Coulostatic Method for Rapid Estimation of Corrosion Rate; Application to SB46 in 1N H₂SO₄ and SS41 in Distilled Water

Abstract

A coulostatic method for rapid evaluation of corrosion rates was developed and applied to mild steels in aqueous solutions. In this method, the decay of polarized potential was recorded on open-circuit after applying a small amount of charge. According to the theory developed, polarization resistance, R_p, for SB46 immersed for 2 hours in 1N H₂SO₄ was estimated to be 7.9Ωcm². This agrees fairly well with the value of 5.6Ωcm² obtained by polarization curve measurement. The method is also applied to SS41 in distilled water. The R_p values obtained were 2.4kΩcm², 2.1kΩcm² and 1.1kΩcm² for immersion times of 45, 51 and 74 hours, respectively. These values are similar to the average polarization resistance, 2.2kΩcm², or the corrosion rate of 21mdd obtained from the weight loss measurement at the immersion time of 75 hours. The coulostatic method developed in this study can be applied without ohmic drop correction, even in distilled water and the time needed to complete the measurement is considerably shorter compared to the usual linear polarization method.