Department of Fighting the Last War… let’s talk about ideas that could have prevented the Titan tragedy.
The potential for failure of a pressure vessel is something that aviation has been dealing with since at least the 1930s (Boeing 307). The cycles of pressurization and depressurization are known to cause metal fatigue and, sometimes, lead to catastrophic failure. Certification authorities, such as the FAA, require structural analysis to certify a cycles or hours limit and this may be extended once there is more experience with the airframe. Running the cycles up to 90,000 (many short hops) contributed to the failure of Aloha Airlines Flight 243, a Boeing 737.
The reasonable standard of safety for deep-sea exploration and tourism is lower than for commercial airline travel. However, what about a rule that you have to build at least two of each design and use one as a sanity check on the pressure vessel design and ability to tolerate cycling fatigue? Don’t send humans on a 50th dive in a machine unless its sister ship has done at least 100 or 150 robot-only dives to the same depth. (If additional protection from fatigue-related failures is desired, increase the number of sister ships and the multiplier for how many dives they must survive compared to the human-occupied dives.)
Note that this procedure wouldn’t guarantee safety. Portions of the de Havilland Comet were subjected to 16,000 simulated cycles and the finished design nonetheless suffered a catastrophic failure with passengers on board (though the airplane that failed had some construction method differences from the prototype that was tested). But it is better than finding out the cycle limit with humans on board. And every machine that goes to the ocean floor will have a cycle limit.
Cycle limits? That sounds like something an experienced 50-year old white guy would say. Unfortunately, the CEO of OceanGate said he didn’t hire ‘50-year-old white guys’ because they weren’t ‘inspirational’. ”
https://nypost.com/2023/06/21/why-stockton-rush-ddnt-hire-50-year-old-white-guys-for-titanic-sub-tours/
Is there really much of this deep sea tourism that the government needs to get involved with rules and regulations and a bureaucracy to enforce those rules and regulations? I mean, from a societal point of view, who really cares about the risks the uber wealthy take in order to amuse themselves?
Jdc: when I wrote “rule” I didn’t mean a government-enforced rule. It could be simply a practice that people in the industry adhere to.
From a book edited by a 50+ year old white guy, written by a bunch of 50+ year old guys.
“Regulatory agencies require that a fatigue analysis be submitted for review if the lifetime full-pressure range cycles exceed the calculated maximum allowable cyclic life of the pressure hull structure. To arrive at the equivalent number of cycles a submersible may attain. a hypothetical dive profile that might be encountered during the operational life of the submersible should be developed. The dive profile must then be converted into equivalent full-depth cycles, which are compared to the calculated cycles to determine if the calculated maximum allowable cycles are exceeded. If it is exceeded, a fatigue analysis must be performed.”
E. Eugene Allmendnger, “Submersible Vehicle Systems Design”, SNAME, 1990.
Another excellent book, written by a 50+ year old Asian guy. Really good insight into the development of deep sea submersibles in China. No mention of carbon fiber only Titanium.
Weicheng Cui, “Multidisciplinary Design Optimization and Its Application in Deep Manned Submersible Design”, Springer, 2020.
Section 7.1 Reliability Based Design of Manned Cabin, is a really good detailed section going from the calculation to the destructive testing of a titanium sphere.
Interesting thoughts! Has anyone found much detail on the company that some reports indicate was the actual manufacturer of the carbon fiber portion (Spencer Composites)? One report says they were given only six months to construct it…seems pretty crazy!
“Crushing carbon fiber with hydraulic press”. Good lateral and compression strength, but very poor longitudinal?
Fascinating video! Not being a scientist, does this imply it was crushed from “sides” or “ends”? Seems like the demo models of tubes collapsed easily in both scenarios. Thanks.
To me it implies that carbon fiber is not great at compression loads, except for the solid square tile. And unlike steel, it disintegrates suddenly and catastrophically.
If you watch hydraulic press clips operating on certain types of steel, it bends slowly, almost behaving like a fluid, but does not disintegrate.
I imagine that this feature would give an operator more time to react to suspicious noises like creaking (provided that the operator is a 50-year-old white male with experience).
Carbon fiber is also horrible in maintenance. If you tighten a screw too hard, it’s game over.
Other reports say Spencer has denied its hull was the one that imploded, but that its hull was subsequently repaired or rebuilt by aerospace contractors Electroimpact and Janicki Industries.
Surprised there was never a single interview with the Oceangate staff about their practices. We don’t know what inspections were being done. They should have done complete xrays of the thing in the off season. Being the 1st dive of the season, it should have been like new. There’s only 1 man’s testimony that they never did a single xray & relied on health monitors to report realtime deformations. Sounds familiar to Elon’s early claims that starship would rely on health monitors rather than overhauls.
