METHOD FOR PREVENTING CRACK IN SEGMENT IN STEEL PIPE EXPANDER

PURPOSE:To prevent the crack in a segment in the stage of expanding a pipe having the same outside diameter and different wall thickness with a steel pipe expander in a method for expanding said pipe by making the radius on the effective expanding surface of the segment larger than the radius of the pipe corresponding to the central value of a max. wall thickness and a min. wall thickness. CONSTITUTION:A segment 8 of which the effective expanding surface is made larger than the radius of a pipe 9 corresponding to the central value of a max. wall thickness and a min. wall thickness is used in expanding said pipe 9 having the same outside diameter D and different wall thicknesses (t). Such segment 8 is capable of receiving the load to be exerted on the effective expanding diameter thereof at both ends B along the longitudinal direction thereof, whereby the tensile stress generated in the recess 15 of the segment 8 mounted with a T guide 8-1 is suppressed low and the crack in the segment 8 is prevented.