Criteria for Post Weld Heat Treatment

[qaisarabbas]

We all know that requirement for pre-heating and post-heating during welding comes from either of the cases as per construction code:
1. Service requirement
2. Material requirement
3. Thickness requirement
4. Operating conditions requirement
Would appreciate if anybody can suggest a single document / consolidated table mentioning all these conditions at the same time. This would serve a quick reference in planning and deciding WPS requirements.

Regards - Qaisar

[ashfaqanwer]

Your requirement is explicitly listed in API 582. Have a look at Section 9 for PWHT and Appendix A for welding consumables.

Its a great API for getting quick handy guidelines. For any other specific question regarding this API, you may write to me at ashfaqanwer@thepetrostreet.com

Hope this would help.

[qaisarabbas]

Ashfaq,

Thank you for your guidance. I have gone through the said API and found it very relevant and informative specially for new inspection / maintenance engineers. Contents are very crisp and clear.

One thing, still un-answered for me, is that what is the guideline or criteria for:
1. "PWHT of Socket Welds / Partial Penetration Welds"
2. "PWHT of Repaired Welds"

Regards - Qaisar

[Nabeel Ahmed Qureshi]

Recently encountered with a very intresting situation & would like to seek any one's advice on this issue.
If a piping weld joint is to be both radiagraphed & stress relieved then as per code PWHT shall be done before doing radiography of that joint. My question is that if a joint has been stress releived (having 6mm thickness) & upon doing RT, porosity is noticed in caping (2~3 mm deep) then is it necessary to stress release that joint after doing repairs?

[ashfaqanwer]

Qaisar,
Point wise reply is as follows:
1. See ASME B 31.3 Sec. 331.1.3 (b) and you will get the appropriate answer for your query.
2. Preferably, deal all the repaired welds in the same way you deal the new ones but for some specific case (repaired area versus original) see ASME PCC-2 for guidance as it waives off PWHT works in certain cases.

Hope this would help.

[ashfaqanwer]

Nabeel,
Yes for sure, after carrying out the repairs, you have to perform stress relieving (if mandatory).
And stress relieving before radiography is itself a long discussion, if you are interested I can give my inputs on the same.

[Nabeel Ahmed Qureshi]

Ashfaq,

It is clearly mentioned in ASME Sec.VIII to do PWHT before doing RT. This is the info available to me as per ASME Sec VIII.
Clear cut guidelines does not leave any point of discussion? What do you say about this?

[ashfaqanwer]

Yes, but practically the matter is somewhat different. At the time of plant construction ,usually it is not economically feasible to perform radiography after PWHT operation as you may have repairs in already heat treated weld joints, carry out repairs and then re-do the PWHT operation.
Therefore, construction contractors are normally allowed to carry out PWHT after radiography (clearance of weld joint). The only defect which can come up after uncontrolled PWHT operation is crack and for that, UT control is practiced on some critical weld joints; those having rigid constraints or having higher Cr content (> 5%).

[ashfaqanwer]

Nabeel,
See this thread also.
http://www.hghouston.com/dcforum/DCForumID2/352.html