General Corrosion on stainless steel

Normally stainless steel does not corrode uniformly like ordinary carbon and alloy steels. However, with some chemicals, mainly acids, the passive layer may be attacked uniformly depending on concentration and temperature and the metal loss is distributed over the entire surface of the steel. Hydrochloric and sulphuric acids at some concentrations are particularly aggressive towards stainless steel. General corrosion can be quite destructive and happen to the entire surface at once.

• Pitting Corrosion on stainless steel

The passive layer on stainless steel can be attacked by certain chemical species. Chloride ion is the most common of these and is found in everyday materials such as salt and bleach. Harsh pitting corrosion is a localized damage that eats pits into stainless steel. In addition to chloride ion, can be caused by elevated temperatures for extended amounts of time or lack of oxygen to the surface.

• Crevice Corrosion on stainless steel
  

Stainless steel requires a supply of oxygen to make sure that the passive layer can form on the surface. In very tight crevices it is not always possible for the oxygen to gain access to the stainless steel surface thereby causing it to be vulnerable to attack. Crevice corrosion is avoided by sealing crevices with a flexible sealant or by using a more corrosion resistant grade.

• Galvanic corrosion on stainless steel
  

If two dissimilar metals are in contact with each other and with an electrolyte (e.g. water or another solution), it is possible for a galvanic cell to be set up and to accelerate corrosion of one of the metals. It can be avoided by separating the metals with a non-metallic insulator such as rubber.

• Stress Corrosion Cracking (SCC) on stainless steel
  

Stress Corrision Cracking is a relatively rare form of corrosion, which requires a specific combination of tensile stress, temperature and corrosive species, often the chloride ion, for it to occur. SCC can occur typically in hot water tanks or swimming pools. But if it does happen, it can be rapid, breaking down the mechanical properties of steel in days rather than months or years. Another form known as sulphide stress corrosion cracking (SSCC) is associated with hydrogen sulphide in oil and gas exploration and production.

• Intergranular Attack on stainless steel
  

Intergranular Attack is also a quite rare form of corrosion. If the carbon level in the steel is too high, chromium can combine with carbon to form chromium carbide. This occurs at temperatures between about 450-850 C. This process is also called sensitisation and typically occurs during welding. The chromium available to form the passive layer is effectively reduced and corrosion can occur. This corrosive harm happens between the grains and can be avoided by using a low-carbon stainless steel or uniform heating and rapid cooling of the steel.