Corrosion rate monitoring with computerized systems

Abstract

Some observations concerning the aims of corrosion rate monitoring, the choice of the electrochemical parameter, the opportunity of optimising the measurement technique and the usefulness of developing specific software for computerised systems are made. The basic concepts for the evaluation of the mass loss of metals or alloys are introduced and some mathematical formulas of the method of successive approximations are given. A short description of the SOFTCOR-DC-PHTS code is given, Which concerns its improvements and the most important points and stresses the significant differences between this program and commercial software and the potentialities of the present method. The experimental applications, concerning the behaviours of Armco iron and SA 182 grades F11 and F22 carbon steels in inhibited 5% by weight HCl solutions at 75°C and SA 106 grade B carbon steel in solutions containing 100 gl⁻¹ of EDTA at 100°C and different pH values, have demonstrated the existence of a discrepancy between direct and electrochemical determinations of the corrosion rate. The value of the electrochemical determination of the corrosion rate, obtained through potentiostatic measurements with a polarization time of 1 s, was higher than the mean value of the direct evaluation from weight loss data. The present results show that the electrochemical technique cannot reproduce the true behaviour of a corrosion process. However, the SOFTCOR-DC-PHTS program is very useful to deal with the problem of monitoring the corrosion rate of metals in acid media and to process experimental data without the intervention of an operator. Finally, it has been experimentally demonstrated that the determination of the polarization resistance depends on the technique adopted for performing polarization measurements.