Questions about Deep-groove Orbital GTAW Welding

[Guest102023]

We are looking at orbital welding to replace previously used SMAW for a number of thick-wall joints in carbon and low alloy steel, up to 24"OD x 4"T. Quality is at an extreme premium.
In my first cut analysis I came up with the following concerns:

1) At what dimension does narrow-gap become favoured?
2) Is variable penetration a potential issue on carbon and low alloy steel?
3) Will seam tracking be necessary, and if so, what type? (see 1 above)

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[Guest102023]

p.s., positions range from 6G on the largest welds to 2G and 5G.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[weldstan]

1. Narrow groove welding with automatic orbital GTAW is essential for your thickness to compete with manual SMAW or FCAW process. And it should be considered for T > at least 1.5"
2. Variable penetration can be an issue but proper selection of weld parameters (side dwell times, pulse frequency, etc. will mitigate the problem.
3. Seam tracking can be performed by the operator. I am currently unaware of which is the most reliable seam tracking system and I've seen mechanical, electrical and laser based systems.

 

[Guest102023]

Thanks weldstan,
My research tells me that oscillation is normally part of the NG approach. What are the complications with doing this in the 6G position?

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[weldstan]

Only that welding parameters are subject to change but the narrow groove orbital systems that I heave had experience with have multiple parameter changes available as the torch travels about the circumference.
Are you really planning to production weld in the 6G position or are you planning to qualify the operator in the 6G position? If the latter is true, my advice is to qualify in the 2G and 5G position

 

[Guest102023]

I would expect parameters to change throughout the 360° for most welding positions.
Work and therefore operator qualification will include 6G position. Full-scale mock-ups will be made.


"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[pradipgoswami]

Hi Brimstoner,
Your requirements calls for an all position Orbital Narrow-Gap welding system. For 4" wall thickness NGW is most cost-effective solution provided the right welding system is available. Trials for the optimized welding parameters would be required. For welding in any Narrow Groove Joint seam tracking is a MUST. Or else weld bead displacement, lack of sidewall/interlayer fusion are bound to happen. Weld Repair in a narrow groove joint is extremely difficult and nullifies the gained productivity.

You may find good guidelines at this website. Look at the Narrow Gap Welding Handbook.

Hope it will help you.

Thanks

http://www.polysoude.com/documentation-download/

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[Guest102023]

Pradip,
Thanks for those handbook links, they address some of the concerns I have, especially precise fit-up.
Looking at the designs again, the two 24"Ø joints in 6G position are only 2.2" thick, so narrow gap might not be necessary. The 6G position appears at this point to be the most challenging aspect.


"If you don't have time to do the job right the first time, when are you going to find time to repair it?"