Iron and steel structures are damaged by:

Iron and steel structures are mostly victims of corrosion, which is mainly caused by acidic gases present in the air. Sulfur dioxide (SO₂) reacts with moisture and, along with oxygen, forms sulfuric acid. It is this acid that catalyzes rusting, thereby accelerating the rate of corrosion. Iron and steel structures are quite stable in dry conditions, but even a trace of sulfur dioxide in moist air is enough to create a hostile environment that causes corrosion.