Section IX/B31.3 PQR using P-51; question on ôsupplementaryö 1

[tc7]

Hello All,
I rarely work under Section 9, so please have patience.

An upcoming job requires full penetration butt welds on 4-inch NPS Sched 10 pipe for a hot water application and the designers have applied B31.3 “normal” service criteria.

In my file I have a procedure for GTAW on P-51 which was qualified on 3/8” plate, open root wherein backing and trailing gases were used. The material used during PQR was plate certified to SB-265 Grade 2 which puts it in Group P-51. No impact tests were done on this PQR.

Since the production job is calling for ASTM B862 Grade 2, also in group P-51, I feel my qualified plate procedure is applicable.
However, QW-256 imposes QW-403.6 as a supplementary essential and this states that the minimum thickness qualified is equal to the thickness of the test coupon thickness, which was 3/8”. So does this QW-403.6 render me ineligible to weld .120”thick Sched 10 pipe?

It seems that supplementary essentials are only applied when notch toughness is a requirement – and I don’t see that B31.3 has levied a notch toughness requirement on this application.

All advice and comments appreciated. Tthankyou.

 

[metengr]

tc7;
Hope all is well. Based on the anticipated service and your inquiry, you do not need to qualify the PQR with the supplementary essential variable because notch toughness testing has not been invoked.

 

[tc7]

Hello Met-
Doing reasonably well, and same to you.

What is your opinion on this: during the previous plate PQR that I mentioned, the root gap between the plates was recorded as 3/16" with a very high backing gas flow of 45 CFH. This may have been doable on 3/8" thick plate but frankly, I don't see how we can weld thin wall titanium pipe with this wide open root. For purged pipe work I would rather close the root to a zero gap. Does Section IX allow me to reduce the root gap from 3/16" to zero" without requalifying as long as I keep the backing gas flow rate the same ?

I am also curious about cross qualifying 3/8" plate to .120" wall pipe, it just isn't the same. Why don't the piping codes insist that production joint be duplicated during PQR for GTAW work?

Thanks again for your thoughts.

 

[metengr]

tc7:
QW-256 for the GTAW process does not require a change in root gap spacing of a weld joint QW-403.10 as an essential welding variable. Therefore, you have flexibility to reduce the root gap to zero provided you have this addressed in your WPS.

Your second question refers to qualified plate thickness. If you review QW-256 and Qw-403.8, the minimum thickness for qualification using a 3/8" thick coupon is 1/16" to 2T, see QW-251.1. The 1/16" minimum qualified thickness for weld coupons 3/8" in thickness and under has been demonstrated to suitably cover the range of 1/16" to 2T. If the weld coupon exceeds 3/8", the minimum thickness qualified jumps to 3/16", per QW-451.1.

 

[tc7]

OK, Metengr
Looks like I'm all set. Thanks again for your quick response and great expertise.
tc7

 

[DekDee]

tc7,
You have got all the technical responses above but there is one thing you touched on that needs looking at - IMHO, the difference between your original PQR and the proposed production joint.
Metengr has been involved in another post where the discussion revolved around the requirement to use sound engineering judgement as the code cannot possibly cater for every situation.
I have read previously with Duplex and Super Duplex there are important factors related to the joint configuration that can affect the chemical properties (not sure about metallurgical properties)based on the root gap, the amount of subsequent dilution of the weld metal and the varying exposure to the purging gas.
I have no idea if this is applicable to welding titanium but if I was the client I think I would prefer (obviously a big difference to require) a PQR that was qualified on something a little bit closer to what you are actually welding - irrespective of what the code allows.
Regards,
DD