Effect of insufficient homogenization during the extrusion of polyethylene pipes on butt fusion joint integrity

This paper describes an investigation into the effect of insufficient homogenization of pigmented resin in polyethylene (PE) pipes on the integrity of the subsequent butt fusion joints and the development of a test to quantify the amount of windows in the pipe. Analysis was carried out on a number of PE pipes, made using both pre-compounded and in-line compounded resin on the same pipe extruder but using different extrusion conditions to obtain different degrees of homogenization. Tensile tests using waisted tensile specimens were carried out on the butt fusion joints from these pipes. It was found that the level of windows increased with decreasing degree of homogenization in PE pipes. The energy to break and extension to break of the butt fusion joints reduced with increasing level of windows. The higher the level of windows in pipe walls, the more the butt fusion joints tended to fracture in a brittle mode.