Practice Case 6 – Backing For Welding Procedure Qualification

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This article discusses this question: If a procedure qualification has been qualified with backing, can it be used only with backing? Can it be used for welding without backing as well? Is backing for welding procedure qualification an essential variable?

backing for welding procedure qualification

Consider the following question asked in Interpretation IX-17-15.

“Background: A PQR consists of a GTAW root without backing and SMAW fill.

Question: Can a WPS be written for SMAW without backing?”

This occurs frequently. For a person familiar with Section IX, this question would not cause a bother. One might even consider the question to be too rudimentary. But for a beginner, these kinds of questions do occur in mind, and it is important to precisely know how to approach such questions.

We shall examine two aspects of the situation here. One, the PQR consisted of two processes. Can the WPS be written with any one of them singly used?

Two, is it alright to not have backing in production job when the PQR was done with backing?

Let us examine the first question. The procedure qualification was done by combining multiple processes.

For such PQRs, Section IX permits us to use each of the processes singly or in any combination. For example, a PQR has been qualified with the combination of GTAW, SMAW and SAW processes. Using this PQR, you can write a WPS for only GTAW, or only SMAW, or only SAW, or only SMAW + SAW, or only GTAW + SMAW, or any other possible combination of these three processes.

It only needs to be kept in mind that the PQR must have recorded the individual weld metal thickness deposited by each of these processes in the procedure qualification test coupon. The range of qualified thickness for each processes (as determined through QW 451) then must be adhered to, in production WPS.

The moral of the story is that multiple processes in a single procedure qualification test coupon can be treated as individual PQRs, and can be used singly or combined (in any combination), provided all variables (essential, non-essential and supplementary) are applied for each of the processes. This has been addressed in QW 200.4(a).

Next, let us see the question of backing. The PQR in question was made without backing for the GTAW process. For the SMAW fill weld, the GTAW deposit served as the backing. While writing a WPS for the SMAW process, is it compulsory to use backing?

See, backing is not an essential variable for procedure qualifications. Backing is only an essential variable for performance qualifications.

Using the PQR in question, a WPS can be written – with backing, as well as without backing; for both GTAW and SMAW processes. However, if the production joint is without backing, then the welder performing the weld must have been essentially qualified without backing.

If the production joint is with backing, then the welder needs to have been qualified in any one of the conditions – with backing or without backing.

So, the essence of the discussion is – backing is not an essential variable for PQRs. A PQR qualified with or without backing can be used for making production welds with or without backing. Only, a suitably qualified welder is required.

So this was about the question of without backing or with backing for welding procedure qualification. We also saw that a PQR qualified with multiple processes can serve a production weld for either one of the processes, or multiple of them, in any combination.

Do leave your thoughts in the comments section below.

See More:

Practice Case 3 – WPS For Dissimilar Base Metal Thickness

Commonly Asked Questions On WPS With Toughness Requirement

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