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Engineering assessment of the OceanGate Titan failure

65 points by harambae 3y ago

rich_sasha 3y ago
I know nothing, literally nothing, about material engineering, past what I can skim off wikipedia and ingest on cycling websites. But I always thought composite nonmetal materials are hard to test nondestructively, which is the main limiting factor for their use in aerospace. Metals can be X-rayed to assess their condition, carbon not. Is that wrong? What am I missing? Just curious.
- ceejayoz 3y ago
  I don't think you're missing anything. Others, including those in-the-know, were left scratching their heads too. https://www.nytimes.com/2023/06/20/us/oceangate-titanic-missing-submersible.html https://www.nytimes.com/2023/06/20/us/oceangate-titanic-miss... > Years before OceanGate’s submersible craft went missing in the Atlantic Ocean with five people onboard, the company faced several warnings as it prepared for its hallmark mission of taking wealthy passengers to tour the Titanic’s wreckage. > OceanGate’s director of marine operations, David Lochridge, started working on a report around that time, according to court documents, ultimately producing a scathing document in which he said the craft needed more testing and stressed “the potential dangers to passengers of the Titan as the submersible reached extreme depths.” > Two months later, OceanGate faced similarly dire calls from more than three dozen people — industry leaders, deep-sea explorers and oceanographers — who warned in a letter to its chief executive, Stockton Rush, that the company’s “experimental” approach and its decision to forgo a traditional assessment could lead to potentially “catastrophic” problems with the Titanic mission.
  - ramesh31 3y ago
    My question is just... why? It's not like carbon fiber was any cheaper than just making the thing out of steel or titanium like literally every other submersible. It just doesn't make any sense. You have none of the weight penalties that exist in aviation, so the heavier and the thicker the better.
    - SV_BubbleTime 3y ago
      As I understood it, you do have a weight penalty for a sub. You need to get back up by powered movement, or down by it. You are limiting your dive time either way. They can’t use foam for flotation at that depth. There is a concrete like “synthetic foam” if you want unpowered rise to surface but it’s expensive. I read early on they wanted carbon to be light enough to get back up by releasing weights on powerloss. From what I have seen of the hull, it was a tube. I can’t remeber seeing a view with a complex or even drafted shape to it. I suspect that spinning carbon by fiber would take far too long, and think they probably used narrow weave to do it. It would have been cheaper than the required thickness of titanium, which is the same strength as steel, but 40% the weight and still a little heavier than aluminum. Who knows!? Nothing they did showed that they ever chose the more expensive option. Carbon was likely just the cheapest thing they could use for their goals.
      - hef19898 3y ago
        Especially if you buy your material because it is past shelf lofe, don't use an autoclav and forgoe curing. Fun experiment: Take a roll from some toilet paper, squeeze it somewhat evenly at the ends. It is kond of stable. Then peel the layers apart, ans squeeze again. The same would happen if the composite tube delaminated at one of the end cap rings. This whole thing is beyond infuriating.
        SV_BubbleTime 3y ago
        > don't use an autoclav and forgoe curing. I haven’t read that. But, that’s not an option. Carbon won’t just cure on its own, ever. It will be a shitty sticky mess forever. It had to be cured somehow. As to the carbon expiration. I don’t know what that was. I suspect it could be epoxy like in prepreg, but I doubt prepreg here. And it could be shelf life of the carbon itself as it can be hydrophilic in some cases.
        buildsjets 3y ago
        Allegedly, they bought expired (out of freezer time) prepreg from Boeing Surplus. Boeing has released a statement that they have no records of this, so it likely passed through a third party before he acquired it.
  - rich_sasha 3y ago
    I was more referring to TFA which seemed to assert that you can test carbon fibre, with some kind of EM radiation. That it was all a mess at OceanGate, that bit I got :)
- 2-718-281-828 3y ago
  well, a carbon frame is trash after a single crash even if it seems alright due to microscopic fissures. that's also the point cameron's making. the compound carbon material will progressively deteriorate with every dive due to the immense pressure difference from surface to target depth. extremely small deformations cause tearing and delamination. so small you can't see it. but one dive too many and it just cracks.
- icegreentea2 3y ago
  You can ultrasound and radiograph CF to do NDT. I think the challenge is just more that we have over half a century headstart working with Al in aircraft to understand their failure modes and how to adequately test for them. Our understanding of CF (+CF's inherent nature of having more sudden failures) makes designing adequate NDT regimes more challenging. That said, we are seeing much more CF (and CF composites) being deployed into commercial aerospace (famously the 787 wings, but also the A350,
  - hef19898 3y ago
    The whole fusselage of the 787 and A350 is composite, not just the wings. Composite wings are old news. Strutural repairs are tricky so.
- buildsjets 3y ago
  The typical method to inspect composite parts is through-transmission ultrasonic. Essentially, two streams of water are aimed at the part from opposite sides, one stream of water has a ultrasonic generator embedded in it, the other side has a transducer, and you scan/raster the stream of water across the part to inspect it. There are limits on how thick of a part you can inspect with this method, and this hull significantly exceeds how thick we would use these materials in aerospace designs.
