GMAW shotcircuit - Lack of fusion

[W1987]

Hello everyone,

I have a question about GMAW short-circuit. This process was selected for some out-of-position joints, and it is not possible to use another process or change the transfer mode. We have encountered lack of fusion in these field welds.

I believe that increasing the joint angle, using more straight welds instead of weaving, and reducing the electrode extension (6–12 mm) could help improve the weld quality.

Can anyone share their experience on how to prevent this defect or provide recommendations for training the welders?

Thanks!

 

[DekDee]

Impossible to answer without relevant information.
Type of joint, material thickness, welding position/s etc.

 

[W1987]

The type of joint is double bevel side with back gouging (arc air + grinding), the angle of bevel varies from 50 to 60 degrees and the root opening varies from 3 to 4 mm.

The materiales thickness is 20 mm, it is a low alloy steel welding with ER110S-G, preheat is 120°C, welding positions are 2G (horizontal) and 3G (vertical).

All passes have acceptable visual inspection. The lack of fusions were detected by ultrasonic testing.

Thanks!

 

[Tmoose]

What up-to-date qualifications, if any, do your welders have?

Low Voltage Short Circuiting-GMAW

"Cold lap" is a constant major concern.

"One bad characteristic, however, is that the quick freeze puddle has a tendency to "cold lap" when not carefully deposited with the correct technique by a skilled welder. This bad characteristic is often why the process is written out of purchase specifications.

Because of the same bad characteristic, ASME Section IX applied special variables when the GMAW-S process is used. When qualifying a welding procedure, the variable QW-403.10 limits the base metal thickness qualified to a maximum of 1.1 times the test coupon thickness for procedure qualification test coupons less than l/2 inch thick. The variable QW-404.32 also limits the deposited weld metal thickness range to a maximum of 1.1 times the deposited thickness of the procedure qualification test coupon for deposits less than 1/2 inch thick.

The welding technique employed when welding the GMAW-S process is also unique. There are techniques for groove root pass and for fillet welding that will produce soundly deposited welds. But the technique is so different from the spray, globular or pulsed modes of transfer, that Section IX applies a special variable for the GMAW-S process for welder performance qualification. When qualifying a welder, the variable QW-409.2 becomes an essential variable which requires requalification of the welder if he changes from spray arc, globular arc or pulsating arc to the low voltage short circuiting arc, or vice versa. The variable QW-404.32 also limits the deposited weld metal thickness for performance qualification as noted above.

 

[David3399]

QW-403.10 no longer exists.

 

[weldstan]

GMAW-S is not recommended for such thicknesses and many owner/engineers place restrictions on thickness because of what you are experiencing. Qualify welders on 20mm thick coupons and perform bend test plus UT. Pulsed spray would be a better solution to your problem but it seems you cannot use it. Why?