Stress and Temperature Effects on Ultrasonic Properties in Cross-Linked and High Density Polyethylene

Cross-linked polyethylene is widely used in the manufacturing of rotationally molded tanks for the agriculture, petroleum, and chemical industries. These tanks are exposed to a number of environmental effects, which can lead to material degradation. Measuring ultrasonic wave speed change in the outer wall of the tank is a method that shows promise for evaluating the ultraviolet (UV) degradation effects. In order to evaluate the UV effects in the field, however, the effect of stress and temperature on the wave speed first must be established. A series of tests was performed to establish the ultrasonic properties in cross-linked as well as linear polyethylene at a range of temperatures from $−6°Cto44°C$ (⁠$22°Fto112°F$⁠). The change is linear, as expected. For the stress tests, the velocity decreased with tension, also as expected. Tests were performed from approximately $689kPato9.6MPa$$(100to1400psi)$⁠. Results from these tests were incorporated into the overall algorithm used for evaluating tank degradation.