Corrosion failure analysis of downhole oil tube

Acidizing technology was commonly used in oil and gas well stimulation and production, and corrosion failure of oil tube during the acidification process was a main form of tubing failure. Chemical composition analysis, metallography analysis, residual stress test, microstructure analysis at corroded areas and the adaptability evaluation of oil tube were used to investigate the helical corrosion failure of oil tube during acidification process. The analysis results showed that chemical composition, tensile strength, elongation, yield strength and hardness of the failure oil tube were agreed with technology agreement, and microstructure was tempered sorbitic, but ribbon segregation and residual stress existed in oil tube. Corrosion unique topography was formed by helical internal tensile stress, the products were mainly composed of CaCO₃, Fe₂O₃. Severe corrosion would happened at 105 ℃ when diverting acid were used on site. The corrosion rate could reach 126.45g/m²·h.