Technical Analysis on Titan Sub (Titanic Sub)

[russ_watters]

And if you ban this, do you also ban space tourism?

I don't see that anyone suggested banning it (at least before you brought it up -- I didn't read through all the rest of the posts). But no, I wouldn't ban either. Nor would I allow a free-for-all if possible. The fact it happened international waters and the perpetrator died in it may make this particular incident impossible to prosecute, but it sure looks like murder to me. And there's no jurisdictional issue for criticism.

Which one did you have in mind?

The lack of safety factor is the eye-popping one to me. Having an appropriate safety factor (which is generally higher for larger risks/life safety) is a pretty basic engineering principle. Heck, I design air conditioning systems with safety factors and the main risk there is someone might be a touch warm for a couple of hours on the hottest day every couple of years (also, money). Life safety engineering scares the hell out of me as it is.

More specific and not necessarily inviolable: spheres are stronger than cylinders.

Similar: you can't push a rope (that might be Navy as much as engineering....).

Related but bigger than just engineering: if everyone else does something successfully one way, you should consider why and be careful doing it another way. This applies to both being cylindrical and using carbon fiber.

This operation had a tech-bro hubris feel to it to me. Tech-bros don't care about things going badly because there's no personal risk. It's just other peoples' money, and even the ones who eventually go to jail don't seem to see it coming (nor did this one see death coming).

I don't believe diving to the Titanic can be done safely - and I am defining "safely" as a 99% survival rate. There seem to have been about fifty manned dives, and one failure.

Several things I take issue with here:

1. I don't think it's correct to use the claimed outlier in the risk analysis. In other words, it sounds like you are saying that prior to this incident nobody had died visiting the Titanic. That sample size is small though.
2. Because of #1 I don't believe the occupants of the sub expected that they were undertaking about the riskiest adventure trip there is. 99% survival rate is on par with attempting Mt Everest or space travel. Not Blue Origin either -- actual space travel.
3. Nor do I think visiting the Titanic inherently is as risky. Pressure is what I'd call a "passive" risk. It's always there and it's big, but it never changes. It's always exactly the same. And because of that, it's relatively simple/straightforward; once you've engineered for it, there's not much else to do. Space travel on the other hand involves massive complexity. Everest involves massive uncertainty/variability.
4. Stories are coming out of the woodwork now about people in the know who raised alarms. This particular outfit was known to be much, much more dangerous than the baseline risk.

Late edit:

Now, if you want to argue it should be safER, OK, how much safer? Factor of 2? Factor of 10? And how do you verify this number?

That's not how it works. Safety factor is an exact percentage of a design rating, not a failure/accident probability. They vary based on things like risk and predictability:
https://en.wikipedia.org/wiki/Factor_of_safety

I can't say if it should be 25% or 100% here, but note that the decision on the value includes mitigation; lower safety factors require more testing, quality control, etc. to provide "safety" in a tighter design tolerance. The point is: if it isn't a cookie-cutter scenario they require a detailed risk analysis to establish the value. And the value is never zero because that basically guarantees failure.

 

[Astronuc]

Consider something like a plastic drinking straw failing in excessive suction/external pressure, with the result that it is no longer round - it is compressed to a flat strip with only open parts at the edges of the strip where the bending rigidity stops it from folding against itself? It is elastic deformation (remove suction and the straw reopens), but do you have another term for it besides "collapse"?

One could do a test. I'm not sure I can pull a complete (or near vacuum) with my mouth, but if one has a vacuum pump that might work. With what I could draw, there is some permanent deformation and the straw cross section is oval with a sharp profile where bending was the greatest. But that's a thin wall plastic, not a metal or brittle composite.

Pinch the straw between one's figures as see a difference. Then repeat several time.

One could also freeze the straw and perform the same experiment.

Do brittle materials have deformation through formation of stopped cracks?

It depends on the bulk and local stress states and microstructure. It's possible a crack once initiated becomes arrested - depending on the stress level.

Cracks which propagate only a small distance to obstructions, cause deformation, redistribution of loads, generate acoustic effects (both in creation and while sitting there as cracks) - but do not initially propagate through, nor connect to leak water through?

In brittle materials, the deformation is very little. I don't know about carbon fiber composites, since I have not researched them.

Until there is enough pre-failure brittle deformation accumulated that the cracks propagate by linking up to stopped cracks?

