a welding collar contains a collar body of fusible plastic and a heater coil , disposed in its inside surface , which is spaced apart from a free collar end by a front zone . this welding collar is improved in that pipelines with ends which are not precisely cylindrical , and especially pipelines made from material in rolls , can be welded in a problem - free and reliable manner . the sum of the length of the front zone and the axial length of an inner zone adjoining the heater coil , with which the inserted pipe comes in contact , is at least approximately equal to the length of the heater coil . the insertion depth is greater by at least a factor of 1 . 4 than the inside diameter of the collar body .