Butt Fusion Joining of Dissimilar Polyethylene Piping Materials

摘要

Butt fusion joints were prepared from all combinations of three commercial polyethylene piping materials using selected temperatures and joining pressures. An ultrasonic inspection method was used to examine joints for possible flaws. Short-term tests (tensile and twist) were conducted on chosen combinations. All combinations were tested in methane stress rupture tests at 23C and selected combinations were tested at 49C. Strength at 100,000 hours was predicted for joined specimens by linear regression analysis. Scanning electron and option microscopy were used to examine the fracture surface and the area around the failure of several joints. It was found that good joints can be prepared from dissimilar materials. Predicted 100,000 hours strength of good joints is equal to the long-term strength of the pipe for the weaker of the two materials. Long-term failure of stress-rupture specimens apparently involves slow crack growth beginning at a stress concentration at the acute angle formed by the bead and inside surface of the pipe wall. The crack did not propagate along the joint interface or a morphological boundary but through material apparently unaffected by the joining process.