A New Methodology for Monitoring Corrosion Under Sales Gas Conditions Using the Quartz Crystal Microbalance

A new method for measuring corrosion of iron under sales gas conditions has been developed using the quartz crystal microbalance (QCM). This method is among the first to replicate the formation of black powder on the lab scale to better understand its formation, and devise mitigation/inhibition strategies. This method will allow for more efficient development of improved corrosion management programs for systems historically difficult to model in the laboratory.  This work is among the first to use iron-coated QCM crystals for corrosion testing. For this project, a custom-built gas delivery system and Hastelloy test vessel were fabricated. The new method allows for the measurement of small weight changes caused by the oxidation of iron in the presence of a thin condensed water layer containing O₂, CO₂ and H₂S. The ability to measure corrosion due to formation of a condensation layer on the iron coated surface is discussed in some detail. The method allows the quantification of the amount of water that is condensed on the probe surface. Increases in weight of the iron layer on the QCM crystal due to corrosion are recorded as a frequency drop. Using the Sauerbrey equation, frequency drop values can be converted to weight gain measurements, which can in turn be used to calculate the corrosion rate. Effects of ΔT, oxygen and carbon dioxide concentrations on the corrosion rate are discussed. It was observed that the relative humidity inside the test vessel had the greatest effect on the corrosion rate.