Electrochemical Pitting Corrosion
Electrochemical pitting is the process where passivated metal surfaces are attacked by chloride ions, creating deep pits. This leads to destruction of the microstructure.
Physico-chemical mechanism of action
Passivated metal forms a protective layer that repels anionic attacks. Chloride ions are particularly aggressive and can break through this layer. This leads to electrochemical reactions where material is removed from the surface, creating deep pits.
Metallurgical relevance & risks in welding
Electrochemical pitting can cause destruction of the microstructure, especially when chloride ions are present in the environment or in the weld pool. This can lead to cracks, loss of strength and toughness, and corrosion problems after welding.
Workshop practice & instructions
Avoid chloride ions in the environment and in the weld pool. Keep humidity low and use clean materials. For highly corrosion-prone steels, a pretreatment with passivating chemicals can be helpful. Continuously monitor the surface for signs of corrosion.