Nonlinear ultrasonic evaluation of high-density polyethylene natural gas pipe thermal butt fusion joint aging behavior

High-density polyethylene (HDPE) pipes are widely used in urban natural gas pipelines. Thermal butt fusion (BF) welds are the weakest components of pipelines. Welding joint aging causes degradation of the PE thermal BF joint material properties. Using the nonlinear ultrasonic technique as a nondestructive testing (NDT) method was proposed for evaluating aging damage. Nonlinear ultrasonic measurements were conducted for HDPE thermal BF joint samples exposed to compression creep. Ultrasonic harmonics are generated due to aging damage. The acoustic nonlinearity parameter β based on the fundamental and second harmonics is calculated. The results indicate that β is sensitive to the variation in HDPE specimens under different aging conditions. This NDT method is useful in tracking microstructural changes in BF joints due to aging during the service process.