Why is Oxy Acet not good for structural work

[woodlandfarms]

I am quite a newb at all of this, but I read a comment in the post about electrical welding being an issue. My inexperienced response was to go Oxy, but another post suggests it would not work for structural work.

I thought all welding is in the end is melting metal to metal.

Is it because the torch heats a lot of metal, making it brittle over a large area?

Carl

 

[J_J]

About the only reason to switch from arc welding to oxy/acetylene , would be if you had a pace maker. Arc welding is forbidden.

 

[Gary Fowler]

As with any welding, you have to get both pieces to the melting point at least on the surface. Arc welding melts both pieces and the rod by only heating the surface and a small area directly under the arc. For OA welding, you have to bring the whole piece up to temp or at least part of it far enough from the weld area to reduce the heat sink effect so that you can keep the weld area at melting point. Imagine the BTU's that you would have to pump into a piece of 1" plate to get it hot enought to melt. With arc welding, you just have to strike the arc and it instantly heats the fusion area. As far as strength, properly welded, OA weld would be just as strong as the filler wire you used to weld with on mild steel material which is the majority of steel that is used in fabrication. Lots of still in service small high pressure natural gas line were welded with OA. OA welding came before arc welding. Higher alloys that have been tempered or otherwise heat treated would loose most if not all of that treatment with OA welding whereas with arc welding some of the heat treatment could be retained with a cold welding technique, ie weld a bit, stop let cool and weld a bit more.

 

[slowzuki]

Giant heat affected zone with O/A. Bad for cold rolled, not as bad for hot-rolled but not great. Very difficult to build fillets on large plate and weird fit ups with O/A. There's a reason why rivited boat construction was the norm up to electric arc took over.

 

[Tractor Seabee]

OA can be a lot slower if multiple passes are required due to material thickness. In my younger day as a pipefitter welder we but welded XH pipe up to 2" dia. We could do that in one pass around wher arc wopuld be at least 3. Then it was faster and no cleanup between passes. in later years I was one of few that could still do it well. Was called out to weld in places where the fire dept would not allow arc welding or the sparks spraying down from the arc were in compatible with operations below. Yeah it was hot work. I did a 8" vertical pipe runs that had a horizontal joints every 10'. They had a welder who claimed he could do it. They filled it with water and every joint leaked bad. The union sent me out to bail then out. Had to chip out every weld (no sparks allowed so grinder was out and it was 3" from the wall. The welds looked fairly good but the top pipe was welded but the weld was overlapped on the bottom pie and not fused at all. Horizontal withOA is the hardest posistion. That 8" pipe took a #6 tip to do in one pass and created a lot of sweat. 100+ welds later put the test on, 100% passed. No I did not do the chipping, the first welder got that job. I doubt he ever said he could do it again. This was all before MIG was usable for field welding.

I still use OA on lighter material when I can do in one pass. I have done 1/2" material in one pass but do not reccommend it. I was pressure vessel and ASME power piping certified for both OA and arc. Never did really like welding though preffered to work as the fitter.

Yes, I have an ac/dc arc welder also.

Ron

 

[Mark @ Everlast]

Not good for structural work? From my information, it is an approved process by the FAA...and OA has built some of the oldest equipment out there...including ships.

 

[JB4310]

I was just gonna say because it's nearly impossible to do, at least for me anyway. Consumables would be more expensive I believe, and how could you get any serious penetration??

It's got to be so much harder to master I would think.

JB

 

[Shield Arc]

OA can be a lot slower if multiple passes are required due to material thickness. In my younger day as a pipefitter welder we but welded XH pipe up to 2" dia. We could do that in one pass around wher arc wopuld be at least 3. Then it was faster and no cleanup between passes.

My brother-n-law was just telling me a few months ago that he built the oxygen acetylene system for the welding school at Hunters Point Naval shipyard, (early 1960s) he welded every joint with O/A. I asked him why he didn't Tig weld them. He replied O/A was faster.

 

[k0ua]

I am thinking that welding heavy thick steel with O/A is just not cost effective. The size of the tips need and the quantity of expensive gas required to heat it up may be doable but why would you want to when you can stick weld heavy things for next to nothing in cost? Am I missing something here?

James K0UA

 

[Mark @ Everlast]

O/A was used to weld heavy plate on ships and tanks and steam boiler works...before other processes were perfected. Nowadays its a little outdated, but it will never be replaced...

In school they taught us to O/A weld before they'd let us proceed to other processes. We had to pass 1/4" plates for the final with O/A...not thick, but most had practiced 1/8" exclusively.lol