During rolling of thin-walled seamless pipes at the rear ends, a defect in the form of end folds occurs, which leads to an increase in the consumption coefficient of the metal. To identify the causes of the formation of this defect, the mathematical modeling of rolling processes in the QForm VX software was carried out. The simulation results showed that the main factor in the formation of end folds at the rear ends of the pipe billets is an increased relative compression along the wall of the pipe billet in the first pass, which leads to flattening of the rear end of the pipe billet and formation of longitudinal folds. To prevent the formation of end folds, it is proposed to install an additional sleeve with a mandrel. As a result of the research, the values of relative compressions were determined, at which a defect is formed for rolling with a new mandrel installation option. It was found that with relative compression along the wall in the first passage from 30.0 %, a defect in the form of folds (“fins”) at the rear end of the pipe billet is formed. With a relative compression of the wall in the first passage up to 39.4 %, the installation of sleeves reduces the formation of “fin” defects at the rear end of the pipe billet; with a relative compression from 39.4 % to 41.8 %, its installation does not prevent the formation of these defects. The optimal distance between the mandrel of the automatic mill and the sleeve is 20-30 mm