This article covers only a couple of the questions that get commonly asked pertaining to qualification of WPS with toughness testing. Surely many more interesting issues can be explored around the subject. Do feel free to add your own insights in the comments section below.
Using a PQR Qualified With Toughness For Joints Not Requiring Toughness
Can a PQR qualified with toughness requirements be used for joints without toughness requirements?
Suppose that a PQR has been qualified for a production joint that requires toughness properties. Following are the variables of the PQR (only the variables pertinent for this discussion have been included):
|Variable||Value used in procedure qualification||Qualified range in production joints (with toughness requirement)|
|Process (QW 253)||SMAW||SMAW|
|P number (QW 403.11)||P-No. 3 + P-No. 3||P-No. 3 + P-No. 3|
|Group number (QW 403.5)||Gr. No. 3 + Gr. No. 3||Gr. No. 3 + Gr. No. 3|
|Base metal thickness (QW 403.6, QW 403.8)||20 mm||16 mm to 40 mm|
|Filler metal (QW 404.12)||E9018-G of ABC trade name.||E9018G of ABC trade name only.|
|Filler metal size||Diameter 4.0||Dia. 4.0 mm and lower (owing to QW 409.1)|
Now, there is a production job that does not have toughness requirements, needing to be welded. The joint is 10 mm thick, one of the base metals is of P-No. 1 and other is P-No. 3, needs to be welded with a dia. 5 mm E9018-G electrode of XYZ trade name.
Can the above PQR be used for this joint?
The variables of the production joint described above are outside the qualified range shown in the table above. However, the answer to the question asked just above is – yes.
All the variables shown in the table are supplementary essential variables, and need to be taken into account only when the toughness is a consideration in the production joint. For a joint that does not require toughness properties, it does not matter whether toughness testing was done in a PQR or not.
A PQR qualified with toughness tests, when being considered for a production job that does not require toughness, has to be reckoned only with respect to essential variables. The supplementary essential variables have to be completely disregarded.
In replying to a question involving this matter, ASME affirmed to this understanding (as discussed above), in Interpretation IX-17-48 (qs 1).
The PQR indicated in table above is very much suitable for the production joint in question. A separate WPS may be written with the PQR, in which the variables have to be reckoned by ignoring the supplementary essential variables.
Note that a separate WPS would need to be written if one wants to use a PQR qualified with toughness tests for non-toughness applications. It is not permissible to use the WPS that was written keeping supplementary essential variables in reckoning.
The following question was asked in the Inquiry to Committee, as given in the Interpretation IX-17-48:
“Background: A PQR is run respecting supplementary essential variables for toughness applications.”
Question (1): Can a WPS be written for non-toughness applications?
Reply (1): Yes.
Question (2): For non-toughness applications can supplementary essential variables that may be addressed in the WPS be violated?
Reply (2): No.”
The lesson here from the question 2 above is that once a WPS is written, its’ sanctity must be respected at all times. The referred PQR may be good enough for variables beyond the range specified on the WPS, as per the rules of Section IX. In that case, a separate WPS (with the support of same PQR) must be written to serve the new variables.
What Happens If One Base Metal Requires Toughness While Other Doesn’t?
WPS for applications where one base metal requires toughness while other doesn’t.
Suppose that a PQR has been qualified with toughness tests. It is required to weld a production joint in which one of the base metals has been tested for toughness while the other hasn’t. How are the variables to be reckoned then? Consider the following example.
