Surface Corrosion: A Look Beneath the Surface
Corrosion on metal surfaces is a complex process that can manifest itself in various forms: surface corrosion, pitting corrosion, and perforation corrosion. Each of these forms has its own characteristic features and effects on material integrity and is defined in terms of terminology by DIN EN ISO 8044.
Surface corrosion manifests as uniform material loss over large areas and is often the first visible sign of a corrosion problem. At the molecular level, metal ions lose electrons (oxidize) in anodic areas and are removed from the metal surface, while in cathodic areas, the metal is reduced to metal oxide—commonly known as rust. This uniform loss of the structural metal leads to a gradual decrease in material thickness across the entire affected surface.
Pitting corrosion, by contrast, is uneven. It occurs when certain areas of the surface are more susceptible to corrosion, resulting in visible pits. These can have far-reaching structural consequences, as they create weak spots in the material.
Pitting corrosion is a unique phenomenon that, despite its localized nature, can lead to serious damage. It typically begins at microdefects or impurities on the metal surface and can be exacerbated by a series of complex mechanisms.
A key factor in pitting corrosion is the restricted oxygen supply inside the pit, which prevents the metal—such as a zinc layer—from repassivating and creates an aggressive, corrosive environment. The discrepancy in oxygen content between the interior of the hole and the surrounding surface creates a concentration gradient that promotes the corrosion reaction. The small size of the hole compared to the rest of the metal surface, which acts as a cathode, leads to an increased corrosion rate, as the reaction area of the anode is small and that of the cathode is large.
PFINDER tackles the challenge of various corrosion phenomena by developing solutions that minimize the interaction between anodic and cathodic areas. The surfaces are shielded from corrosive media by a barrier, which inhibits corrosion mechanisms and ensures the long-term stability of your components.
Discover with us how our approach to corrosion protection not only treats the symptoms but addresses the root of the problem to ensure the longevity of your projects.