Dear Sir/Madam

As a marine surveyor I sometime deal with containerised cargoes damaged by water (sea/rain) having entered the container through holes caused by either corrosion or mechanical damage usually by container spreaders.

On occasion it has been necessary, (without the assistance of metallurgists for cost-conscious principals), to provide an approximate "age" of the damage so as to try and estimate, without guarantees, the most likely place where the damage may have occurred (for liability/recovery purposes).

Is there an acknowledged period of time following physical damage to steel plate (in otherwise good condition and without any prior damage), within which the external sign of red rust (ferrous oxide/corrosion) is just NOT visible but that, after such period of time, red rust will be visible?

By way of illustration:  

The roof of a steel shipping container is pierced by the metal spear of the lifting spreader today, 17 March (Sydney time), exposing the steel.

Will the exposed steel surfaces develop red rust within say 12 hours? 24 hours? some other period of time?  

Thanks and regards

Glenn Mathias