Theoretical and experimental investigation on the erosion-corrosion failure of an L245N steel elbow pipeline in a gas field produced water system

This study presents a comprehensive failure analysis of an L245 N steel elbow retrieved from a station in a North China gas field. By integrating macroscopic examination, microscopic characterization (SEM/EDS), and corrosion product analysis (XRD) with Computational Fluid Dynamics (CFD) simulations, the failure was conclusively identified as localized erosion-corrosion. The internal surface of the elbow exhibited significant perforations characteristic of erosion damage. This partial failure contrasts with the negligible uniform corrosion rate (0.011 mm/a) recorded in the high-salinity (Total salinity>29000 mg/L) water, suggesting that erosion is the primary threat. The failure is driven by a synergistic mechanism where wall shear stress accelerates the mechanical stripping of protective films, thereby intensifying particle impingement on the exposed substrate. Meanwhile, the siliceous material detected on the inner surface was presumed to be sedimentary argillaceous quartz particles from the water, which further proves that erosion is the primary reason of pipeline failure. To further verify this mechanism, 27 different conditions were analyzed through CFD simulations, we found that erosion rate increases sharply with inlet velocity growth. When the velocity increased from 4 m/s to 10 m/s, the maximum erosion rate surged by over 100 times. The simulated erosion hotspots align closely with the actual perforation locations, demonstrating that the simulation results are highly consistent with the observed failure. These findings emphasize flow velocity as the most determinant risk controller, providing a consistent explanation for the pipeline failure from both experimental and theoretical perspectives.