A numerical modeling of natural convection air cooling of a butt-fusion weld

Butt-fusion welding is the process of heating up two pipe ends with a hot plate and joining them together, creating a weld between the two ends. This is the predominant technique used for fusion joining of polyethylene pipes. In this work, a model of a fused High Density Polyethylene (HDPE) pipe is designed using a thermal analysis simulation in SolidWorks to determine the cooling rate of the weld based off thermal and physical parameters. Numerical simulations are performed to analyze the influence of varying pipe outer diameters, wall thicknesses, heat soak times, and temperatures of the pipe’s environment. The cooling process of the pipe is tri-modal; natural convection inside and outside the pipe, conduction axially and a radiant component due to initial high temperatures of the melt. Temperature dependent thermal properties of HDPE were found and are built into the model. This thermal model is used to run a full factorial design from which an analysis of variance is coded. This analysis can be used to develop an empirical relationship based upon the four parameters previously mentioned and returns an approximate cooling time for the weld. It was found that the diameter, wall thickness, environment temperature, and heat soak time are directly proportional to the cooling time of the weld, primarily due to the fact that a longer heat soak time causes a higher axial temperature gradient along the pipe. This model approach and resulting algorithm are capable of determining post-weld thermal results and providing more knowledge in the cooling process of butt-fusion welds in HDPE.