Sequence Back Weld

[nabeel3]

Dear All

Our Company is planning to start welding for 12 mm shell in a carbon steel A 36 Tank. For getting complete penetration we have to do back gouging and weld. After how many pass in the front side shall we back gouge and do back weld. This question arises due to consideration for welding distortion. I have read some where that proper weld sequence will reduce distortion in the weld metal. Or is it enough to finish weld in face side and then go back and do back weld.

Regards

 

[Dhurjati Sen]

Your fabricator would know best, and then the welders.
However, the fit-up is more important than the welding sequence.
Still, after the root from any side, simultaneous welding from inside and outside would minimize distortion to a great extent.

 

[nabeel3]

Hello Mr Sen

The requirement is to grind the root pass , Do DPT and then back weld. Is it OK to grind and weld from back side when welding is ongoing in front side. I mean when the root pass is lost

 

[Dhurjati Sen]

You can grind the root pass and do back gouging too. Also LPI of the root.
Then simultaneous welding from both sides would do no harm.
But, what is the tank service?
Is it not going for too great a quality, or the client / regulations demand it?

 

[nabeel3]

Sen,
Water tank

 

[r6155]

Try with 6010 electrodes and avoid gouging.

 

[nabeel3]

Try with 6010 electrodes and avoid gouging.

If i avoid back gouging with E6010 , will it be considered as full penetration weld

 

[r6155]

6010 is widely used in pipes, making it impossible to access the interior.

 

[weldstan]

Why would you want to use manual SMAW on a 12 mm wall tank? This is far too inefficient. Most tank manufacturers use ASAW for the circ seams and FCAW for the vertical seams. Finally welding from one side only with E6010will no t decrease distortion,

 

[gtaw]

You didn't mention the governing standard, but all the fabrication standards I've worked with require CJP welds to be made with backing, double sided groove welds that have been back gouged and back welded, or the WPS for CJP without either backing or back gouging must be qualified by testing.

As for the welding process, FCAW is viable for shop or field applications. Gas shielded FCAW typically has superior low temperature toughness and produce less fumes (smoke) when compared to self shielded FCAW.

The back gouge operation can be by grinding or carbon arc gouging. There are other options, but the two mentioned are used extensively.

The back gouged root can be checked using magnetic particle testing with dry magnetic particles to ensure the back gouge is deep enough to have sound metal. MT is cleaner and faster than penetrant testing and it eliminates the possibility of contaminating the root with oil based penetrant and the potential for porosity if the penetrant isn't completely removed prior to back welding.

Just my thoughts on the subject.

 

[r6155]

More data: tank diameter / height, wind, seismic, type of roof, corrosion, API 650?