A half-mold for a corrugator for making pipes with transverse ribs. The half-mold comprises two sides located spaced apart from each other and a semi-cylindrical base surface linking the two sides. Directly mounted forming elements bent in the shape of a semicircle which define the outer surface of the pipe with transverse ribs are removably fixed on the base surface. The directly mounted forming elements bent in the shape of a semicircle are removably fixed with fixing elements on the half-mold.