Feasibility of Nonlinear Ultrasonic Method to Characterize the Aging Degree of Polyethylene Pipes

Polyethylene pipe finds it hard to avoid aging in outdoor water and gas transmission, and its aging degree is difficult to be evaluated intuitively. Conventional methods for determining whether polyethylene pipes must be replaced or maintained mostly involve destructive testing. Polyethylene aging causes a change of microstructure, resulting in mechanical property changes. Hence, this study presents a nondestructive evaluation technique for evaluating the aging degree of polyethylene pipes by single-transducer single-sided detection. It explored the potential relationship between polyethylene aging degree and ultrasonic nonlinear parameters. Firstly, it denoised ultrasonic signals of polyethylene pipes with different exposure times. Then, it calculated the nonlinear parameter, and the relationship between the nonlinear parameter and the exposure time of polyethylene was established. And the relationship between the tensile strength and the exposure time of polyethylene was also established in combination with the tensile test data. Finally, the nonlinear parameters and tensile properties were found to exhibit opposite trends with similar rate of change. Its findings verified the feasibility of characterizing the aging degree of polyethylene pipe using the nonlinear ultrasonic method.