A Model for Predicting Temperature of Electrofusion Joints for Polyethylene Pipes

Polyethylene (PE) pipe with electrofusion (EF) joints is widely used in the areas of gas distribution. Understanding and predicting the temperature during welding is crucial for ensuring the joint quality. The EF joining is generally conducted by applying a constant voltage to the heating wire. As the welding process develops, both the temperature and the resistance of the heating wire increase, which leads to a decrease in the rate of power input with increasing fusion time. However, the existing models for temperature prediction have not taken the change in the rate of power input into account. By comprehensively considering the variation in the rate of power input, the phase transition of PE and the thermal contact conductance between the heating wire and PE, the authors established an analytical model for predicting the temperature. Experiments are designed and the power inputs measured are shown to be in good agreement with the analytical results, in contrast to the interrogative measured temperature. In order to verify the temperature fields, the authors employ a new “Eigen-line” method based on ultrasonic tests which overcomes the difficulties found in the measuring methods by thermocouples. The experimental results also show good agreements. The developed model is then used to investigate the influence of the decline in the power input, physical properties of PE and the thermal contact conductance between heating wire and surrounding PE. It is found that the average power input is in proportion to the input voltage, and the temperature profile is greatly affected by the power decline and specific heat capacity. The proposed model can be used to optimize the welding specification.