Study on the mechanical behavior of threaded joints of coring tools under compressive-torsional loading

During the process of oil drilling and extraction, the drill-column often fails under compound load conditions, and most of the studies on oil pipe threaded joints focus on the drill pipe threaded joints, but there are few studies on the coring tool threaded joints. Based on this, a study was conducted on φ121 coring tool threaded joints, revealing different mechanical characteristics of normal and specialized threaded joints which are subjected to combined axial and torsional loads. Results showed that: under the upper buckling torque, stress concentration of the normal threaded joints appears close to the shoulder area, whereas the stress distribution is more regular and dispersed for the specialized threaded joints, focusing around the primary two shoulders. The contact pressure at the shoulder of specialized threaded joint behaves lower than that of the normal threaded joint, indicating the primary two shoulders of specialized threaded joint can reduce the axial pressure caused by upper buckling torque. Furthermore, within the range of 0 to 100 kN axial pressure, the extreme operation torque of specialized threaded joints is significantly higher than that of normal threaded joint, demonstrating superior load-bearing performance.