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I have just seen an awesome demonstration
with MIG using 3% Hydrogen and 97% Nitrogen as the gas and the Hydrogen allows
the weld to go much faster and deeper penetration. It was done by BOC
(British Oxygen) . The hydrogen gets rid of any oxides etc. Very
impressive. However this was with gas flooding of the back of the weld. Hugh From: owner- Hi Jim. Thanks for that. I haven't done a
lot of MIG welding so was just curious. My vessel is TIG welded on all the
roots and stick weld cover passes with E7018 but that's because I'm just an old
guy and it's what I have the most experience with. Plus, I don't have a MIG
machine. I too have seen cracked welds and always thought it was from not
pre-heating. I like laying down the TIG roots because I can see it good (
again, getting old and blind ) and it's easy to clean up for the next pass. I just
take the torch and heat the area up a bit, lay down a bead and then clean it up
with a wire wheel or grinder for the next pass. I usually take the drill and
knock off a little where I stopped so I've got a nice clean place to start
again. It sounds more complicated than it is. Like most things, good
preparation makes the job go smoother and there's less back tracking. This is
especially important with welding. It really sucks when you get a weld you
don't like and have to gouge it out and do it again. I know that the iron
workers are all using flux core machines now, and that's all critical stuff
making buildings etc. The guys doing pressure vessels I've seen, do it the way
I'm doing it, but that's in the field. I think the production shops use robots
to weld tanks but I've never seen it. I was doing a job at NASA once and these
guys made a tank right there in the dirt from 1 inch stainless. It was
quite a task. The end cap was the best. They had a bunch of pre-formed pie
shaped pieces, and TIG welded all the roots. After several passes with that,
the last cover pass was stick. This thing was 12 feet across with domed ends,
and about 25 feet long. The one end was on a track and moved into position with
big flanges and O rings and pneumatic clamps. It was used as a vacuum
chamber to test the satellites they were going to build. Really cool
watching that job progress. These were "boilermakers" doing the work.
Very cool. Kind of looked like a big psub hatch! Frank D.
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