Surface Galling Mechanism Analysis of Rotary Shouldered Thread Connection

Abstract

In this paper, surface galling failure process and mechanism of drill pipe’s rotary shouldered thread connection (RSTC) was studied by means of full-scale make-up and break-out (M&B) testing. The results showed that surface galling damage mainly appearred at the positions of leading flank, bearing flank and make-up shoulder of RSTC. The galling damage of three different positions was a process of mutual independence and mutual promotion, and they might appear simultaneously, and also appear at different stage. The surface galling failure was mainly due to metal’s plastic deformation and peeling off under the effect of compressive stress caused by friction and compression effect among the contacting metal surface. During M&B testing, deformed and peeling metal accumulated continually and resulted in "cold welding" at local position. In the subsequent M&B process, "cold welding" metal was torn open and peeled off from metal matrix, and metal surface galling was getting serious gradually. M&B testing results showed that torque load and thread compound had decisive influence on surface galling damage, while the influence of RSTC’s surface wear, rearranging, torque fluctuations and tensile load was not obvious.