Abstract: A method of longitudinally seam-welding steel pipes comprises the steps of providing a conductive net-like enclosure tube around a cable for supplying a direct electric current from the power source to the welding head; and conducting a direct electric current through the enclosure tube and through the steel pipe in a direction opposite to that in which the direct current runs through the cable. Apparatus for longitudinally seam-welding steel pipes comprises an electrical cable coupled to a welding head, a net tube surrounding the cable, and a device for supplying a direct electric current to the cable in a first direction and to the net enclosure tube and steel pipe in the opposite direction. The direct currents flowing in the enclosure tube and in the steel pipe is adjustably controlled to minimize the magnitude of a magnetic field created around the net enclosure tube and producing a welded steel pipe seam.

Abstract: In longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove by the GMA welding process which comprises using direct electric current supplied to a plurality of consumable electrodes in tandem through at least one cable as the welding current, at least two even-numbered consumable electrodes are used, half of said consumable electrodes being connected to said direct current so as to be positive in polarity and the remaining half of said consumable electrodes being connected to said direct current so as to be negative in polarity, to enable lines of magnetic force produced by said direct electric current for welding flowing through said at least one cable introduced into said pipe-blank to cancel each other, thereby preventing magnetization of said pipe-blank and the resulting magnetic arc blow of the welding arc.

Abstract: In longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove by the metal arc welding process which comprises using direct electric current supplied to a plurality of consumable electrodes in tandem through at least one current supply cable as the welding current, an even number of consumable electrodes are used; half of said even-numbered consumable electrodes are connected in the reverse-polarity manner, i.e., to be positive in polarity, and are used as leading electrodes, and the remaining half are connected in the straight-polarity manner, i.e.

Abstract: In longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove by the reverse-polarity GMA welding process comprising using direct electric current supplied to a consumable electrode through a cable as the welding current with said consumable electrode as the anode, the direction of said direct electric current for welding flowing through said cable introduced into said pipe-blank is set in the same direction as that of welding, thereby preventing occurrence of a magnetic arc blow of the welding arc from said consumable electrode toward the upstream side of the welding direction, i.e., in the opposite direction to that of welding.

Abstract: After longitudinally seam-welding a pipe-blank for welded steel pipe from the inside along a groove by the arc welding process which comprises using direct electric current supplied to a consumable electrode through a cable as the welding current, the polarity of said consumable electrode applied for said longitudinal seam-welding is switched over to the opposite polarity, an arc from said consumable electrode is ignited again on a tab plate attached to the end of said pipe-blank on the completion side of said longitudinal seam-welding to cause a direct electric current for eliminating magnetism to flow through said cable in the opposite direction to that of said direct electric current for welding, thereby eliminating residual magnetism in said pipe-blank produced by said direct electric current for welding flowing through said cable introduced into said pipe-blank during said longitudinal seam-welding.

Abstract: In a gas shielded arc welding method for a long seam of formed pipe and the like, an improved method of setting up a welding voltage-current such that incomplete short circuiting transfer is performed with a high speed of more than at least 3m/min. and particularly, 5m/min. or more, without requiring stopping of the arc at short circuiting intervals.

Abstract: A method of large current gas shielded arc welding wherein the welding is accomplished at high speed by a single electrode or tandem sequence electrodes in an atmosphere of a mixed shielding gas comprising essentially of an inert gas with an addition of less than 30% of carbon dioxide gas or less than 5% of oxygen and supplied at an overall flow rate of 50 to 200 l/min by using large diameter solid wire consumable electrodes of low alloy steel material with a diameter of 3.0 to 6.4 mm .phi. under the following conditions: welding speed 300 to 1500 mm/min; welding current, 600 to 1500 amp; and arc voltage, 23 to 36 volts. With this method, the welding of steel can be accomplished at high speeds with a reduced heat input and an improved efficiency and it is particularly well suited for the welding of open tubes for very low temperature line pipe which must retain a high degree of toughness at very low temperatures.

Abstract: In a multiple electrode gas shielded arc welding method wherein a plurality of electrodes are arranged along the welding seam line of a piece of metal to be welded and the continuous gas shielded arc welding of the piece is accomplished simultaneously by the electrodes, the chemical composition of a mixed shielding gas fed to the electrodes is selected in such a manner that the chemical composition of the shielding gas fed to the leading electrode or electrode group differs relative to that fed to the trailing electrode or electrode group to have a different active gas volume ratio and in this way the chemical composition of the weld metal layers formed by the preceeding and following welding operations are homogenizing to ensure uniformity of the properties at every positions in the weld zone.

Abstract: In a method of multiple electrode gas shielded arc welding wherein a plurality of electrodes are arranged along the welding seam line of a piece of metal to be welded and continuous gas shielded arc welding of the piece is accomplished simultaneously by the electrodes, the chemical composition of the electrode wire of the electrode or electrode group for depositing a preceeding layer or layers is selected to differ from that of the electrode wire of another electrode or electrode group for depositing a subsequent layer or layers, whereby the chemical composition of the weld metal made by the preceeding welding operation is brought near to that of the weld metal made by the following welding operation and thus the uniform properties are ensured for welding metals at the respective positions in the weld zone.