A study of the micro-mechanical properties of butt fusion-welded joints in HDPE pipes using the nanoindentation technique

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

“…Because the crystallisation condition of PP in Swartjes' study [142] was similar to that of PP in the butt fusion welding process, the crystalline structures in Figure 2-66a to d [142] can be perceived as the crystalline structures in the layer 2 and 6, layer 3, layer 4 and layer 5 respectively. This result can be used to explain the results from the study of Muhammad et al [34]. The region closer to weld interface experienced higher temperature and lower cooling rate which is a better crystallisation condition for polymer.…”

“…Although some studies have been performed on how insufficient homogenisation of HDPE and CB can affect the HDPE pipe mechanical performance, there is little research about how this insufficient homogenisation influences the joining and joint performance of HDPE pipes, which is important to achieve the structural integrity of PE pipelines. Butt fusion welding is commonly used to join HDPE pipes because of its accurate controlling of the welding surface alignment and welding temperature, and ability to weld components with complex geometries [33,34].…”

“…Muhammad et al [34] cut a microtome slice which covered the MZ and HAZ from the butt fusion welded joint made from PE 100 pipes (Figure 2-57 [34]) and observed the microtome slice using transmission light microscope (TLM) with polarised light. Due In MZ, the highest hardness and elastic modulus existed at the weld interface (0.053GPa and 1.41GPa respectively) and then dropped to the lowest (0.052GPa and 1.37GPa) when approaching the end of MZ.…”

“…The hardness and elastic modulus of HAZ were higher than those of the MZ. The thermal properties of a microtome slice extracted from the MZ and a microtome slice from the parent pipe (as shown in Figure 2-57 [34]) were investigated by using DSC. The result (Figure 2-59 [34]) showed that both the crystallinity (67.8%) and melt point (129 o C) of the MZ were higher than those of the parent pipe (63.8% and 127 o C).…”

“…Hence the thickness of the HAZ was measured as 4.8mm. Assuming the thickness of HAZ did not change along the pipe thickness, the image of the distribution of MZ and HAZ in the butt fusion welded joint is shown in Figure 2-60 [34]. Figure 2-60 showed that the boundary between HAZ and the parent pipe was just at the corner between the weld bead and parent pipe which can result in stress concentration.…”