Deletion of Backing Gas

[AWeld1]

We have a WPS for Stainless Steel that was supported by PQR with backing gas. We used this WPS to weld plate with thickness ranging from 1.5mm - 2.4mm.

If we are going to deleted/remove backing gas and no root gap (square joint), do we need to make a new PQR?

As per ASME IX ed. 2013:

QW-200.1
(c) Changes to the WPS. Changes may be made in the nonessential variables of a WPS to suit production requirements without requalification provided such changes are documented with respect to the essential, nonessential, and, when required, supplementary essential variables for each process. This may be by amendment to the WPS or by use of a new WPS.

Table QW-256: 408.5 refers to the deletion or change in backing flow is nonessential varialble.

QW-408.5 The addition or deletion of gas backing, a change in backing gas composition, or a change in the specified flow rate of backing gas.


QUESTIONS: with regard to the DELETION/REMOVAL of backing gas for the actual work condition:

1. Is it correct to say that referring to Table QW-256 we can change our WPS without the re-qualification of the PQR?
2. Does QW-408.8 refers to the deletion of backing gas?

Please correct me if I am wrong.

Thank you

 

[AWeld1]

GTAW PROCESS is used in this procedure.

 

[metengr]

Not enough information - what are your base materials you are joining? 2013 Edition of ASME Section IX states

Besides QW-408.5 read on in QW-256 for the variables below

QW-408.9 and QW-408.10 both are essential variables with backing gas deletion or change in composition.
Variables Essential
.9 − Backing or ϕ comp. X
.10 ϕ Shielding or trailing X

 

[AWeld1]

The base material is 316L 1.2mm plate. I understand that if we are going to weld stainless steel we will need backing gas. But with regard to ASME IX, which one will rule, QW-408.5 or QW-408.8? It was defined also in ASME that backing gas includes argon.

 

[metengr]

Well, if you know how to review WPS essential variables in Section IX, you evaluate each variable brief listed by welding process. Since QW-408.8 is not applicable to the GTAW process based on the list of variables stated in QW-256, it does not apply. Article IV is applicable to specific welding processes.

So, in your case with the base materials, no re-qualification is necessary with the deletion of backing gas.

 

[AWeld1]

Is it correct to say that QW-408.8 is only applicable for double V groove and that requiring back weld or for combination weld such as GTAT/SMAW?

 

[metengr]

No. Did you review the applicable list of essential variables for WPS qualification for the GTAW process in QW-256? There is NO QW-408.8 for the WPS. This variable applies only to WELDER PERFORMANCE QUALIFICATION, see QW-356.

 

[AWeld1]

Thank you very much. It's now clear. What we did is we made a new WPS using the existing PQR. In the new WPS and deleted backing gas for the above mentioned material. I already reviewed QW-256, what I dindnt notice was that QW-356 was for the welders performance.

One more thing, it was also mentioned in QW-200.1 if im not mistaken,in letter "c" if there will be changes in wps for nonessenstial variable, i should be documented. It may be by amendment of the WPS or use a new WPS.

In my understanding, it is not mandatory to amend the WPS as long as there will be a documetation that there was a change in nonessential variable with respect to essential and supplementary variable.

Having that notion, is it correct not to make changes in the existing WPS and just incorporate to the Method Statement that Backing gas will no longer be used during actual welding?

Will it be allowed that the Method Statement will serve as the documentation record for the deletion of the backing gas during the actual welding work?

this is based on the QW-200.1 letter "c"

Thank you.

 

[metengr]

Yes

 

[AWeld1]

Thank you very much sir. I really appreciate it.