  - buildsjets 3y ago
    Here's an example. Appears to be inspecting a CFRP jet engine fan case, which are some of the thicker composite layups you see in aerospace. The way this method of inspection works, you also have to fabricate a part with known defects of various sizes (simulated with a little piece of Kapton tape in the layup) in order to determine the minimum size defect that the machine can detect for a given type of part. https://tecscan.ca/ultrasonic-testing-defect-sizing-in-composite-structures/ https://tecscan.ca/ultrasonic-testing-defect-sizing-in-compo...
MobileVet 3y ago
> From all available sources, it is apparent that the viewport was designed and certified down to a depth of 1300 meters, not 4000 meters. Wow. What kind of hubris could look past that huge red flag? Apparently the kind that thinks it is interesting that it deforms by several inches and not scary
- jamincan 3y ago
  It's pretty much 1/3 the depth which is suspiciously close to a 3x safety factor which is what I've always heard engineers use. They certainly seemed cavalier with safety, so it wouldn't surprise me if they reasoned about it in that way.
  - hef19898 3y ago
    And there is a reason it is called safety factor. Whether it is 10, 5, 3 or 1.1 doesn't matter, it is not be used.
  - SV_BubbleTime 3y ago
    A rocket might have a factor of safety of around 1.1. This is because at 1.3, they’ll never leave the ground. This is why they are so carefully monitored and tested, and still fail. It’s all relative. Good engineering doesn’t mean higher number. No one knows what the FOS for this sub was. Given the information from the CEO, things like that were just slowing down innovation! EDIT: Not all rockets, just using an example.
    - plegresl 3y ago
      Falcon 9 uses a factory of safety of 1.4: https://www.nasa.gov/pdf/164283main_2nd_exp_conf_24_Commercial%20Opportunities_SpaceX_MrEMusk.pdf https://www.nasa.gov/pdf/164283main_2nd_exp_conf_24_Commerci...
    - 2-718-281-828 3y ago
      very interesting point!
- 3y ago
hef19898 3y ago
After an initial reluctance to follow this story, mostly due to the hysterical media coverage of a pointless rescue operation, my engineering half of my brain got interested. I am by no means a materials engineer nor a naval architect, but I was involved in some Design FMEAs and wrote thesis about the manufacturing of structural, pressurized aerospace carbon fiber parts. Some things I came across, which are in line with the article and the first spurce video: - The view port was not rated for the intended operating depth, if true I am out of words... - the pre-preg material was apparently beyond shelf life, if true almost as bad as the view port. When pre-preg is beyong shelf life, the resign doesn't reliable bond anymore. That means basically delaminated layers before the "vessel" saw water for the first time - 480(!) layers of carbon fibre, that carries the risk of prematurw dryong of the resin during production. Impact, see above. - not curing and no auto-clav, again with the same results as above - The mating rings for the emd caps have been glued on. Nothing wrong with that per se, but a bond supposed to sustain repeated dives to 4,000 m needs to be very precise. Ocean Gate applied the glue manually by hand, with inconsistent thickness in a non-clean enviroment. No idea to which tolerances the CFC hull and rings have been machined, but based the video of the bonding (they used chains attached to gate crane) they didn't seem to be too precise. The results are a high potential of foreign objects and debris being glued in, non-defined wiggle room between the CFV hull and the titanium rings and end caps and yet another strucural weakness of the vessel. - they also used titanium fibre. If trued, it doesn't matter because the preasure was applied from the outside, all the tensile streangth of carbon and titano fibers only worls against preasure from inside the vessel. - No back-ups, exposed wiring at the outside, flamable material at the inside, no telemetry, no emergency beacon, only wireless (!) controls (and they didn't even do enough testing to find key mapping errors of their Logitech controller...) - Despite claiming otherwise on their homepage (archive.org still has it) they did attach equipmwnt directly to the carbon hull on the inside by screwing (!) to the hull. Result, all the fibers cut by the screws don't take any load whatsoever anymore, increased risk of delaminations (the hull is compressed, the screw on the inside isn't) - Safety culture: completely absent, to the point of being proud about it. Unable to distinguosh between vessel certification and proper operations (there is a reason that aerospace certifies the design, production, maintenance and operations organisation seperately), firing people raising concerns, I am out of words here.. - The vessel can only be opened from the outside (!), so even a perfect dive can lead to suffocation is the vessel isn't located fast enough... I could go on, but calling this abomination "engineering" is an insult to the universe. Finally, some potential failure modes: - the view port (obviously) - the hull (delamination, stress, bad material, intentionally induced defects...) - the bond between the rings for the end caps and the hull (weakened bond due to different deformation of the two materials, weak bond due to foreign objects, inconsistens bond due to bad application of the glue...) All in all, from design over manufacturing to maintenance and operations, this thing was a death tral whos only upside was a quick death in case of an implosion.
nonrepeating 3y ago
One can take comfort from this in a perverse way. The failure of the submersible was entirely predictable and should surprise no one. The alternative would be more troubling.
- JKCalhoun 3y ago
  And perhaps like the Tacoma Narrows bridge it will end up being a cautionary tale for future engineers.
  - throwway120385 3y ago
