Method and device for the welding of pipes

A method of welding a pipe of a weldable polymer material to a muff of a weldable polymer material, where the pipe has ends, where the method comprises:

• placing the muff with an overlap over the ends of the pipes;
• welding the muff to the ends of the pipes through placement of an electrically conducting band that is permeable to molten plastic between the pipe and the muff;
• connecting a power supply to the band through feed cables;
• measuring the initial ambient temperature of the weld;
• calculating the initial resistance of the band, wherein the initial resistance of the band is calculated as a ratio of voltage across the band and current supplied to the band before the band is heated;
• supplying an electrical current in order to heat the band and the surrounding polymer material such that they melt together around the band in order to form a weld, wherein the current is supplied such that the temperature of the band is caused to reach a first target value of temperature during a heating phase, wherein the temperature of the band is caused to reach a second target value of temperature during an equilibrium phase, and wherein the first target value of temperature is higher than the second target value of temperature;
• measuring a voltage across the band;
• measuring the electrical current supplied to the band;
• causing the electrical current supplied to the band to increase;
• calculating the resistance of the band based on the voltage and the measured current;
• calculating the change in resistance as a difference between the resistance of the band and the initial resistance of the band;
• calculating the increase in temperature of the band based on the change in resistance based on the change in resistance and a material-specific conversion factor;
• calculating the temperature of the weld through adding the initial ambient temperature of the weld and the increase in temperature of the band;
• and
• terminating supply of current to the band based on the calculated temperature of the weld,
• wherein the calculated temperature of the weld is compared with a pre-determined final temperature of the weld, and
• wherein the supply of current to the band is terminated when the temperature of the weld has reached the pre-determined final temperature of the weld.