Failure Analysis of P110 Tubing Coupling Fracture in an Oil Well
In order to find out the reason of the frac-ture and guide the safe production in the later stage of oil recovery,the causes of the short term fracture of the tubing coupling were studied by means of macro-scopic morphology,chemical composition,physical and chemical properties,energy spectrum and scan-ning electron microscope analysis.The results showed that the fracture of the pipe coupling was affected by non-metallic inclusions,and the impact performance was poor,which did not meet the requirements of the standard specification.There was flow-field induced corrosion at the threaded coupling,which was the re-sult of H2S and CO2.Local corrosion pits were formed at the root of the thread tooth,forming a fatigue source,fatigue cracks extended to a certain extent,brittle fractures were produced in the acidic corrosion environment,and a small number of secondary cracks were found in the section.It was concluded that the fracture failure of the pipe was mainly caused by cor-rosion and fatigue fracture caused by non-metallic in-clusions,H2S and CO2,and the sulfide stress corro-sion cracking had an effect on the fracture of the pipe.It was recommended to use sulfur-resistant tubing for Wells with high H2S content,reduce the content of in-clusions,improve the heat treatment process of materi-als,and select materials with strong stress corrosion cracking resistance.
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