Effect of carbon black distribution on the properties of polyethylene pipes part 2: Degradation of butt fusion joint integrity

As a continuation of the previous work (Deveci, Antony, & Eryigit, 2018), we investigated the effect of carbon black distribution on the degradation of mechanical properties of butt-fusion joints and overall mechanical integrity of high-density polyethylene pipelines. Polyethylene pipes with similar carbon black concentrations but different distributions were produced with industrial scale compounding and extrusion equipment. Waisted tensile specimens were milled directly from the butt-fused pipe samples and elongated to fracture. Carbon black distributions at the butt fusion interphase, both in axial and radial directions, were investigated using stereo and scanning electron microscopy. A significant decrease in joint integrity, measured as work of fracture, was observed for the welds made with high-density polyethylene pipes with inhomogeneous carbon black distributions. It was found that the width of areas that do not contain carbon black (windows) can significantly enlarge at the butt fusion interphase due to shearing, resulting in brittle failures at the butt fusion interphase with a magnitude related to the level of inhomogeneity. •The integrity of polyethylene pipe joints was severely affected by the presence of domains with less or no carbon black.•The size of domains with no carbon black was magnified during the fusion process on radial direction due to shearing effect.•Mechanical degradation of butt fusion joints was associated with brittle type failures at the fusion interphase.