5 ms·

Maybe somebody can explain this to me. Welds are supposed to be tested at the weld level, not at the vehicle level. So what is wrong with their process or QA?

ceejayoz 7y ago
Isn’t the entire prototype part of the QA?
gpm 7y ago
I'm not a welder, but you're talking about A prototype that was manufactured in a tent and in a field, with welds being done in that field only a few days ago. I doubt much QA or weld level testing was done. A prototype on which they knew welds were less than ideal... And specifically a prototype of a rocket being built with new materials and new manufacturing methods. Rockets have the nearly unique distinction of having to be strong enough and no stronger because being stronger wastes mass which lowers the very important payload to orbit number. Bursting a few pressure vessels as they figure out where that point on the strength curve is seems pretty reasonable to me. We don't (yet) know at what pressure this burst at, if it burst near the total pressure needed to achieve their safety margin I imagine they will be ecstatic. I wouldn't interpret this test failure as a process, or QA failure without more information.
- redis_mlc 7y ago
  > A prototype that was manufactured in a tent and in a field, with welds being done in that field only a few days ago. I doubt much QA or weld level testing was done. What you're describing is how farm tractors are repaired, not how aerospace mfg. is conducted. You can't "test out" bad metallurgy, welding or mfg. in rockets.
  - gpm 7y ago
    What I'm describing is literally how this rocket was made... literally the whole thing is being live streamed by people living nearby with both 24/7 cams on the facility and frequent higher quality closer films and pictures being taken. Occasionally there are tweets from Elon about the process too. You are far from the only one who is skeptical that this is a valuable process, but there isn't any room to debate that it is what they are doing. Edit: Here is a recent timelapse of some of that welding, as an example: https://www.youtube.com/watch?v=J7bIvLhI1hY https://www.youtube.com/watch?v=J7bIvLhI1hY
    - jiggawatts 7y ago
      I keep thinking of the story "Have Space Suit—Will Travel", except it now it is "Have Welders—Will Construct Space Craft". What SpaceX is doing is both crazy complex rocket science, yet it's also quaintly pedestrian. It makes space feel more accessible to me.
  - thereisnospork 7y ago
    What's a rocket but a tractor with a few tens of thousands of lbs of fuel and oxidizer strapped to it? There's a reason SpaceX is eating "big aerospace's" lunch and tests like this are part of it.
- WalterBright 7y ago
  > Rockets have the nearly unique distinction of having to be strong enough and no stronger More precisely, airplanes are designed to being 50% stronger than the max load it would ever see. Rockets are designed to something like 10% stronger.
  - gpm 7y ago
    SpaceX is apparently aiming for a 1.4x safety factor: https://twitter.com/elonmusk/status/1215719463913345024 https://twitter.com/elonmusk/status/1215719463913345024 But my point here actually was the difference between "at least x times stronger than it needs to be", and "exactly x times stronger than it needs to be". Usually things are manufactured to the first spec, rockets are much closer to the latter spec because keeping weight down is so important. I suppose airplanes must also be closer to the latter spec than most things, but they should still be more forgiving than rockets.
frankharv 7y ago
You are right. At the very basic levels we have PT. This is a test with dye sprayed on the weld and a developer sprayed on to show the defects. This is very commonly done. Next we have UltraSonic(UT) testing. This requires expensive equipment and a good examiner to interpret. Third we have X-Ray. This is used on welds that are very important as it is also hard to do and interpret. It also requires the weld to be ground smooth to distinguish flaws from ordinary weld. I am sure there are a variety of other non destructive testing (NDT )techniques. These are the common ones used in industry. I do want to mention that pressure vessels are hard to make. Especially something so large. This could actually be a design problem and not welds. Pressure vessels are often tested at 5/3 their working pressure. So failures at testing are not uncommon.
- frankharv 7y ago
  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 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.
  - jeanvalmarc 7y ago
    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!
  - gpm 7y ago
    > 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 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 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.

ceejayoz 7y ago

Isn’t the entire prototype part of the QA?

gpm 7y ago

I'm not a welder, but you're talking about A prototype that was manufactured in a tent and in a field, with welds being done in that field only a few days ago. I doubt much QA or weld level testing was done. A prototype on which they knew welds were less than ideal... And specifically a prototype of a rocket being built with new materials and new manufacturing methods. Rockets have the nearly unique distinction of having to be strong enough and no stronger because being stronger wastes mass which lowers the very important payload to orbit number. Bursting a few pressure vessels as they figure out where that point on the strength curve is seems pretty reasonable to me. We don't (yet) know at what pressure this burst at, if it burst near the total pressure needed to achieve their safety margin I imagine they will be ecstatic. I wouldn't interpret this test failure as a process, or QA failure without more information.

redis_mlc 7y ago
> A prototype that was manufactured in a tent and in a field, with welds being done in that field only a few days ago. I doubt much QA or weld level testing was done. What you're describing is how farm tractors are repaired, not how aerospace mfg. is conducted. You can't "test out" bad metallurgy, welding or mfg. in rockets.
- gpm 7y ago
  What I'm describing is literally how this rocket was made... literally the whole thing is being live streamed by people living nearby with both 24/7 cams on the facility and frequent higher quality closer films and pictures being taken. Occasionally there are tweets from Elon about the process too. You are far from the only one who is skeptical that this is a valuable process, but there isn't any room to debate that it is what they are doing. Edit: Here is a recent timelapse of some of that welding, as an example: https://www.youtube.com/watch?v=J7bIvLhI1hY https://www.youtube.com/watch?v=J7bIvLhI1hY
  - jiggawatts 7y ago
    I keep thinking of the story "Have Space Suit—Will Travel", except it now it is "Have Welders—Will Construct Space Craft". What SpaceX is doing is both crazy complex rocket science, yet it's also quaintly pedestrian. It makes space feel more accessible to me.
- thereisnospork 7y ago
  What's a rocket but a tractor with a few tens of thousands of lbs of fuel and oxidizer strapped to it? There's a reason SpaceX is eating "big aerospace's" lunch and tests like this are part of it.
WalterBright 7y ago
> Rockets have the nearly unique distinction of having to be strong enough and no stronger More precisely, airplanes are designed to being 50% stronger than the max load it would ever see. Rockets are designed to something like 10% stronger.
- gpm 7y ago
  SpaceX is apparently aiming for a 1.4x safety factor: https://twitter.com/elonmusk/status/1215719463913345024 https://twitter.com/elonmusk/status/1215719463913345024 But my point here actually was the difference between "at least x times stronger than it needs to be", and "exactly x times stronger than it needs to be". Usually things are manufactured to the first spec, rockets are much closer to the latter spec because keeping weight down is so important. I suppose airplanes must also be closer to the latter spec than most things, but they should still be more forgiving than rockets.

frankharv 7y ago

You are right. At the very basic levels we have PT. This is a test with dye sprayed on the weld and a developer sprayed on to show the defects. This is very commonly done. Next we have UltraSonic(UT) testing. This requires expensive equipment and a good examiner to interpret. Third we have X-Ray. This is used on welds that are very important as it is also hard to do and interpret. It also requires the weld to be ground smooth to distinguish flaws from ordinary weld. I am sure there are a variety of other non destructive testing (NDT )techniques. These are the common ones used in industry. I do want to mention that pressure vessels are hard to make. Especially something so large. This could actually be a design problem and not welds. Pressure vessels are often tested at 5/3 their working pressure. So failures at testing are not uncommon.

frankharv 7y ago
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 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.
- jeanvalmarc 7y ago
  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!
- gpm 7y ago
  > 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 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 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.