Corrosion at the Steel–Medium Interface

Abstract

Corrosion on the interface between a metal alloy, such as steel, and a wet, permeable non-metallic medium is of considerable practical interest. Examples include the interface between steel and water, the atmosphere or concrete, as for steel reinforcement bars; between metal and soil, as for buried cast iron or steel pipes; deposits of some type, as in under-deposit corrosion; and the interface with insulation, protective coatings, or macro- or micro-biological agents. In all cases, corrosion initiation depends on the characteristics of the interfacial zone, both of the metal and the medium, and the spatial variability. For (near-)homogeneous semi-infinite media with good interfacial contact, the pitting, crevices and general corrosion of the metal will be largely controlled by the metal (micro-)characteristics, including its inclusions, imperfections and surface roughness. In other cases, these may be overshadowed by the macro-characteristics of the medium and the degree of interfacial contact, possibly with severe resulting corrosion. Where the build-up of corrosion products can occur at the interface, they will dominate longer-term corrosion and govern the long-term corrosion rate. For media of finite thickness, diffusion issues and material deterioration may also be involved. The practical implications are outlined. It is argued that with the presence of a suitable medium, it is possible to achieve negligible long-term corrosion but only if certain practical actions are taken.

Effect of Copper and Nickel Content on the Corrosion Mechanisms in Ferritic Matrix Gray Cast Irons under Simulated Marine Environments

“…From the obtained corrosion curves, the presence of two inflection points, which were named "t A " and "t B ", could be observed. This suggests the existence of an additional mechanism to the two classics described in the literature [2,6,8]. However, what this additional mechanism corresponds to has not yet been determined.…”

“…In these locations, the material was exposed to the air near the coasts and submerged under different types of water. In his research, it is possible to appreciate that the behavior of gray castings is similar among self-weathering steels, that is, they possess a bimodal behavior [8]. The literature contains numerous studies on the corrosion of gray cast iron submerged in water or buried underground, but few regarding its behavior in atmospheric conditions.…”

“…According to the literature, low-and medium-alloy steels as well as castings show a variation in behavior when exposed to marine atmospheres, observed in corroded thickness versus exposure time curves, where a short-and long-term corrosion mechanism is demarcated, determined by the presence and absence of oxygen, named the aerobic and anaerobic stages, respectively [9]. This behavior was termed bimodal [8]. Given that castings and steels possess a microstructure whose matrix is similar, it is expected that the resulting corrosion products will be similar.…”