Corrosion at metal interfaces-A study of corrosion rate and solution properties, including electrical conductance, viscosity, and density

In this paper, we attempt to correlate the rate of corrosion at the metal surface with bulk solution properties such as electrical conductance, viscosity, and density. The premise is that the process solution environment within the pipe or refinery equipment controls the severity of the corrosion at the metal surface. Furthermore, the migration of a protonated amine to the metal surface (instead of a proton in acid solutions) is the rate-determining step. For this study, the corrosion rate and solution properties of a single neutralizer salt (DEA·HCl) plus ammonium chloride, were examined more closely at fixed temperature, pressure, and composition. The metallurgy was restricted to carbon steel. Metal coupons of the game geometry and size were used to collect corrosion rate data in a non flowing static environment. Under such conditions, the experimental data support the hypothesis that the corrosion rate at the metal surface is strongly influenced by the diffusion of the protonated amine. Diffusion, like all transport properties (i.e., electrical conductivity, viscosity, density, and diffusion coefficients), is a function of temperature, pressure and solution composition (Dillon, C. P. Materials Selector for Hazardous Chemicals; Materials Technology Institute: St. Louis, MO, 1997; Vol. 1, p 69). The diffusion coefficient plus the Reynolds and Schmidt numbers determine mass-transfer-limited electrochemical processes (Eisenberg, M.; Tobias, C. W.; Wilke, C. R. J. Electrochem. Soc. 1954, 101, 306). The practical significance of this study lies in its ability to define, select, and/or screen neutralizer candidates via analytical measurements of their solution properties. Any mitigation in the corrosion rate resulting from a judicious choice of the neutralizer amine can have a significant economic impact.