In the case of Titan, there may have been little evidence externally (by sight) that any cracking had occurred. Apparently, there was not testing performed. I'm still trying to understand the titanium-CFC combination.

Some information on the design of Titan's hull.
https://web.archive.org/web/2021080...bmersibles-under-pressure-in-deep-deep-waters
I haven't verified.

The Wikipedia article (unverified information) has the following:

The entire pressure vessel consisted of two titanium hemispheres with matching titanium interface rings bonded to the 142 cm (56 in) internal diameter, 2.4-metre-long (7.9 ft) carbon fibre-wound cylinder.

I don't know how reliable the information is.
https://en.wikipedia.org/wiki/2023_Titan_submersible_incident

I do not find the hull dimensions in the cited reference [12].
https://www.autoevolution.com/news/...g-on-its-way-to-the-titanic-wreck-216772.html
https://web.archive.org/web/2023062...g-on-its-way-to-the-titanic-wreck-216772.html

I would not trust Wikipedia with respect to information concerning the specifics of Titan. Official data seems to have disappeared from public view. We will have to wait for the published investigation reports.

OceanGate has removed their material. The following is archived.
https://web.archive.org/web/20230619233914/https://oceangate.com/our-subs/titan-submersible.html

 

[Vanadium 50]

Maybe the subsequent dive is 0.99-0.97 of that,

Maybe.

I have very little experience with pressure vessels, mostly watch other people buy them. (Had an application where one would be filled with lead perchlorate - you don't want that leaking!). I do however, know a little bit about superconducting magnets and magnetic forces are like a pressure (outward, not inward).

Some magnets "train" - i.e. they become stronger with use. The phenomenon is not well-understood. Others degrade over time, but eventually hit a plateau. And rarely you get a dog that just gets worse and worse.

As far as scale model testing, the problem is that various effects scale differently. Taking the magnet as an example, if I scale it up by x, the pressure is constant, but the pressure per unit mass is not. If you are driven by material flaws a smaller device will perform ,uch better than a full-sized one. And so on.

FWIW, I think cycling fatigue was the culprit (I may have been the first to have brought it up) but probably at the junction between bell and cylinder. I also suspect a cascading failure - a bad spot developed, the loads transferred away from the spot causing other bad spots to develop until the whole thing "unzipped".

 

[DaveC426913]

So ... they would very likely have survived if he had built and used a new vessel instead of recycling a used one to save time and/or money.

...is what I'm hearin'...

 

[russ_watters]

In the case of Titan, there may have been little evidence externally (by sight) that any cracking had occurred. Apparently, there was not testing performed.

There was obvious (if qualitative and not visual) evidence: loud cracking noises.

During a trip on board the Titan off the coast of the Bahamas in April 2019, Karl Stanley, an expert in submersibles, knew immediately that something was off: He heard a cracking noise that got only louder over the two hours it took for the submersible to plunge more than 12,000 feet.

https://www.nytimes.com/2023/06/23/us/titan-safety-warnings-titanic.html

They were hearing the vessel destroy itself with every dive!

 

[russ_watters]

To expand - I understand the "there outta be a law" reaction to tragedy. But how much in the way of resources should we spend saving stupid rich people from themselves?

Is that all about regulation or is there an implication for search and rescue too? Because SAR can't discriminate on the basis of wealth or stupidity. That would not be morally acceptable even if we dislike the people we abandon.

 

[russ_watters]

Alvin Dive Statistics
https://www.whoi.edu/what-we-do/explore/underwater-vehicles/hov-alvin/dive-statistics/

I was hoping to find how many dives they have performed at 4000 m and deeper.

I'm not sure how much depth per dive matters. I'm a bit thin on this for metals much less composites, but I don't think there's a "no damage" threshold for fatigue. I feel like it would be quadratic with depth; 5,000 dives at an average of 2,000m = 1,250 at 4,000m (this would align with the noise report I quoted/linked). Really impressive career either way.

 

[Astronuc]

There was obvious (if qualitative and not visual) evidence: loud cracking noises.

https://www.nytimes.com/2023/06/23/us/titan-safety-warnings-titanic.html

They were hearing the vessel destroy itself with every dive!

I had heard that there were sounds, but I didn't know the details.

Looking at one comment in that article:

In the April 2019 email to Mr. Rush, Mr. Stanley said the loud cracking sounds that they had heard during their dive “sounded like a flaw/defect in one area being acted on by the tremendous pressures and being crushed/damaged.” He wrote that the loud, cracking noise signaled there was “an area of the hull that is breaking down.”