    The kinds of people who make these stupid decisions are never the same people who actually learn lessons the easy way like you're proposing.
    - Arrath 3y ago
      This case was kind of the exception that proves the rule, beyond the 4 others caught in it.
    - tivert 3y ago
      > The kinds of people who make these stupid decisions are never the same people who actually learn lessons the easy way like you're proposing. It's quite possible it could lead to new regulations that would make similar stupid decisions illegal. It might be time, it sounds like the whole human-occupied submersible industry is entirely unregulated.
kodah 3y ago
> It was previously stated by the CEO that each time he descended to that depth, the viewport deformed several inches inward. It takes an incredible level of density to ignore this once, but multiple times? Can someone tell me what happens to a human body when suddenly exposed to ~5000 psi? Edit: I looked it up. The human body almost instantly incinerates. It takes a matter of milliseconds.
- moritonal 3y ago
  You know how you're generally accustomed to being somewhat solid? Imagine you were now liquid.
- longitudinal93 3y ago
  From what I've read here your body is suddenly exposed to the equivalent pressure of 100 fully loaded semi trucks sitting on you, while simultaneously the sudden compression of the air would cause a brief flash with a temperature equivalent to the surface of the sun. Mercifully you'd be turned to goo within a split second.
- myself248 3y ago
  I love the expression "you stop being biology and briefly become physics".
- anon_cow1111 3y ago
  >Edit: I looked it up. The human body almost instantly incinerates. It takes a matter of milliseconds. This is most likely BS- consider that a shotgun shell is made from a low melting-temp plastic and handles higher pressures and temperatures without issue (and repeatedly if you're reloading them). Probably your hair and light clothing would burn somewhat during an implosion, but would be extinguished as soon as the water hit it. Then it would stop being hair and light clothing just due to the kinetic energy of water hitting you at cannon-ball velocity.
  - kodah 3y ago
    Feel free to give this a read, it has an answer for your assertion about waters role: https://mindofjp.medium.com/what-really-happens-to-a-human-body-at-titanic-depths-3f46ab545e0e https://mindofjp.medium.com/what-really-happens-to-a-human-b...
pugworthy 3y ago
> It was previously stated by the CEO that each time he descended to that depth, the viewport deformed several inches inward. Dear lord even if it is/was supposed to do that, this would be disturbing to look at.
- Arrath 3y ago
  I can't imagine a shorter path to making my lizard brain scream "SURFACE NOW"
AdamH12113 3y ago
> It was previously stated by the CEO that each time he descended to that depth, the viewport deformed several inches inward. Is that normal for a submersible viewport? I feel like that's probably not normal.
- parl_match 3y ago
  At those pressures, it's not particularly unreasonable for their to be flex and shift in materials. That would be baked into design, maintenance, and monitoring. However, the lack of safety culture, testing, or modeling is more red flags than a communist rally. More succinctly: It's probably "normal", but OceanGate didn't know if it was "normal".
gcanyon 3y ago
"each time he descended to that depth, the viewport deformed several inches inward" That's gonna be a no^∞ from me.
toss1 3y ago
>>Consider the fact that most engineers can explain the cause of ..., and the space shuttle Challenger disaster (where Morton Thiokol was told to take off their engineer hats and put on their manager hats when considering O-ring temperature certification). The money phrase: >>take off their engineer hats and put on their manager hats This is what kills people. To boil it down to one short course in engineering ethics: Whenever anyone tells you to do act like a manager instead of an engineer when making a technical decision, tell them, in no uncertain terms, and as politely or impolitely as needed to make the point: to fuck off; physics is physics, and neither knows about, cares about, nor yields to human concerns. (Unless, of course, you are OK with living decades of your remaining life after the accident knowing you accepted a blood-money paycheck to do bad engineering.) Is your current job, or your company's immediate future worth possibly killing people?
coffinbirth 3y ago
[flagged]
engineer_22 3y ago
This isn't an engineering assessment, at best it's speculation about what caused the loss of the Titan.
- hef19898 3y ago
  Whatever the exact failure mode, it was the most dangerous thing that let to Titan's destruction and the death of five people: the combination of stupidity and hubris.
  - engineer_22 3y ago
    Speculation
    - hef19898 3y ago
      Of course, we have to wait for the various investiagtions before we know for sure.
ghostpepper 3y ago
> Consider the fact that most engineers can explain the cause of the Hyatt Regency walkway collapse (if you can’t, you shouldn’t be an engineer), the Tacoma Narrows bridge failure, the Union Carbide Bhopal disaster, and the space shuttle Challenger disaster Does anyone know of a good documentary about famous engineering failures? Bonus points if they actually go into detail about the scientific explanation, as opposed to focusing on the human failures
- philjohn 3y ago
  Fascinating Horror and Plainly Difficult are OK - Plainy Difficult tends to go more into the mechanics of disasters, but both are operating under the constraints of a 10-15 minute YouTube video.
- hef19898 3y ago
  One thing that cannot be stressed enough, every system (I like the systems engineering way of thinking that goes beyond the single product to include everything from operations to maintenance, I come professionally from the point where Supply Chains meet design), every engineering project has to account for operating procedures, manufacturing procedures, training and human factors. In all seriousness, the series about Chernobyl is great in driving that point across.
