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SOLUTIONS: Stainless Steel Stainless steel corrosion types A very thin layer of chromium oxide which is formed on the surface of the metal protects stainless steels against Corrosion. This passive layer can be damaged by mechanical or chemical action.

If the protecting layer is destroyed in an aggressive environment, the material will corrode.

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Cr depleted regions. These regions then have a decreased corrosion resistance.

The precipitation of chromium carbides can be prevented either by a low C content or by a stabilizing elements like Nb or Ti.

Pitting corrosion

Different types of corrosion can occur and the choice of stainless steel is based on the requirements from the actual environment.

General corrosion

This is a corrosion attack that proceeds at the same rate over the entire surface. It occurs almost exclusively in acidic or strongly alkaline solutions. The resistance against general corrosion is mainly improved by increasing the content of Cr and Mo in the steel. Intergranular corrosion

This is a type of localized attack which is highly destructive, resulting in holes in the metal.

This kind of attack is most commonly found in stainless steel in chloride containing environments. The resistance against pitting is improved with increased Cr and Mo contents. Also N has a favourable influence.

The Pitting Resistance Equivalent, PRE, is a way of describing the relative influence of the mentioned elements. One way of expressing PRE is: PRE = %Cr + 3.3 x %Mo + 16 x %N.

A localized attack at and adjacent to the grain boundaries is called intergranular corrosion. Some stainless steels can be made sensitive to intergranular corrosion by elevated temperatures (500 °C-900 °C) at which carbide precipitation occurs at the grain boundaries resulting in

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The maximum temperature at which a specimen in a special test solution shows no signs of pitting corrosion is called the Critical Pitting Temperature (CPT).