Apparently, after that dive or season, "he [Rush] made some changes to the Titan, including building a new hull, and called off the planned dives for that year." So it was a new hull (new materials?, new design?, ??)

Another statement in the article:

Saltwater that had been trapped in between different materials in the vessel from dives in 2021 and 2022 worked its way through fibers and softened it up, making it more susceptible to a leak, experts said.

It occurred to me regarding Titanium and Carbon mating could be problematic in seawater. Carbon is more noble than Ti, so the Ti could begin to corrode, and possibly, the carbon composite reacts with elements in seawater, including dissolved oxygen. AND, if the infiltration occurred at depth at 370-380 atm, could the seawater expand at 1 atm?

Lots of aspects to investigate. This will be one of the classic cases in failure/forensic analysis - unfortunately.

 

[russ_watters]

I think this is the crux here. The passengers in the sub were technically trained people capable of decision (maybe not the 19 yr old?).

I'm seeing the CEO and and a deep sea diver/explorer, but the other three were a kid and two businessmen with no relevant expertise beyond "adult". So one perpetrator, one accomplice and three victims.

That being said I believe that any expectaton of extraordinary emergency response should be predicated upon some robust and sufficient pre-certification, and that should be a societal norm. If you want to just hang your hindquarters way over the edge then go for it, but don't expect me to help pay the piper.

And how many bodies are adrift in the Mediterranean today?

Ehh?? Were those bodies in the Med previously on certified craft?

Besides being incorrect/illogical, such emergency response priority grading is wholly immoral. Western societies, at least, do not operate that way.

 

[hutchphd]

Besides being incorrect/illogical, such emergency response priority grading is wholly immoral. Western societies, at least, do not operate that way.

I think I was unclear. The priority I was referencing has taken place. Witness the resources expended to save the refugees off Greece (~Nada) relative to the huge response for 5 people who should have known better and were under no duress to be in that foolish submersible.

I'm seeing the CEO and and a deep sea diver/explorer, but the other three were a kid and two businessmen with no relevant expertise beyond "adult". So one perpetrator, one accomplice and three victims.

Unless there was true malfeasence, every one of them had the resources to seek out and the intelligence to recognize the need for expert analysis. This craft had no certification or record. They were not victims, they were gamblers.

 

[berkeman]

Perhaps one finding of the USCG investigation will be that for any future uncertified activities like this either they will need to provide their own emergency response effort, or they will be billed for any assistance requested from government agencies. That seems fair to me, and should be part of the contract agreement that is signed before passengers/tourists embark on these adventures.

Certainly, if the Park Service or a similar agency has to rescue you from an emergency in the wilderness and you are found to be negligent in creating that emergency yourself (like crossing out-of-bound lines clearly marked in ski areas), you are billed for the rescue.

https://content.time.com/time/nation/article/0,8599,1892621,00.html

 

[russ_watters]

I've seen this. My reaction is "so what?" It's not the part that failed. Lots of high-tech projects use low-tech parts. One of the Fermilab accelerators uses magnets from automatic car windows. A popular cable for experiments is ethernet, and HDMI is starting to gain popularity. One LHC experiment is shimmed with US dimes. One Fermilab experiment has detectors registered with tongue depressors.

There's plenty to complain about, but IMO, "Nintendo" is not one of them.

One thing that surprises me is the lack of telemetry involved. Add an optical fiber to the umbilical and you have all the bandwidth you need - a text every 15 minutes?

These are the same complaint. The alternative to "Nintendo" isn't 'ten-million-dollar-custom-control-and-telemetry-system' it's "iPad". It's not that they went for $100 instead of $1000 for the operator interface it's that they went with nothing instead of something for the telemetry.

And yeah, that wouldn't kill anyone, but it speaks to the "how-is-this-so-cheaply-built-when-I'm-paying-a-quarter-mil" aspect.

I can't speak to other navies, but the US Navy takes sub safety very, very seriously. It only takes one slip up down.

Fixed for you.

 

[russ_watters]

Perhaps one finding of the USCG investigation will be that for any future uncertified activities like this either they will need to provide their own emergency response effort, or they will be billed for any assistance requested from government agencies. That seems fair to me, and should be part of the contract agreement that is signed before passengers/tourists embark on these adventures.

