From my hull survey days, this kind of damage is only picked up through either physical tank inspections and/or NDT, such as ultrasonics. Having crawled through my share of tanks, this is a very hit and miss technique. Tanks are cramped, dark and there are large areas, where it just doesn't matter how tiny and flexible you are you just can't fit. It's mostly all mk1 eyeball as well, because it's hard enough to get in yourself let alone with testing equipment. I've done some work with drones, but it is still limited and visual only.
Ultrasonic thickness testing is good, and can be easily done from the outside during dry docking, but it only tests a local area (testing 10% of a hull would be a big task) and from this position doesn't test any of the internal stringers and stiffners (which rely on the above mk1 eyeball).
Some of the very modern phased array ultrasonic systems can do large areas quickly, however they are hideously expensive and require a phd in rocket science to understand.
Some corrosion can happen reasonably quickly as well. I remember a case of microbial corrosion that ate a tank away in about a six month period.
The issues with T23's are more around structure / design & how hard they have been worked, rather than 'rust & corrosion'. Mid-life updates addressed some of these issues, but hull flex & fatigue cracks in the areas in question only really get picked up now, as the technology has moved on since the early 2000's & the need to have a vessel that will continue to be worked hard, means that 'life-extensions' really means that you have to strip everything out / go back to bare metal.
Overall, it is well understood in tier 2 & 3 naval circles, that the RN generally have well designed ships that will usually last closer to 40 years. The costs of upkeep & the CONOPS / CONUSE of the RN is often very different from these nations & continuity of fleet equipment often means that they either have older RN vessels in their inventory & access to the spares, or are prepared to remove 'older' components & replace them with local / regional equivalents.
Albion & Bulwark - Built in the very late 90's, not completed until 2001 / 2003
(I know because I worked on em !). before being handed over to the RN. As stated elsewhere, they haven't exactly had their necks wrung, so at just over 20 years old they would be a good purchase for the likes of Brazil / Chile / India / Pakistan / Indonesia, if they have the 'need' for a multi role / multi capability vessel.
Fort Victoria - COULD be a good 2nd hand purchase, but ONLY if the country in question is prepared to dry dock her for about 2 - 5 years & gut the engine rooms / running gear / replace most of the pipework systems / HVAC / Firefighting, while retro-fitting Combat Systems.
Time & cost heavy exercise for a ship the was commissioned in the late 80's / early 90's.
WAVE Class - similar ages to Albion & Bulwark, but are limited by their top speed ! AGAIN, ideal purchase for Tier 2 or 3 navies to replace any ex- WW2 / Pre 1990's / single skinned tankers.
SA
