Abstract: Mash seam welding process and apparatus, wherein two plate-like workpieces having different thickness values are fed and guided by a guiding device such that a length W.sub.H of contact of the thick plate-like workpiece with one of two roller electrodes is smaller than a length W.sub.M of contact of the thin plate-like workpiece with the other roller electrode. In this arrangement, the amount of mashing of the thick plate-like workpiece by the roller electrode is made larger than that of the thin plate-like workpiece by the other roller electrode, so that an interface of the two plate-like workpieces is positioned intermediate between the pair of roller electrodes, whereby a weld nugget formed intermediate between the roller electrodes extends across the interface, permitting the weld to have a sufficient strength owing to a nugget ratio, which is a ratio of a width dimension W.sub.N of the weld nugget in the direction of the interface to a width dimension W.sub.G of the interface.

Abstract: Seam welding process and apparatus, wherein two plate-like workpieces are fed in a feeding direction toward a pair of roller electrodes, by guide rollers rotated by a driving device, while the workpieces are guided by a guiding device such that the edge portions overlap each other with a predetermined lap amount so that the overlapping edge portions are squeezed by the roller electrodes, and the edge portions are continuously welded together with a welding current being applied between the roller electrodes.

Abstract: The nonfreezing pipe with a double wall construction comprises an inner shell having openings at its opposite ends, an outer shell extending axially around the inner shell to form an annular space surrounding the inner shell, and at least one end closure member connecting between one end of the outer shell and the external wall portion of the inner shell. The annular space is evacuated.

Abstract: Mash seam welding process and apparatus, wherein two plate-like workpieces having different thickness values are fed and guided by a guiding device such that a length W.sub.H of contact of the thick plate-like workpiece with one of two roller electrodes is smaller than a length W.sub.M of contact of the thin plate-like workpiece with the other roller electrode. In this arrangement, the amount of mashing of the thick plate-like workpiece by the roller electrode is made larger than that of the thin plate-like workpiece by the other roller electrode, so that an interface of the two plate-like workpieces is positioned intermediate between the pair of roller electrodes, whereby a weld nugget formed intermediate between the roller electrodes extends across the interface, permitting the weld to have a sufficient strength owing to a nugget ratio, which is a ratio of a width dimension W.sub.N of the weld nugget in the direction of the interface to a width dimension W.sub.G of the interface.