Fracture failure analysis and research on slip of casing head

Abstract

In this paper, macro and micro analysis is made on the slip of casing head which is fractured in situ. Visual inspection and microscopic analysis of fracture surface shows that the feature of crack is intergranular brittle fracture. The final crack originates from the root of the slip tooth and extends along the longitudinal, radial and circumferential directions. Because the initial crack is closer to the end of the slip, the longitudinal crack first reaches the end and then complete fracture is caused. The metallographic analysis shows that the microstructure of material has not been completely transformed into a sorbite, indicating that there is a defect in the heat treatment process. The minimum average impact energy of three samples is close to the minimum requirement, which shows the brittleness of material increases and the impact toughness decreases a lot at −29 °C. The finite element analysis shows that the high stress is mainly distributed in the shoulder area of slip, with the maximum stress being 875.5 MPa, which exceeds the allowable yield strength of the material. To ensure the safety of wellhead, the split-type slip can be used to reduce the stress concentration of slip. These test results provide powerful guidance for design, material selection and maintenance of slip to effectively reduce the accident in the process of oil and gas development.