Inhibition and co-condensation behaviour of 2-mercaptoethanol in top-of-line CO2 corrosion environments

Top of line corrosion (TLC) is a significant problem in oil and gas transportation pipelines, leading to both economic and production loss. Conventional organic corrosion inhibitors typically fail to provide effective protection for this particular type of corrosion. As such, the chemical inhibition of TLC relies on volatile compounds which can partition from the aqueous to the condensate formed at the top of the pipeline. Studies have shown that thiol compounds, through their high affinity for metallic surfaces, are providing effective inhibition in such environments, yet their inhibition mechanism and co-condensation characteristics are yet to be fully determined. This work studies the efficiency, adsorption mechanism and condensation behaviour of 2-mercaptoethanol (2-ME) as a volatile corrosion inhibitor in CO2-containing TLC environments through a novel direct assessment of condensate chemistry and real-time TLC measurements. Experimental analysis of condensate partitioning is performed through the implementation of a biochemical technique which targets sulphydryl groups, coupled with a miniature electrode configuration for real time, in-situ electrochemical TLC measurements. The proposed assay results in a rapid, cost-effective screening technique that can monitor thiol-based chemistries that condense in conjunction with the water phase. The new developed biochemical methodology identified that from 20 ppm of 2-ME added to the bulk solution, only around 12 ppm was present within the condensate. Additionally, 2-ME addition into the system resulted in a corrosion inhibitor efficiency of 93.8% where the chemical act as a mixed-type corrosion inhibitor. The corrosion and condensation experiments are complemented with surface characterization via XPS and STEM-EDX techniques. The surface characterization analysis showed a compact inner layer containing sulphur which is related to adsorption of the thiol.