IT IS NOT JUST ANOTHER Cr-Mo steel. Hence one has to ensure that a through PWHT is performed on weld of this grade.

 

I have cross referred the clauses of D-10.10, you had mentioned in your earlier email.But AWS interpretation(see attached) looks different.

 

Also see below the purple colored text on what AWS recommends on uniformity of temperature for a PWHT operation.

 

I would say discuss this issue with the PWHT contractor such that the temperature could be maintained within the range as specified above.

 

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist & Consultant
Ontario, Canada.
Email-pgoswami@sympatico.ca,
pgoswami@quickclic.net

http://www.scribd.com/doc/47805169/Q110-Welding-of-9Cr-1Mo-V-Grade-91-and-9Cr-2W-Grade-92

 

D -10.10

11.1 Temperature Uniformity. Requirements regarding temperature uniformity are generally specified separately for the heating/cooling and hold portions of the PWHT cycle. ASME Section III limits temperature variation during heating and cooling to not more than 250°F (138.9°C) within any 15 ft (4.6 m) interval of weld length. This limit generally acts as a circumferential temperature gradient due to the fact that it is most often applied to  heating of circumferential butt welds. The requirement in B31.3 which states "The heating method shall provide the required metal temperature, metal temperature uniformity,... " does not provide useful guidance. Generally, the required uniformity during the hold period amounts to staying within the bounds of the maximum and minimum temperature requirements specified by the codes.

Concerns about temperature uniformity during PWHT are related to the resulting stresses and possible distortion or cracking which could occur as discussed in 11.2 and 11.4. Use the lesser of the maximum temperature differences shown below or that provided in the governing document for PWHT.

Maximum Recommended Temperature Differences for PWHT:- During heating and cooling, the maximum temperature difference within the heated band should be 250°F (139°C) or as limited by the maximum axial temperature gradient.During hold, the maximum temperature difference within the soak band should be 100°F (55°C) or the allowed temperature range, whichever is less. During hold, the maximum temperature difference around any circumferential plane within that portion of the heated band outside of the soak band should be 100°F (55°C)

-----Original Message-----
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of sandeep monody
Sent: Wednesday, March 28, 2012 2:58 AM
To: Materials & Welding
Subject: Re: [MW:14003] PWHT OF P91 BY INDUCTION HEATING

Dear Pradip Sir,

Thank you very much for your valuable information. Still some doubts are there as given below.

As per AWS D10.10( Clause2.3.1)temperature variation up to 83deg is acceptable and AWS D10.10 itself says that there is no way to eliminate temperature variation though out the wall thickness(Clause 2.3).

Actually in our site we have materials with various thicknesses and some up to 139mm and now question is.. what will be the temperature variation for 139mm thickness(On jobs its not possible to measure inside temperature).

Have any equation or formula to find out the temperature variation throughout the thickness?

Have any role of Thermal conductivity of P91 in this case?

Is it possible a uniform temperature at OD and ID regardless of thickness?

Awaits for your reply

Thanks and regards

Sandeep
QC Engineer

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