Mechanical Performance Test and Failure Analysis on Cold Assembled Aluminum Alloy Drill Pipe Thread Pair

Abstract:

Compared with the traditional steel drill pipe, aluminum alloy drill pipe has the advantages of low density, high specific strength, non-magnetic and etc., so it has great advantage in deep and ultra-deep drilling operations. In practice, for aluminum alloy drill pipe, the connecting and dismounting at two ends are realized by the screws on the steel joints, while the fasten connection of aluminum alloy drill pipe and steel joint is realized by interference fit. With the cooling source of liquid nitrogen, 50mm 7075 aluminum alloy drill pipe and steel joints were connected with interference by “cold assembly”, the magnitude of interference between aluminum alloy drill pipe and steel joints were 0.1, 0.15 and 0.2mm respectively. The tensile and torsion tests were carried out on the assembled aluminum alloy drill pipe (both ends with steel joints). In this paper, the reliability of the connection between aluminum alloy drill pipe and steel joint was evaluated, and the fracture surface of specimen are analyzed macroscopically and microscopically to elaborate the fracture mechanism. The results show that the interference assembly of aluminum alloy drill pipe and steel joint can be realized by “cold assembly”. The aluminum alloy drill pipe with magnitude of interference of 0.15mm has better comprehensive properties, and it can bear larger tensile strength and anti-torsion limits, and the fracture mode is brittle fracture.

Key words:aluminum alloy drill pipe; cold assembly; interference fit; fracture mechanism