Technical Analysis on Titan Sub (Titanic Sub)

[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?

 

[Vanadium 50]

1960 tech was ok?

1960's tech put a man on the moon.

 

[pinball1970]

1960's tech put a man on the moon.

9 years was a long time in the 1960s.

 

[DaveC426913]

That's real?

Dunno.

But the crewmember

• is sitting on a flat floor with no equipment nearby, and
• has a mission patch that seems to check out.

 

[pinball1970]

1960's tech put a man on the moon.

1960 You not amazed by that? 5 miles down, I had to use one of those conversion things to get the PSI.

1960 fit for purpose but fast forward to 2023 at half the depth and this.

 

[pinball1970]

Dunno.

But the crewmember

• is sitting on a flat floor with no equipment nearby, and
• has a mission patch that seems to check out.

View attachment 328423

I'm sorry for the kid to be honest. Did he look into all this, risk, design, protocol tests? Of course not. He was with his dad right?
That angers me, he did not know anything, as much as me before it happened.
He wanted to do the Rubik's cube at low depth.

 

[Astronuc]

The depths, PSI are crazy there.
1960 tech was ok?

Yes, the descent was made in the Trieste bathyscaphe.

Trieste is a Swiss-designed, Italian-built deep-diving research bathyscaphe which reached a record depth of about 10,911 metres (35,797 ft) in the Challenger Deep of the Mariana Trench near Guam in the Pacific. On 23 January 1960, Jacques Piccard (son of the boat's designer Auguste Piccard) and US Navy Lieutenant Don Walsh achieved the goal of Project Nekton. It was the first crewed vessel to reach the bottom of the Challenger Deep.

https://en.wikipedia.org/wiki/Trieste_(bathyscaphe)

A separate pressure sphere held the crew. "To withstand the enormous pressure of 1,250 kilograms per square centimetre (123 MPa) at the bottom of Challenger Deep, the sphere's walls were 12.7 centimetres (5.0 in) thick; it was over-designed to withstand considerably more than the rated pressure. The sphere weighed 14.25 metric tons (31,400 pounds) in air and eight metric tons (18,000 pounds) in water. . . "

The personnel sphere (gondola) is composed of a high strength steel described as a non-fatiguing chrominum-nickel-molybdenum [steel] alloy. The original (first) sphere was made by Terni (it was limited to a depth of ~20,000 ft (~6100 m), while a second sphere was made by Krupp Steel Works (had not depth limit!); ostensibly the same or similar alloy. The Krupp sphere was used in the deep dives.
https://apps.dtic.mil/sti/pdfs/AD0616288.pdf

From the Wikipedia article, "Trieste was fitted with a new pressure sphere in the winter of 1958,[5][6] manufactured by the Krupp Steel Works of Essen, Germany in three finely-machined sections comprising an equatorial ring and two caps, and by the Ateliers de Constructions Mécaniques de Vevey."

I cannot readily find the composition, but from the description, I suspect it is similar to HY-80.
https://en.wikipedia.org/wiki/HY-80

Dives of the Bathyscaph Trieste, 1958-1963: Transcriptions of sixty-one dictabelt recordings in the Robert Sinclair Dietz Papers, 1905-1994
https://library.ucsd.edu/speccoll/DigitalArchives/smc0028/Dives_Bathyscaph_Trieste_Dictabelts.pdf

Another historical document (1976) on the technology
https://seawifs.gsfc.nasa.gov/FRANKLIN/DOCS/Manned_Submersibles_by_R.Frank_Busby.1976.reduced.pdf

 

[pbuk]

1960 fit for purpose but fast forward to 2023 at half the depth and this.

The passage of time does not prevent poor design choices. The Trieste was a steel sphere, the Titan a composite cylinder. You seem to have concluded that the designers of the Trieste were ahead of their time; an alternative conclusion is that the designer of the Titan was negligent. There seems to be a lot of evidence confirming the latter.

 

[Astronuc]

In 2019, the submersible expert Karl Stanley warned OceanGate's CEO that more tests were needed.
https://www.yahoo.com/news/submarine-expert-desperately-tried-dissuade-075202012.html

In April 2019, Karl Stanley, who runs his own deep-sea exploration company in Honduras, took a 12,000-foot plunge inside the Titan off the coast of the Bahamas and said he heard a large cracking sound during the two-hour dive.

A FOX News video had an interview with a Dallas, TX businessman, Victor Vescovo, founder of Caladan Oceanic, his own marine submersible operation, had expressed concern about the carbon-fiber composite hull and OceanGate's lack of testing.

