Method of molding high expansion pipe and the high expansion pipe

Abstract

When a flaring punch 2 is pressed into a pipe P from an end thereof to form a concentric or eccentric flared portion Pa, the taper angle θ of the flaring punch is adjusted to apply axial compressive forces to the flared portion Pa thereby to maintain the wall thickness of the flared portion Pa at 70% or greater of the wall thickness of the blank pipe. If the flared portion is formed by a plurality of flaring punches 2A, 2B, 2C having different maximum diameters at a plurality stages, then regions where the elongation is maximum are not localized, preventing the wall thickness from being locally reduced. If an eccentric highly flared pipe where the center of the flared portion Pa and the center of the pipe P are displaced from each other is formed, then a seam-welded region s of the pipe P is aligned with the direction in which the amount ε of eccentricity is maximum, making the flared pipe resistant to being ruptured.

Dependencies are inferred from the claim text.