The physical integrity of a metal coating is as important as its chemical barrier properties in many applications. Selecting the best metal coating for an application requires evaluating all effects of the specific environment, including thermal and mechanical conditions. There are three main types of exposure to which coatings are subjected: atmospheric, immersion and underground exposure. The main difference between atmospheric exposure, immersion and underground exposure is weather resistance.
A coating under atmospheric exposure must endure a variety of conditions, including heating and cooling, oxidation, and wetting and drying. Immersion coatings are primarily subjected to water solutions ranging from pure water to high concentrations of various chemicals. Coatings used in underground applications must be resistant to ground water and soil forces, so they are generally applied thicker than atmospheric or immersion coatings.