To easily connect stainless steel pipes to each other by using a conventional flange joint by butting the steel pipes where a taper-shaped flange part is formed by expansively opening a stainless steel pipe end part against each other through annular packing having an almost triangular cross section, and fastening them by bolts through a flange joint.

When stainless steel pipes 7 are connected to each other, first of all, the stainless steel pipes 7 are fixed to a clamp device, and a roller shaft of a work roller shaft 6 to support plural cylindrical molding rollers 6a is fitted to and installed in a chuck part of a rotary shaft 5. Next, a rotary device is advanced, and a cylindrical roller surface is pressed to a steel pipe end part 7c, and the steel pipe end part 7c is expansively opened in a taper shape, and a taper-shaped flange is formed. Next, both triangular slant faces are butted against each other so as to contact with an inner peripheral surface of the taper-shaped flange by using packing by covering a surface of a core body 11 having an almost triangular cross section with an elastic material 11a, and they are connected to each other by fastening an outer peripheral surface of a flange part by a loose flange joint 9 and bolts-nuts 9a.