For the coil designer, coil corrosion can seem to be one of life's great mysteries. Combinations of metals in coil construction along with wide variations in operating environments can make the mechanisms of corrosion complex to say the least. When movement of a corrodent over a metal surface (i.e. through coil tubes) increases the rate of attack due to mechanical wear and corrosion, the attack is called Erosion Corrosion, and is considered a "localized" form of corrosion. Failure of water coils due to erosion of tube surfaces can many times be avoided with proper coil design.