Victor Vescovo is a Dallas businessman and submersible pilot. He was friends with two of the victims, British adventurer Hamish Harding and French Titanic expert Paul-Henri Nargeolet.

https://www.fox4news.com/news/team-of-investigators-to-probe-titan-submersible-implosion
https://www.fox4news.com/news/titan-submersible-victims

Investigators from the United States, UK, France and Canada are working together to try and figure out what caused a submersible to implode eight days ago.

The U.S. Coast Guard's Marine Board of Investigation will work with authorities from Canada, the U.K. and France.

Vescovo apparently discourage folks from joining the OceanGate dives due to concerns over safety.

 

[Astronuc]

David Pogue's account (journal) of his experience with Titan.
https://nymag.com/intelligencer/2023/06/what-i-learned-on-a-titanic-submarine-expedition.html

Last summer, for a CBS News Sunday Morning story, I joined OceanGate for a dive on its Titan submersible. I never saw the Titanic. We were only 37 feet below the waves when mission control aborted our dive.

The dive was supposed to happen during July 2022

He [Paul-Henri Nargeolet] observed the testing and construction of the Titan and is completely satisfied with its design. “I will say, in the world of the submarine, there was a rule: no carbon fiber,” he says in his French accent, laughing. “But he was working with Boeing, with big company. And when you see the way they were doing the cylinder — it’s not in a garage, you know, with glue and stuff like that. It’s very well done.”

Rush says that the Titan has already made 20 uneventful dives to Titanic depths, which also calms me. And above all, Rush himself pilots most of them. Why would he drive the Titan if he has any concerns about its integrity?

So, if Pogue's dive had been successful to the Titanic, the recent failure probably would have happened earlier during a previous successful dive.

I also know stuff goes wrong in the North Atlantic. In 2021, Mexican YouTuber Alan Estrada filmed the return of the Titan dive before his own. When the sub rose to the surface, the OceanGate crew couldn’t get it back onto the ship. Its occupants spent 27 hours inside before they could be rescued.

Red flag.

I’m slowly realizing the Titan doesn’t actually make it to the Titanic very often. On each of the nine OceanGate expeditions so far, Titan reached the shipwreck twice, once, or not at all. Indeed, Rush explains, that’s why only six paying customers are onboard, enough for two dives; he has learned he can get only two or three good dive days a week. Tomorrow, day one, will be our CBS dive. After that, the selection of “mission specialists” for each dive depends exclusively on Rush’s mysterious internal logic.

Thursday, June 22, 2023​

They’ve just found the debris of the Titan.

Everyone’s suddenly a carbon-fiber expert. But if you really want to know what happened, I think Alfred McLaren, a retired Navy sub captain who has spent a cumulative 5.75 years of his life underwater, has the most plausible explanation.

It wasn’t the carbon fiber itself. It was the three dissimilar materials: carbon fiber, titanium, and plexiglass. “They have different coefficients of expansion and compression,” he tells me in another CBS interview. “You make repeated cycles in depth, of course you’re gonna work that seal loose.”

We'll once the debris field map is published, which would show the pieces of hull (and end caps) and where they landed.

And apparently, pieces of Titan have been retrieved from the site.

Imploded Titanic submarine seen for first time as pieces recovered from sea floor
https://www.yahoo.com/news/imploded-titanic-submarine-seen-first-144824288.html

Edit/upate: https://www.bbc.com/news/world-us-canada-66045554
One of the images shows a Ti cap. Window is missing, but could have been removed.

Description of the debris found earlier, which indicated Titan had failed, ostensibly by implosion.

 

[Vanadium 50]

Red flag.

Um why?

Had they built a better pressure vessel, would this not have happened? Does a failure of the lifting device (we used to call them "cranes", but that's not as cool) tell us anything about the integrity of the hall?

If you want to say it's a general pattern, do we apply it uniformly? I had a car with a rafio problem - does that make it unsafe to drive? Isn't that a pattern of failures?

And isn't aborting a dive when conditions are too risky argue against the idea that OceanGate takes needless risks because they need the cash?

 

[BillTre]

Um why?

Looks like not great planning.
This seems like a predictable problem.

 

[Vanadium 50]

Sure, but the better evidence is that they sunk their vessel.

Looking back one can find these examples everywhere, including things that did not end in disaster. It's easy to look back and say "They should have known!"

This seems to be different than the Boston Molasses Flood of 1919, where the tank began to leak and the solution was "paint it brown".

 

[russ_watters]

1960 You not amazed by that? 5 miles down, I had to use one of those conversion things to get the PSI.

The moon landing amazes me. The amount of technology that had to be invented from scratch and massive complexity of the craft with so much that can go wrong is mind boggling. Many of the astronauts started their careers flying prop planes, because jets hadn't even been invented yet.

