PURPOSE: An internal coated steel pipe is closed at the end, and the inside is cooled by water. A flange is formed by welding an annular body on the outside of cooled portion to rapidly and assuredly provide a flanged steel pipe without damaging the internal coating.

CONSTITUTION: An annular body 3 is mounted onto the outside periphery of the internal coated steel pipe 1 end. Into the pipe inside, the stopper 2 is inserted by sliding the periphery of annular packing 23, then the fastener 25' is tightened so that the packing 23' inside firmly contacts the pipe inside. This defines the closed internal portion at the steel pipe end. Water is circulated through the inlet 26 and the outlet 27 to sufficiently cool the coated layer 12. The annular body 3 is welded to the desired location of the pipe 1, water is exhausted from the outlet 27, and the stopper 2 is removed to complete flange attaching.