To quote...." Corrosion resistance can however be adversely effected if the component is used in a non-oxygentaed environment, typical example being underwater keel-bolts buried in timber..chromium oxide is the invisible passivation layer that is formed when exposed to oxygen that keeps the lustrous and rust free look ".
![Geek :geek:](./images/smilies/icon_e_geek.gif)
I had a feeling the answer was just to obvious for you Dave... hey.... I am a simple man.
![Wink ;)](./images/smilies/icon_e_wink.gif)