Steel Alloy of modern / Cold War Subs

[Mike_John]

Hi!

I am wondering why in the newest American Seawolf Subs only HY-100 steel (Yield of 100,000 psi) is used, while there were rescue Subs in the 1960s (!) that already had HY-140 steel. Los-Angeles-Subs only have HY-80 steel alloys, what technichal reason is there to use not steel with higher yield?

High Yield is a very important attribute of submarine steel alloys, so why didn't they take the maximum available high-yield-steel they could get. We also have this problem with the Russian Navy titanium subs. Titanium has a quiet low yield, so it's difficult to give a save diving depth compared to higher yield steel alloys used in other subs.

 

[kato]

With HY-140 steel, the three Seawolfs wouldn't have cost $13 billion, but $60-$70 billion.
$100 billion if you include the industry costs for even being capable of turning out that much - HY-140 isn't in large-scale production anymore since the late 70s or so. Same goes for HY-130 and HY-150, realistically. And HY-170 of course.

 

[Mike_John]

The steel is THAT expensive? I didn't know that! I thought, electronics would be much more expensive than the "raw materials" like steel for the hull. Although I know that there is much know-how in steel-engineeing. But your cost calculation lets me come to the conclusion, that the hull-material is the _main_ factor for construction costs. I thought, sonar, radar, weapons and the reactor together were the main costs...

If your calculation is right, the russian titanium boats would be cheap compared to a boat that would have been constructed by HY-150 or higher steel!

 

[nevidimka]

I'm sorry, but what advantage does titanium hull give compared to steel?
I believe strength n dive depth?

And what russian sub's types that are using titanium in their construction?

 

[Mike_John]

Advantages of Titanium:

-Light, compared to steel -> you can use a heavier propulsion -> higher speed
-Low magnetic signature
-high strength (it is said, that some russian subs can dive to 1.000 m and above, though "save depths" only were about 600 m)

Disadvantages:

-very expensive material
-very expensivt build costs
-low yield

Alfa, Mike and Delta class submarines use respectively used an titanum alloy for example.

 

[Gryphon]

Stronger?

Earlier in this thread thread, it was mentioned that HY-100 series steels were stronger than available Titanium alloys. If this is true, why would the use of Titanium enable greater diving depths for the Russian subs that use it? Isn't it their double hull designs that give them the extra strength for deeper dives?

I have read that Russia has enormous Titanium resources, therefor it is easier, or not as prohibitively expensive for them to use it.

 

[gf0012-aust]

A number of subs have titanium as part of their build structure. The major difference is that the russian/soviet subs had entire hulls made of it.

I'm not sure why you see titanium as an advantage. the Mk48 ADCAP was designed to kill titanium hulls. The Oyashios have steel hulls and yet are considered to be the deepest diving conventionals in the world with nuke depth performance.

The advantages of titanium that were prevalent in the 70-80's are certainly not as distinct nowadays.

Esp when you factor in that currently a $500,000 - $1m dollar current tech large torpedo will kill a $1bn sub.

The economies and efficiencies of scale don't justify it.

 

[crobato]

The steel is THAT expensive? I didn't know that! I thought, electronics would be much more expensive than the "raw materials" like steel for the hull. Although I know that there is much know-how in steel-engineeing. But your cost calculation lets me come to the conclusion, that the hull-material is the _main_ factor for construction costs. I thought, sonar, radar, weapons and the reactor together were the main costs...

If your calculation is right, the russian titanium boats would be cheap compared to a boat that would have been constructed by HY-150 or higher steel!

Its not just the steel that is expensive, but _working_ with the harder steel also makes it more expensive because you are working against a much harder material. That goes down the line since that also raises your tooling requirements, being forced to bend harder steel. And that will make your refits more expensive too, since you have to work against the harder metal. And finally, even makes scrapping more expensive too, since you have to cut that harder metal. From crib to grave, it just makes the sub more costly just to work on it.

 

[alexsa]

Its not just the steel that is expensive, but _working_ with the harder steel also makes it more expensive because you are working against a much harder material. That goes down the line since that also raises your tooling requirements, being forced to bend harder steel. And that will make your refits more expensive too, since you have to work against the harder metal. And finally, even makes scrapping more expensive too, since you have to cut that harder metal. From crib to grave, it just makes the sub more costly just to work on it.

And another issue is the higher risk of brittle fracture. Higher tensile steels have a higher yeild point but are more brittle than lower tensile options. Low temperatures will simply agrrevate the problem making the use of HY140 in large structures a challenge. Stress point minimisation on the structure would be critical.

Large merchant ships in the 70's and 80's (tankers and bulk carriers) where constructed largely of high tensile steel to reduce scantling size but this was discontinued after a spate of catestrophic hull failures (which in the case of a bulk carried inevitabley led tothe loss of ship and crew). These ships are now largely built of mild steel with high tensile only used in certain areas. As a result the mass of the hull has increased but the arrangment gives the hull more flexilbity and reduces the potential for structural failure due to stress (mind you if you let it rust or damge it all bets are off).

