A NUMERICAL-METHOD FOR THE EVALUATION OF THE CORROSION RATE OF A METAL

A new numerical method has been developed for the determination of the values of the corrosion current density and polarization resistance. Though requiring, in principle, preliminary knowledge of the values of the Tafel slopes, the method differs substantially from the technique of the linear response because its formulation is of a global type and is independent of the geometrical shape of the polarization curve near the corrosion potential. After illustrating the mathematical concepts on which the method is based, the author examines the behaviour of the characteristic function R(DELTAE), which plays the same role of the quantity (alpha + beta) in the theory of the linear response, in order to demonstrate that, under appropriate conditions, it can be considered independent of the Tafel slopes so that it is no longer imperative to use their exact values. Some applications are then presented which refer to two systems, ARMCO iron + H2SO4 at different pH and ARMCO iron + 1 N H2SO4 + Borg P16, both at 25-degrees-C. All the polarization curves examined were interpolated with the INTER program, while the integrals were calculated numerically by the Simpson method. The results obtained were quite satisfactory and show the validity of this formulation for corrosion monitoring.