RE: [MW:9964] Change in sequence of PWHT cycle

Hi JJ & Mr Latake,

 

The PWHT cycles is questions are :-

1. 600-640 Deg C for 2 Hrs followed by 687 Deg C for 8 Hrs.
2. ALTERNATIVELY
3. 687 for 8Hrs followed by 600-640 for 2 Hrs?

As explained by Mr Latake, the first PWHT cycle @ 600-640 Deg C is close to the ISR cycle followed for fabrication of thick-walled Cr-Mo or Cr-Mo-V reactors.The necessary functions of ISR are to cause safe dehydrogenation and  partial relaxation of residual stresses of weld and HAZ which adds to improvement of ductility and notch toughness. The second PWHT @ 687 Deg C would cause the proper softening of weld and HAZ and would cause softening of the  precipitated carbides (especially for Cr-MoV) steels during the ISR..

 

If the PWHT cycle is reversed then so called ISR cycle(600-640 Deg C) will become redundant. If the component size is thick, typically 6 inches or more straight exposure to actual PWHT temperature (687 Deg C ) may cause typical stress-relaxation cracking. The change of PWHT sequences may not be felt on a short term basis, such during fabrication or procedure qualification. If the material is a Cr-Mo-v steel then there could be significant impact should secondary carbides precipitate during the 640 deg PWHT cycle.

 

The typical weld and BM various mechanical properties with the above altered PWHT cycles may be close or almost the same. however the effects could be on the long term , i.e service induced failures or damages.

 

The attached article of  Arcelor sheds some lights on this issue.

 

Thanks.

 

 

Pradip Goswami,P.Eng.IWE

Welding & Metallurgical Specialist & Consultant

Ontario,Canada.

Email-pgoswami@sympatico.ca,

pgoswami@quickclic.net

 

---

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Santosh
Sent: Monday, February 21, 2011 1:20 AM
To: materials-welding@googlegroups.com
Subject: RE: [MW:9956] Change in sequence of PWHT cycle

Dear JJ,

 

Can you please state purpose of these two different PWHT cycles?

 

It seems that first cycle (660 - 640 °C for 2 hrs) is for intermediate stress relief (ISR) after welding and second cycle (687 °C for 8 hrs) is for final PWHT. 

If these two cycles are ISR & final PWHT, ISR shall be done immediately after welding.

 

Regarding effect of PWHT, any heating above 480 °C is considered to have effect on mechanical properties of metal (reduction in yield strength and tensile strength).

Irrespective of the sequence of PWHT / heating cycles, total effect on mechanical properties will be same. Total effect on tensile properties is calculated by finding the "Holloman Parameter (HP)" for each individual cycle and then adding together. For more information, see below links from Dillinger web site.

 

http://www.dillinger.de/hollomon/help.shtml.en 

 

http://www.dillinger.de/hollomon/examples_js.shtml.en

 

Regards,

 

 

Santosh Latake

 

---

From: materials-welding@googlegroups.com [materials-welding@googlegroups.com] on behalf of joshi jaydeep [jaydeep.p.joshi@gmail.com]
Sent: Saturday, February 19, 2011 11:41 AM
To: materials-welding@googlegroups.com
Subject: [MW:9941] Change in sequence of PWHT cycle

Dear all,

 

 

I have and PWHT cycle of 600-640 Deg C for 2 Hrs followed by 687 Deg C for 8 Hrs.

 

will it make any difference in any of the properties of WM &/or BM if I change the sequence of PWHT cycle i.e.first cycle of PWHT for 687 for 8Hrs followed by 600-640 for 2 Hrs?

 

Material: LAS

 

regards,

 

JJ

 

 

--
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.

--
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.