Certainly, if the Park Service or a similar agency has to rescue you from an emergency in the wilderness and you are found to be negligent in creating that emergency yourself (like crossing out-of-bound lines clearly marked in ski areas), you are billed for the rescue.

https://content.time.com/time/nation/article/0,8599,1892621,00.html

Billing for the rescue is one thing, but as a first responder do you really see just...not responding... as a viable ethical/moral choice? Isn't there an oath or something?

And a point of order here: The bulk of the rescue effort was not for a deep sea submersible it was for a craft lost on the surface.

 

[russ_watters]

There's info in the article that makes me question the "out of date" CF and the 7 vs. 5 inch stories.

Indeed, suggests the media reports of no safety factor but a rounding error are wrong/a misunderstanding. That makes more sense given that it didn't fail immediately. I was wondering how it could last so long given that it's been screaming at occupants for years that it was failing.

 

[berkeman]

Isn't there an oath or something?

Just for docs, with a little bleed-over (pun intended) for first responders. Docs by oath cannot distinguish betwee patients (Pts) based on bad behavior. They treat the drunk who caused the DUI crash with the same basic priority as the family he just crashed into.

And a point of order here: The bulk of the rescue effort was not for a deep sea submersible it was for a craft lost on the surface.

Wakarimasen. The submersible was reported for a loss of communication at 1.75 hours into its dive, no?

 

[russ_watters]

I think I was unclear. The priority I was referencing has taken place. Witness the resources expended to save the refugees off Greece (~Nada) relative to the huge response for 5 people who should have known better and were under no duress to be in that foolish submersible.

I've only read a bit on the Greek situation (which, yes, says something), but one wrong does not make a right.

Unless there was true malfeasence, every one of them had the resources to seek out and the intelligence to recognize the need for expert analysis. This craft had no certification or record. They were not victims, they were gamblers.

I have a professional engineer license, so I don't accept that. More to the point, I'm legally obligated to not think that way. There's qualified people and there's not qualified people. Those three - regardless of how smart and adult one thinks they were or should be - were not qualified people.

 

[russ_watters]

Just for docs, with a little bleed-over (pun intended) for first responders. Docs by oath cannot distinguish betwee patients (Pts) based on bad behavior. They treat the drunk who caused the DUI crash with the same basic priority as the family he just crashed into.

Right, but what if they're rich so I hate them - can I let them drown/suffocate then?

[edit] If too chippy: yes, that's the sort of oath I'm talking about. Even if you're looking to save the life of a potential murderer you do it because that's the moral requirement.

Wakarimasen. The submersible was reported for a loss of communication at 1.75 hours into its dive, no?

[Ironic googling commences]

There was never any chance of an under-sea rescue and P-3s don't look for [these type of] subs. No, the only real chance of rescue was if they had surfaced and were lost, which had happened before. That's what the vast majority of the SAR was after as far as I can tell. Looking for them on the surface.

[edit] Personally I'm shocked at how easy it was to find the wreckage on the bottom, but again that was not a rescue effort.

 

[berkeman]

Right, but what if they're rich so I hate them - can I let them drown/suffocate then?

Sure. They've hired their own SAR team, so we stand by.

 

[Astronuc]

Orthotropic materials are a subset of anisotropic materials; their properties depend on the direction in which they are measured. Orthotropic materials have three planes/axes of symmetry. An isotropic material, in contrast, has the same properties in every direction.

Ref: https://en.wikipedia.org/wiki/Orthotropic_material
https://help.solidworks.com/2012/english/solidworks/cworks/isotropic_and_orthotropic_materials.htm

Now I'm wondering about the pitch of the carbon fibers around the hull. Were they in the optimal orientation for the various stress states?

I still don't quite understand the use of Ti in conjunction with the CFC. I could understand a Ti shell overlaying the CFC and welded to the Ti rings at the ends. I don't yet understand the end configuration. Could seawater have infiltrated the interfaces?

Where did the cracking occur?

I hope they recover as much debris as possible to be able to reconstruct the hull, or enough to determine a probably root cause of failure.

--------------------------------
While I was looking for information on Titan's hull design, I found this article:
https://www.cbsnews.com/news/titani...-transcript-with-oceangate-ceo-stockton-rush/

POGUE: How many backup systems do you have for the thing collapsing?

RUSH: So the key on that one is, we have an acoustic monitoring system. Carbon fiber makes noise. There're millions of fibers there. There are 667 layers of very thin carbon fiber in this five-inch piece.

