Expediency of ultrasound control inspection when diagnozing drilling tools
During operation a drill string undergoes rotational and translational movements and, in addition, due to the interaction between the cutting tool and the rocks - the cutting factor with all the loads appearing in this process - there occurs one more force effect on the drill string - torsion. As a result of these forces, the drill string is deformed and, consequently, deviates from the straightness. The most dangerous for the drill strings are alternating loads (for example, the vibrating effect and clearly expressed heterogeneity of the rock, i. e. its density), which may be several times lower than the static ones, but constantly change the direction vector, thereby, creating conditions for the gradual intensification of fatigue destruction of the pipe body. The situation is complicated by the fact that such loads are difficult to predict, and the time of their impact is quite long. The most loaded sections of drill pipes - connecting threads - are especially susceptible to fracture-shaped defects development. These elements in their profile have a minimum cross-sectional area, besides, the thread is a concentrator of increased internal stress, especially in the zone from the first to the fifth coil. Thus, the threaded sections of pipes are the most responsible loaded elements, responsible for the reliability and safety of a drill string operation and requiring careful monitoring of the technical state by non-destructive methods.