Effect of Temperature on the Loss of Ductility of S-135 Grade Drill Pipe Steel and Characterization of Corrosion Products in CO₂ Containing Environments

Evaluation of loss of ductility of the API S-135 grade drill pipe steel was studied at different temperatures from 298 K to 448 K (25 °C to 175 °C) in CO₂ containing solution using a constant extension rate test in connection with a high-temperature/high-pressure autoclave. The effect of temperature on the composition and morphology of corrosion product layers of this steel were also investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results indicated the change of loss of ductility with temperature and the maximum loss of ductility was observed at 448 K (175 °C). XRD studies of the specimens revealed the formation of iron carbonate on the surface. SEM study of the surface of the specimens showed a rhombohedric crystalline iron carbonate layer above 373 K (100 °C), while no FeCO₃ was detected at temperatures below 373 K (100 °C). Also, the crack size and depth of the cracks increased with temperature.