But a deep see submersible is just a spherical metal ball (well....most of them). There's exactly one major engineering problem to solve. And yes it's big, but its straightforward and its always exactly the same. And the problem itself is probably something you can find in a sophomore Statics book. It's that simple from a conceptual standpoint. My suspicion is the main problems were in metallurgy and manufacturing (how to make your spherical metal ball as uniform as possible). Also how to cut holes in it without weakening it too much.

I mean - has there ever been a catastrophic deep submersible accident before? There's a wikipedia article listing sub accidents for the past 20 years, and there's only one entry for a dsv, and it's new.

 

[russ_watters]

They're picking up wreckage of the sub and have said to have found "presumed human remains". I shudder.
https://www.cnn.com/2023/06/28/americas/titan-submersible-debris-st-johns/index.html

Note, the handful of photos show obvious large parts of the external structure intact, but I haven't seen anything yet might look like the remains of the pressure hull. My first thought was "shattered glass bottle" but the fibers may prevent it from completely pulverizing.

 

[256bits]

But a deep see submersible is just a spherical metal ball (well....most of them). There's exactly one major engineering problem to solve. And yes it's big, but its straightforward and its always exactly the same. And the problem itself is probably something you can find in a sophomore Statics book. It's that simple from a conceptual standpoint. My suspicion is the main problems were in metallurgy and manufacturing (how to make your spherical metal ball as uniform as possible). Also how to cut holes in it without weakening it too much.

Thick or thin walled pressure vessel.

for a thick walled, there is the immediate calculations to be done with the Lame equations.
https://www.hkdivedi.com/2019/11/thick-cylinder-lames-equation.html

At the depth of the Titanic,
for a 2m dia, .25 m thick shell, one gets a tangential stress of only 30, 000 psi on the inner wall, with a tangential stress of 26,000 on the outer wall. The actual stresses aren't all that serious on their own.
Thinner the wall wrt the diameter and the stresses go up.
Radial stress is 0 ( 14.7 on the inner wall and the outer wall follows the pressure from the sea water at depth.

But as for most things, other considerations follow.
A slender rod can take the compression, and not fail from the compression stress alone - they fail by buckling.

See the pictures of the tanker implosions. Once the failure starts there is no negative feedback to counteract. the process continues to final completion equalizing the pressure differential between inner and outer.

If one relies simply only on the Lame equations, the thickness of the vessel can be very 'thin' and not fail( implode) if stresses would be evenly distributed throughout the material, no defects within the material , no stress concentrations with viewports, attachments, etc. The perfect vessel made with the perfect material would just compress and shrink evenly, be it either a cylinder or a sphere.

Of course, nothing is perfectly round, nor made out of a perfect material.
Adding in different materials, one for the shell, and another for the end caps of a cylindrical pressure vessel does complicate the " do we have this correct" checking off.

 

[Rive]

I haven't seen anything yet might look like the remains of the pressure hull.

So far what I've seen is the nose cone (looks intact, but it's without the window part?) and the two ring-like pieces attaching the front- and back cones to the tube.

Some news mentioned that the tail cone found too, and some others implies that the rest is in a shape according to the implosion...

1960 tech was ok?

I think the difference between the old and new tech would be nothing dramatic. New tech allows more homogenous and strong material, better quality check and more precise manufacturing => a bit thinner hull, based on less conservative over-design. But the very basis of withstanding high pressure is the very same: solid metal, and lot of it.

 

[Vanadium 50]

But a deep see submersible is just a spherical metal ball (well....most of them). There's exactly one major engineering problem to solve.

You had one job! One job!

I'm not sure I agree with this. Think about the umbilical. If I go to Tru-Valu Hardware and pick up a 2-/12 mile spool of cable, and hang it off a 2-1/2 mile tower. it will yield under its own weight. In fact, for ordinary steels at the short-sample limit you can do about 1.5 miles.

Solvable? Sure. You can pick a different steel (but this often comes with other problems, like workability) and figure out how to test miles of cable so there are no weak spots, and so on. And that's just yield. What about creep? But this is engineering.

And that's after 60 seconds of thought. There could easily be others.

 

[russ_watters]

I'm not sure I agree with this. Think about the umbilical.

I thought the Titan didn't have an umbilical?

Regardless, that doesn't seem to me like a particularly difficult problem, and it's one (the solution anyway) that doesn't really scale/get worse with depth. And it's not necessarily life safety critical if you have one and it fails.

 

[Astronuc]

Former National Transportation Safety Board investigator Tom Haueter called the probe "uncharted territory" that could take "months" to analyze the failures.

"This is the first fatality on a passenger carriage submarine I can think of and certainly the first one going into Titanic at this depth," Haueter told ABC News.

