On 11/03/2019 21:20, Brian Gaff wrote:
water and air usually or maybe the plating was naff?
Brian


It is actually quite surprising how slowly iron corrodes under normal
but adverse conditions. The upper bound on metal loss rate is usually
assumed to be 0.1 mm / year even in marine environments. You can get
*pitting* at much greater rates than this, which is why car bodywork was
so dreadful a few decades ago before manufacturers bothered properly.

But 0.1 mm/year explains why Victorian Piers and lock gate mechanisms
are still there, even without repainting.