The present invention relates to a technique of manufacturing a metal-plated steel pipe, of which inner and outer faces or any one of them are subjected to molten metal-plating, by a continuous steel pipe manufacturing line.
Hitherto, as one of representative methods of performing molten metal-plating on a steel pipe, there is a known hot-dipping method. Further, in recent years, a method of manufacturing a molten metal-plated steel pipe in a continuous steel pipe manufacturing line has been proposed from the viewpoint of a decrease in the cost. As one of the methods, Japanese Patent Application Publication No. S52-43454 discloses a technique of manufacturing an outer-face plated steel pipe in a manner such that a steel sheet is continuously cold-formed into a tubular shape and the result is welded and is plated with molten metal. Furthermore, there is a growing need to perform an inner-face metal plating in recent years. Therefore, JP-A No. H05-148607 discloses a method of easily plating both inner and outer faces of a steel pipe with molten metal in a continuous line in a manner such that one face in a steel sheet corresponding to the inner face of the steel pipe is subjected to plating in a steel pipe manufacturing line, the result is cold-formed into a tubular shape, a longitudinal end face of the steel sheet is welded, and the outer face of the steel pipe is subjected to molten metal-plating.