4 - Corrosion in Aqueous Solutions and Soil

Abstract

Corrosion of metals in aqueous solutions and soils is essentially oxygen corrosion with a cathodic partial reaction. Estimation of corrosion results from the consideration of characteristics of the soils and of the installed object. A relatively high degree of corrosion arises from microbial reduction of sulfates in anaerobic soils. Here, an anodic partial reaction is stimulated and the formation of electrically conductive iron sulfide deposits also favors the cathodic partial reaction. In addition, corrosion susceptibility in aqueous media is assessed on the basis of the rating numbers that are different from those of soils. An increased occurrence of corrosion is generally found only in the splash zone. In particular, severe local corrosion can occur in tidal regions due to the intensive cathodic action of rust components. Because cathodic protection cannot be effective in such areas, the only possibility for corrosion protection measures in the splash zone is increased thickness of protective coatings. Anodic enhancement gives rise to high corrosion susceptibility. The danger due to the contact with foreign cathodic structures must be treated just as seriously as the danger from emerging stray currents.