It makes noise, and it crackles. When the first time you pressurize it, if you think about it, of those million fibers, a couple of 'em are sorta weak. They shouldn't have made the team.

And when it gets pressurized, they snap, and they make a noise. The first time you get to, say, 1,000 meters, it will make a whole bunch of noise. And then you back off, and it won't make any noise until you exceed the last maximum.

And so when, the first time we took it to full pressure, it made a bunch of noise. The second time, it made very little noise.

We have eight acoustic sensors in there, and they're listening for this. So when we get to 1,000 meters, if all of a sudden we hear this thing crackling, it's, like, "Wait, did somebody run a forklift into it? You know, has it had cyclic fatigue? Is there something wrong?"

And you get a huge amount of warning. We've destroyed several structures [in testing], and you get a lotta warning. I mean, 1,500 meters of warning.

It'll start, you'll go, "Oh, this isn't happy." (LAUGH) And then you'll keep doin' it, and then it explodes or implodes. We do it at the University of Washington. It shakes the whole building when you destroy the thing.

So that's our backup for the hull. And we're the only people I know that use continuous monitoring of the hull.

POGUE: So if you heard the carbon fiber creaking—

RUSH: If I heard the carbon fiber go pop, pop, pop, then the gauge says, "You're getting a whole bunch of events."

POGUE: Could you get three hours back to the surface in time?

RUSH: Yes. Yes, 'cause what happens is once you stop going down, the pressure, now it's easier. You just have to stop your descent. And so that's what we did a lotta testing on. You know, what kinda warning do you get?

I read that I think WT*!? So, conceptually, the hull design is problematic.

Maybe they heard pop, pop, pop, . . . , BANG.

 

[jedishrfu]

Here's a Jalopnik article on the sub:

https://jalopnik.com/the-titan-submersible-was-designed-and-built-even-worse-1850570095

 

[DrClaude]

I've seen this. My reaction is "so what?" It's not the part that failed. Lots of high-tech projects use low-tech parts.

This video has compelling arguments as to why this is actually a big deal (timestamped at 13:12, but the entire video is worth watching):

 

[TeethWhitener]

Saw some interesting speculation on instagram (I know I know) that this is analogous to the 1996 Mt Everest disaster (of Krakauer “Into Thin Air” fame), in that it may actually boost deep sea tourism. The argument for Mt Everest was that until these rinky dink companies popped up, you had to be a legitimate mountaineer to climb Everest. But after the disaster, rich folks realized they could just pay a company to drag them up the mountain. Essentially, the disaster was an advertisement for the existence of these “adventure” companies, and indeed, Everest tourism has subsequently skyrocketed, with often long waiting lines to get to the summit (of up to two hours! Seriously, people have complained of their oxygen tanks running out while they’re waiting in line to get to the Everest summit like it’s Space Mountain). Some folks are wondering if this is the same moment for deep-sea tourism.

Also, yeah the fact that carbon and titanium are at opposite ends of the galvanic series and you’re tossing the thing in saltwater raises some eyebrows. But at least according to Wikipedia, OceanFateOceanGate had made a dozen or so excursions to this depth, which is comparable to the number of crewed Dragon SpaceX missions.

 

[pinball1970]

Why does that surprise you? There's no question that this project was done on a budget.

This is the vessel built with expired materials.
(WaPo, "Titan CEO spoke of ‘discount’ parts, journalist invited on submersible says")It is controlled with a Nintendo console (BBC News, Titan sub: Cramped vessel is operated by video game controller). There may be nothing wrong with this per se, but I see Nintendo consoles at yard sales for 10 bucks.

There have been questions about the thickness of the CF (https://www.cnn.com/2023/06/21/us/titan-sub-safety-oceangate-employees/index.html)

Nothing like a black box?

I had heard that there were sounds, but I didn't know the details.

Looking at one comment in that article:Apparently, after that dive or season, "he [Rush] made some changes to the Titan, including building a new hull, and called off the planned dives for that year." So it was a new hull (new materials?, new design?, ??)

Another statement in the article:It occurred to me regarding Titanium and Carbon mating could be problematic in seawater. Carbon is more noble than Ti, so the Ti could begin to corrode, and possibly, the carbon composite reacts with elements in seawater, including dissolved oxygen. AND, if the infiltration occurred at depth at 370-380 atm, could the seawater expand at 1 atm?

Lots of aspects to investigate. This will be one of the classic cases in failure/forensic analysis - unfortunately.

