[TMPost]

Howdy,
We are in a new business installing helical piers (schedule 40 and 80 steel pipe - multiple diameters but 3-1/2" is common). We have a machine with a rotary head that screws the helix/pipe into the ground and most times we have to weld pipe extensions of 7' long to go deeper into the ground. Some of our piers already have couplings on them but some do not (depends on what we order). So, we are welding the upper pipe section to the coupler and/or welding a coupler to the bottom section and welding it all together - and then using the machine to drive the whole thing into the ground. We can have some pretty high torque screwing these piers into the ground and don't want to break the welds. Currently we have a generator welder Lincoln Outback 185 and using 1/8" 7108 Excalibur rods at 115-120 Amps. It has been suggested that we should be doing a quick burn around the pipe with 6010 and going over that with the 7018. We've tried that and broke quite a few welds and ultimately just started using the 7018 with better results.

What would you experienced welders recommend? There's a lot of information out there on end welding pipe sections together with a root pass, etc. but not too much that I could find on welding couplers and smaller pipe together (always the pipe is in a vertical position so we just chase the weld around horizontally).

Also, is it better for our application to be doing a fillet type weld or just to drag the rod around the seam of the coupler/pipe?

Thanks for your help...

[Coldman]

6010 rods are weaker at 60ksi and not even as strong as your parent metal. You don't want failure at the welded joint it should always be stronger than the parent. 7018 will do this for you as you have found. If you have good penetration, and a large enough well formed bead you won't have any problems.

[Poland308]

Are your couplers threaded and then your welding over the threaded joints?

[TMPost]

Couplers are not threaded. The pipe just slips inside and there's maybe a 1/16" gap all around or so depending on if we have to plumb it much before welding.

What about a fillet type weld or just chase the pipe/coupler seam around?

We will be putting about 8000 ft. lbs. on a couple pipes later this week and I'm curious if its going to hold - fillet vs. seam weld...

[Coldman]

Just to get the terminology right for my better understanding:
What you call couplers I presume they are actually socket weld joints. This is a valid, strong joint joint if the fillets are large enough. Generally at least two runs are required, more for larger sizes. As a general rule the leg length should equal the wall thickness of the coupler. Also the pipe should not be bottomed out in the socket, leave about 1/16" gap to allow for shrinkage.

What you call seam weld I presume to be a butt weld joining the two ends of pipe together. This is also a valid, strong joint if done properly in single vee butt edge preparation with included angle between 60* and 70*, 0-1mm land and gap 2-3mm. Full penetration weld with reinforcement both inside and outside.

Either method will do the job for you because the resultant weld, if done properly, will be stronger than the parent metal.

[Poland308]

Totally agree with ace. Last nuke I was at they required a 2 to 1 ratio on the fillets of a socket weld and proper pre heat. If this is a can't fail sorta deal. That may help with the stress your pipe sees.

[TMPost]

I'll try to post some pics so you can see exactly what we are doing. I seriously can't find any other information on what we do - so, any experienced input will be really helpful. We will be on a job tomorrow and I will take some detailed photos and then maybe you guys can further give some input. I appreciate what you have said so far. Thank you!

The couplers just slide over the pipe and cover approx. 1-3/4" of the end of the pipe - they are about 3-1/2" tall - pics will tell all and I'm sure you guys will get it right away.

[Poland308]

If you weld those type of couplings make sure you follow the above advice about not bottoming out the pipe in the coupler. That will cause a crack almost every time.

[Otto Nobedder]

I'll try to post some pics so you can see exactly what we are doing. I seriously can't find any other information on what we do - so, any experienced input will be really helpful. We will be on a job tomorrow and I will take some detailed photos and then maybe you guys can further give some input. I appreciate what you have said so far. Thank you!

The couplers just slide over the pipe and cover approx. 1-3/4" of the end of the pipe - they are about 3-1/2" tall - pics will tell all and I'm sure you guys will get it right away.

You are describing a "socket-weld coupler", as someone already said. The advice on fitting this, so far, is dead-on. Don't bottom them out like you're sweating copper pipe, as you need 1/16 - 1/8 " to allow the weld to shrink without compressing the pipe in the bottom of the joint (and placing the weld under significant tension before it sees any other load).

I would go 7018 all the way with this weld. 6010 roots in socket welds can be problematic when applying torque is the primary goal. Hell, it can be problematic when retaining pressure is a goal, if the welder is not highly experienced. You don't have a real gap to fill, so the main purpose of the 6010 is defeated out of the gate..

Steve S

[Poland308]

image.jpg (46.99 KiB) Viewed 1439 times

Snapped a few pics of a 2 in socket weld from today just for this line.
Middle pic is a tie in.

[Coldman]

I can't quite tell from the photos with certainty but it is possible that the horizontal bead leg length might be less than the vertical leg length. If so another run is recommended.

[Poland308]

Had to take the pics at a funny angle due to the sun.

[TMPost]

Great information - thanks for the tips. Here's a few pics from today of what we do. We did hold the pipe extension up about 1/4" from the coupler/bottom pipe and have started using only 7018. Had a 3 post section today that went down 21' in depth - 8000 ft lbs of torque on it and never broke a weld. It's brutal when you break one because it means digging with a shovel down to re-tack the coupler, and then pull the section up to where you can weld it again. I think we are on the road to never seeing a broken weld again. I really appreciate the insights and comments!

[TMPost]

oooppps, sorry for the sideways pics.