September 6, 2016

Pressure Hull Alloys Debate: Titanium Alloy versus Steel Alloy

Cutaway diagram of a Soryu submarine which uses NS110 pressure hull steel. The diagram displays the cylindrical pressure hull shape, which is rounded at the ends. The diagram by "wispywood2344" was in the article of October 26, 2015. larger version is at http://blog.livedoor.jp/wispywood2344/others/Soryu_cutaway.
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This article is about pressure hull materials, with the costs and benefits of using Titanium (Ti) alloy or Steel alloys. My friend has provided the following comments comparing Japanese submarine steel NS110 for Soryus with the Titanium alloy used for the deep diving Japanese manned research submersible Shinkai 6500.

For Shinkai 6500 Ti alloy was selected due to its light weight.  Light weight is important because Shinkai needs to regulate its buoyancy and if it were excessively heavy its range/endurance would be too limited. It relies on limited battery power. 

In contrast retired US deep sea submersible NR-1 avoided battery limitations by being nuclear powered and may have been able to dive to 1,000+ meters.

To achieve Shinkai's maximum diving depth of 6,500m [hence "Shinkai 6500"] the pressure resisting configuration of two pressure hull spheres is used.

If fighting naval submarines also used two pressure hull spheres they could also achive 1,000+ meter depth, but they would have severe fighting limitations. For example they could not move at a useful fighting speed of 4 to 20 knots. A fighting submarine uses at least one pressure hull which is shaped like a cylinder (with rounded ends) reinforced by inner or outer frames.

The weight of NS110 hull may be around 30% heavier that of Ti alloy.

So NS110 hull may be able to achieve nearly the same strength as that of Ti alloy. NS110 is no doubt expensive, but Ti alloy is much more expensive.

PETE ADDED BACKGROUND

Titanium alloy is lighter than steel alloy in at least two respects:

1.  Ti (per cubic centimeter) is lighter than steel, and

2.  Ti alloy can be built thinner than steel alloy to provide the same pressure hull strength.

The Soviets/Russians on a large scale developed Ti alloy for submarine pressure hulls from the 1960s-80s, but there were many downsides. Ti proved expensive to mine and process. Ti alloy was difficult to form/work or roll for pressure hulls. It was difficult to weld. All this made it more difficult to maintain and repair subs.

Most notably the Soviet/Russia's Alfa class SSN used hundreds of tonnes of Ti alloy and may have test dived to 1,300 meters. This was a highly risky glory test which destroyed many fittings (like sonars) that were outside the pressure hull.

Later the huge (48,000 tonnes (submerged)) Typhoon class SSBNs used thousands of tonnes of Ti alloy for their multiple pressure hulls. This Ti alloy formed a major cost component of the 6 Typhoons. But these 6 alone represented one of the Soviets' major defence projects that bankrupted and demorilised the Soviet Union from the late 1980s (more see http://gentleseas.blogspot.com.au/2015/07/previous-use-of-titanium-in-russian.html).

Ti alloy, for submarine pressure hulls, can thus be thanked for helping break up the Soviet Empire. The more practical alternative of high yield steel alloy NS110 (and less known foreign equivalents) exists today. I calculate NS110 may permit an operating depth of 600m (redded further down in this Submarine Matters article of January 20, 2015).

Pete and friends

21 comments:

Anonymous said...

So I suppose if we want to bankrupt Putin's efforts to revive the Russian submarine
fleet, we should convince the Russians to make their submarines out of this:

http://www.nextbigfuture.com/2016/07/titanium-gold-alloy-that-is-four-times.html

:)


Of course, if you're really determined to make a submarine out of a lightweight
non-magnetic metal that's cheaper than titanium, an example of such a submarine
already exists:

https://en.wikipedia.org/wiki/Aluminaut

Josh said...

@Pete:

How useful is it to have a deep diving capability? Does operating deep involve any trade offs besides expense of the hull? Is it at all problematic to launch weapons for example? Do detection ranges of enemy ships go down with deep depth? Minimally there are some areas, notably the SCS, where depths will be limited regardless of hull type. Combustion based AIPs also are depth limited since they can't vent exhaust below certain depths/pressures.

Cheers,
Josh

Peter Coates said...

Hi Anonymous

The challenge of finding alloys strong enough for deep submarine diving, while light enough to allow a sub to move at useful military speeds (say 4 - 20 knots) is daunting.

Thanks for https://en.wikipedia.org/wiki/Aluminaut . Very interesting mission it had
https://en.wikipedia.org/wiki/Aluminaut#1966:_Helping_recover_a_lost_unarmed_atomic_bomb

Pete

Peter Coates said...

Hi Josh

Lots of questions that you or others may care to answer.

