Drill withstand long-term work in tension, Drilling String Crossover Sub compression, bending, twisting and cutting complex stress, and in some regions produce frequent alternating stress, such as normal drilling in and near the point of the drill, drill accident processing card drill and bend in the eyes of the well drilling operation when the free section, when the stress reaches a sufficient strength and a sufficient number of alternating, will produce fatigue damage.
Critical speed of vibration caused damage. When the rotational speed of the drill string reaches a critical speed, make drilling vibration, longitudinal vibration and lateral swing in two forms, while a certain depth in the two forms will coincide with the vibration, this vibration will drill under alternating stress, prompting drill premature fatigue. Various steel drill pipe depth critical speed and two vibration coincides shown in the following table as a reference.
Jump when drilling drill, do not drill, drill even have a vertical vibration, but also to drill the transverse vibration of the tool pressed portion of damage is very serious, so drilling in gravel, crossover drilling the most accident-prone collars ʱ??
Drill wells in the eyes of bending rotation, necessarily to its own axis as the center of rotation, this part of the wall by the side of the drill pipe under pressure from the side wall of the tensioning, per rotation, alternating tension and compression stress once thus formed frequently alternating stress, prompting drill early damage.