Investigation on the corrosion causes of 3Cr tubing in a gas-lift well

The corrosion causes of 3Cr tubing were analyzed by physical and chemical performance tests, metallographic examination of the tubing material, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and Xray diffraction (XRD) analysis of the corrosion morphology and corrosive products, in order to figure out the main causes of the corrosion and draw up useful suggestions for the preventive measures. The results indicated that the mechanical properties and the chemical composition of the coupling and tubing material all meet the corresponding standard requirements. The form of the corrosion was oxygen corrosion, the main causes for the corrosion was the gas lift operation in the a-annulus, in which the injected nitrogen gas contain a certain amount of oxygen, and resulted in the occurrence of the dissolved oxygen corrosion on the outer surface of the tubing.