How old are the welds in question? What is the wall thickness?
The PQR is the proof of the procedure and if no preheat was done chanses are you are not dealing with heavy wall material, and it is limited to a range of wall thickness.
The point being that if the PQR was done with out preheat, Preheat would become a Nonessential variable until you change it by 100 F.
You might check that the thickness of the work is in the range of the Procedure.
For the most part Preheat is to prevent the weld from cooloing to fast and developed problems like "Cold or Delayed cracking"
Dr. Crisi and a lot of other people on this board can give you a much better explaination if you need it.
Thank you very much for your quick reply. Our Power Plant erction was completed in 1999. From June 1999 plant is under operation. Power Plant is located in TURKEY
There were main steam line size is OD 416mm Sch 80
material SA335 P22 (P5A) PQR is also with out preheat. I have scanned PQR&WPS for mentioned material. May I sent you scanned PQR&WPS by this forum system?
You can send it to my e-mail.
Just click on my "Login or user name"
Just to clarify a point of Ron's. According to ASME section IX, preheat is an essential variable. It requires requalification if it is to be decreased more than 100 Degrees F. (QW406.1) It is also a supplementary essential variable (when impact testing is required) and requires requalification if interpass temperature is raised by more than 100 degrees F. (QW406.3) This applies to the common arc welding processes. Other processes have different requirements.
In first place, I'd like to thank RonG for his kind words on my person.
Secondly, let's look at your problem with "horse sense".
Your steam line (by the material it's made of I guess it carries superheated steam) was put in service in June, 1999 (two years ago) and, thanks God, it hasn't busted yet. So, we can safely assume that the chances to bust someday are remote or none. If I were you I wouldn't mind about the existing welds, but I'd definetely mind about FUTURE welds, so that the problem you've run into won't happen any more. Take into account RonG's and G. Roberts' advice to write (and put it into practice when it's used) the correct WPS for high pressure steam lines.
Warning! High pressure, high temperature steam lines are subjected to two problems you're not free from: creep, which occurs when the line is subjected to temperatures higher than 350 ºC for long periods of time, and graphitization, occurring at temperatures above 400 ºC, also for long periods.
SA 335 Grade P22 contains Molidbenium, which diminishes, but not precludes, the danger of creep. So, be careful and carry out annual inspections on the line to check its conditions.
Giovanni S. Crisi
´Sao Paulo - Brazil
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