Application of electrochemical methods of corrosion rate determination to systems involving corrosion product layers: Part 1: Linear polarization resistance measurement as an example of a simple method that can be performed with commercially available instruments

The polarization resistance is often measured to determine the corrosion rate. However, the electrochemical response signal may become distorted by the presence of a corrosion product film on the metal surface. A number of methods have been devised to overcome this difficulty, but these frequently require more sophisticated methods and/or equipment than is available for on-site corrosion monitoring. Contrarily, when the basic linear polarization method is applied, the slow response obtained may necessitate taking measurements under non-steady state conditions, thus introducing an error into the obtained value of the polarization resistance. This error is dependent on the protectiveness of the corrosion product film, and hence on the time of exposure. The same holds for the conversion factor needed to calculate corrosion rates from the polarization resistance values. For such cases it is proposed to introduce an empirical conversion factor in which all time dependent factors are combined.