The evaluation of corrosion rate through an inversion method

The basic ideas of the inversion method for computing the corrosion rate of a given metal or alloy in an aggressive environment are expounded and the main mathematical equations are given. It is also shown that the correct application of this numerical technique needs, in principle, a preliminary knowledge of the values of the anodic and cathodic Tafel slopes, Ba and Bc. It has been proved that Ic does not seem to depend critically on the random choice of the values of Ba and Bc when they are rather close to the true ones. Examination of some artificial data showed that the approximate polynomial of the fourth degree gives very accurate values of ΔE as a function of w over the interval [− 0.5,0.5]. The inversion method has been used to compute Ic relating to Armco iron in H2SO4 solutions at various pH values and at 25 °C, and in 1 N H2SO4 and HCl solutions containing suitable corrosion inhibitors at 75 °C. Polarization measurements, performed using current transients and experimental data corrected to account for the contribution of the ohmic drop to the electrode potential, were generally best-fitted over the ΔE interval [− 50, 50] mV using the INTER1 program. The actual values of Ba and Bc were obtained by analysing the polarization curves examined by the NOLI method. The analysis of the behaviour of these electrochemical systems has given satisfactory results compared with those obtained by the NOLI and linear polarization methods.