Butt fusion welding is one of the main methods of connecting polyethylene pipes, widely used in the construction of large diameter thick wall pipes. However, the butt fusion joints are the weak link in the polyethylene pipeline. The butt fusion welding parameters such as the heat plate temperature, heating time and welding pressure affect the properties of welded joints. Previous studies have shown that the welded joint properties are related to the size and shape of the molten zone. The molten zone characteristics can be used to assess the welding process parameters for butt fusion welding. In this study, during the butt fusion welding, the changing state of the molten zone was recorded to obtain the optimal welding process parameters. The real-time video recording of the whole process for polyethylene butt fusion welding was proposed, using ultrasonic phased array focusing and imaging techniques. The ultrasonic signal was detected at the boundary of the molten zone based on the acoustic impedance contrast between the molten and unmolten zones. According to the change of boundary ultrasonic signal, the changing state in the distance of the molten zone was recorded and compared in real time. This experimental method is provided to evaluate the welding process parameters for polyethylene butt fusion welding.

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