Probe into Water Chemistry Effects on Internal Corrosion Risk for Sour Gas Pipelines

Wet sour gas pipelines are subjected to corrosion deterioration mechanisms resulting from interactions between the fluid and piping material. Acid gases, condensation rates, water chemistry, and temperature are the key factors in determining the corrosivity of sour gas streams. This work investigated the corrosion risk of a new wet gas pipeline through laboratory experiments and corrosion modeling. The tests were carried out in Hastelloy autoclave rotating cage system used to generate controlled dynamic conditions inside the reactor to mimic the environment inside the pipeline. The results showed high bottom of the line corrosion (BLC) rate reaching 38.9 mpy ($0.99\mathrm{mm}/\mathrm{year}$), while the measured pitting rate was 17 mpy ($0.43\mathrm{mm}/\mathrm{year}$). The corrosion modeling results showed a severe BLC rate exceeding 200 mpy ($5.08\mathrm{mm}/\mathrm{year}$). The observed high BLC was attributed to the absence of bicarbonate which led to a low pH of 3.9. At this pH, the formation of stable iron sulfide is unlikely. Top of the line corrosion (TLC) rate was observed to be moderate reaching up to 7.8 mpy ($0.20\mathrm{mm}/\mathrm{year}$). This is mainly because of the low condensation rate and formation of a protective iron sulfide layer, which confirmed that iron sulfide scale characteristics are the main factor influencing the TLC rate in sour environments. The expected threshold concentration required of bicarbonate to show some reducing effect on the corrosion rate and pH based on historical data analysis and predictive modeling of real-field conditions is discussed in this work. The results and conclusion detail the path forward for the findings.