ASME Sec. IX QW-200.4 - combination of WPS

[nathanael87]

I have a WPS with two SMAW processes for example E6010 root and E7018-1 fill and cap.
According to ASME Sec. IX QW-200.4 I can use just one of those filler metals individually in a joint.
eg. I can use this WPS to use E7018-1 for an entire weld - root, fill and cap. We use this for welds on vessels.
What sort of calculations are required to determine if welding with that filler metal alone will be suitable for a particular joint?

I understand that E7018-1 is only going to improve the weld whilst losing a bit on penetration characteristics, and freezing at a slower rate (why it isn't used on piping as there would be a risk of more icicles).

Now, say in the case of a different procedure with GTAW/SMAW for P5B 5Cr eg. ER-80S-B6 root, E-8018-B6, apart from GTAW having excellent penetration and being a cleaner weld. Is there any other benefit to it? Depending on the process running through the pipe, is having the GTAW root going to be that much better?

The reason I ask this is because we have a tie-in weld on a long line and using shielding gas will be difficult and costly.

 

[SectionIX]

You could use an individual process, or in this case, electrode classification. However, you are still bound by, amongst others, the maximum qualified thickness for each process/electrode as noted on the PQR. There are no calculations, per se, but the filler metal must match or exceed the mechanical properties of the base metal.

If the maximum qualified thickness for the E7018 is 10 mm, you cannot weld a 12 mm joint and retain code compliance. Other issues as you have pointed out are root penetration challenges using low hydrogen. Also, you need to insure your welders are qualified to make this all low hydrogen weld,as most qualify using a cellulosic root with low hydrogen remainder, and deletion of backing (cellulosic) is an essential performance variable for the SMAW process (among others).

In a shop environment, GTAW would generally be superior to SMAW (depends on personnel, equipment, shop conditions, etc.) A GTAW root would generally be superior to an E7018 root, but as you have indicated, making field welds with GTAW can be problematic due to shielding gas concerns. Issues such as piping material, service conditions, flow product) will ultimately determine the best pocess to use for that applicaton.

 

[weldstan]

It appears that you have misread QW-200.4. Your WPS using E6010 for the root and E7018-1 and so qualified permits you to make the weld in question using E6010 for the root passes followed by E7018-1 for the fill passes subject to the base metal thickness range and the deposited weld metal range of each electrode classification (F-No.).

 

[nathanael87]

Thank you for your responses.

@SectionIX
Yes, that's exactly what I was thinking too. It will require a process engineer and reliability engineer to decide if SMAW only will be adequate for the P5B process. We will need to perform welder qualifications in that case to weld with F4 without backing (we currently do this for boilermakers for welding P1 vessels without a 6010 root). But, to sum it up I can still use my WPS in question as long as I maintain essential and required supplementary essential variables as well as the base and weld metal thicknesses permitted for that process.

@weldstan
I don't see how I have misread it. He's the excerpt I am talking about:

"When following a WPS that has more than one welding
process, filler metal, or set of variables, each process, filler
metal, or set of variables may be used individually or in
different combinations, provided
(1) the essential, nonessential, and required supplementary
essential variables associated with the process,
filler metal, or set of variables are applied
(2) the base metal and deposited weld metal thickness
limits of QW-451 for each process, filler metal, or set of
variables are applied"

That tells me that I can weld an entire weld with just one of the processes of a WPS assuming I follow the above rules.

 

[weldstan]

Yes that is also true. I misread your question.
You could also use a PQR qualified with GTAW and support a WPS using GTAW for the root passes and SMAW with the E7018-1.