Intergranular Corrosion – Intergranular corrosion, as the name implies, is the selective attack of a metallic component at the grain boundaries by a corrosive medium. Several conditions can lead to a material being susceptible to intergranular corrosion. In some environments the grain boundary of a metal simply exhibits the most reactive nature. Because of thermal mechanical processing, metallic compounds may tend to precipitate and migrate to the grain boundaries. If these are more reactive than the metallic matrix, they can be selectively attacked. Metallic reactions can cause areas adjacent to the grain boundary to be depleted of some element, rendering this zone less resistant to attack. A commonly encountered form of intergranular corrosion is the attack of non-stabilized austenitic stainless steels due to the formation of chromium carbide precipitates and the subsequent depletion of chromium.

Erosion Corrosion – Erosion corrosion is the acceleration or increase in rate of deterioration or attack on a metal because of relative movement between a corrosive medium and the metal surface. Generally the movement is rapid and the effects of mechanical wear or abrasion are involved. Metal is removed from the surface as dissolved ions or corrosion products are mechanically swept away from the metal surface.

Galvanic Corrosion – Galvanic corrosion results from the electrical coupling of two dissimilar metals in a corrosive medium resulting in the attack of the less resistant metal. The metallic differences may be due to metallic structure as well as composition. The less noble material becomes anodic while the more noble becomes cathodic. The anodic material actually protects the cathodic leading to its own accelerated decay. Ranking of materials in an electromotive force (EMF) or galvanic series in a specific media will help determine the propensity of two materials for this type of corrosion. The farther apart the materials are in the series, the greater is the likelihood of attack of the less noble material.