It may have been covered already. If they cannot retrieve the debris or a significant amount of it what will they be investigating exactly?

Apparently there was no black box type info or coms from the vessel back to the ship bar texts, no instrument data.

Will they just look at the history? Design, materials and COP for dives as discussed?
E mails, conversations?

The other thing I wanted to ask was about inspections, like they have with air craft to see signs of stress, fractures etc. Did Titan have any? I cannot find much info on that, only the spec on wiki

 

[Vanadium 50]

I don't see that anyone suggested banning it

I believe I also said "regulate into oblivion".

Let's talk safety factors. Normally, I like to see at leas 2, and more is better. But a safety factor of 2 here would make the vehicle too heavy to ascend. So that's oit. On the other hand, we now have tragic evidence that 1.02 isn't enough. So what number do we use? 1.1? 1.9? If it helps, Alvin would be 1.67 or so.

As far as we can tell, the risk is on par with the examples you have: space tourism and climbing Everest. Statistics are small, so we don't and really can't know which is worse, but I'd like people to be at least thinking more concretely than "Space tourism good - sub tourism bad" and :Elkon Musk hero - Stockton Rush evil."

I build one-of-a-kind devices for a living. Fortunately, the risk to human lives is less than with spacecraft or submersibles. I think the best you can do would be about a 99.5% success rate - one time in 200 some unforeseen combination of events will cause a failure, and milliseconds later everybody is dead. This is a pure guess. But I believe even if a careful analysis showed it was 99.999%, the actual odds would be closer to 99.5%.

I think that's the best you can do without the resources of a major world government. (And Rush did something like 10-15x worse) So one question is "Is this enough?" another is "How high a priority should it be to protect people with more money than sense from other people with more money than sense"?

 

[russ_watters]

As far as we can tell, the risk is on par with the examples you have: space tourism and climbing Everest. Statistics are small, so we don't and really can't know which is worse, but I'd like people to be at least thinking more concretely than "Space tourism good - sub tourism bad" and :Elkon Musk hero - Stockton Rush evil."

I build one-of-a-kind devices for a living. Fortunately, the risk to human lives is less than with spacecraft or submersibles. I think the best you can do would be about a 99.5% success rate - one time in 200 some unforeseen combination of events will cause a failure, and milliseconds later everybody is dead. This is a pure guess. But I believe even if a careful analysis showed it was 99.999%, the actual odds would be closer to 99.5%.

Those were your examples and I was disagreeing....

I have a another concern though about the numbers: where are you getting the total number of dives for a 1% failure rate? Is that the number of dives to the Titanic specifically? To that or some close threshold depth? Alvin has 5,000 dives so I don't agree this is a 1% risk of failure activity even if you include the outlier in the statistics, which i still disagree with.

[Edit] Actually what you said is you don't think it can be done with 1% failure rate and alluded to an actual 2% track record.

 

[Vanadium 50]

Did I say 1%? I was thinking around 3%, which is the same scale as rocket failures. Of course, as you say, we are (fortunately) dealing with small statistics. That makes fine comparisons impossible.

But it's more or less the number of failures divided by the number of manned Titanic dives.

 

[Astronuc]

Will they just look at the history? Design, materials and COP for dives as discussed?
E mails, conversations?

The US Coast Guard (USCG) is tasked with determining the cause of casualty and the deaths of 5 individuals. To do that, they will have to look at all records (design & manufacturing, repairs, . . . . ), history, . . . .
https://www.physicsforums.com/threads/about-the-news-of-missing-titan-sub.1053432/post-6908361

It may have been covered already. If they cannot retrieve the debris or a significant amount of it what will they be investigating exactly?

Without the debris, they would have only available records.

In 2010 PH Nargeolet (one of the passengers on Titan) participated the search Air France 447 which crashed in the Atlantic. The black box and wreckage (debris field) was not determined until April 2011, when sidescanning sonar revealed the debris field at a depth of 3,980 metres (2,180 fathoms; 13,060 ft).
https://www.foxbusiness.com/video/6329798006112
https://en.wikipedia.org/wiki/Paul-Henri_Nargeolet#Premier_Exhibitions,_Inc.
https://en.wikipedia.org/wiki/Air_France_Flight_447#2011_search_and_recovery

Apparently there was no black box type info or coms from the vessel back to the ship bar texts, no instrument data.

One outcome may be a requirement that 'all' manned submersibles be equipped with a 'black box' and 'voice recorder' similar to aviation, and a requirement for some kind of telemetry system.

