Evaluation of Corrosion Resistance on Domestic Coiled Velocity Pipe String Serviced for 3 Years

The corrosion resistance of the coiled velocity pipe string serviced in Changqing oil field for 3 years was evaluated by ultrasonic thickness gauge, X-ray diffraction (XRD), scanning electron microscopy with energy spectrometer (EDS) and laser confocal scanning microscopy (LCSM). The results showed that there was no serious erosion of wall thickness and no groove corrosion in the entire column. The maximum corrosion rate of the tubular wellhead pipe was 0.032 mm/a on one side and 0.064 mm/a on both sides. The maximum corrosion rate of the bottom hole pipe was 0.077 mm/a on one side and 0.154 mm/a on both sides. The corrosion resistance of the domestic coiled velocity pipe string was good. The corrosion products was a mixture of FeCO₃ and iron oxide, and the corrosion of coiled velocity pipe string in original gas well was dominated by carbon dioxide and oxygen corrosion.