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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