The other thing I wanted to ask was about inspections, like they have with air craft to see signs of stress, fractures etc. Did Titan have any? I cannot find much info on that, only the spec on wiki

It's not clear that there were any rigorous inspections. Hopefully, the USCG will review what was done with the 2019 hull.

According to what I have read, Rush eschewed non-destructive testing, and OceanGate terminated David Lochridge who raised significant safety concerns.

In their lawsuit, OceanGate accused Lochridge of breaching his contract by discussing the company's confidential information with the Occupational Safety and Health Administration "when he filed a false report claiming that he was discharged in retaliation for being a whistleblower."

https://abcnews.go.com/US/lawsuit-alleged-flaws-titanic-submersible-now-missing/story?id=100251012

In his lawsuit, Lochridge, originally from Scotland, claimed that when he joined OceanGate, the company's chief executive officer, Stockton Rush, who is believed to be aboard the missing submersible, tasked him to conduct a quality control inspection to "ensure the safety of all crew and clients during the submersible and surface operations" of the experimental vessel.

Lochridge, according to the suit, raised concerns about the design of the submersible's hull, particularly that it was made of carbon fiber instead of a metallic composition.

Lochridge, according to the suit, objected to OceanGate's and its CEO's "deviation from an original plan to conduct non-destructive testing and unmanned pressure testing" on the Titan.

"Lockridge disagreed with OceanGate's position to dive the submersible without any non-destructive testing to prove its integrity and to subject passengers to extreme danger in an experimental submersible," the suit said.

OceanGate, according to the lawsuit, intended for the Titan to carry passengers to extreme underwater depths of 4,000 meters, "a depth never before reached by an OceanGate manned submersible composed of carbon fiber."

It's possible that the carbon-fiber composite would have passed an NDT inspection, but that inspection would have provided a 'baseline' or reference for subsequent in-service inspections (ISIs). But one question to be answered, would subsequent NDT have revealed any changes in the material. Ostensibly, if designed and applied correctly, an NDT system would have detected material (CFC) changes (i.e., degradation, or loss or diminishment of structural capability). Instead, Rush put some acoustic monitoring system to indicate the response of the hull to the pressure loading - however, at depth, once it gets going (from an already diminished state), crack propagation would occur in a matter of seconds, or perhaps fractions of seconds leaving little or no time to response, i.e., stop the descent and begin the ascent to lower the pressure/stress.

As for Titan, they have discovered the front and back ends of the hull/chamber, so ostensibly those can be retrieved.

 

[Vanadium 50]

It's not clear that there were any rigorous inspections

Certainly not independent ones.

But what do you inspect for? You can't magnaflux it. A broken fiber embedded in epoxy looks pretty much the same as intact fiber. I suppose you count x-ray it and go over the prints with a microscope (or better still, a comparison microscope from when the pressure vessel was new) but if you think your radiologist takes a long time to get back to you, give him literally thousands of pictures to analyze.

IMHO, the best data you can get is a bunch of strain gauges so you can compare the deflection with what you think it should be, and if it is growing or even changing in an unexpected way. The problem with this is you might not get a dive's worth of warning.

I'll repeat my belief that the failure was most likely at the cylinder-bell attachment. Not only is this a likely spot, it's probably hardest to inspect. You don;t want to change the design to make it easier to inspect if it weakens it.

 

[russ_watters]

Did I say 1%? I was thinking around 3%, which is the same scale as rocket failures. Of course, as you say, we are (fortunately) dealing with small statistics. That makes fine comparisons impossible.

But it's more or less the number of failures divided by the number of manned Titanic dives.

Looking back you said 2% (one in 50). But yeah, I think that's a weird choice to set the target or expected safety bar at 'gross negligence'. I think you're off on what the actual normal/expected safety level for this activity is by a factor of 100 to 1000. And I'd bet the occupants and investors agree. But hey, if OceanGate survives as a company and people keep lining up for the exciting chance to be on one of the lucky 49 excursions next year we'll know.

 

[russ_watters]

BTW, I'm not really clear what drives rich people to be carried up climb Mt. Everest or visit the Titanic, but if it's the price tag itself (and the exclusivity that comes with it?), I don't see that as a very good reason. Yes, $250k is a lot of money for a "seat" on this sub or on Blue Origin, but Everest can be done for well under $100k. And these prices are actually accessible to millions of motivated "normies". You just have to forgo your boat/vacation home.

