Calibration of hem rolls in the production of roller forming longitudinal welded pipes

The quality of butt joints during the installation of main gas pipelines and indicators of their operational reliability depend to a large extent on the degree of deviation of the cross section of the pipe from the circle, especially in their end parts. Modern regulations of the quality of tubular products for the transportation of hydrocarbons, especially for underwater pipeline crossings, impose severe restrictions on the deflection of profile cross section from the circle. Tolerances in some cases do not exceed 3...5 mm, which corresponds to 0.45...0.8 % of the pipe diameter. In practice, the production of longitudinally welded pipes in the RBE-LSAW line using hem rolls by the HAEUSLER company can not consistently provide the quality of the hem geometry zones. The technique of calibrating hem rolls for the marginal portion of the blank for large diameter pipes which provides monotone transition of the hem zone to the main perimeter molded earlier on the roller sheet bending machine without local deviations from the circular geometry.