Failure in Bend Test-Combination Process GTAW+GMAW As per ASME Sec.IX-Procedure Qualification

[Quality2479]

Hi,

Good Day Everyone

Code- ASME Sec.IX
Process - GTAW+GMAW
Type- Automatic Welding
Pipe Size & Material - Dia 6" Sch.80 (10.97mm), SA106 Gr.B
Welding Consumable used - GTAW-ER70S-2 (Shielding Argon 99.997%) and GMAW-ER70S-2 (Shielding 80%Ar+20%Co2)
GTAW Deposition-3.8mm, GMAW-7.17mm
100% RT acceptable joint.

Inspite of clearing 100% RT of PQR sample, our test sample was failed in Bend Test and found with open cracks, we are not able to make it why?, the welding consumable selection was according to the Electrode manufacturer and process selection was as per the Welding machine manufacturer, all the welding parameters were recorded and found the Maximum heat input as 1.9Kj/mm.

Can any one advice on this? so that we can goahead with some changes in Procedure Qualification.

Thanks in advance.

 

[fegenbush]

This failure is common in short circuit GMAW. Please see the following article for information from the National Board

http://www.nationalboard.org/index.aspx?pageID=164&ID=179

 

[metengr]

I would suspect lack of fusion weld defects associated with the GMAW process (poor technique can also have it occur with the GTAW process). If you know the exact location of the cracks from the bend test sample, you should be able to determine if it was within the GMAW deposit.

 

[jimmy23]

It seems like you need to increase you WFS to increase amperage into the spray mode. I don't know your parameters but estimating a travel speed of 12 inches per minute and 22 volts, you end up with approx 170 - 180 amps. Too low for spray mode. Filling the joint with GMAW-S is not a good idea. You need the penetration of spray. Turn up the heat.....a good welder should be able to recognize good penetration. We have used STT (GMAW-S) for root passes on thousands of butt welds but never to fill and cap.

If you don't want to crank up the heat then change your gas to at least 90/10 or better yet 92/8 composition. It's harder to maintain spray mode with 20% CO2.

 

[jimmy23]

Sorry...missed the Kj/mm...thought it was 19000J/in. I would change gas.

 

[DekDee]

Quality2479,
As metengr and fegenbush have stated GMAW (especially short circuit) is susceptible to lack of fusion, both lack of side wall fusion and lack of inter run fusion.(both types of defects that can be missed with RT.)
Are they actual cracks or LOF - what did the laboratory state on your report ?
Try UT or a macro on the remaining coupon (either side of where the bend samples were removed.

I always maintain GMAW on anything above 8 mm needs to be welded as "hot" as possible to avoid LOF problems.
If it is a pipe welded with an automatic process I am presuming the coupon was in the 5G or 2G position - what was the torch angle ?
LOF in GMAW also comes from incorrect torch angle.

A bit more info - amps, volts, travel speed,position, torch angle and we may be able to help further,
Cheers,
DD

 

[weldstan]

If your GMAW process is at 1.9 KJ/mm (48.26 KJ/in)it is doubtful that short circuiting transfer is occurring. Most likely glpobular (near spray). Do check the voltage though to confirm. E70S-2 is not the preferred wire for GMAW for globular (near spray transfer). E70S0-6 will perform better.

Do address Metengr & DekDee and other re short circuiting transfer.

 

[gtaw]

There are several issues to consider regarding the welding conditions. The welding parameters, i.e., voltage, amperage, wire feed speed, and travel speed are important bits of information. Additionally, the position in which the welding is performed as well as the progression all provide insight as to how the test assembly was welded. We need details, the more the better.

Likewise, it is important to know the location of the defects that were observed when the guided bend tests were performed.

Assumes made by individuals trying to help you may be incorrect. We can only respond based on the information you provide.

Assumption:
Pipe welded in the fixed position.
Welding performed in multiple positions
GMAW transfer mode - short circuiting or pulsed (necessary for all position welding
Technique - unknown, but heat input suggest a weave technique was used.
Electrode diameter - unknown, assumed to be 0.035 to 0.045 inch

What else can you tell us?


Best regards - Al