I'd be willing to pay maybe $50k to ride to the Titanic with James Cameron and if $250k could get me a ride to the ISS (it can't; it's low by a factor of 100+....c'mon, Powerball!) I'd liquidate my 401k this afternoon, but I'm not going up Everest nor riding to the Titanic in a Pinto even if it's free. And I think I'd have been able to recognize that being able to spend that kind of money like it's nothing isn't a magic Get-Out-of-Death Free card, it's reckless hubris.

I've been skydiving and scuba diving(cheap) and I have a pilot's license(expensive for a normie). I'm up for an adventure, but safety is stand-alone/not about the money. I feel like these people forgot that.

 

[Astronuc]

But what do you inspect for? You can't magnaflux it. A broken fiber embedded in epoxy looks pretty much the same as intact fiber. I suppose you count x-ray it and go over the prints with a microscope (or better still, a comparison microscope from when the pressure vessel was new) but if you think your radiologist takes a long time to get back to you, give him literally thousands of pictures to analyze.

I'll have to look into the methods of NDT for carbon-fiber composites.

Meanwhile, I found: Nondestructive testing and evaluation techniques of defects in fiber-reinforced polymer composites: A review
https://www.frontiersin.org/articles/10.3389/fmats.2022.986645/full

I would prefer to collect and review other journals, preferably peer-reviewed.

As for radiography (and even UT), I've seen automated systems for detecting small discontinuities in welds and metal walls. I have not looked into ceramics or carbon fiber composites.

One would look for changes in baseline signatures, acoustic or otherwise, either more reflections, or more transmission, or both.

There are challenges to UT.

As known from other anisotropic media in addition to well-known longitudinal and shear waves modes appear neither being pure longitudinal nor shear waves. Their specific behaviour sensitively depends on direction of propagation, polarisation and anisotropy of material properties [3]. In addition, plate modes (Lamb modes) may occur at oblique incidence if a sufficient small thickness to wavelength ratio exists [4].

Considering the influence of integrated sensors and actuators with their very different acoustic properties (acoustical impedance of piezoceramic differs from that of CFRP by scale of 10), the conditions for the propagation of ultrasonic waves increasingly get complex. Fortunately the normal incidence of longitudinal waves to the plate corresponds to the existence of the pure longitudinal wave mode [3] and admits the detection of most structural flaws with sufficient sensitivity.

Other problems arise from the layered structure [5]. The material is a combination of alternating layers (fibres in the matrix, epoxy layers, insulation layers, piezoceramic plates) of different thickness, density and elastic properties. At each interface partial transmission and partial reflection with different amounts depending on the acoustic properties take place. So reflectivity and transmissivity of layer's interface are important for the ultrasonic response of the whole structure. The numerous interfaces produce a large number of echos because multiple reflections and interference effects occur. Local variations of ultrasonic velocity in the plate's plane make it more difficult to predict and eliminate the influence of these multiple reflections.

https://www.ndt.net/article/ecndt98/aero/015/015.htm

Perhaps a phased-arrayed UT system (as described in the following articles) could be used with computed tomography.
https://www.qualitymag.com/articles...ing-of-fiberglass-and-carbon-fiber-composites
https://www.zetec.com/blog/understanding-ndt-of-carbon-fiber/

Also
https://www.compositesworld.com/art...testing-can-find-flaws-in-composite-materials

 

[Vanadium 50]

It appears that the cylinder is not entirely carbon fiber composite either, There is some metal as well, but I don't have a feel for whether it is better described as
metal reinforced with carbon fiber" or "carbon fiber reinforced with metal." The metal of course makes x-raying it harder to do.

Right now I don't have a better idea than an array of strain gauges. That has, as I think I mentioned that it may not send a clear enough or fast enough alert to do anything about it. They also suffer from the problem that where you most want a measurement is usually where something else is - a bolt, a rib, a penetration, whatever.

 

[pinball1970]

Some informative engineering posts that I am reading, appreciated. I don't get all the terms and techniques so quite a lot of googling going on.
Whilst looking I came across the Marina Trench expedition 1960.
Piccard. Apologies if this has been mentioned already.
The depths, PSI are crazy there.
1960 tech was ok?

 

[DaveC426913]

...where you most want a measurement is usually where something else is - a bolt, a rib, a penetration...

... a mounting screw or three...

 

[pinball1970]

... a mounting screw or three...

View attachment 328422

That's real?