P91 Pre-Heat and PWHT Time Interval

[newbeehere]

Sirs;
During our inspection, the owner representative questions us: What is the interval time between your Pre-heating and PWHT.
Pre-heating is carried out during welding, afterward the PWHT will be done.

And, what closest ASME code could be supported for this article.

Thank so much

 

[stanweld]

Do you carry out PWHT immediately after welding and after allowing the temperature to decrease below 200F? Or do you provide a dehydrogenation intermediate heat treatment after weld completion and then after a few days/weeks time interval go into PWHT? If the latter, the Owner is concerned with the potential for stress corrosion cracking if water contacts the weld during the the time interval between weld completion and PWHT.

 

[DSB123]

newbeehere,
P91 final properties are very dependant upon the correct Pre-heat and PWHT conditions. Do a search on P91 as there are numerous threads on this subject with good contributions from posters such as Davefitz, Meteng, etc. All your questions should be answered by a simple search in these forums.

 

[unclesyd]

Aside from the sage advice given above here is a very good paper on the welding of the 91"s from Sperko Engineering.

http://www.sperkoengineering.com/html/Grade 91 R 10-05.pdf

I don't know whether this is the place to mention the Tip Tig welding process but here goes anyway. I have some preliminary information about some outstanding results welding P91. Unfortunately my source had a heart attack and now has a defibrillator and can't get near a welding shop, another excellant welder taken out of the loop.
This wouldn't be anything to run our a grab and expect the goose to lay a golden egg, but, If you have a large project upcoming I think it would be worthwhile to investigate the process.

Here are two approaches to get some preliminary information on the process, both have essentially the same information.

http://tiptig.com/

http://www.weldreality.com/TIP-TIG-Welding.htm