- tylergetsay 3y ago
  There's a podcast called "well there's your problem" that covers them. their style isn't for everyone but I find it very entertaining
- tzs 3y ago
  I don't think it is currently available on streaming or disc, but if it ever becomes available again the TV series "Seconds from Disaster" [1] would be a good choice. It is excellent. [1] https://en.wikipedia.org/wiki/Seconds_from_Disaster https://en.wikipedia.org/wiki/Seconds_from_Disaster
toss1 3y ago
I own a carbon fiber design & manufacturing shop that does aerospace and undersea work. Watched the video by "Just Alex" and the section the bonding of the titanium end-caps and the cylinder absolutely gave me the creeps. The video was absolutely right to mention lack of dust-free environment (vs open warehouse), lack of temperature control, and lack of degassing equipment. We also have no idea about the properties of the epoxy used to bond it, whether it has the suitable amount of compliance, properties under temperature change, etc. Worse yet, I saw no precautions being taken to avoid entrapped air in the bond, in fact, it seemed quite likely, and the sections with entrapped bubbles would be NOT bonded. Same for any sections with entrapped dust, debris, or whatever else was floating around that warehouse. I would want to see, along with the all of the above steps, either or both applying very substantial pressure to the Ti/Carbon parts while curing to force out any air, and/or doing the whole process in a vaccum environment. The out-of-date carbon fiber? Sure, it is fine, for some months, for noncritical applications. For critical applications? NO WAY. And the CEO's claim that aerospace needs to be more stringent than undersea 5000psi is just beyond stupid. You need absolutely the best bond between layers that you can get. Also, the 480-odd layer layup and cure is hugely experimental by itself, and I've read elsewhere that the shop was given six weeks to design and fabricate the hull. Insane. I'd feel like six weeks to design and run a few initial proof-of-concept tests of a 5-inch thick layup would be too quick. I could keep going for pages just on the carbon-fiber crimes I've read about. My absolute disgust for the CEO grows every time I read more. He got what he deserved, but the passengers he suckered into taking the trip did not.
- hef19898 3y ago
  So I am not the only one who got creeps seeing the bonding video then. Wholeheartedly agree with your post.
- mikewarot 3y ago
  >I own a carbon fiber design & manufacturing shop that does aerospace and undersea work. Would you expect carbon fiber to actually do anything useful in compression? I fail to see how what is essentially magic string does anything helpful in the case of a submarine hull. It's the opposite of most applications, where the carbon fibers are in tension. The only compressive strength I can see is from the matrix the fibers were embedded in, and given all the things you've noted... that's going to be way below optimum, and there are going to be voids for crack formation everywhere.
andreskytt 3y ago
A very interesting case where the design of the system stems directly from the design of the team designing and building it.
gdcutting 3y ago
Rush's stated reason for using carbon fiber over materials (ti or steel) which are much more accepted in submersible design world was to save money. A question I haven't seen asked elsewhere is, how much money are we talking about saving here? Clearly in retrospect whatever amount of money we're talking about is worth a lot less than five human lives and the recovery costs, but of course Rush didn't think his design would fail or he wouldn't have done it. I would like to see an informed estimate of the cost difference between other hull materials given the Titan's size. Obviously there are a lot of choices of material, and information that isn't publicly available about the design, but I'm sure there are some folks out there who could give a knowledgable comparison which would help us to quantify the decision-making process here. Sure, titanium or appropriate steel would be more expensive, but it's hard for me to imagine that we're talking about an amount of money that would simply make the project unprofitable, since there are plenty of other submersibles out there built without carbon fiber hulls, and those companies are making money. Even if we were talking about a difference of some hundreds of thousands of dollars (can't imagine it would be more) between the two materials, we're still talking about life-or-death here (and one of those lives was Rush's). And while obviously the overhead costs of operating a submersible business are very high, these customers are paying $250k/dive. It seems like if Rush had said to people, "We went with ti over carbon, which would have saved money, but now we can be much more sure that the material won't fail catastrophically," anyone with that kind of money would have been happy to pay an extra, say, $10k or $20k or $50k/dive to make sure that they didn't die. My take on the situation is that the money was less important in his calculus than the ego aspect of wanting to be seen as a maverick and showing the rest of the sub engineering community that he was right against their conventional wisdom. Being seen an 'innovator' seems to have been a powerful motivation for Rush. Often the actual amount of money matters much less to people than the 'animal spirits' (to use Keyne's phrase) underlying those decisions. Maybe I'm just trying to give Rush the benefit of the doubt, since putting people's lives at risk just so he could further enrich himself (and it doesn't seem like we're talking here about a guy that could barely afford lunch) is just evil. Maybe he was greedy and cheap (which doesn't necessarily mean that he didn't have a lot of good qualities). Thoughts? I'd love to see someone run the numbers.

