GTAW Portion of Weld Qualification Failed

[91RepairGuy]

Our company recently needed to increase our thickness range for manually welding P1-P1. We used 1.5" thick SA-516 plate with a 37.5-10 degree compound bevel for the test coupon. The root passes were welded with ER70S-B2 using GTAW, 3/4" deposited metal thickness. The balance was welded with E7018 using SMAW, 3/4" deposited metal thickness.

The following data was recorded:
Position of Groove: Flat 3G
Weld Progression: Uphill
Preheat: 200F
Interpass: 600F
PWHT: 1150F +-25F
Time: 1.5 hrs
Rate above 600F: DNE 250F/hr
Shielding gas: 99.9% argon
Current: direct
Polarity: GTAW-str, SMAW-rev
Amps: Root 100-150, Cover 110-175
Technique: Root-stringer, Cover-weave
Electrodes: single

The coupon was completed and sent out for PWHT and destructive testing. Failure of the GTAW portion was discovered while performing side bends and no tensile pulls were performed. The SMAW portion appeared to be satisfactory with no visible defects. The GTAW portion had multiple separations, approximately 1/8" wide. Many of these defects were parallel to each other and stacked two high (seems to be consistent with the location of the stringers in the root pass). Each weld pass was power cleaned with a new wire wheel.

No visible indications were visible in the parent metal, although defects are present in the weld metal, adjacent to the parent metal. I have photos available for analysis.

Is there an issue with depositing 3/4" GTAW weld metal thickness? Would you recommend a minimum number of GTAW passes when the procedure is re-qualified? We would like to understand what happened to cause the multiple defects in the GTAW portion of the weld. Your assistance is greatly appreciated

 

[metengr]

These appear to be lack of fusion weld defects.

 

[metengr]

PS, the filler metal should be ER70S-2, not ER70S-B2. See SFA 5.18.

 

[Kiwi2671]

91repairguy,
As metengr has stated looks like LOF indications.
Why are you doing 3/4" GTAW ?
Why are you running GTAW stringers ?
Are you keeping minimum preheat temp on the whole time ?

The normal practice for thick pipe or plate welding is 2 runs only with GTAW then remainder with SMAW.
Good luck with your retest,
Regards,
Kiwi

 

[stanweld]

We have never had a problem qualifying as you have using ER70S-2 or ER70S-6 for the GTAW portion. Sometimes silica glass deposits will be left on the weld bead using ER70S-2 due its multiple deoxidizing elements. Failure to remove those deposits have led to LOF flaws.

 

[Mr168]

That is indeed lack of fusion, though I'd sooner expect far too low an amperage/very poor bead profile (cold lap) more so than inclusions. Silicon deposits would be considerably more inconsistent than that, e.g. scattered along the length of the joint.

That being said, I've seen a lot of failed bend tests, but never have I seen one fail so consistently across the strap as this one!

Kiwi: Per ASME IX, the 3/4" GTAW deposit nets him qualified thickness up to 8". Splitting a 1.5" PQR coupon 3/4" - 3/4" between two processes is typical.

 

[mrfailure]

I agree that lack of fusion occurred. This most often most commonly occurs because of an incorrect gun angle. Insufficient heat (current) can also be a culprit.

Good luck!

Aaron Tanzer

http://www.lehightesting.com

 

[Kiwi2671]

Hi Mr 168,
Thank you for the response - I am actually well aware of Table QW 451.1.
I am just unsure of why anyone would want to qualify deposited weld metal (GTAW) to 8" thick.
The "typical" use of very thick piping is carbon or chromolly steam piping in Power Stations and that is nearly always (at least in this part of the world)done with 1, 2 or sometimes 3 runs GTAW and balance with SMAW,
Regards,
Kiwi

 

[weldtek]

kiwi,
I'm with you on this but, on the other hand, when you consider that depositing say 3/8" thickness using GTAW yields 3/4" qualified deposit thickness and depositing just another 3/8" in thickness takes you all the way through 8" qualified deposit thickness, some may choose to do so for the increased flexibility.
The need may not come up often but if and when it does it's covered.

 

[Mr168]

Kiwi: Our most common uses for it in new plant construction are on weld repairs, and for heavy-walled orbital GTAW applications. Most of the heavy wall feedwater and main steam lines I've dealt with in recent years have been welded narrow groove GTAW in the field.