Re: "How useful is it to have a deep diving capability?" Historically Russia has put great store on Ti pressure hulls (eg. the Alfa class) to dive so deep it evades Western torpedos and perhaps depth charges.

Japanese sub tactics particularly rely on deep diving:

See article http://gentleseas.blogspot.com.au/2016/08/japanese-submarine-tactics-combat.html of Aug 30, 2016

"After firing their torpedos, Japanese submarines will dive very deeply at maximum speed to avoid enemy counter attacks. Japanese submarines can dive deeper [maybe 600+m] than the crush depth of average torpedos. If the maximum speed of LIBs-Soryus is 4-5 knots faster than that of AIP/LABs-Soryus, then LIBs-Soryus can reach maximum submerged depth vital seconds earlier than AIP/LABs-Soryus. This may considerably improve the survival rate for LIBs-Soryus in combat.

The relatively strong steel hull of Japanese submarines [no Titanium used] enables application of these hit and run tactics."

Japanese pressure hulls capable of deep diving tend to be restricted to little or no hull cutting. So engine maintenance is minimised. On rare occasions for maintenance, engines need to be dis-assembled piece-by-piece with parts put through existing hatches. No extensive Collin's cutting (ie. "sun-roofs") is possible.

Regards

Pete

Josh said...

Pete:

It seems questionable to me that the Japanese actually practice deep dives as a standard post firing tactic. First, it implies that there are either issues with target detection or weapon launch at depth, or else why not always be at deep depth? Second, it assumes that the firing sub will be taken under counter fire. There certainly is the possibility since torpedo launches require a number of activities that can create noise, but I'd assume evasion involves hull popping and speed related noise that are something you'd do only when positively under fire. It also doesn't seem like a hard technology to counter: the ADCAP version of the Mk48 specifically extended depth and speed to engage Alpha type targets (the Papa having preceded it and Mike following it).

Diving deep definitely has its advantages and it seems like the Japanese go to great lengths to extend that depth, but I would doubt that torpedo evasion is chief driver of the requirement - a sub design that has to soldier on for two decades could be quickly overtaken by much simpler update to an opponent's torpedo technology.

I would guess the real value of deep diving is likely detection avoidance, particularly by ship and aircraft based sensors.

Cheers,
Josh

Anonymous said...

Hi Pete

As crushing strength changes inversely with curvature radius of cylinder, the crushing strength of aft and fore parts of pressure hull (narrow part of 1 & 2, 11, 12) is higher than that of other parts made of the steel with the same thickness and proof strength.

According to modern concept of quality control, uniform failure of material is desirable and partial excess strength is needless. Therefore, aft and fore pressure hull may be made of the steel with thinner and same strength (NS110), with same thickness and lower strength (NS80), and so on.

As NS80 is less expensive and more weld-friendly than NS110, partial adoption of NS80 for pressure hull is rational design.

Regards
S

Peter Coates said...

Hi Josh [at 7/9/16 11:55 PM]

Your points may be valid.

I rely on commenters knowledgable about the Japanese Navy to address your points.

Regards

Pete

Peter Coates said...

Hi S [at 8/9/16 8:59 AM]

Thanks for your comments on pressure hull curvature-strength and also on possible use of NS80.

Regards

Pete

Anonymous said...

Hi Pete

MK48 and ADCAP MK48 adopt swash plate piston engine using Otto fuel II [1, 2] which emits nitrogen as exhaust gas. As the efficiency of this engine will be affected by exhaust back pressure [3], i.e., depth, MK48 or ADCAP MK 48 obviously cannot maintain its performance [1] in very deep water. Therefore deep diving tactics is effective for this type of torpedo, and for VA-111 Shkval which uses super cavitation whose generation is significantly inhibited by high hydro pressure.

By the way, reference 3 introduces quite interesting video of swash plate piston [4].

[1]https://en.wikipedia.org/wiki/Mark_48_torpedo
[2]https://en.wikipedia.org/wiki/Otto_fuel_II
[3]https://web.archive.org/web/20010401035621/http://www.janes.com/defence/naval_forces/news/juws/juws010202_1_n.shtml
Chapter “Torpedo Engines” describes MK46 which adopts the same swash engine and Otto fuel II system as MK48.
”The MK 46 cam-piston engine is essentially a constant torque output device, with the torque dependent on combustion pressure and back pressure. Fuel pump output pressure (combustion pressure) is controlled by an internal regulator that is referenced to sea pressure to maintain nearly constant shaft output torque as the sea pressure increases with depth. Constant vehicle speed is then maintained at all running depths.”
[4] https://www.youtube.com/watch?v=eRCUqcwqu5w&feature=related

Regards
S

Peter Coates said...

