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PQR with PWHT and impact test, ASME IX, QW-407.2

PQR with PWHT and impact test, ASME IX, QW-407.2

Postby hanyu » Fri Oct 04, 2013 12:14 pm

Having a PQR with material "SA-204 A" in thickness 30 mm which has been performed with PWHT and impact test, I would like to know if I can weld the same material in different thicknesses when the project calls for PWHT and impact test. My query arrives by the fact that the PWHT holding time depends on the thickness and taking into consideration the QW-407.2 I suppose (if I understand well) that for this project I cannot use this PQR. Could you please give me your opinion.
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Re: PQR with PWHT and impact test, ASME IX, QW-407.2

Postby alesio » Sat Oct 12, 2013 9:20 am

The change of PWHT time & thickness range is considered supplementary essential variable not for all welding processes but only for the processes as specified by the tables QW-252 to QW-265. So if for example you have welded the PQR test specimen using GTAW and SMAW processes then such a change is considered essential variable and you have to comply with QW-407.2 according to which the PWHT time of PQR shall be at least 80% of the production welding time. The SA-204 A has P-no:3 and Group-no:1 and thus the PQR test specimen (thickness 30 mm) had to be subjected to PWHT at 595 deg C for 72 minutes (ASME VIII, table UCS-56). In this case the 72 minutes are the 80% of the maximum time that qualified by this PQR and consequently the maximum time is 90 minutes. So, by the table UCS-56 of ASME VIII arises that the maximum thickness qualified by his PQR is 37.5 mm.
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Re: PQR with PWHT and impact test, ASME IX, QW-407.2

Postby mohd » Sat Nov 30, 2013 4:25 pm

Dear Mr alesio,

Regarding 80% rule, your example is clear.

But supposing that the PQR run for 2 cycles including repair possibility, so the total time would be 72x2=144 minutes, does this PQR qualify for WPS with impact to weld base metal with thickness up to 75 mm? (144/0.8=180 minutes, 180/60=3 hours, 3x25=75 mm)

regards,
mohd
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Re: PQR with PWHT and impact test, ASME IX, QW-407.2

Postby alesio » Sun Dec 01, 2013 10:47 am

Dear Mohd,

Many thanks for your valuable comments that help us to see this issue in further detail since most of times it is indeed necessary the PWHT holding time of PQR to permit at least two PWHT cycles of production weld so as to to cover the case of repair.

Regarding your query for maximum qualified thickness 75 mm, please note that it cannot happen since the PQR performed with material thickness 30 mm and thus the range T of base metal qualified is 5 mm up to 60 mm as per ASME IX, table QW-451.1. For that range of base metal thickness qualification there are two cases T <= 50 mm and 50 mm < T <= 125 mm as per ASME VIII, table UCS-56. Lets examine the worst case with respect to PWHT holding time that is when the base metal thickness is 60 mm. So, when the production base metal thickness is 60 mm then the minimum holding time of PWHT shall be 120+6=126 minutes. Since we have at our disposal up to 180 minutes of PWHT holding time (as you have told 144/0.8=180 minutes), it is clear that this PQR qualifies for welding base metal with thickness 60 mm and thus the range T of base metal qualified (5 mm up to 60 mm) isn't restricted.

Could you please let us have your comments?

Thanks
Alesio
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Re: PQR with PWHT and impact test, ASME IX, QW-407.2

Postby mohd » Sun Dec 01, 2013 3:27 pm

Well said, Mr alesio,

Though the PQR has been qualified with impact and thus the qualification range of base metal thickness will be 16 mm up to 60 mm when impact requirement apply for the production welds as per QW-403.6.

As you have explained:
1. If the PQR has been qualified with two PWHT cycles (144 minutes == 80% == 180 minutes), then we can use this PQR to support WPS up to 60 mm base metal thickness when impact requirement apply.
2. If the PQR has been qualified with one PWHT cycle (72 minutes == 80% == 90 minutes), then we can use this PQR to support WPS up to 37.5 mm base metal thickness when impact requirement apply.

Please note that I agree with both of the above statements

regards,
mohd
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Re: PQR with PWHT and impact test, ASME IX, QW-407.2

Postby alesio » Sun Dec 01, 2013 8:06 pm

Dear Mohd,

You are right that the lower limit of base metal thickness qualification is 16 mm (not 5 mm as I told) since the project calls for impact test and thus the requirement of QW-403.6 applies.

Thanks
Alesio
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Re: PQR with PWHT and impact test, ASME IX, QW-407.2

Postby mohd » Tue Dec 03, 2013 5:17 am

dear alesio,

Provided that the PQR test specimen has been subjected to PWHT for 72 minutes,

1. Does this PQR support WPS without impact requirement with two PWHT cycles for repair works?
2. Does this PQR support WPS with impact requirement with two PWHT cycles for repair works?

what is your opinion?

regards
mohd
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Re: PQR with PWHT and impact test, ASME IX, QW-407.2

Postby alesio » Tue Dec 03, 2013 8:53 am

Dear Mohd,

Please find here below my interpretation regarding your queries:

1. QW-407.2 is a supplementary essential variable (applicable only when impact requirement apply) and thus this PQR supports WPS without impact requirement with two or more PWHT cycles.
2. When impact requirement apply then the 72 minutes of PQR's PWHT can qualify for maximum 90 minutes of production weld PWHT and thus cannot qualify for two PWHT cycles (72x2=144 minutes). In such a case we had to perform PQR's PWHT for at least 115.2 minutes (144x80%=115.2).

regards
Alesio
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Re: PQR with PWHT and impact test, ASME IX, QW-407.2

Postby mohd » Tue Dec 03, 2013 9:50 am

dear sir,

Now it's clear.

Thanks for your valuable time.

regards,
mohd
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