The welds you speak of are little or no no different than welding the cast iron pots together as they are all made in-house. The life-size crane rails they moved on were about as ridiculous of a repair - neither were "allowed" to fail really as lives on the floor were at stake - and enough paid the ultimate price too... I also always got a kick out of the submerged stuff as you do not see a lot of that, but boy can it be pretty and penetration? errr... Yeah - they make boilers and pressure vessels frequently with the submerged processes - as gas just ain't good enough.
I have been out of any that sort of super high tech stuff for a lifetime now, so not much do I recall. GM still uses that process to make the pots though, saved them several months of labor and they got a better product. What always scared me though was in process repairs they would do - water cascading down a pot to keep it cool and they'd get up there at a burn through spot and hold a piece of quarter inch plate to divert most of the water and make a bit of weld and pull the plate back really quick-like, so the pot did not overheat and blow (the molten cast iron) through in front of them. I was so glad I never got to "try that one." Better to explain (or more likely nod head in a conference room) than do that sort of thing! It took a lot of nerve in the foundries.
Assembly, totally different; almost comical. I have a set of photos somewhere showing me with a giant gaggle of robots leaning in with them to make welds for a robot that had gone on the fritz and they did not want to stop the process. I was simply running mild steel, MIG with Argon CO2; something anyone should be able to do if they have any desire at all..
