Abstract
Welding of polyethylene (PE) pipes for gas pipelines is recommended to be performed at ambient air (AA) temperature from minus 15 to plus 45 °C. The present work proposes a mathematical model of the thermal process for butt-welding of PE pipes, which takes into account the latent heat of phase transitions in the temperature range. Correspondence of the model to the real thermal process is confirmed by comparing the experimental and calculated temperatures. At a temperature from the permissible temperature range in the heat affected zone (HAZ), a cooling rate is provided in the optimum interval, which ensures the formation of the structure of the welded material that provide sufficient strength. Thus, for welding PE pipes at AA temperatures below the normative it is sufficient to establish the cooling rate in the optimum interval in the HAZ while maintaining the other technological parameters of welding. Mathematical modelling shows that the necessary cooling rate in the HAZ is obtained by preheating the ends of the welded pipes to the permissible temperature along the outreach length equal to the fivefold thickness of the pipe, melting in regular mode and cooling the welded joint in the heat-insulating structure of the calculated size.
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