Why the Maunsell sea forts have decades rather than centuries left

How much longer are the Second World War Maunsell sea forts likely to survive?

Probably decades, not centuries, because saltwater corrosion will eventually let a major storm crack or collapse the structures.

The surviving wartime sea forts were intended as temporary military structures and have already lasted far longer than planned. Continued exposure to salt weakens them. The expectation offered here is that a major storm will eventually cause damaged structures to crack or collapse. Their remaining life is estimated in decades rather than centuries, without a precise structural assessment or date. Visiting them is recommended as a way to learn from the surviving installations.