Mig Weld as strong as Stick Weld??

[jvo]

Okay guys, this is a professional question from my workplace. This is not a sheet metal welding question, but I know there's a lot of welding experts in the background here on this site. Here's the problem. At the location, of which I am the branch manager, I hired a fella that's an all around handy man. He is very proficient at welding and fabricating, and we are in the process of apprenticing him to be a heavy duty mechanic. He just finished building a piece of equipment for us that will enable one of our tandem axle 8 wheel air boosters ( a set of 8 wheels ), that will hook onto the back of an oilfield drilling rig which is on its own set of 16 wheels. This rig is about 30 years old, and the only way to be able to hook more wheels onto it so we can legally pull it down the road is to engineer our own solutions. I will also add that the design is proven, as we are building it the same as the one we used at a company I worked for about 10 years ago. They are one of our competitors and the narrow minded fellers won't lend us their bracket to use when we move that particular rig. We sent a couple guys out to measure the back end of the rig, and we built a "bracket" that pins onto the rig, and also pins onto the front of our 8 wheel booster. The booster bracket has a 10 inch by 10 inch box tubing beam that has a half inch wall thickness, and this beam is 8 feet long. We cut some plates about 3 feet tall out of 1 inch thick material, and those plates will have 2 and a half inch diameter pins through the leading edge of them to pin to the back of the rig. I am trying to describe this so you realize it is quite large. When fully loaded the 16 wheels will have a gross weight on them of more than 65000 lbs. and the 8 wheel booster will have more than 25000 lbs on it. This bracket holds the booster to the rig. The fella that did the welding on this bracket did the job with a Miller 250 mig welder. Our equipment manager from our head office came by yesterday and was very impressed with the job that we did, but had to complain that we should have stick welded it, as it would have been much stronger. My man, Frank and the certified welder from the other branch got into a discussion about this, and Frank told him that Caterpillar and many other big companies use mig welding to build their big equipment. He also tells me that most of our heavy haul trailers are built using mig welding techniques. So......, my question is fairly obvious. Is there that big an advantage to using a stick welder or does the mig work just about as well? Sorry this isn't a sheet metal question, unless you consider it is 1 inch thick sheet metal being welded to a half inch thick piece of box tubing. Thanks for any responses. John V.O.

[norm]

if it is done correctly

mig is just as strong as arc welding

[jlrussell4]

Hi John,

Here is what I have always been told. IF it is done correctly, the mig is as good as a stick weld. The problem seems to come from the fact that a mig weld can look good without proper penetration. Welding with an arc welder usually gets good penetration. I guess the great equalizer in all of this is the weldor (he who does the job).

[Dawai]

No bevel, no assured penetration. When you watch the back side of a proper penetrating weld it almost falls out.. I have been inside tanks with them welding the outside.. when it all flows together, the right heat.

I don't have a nice mig, I have a small underpowered home unit. A Lincoln 135 220 volt with Argon.. did have tri mix, ya know where it had oxygen to heat up the welds and promote the fusing together? Doing mostly sheetmetal here so the trimix had to go.. hole, hole, hole

I don't trust the lil mig for structrual welds over 1/4" thick.. I'll grab my stick.. or my tig.. mucho more preperation on the tig welding thou.. must be clean enough to eat off of

What the heck do I know? I have made my career as a industrial electrican, almost blind at times.. weld by sound..

[Boogiemanz1]

When I worked in the oil field everything was stick welded. Several of my friends work building heat exchanger units which weigh 100,000 lb or more....they will not accept anything but a stick welded joint on the lifting lugs, even though the rest is mig welded..............john

[Hairy-Neil]

When I worked in the oil field everything was stick welded.............john

You don't see many boilersmiths using a MIG either. ;)

[captainkirk]

I also have seen really good "looking" MIG welds fail because of a lack of penetration.
I think rather than say one is stronger than the other which is an incorrect statement the fellow should have said, that it has been his observation that the MIG welds he has seen have been lacking in proper penetration and therefore he has a lack of faith in their being as strong as the ones he has seen done with a stick welder.
It is more a statement of "faith" than it is a statement of strength, but it is fair to say that most projects that require high strength welding would have less of a chance of failure if stick welded rather than MIG welded due to the stick tending to be more forgiving of a less than "perfect setup".
Its kind of like saying is it better to cut down a tree with an axe or a Samurai sword. The sword in the right hands will take down the tree just as effectively but finding just the right set of hands is the hard part, and if everyone standing around is named Fred, Bob, Stanley etc. the wise decision would be to employ the axe. It's just a better bet, same with the welding issue likely the stick weld is just a better bet. especially if your the one standing at the bottom of the hill when this thing is moving.

[rsanter]

seems to me the issue of a strong MIG weld is the penetration. it would also follow that the thicker the material you are welding the bigger the MIG you need and the bigger the wire you need.
1)I belive it comes to economics. look at the cost of the arc welder rated to do the job and a MIG rated to do the job.
2)the other point would be that of inspection/verification. for certified work you will not want a process that can look good and not be good. for inspection procedured you will want to have a process where the visual result has a direct correlation to the quality of the product.
3) I have seen the mig weld process used for very thick material, however the units I have seen are automated and will not only use a shield gas but will also deposit a carbon type sand over the weld area as it welds to prevent excess stress in the weld area due to faster air cooling

bob

[jvo]

Thanks guys, that's what we needed to know. Frank did bevel all his joints when he welded this thing up. Sounds like its definitely not inferior if the proper steps are taken. We'd be glad to stick weld it, but they barely gave us a mig welder, let alone a big stick unit. The biggest reason we did this to begin with, is that we get stuff done here. If we waited for head office, it would be another year, (that's how long we've been waiting for this till now). Thanks again. John V.O.

[Gene_Olson]

You need the right rod too.
Sometimes in repair situations it is impossible to get at the weld area really well for weld prep.
Then something like a 6010 rod (DC) tends to burn in pretty good in spite of some rust and dirt. Given the same situation the mig would have left a pretty looking bandaid blister on top.
This is not to say that you shouldn't be prepping the weld area.

G.

[seven]

Hi All,

Nothing wrong with MIG. In fact it's a low hydrogen process so the welds may well have a higher strength than a conventional stick weld.

Below is a pic of one of my little babies. A BS 5500 Cat 2 (10% X ray) pressure vessel, about 20 feet high, made in 1/2" plate and MIG welded. The lower pic shows a weld tee. Silver areas are where the slag has been removed.
Hope this is of interest.

Cheers,
Paul G