THE INFLUENCE OF CLEARANCE OF SECONDARY SHOULDER ON PERFORMANCE OF DOUBLE SHOULDER DRILL PIPE JOINT

The double shoulder drill pipe has been widely used with the increase of well depth. Compared with a standard API drill pipe joint, a secondary shoulder is a significant feature of a double shoulder drill pipe joint, which offers an additional loading surface and mechanical stop to ensure the high torque resistance and good seal performance of a joint. According to the mechanical characteristics of a double shoulder drill pipe joint, a suitable clearance should be obligated in front of a secondary shoulder. The magnitude of the clearance determines the loading ratio of a secondary shoulder, which affects the stress distribution of a joint. The results show that the threads near a secondary shoulder will bear more stress and the failure risk of a secondary shoulder is increased when the clearance is small. However, when the clearance is large, the primary shoulder and the threads near a primary shoulder bear more loads. A suitable clearance of a secondary shoulder can improve the performance of a joint by optimizing its stress distribution.