The PQR has been qualified on a test coupon of 40 mm thickness, both base metals of P-Number 3 [say, base material of EN 100216-2: 16Mo3 (this is a P-No. 3, Group No. 1 material) has been used], welded with a dia 5.0 mm E7018-A1 electrode. Impact testing has been done. This information is tabulated below for reference:
|Variable||Actual value adopted in PQR test coupon||Qualified range|
|Base Metal, Thickness||16Mo3 + 16Mo3, 40 mm thickness||16 mm (QW 403.6) to 200 mm (QW 451).|
|P Number, G Number||P-No. 3, G-No. 1 + P-No. 3, G-No. 1||P-No. 3, G-No. 1 + P-No. 3, G-No. 1|
|Filler Metal & Size||E7018-A1, Dia 4.0.||E7018-A1, Dia 4.0 and lower.|
Now, imagine that a production joint having the following variables needs to be welded:
Base Metals: 16Mo3 + SA-515 Gr. 70 (P-No 3, G-No. 1 + P-No. 1, G-No.2).
Thickness: 20 mm to 5 mm.
Filler Metal: E7018-1 of Dia 5.0.
It has been specified that the 16Mo3 has been tested for toughness, while the SA-515 Gr. 70 does not require toughness testing.
Can the PQR tabulated above be used support a WPS for this joint?
The answer to this question depends on whether the weld joint has been specified to have toughness properties or not. This is generally addressed by the construction code.
In my experience, if one (or both) of the base metals of the joint does not require toughness property, then the weld joint (that is, the weld metal) would not require it too.
Anyway, for this discussion, assume that the weld joint is not required to have toughness property, as per construction code. Lets us examine each of the variables individually.
Base Metal Thickness
The thinner material SA-515 Gr.70 does not meet the qualified range set by the PQR (when toughness is considered).
However, since it does not require toughness testing, QW 403.6 is not applicable. The thickness has to be reckoned therefore as per QW 451. A 40 mm thick PQR qualifies base metals from 5 mm to 200 mm. Thus, the SA-515 Gr. 70 metal is qualified to be welded using the referred PQR, as far as thickness is concerned.
The 16Mo3 part is qualified to be welded by the PQR regardless of toughness. Hence, the joint is good enough to be welded by the referred PQR, as far as base metal thickness is concerned.
A very similar question addressing the same issue has been answered to by the Committee in an Interpretation, IX-20-33.
P-Number And Group Number
When this happens in a production joint (one part requires toughness, other doesn’t), while determining a PQR’s eligibility for welding such a joint, each part should be treated individually.
Here, the 16Mo3 part of the production joint satisfies the QW 403.5. As regards the SA 515 Gr 70 part, since it does not require impact testing, QW 403.5 does not apply to it. Its applicability therefore has to be judged with respect to QW 403.1/QW 424, which permits that a P-No. 3 + P-No 3 PQR is good enough to support base metals of P-No. 3 + P-No. 1.
Hence, the joint is good enough to be welded by the referred PQR, as far P Number and Group Number are concerned too.
An Interpretation addressing a similar subject is IX-21-11.
When toughness is a consideration, QW 404.12 (a supplementary essential variable) prohibits change of filler metal to any other within any SFA specification (except some exemptions).
Here, however, since the weld joint does not require toughness testing, QW 404.12 is not to be considered. The proposed E7018-1 electrode for the production joint has same F-Number and same A-Number as the E7018-A1, thus – QW 404.4 and QW 404.5 are satisfied.
Hence, the joint is good enough to be welded by the referred PQR, as far as filler Metal grade is concerned too.
Filler Metal Size
When toughness is a consideration, QW 409.1 (a supplementary essential variable) prohibits increase in heat input. Hence, use of a higher size (which will entail a higher heat input due to higher current and voltage) is restricted.
Here, however, since the weld joint does not require toughness testing, QW 409.1 is not applicable. Thus, increase in heat input is immaterial, and a Dia 5.0 electrode is very much permissible for the production joint.
Note that if the weld joint IS specified to have toughness property, by the construction Code, then all supplementary essential variables would remain in force, and the PQR indicated in table above cannot be used to support the production joint in question.
Upgrading a PQR Qualified Without Impact Tests for Applications Requiring Toughness Property
Suppose that you have a PQR in your hands that has been qualified covering all Section IX-required tests, except impact tests. Now, it is required to use this PQR to support a WPS for an application that requires toughness. In this situation, it is necessary to carry out another procedure qualification to support the production WPS.
