Sub Arc welding

Date 12-03-2010 01:54

I wouldn't think it would pose much of a problem, plenty of tanks built with sub arc the very way you are describing out of 1/4" material. All that I have seen incorporate a backing ring on the joint. Bulk storage propane tanks are one example and they are pressure vessels.

By Tommyjoking (****)

Date 12-03-2010 04:03

I agree the vessel shop I worked in built lots of containment tanks as well. They would sub arc all the seams they could....they built some small tanks that I believe were around 12-14 gauge heads and all....those were sub arced as well. Just a matter of your wire size, power supply, feed speed and joint.

By 803056

Date 12-03-2010 20:59

We used to weld as thin as 3/16 inch thick material with SAW using copper backing in a single pass.

Al

By TimGary (****)

Date 12-04-2010 02:16

We used to sub arc 5/16" heads and shells in one pass, using ceramic backing tape.
Works real well, when every things right.
When it messes up though, it really messes up.
Spent about 2 weeks once re-inspecting (X-ray) numerous repairs caused when the backing tape peeled away from the inside of the vessel during the welding process.
Had to repair the repair of the repair.... etc.
No fun on that one.

Tim

By welder5354 (**)

Date 12-04-2010 21:00

Tim, how about if we welded the inside of the vessel first and then used the sub Arc process on the outside.
If that was the case, would we still get good fusion that would past X-ray.
I was thinking on welding the inside with GMAW, MCAW or FCAW. And then that first pass would be our backing.
tks

By TimGary (****)

Date 12-05-2010 04:51

Yeah, that's the sure way to get it done.
The thing about complete welding in one pass is it halves the labor cost.
It just takes good operators who know what they're doing, and someone watching the inside, ready to shut down the SAW, in case of trouble.
If you hand weld the root from the inside, I suggest MCAW.

Tim

By welder5354 (**)

Date 12-04-2010 20:54

Al, so how would you use copper backing on a round tank.

I guess your just talking about straight runs.
Lets say you have 15 ft long tank and your going to weld the longitudial seam on top.
How do you attach the copper strip underneat the weld that your going to sub Arc on top which will be
in the flat position for welding. This is all new to me, so i'm trying to get some ideas on tank welding.
Normally, i do pipe welding.
tks

By 803056

Date 12-04-2010 23:17

The longitudinal seam could use a 16 inch heavy wall pipe with a copper bar attached as the backing. The pipe would act as a beam for stiffness and support and the copper bar at the 12 o'clock position on the support pipe would provide the backing. Think "seamer!"

The circumferential joint between the sheel and the head could use a piece of woven metal mesh stretched loosly between two rollers. The mesh, encircles the two wheels like a mini conveyer belt. The belt would support a bed of flux which would act as the backing to prevent the weld from fusing to the woven mesh.

Best regards - Al

By welder5354 (**)

Date 12-06-2010 00:22

Tommy
Do you have any procedures tucked away as to what paramenters you used back then.
That would include wire size, flux type, power source used. Or do you have all this stored in the Archives
and never (or want) to be seen again?
Tks

By pipe hand (*)

Date 12-06-2010 13:09

i have run sub arc on pipe 10 inch and up std. and heavy wall mig root and sub arc out x ray a lot of welds we used 5/32 wire flux i don't remember.

By Tommyjoking (****)

Date 12-07-2010 03:47 Edited 12-07-2010 03:50

Sorry I very rarely ran the sub arcs, I worked as a fitter/fab most of the time and spent the rest of the time burning rods or wire. I know on the small tanks (very thin) they used normal welder size PS and run small wire like .032 or .045. The stuff that was 1/4 to 5/16 I want to say was a a .080+?? wire (long long time ago man). BUT I do remember they did not use any kind of backing. I reckon you could roll some test strips in a small diameter and try to figure if your equipment can do it before you start. The backing is a good idea if you cannot quite run fast or low enough to make it work otherwise If you had a good subarc operator there were few things to repair usually, they made tanks in that thickness daily. They of course pressure tested these tanks with a few psi of air and then used simple soap and water qc to check for leaks.

Sorry that is not much help