Corrosion Types and Prevention in Engineering

Hydrogen Embrittlement (a.k.a. Hydrogen Damage)

Hydrogen embrittlement is an engineering consideration with high-strength steels, titanium, and other high-strength specialty metals.

Hydrogen blistering can occur when hydrogen enters metal because of the reduction reaction on a metal cathode. Single-atom, nascent hydrogen atoms diffuse through the metal until they meet and bond with another nascent hydrogen, usually at inclusions or defects in the metal.

The resultant stable diatomic hydrogen molecules are then too large to permeate the metallic grain structure to outgas and become trapped. Eventually, a gas blister builds up and may split the metal, as shown in the photo below.

Intergranular Corrosion

Intergranular corrosion occurs at or adjacent to the grain boundaries of an alloy. A highly magnified cross-section of commercial alloys shows a granular structure. Each grain has a clearly defined boundary that chemically differs from the metal within the grain center. Heat treatment of stainless steel and aluminum alloys accentuates this problem.

Pitting Corrosion

Passive metals like stainless steel resist corrosive media and can perform well over long periods. However, if corrosion does occur, it forms pits randomly.

Pitting is most likely to occur in the presence of chloride ions combined with depolarizing agents such as oxygen or…