ORIGINAL ARTICLE The effect of friction welding on the mechanical properties and corrosion fatigue resistance of titanium alloy drill pipe Yisheng Mou 1 | Zhanghua Lian 1 | Wei Li 2 | Xiankang Zhong 1 | Jiuyi Li 1 | Yuantai He 1 | Jinchao Cao 1 | Noam Eliaz 3 1 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, China 2 Department of Civil and Environmental Engineering, Rice University, Houston, Texas, USA 3 Department of Materials Science and Engineering, Tel-Aviv University, Tel Aviv, Israel Correspondence Zhanghua Lian and Xiankang Zhong, State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China. Email: 18229099371@163.com; zhongxk@yeah.net Funding information National Natural Science Foundation of China, Grant/Award Number: 51974271; Scientific and Technological Innovation Team for the Safety of Petroleum Tubular Goods in Southwest Petroleum University, Grant/Award Number: 2018CXTD01 Abstract Titanium alloys are the best candidates to replace steels for drill pipes in horizontal wells. However, friction welding (FW) may significantly change the properties of titanium alloy drill pipes. In this work, the microstructure, tensile and impact mechanical properties, and corrosion fatigue performance of the FW zone were compared with those of the base alloy. The results show that the base material is mainly composed of equiaxed globular α (hcp)-Ti, while the acicular α + β (bcc)-Ti is dominant in the FW zone. Due to these differ- ences in microstructure, the FW zone has higher strength but lower stiffness and toughness than the base alloy. In addition, the fatigue performance and corrosion resistance of the material decrease in drilling fluid. These results indicate that FW zones in titanium alloy drill pipes might be the weakest region where crack, fracture, and corrosion are more likely to occur. KEYWORDS corrosion fatigue performance, corrosion resistance, friction welding, mechanical properties, titanium alloy drill pipe 1 | INTRODUCTION With rapid energy consumption, the supply of conven- tional onshore oil and gas resources cannot meet the fast growth of energy demand. 1 Therefore, the exploitation and production activities of unconventional resources have drawn increasing attention from the oil and gas industry. 2,3 Horizontal well is one of the advanced oil and gas exploitation technologies, which has been widely used in both thin and fractured reservoirs since it can increase output and save costs. 4 However, the current required horizontal section length has sharply increased, 5,6 and the required dogleg severity in build-up sections has also increased significantly. 7 In this environment, a steel drill pipe with high stiffness has to bend itself in order to fit the borehole trajectory and endure high alternating stress during the rotary drilling, which could lead to corrosion fatigue fracture within a short period. Therefore, in order to ensure drilling operation safety, lightweight metallic materials such as titanium alloys have shown great potential since they can effectively reduce friction and lower tensile stress level. 8,9 Meanwhile, titanium alloy has a higher strength and better corrosion resistance compared with steel carbon of the same grade. 10,11 Friction welding (FW) technology has been widely used in manufacture of carbon steel drill pipes. 12–14 Recently, it has also been applied in the manufacture of Received: 23 June 2021 Revised: 12 October 2021 Accepted: 18 October 2021 DOI: 10.1111/ffe.13609 466 © 2021 John Wiley & Sons, Ltd. Fatigue Fract Eng Mater Struct. 2022;45:466–481. wileyonlinelibrary.com/journal/ffe