Control of corrosion
In order for corrosion to occur, we require a susceptible material, an environment that will cause cracking of that material and a high enough stress or stress intensity factor. Therefore there are a number of approaches that we can use to prevent corrosion or at least to give an acceptable lifetime. In an ideal world a corrosion control strategy will start operating at the design stage and will focus on the selection of material, the limitation of stress and the control of the environment. The skill of the engineer then lies in selecting the strategy that delivers the required performance at minimum cost. In this context we should appreciate that a part of the performance requirement relates to the acceptability of failure. For the primary use in the chemical or oil & gas industry we obviously require a very low risk of failure. For the for water, air or decorative applications on a light switch, the occasional corrosion is not going to be a serious problem, although failures would have an undesirable impact on production or cost involved, product returns and the corporate image.
Corrosion control requires a change in either the metal, the environment, smooth surface, the stability of the metal or creating a barrier.
Type of alloy
The first approach - changing the metal - is often the easiest, but often expensive. Also, highly alloyed materials, which are very resistant to general corrosion, are more prone to failure by localized corrosion mechanisms such as stress corrosion cracking.