Abstract: First a metallic pipe is tapered, so that it is substantially closed at its end, and so that its cross-section is reduced. Then it is pressed hard against a mold electrode, and a large electric current is passed through it to the mold electrode, so that the end softens, but does not melt, and by the pressing (which may be of the order of 2.5 tons weight) the end is formed into a lump, with no trace remaining of the hole through the pipe within the lump. In certain embodiments, the mold electrode may be formed with a notch, and/or a depression, and may be inclined at an oblique angle to the axis of the pipe, and may be moved sideways or at an oblique angle to the axis of the pipe as the current is passed and the lump formed.