I think they should’ve realized they had a problem when their safety plan relied on real-time monitoring of the pressure hull’s structural integrity in order to detect if it was about to implode or not. I’m a software guy so this isn’t really my area of expertise, but it seems incredible to me that they rejected materials with a known history of safe use in favor of using a material with known disadvantages and unpredictable wear properties. It would be one thing if they e.g. knew it was safe for ten dives and planned to replace the hull after every ten dives. It sounds like they really had no idea how many dives it was safe for, either from theory or from experiment. The whole thing reminds me a bit of Boeing’s MCAS in that they attempted to paper over a problem by adding complexity with a crappy solution (although I think that should’ve been safe in theory, if done properly, although the pilots should’ve been trained on it).
What is the elevation of the factory that made the composite airframes for B787?
MLZ: Probably sea level. Remember that aviation/space pressure vessels have the pressure on the inside and the differential is 6-15 psi. These submersibles are handling pressure from the outside at up to 16,000 psi (Challenger Deep). So the fact that pressurized composite airframe failures are rare doesn’t necessarily mean that submersibles should be built from composites. (I am aware of at least some catastrophic windshield failures in the composite pressurized Lancair Evolution. I don’t know of a composite airframe failure in which the fuselage itself failed.)
It doesn’t really bother me that a few people die once in a while doing risky things. Mount Everest takes plenty of tourist climber lives and they know the risks. There are plenty of YouTube videos from 2022 that made the risks and corner-cutting of Titan obvious, and I expect most of these people did the due diligence and accepted the risks. And I don’t think kids should be prevented from taking risks if their parents permit it. Laura Decker circumnavigated the world on a sailboat at 14-16, and Abby Sunderland made an attempt to beat that record before her Indian Ocean demasting. There are several teens who circumnavigated in small planes, like Matt Guthmiller.
The reason why the Titan guy didn’t pay for certification is that destructive testing is so expensive it raises the barrier to entry too high. One-of-a-kind carbon fiber reinforced resin Imoca 60 foiling sailboats are not destructively tested before participating in the 3-month Vende Globe Antarctica circumnavigation race beyond hope of rescue.
I personally started a small business to import toys to the U.S. and was required to destructively test 10 toys per color for lead and phthalates by the CPSC at one of their approved labs. Lab staff scraped paint off of each toy to test. I asked if I could just test the paint: Nope. This not only cost me a bundle, making the whole enterprise unprofitable, but it prevented product design and innovation that would involved more than one color per model. I should have been allowed to simply have the wet paint tested.
The Titan hull was subject to cyclic stress fatigue, and the Spencer Composites version was redone by Electroimpact a couple of years ago because of that. Perhaps this should have been done annually, but on the other hand all these issues were public prior to this year and would have come up in a due diligence check (i.e,, a Google search).
> The Titan hull was subject to cyclic stress fatigue, and the Spencer Composites version was redone by Electroimpact a couple of years ago because of that. Perhaps this should have been done annually
I have not seen any reports that the stress was predictable or that there was any number of times the sub was known to be able to safely dive. A submersible expert (he takes tourists down to 2,000 feet off the coast of Roatán on one he built himself) said he heard cracking on an early test dive and thought it was indicative of the material starting to fail:
https://www.youtube.com/watch?v=0mSq6ibKKXQ
The fact that the CEO was onboard and is now dead, at great harm to his business, if not the entire industry, very strongly suggests that he was not accurately assessing the risks or communicating them to his customers.
> destructive testing is so expensive
It’s even more expensive when you do it with people inside. Is destructive testing even the standard for submersibles? I think the standard is to do testing in a pressure chamber and verify an adequate safety margin; as far as I’m aware, a standard metal pressure hull will remain perfectly usable after such a procedure (you’ve only put it through one pressure cycle, and presumably it should be able to withstand many).
Comments on the video I linked:
> The fact that he heard cracking in the hull and kept hustling people to ride in it while suing everyone who warned him is absolutely criminal.
> This is the first catastrophic failure of a sub hull in the 60 years of deep sea submersible exploration. Stockton Rush cut corners left and right because he claimed that the industry safety standards restricted “innovation”. The fact that he ignored warnings from experts in this field and never tested it below 3000 feet before taking passengers is absolutely criminal.
I am *very* surprised that 737 didn’t snap in half after the top of the fuselage peeled off. Impressive. What a flight this must have been for the passengers that survived.
As for the Titan, this is typically Silicon Valley hubris. Turns out “move fast and break things” isn’t such a hot idea for a deep sea submarine that goes 2-3X deeper than a Navy sub. From an engineering perspective, there were so many errors here it’s hard to know where to begin.
Where was his board? His investors?
Another area that should receive more stress tests are bicycles, especially e-bikes. There is very little regulation and forks of e-bikes fail because they are not made to deal with the additional load.
In general, fork stress testing seems to be voluntary and the situation only somewhat worked because the topic was well understood in the area of steel bikes.
The joys of carbon fiber bike maintenance:
https://en.brujulabike.com/why-forks-break-road-bikes-solution/