Hi vdao3004
According to ASME IX, you do NOT need to do two test plates. You only need to do one, with a PWHT of at least 80% of the time that you will be using in production. Thus you may have a longer time on your PQR test piece as what you use in production, but not more than 20% shorter. I mentioned the short time test piece only because this is required in some client specifications. If it is not required in your client specifications, then you only need to perform the long PWHT time on your PQR test piece.
My understanding has always been that if you have qualified your PQR on 1", and used a 1hr holding time, then in production you may not hold the PWHT longer than 75minutes, irrespective of the material thickness. (In essence, you can then only weld 1.25" with that procedure, to still comply with the ASME VIII requirement of 1 hour per inch of thickness.) This is why it is important to decide up front what thickness you will be welding in production, and tailoring your PWHT to suit. (e.g. 1" qualifies 2" production, which requires 2hrs PWHT, according to ASME VIII. If you want to include the posibility to PWHT twice, just in case you need to perform a repair/modification after you have PWHT'ed your vessel, then double that to 4hrs. You will then perform a PWHT of 4hrs on your PQR test plate.)
I just want to check the code interpretations and see if they say anything different. I will let you know tomorrow, if I can get me hands on the ASME IX interpretations at the office.
Just an aside: Only if your test plate exceeds 1.5" thickness, are you qualified up to 8" thickness.
Regards
Niekie
Hi vdao3004
I have confirmed the statement I made yesterday regarding the PWHT times. I will attach two code interpretations that illustrate the point. The fist shows that you can not have a longer PWHT in production, even if the material is thicker than your test plate, and the second shows that you may exceed the production PWHT time on your test plate.
Regards
Niekie