Quantification of hydrogen evolution in corrosion testing by buoyancy measurements

This article describes an improved method for quantifying the hydrogen evolution rate in corrosion testing by using buoyancy measurements. H ₂ gas bubbles are collected in an inverted beaker hanging in the test solution, and the collected gas volume is determined by measuring the buoyancy the gas exerts on the inverted beaker. The new test setup and procedure are described, together with a detailed discussion of limitations and error sources. The results of tests on an inert cathode and on magnesium electrodes subject to uniform and localised corrosion are presented. The method provides a useful tool for studying the H ₂ evolution in corrosion testing in terms of accuracy, precision, and sensitivity. Knowledge of its limitations is however important. The results obtained in this study show that the method can be regarded as very accurate down to a current density around 5 mA/cm ² and within − 20% accuracy down to around 1 mA/cm ² . Valuable semi-quantitative or qualitative information can be obtained for current densities as low as 0.1 mA/cm ² if the performance of the method has been properly characterised. These results partly depend on the generation of a high supersaturation prior to, or during the initial part of, the test. A general conclusion is that volumetric gas measurement has an inherent negative bias when it comes to quantifying the total production in a gas evolving electrochemical reaction due to the supersaturation needed to form gas bubbles.