Haueter said a big part of the investigation will involve metallurgy specialists looking at the materials the submersible was made of to see what could have failed. The pressure vessel area -- the compartment where the passengers were -- may also reveal what failed, he said.

https://www.yahoo.com/gma/debris-titan-submersible-brought-ashore-161416927.html

Investigators will also look at its design, diving history and maintenance, he said. What is learned could improve what he called a very small industry.

"I think there are things they'll be able to learn to say, OK, if we're going to do this again and allow people to descend to these incredible depths and amazingly high pressures, that here's things that should be considered when developing these types of vehicles," Haueter said.

On Wednesday evening, the TSB of Canada, which is assisting in the investigation, said in a statement that they had completed “collecting relevant documents and completed the preliminary interviews with those on board the support vessel Polar Prince.”

I'm curious about the end caps. The front nose cap seems to have detached from the Ti ring, which was somehow fastened/jointed to the CFC shell. It's possible failure could have occurred at the location, or otherwise the hull collapsed at half length. Also to be answered - Was the rear end cap still attached to the hull shell?

 

[Astronuc]

Radial stress is 0 ( 14.7 on the inner wall and the outer wall follows the pressure from the sea water at depth.

The outer wall of the hull experiences a pressure of about ~5500 psi (~375 atm, 37.9 MPa), or a slightly greater (I'm finding different numbers).

Many engineering calculations assume uniform bulk properties. One could use a FE code to look it deviations from nominal properties and geometric dimensions.

 

[snorkack]

But as for most things, other considerations follow.
A slender rod can take the compression, and not fail from the compression stress alone - they fail by buckling.

Or shear, or axial splitting.

See the pictures of the tanker implosions. Once the failure starts there is no negative feedback to counteract. the process continues to final completion equalizing the pressure differential between inner and outer.

Is the crushed tanker under elastic stress?

 

[jedishrfu]

Another video related to sub implosions and sub rescue operations:

 

[Astronuc]

• OceanGate hired teenage interns to design the Titan's electrical systems, The New Yorker reported.
• "The whole electrical system — that was our design," the former intern Mark Walsh said in 2018.
• A community college that sent interns to OceanGate stopped offering internships with it in 2019.

https://www.yahoo.com/news/stockton-rushs-oceangate-had-college-043106609.html
Keep in mind this is Insider.

I'll wait for an official report from an official organization.

The ambitious seafaring company previously touted its partnerships with NASA, Boeing, and the University of Washington on the Titan's design. These claims were later denied by Boeing and the University of Washington, who said they did not work on the Titan submersible.

Washington State University said in a statement to the local daily newspaper the Everett Herald on June 22 that they did not "have an alliance with OceanGate."

OceanGate's former finance director said she quit when Stockton Rush asked her to be the Titanic submersible's chief pilot after firing the original one for raising safety issues: report
https://www.yahoo.com/news/oceangates-former-finance-director-said-051737973.html

Some pretty strange/disturbing revelations coming out of OceanGate.

I have to wonder if they have a licensed structural engineer do the stress/design analysis? I wonder if they even did a valid stress analysis.

Edit/update:

The MBI will look into any accountability aspects and can make recommendations for civil or criminal sanctions if necessary. The investigation can determine "whether an act of misconduct, incompetence, negligence, unskillfulness, or willful violation of law" contributed to the accident.

Any subsequent enforcement will be pursued under a separate investigation, Neubauer said.

The Marine Board of Investigation will produce a report with its findings, which will be sent to the Coast Guard Commandant and international maritime partners in an effort to improve safety measures for submersibles worldwide, according to Neubauer.

https://www.yahoo.com/news/titan-investigators-try-why-sub-181658100.html

 

[russ_watters]

I was thinking of following-up my semi-hyperbolic post about the pressure hull being a pretty basic college statics problem (at least when viewed simplistically) with one about this new college interns story, but decided against it. It's tough to know how much of that is bragging/how much real responsibility the interns actually had. After all, an intern working for my company might say they designed the pharmaceutical cleanroom the drugs you are taking were manufactured in.

 

[Ivan Seeking]

I was trying to find a source to confirm this and haven't spotted one yet. However an engineer from the submarine community stated in an interview that carbon fiber has already been ruled out as unsafe for salt water submarines [at least]. The claim was that where you have a joint between carbon fiber and titanium, as at the end caps, because carbon is a metal, you get current flow between the dissimilar metals. This in turn starts to break down the epoxy used in the carbon fiber, which eventually begins to delaminate.

The claim was that this was clearly established some years ago. Additionally, carbon fiber is appropriate for tension, not compression. And lastly, cycle testing was refused. And that is where the problems occur. It isn't just the pressure. It is the number of pressure cycles that causes problems.