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Corrosion damage can be apparent in many different ways, including loss of material, surface pitting, and the buildup of corrosion deposits, but it is convenient to classify corrosion by visual observation of the corroded material before any cleaning is conducted. There are generally considered to be eight basic forms of corrosion.

 General attack (uniform corrosion)

 Galvanic corrosion

 Crevice corrosion

 Pitting

 Intergranular corrosion

 Selective leaching

 Stress corrosion

 Erosion‐corrosion

Although the distinctions between the eight basic categories of corrosive attack have become blurred, particularly when fundamental mechanisms are considered, this classification may help (at least in the first instance) to simplify the analysis. The identification of the factors associated with the forms of corrosion can guide failure investigators. A listing of the most important factors would ensure that engineers with little or no corrosion training are made aware of the complexity and multitude of variables involved.

Temperature can affect the corrosion behavior of materials in different ways. If the corrosion rate is only controlled by the metal oxidation process, the corrosion rate will increase exponentially with an increase in temperature. The higher the fluid temperature the faster the rate of oxidation. Experience shows that corrosion is more pronounced in hot water lines. Galvanic corrosion, also known as electrolysis, occurs when different metals come into contact with each other. Chemical composition of the fluid may have differing effects on the corrosive forces at play. When water velocities exceed 4 ft/s in oversized circulation pumps, installation of undersized distribution lines, multiple or abrupt changes in the direction of the pipe, corrosion may take place. The pH of a solution is also an important factor in the corrosion of materials.