Determination of Welding Modes for Polyethylene Pipes With Electric Welded Couplings in the Range of Low Climatic Temperatures

This paper presents a technology for welding polyethylene pipes with embedded heaters at air temperatures that are lower than those recommended by regulatory documents. Unlike existing welding techniques, which involve separate heating and cooling operations at permissible temperatures, our proposed method incorporates additional steps: preliminary heating and temperature equalization. Moreover, instead of allowing standard free cooling, our approach uses controlled cooling to manage the movement of the crystallization front. The control function for cooling is calculated by solving the inverse problem of heat conductivity to determine the heater's power as a function of time, based on specified temperature data. The temperature information used for these calculations comes from analysis of the welding thermal mode under normal conditions. We solved specialized model problems to examine how the distance of the temperature setting points from the heater affects the accuracy of the inverse problem's solution. Our findings indicate that, for practical accuracy in determining heater power during the cooling stage, temperature data should be recorded at a distance of 1 mm from the heater.The implementation of this proposed welding technology is complex due to the difficulty in determining the parameters for heating, temperature equalization, and cooling control functions at naturally low temperatures for pipes of different diameters within the welding machine. Consequently, calculating all parameters and functions for low-temperature welding through mathematical modeling of the thermal process and solving inverse heat conduction problems cannot be conducted directly within the welding machine. We propose methods for deriving simple formulas to calculate the parameters of welding modes under low-temperature conditions, enabling rapid calculations. The methods can be used to find welding modes for polyethylene pipes with other types of parts. Tests for resistance to delamination have shown that welded joints produced using the proposed technology with preliminary heating, temperature equalization and controlled cooling to manage the movement of the crystallization front are no less strong than joints obtained by welding under normal conditions.