Abstract: In a method of correcting a distorted pipe end to an original substantially true circular cross-section, external loads are applied to the outer peripheral surface of the pipe adjacent to the end thereof to forcibly deform the pipe end to the substantially true circular cross-section. The external loads are maintained to keep this substantially true circular cross-sectional shape while an internal pressure is applied to the inner peripheral surface of the pipe end until a circumferential stress produced in the pipe reaches an amount which exceeds the yield stress of the pipe to give a radial permanent deformation to the pipe for thereby producing a circumferentially uniformly distributed residual stress in the pipe.

Abstract: A tube-hole structure for an expanded tube-to-tube-sheet joint which is formed by axially moving a rod within each tube member in each tube hole of the tube sheet by external drive means, thereby imparting an elastic mass placed inside the tube with a sufficient compressive load to expand the tube uniformly in the radial direction to provide a rigid joint between the tube and tube hole, characterized in that each tube hole has at least one circumferential groove with an axial dimension or length of 1.5/.beta. to 3.0/.beta. (.beta. being ##EQU1## WHERE R is the mean radius of the tube member to be expanded, t is the wall thickness of the tube, and .nu. is the Poisson's ratio).

Abstract: Disclosed is a tube expander adapted for use in fixing tubes to a tube plate of a boiler or a multitubular heat exchanger. The expander incorporates an elastic expanding medium adapted to be inserted into a tube to be expanded radially against a wall of a tube-receiving bore of the tube plate. The expander further includes a pressurizing rod passing through the expanding medium, a pressurizing rod head provided at one end of the pressurizing rod, a back-up ring adapted to be supported straddling said tube receiving bore and slidably passed by the pressurizing rod, and seal rings disposed at both sides of the pressurizing rod. The seal rings are made of a hard elastic material of a hardness greater than that of the expanding medium, and each of them is provided with at its portion confronting the end of the expanding medium with a conical recess.