This article discusses a few examples showing change of Group Number in welding, which is a supplementary essential variable in ASME Section IX. How to judge applicability of a PQR for a production weld when only the Group number is different, while all other essential and supplementary essential variables are satisfied?
The issue has been explained through the use of few example cases, that were asked to ASME, and which were responded to by ASME through Interpretations.
- Consider the following question asked in Interpretation IX-86-75.
“Does a PQR for joining P-No. 3 Gruop No. 3 to P-No. 3 Group No. 3 base metal qualify for the joining of P-No. 3 Group No. 3 to P-No. 3 Group No. 1 base metal where notch toughness testing is required?”
When toughness has been specified as a requirement, QW 403.5, which is a supplementary essential variable, comes in force. QW 403.5 stipulates that the procedure qualification should be done with the same P-No Group-No. combination as that would be encountered in production.
In the question asked above, the Group-No. of the base metal to be used in production weld is Group-No 1, while the procedure qualification has been done with a Group-No. 3 base metal combination. Hence, the PQR in question is not adequate to support the weld in question.
Some exemptions appear too in QW 403.5, to override the restriction described above. However, the conditions given in question do not qualify for the exemptions.
In order to meet the requirement of production weld in above case, as per the stipulations of QW 403.5, one of the following needs to be done as a minimum:
- Prepare an additional coupon with P3 G3 + P3 G1 base metal combination, and do only toughness testing. Note: Instead of the P3 G3 + P3 G3 PQR that the inquirer has, had a P3 G3 + P3 G1 PQR (with all tests) been available, it would have supported both P3 G3 + P3 G3 combination, as well as P3 G3 + P3 G1 combination, in accordance with QW 403.5.
- Qualify a second PQR (with all tests) with P3 G1 + P3 G1 base metal combination. Then the P3 G3 + P3 G3 PQR which is already available, and the newly qualified PQR with P3 G1 + P3 G1 combination are collectively good enough to support a P3 G3 + P3 G1 combination in production weld.
- Consider another similar question, asked in Interpretation IX-83-92.
“Question (1): A procedure has been qualified to satisfy all requirements, including notch toughness, for welding P-No. 1, Gr-No. 1 to P-No. 1, Gr-No. 1 base metals. Is it necessary to make a procedure qualification test to determine notch toughness only (QW 401.3) for welding P-No. 1, Gr-No. 2 to P-No. 1, Gr-No. 2 base metals, with all other essential variables the same?”
Let us lay out the given information in simpler terms.
Available PQR: P1 G1 + P1 G1.
Production requirement: P1 G2 + P1 G2.
Group number of the base metal is a supplementary essential variable; it becomes applicable when toughness is a consideration.
Since the Group number of the base metal to be used in production is different from the one used in PQR, the available PQR cannot be used to support the production joint, so a new procedure must be qualified. However, P numbers are same. So, QW 403.11 is satisfied.
When such situation occurs, per QW 401.3 (QW 401.1 in 2021 edition) permits us to prepare an additional test coupon with the same essential variables as used in the existing PQR, and use a base metal with right Group number (in this case P1 G2 base metal), and perform only toughness tests.
Hence, it is needed to qualify a new PQR, in which the test coupon will be made up of P1 G2 + P1 G2 base metals combination, and only toughness tests need to be performed.
It may also be noted that if a P1 G1 + P1 G2 PQR is available, it permits welding of all three combinations, viz. – P1 G1 + P1 G2, P1 G1 + P1 G1, and P1 G2 + P1 G2. This is permitted in QW 403.5.
It is therefore worth keeping in mind that while qualifying a PQR, it is worthwhile to use base metals of same P numbers but of different Group numbers. This widens the range of qualified base metals for that PQR.
- A very similar question has been asked in the Interpretation IX-86-78. The question is reproduced below for reference:
“Question: A PQR exists for welding a P-No. 1 Gr. No. 2 material to a P-No. 1 Gr. No. 2 material with acceptable notch toughness properties. Does this PQR qualify for welding a P-No. 1 Gr. No. 1 material to a P-No. 1 Gr. No. 2 material where notch toughness is required?”
The conditions of this question too do not qualify for the exemption given in QW 403.5. In order to meet the specified production requirement, one of the following is required as a minimum:
- Prepare an additional coupon with P1 G1 + P1 G2 base metal combination, and do only toughness testing.
- Qualify a second PQR (with all tests) with P1 G1 + P1 G1 base metal combination. Then the P1 G2 + P1 G2 PQR which is already available, and the newly qualified PQR with P1 G1 + P1 G1 combination are collectively good enough to support a P1 G1 + P1 G2 combination in production weld.
Alternatively, a full fledged PQR with P1 G1 + P1 G2 combination (in lieu of the existing P1 G2 + P1 G2 PQR) would have been good enough to support both P1 G2 + P1 G2 as well as P1 G1 + P1 G1 combinations.
- Consider yet another similar question asked in Interpretation IX-89-75.
“Question (1): A procedure qualification using the SMAW process in a V-groove joint has been qualified with acceptable bends, tensiles and charpy V-notch impact specimens, using P-No. 1 Gr. No. 2 material welded to a P-No. 3 Gr. No. 3 material. Does the procedure qualification support the welding of P-No. 1 Gr. No. 2 material together when notch toughness tests are required?
Question (2): Does the procedure qualification support the welding of P-No. 1 Gr. No. 2 material to P-No. 3 Gr. No. 3 material?
Question (3): Does the procedure qualification support the welding of P-No. 3 Gr. No. 3 material together?”
Consider the question (1) above.
When toughness is a consideration, supplementary essential variables become additional essential variables. QW 403.5, which deals with P-Numbers and Group Numbers, is a supplementary essential variable. Per QW 403.5, procedure qualification must be qualified with the same P Number Group Number combination as that in job.
The production weld in question has P1 G2 + P1 G2 combination. It is not the Group numbers alone that are different; the P numbers are different too. The reply given by ASME to this question is a ‘no’. This question would have begot a ‘no’ answer even if toughness had not been a consideration. A P1 + P3 PQR cannot support a P1 + P1 combination.
In order to support the P1 G2 + P1 G2 combination specified in question, a PQR with P1 G2 + P1 G2 combination, or a PQR with P1 G1 + P1 G2 combination, is required.
Consider now the question (2) asked in the Interpretation above.
The specified combination is exactly same as the one qualified in procedure in question. Therefore the procedure in question very much supports the welding of combination specified in question. The answer given by committee is yes too.
Consider now the question (3).
Similar to the reasoning given for the question (1) above, the specified combination of P3 G3 + P3 G3 cannot be supported by the P1 G2 + P3 G3 procedure in question. This question would have fetched a ‘no’ answer even if toughness hadn’t been a consideration. A P1 + P3 PQR is grossly inadequate to support a P3 + P3 weld, in accordance with QW 424.
So this was about Group numbers in welding PQR, and its applicability to production welds. Please do let know your thoughts in the comments section below.
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