Improving the Durability of Drill Pipe Subs by Electromechanical Processing

Increasing the durability of drill pipe subs is a pressing problem, a solution to which will improve the efficiency of oil and gas companies when drilling wells. Outer diameter wear, tears on the end surfaces of couplings and the end surfaces of pins, as well as blemishes on external and internal conical rotary-shouldered connections are the most typical defects of the subs. A study and comparative bench tests of the 5135 steel subs with the Z-117 screw were conducted. Testing of the subs with hardening of the work surface by electromechanical processing was done in comparison with the base technology (hardening and high tempering) and carbonitriding. The drill pipe subs were manufactured and hardened by OOO Alexandrovsky Drilling Equipment Plant on the 1М63 machine modernized for electromechanical processing. The comparative bench tests of the drill pipe subs were conducted by OOO Kovrovsky Drilling Equipment Plant on the coupling makeup machine MC-4 by screwing on / unscrewing threaded connections, taking into account the Russian Federation standards and recommendations of the American Petroleum Institute API 7. Electromechanical processing, being one of the method of hardening by a concentrated flow of electric energy of industrial frequency, builds up a gradient layer with the hardness of 52–56 HRC on the surface of the drill pipe subs. The results of the screwing on / unscrewing tests of threaded connections with a toot-joint thread demonstrated high efficiency of carbonitriding and electromechanical processing (500 and more cycles) as a method of increasing hardness of the work surfaces and low efficiency of the current bulk heat treatment (up to 47–66 cycles).

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