Abstract: In drilling operation, bottom hole assembly failures take place frequently, which occurs at the thread connection, where stress concentrates relatively. Study is aimed at box threads of Φ177.8mm drill collar to analyze and calculate drill collar box thread with different stressrelief grooves using finite element method, the stress concentration of thread end of 3 types of box threads is gained under same boundary condition and load. The calculation indicates the stressrelief grooves designed by the authors with better effect and best resistance of fatigue, so the grooves are recommended.

Key words: finite element, box thread, stress distribution, stress reliefgrooves