Abstract: Steel strip (1) is cleaned by shot blast machine (3) and its upper surface is coated with zinc in molten plating device (4). The strip is formed by roll forming machine (6) into a tube and the outer surface of the tube is coated by plating device (11).

Abstract: A connection structure and method comprising the steps of providing a cylindrical joint member for connecting a first pipe and a second pipe inserted into opposite ends of said cylindrical joint towards the center of said cylindrical joint member and holding said pipes in such a position that their ends are separated only by a narrow gap, and compressing both ends and the center of said cylindrical joint member to form airtight seals between said first and second pipes and the ends of said cylindrical joint member and also between the ends of said first and second pipes and the middle part of said cylindrical joint member.

Abstract: A joint is formed at adjacent ends of tubes (5, 7) by inserting the ends of the tubes into opposite ends of sleeve (1) until the tube ends engage centrally positioned inwardly extending protrusion (3). The sleeve (1) is crimped inwardly into frictional engagement with the tubes (5, 7), only at the middle portion and at the end portions of the sleeve to partially deform the sleeve and the tubes at the adjacent ends of the tubes and at positions of the tubes displaced from the tube ends.

Abstract: This invention relates to the means of continuously seam-welding the areas to be joined together of steel strips formed like tubes in the production of hot-dip metal-coated steel tubes from steel strips in a continuous supply. This seam welding device is capable of manufacturing electric seam-welded tubes with high efficiency and operational safety.