Complex application of the method of acoustic emission and energy approach to determine the residual life of a structure under effect of long-term static load, corrosion and material degradation

A comprehensive method of applying acoustic emission (AE) and the previously developed energy approach to determine the residual lifetime of thin-walled structural elements under conditions of long-term static load, corrosive environment effect and operational degrada­tion of materials is developed. The method is based on the first law of thermodyna­mics of the balance of energy components and the work of external forces, as well as their rates of change for an elementary jump of crack propagation. The hypothesis of a linear relationship between the size of the area of the active crack and the number of acoustic emission pulses released at the same time is assumed. The change in the characteristics of the oil and gas pipeline material during its operational degradation is mathematically mo­deled by a linear depen­dence on time. The above-formulated problem of determining the residual lifetime of a thin-walled structural element was solved using the energy approach and reduced to a differential equation with initial and final conditions. In the mathematical problem obtained in this way, two parameters are unknown: the size of the initial plane crack and the loading parameter of the material near it. These parameters were determined as follows. With the help of the AE device, during the given time (150 hours), the number of AE pulses and the rate of their counting were recorded. These values were introduced into the established formulas for determining, the area of the initial crack and the parameter of loading of the material in its vi­cinity. To demonstrate the application of this complex method, a nume­rical experiment was performed and the residual life of a X70 steel plate was determined.