Common types of Corrosion
- General (uniform) corrosion
- Localized corrosion
Pitting corrosion
Crevice corrosion - Stress corrosion cracking
- Sour gas cracking
- Intergranular corrosion
- Microbiologically influenced corrosion
- Galvanic corrosion
General (or Uniform) Corrosion
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What it is: The most well-known type of corrosion is also the easiest to spot and predict. It is unusual-- but not unheard of-- for general corrosion to lead to disastrous failures. For this reason, general corrosion is often regarded as an eyesore rather than a serious problem. General corrosion occurs relatively uniformly across a metal surface, and is typically measured in milligrams per square centimeter of exposed material per day. How it forms: In a marine or other corrosive environment, the surface of carbon or low-alloy steel, when exposed to caustic substances begins to break down. Stainless steels will not suffer from general corrosion but can be affected by localized corrosion. General corrosion can be measured by:
Potential Solutions: 316/316L Stainless Steel
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Localized Corrosion: Pitting and Crevice Corrosion
| What it is: Pitting corrosion causes small cavities, or pits, to form on the surface of a material. Although detectable by thorough visual inspection, these pits can grow deep enough to perforate tubing. Pitting is more often observed in high-chloride environments at elevated temperatures. How it forms: When the protective layer of oxide (or passive oxide layer) on the surface of the metal breaks down, the metal becomes susceptible to loss of electrons. This causes iron in the metal to go into solution in the more anodic bottom of the pit, diffuse toward the top, and oxidize to iron oxide, or rust. The iron chloride solution concentration in a pit can increase and become more acidic as the pit gets deeper. This results in accelerated growth of the pit, perforation of tubing walls, and leaks. |