65 points by harambae 3y ago

I know nothing, literally nothing, about material engineering, past what I can skim off wikipedia and ingest on cycling websites. But I always thought composite nonmetal materials are hard to test nondestructively, which is the main limiting factor for their use in aerospace. Metals can be X-rayed to assess their condition, carbon not. Is that wrong? What am I missing? Just curious.

ceejayoz 3y ago
I don't think you're missing anything. Others, including those in-the-know, were left scratching their heads too. https://www.nytimes.com/2023/06/20/us/oceangate-titanic-missing-submersible.html https://www.nytimes.com/2023/06/20/us/oceangate-titanic-miss... > Years before OceanGate’s submersible craft went missing in the Atlantic Ocean with five people onboard, the company faced several warnings as it prepared for its hallmark mission of taking wealthy passengers to tour the Titanic’s wreckage. > OceanGate’s director of marine operations, David Lochridge, started working on a report around that time, according to court documents, ultimately producing a scathing document in which he said the craft needed more testing and stressed “the potential dangers to passengers of the Titan as the submersible reached extreme depths.” > Two months later, OceanGate faced similarly dire calls from more than three dozen people — industry leaders, deep-sea explorers and oceanographers — who warned in a letter to its chief executive, Stockton Rush, that the company’s “experimental” approach and its decision to forgo a traditional assessment could lead to potentially “catastrophic” problems with the Titanic mission.
- ramesh31 3y ago
  My question is just... why? It's not like carbon fiber was any cheaper than just making the thing out of steel or titanium like literally every other submersible. It just doesn't make any sense. You have none of the weight penalties that exist in aviation, so the heavier and the thicker the better.
  - SV_BubbleTime 3y ago
    As I understood it, you do have a weight penalty for a sub. You need to get back up by powered movement, or down by it. You are limiting your dive time either way. They can’t use foam for flotation at that depth. There is a concrete like “synthetic foam” if you want unpowered rise to surface but it’s expensive. I read early on they wanted carbon to be light enough to get back up by releasing weights on powerloss. From what I have seen of the hull, it was a tube. I can’t remeber seeing a view with a complex or even drafted shape to it. I suspect that spinning carbon by fiber would take far too long, and think they probably used narrow weave to do it. It would have been cheaper than the required thickness of titanium, which is the same strength as steel, but 40% the weight and still a little heavier than aluminum. Who knows!? Nothing they did showed that they ever chose the more expensive option. Carbon was likely just the cheapest thing they could use for their goals.
    - hef19898 3y ago
      Especially if you buy your material because it is past shelf lofe, don't use an autoclav and forgoe curing. Fun experiment: Take a roll from some toilet paper, squeeze it somewhat evenly at the ends. It is kond of stable. Then peel the layers apart, ans squeeze again. The same would happen if the composite tube delaminated at one of the end cap rings. This whole thing is beyond infuriating.
      - SV_BubbleTime 3y ago
        > don't use an autoclav and forgoe curing. I haven’t read that. But, that’s not an option. Carbon won’t just cure on its own, ever. It will be a shitty sticky mess forever. It had to be cured somehow. As to the carbon expiration. I don’t know what that was. I suspect it could be epoxy like in prepreg, but I doubt prepreg here. And it could be shelf life of the carbon itself as it can be hydrophilic in some cases.
        buildsjets 3y ago
        Allegedly, they bought expired (out of freezer time) prepreg from Boeing Surplus. Boeing has released a statement that they have no records of this, so it likely passed through a third party before he acquired it.
- rich_sasha 3y ago
  I was more referring to TFA which seemed to assert that you can test carbon fibre, with some kind of EM radiation. That it was all a mess at OceanGate, that bit I got :)
2-718-281-828 3y ago
well, a carbon frame is trash after a single crash even if it seems alright due to microscopic fissures. that's also the point cameron's making. the compound carbon material will progressively deteriorate with every dive due to the immense pressure difference from surface to target depth. extremely small deformations cause tearing and delamination. so small you can't see it. but one dive too many and it just cracks.
icegreentea2 3y ago
You can ultrasound and radiograph CF to do NDT. I think the challenge is just more that we have over half a century headstart working with Al in aircraft to understand their failure modes and how to adequately test for them. Our understanding of CF (+CF's inherent nature of having more sudden failures) makes designing adequate NDT regimes more challenging. That said, we are seeing much more CF (and CF composites) being deployed into commercial aerospace (famously the 787 wings, but also the A350,
- hef19898 3y ago
  The whole fusselage of the 787 and A350 is composite, not just the wings. Composite wings are old news. Strutural repairs are tricky so.
buildsjets 3y ago
The typical method to inspect composite parts is through-transmission ultrasonic. Essentially, two streams of water are aimed at the part from opposite sides, one stream of water has a ultrasonic generator embedded in it, the other side has a transducer, and you scan/raster the stream of water across the part to inspect it. There are limits on how thick of a part you can inspect with this method, and this hull significantly exceeds how thick we would use these materials in aerospace designs.
- buildsjets 3y ago
  Here's an example. Appears to be inspecting a CFRP jet engine fan case, which are some of the thicker composite layups you see in aerospace. The way this method of inspection works, you also have to fabricate a part with known defects of various sizes (simulated with a little piece of Kapton tape in the layup) in order to determine the minimum size defect that the machine can detect for a given type of part. https://tecscan.ca/ultrasonic-testing-defect-sizing-in-composite-structures/ https://tecscan.ca/ultrasonic-testing-defect-sizing-in-compo...

