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Comment by frankharv | Hacker News Reader

I really don't understand the build method they use. Ideally you would use a turntable to rotate the cylinder while welding the sections together with a sub-arc machine. https://www.youtube.com/watch?v=j-hfExEmGsE

Elon blaming "settings" seems like a silly explanation. There should be weld engineers and destructive testing done before the first beads are welded on an actual tank.

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I've set up automated welding cells, and the "settings" excuse sounds totally reasonable to me haha. There are indeed a million settings (weld weave pitch and amplitude, wire feed speed, linear feed speed, gas flow rate, amperage, etc.) that are hard to tune 100% correctly and don't have "analytic solutions" (i.e. you tune some values like a monkey until it gives the result you want). Seems like this tank failure was their "destructive testing," although most people would probably have used smaller samples to save money. As someone else said: pressure vessels are hard!

> Ideally you would use a turntable to rotate the cylinder while welding the sections together with a sub-arc machine. https://www.youtube.com/watch?v=j-hfExEmGsE

Uh, at least in the video that steel is pretty thick. Starships skin is slightly less than 4mm thick... while in that video they have a 2cm deep groove, would the same technique actually work?

For what it's worth, ULA stainless steel (<1mm thickness) upper stages are resistance welded instead https://www.youtube.com/watch?v=o0fG_lnVhHw&t=41m10s

That said, I think a lot of the decisions right now are based on "what can we quickly experiment with" not "what is a good long term plan". Building a 9m turntable (diameter of the rocket) would take a long time.

I agree a 9m turntable would take some time to make. But once made you could crank these vessels out very fast. 4mm skin sounds OK and I am sure there are some structural supports inside to keep it from collapsing. I am not a weld engineer so I cannot say if Sub-Arc would be the best technique. I know that ships skins are being built with it.

You’re talking about production engineering. You don’t really do that until your design starts to be nailed down. It’s not.

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