PURPOSE: To produce the metal composite pipe of smooth and highly aesthetic weld face by making the overlap width of the end parts of the metal plate covering the outside circumference surface of a steel pipe of less deviations in outside diameter as narrow as possible and supplying the current of a small ripple factor to the overlap part.
CONSTITUTION: The overlap part 3 of a covering metal plate 2 such as of stainless steel or Al is positioned to the bottom surface of an upper electrode 4 and a metal pipe 1 covered with the metal plate 2 is advanced at a specified speed in the pipe axis direction between the roll 4 and lower electrode roll 5. At this time, the overlap width of the metal plate 2 is made the length less than about 4 times the thickness of the metal plate 2. Along with the advancing of the covered steel pipe 1, the current of less ripple factor, e.g., 3-phase AC having undergone halfwave rectifying, DC, square wave current or high frequency current, is supplied to the overlap part 3 through the electrode rolls 4, 5. The entire part of the overlap part 3 is melted by this welding current and is rolled smoothly nearly equal to the thickness of the metal plate 2 by the screw-down force of the electrode roll 4.