Interesting Welding Statement.

[AlanB]

I thought some here may find this interesting.

I am getting a large tank made for here at my day job.

The body is 8' tall and 5' diameter, made from 3/16 hotrolled.

So I was at the fabricators yesterday to work out some questions / problems and got to hang around to watch the body get formed.

3 guys, working real well together rolling a BIG (at least in my scale of things) sheet through a big roller.

So they get the primary rolling done, and get too the point where they are going to tack the thing together, and the guy goes out and gets an old lincoln Buzz box. There is a new Millermatic 350 digital Mig sitting beside the roller, plugged in. My point I am trying to stress is he went out of his way, to go get this thing and do the welding with 7018 stick. (DC+ by the way, Murex (by Lincoln) rods)

I could not stand it, so I asked the lead guy why, my teaching has always been that mig yeilds about 70,000 lb strength (same as 7018) and his answer was that the 7018 would be a more ductile weld and would respond better to running through the roller and getting the "roll" in the area as opposed to the straight edges you get on the leads of a sheet.

Anyway, in the 3+ days I have been welding I had never heard that one, and it was coming from someone that has been doing it at least 5 days in a row so I will assume there is something too it.

Just thought I would share, I have to ask the Lincoln guys now what the science is behind it, or is it just a shop belief.

[Inkomodius]

True! MIG welds are very hard and brittle. Any time I tack pieces together for slip rolling with a mig, they break if there is any deflection. Where as 7018, or TIG welding them provide a more maluable weld. I also learnt this from doing auto body, tack it with MIG then try to hammer form it, it cracks every time. Also if the vessle is a pressure vessel, I have never seen anyone use MIG to build them up here and up here all we do is pressure (mostly) because MIGs have a cold start and dont get full penetration off the start which usually leads to pinholes. Stick and TIG you can use your arc to preheat before applying filler metal.

[czechsonofagun]

That's very interesting. Thanks for sharing.

[crbr]

Originally Posted by Inkomodius

..........and up here all we do is pressure (mostly) because MIGs have a cold start and dont get full penetration off the start which usually leads to pinholes. Stick and TIG you can use your arc to preheat before applying filler metal.

Isn't full penetration dependant on the weld joint preparation? Full double bevel with (or without) backing?

Interesting thread and info.


I can appreciate info from those that have been there with stick in hand.

[alltoys]

Originally Posted by crbr

Isn't full penetration dependant on the weld joint preparation? Full double bevel with (or without) backing?

Interesting thread and info.


I can appreciate info from those that have been there with stick in hand.

Absolutely! In this case the Fitters are fitting the piece together 7018 will bend and distort if needed without breaking. Once the entire piece is put together with ends and those seams will be fitted with 7018 also I would assume. Once it is all together it could be welded with a Flux Core Mig on the inside then grind out the seams to expose the inside weld to the outside. There by welding it with a Flux Core Mig or by Stick from the outside making it a a full 100% weld.

[Flatheadyoungin]

I didn't make it to pipe welding level but my instructor always said something about MIG wasn't approved for pipe.......dunno.....

I broke out the ole' stick the other night and realized just how much I missed it......

[alltoys]

Originally Posted by Flatheadyoungin

I didn't make it to pipe welding level but my instructor always said something about MIG wasn't approved for pipe.......dunno.....

it......

Not entirely true. There are processes that allow MIG for pipe I know because I have been welding it for over 30 years. Some of the largest pipe lines have been welded with automated MIG process. These pipe lines supply oil from the high Arctic to the US through Canada. Also these procedures were developed by ASME - American Society of Mechanical Engineers, an American Government Agency.

Only thing about MIG is the cold start and for Tacking/fitting it is not desirable.

[Flatheadyoungin]

i recall him saying something about the automatic migs too....

i guess it just suprised me because i was always impressed with mig not having and slag to build up.....just all metal.......

Originally Posted by alltoys

Not entirely true. There are processes that allow MIG for pipe I know because I have been welding it for over 30 years. Some of the largest pipe lines have been welded with automated MIG process. These pipe lines supply oil from the high Arctic to the US through Canada. Also these procedures were developed by ASME - American Society of Mechanical Engineers, an American Government Agency.

Only thing about MIG is the cold start and for Tacking/fitting it is not desirable.

[Inkomodius]

Sorry I shouldnt have used the term full penetration it is an issue of lack of fusion. With MIG when you first pull the trigger your depositing material right away, however the substrate isnt fully heated yet and doesnt allow full fusion. Do a sample weld and cut out your start and it will most likely fail. With Stick you strike your arc, pull away slightly and it preheats without deposition allowing full fusion right off the start.

But as far as brittle, MIG is the most brittle.

And I have heard of people getting their MIG root ticket, however all procedures by the companies up here call for 6010 root 7018 fill and cap. Im not B pressure myself, nor do I want to. Ive been around it long enough to know none of the companies up here call for it or allow for MIG in their procedures, at least not yet.

[mbohuntr]

I was old school as well until I took a cert test with .045 hardwire on 3/8" plate DOWNHAND!!! I couldn't believe you could spray arc downhand and pass both a root and face bend!!! I guess you are never too old to learn...