Microstructural investigation of butt-fusion joint of high density polyethylene pipes using X-ray scattering

Polyethylene pipes in gas and water applications have proven to be reliable over their 70 years of successful use. In designing a sound polyethylene piping system, the structural integrity of the joints between pipes is of importance. Among variety of pipe joining methods the butt-fusion method is the most widely used. During butt fusion, a melt fusion zone (MFZ) is formed, which contains various morphologies due to the difference in flow behavior within MFZ. In this study MFZ of polyethylene pipe joint was investigated employing synchrotron X-ray scattering at various locations of MFZ by changing the X-ray incidnet angles to probe the 3-dimensional structural features. Our results confirmed the combination of pressure and melt flow during joining process resulted in a complex structure. It was notable that the boundary of MFZ against the base material was found to be very different depending on the structures involved such as crystallographic unit orientation, lamellae orientation, crystallinity and spherulitic morphology.