Analyzing Failure of Casing Head Slip Hanger

The reasons for failure of a casing head slip hanger were analyzed by applying the techniques of optical microscopy, scanning electron microscopy, and energy dispersive spectrometry. Results show that the composition and tensile mechanical properties of the slip are all in accordance with the corresponding parameter requirements of standard GB/T 22513-2013. Furthermore, the structure of slip material has not been completely transformed into sorbite with good comprehensive properties, and a significant amount of ferrite still exists in it. The impact toughness results show the characteristics of low-temperature brittleness. Microscopic analysis shows that the corrosion products mainly come from circulating mud during drilling and that the action of stress corrosion generated the initial crack. The fracture characteristics develop from transgranular ductile fractures to local intergranular brittle fracture characteristics. The crack continues to expand along the root of the screw teeth with the stress concentration under the axial load and circumferential Mises stress until brittle breaks occur. To prevent failure from taking place, it is recommended to control the heat treatment process of the slip material to optimize the microstructure and enhance the toughness of the material, to install the slip hanger correctly, and to make sure the slip and casing are tightly held in place.