Methods to Calculate Corrosion Rates for Alloy 22 From Polarization Resistance Experiments

The general corrosion rate may be measured using immersion tests or electrochemical tests. The electrochemical tests are fast and can be used for a rapid screening of environmental effects such as temperature and electrolyte composition. The electrochemical tests are described in ASTM standards G 59 and G 102. The basis of these tests is to calculate the resistance to polarization (R_p) in a voltage vs. current plot and to convert these values to corrosion rates using the Faraday law. Commercial software can calculate the corrosion rate based on inputs from the operator. This paper discusses three ways of calculating the corrosion rate (Methods 1, 2 and 3) based on a fixed set of acquired data of voltage vs. current. The conclusions are that the way the corrosion rate is calculated does not impact greatly on the absolute value of the corrosion rate. Variations in the acquired data (current, potential) from one experiment to another seem more important that the manner the data is fitted with the R_p slope.