Hi Josh

Re what you said at 7/9/16 11:55 PM

I agree that the real value of Japanese subs of deep diving after firing their torpedos "is likely detection avoidance particularly by ship and aircraft based sensors".

The https://en.wikipedia.org/wiki/Type_89_torpedo that Japanese subs use are reputedly similar or even a variant of Mark 48s, which can be fired quietly.

As Russian Alfa subs may have been able to regularly dive to 800-1,000 meters it is logical they (and current Yasen SSNs and Kilos) could operate torpedos with 1,000m operationg depths. Easily able to hit 600m diving Japanese subs. Meanwhile Japan's other main opponents, China and North Korea, may have less efficient torpedos and sensors than the Russians.

So it seems Japanese subs mainly need to evade sensors. No doubt the Japanese have methodically studied thermoclines patterns along their Sea of Japan down to South China Sea patrol routes (for offensive and defensive purposes).
http://gentleseas.blogspot.com.au/2016/08/chinas-current-ssbns-limited.html

I have less of a feel for lightweight torpedos.

Pete

Peter Coates said...

Hi S [at 8/9/16 9:44 PM]

Interesting reference on Mark 48s and how they function.

The capabilities of enemy torpedos are also interesting. Max operating depth seem highly classified?:

- the Russian 533mm https://en.wikipedia.org/wiki/Type_53_torpedo is shared with China - I don't know if N Korea haas them.

- Russian 650mm https://en.wikipedia.org/wiki/Type_65_torpedo shared with China

- Russian lightweight torpedo https://en.wikipedia.org/wiki/APR-3E_torpedo shared with China

- Russia's https://en.wikipedia.org/wiki/VA-111_Shkval exported to Iran and other countries, probably China.

Here's a useful reference http://www.naval-technology.com/features/featurethe-worlds-deadliest-torpedoes-4286162/ :

- DCNS F21 HWT can be operated in depth ranging "from 10m to 500m"
- SAAB's Torpedo 62 (Torpedo 2000) "operates at depths of 500m"
- EuroTorp's MU90/IMPACT LWT "operating at depths of more than 1,000m"

Regards

Pete

Anonymous said...

Hi Pete (at 9/9/16 5:46 PM)

In submarine operation, effect of internal wave which sometimes slides submarine downwards to depth should be considered. On 10 April 1963, USS Thresher (SSN-593) had collided huge internal wave (350m) which immediately carried the submarine to depth exceeding crushing limit.

Taking account of collision with huge internal wave, the maximum operational depth of Alfa-class submarine is set shallower than 800-1000m. I am expecting this depth may be around 600-700+x m.

Regards
S

Peter Coates said...

Hi S [at 9/9/16 9:41 PM]

Thanks for your comments on "internal waves". I had never heard of them.

Such waves indeed would persuade submarine captains not to patrol at their maximum operating depth.

I did some research indication: "Where low density water overlies high density water in the ocean, internal waves propagate along the boundary. They are especially common over the continental shelf regions of the world oceans and where brackish water overlies salt water at the outlet of large rivers." https://en.wikipedia.org/wiki/Internal_wave#Internal_waves_in_the_ocean

And more specifically:
"Submarines transiting through the Straits of Gibraltar run into internal waves. A sub will sink about 30~50 feet, pass through it in a few minutes, then rise up the same distance. It is a well known phenomena and the diving officers of the watches are briefed about it before entering the straits and told not to compensate ballast because of it is transitory nature." in comments at http://doubtfulnews.com/2013/02/internal-waves-look-scary-but-are-essential/

I wonder if a submarine's navigational sonar sensors could detect internal waves in front of (or above) the submarine?

Regards

Pete

Anonymous said...

Hi Pete

If the submarine at maximum operating depth crushes by collision with internal wave, it may belong to design basis accident, because existence of internal wave and its risk are known. Unless the government proves design validity of crushed submarine, it must pay huge amount of compensation and consolation money to submariners’ family. I think crushing depth is set by taking into account of maximum operating depth and enough safety margins including internal wave to assure safety at maximum operating depth for normal situation.

Understanding of internal wave has been acquired for years, but there are so many things remained to be clarified. Research on submerged turbulence detection with optical satellites is reported, but the detection by submarine's sonar sensors is much more difficult.

Regards
S

Anonymous said...

Hi Pete

I agree your opinion (11/9/16 3:39 PM). If submarine slides downwards beyond the maximum operating depth by collision with internal wave, its hull may be damaged depending on the depth after collision. If submarine with maximum operating depth of 600m slides to 950m, some damage of pressure hull is expected.

Conversely, the well safety margined 600m-class submarine might escape from existing torpedo attack, at least once.