MobileVet 3y ago

> From all available sources, it is apparent that the viewport was designed and certified down to a depth of 1300 meters, not 4000 meters. Wow. What kind of hubris could look past that huge red flag? Apparently the kind that thinks it is interesting that it deforms by several inches and not scary

jamincan 3y ago
It's pretty much 1/3 the depth which is suspiciously close to a 3x safety factor which is what I've always heard engineers use. They certainly seemed cavalier with safety, so it wouldn't surprise me if they reasoned about it in that way.
- hef19898 3y ago
  And there is a reason it is called safety factor. Whether it is 10, 5, 3 or 1.1 doesn't matter, it is not be used.
- SV_BubbleTime 3y ago
  A rocket might have a factor of safety of around 1.1. This is because at 1.3, they’ll never leave the ground. This is why they are so carefully monitored and tested, and still fail. It’s all relative. Good engineering doesn’t mean higher number. No one knows what the FOS for this sub was. Given the information from the CEO, things like that were just slowing down innovation! EDIT: Not all rockets, just using an example.
  - plegresl 3y ago
    Falcon 9 uses a factory of safety of 1.4: https://www.nasa.gov/pdf/164283main_2nd_exp_conf_24_Commercial%20Opportunities_SpaceX_MrEMusk.pdf https://www.nasa.gov/pdf/164283main_2nd_exp_conf_24_Commerci...
  - 2-718-281-828 3y ago
    very interesting point!
3y ago

hef19898 3y ago

After an initial reluctance to follow this story, mostly due to the hysterical media coverage of a pointless rescue operation, my engineering half of my brain got interested. I am by no means a materials engineer nor a naval architect, but I was involved in some Design FMEAs and wrote thesis about the manufacturing of structural, pressurized aerospace carbon fiber parts. Some things I came across, which are in line with the article and the first spurce video: - The view port was not rated for the intended operating depth, if true I am out of words... - the pre-preg material was apparently beyond shelf life, if true almost as bad as the view port. When pre-preg is beyong shelf life, the resign doesn't reliable bond anymore. That means basically delaminated layers before the "vessel" saw water for the first time - 480(!) layers of carbon fibre, that carries the risk of prematurw dryong of the resin during production. Impact, see above. - not curing and no auto-clav, again with the same results as above - The mating rings for the emd caps have been glued on. Nothing wrong with that per se, but a bond supposed to sustain repeated dives to 4,000 m needs to be very precise. Ocean Gate applied the glue manually by hand, with inconsistent thickness in a non-clean enviroment. No idea to which tolerances the CFC hull and rings have been machined, but based the video of the bonding (they used chains attached to gate crane) they didn't seem to be too precise. The results are a high potential of foreign objects and debris being glued in, non-defined wiggle room between the CFV hull and the titanium rings and end caps and yet another strucural weakness of the vessel. - they also used titanium fibre. If trued, it doesn't matter because the preasure was applied from the outside, all the tensile streangth of carbon and titano fibers only worls against preasure from inside the vessel. - No back-ups, exposed wiring at the outside, flamable material at the inside, no telemetry, no emergency beacon, only wireless (!) controls (and they didn't even do enough testing to find key mapping errors of their Logitech controller...) - Despite claiming otherwise on their homepage (archive.org still has it) they did attach equipmwnt directly to the carbon hull on the inside by screwing (!) to the hull. Result, all the fibers cut by the screws don't take any load whatsoever anymore, increased risk of delaminations (the hull is compressed, the screw on the inside isn't) - Safety culture: completely absent, to the point of being proud about it. Unable to distinguosh between vessel certification and proper operations (there is a reason that aerospace certifies the design, production, maintenance and operations organisation seperately), firing people raising concerns, I am out of words here.. - The vessel can only be opened from the outside (!), so even a perfect dive can lead to suffocation is the vessel isn't located fast enough... I could go on, but calling this abomination "engineering" is an insult to the universe. Finally, some potential failure modes: - the view port (obviously) - the hull (delamination, stress, bad material, intentionally induced defects...) - the bond between the rings for the end caps and the hull (weakened bond due to different deformation of the two materials, weak bond due to foreign objects, inconsistens bond due to bad application of the glue...) All in all, from design over manufacturing to maintenance and operations, this thing was a death tral whos only upside was a quick death in case of an implosion.

nonrepeating 3y ago

One can take comfort from this in a perverse way. The failure of the submersible was entirely predictable and should surprise no one. The alternative would be more troubling.

