WPS with impact tests and PWHT

[tonnesen]

I have a question concerning QW-407.2, when I qualify a WPS according to ASME Section IX with impact tests and PWHT this variable becomes essencial, so my question is if my coupon for the PQR is 25 mm and the PWHT is 1 hr, the range of thickness qualified is from 16 to 50 mm.
Now suppose that in production weld I have thickness of 50 mm being welded, the PWHT required will be 2 hr, but my PQR was qualified only with 1 hr, so my question is, when qualifying a PQR should I use the time range for the greatest thickness in the range or I will qualify the time per thickness rate?

If the situation was coupon 25 mm thickness, with impact tests and PWHT used in the qualification was 2 hr, in the production weld could I use PWHT of only 1 hour? No, right?

 

[weldtek]

QW 407.2 is pretty clear. Where impacts apply, you must qualify the coupon with the time at PWHT which will represent that to be used in production, ( within 80%) Your 1" coupon, PWHT'd for 1 hour, is good for 1.25 hours of PWHT and therefore will restrict the max thickness to be welded accordingly. See applicable design code.

 

[metengr]

.....and the reason for this time restriction is that weld metal and even certain base material weld heat affected zone notch toughness values can degrade with prolonged exposure to PWHT.

 

[tonnesen]

weldtek and metengr,

thank you for your aswers.

I agree with you about the PWHT limiting the maximum thickness qualified, but what about the second question? If I use a 50 mm coupon the range qualified will be from 16 to 62,5 mm (1,25 x coupon thickness), but if my production weld is 16 mm should I use the time at PWHT temperature qualified or can I use less time since the thickness is only 16 mm? What I'm trying to say is QW 407.2 limits the maximum and minimum thickness qualified or just the maximum and why?

 

[moseley]

tonnesen,
Wow what a "kinda" loaded question. As for your 2nd question.... if you did use a 25mm coupon in qualification and performed PWHT at 2 hours (hypethetically), you would then be qualified (with Impact testing applied)as follows:
Minimum thickness: 16mm
Maximum thickness: 50mm
PWHT time at temperature: you would be qualified to perform PWHT on welding through the entire range of thickness qualified (could perform an aggregate PWHT soak of up to 2.5 hours).

This Supplemental Essential Variable gets the best of them, but if you just remember to always look at the maximum thickness that you would be able to weld with the coupon being used in qualification and then perform the PWHT at a minimum soak time of 80% of that you would be covered. If this didn't quite answer your question; you can always perform less soak time than the maximum qualified, but never above the maximum allowed (i.e. 1 hour coupon PWHT will not qualify 2 hours of production PWHT but 1.6 hours (1 hour 36 mins) would. Hope this helps, if not; let me know and I'll try to explain a little different.

 

[tonnesen]

Ok, thank you all!

So, I can PWHT the thickness at the production accordingly to the design code recomendations time/in, with the maximum time and thickness limited by the time at the qualification x 1,25.