It is quite an annoying fact that metal rusts. Just to prove the point that nothing lasts forever even something as seemingly permanent as metal eventually finds an ending. Metal structures are vitally important and the last thing we need is it failing due to rust issues. Why does this happen and can anything be done to prevent it?
Rust occurs when oxygen and water are combined and cause friction on the surface of the metal. A simple experiment with 3 nails can demonstrate this. If one nail is simply left to the elements it will rust slowly. If one is completely submerged in water it will aslo rust at a slower rate. The nail that is half submerged will rust very quickly if left untreated.
Treatments include rust minimising paint and/or electroplating of the metal with rust resistant metals such as Nickel composites. Nickel is extremely adverse to rust but it is expensive so cannot be used in large amounts.
One of the most interesting examples is that of the North Sea platforms. These mega structures are constantly buffeted by strong waves and winds. Combine this with salt water and the designers have quite a challenge.