Abstract: A process and apparatus for continuously transforming a flat metal strip into an elongated pipe, in which the strip is fed through a forming tool along a curved forming path wherein the longitudinal edge portions are progressively turned up into cross-sectionally arcuate portions leaving between a substantially cross-sectionally rectilinear section, the width of which progressively decreases during travel of the strip through the forming tool. The curved forming path in the tool is such that it has a radius of curvature R(z) in its longitudinal direction, the arcuate portions each having a radius r.sub.o and the decreasing width of said rectilinear section being 2x(z) (wherein z is the distance of travel through the tool). The radius of curvature R(z) is controlled in sole dependence on r.sub.o and the differential quotient x'(z).