Yes, but not only, there is number of pressurizing/de-pressurizing cycles to be taken into account (that lead to fatigue), this is more known for hulls of (pres

Yes, but not only, there is number of pressurizing/de-pressurizing cycles to be taken into account (that lead to fatigue), this is more known for hulls of (pressurized) planes. They esperience at least two full cycles per flight, a submarine has as well at least two of them, but with much larger pressure values, for each immersion. Some reference: https://navalpost.com/how-deep-can-a-submarine-dive/ https://navalpost.com/how-deep-can-a-submarine-dive/ AFAICT, steel is still preferred to titanium because (besides the costs) this latter tends to become (after a certain number of cycles) more brittle than the particular kind of steel used in submarines.