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My limited knowledge in engineering tells me:

  • Titanium is expensive, stronger and heavier than aluminium, lighter and weaker than high yield steel.

  • The most significant advantage of titanium is the good strength to weight ratio.

  • In case of submarines, weight is not really a big concern, as long as the weight is manageable (less than the displacement and bigger than displacement - maximum ballast mass).

The mentioned points exclude the use of titanium. Since the designers decided otherwise, and surely had some good reasons, I wonder where my misunderstanding is?

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    $\begingroup$ Does titanium rust / corrode in seawater? $\endgroup$ – Solar Mike Sep 15 '18 at 21:45
  • $\begingroup$ Wikipedia told me that titanium is virtually corrosion-free. Otoh traditional steel hulls seem to cope with seawater, so I am inclined to believe that corrosion resistance isn't the deciding factor. $\endgroup$ – Martin Sep 15 '18 at 21:53
  • $\begingroup$ Your point two is a reason for titanium, not against. Point 1 is fairly irrelevant, since it compares density but ignores strength - on that measure, wood would be a much better (and cheaper) material than any metal! $\endgroup$ – alephzero Sep 15 '18 at 22:18
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    $\begingroup$ Engineers would choose titanium if they can afford it. So basically the flowchart goes like this. Can you afford titanium? Yes, do. No then you will have to look into alternatives. $\endgroup$ – joojaa Sep 15 '18 at 23:52
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    $\begingroup$ Weight IS a problem. High strength hulls are required to go the desired depths; High strength > high weight ( too much weight and they don't come back up). That is why steel hulls are high strength steel . . They were HY 80 ( high yield 80,000 psi yield) ; The Navy was working on HY 100 last I knew. These higher strength steels bring problems with welding and toughness that I know of and likely more problems = $$$$. But that is what is required to go deep. High strength titanium has similar problems , I doubt corrosion resistance was a significant factor. $\endgroup$ – blacksmith37 Sep 16 '18 at 0:40
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the former soviet union had plentiful stores of titanium on hand, so its expense was not an issue.

Being nonmagnetic, a titanium hull would be more difficult to detect with magnetometers.

Note also that in a properly-designed submarine pressure hull, the limiter is not tensile strength but compressive yield strength and elastic modulus, since the hull will fail by compressive collapse like a short column or buckling as for a long column.

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  • $\begingroup$ This statement 'Being nonmagnetic, a titanium hull would be more difficult to detect with magnetometers.' is also holds true for SR71 blackbird. $\endgroup$ – Sam Farjamirad Sep 16 '18 at 19:23
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    $\begingroup$ yes, and the SR71 was also built from russian titanium, purchased through a shell company so the russians couldn't find out the USA was buying it! $\endgroup$ – niels nielsen Sep 16 '18 at 19:31
  • $\begingroup$ And some in the USA like to pretend they are not getting Ti and Cr from Russia. $\endgroup$ – blacksmith37 May 3 at 0:54
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It was more a political decision than engineering. The problems with fabricating thick titanium plate are enormous = expensive, and the Russian engineers did a remarkable job. There is much information on the web, but I could not find information on the particular alloy , thickness, strength, toughness, etc. An interesting summary is "Unravelling a Cold War Mystery".So the titanium hulls technical success and a functional failure, as all these subs have been decommissioned. The cost of the titanium does not justify possible advantages. Remember the political decision Russia made not to have containment for the Chernobyl class nuclear reactors ? Politicians should probably not make engineering decisions.

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