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

Cross linked polyethylene is widely used in the manufacturing of tanks for the agriculture, petroleum and chemical industries. These tanks are exposed to a number of environmental effects, which can lead to material degradation. Ultrasonic wave speed change is a method that shows promise in evaluating the UV degradation effects. In order to evaluate the UV effects in the field, however, the effect of stress and temperature on the wave speed must first be established. A series of tests were performed to establish the ultrasonic properties in cross linked as well as natural polyethylene at a range of temperatures from −6 deg C to 44 deg C (22 deg F to 112 deg F). The change is linear, as expected. For the stress tests, the velocity decreased with tension, also as expected. Tests were performed from approximately 689 kPa to 9.6 MPa (100 psi to 1400 psi). Results from these tests were incorporated into the overall algorithm used for evaluating tank degradation.