<p>Polyethylene (PE) pipes are widely used in oil and gas transportation, municipal construction. Electrofusion (EF) welding is one of the most common method for connecting PE pipes. The quality of EF welding joint is crucial for the safety of piping system. However, the mainstream&nbsp;approach of EF welding in industry is still with constant voltage, which cannot actively avoid welding defects. At present, there are few researches on the optimal control of EF welding process based on theoretical analysis. In this paper, the nonlinear model prediction control (NMPC) is used in the welding control, by which the real-time decision of the controller is given by iteratively solving the constrained objective optimization problem of each time step. The limit and constraint condition of the welding process is the input power and the maximum temperature in the welding zone while the objective is to minimize the duration of reaching the desired melting zone depth. To make the control practical and robust, the resistance wire in the joint is adopted as the second observer and the influence of the uncertainty in a practical welding system is analyzed and considered. The method is tested on different types of pipe fittings, its stable control performance is verified by ultrasonic testing and infrared testing. The implication of this paper is to introduce advanced control theory combined with theoretical temperature model into the EF welding control, making it more automatic and intelligent.</p>

Optimal Control of Electrofusion Welding Process of Polyethylene Pipes

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

ASME 2021 Pressure Vessels & Piping Conference (PVP2021)

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