JKCalhoun 3y ago
And perhaps like the Tacoma Narrows bridge it will end up being a cautionary tale for future engineers.
- throwway120385 3y ago
  The kinds of people who make these stupid decisions are never the same people who actually learn lessons the easy way like you're proposing.
  - Arrath 3y ago
    This case was kind of the exception that proves the rule, beyond the 4 others caught in it.
  - tivert 3y ago
    > The kinds of people who make these stupid decisions are never the same people who actually learn lessons the easy way like you're proposing. It's quite possible it could lead to new regulations that would make similar stupid decisions illegal. It might be time, it sounds like the whole human-occupied submersible industry is entirely unregulated.

kodah 3y ago

> It was previously stated by the CEO that each time he descended to that depth, the viewport deformed several inches inward. It takes an incredible level of density to ignore this once, but multiple times? Can someone tell me what happens to a human body when suddenly exposed to ~5000 psi? Edit: I looked it up. The human body almost instantly incinerates. It takes a matter of milliseconds.

moritonal 3y ago
You know how you're generally accustomed to being somewhat solid? Imagine you were now liquid.
longitudinal93 3y ago
From what I've read here your body is suddenly exposed to the equivalent pressure of 100 fully loaded semi trucks sitting on you, while simultaneously the sudden compression of the air would cause a brief flash with a temperature equivalent to the surface of the sun. Mercifully you'd be turned to goo within a split second.
myself248 3y ago
I love the expression "you stop being biology and briefly become physics".
anon_cow1111 3y ago
>Edit: I looked it up. The human body almost instantly incinerates. It takes a matter of milliseconds. This is most likely BS- consider that a shotgun shell is made from a low melting-temp plastic and handles higher pressures and temperatures without issue (and repeatedly if you're reloading them). Probably your hair and light clothing would burn somewhat during an implosion, but would be extinguished as soon as the water hit it. Then it would stop being hair and light clothing just due to the kinetic energy of water hitting you at cannon-ball velocity.
- kodah 3y ago
  Feel free to give this a read, it has an answer for your assertion about waters role: https://mindofjp.medium.com/what-really-happens-to-a-human-body-at-titanic-depths-3f46ab545e0e https://mindofjp.medium.com/what-really-happens-to-a-human-b...

pugworthy 3y ago

> It was previously stated by the CEO that each time he descended to that depth, the viewport deformed several inches inward. Dear lord even if it is/was supposed to do that, this would be disturbing to look at.

Arrath 3y ago
I can't imagine a shorter path to making my lizard brain scream "SURFACE NOW"

AdamH12113 3y ago

> It was previously stated by the CEO that each time he descended to that depth, the viewport deformed several inches inward. Is that normal for a submersible viewport? I feel like that's probably not normal.

parl_match 3y ago
At those pressures, it's not particularly unreasonable for their to be flex and shift in materials. That would be baked into design, maintenance, and monitoring. However, the lack of safety culture, testing, or modeling is more red flags than a communist rally. More succinctly: It's probably "normal", but OceanGate didn't know if it was "normal".

gcanyon 3y ago

"each time he descended to that depth, the viewport deformed several inches inward" That's gonna be a no^∞ from me.

toss1 3y ago

>>Consider the fact that most engineers can explain the cause of ..., and the space shuttle Challenger disaster (where Morton Thiokol was told to take off their engineer hats and put on their manager hats when considering O-ring temperature certification). The money phrase: >>take off their engineer hats and put on their manager hats This is what kills people. To boil it down to one short course in engineering ethics: Whenever anyone tells you to do act like a manager instead of an engineer when making a technical decision, tell them, in no uncertain terms, and as politely or impolitely as needed to make the point: to fuck off; physics is physics, and neither knows about, cares about, nor yields to human concerns. (Unless, of course, you are OK with living decades of your remaining life after the accident knowing you accepted a blood-money paycheck to do bad engineering.) Is your current job, or your company's immediate future worth possibly killing people?

coffinbirth 3y ago

[flagged]

engineer_22 3y ago

This isn't an engineering assessment, at best it's speculation about what caused the loss of the Titan.

hef19898 3y ago
Whatever the exact failure mode, it was the most dangerous thing that let to Titan's destruction and the death of five people: the combination of stupidity and hubris.
- engineer_22 3y ago
  Speculation
  - hef19898 3y ago
    Of course, we have to wait for the various investiagtions before we know for sure.

