Explanation of terms of metal materials (IV): Durability

Main forms of building metal corrosion:

 (1) Uniform corrosion. The corrosion of the metal surface makes the section uniform and thin. Therefore, the annual average thickness loss value is often used as the index of corrosion performance (corrosion rate). Steel is generally uniformly corroded in the atmosphere.

 (2) Pitting. The corrosion of metal is pitted and deep pits are formed. The generation of pitting corrosion is related to the nature of metal and its medium. Pitting is easy to occur in the medium containing chloride salt. The maximum hole depth is often used as the evaluation index for pitting corrosion. Pitting corrosion is often considered in the corrosion of pipelines.

 (3) Galvanic corrosion. Corrosion at the contact of different metals due to different potentials.

 (4) Crevice corrosion. Local corrosion of metal surface often occurs in cracks or other hidden areas due to the difference of medium composition and concentration between different parts.

 (5)Stress corrosion. Under the combined action of corrosive medium and high tensile stress, the metal surface produces corrosion and expands inward into microcracks, which often leads to sudden fracture. This failure may occur in high-strength reinforcement (steel wire) in concrete.