Nonlinear Ultrasonic Nondestructive Evaluation Method for Natural Aging Degree of Buried Medium Density Polyethylene Gas Pipeline During Long‐Term Service

ABSTRACT Buried medium‐density polyethylene (MDPE) gas pipelines will undergo thermal‐oxidative aging during long‐term service, causing material performance degradations. Traditional aging evaluation methods are destructive; it is difficult to effectively evaluate the aging degree of MDPE gas pipelines in service. In this study, seven types of PE80 buried pipelines in service for 0–19 years are taken as the research object, nonlinear ultrasonic non‐destructive testing (NLUT), differential scanning calorimetry (DSC) testing, and tensile strength testing are conducted on samples. A nonlinear ultrasound‐based MDPE natural aging performance evaluation method is proposed. The relationship between the nonlinear coefficient ( β ) and oxidation induction time (OIT), and the relationship between β and tensile strength ( σ ) under different aging durations are established, respectively. This study uses β to characterize the OIT and σ of MDPE gas pipelines, yielding average relative errors of 4.8% and 4.1%, respectively, verifying the feasibility of employing β to evaluate the aging degree of MDPE gas pipelines. The comprehensive evaluation model for MDPE pipeline aging performance is established, dividing the aging process into three stages. After 19 years in service, the OIT and σ of the pipeline are 25.7 min and 18.5 MPa, respectively, which are 28.5% and 3.3% higher than the national standard value.