Dear Mohd. Ibrahim,
As per ASME Sec. IX, para QW-403.6, you can very well support 6mm & 40mm PQR(s) to cover wall thickness range from 6 – 200mm, provided PQR should meet the following.
- 6mm PQR should have been qualified with mechanical (Tensile & Bend) and impact toughness test at MDMT (Minus 46 Deg. C).
- The second PQR (40mm thick) need not to be impact tested. (If impact tested, no issues)
Referring to the above clause (QW-403.6), it specifies the requirements on minimum side only. It means that impact toughness test performed on lower thickness shall cover all higher thickness with the support of another PQR qualified in higher wall thickness (with or without impact toughness tested). However, both the PQR essential variables shall be same except that impact test conducted on lower thickness PQR.
Impact toughness requirements are more critical in lower wall thickness compared to higher wall thickness due to change in rate of cooling from the higher temperature to room temperature.
i.e. If wall thickness is less, the rate of cooling also is less (due to surface area) and hence the micro structure will be in coarse grain. Where as higher wall thickness which promotes faster rate of cooling and the grain structure will in fine grain and hence more toughness value obtained compared to coarse grain structure.
Based on the above fact, you can support above two PQR(s) for wall thickness range 6 to 200mm.
Regards,
L. Prabhu kumar,
Sr. Principal Engineer,
Equipments & Materials Dept.,
Saipem India Projects Limited,
Tel:+91 44 43906588, Ext.: 588, Fax:+91 44 66840345,
Mobile Ph. No.: +91 9003010978.
From:
Sent: Wednesday, March 31, 2010 7:56 PM
To:
Subject: [MW:4648] Multiple PQRs for Impact test requirement
Hi Members,
Please provide a solution for the following issue.
Shell Material : SA 516 Gr.70 -- 50 mm Thk
Nozzle : SA 333 Gr.6 --- 7 mm thk
MDMT : - 46 Deg.C
I need to weld the nozzle to shell. I have a PQR with SMAW process qualified in 40 mm thk and another PQR with SMAW qualified in 6 mm thk.
As per Sec. IX if impact test is required the 40 mm PQR will support from 16 mm to 200 mm. base metal Thk. and the other PQR will support from 6 mm to 12 mm thk.
If I club these PQR can I write a WPS to support 6 mm to 200 mm?.
Is there any issue for the missing range of qualification between 12 mm to 16 mm?.
Or is it required to add another PQR to fill the missing thickness range from 12 to 16 mm between the first two PQRs?.
Or can I write a WPS directly with range 5mm to 200mm omiting impact test requirement for this joint as it is a category D joint and excempted from Production Test Coupon?.
Thanks & Regards
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