Fracture failure analysis of the sacrificial anode protector in a water injection well

• Published in: Engineering failure analysis Vol. 112; p. 104479
• Main Authors: Zeng, Dezhi, Zeng, Feng, Peng, Zhengde, Yu, Zhiming, Tao, Ye, Zeng, Wenguang, Guo, Yujie
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2020
• Subjects: Failure analysis; H2S/CO2; Hydrogen embrittlement; Injection well; Sacrificial anode protector; H2S/CO2; Injection well; Sacrificial anode protector; Failure analysis; Hydrogen embrittlement
• ISSN: 1350-6307; 1873-1961
• DOI: 10.1016/j.engfailanal.2020.104479

•The work studied the failure of sacrificial anode protector in H2S/CO2 environment.•Hydrogen atoms diffused into the protector then induced hydrogen embrittlement.•Based on failure reason, the paper put forward to useful and reasonable suggestions. In an injection well, sacrificial anode protectors were installed in order to protect the tubing string. However, one sacrificial anode protector was broken during the lifting process of the tubing string in well workover. The causes for the fracture failure of the sacrificial anode protector were investigated by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometry (XRD) and optical microscope (OM). The metallographic structure of the sacrificial anode protector was pearlite plus reticular ferrite and its chemical composition met the requirements of API Spec 5CT. However, the hardness distribution was inhomogeneous and the yield strength was also lower than the required value. In addition, the impact toughness was poor. The failure of the sacrificial anode protector was the combined consequence of material defects and the harsh service environment. In the CO2/H2S environment, the anode was dissolved and the cathode was subjected to hydrogen evolution. Therefore, hydrogen atoms diffused into the metal and accumulated at crystal defects, thus inducing microcracks. Finally, hydrogen embrittlement fracture failure occurred. In the material selection of the cathode of the sacrificial anode protector, a material with good hydrogen resistance is recommended and the high-temperature exposure time should be prolonged. In addition, it is necessary to design an effective service life for the sacrificial anode protector and replace the sacrificial anode protector in time.