How does one go about doing this additional procedure qualification?
Q1: Are all tests of the original qualification required to be repeated, along with the necessary impact tests?
Answer: No, only the impact tests need to be done. The coupon for the additional procedure qualification only needs to be long enough for accommodating the required impact specimens. This is stated in QW-401.1.
Q2: Is the new coupon, from which only impacts are to be drawn, required to be a replica of the original procedure qualification coupon?
Answer: No, this is not necessary. Let’s examine this for a few supplementary essential variables.
Base Metal Thickness (T)
Suppose that the original PQR is with 1 inch (25 mm) thickness. When impact is not a consideration, the qualified range of T is 3/16 inch (5 mm) to 2 inches (50 mm). If the new coupon is also of T = 1 inch (25 mm), the new qualified range of T is 5/8 inch (16 mm) to 2 inches (50 mm). This is all fine if the production joint falls in this range.
However, what if the production base metal is 3/16 inch (5 mm) thick? In this case, the T of the new coupon should be 3/16 inch (5 mm). The new qualified range of T would now be is 3/16 inch (5 mm) to 2 inches (50 mm). Note that the new coupon is now not a replica of the original coupon w.r.t. T.
Restating the case, the T of new coupon is not required to be same as that in the original PQR. It has to be decided based on production weld requirements. Its’ range is governed by QW-403.6, which is a supplementary essential variable. Interpretations IX-04-04, IX-07-09, IX-17-79, IX-18-34, IX-19-29, IX-78-56, etc. provide wonderful examples that affirm the above understanding.
Suppose that the original PQR is with P-No. 1, G-No. 1 + P-No. 1, G-No. 1 base metals. However, the production weld (that requires toughness) is made up of P-No. 1, G-No. 2 + P-No. 1, G-No. 1.
In this case, the new coupon needs to be made up of P-No. 1, G-No. 2 + P-No. 1, G-No. 1; or, P-No. 1, G-No. 2 + P-No. 1, G-No. 2. Anyone of these combinations would be good enough to support the production requirement. Note that in this case too, the new coupon is now not a replica of the original coupon w.r.t. group number.
Classification of Filler Metal
When impact is a consideration, the Section IX generally requires using the exact same classification of filler metal in production that was used in making the procedure qualification coupon, except for a few exemptions given at QW-404.12. When impact is not a consideration, any other filler can be used too as long as the A-no. and F-No. are same.
In the case discussed above, the filler metal to be used in the new coupon has to be therefore decided based on the requirements of QW-404.12.
Suppose that the original PQR is with E7018-1 electrode. However, the production welds needs to be made with E7018-A1 electrode. In this case, the new coupon needs to be made with E7018-A1 electrode (note that again, the new coupon is not a replica of original coupon w.r.t. filler metal classification).
Suppose that the original PQR is with interpass temperature = 300°C. However, metallurgical considerations dictate that the production weld should be made with interpass temperature = 200°C. In this case, the new coupon needs to be made with interpass temperature = 200°C (note that again, the new coupon is not a replica of original coupon w.r.t. i/p temperature).
Similar judgment should be made when deciding the value of other supplementary essential variables (such as heat i/p, current/ polarity, PWHT time & temperature range, use of single pass per side, etc.) to be used in making the new coupon. However, remember that the value of all essential variables should be same as that in the original PQR. This is a code requirement, and is stated at QW-401.1.
When it is required to upgrade a PQR that was qualified without impact tests for applications requiring toughness, the new coupon – from which only impact specimens are to be drawn – does not have to be a replica of the original PQR coupon. In fact, the values of supplementary essential variables to be used in this coupon have to be decided based on the production requirement. Essential variables however, have to be same as the original PQR.
So these were some of my observations with respect to the applicability of a PQR qualified with toughness for production welds where one or both base metals does not require toughness testing. Do let know your thoughts in the comments section below.