The Measurement of Corrosion Rates of Carbon Steel and Stainless Steel in Geothermal Media by the Polarisation Resistance Technique

Abstract

The polarisation resistance method has been applied to the determination of corrosion rates of low carbon steel and 304, 316 and stainless steels in geothermal media containing hydrogen sulphide. With electrolytes of low conductivity it was essential to design the three-electrode probes so as to minimise the contribution of the ohmic resistance. static step experiments demonstrated that the ohmic contribution was less than 5% of the polarisation resistance. Good agreement was found between weight-loss and polarisation resistance measurements of the corrosion rate for all the metals tested. In the case of the stainless steels the potential took about one hour to reach its steady-state value following the application of a constant current. For the 304 and 316 alloys the form of attack in solutions was observed to be pitting corrosion, but the polarisation resistance method still gave good agreement with weight loss measurements.