Field Corrosion Rates of Oilfield Carbon and Low-Alloy Steels across the Sweet-to-Sour (CO₂/H₂S) Spectrum: A Field Dataset and a Benchmark of Predictive Models

Internal corrosion of carbon and low-alloy steels by dissolved carbon dioxide (CO₂) and hydrogen sulfide (H₂S) is a leading integrity threat in oil and gas production and transportation, yet field corrosion rates are rarely reported together with the quantified partial pressures that control them, which limits validation of engineering prediction models across the full sweet-to-sour range. This work compiles 90 field corrosion-rate measurements from operating oil and gas assets of an anonymous client operator, each paired with the steel grade, the operating temperature and pressure, the gas-phase CO₂ and H₂S contents, water chemistry, flow velocity and inhibitor status. Carbon dioxide and hydrogen sulfide partial pressures and in-situ pH were computed for every record, and each record was classified as sweet, mixed or sour from the pCO₂/pH₂S ratio. Measured rates ranged from 0.12 to 14.97 mm/yr (mean 2.29 mm/yr) and increased significantly with H₂S partial pressure (r = +0.42, p < 0.001) and with decreasing in-situ pH (r = ？0.49, p < 0.001). Uninhibited general-corrosion records (n = 27) were benchmarked against the de Waard-Milliams 1991 model, its scale-corrected form, and a flow-coupled mass-transfer form. The uncorrected model over-predicted field rates by more than an order of magnitude (median measured/predicted ratio 0.05); the scale correction reduced but did not close the gap (median ratio 0.18; 11% of points within a factor of two), and the deviation depended systematically on service regime and H₂S partial pressure. The results provide an anonymized, openly described field dataset and quantify the limits of CO₂-only models in mixed and sour service.