 

[crobato]

Also compared to even the hardest steels, working with Titanium is a major pain. The whole joint for example, have to be shielded with inert gas, so its really hard to imagine building an entire hull would be like.

To be honest the whole idea of building an entire sub with Titanium didn't appear to be recommended by Soviet engineers, but the bright idea of some ambitious admiral and then the requirement is forced down the throat of the shipbuilders, who are not in a position to object unless they want to vacation in the Gulag.

 

[Mike_John]

But boats with a titanium hull showed quiet amazing diving depths, like Mike and Alfa. Especially Alfa-class subs with their powerful propulsion are amazing ships! Of course they are extreme loud and only can use their sensors at low speeds. But for their designation (intercepting US carriers and ballistic subs) they were great boats.

But we know the sowjets were and are able to build great boats without the intense use of titanium (Victor, Akula, coming Graney), so it was only propagandism to build titanium boats...

But back to the thread:

I think you can't compare the contruction of big carriers and tankers with the relative small but massive construction of subs. Of course you also need flexibility of the material in the sub-construction. But the main target should be the "strength" of the ship body. And this can be achieved best with high yield steels.

 

[gf0012-aust]

But boats with a titanium hull showed quiet amazing diving depths, like Mike and Alfa. Especially Alfa-class subs with their powerful propulsion are amazing ships! Of course they are extreme loud and only can use their sensors at low speeds. But for their designation (intercepting US carriers and ballistic subs) they were great boats.

Why were they amazing? They were great designs from a mission perspective based on Russian/Soviet design principles of the day. You wouldn't build a titanium hulled sub nowadays as there are better ways to achieve the objective. I'd argue that they were built to a specific niche tactical objective. Once that capability gets neutralised, they were a very very expensive asset without justification

But we know the sowjets were and are able to build great boats without the intense use of titanium (Victor, Akula, coming Graney), so it was only propagandism to build titanium boats...

Again, why were they great? They were certainly a soviet achievement, but if you read Red Tide Rising (Author, Weir, interviews with Russian and Soviet submariners) the Sov/Russian fleet had appallingly high numbers of failed vessels and deaths of sailors due to poor workmanship.

But back to the thread:

I think you can't compare the contruction of big carriers and tankers with the relative small but massive construction of subs. Of course you also need flexibility of the material in the sub-construction. But the main target should be the "strength" of the ship body. And this can be achieved best with high yield steels.

Of course you can. Carriers and Tankers have far more hull flex and need that needs to be factored in at design.

Also. The strength of the body is not determined by the use of high yield steel.

 

[kato]

If it was just the steel - well, there's graphite-epoxy rated for 250,000psi nowadays.
I don't think anyone's seriously considered graphite-epoxy for submarine pressure hulls yet though, other than for diving planes and such.

 

[alexsa]

I think you can't compare the contruction of big carriers and tankers with the relative small but massive construction of subs. Of course you also need flexibility of the material in the sub-construction. But the main target should be the "strength" of the ship body. And this can be achieved best with high yield steels.

I don't normally ridicule suggestiosn but this is utter rubbish. SSN, SSBN and even SSG the size of collins are not small structures. The DSRV (which uses HY120) uses a sphere structure which naturally self suporting and minimises stress concentration but the submerged displacement of this 'boat' is only about 60 tonnes (less probably, sorry i did not look it up).

To follow your somewhat flawed logic you would build a submarine out of the steel with the highest tensile strength. The problem is it is likley to fracture on impact as oppose to deforming.

 

[EnigmaNZ]

Yes I can see the reasoning. A lower yield steel will deform more as the sub descends, with hull failure being well forecast in advance with appropiate instrumentation. A very high yield steel will give little warning before it fails catastrophically. So a balance has to be found. Also a near miss explosion will deform the hull of the former, but possibly collapse the hull of the latter under some conditions.
Titanium is half the weight of steel, and similar strenght, so prosumably the weight saving is used for a heavier propulsion plant for higher speed, and thicker hull plating with additional ribs, stringers etc that gave the Alfa class it deep diving ability.

 

[alexsa]

To qualify this statement it does not mean you cannot built a large structure our of HY140 it just involves considerable design risk and difficulty and cost. It is just not worth it when you can achieve the saem result wiht a low tensile strenght which is less brittle.

 

[Salty Dog]

To follow your somewhat flawed logic you would build a submarine out of the steel with the highest tensile strength. The problem is it is likley to fracture on impact as oppose to deforming.

Submarine hulls do go through a controlled deformation as they dive. I've been there and have seen it.

They must also repeat the cycle time and time again.

 

[alexsa]

Submarine hulls do go through a controlled deformation as they dive. I've been there and have seen it.

They must also repeat the cycle time and time again.

I know they do ...... I have served on them. It does not alter the fact that ther is little advantage to uing a very high tensile steel when:

1. It cost a great deal more to do so;
2. It is much more brittle; and
3. You can achieve the same with a lower tensile steel whihc is more ductile.

 

[Salty Dog]

can achieve the same with a lower tensile steel

agreed