Is this a normal occurrence on SSNs? Does this also happen to Chinese SSNs? Wouldn't deterioration of the tiles or coatings on this SSN's hull of such a massive degree be seriously detrimental to its stealth capability?
Old anechoic layer was placed as tiles fixed to the hull. New anechoic layer used on Virginia is a continuous mold. This has consequences when hull is deforms during change of pressure.
Every time the sub dives the hull is compressed by water which causes a non-neglible change in size. When it surfaces the hull expands to match atmospheric pressure. While the change of size is not significant the forces that act on the hull and consequently on the anechoic layer fixed to it are tremendous as they are a derivative of the pressure differential. So it is very much like an earthquake on the surface of the hull or a "hull-quake" if you will.
When the hull with tiles is deformed the tiles move independently of each other and often are compressed against each other this - coupled with effect of seawater - causes them to fall off individually after some time. Once an opening in the layer is created more tiles fall off because water puts pressure on the other tiles from their exposed side. But because the tiles are fixed individually to spots on the hull they don't fall off on their own. There needs to be mechanical stress and chemical interaction to get them loose. This is how you get images like this one:
When a hull with molded layer like Virginia deforms the anechoic material doesn't break because it's continuous but it deforms differently from the steel of the hull and begins to peel off from it without breaking its structure. Once that happens then over time due to differences in pressure, temperature, salinity etc the material develops microcracks around the spots where it disconnects from the hull and then water gets inside and it peels off in huge chunks like a blister.
To use biological analogy it's like scales vs skin.
The new technology gives better results on quieting and when done properly stays on the hull longer but when it goes bad it goes bad and is harder and more expensive to replace adding extra time in dock. However I don't think this is the main issue affecting USN submarine readiness and repair time.
From what I've read in official reports the main problem seems to be simply availability of slots due to limited funding. Tools and crews cost money and if USN doesn't pay for them they won't be available on demand. There is also competition for existing funds. Many repairs are done in shipyards other than Groton and Newport and those two already complain about underfunding and inability to increase production rate of Virginias. Columbia has priority so new funding is re-directed there. Boats like USS Boisie which is a 688i commissioned in 1992 simply are not a priority. USS Annapolis from 1992 is slated for retirement in 2027. Boisie isn't probably because all those years in the dock have saved some service life.
Comparing USN's situation to PLAN's is really not constructive because PLAN has active small fleet and expands the infrastructure to match its fleet expansion plans. USN has not enough boats for what its missions are which causes them to be overworked and the infrastructure has been cut to preserve the fleet when budget cuts hit. Still INSURV rates SSNs as highest in condition and readiness while the rest of the fleet fails even more.