ghostpepper 3y ago

> Consider the fact that most engineers can explain the cause of the Hyatt Regency walkway collapse (if you can’t, you shouldn’t be an engineer), the Tacoma Narrows bridge failure, the Union Carbide Bhopal disaster, and the space shuttle Challenger disaster Does anyone know of a good documentary about famous engineering failures? Bonus points if they actually go into detail about the scientific explanation, as opposed to focusing on the human failures

philjohn 3y ago
Fascinating Horror and Plainly Difficult are OK - Plainy Difficult tends to go more into the mechanics of disasters, but both are operating under the constraints of a 10-15 minute YouTube video.
hef19898 3y ago
One thing that cannot be stressed enough, every system (I like the systems engineering way of thinking that goes beyond the single product to include everything from operations to maintenance, I come professionally from the point where Supply Chains meet design), every engineering project has to account for operating procedures, manufacturing procedures, training and human factors. In all seriousness, the series about Chernobyl is great in driving that point across.
tylergetsay 3y ago
There's a podcast called "well there's your problem" that covers them. their style isn't for everyone but I find it very entertaining
tzs 3y ago
I don't think it is currently available on streaming or disc, but if it ever becomes available again the TV series "Seconds from Disaster" [1] would be a good choice. It is excellent. [1] https://en.wikipedia.org/wiki/Seconds_from_Disaster https://en.wikipedia.org/wiki/Seconds_from_Disaster

toss1 3y ago

I own a carbon fiber design & manufacturing shop that does aerospace and undersea work. Watched the video by "Just Alex" and the section the bonding of the titanium end-caps and the cylinder absolutely gave me the creeps. The video was absolutely right to mention lack of dust-free environment (vs open warehouse), lack of temperature control, and lack of degassing equipment. We also have no idea about the properties of the epoxy used to bond it, whether it has the suitable amount of compliance, properties under temperature change, etc. Worse yet, I saw no precautions being taken to avoid entrapped air in the bond, in fact, it seemed quite likely, and the sections with entrapped bubbles would be NOT bonded. Same for any sections with entrapped dust, debris, or whatever else was floating around that warehouse. I would want to see, along with the all of the above steps, either or both applying very substantial pressure to the Ti/Carbon parts while curing to force out any air, and/or doing the whole process in a vaccum environment. The out-of-date carbon fiber? Sure, it is fine, for some months, for noncritical applications. For critical applications? NO WAY. And the CEO's claim that aerospace needs to be more stringent than undersea 5000psi is just beyond stupid. You need absolutely the best bond between layers that you can get. Also, the 480-odd layer layup and cure is hugely experimental by itself, and I've read elsewhere that the shop was given six weeks to design and fabricate the hull. Insane. I'd feel like six weeks to design and run a few initial proof-of-concept tests of a 5-inch thick layup would be too quick. I could keep going for pages just on the carbon-fiber crimes I've read about. My absolute disgust for the CEO grows every time I read more. He got what he deserved, but the passengers he suckered into taking the trip did not.

hef19898 3y ago
So I am not the only one who got creeps seeing the bonding video then. Wholeheartedly agree with your post.
mikewarot 3y ago
>I own a carbon fiber design & manufacturing shop that does aerospace and undersea work. Would you expect carbon fiber to actually do anything useful in compression? I fail to see how what is essentially magic string does anything helpful in the case of a submarine hull. It's the opposite of most applications, where the carbon fibers are in tension. The only compressive strength I can see is from the matrix the fibers were embedded in, and given all the things you've noted... that's going to be way below optimum, and there are going to be voids for crack formation everywhere.

andreskytt 3y ago

A very interesting case where the design of the system stems directly from the design of the team designing and building it.

gdcutting 3y ago

Rush's stated reason for using carbon fiber over materials (ti or steel) which are much more accepted in submersible design world was to save money. A question I haven't seen asked elsewhere is, how much money are we talking about saving here? Clearly in retrospect whatever amount of money we're talking about is worth a lot less than five human lives and the recovery costs, but of course Rush didn't think his design would fail or he wouldn't have done it. I would like to see an informed estimate of the cost difference between other hull materials given the Titan's size. Obviously there are a lot of choices of material, and information that isn't publicly available about the design, but I'm sure there are some folks out there who could give a knowledgable comparison which would help us to quantify the decision-making process here. Sure, titanium or appropriate steel would be more expensive, but it's hard for me to imagine that we're talking about an amount of money that would simply make the project unprofitable, since there are plenty of other submersibles out there built without carbon fiber hulls, and those companies are making money. Even if we were talking about a difference of some hundreds of thousands of dollars (can't imagine it would be more) between the two materials, we're still talking about life-or-death here (and one of those lives was Rush's). And while obviously the overhead costs of operating a submersible business are very high, these customers are paying $250k/dive. It seems like if Rush had said to people, "We went with ti over carbon, which would have saved money, but now we can be much more sure that the material won't fail catastrophically," anyone with that kind of money would have been happy to pay an extra, say, $10k or $20k or $50k/dive to make sure that they didn't die. My take on the situation is that the money was less important in his calculus than the ego aspect of wanting to be seen as a maverick and showing the rest of the sub engineering community that he was right against their conventional wisdom. Being seen an 'innovator' seems to have been a powerful motivation for Rush. Often the actual amount of money matters much less to people than the 'animal spirits' (to use Keyne's phrase) underlying those decisions. Maybe I'm just trying to give Rush the benefit of the doubt, since putting people's lives at risk just so he could further enrich himself (and it doesn't seem like we're talking here about a guy that could barely afford lunch) is just evil. Maybe he was greedy and cheap (which doesn't necessarily mean that he didn't have a lot of good qualities). Thoughts? I'd love to see someone run the numbers.