Technical Analysis on Titan Sub (Titanic Sub)

[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Another historical document (1976) on the technology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.

 

[russ_watters]

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.

I'm not sure if galvanic corrosion has been mentioned in the thread before, but yes it is a known issue correction; not with titanium:
https://www.corrosionpedia.com/galv...ed-to-carbon-fiber-reinforced-polymers/2/1556

The other two issues ("fibers" do nothing in compression and cyclic pressure changes cause fatigue) have been discussed in the thread in some detail. Based on reports of loud cracking noises on prior dives, it's likely those two issues are the ones that doomed the sub.

 

[snorkack]

Another video related to sub implosions and sub rescue operations:

Stupid question: how can a submarine implosion have a bubble pulse frequency or it be usable to determine the depth?

 

[pinball1970]

Stupid question: how can a submarine implosion have a bubble pulse frequency or it be usable to determine the depth?

Thinking same. I can get the note part, Bigger the vessel the deeper the note, longer the wavelength.
(quick google) Translate to depth, deeper it it is, the higher the pressure, higher energy so higher amplitude? Louder? Mind you deeper it is the fainter the signal.
Need a physics/acoustics guy.

 

[snorkack]

Thinking same. I can get the note part, Bigger the vessel the deeper the note, longer the wavelength.
(quick google) Translate to depth, deeper it it is, the higher the pressure, higher energy so higher amplitude? Louder? Mind you deeper it is the fainter the signal.
Need a physics/acoustics guy.

Well, I have the issue with "bigger"/"known volume" here.
For explosion, the pulse frequency is easy. Underwater explosion in homogenous, spherically symmetric water would create a spherically symmetric bubble, apart from the pressure gradient, and that would still leave the axial symmetry intact. One bubble pulsing at one frequency that depends only on explosion power and depth.
But a submarine? Cylindrical vessel full of contents?
If the cylinder fails first at one end, the water hammer would then travel along the cylinder, break the waterproof bulkheads in succession and leave the bubble at the other end. But if the cylinder fails somewhere near the middle but not exactly in the middle then the water hammers travel from the middle towards both ends, creating two bubbles of different sizes and periods. Plus the large internal structures which have further potential to alter the bubble behaviour and split them. Bubbles with similar but different periods, close enough to each other to modify each other significantly...

 

[pinball1970]

Well, I have the issue with "bigger"/"known volume" here.
For explosion, the pulse frequency is easy. Underwater explosion in homogenous, spherically symmetric water would create a spherically symmetric bubble, apart from the pressure gradient, and that would still leave the axial symmetry intact. One bubble pulsing at one frequency that depends only on explosion power and depth.
But a submarine? Cylindrical vessel full of contents?
If the cylinder fails first at one end, the water hammer would then travel along the cylinder, break the waterproof bulkheads in succession and leave the bubble at the other end. But if the cylinder fails somewhere near the middle but not exactly in the middle then the water hammers travel from the middle towards both ends, creating two bubbles of different sizes and periods. Plus the large internal structures which have further potential to alter the bubble behaviour and split them. Bubbles with similar but different periods, close enough to each other to modify each other significantly...

Ok. The physics is beyond me here.

 

[Vanadium 50]

I'm out of my depth here.

Pun intended?

 

[pinball1970]

Pun intended?

Possibly yes. That's bad. Apologies to the people who are human beings on the site.

 

[berkeman]

Possibly yes. That's bad. Apologies to the people who are human beings on the site.

Hey, waitaminute. What about the rest of us?

 

[jack action]

If the cylinder fails first at one end, the water hammer would then travel along the cylinder, break the waterproof bulkheads in succession and leave the bubble at the other end. But if the cylinder fails somewhere near the middle but not exactly in the middle then the water hammers travel from the middle towards both ends, creating two bubbles of different sizes and periods.

When the structure fails, I would expect it to fail everywhere pretty much at the same time.

​

 

[Frabjous]

When the structure fails, I would expect it to fail everywhere pretty much at the same time.

​

I disagree. The composite probably failed at the largest flaw resulting in asymmetric failure.