Based on the analysis of fracture morphology, chemical composition, mechanical properties, microstructure and corrosion product composition, the causes of cracking of casing
collar of an oil well were analyzed.
The results show that the coupling
cracking is mainly caused by the stress corrosion cracking caused by hydrogen sulfide; the casing is exposed to the hydrogen sulfide corrosion medium after entering the well, which causes serious pitting corrosion on the outer surface of the coupling, forming corrosion pits, and the pulling of the coupling. The stress is large, and the interaction between the tensile stress and the corrosive medium eventually leads to stress corrosion cracking of the coupling. To prevent the accident from happening again, it is recommended to use the sulfur-resistant coupling material and connect the special thread to the casing.