Abstract: Device for bending thin-walled pipes from inside by embossing them with eccentric corrugations, comprising an expander block introducible into the pipe to the point of bend, the block being formed by a supporting shoe and a punch whose side facing the pipe has a toroidal surface following the shape of the desired corrugation and which is mounted on the shoe with a provision for positive movement in a radial direction to the pipe surface for making the corrugation on the pipe. In the cross-sectional plane of the pipe the punch has the shape of a ring which is open at the side of the shoe and is composed of individual elements around its parameter, each element being articulated to a movable member of one of the power cylinders whose axes are arranged radially to a cross-sectional plane of the pipe while their stationary members are connected with the supporting shoe.