Fabricating 30" lobster back pipe elbows and welding with Pulsed MIG.

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So this is a little job i've just finished up that I thought might be interesting, especially since this is a 100% xray pipe job that is welded in a way that's not usual.This is for Munkel a little bit as he was asking a while back about running solid wire pulse uphill, Normally I would do this job with a Fronius TPS 2700 but that machine is out of action at the moment so I'm subbing in a Lincoln V-350 PRO running the .035 argon blend pulse program and an LN25 feeder instead, it doesnt do as good of a job as the fronius, but it does show that pulse can make vertical spray arc welding work pretty well.I've been fabricating and welding lobster back elbows made out of 762mm (or 30" in banana's) spiral seam pipe for a fire fighting water supply line in a coal mine.The job starts with a length of pipe with a centerline snapped 180 apart to get the centers for the patterns.

The patterns are done on a computer and printed up on A0 sheets that are taped together.

The pattern is wrapped around the pipe and the lines transferred through to the pipe with a center punch, the punch marks are then joined up with a paint marker to make the cut lines.

Once the length is marked out we take it outside and cut it up with a 9 inch grinder.

Jumping forward a bit just because I didnt take pics in order, this shows the basic setup to put an elbow together, get the bottom section level and square and weld it to the flood rails, then set each section on top and use a digital level to get them to the right angle.

the only problem is that being spiral seam pipe, it isn't flat, straight, square, level or round, so the sections are never cut exactly as they should be and the pipe is never round, this one isn't to bad, but sometimes the sections can be out of round by up to an inch.


I personally  just use a lever tacked to the pipe to get it lined up, sometimes if it's way out a dog and wedge is needed bu this is much faster and does the job 95% of the time, the smallfox wedge inn the prep is to get the angle just right.

The other fun part of being spiral seam pipe is even with good patterning the preps never line up, if it's only about by 1/4 inch your doing well, so once the angle is right you tack it together and knife the prep with a 9 inch hard disk to get the prep consistant all the way around.


Last edited by ttoks; 21 Hours Ago at 06:19 AM.
Reply:once I have a consistent gap with the right angle I bring the gap down to around 1/8", tack it on the outside of the pipe and put a small 1/8 bevel on the inside of the pipe.The root is welded from the inside vertical down running a lincoln V350PRO with .035 Hyundai SM-70 ER70S-6 wire on the .035 pulse program with an LN25 suitcase with 18% Co2, 3% O2 79% argon gas, the V-350 pro pulse program is not a synergic pulse program so wire feed, and pulse gross and trim are all set independently. the root setting I use is 500 IPM with the machine set to 550 (which the the machines estimate for a given wire feed, I often like it set higher than the actual wire feed setting) with a 1/4 stick out and the trim at the max which increases the pulse frequency and narrows the weld pool on the V-350 , this ends up being around 31.5 volts and 190 amps, this ends up not quite being a spray pulse setting, but it punched through the pipe fairly well even though i'm running the root downhill.Downhand part of the root

And the overhead/downhill part of the root.

And this is how much in punches through the pipe, around 2/3 of the way through all the way around as long as the 1/8 bevel and 1/8 gap is consistent.

And the root on all 3 joints for this elbow done.

Then I back grind the outside of the pipe again with a 9 inch grinder with a hard disk to get to clean metal.

I swap out my gas shroud for the cap as I run ALOT of stick out for the cap, going from the tip just inside the shroud.

To recessed in about 1/2 an inch.

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Reply:My stick out for the cap ends up at around the 30mm, or 1 1/4" mark.

And the setting are turned down, 400 IPM, with the machine set to 410, this end up being around 120 amp's at 28ish volts for the cap, this gives a true pulsed spray arc for vertical up, I run alot of stick out to get the overall heat out of the weld pool to make it easier to control going vertical up, but the pulse allows the .035 to spray even with the huge stick out and much lower amperage than would usually be needed for spray transfer, again I'd usually run a fronius TPS 2700 in pulse for this and that machine gives a mucher nice final weld appearance than I can get with the V-350.

Vertical section of the fill/cap on the inside of the elbow.



and vert section on the outside.

Running from 9-12 o'clock in one go.


And all done ready to go be painted and sent to site.

Last edited by ttoks; 21 Hours Ago at 06:24 AM.
Reply:Thank you for taking the time to document this work with photos and a detailed explanation.  Fascinating. Would plasma work for cutting the pipe, rather than a 9" grinder.  That grinder looks like a killer!Lincoln Precision TIG 185.Flex-Loc 150 torch.Super-Flex hose.Lincoln MIG 180.Victor Oxy/Act torch set.DeWalt Bandsaw with SWAG stand
Reply:

Originally Posted by ttoks

And this is how much in punches through the pipe, around 2/3 of the way through all the way around as long as the 1/8 bevel and 1/8 gap is consistent.


Reply:

Originally Posted by WenValley

Thank you for taking the time to document this work with photos and a detailed explanation.  Fascinating. Would plasma work for cutting the pipe, rather than a 9" grinder.  That grinder looks like a killer!