Regards
S

Peter Coates said...

Hi S

Thanks for your two posts above. Internal waves look a real danger to subs.

I've just found internal wave and satellite details at a Submarine Matters article I'd forgotten about "Satellite Detection of Submarines" April 11, 2012 http://gentleseas.blogspot.com.au/2012/08/satellite-detection-of-submarines.html including:

"A US Navy oceanographer from Australia, Paul Scully-Power, who became the first oceanographer in space, flew on the space shuttle Challenger (STS 41G) in 1984.

The US Navy later admitted that the mission had successfully detected the undersea or internal waves generated by a submarine which had been tracked successfully at relatively shallow depths.

This was deemed, "incredibly important to us" and was reported by the Washington Post in 1985 - quoting a senior US Navy admiral at the time. [connect with "Shuttle Flight Yields Data on Hiding Subs," The Washington Post, March 22, 1985, p A10. http://sci.military.naval.narkive.com/mDBp0PgL/submarines-and-sts-41-g ]

Regards

Pete

Anonymous said...

Hi Pete

Taking into account of weight losses by removal oxygen tank and exchange of LABs with LIBs, announced weight gain of submarine (+100 ton) and various factors including magnetic balance of cell modules, I expected arrangement of LIBs for 27SS, 28SS and 29SS.

In 27SS and 28SS, two groups of same with the same arrangement (even number columns of 12 cell modules, groups 3&4) are newly set in set in section 10. Each of two generators arranged parallel to each other section 11 distributes electricity to 240 cell modules in section 5 or 8 and group 3 or 4.

In 29SS, two examples are proposed. By full adoption of NS110, increase in maximum operation depth is possible for example II.

Example I 512 cell modules = 24 columns x 12 cell modules x 2 groups, where submarine length is 74-75m.
Pressure hull consisted of 5 compartments eliminating 4th compartment. Each of two generators distributes electricity to one group of cell modules in sections 5 or 8.

Example II 672 cell modules = 14 columns x 12 cell modules x 4 groups, where submarine length is ca.78-79m
Pressure hull consisted of 7 compartments inserting new compartment between 3rd and 4th compartments. Each of four groups of cell modules is set in four sections, i.e., 5, 8, 10 and new sections. Each of two generators distributes electricity to two groups of cell modules (336 cell modules). 16 columns is better, but submarine becomes too big.

Regards
S

Peter Coates said...

Thanks S [at 14/9/16 9:49 PM]

For the information. You connect pressure hulls, sub's length, number of compartments, and number of batteries in ways that I was unaware of.

If 29SS were to have 672 cell modules (and not 512) then the performance of 29SS may improve in terms of longer time submerged OR greater speed OR improved safety OR a combination of all three effects.

I'll build a future article around your comments.

Regards

Pete

Anonymous said...


In non-AIP Soryu (27SS, 28SS), properties and performance of LIBs will be thoroughly examined and the obtained results will be feedbacked to 29SS. Properties (especially safety) and performance of LIBs must be verified and validated as actual equipment under the real conditions. The elements indispensable for the operation of LIBs such as fire extinguishing systems will be obviously examined. Cutting edge analysis techiniques for system reliabitiy such as failure mode and effects analysis (FMEA) and fault tree analysis (FTA) are applied fordependability management of LIBs. egree of completion of 29SS is expected to be high, because of existence of two pilot models (27SS, 28SS).

Anonymous said...


Hi Pete

I add the explaination of FMEA and FTA. Failure mode and effects analysis (FMEA) and Fault tree analysis (FTA) are widely used for delopment of automobile and airplane. As LIBs are key elements of submarine, FMEA and FTA are definitely applied for LIBs.

FMEA- also "failure modes," plural, in many publications—was one of the first highly structured, systematic techniques for failure analysis. It was developed by reliability engineers in the late 1950s to study problems that might arise from malfunctions of military systems [1].

FTA is a top down, deductive failure analysis in which an undesired state of a system is analyzed using Boolean logic to combine a series of lower-level events [2].

[1] https://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis
[2] https://en.wikipedia.org/wiki/Fault_tree_analysis

Regards
S

Peter Coates said...

Hi

Thanks for the information at 8/10/16 2:30 PM and 8/10/16 3:44 PM.

Safety monitoring (and agreed standards for measuring) of LIBs is critical due to LIBs high energy intensity/high performance.

There is considerable interest from submarine designing companies/countries with the progress of Japan's first use of LIBs on a large scale in submarines.

Even Russia may develop LIBs for SSKs (like the Kalina) rather than developing AIP http://nationalinterest.org/blog/the-buzz/russias-next-submarines-will-be-small-super-stealthy-17964.

Regards

Pete