Nippon Kokan Kabushiki Kaisha

Hiroyoshi Matsubara

Tatsumi Osuka

Itaru Watanabe

Jinkichi Tanaka

Motoaki Suzuki

Kenji Takeshige

Osamu Hirano

Takashi Nagamine

Fusao Koshiga

Toshifumi Kojima

Tadao Sugiyama

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.

Method and apparatus for seam-welding steel pipes

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.

Preventing magnetization of pipe blank in GMA welding

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.

Method for longitudinally seam-welding pipe-blank for welded steel pipe

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.

Method for eliminating residual magnetism in pipe-blank for welded steel

A low alloy steel substantially consisting of Ni-Cr-Cu-Nb system and further adding 0.01 to 0.10% rare earth metals or their alloy thereto, and then being as only hot-rolled by 30 to 80% rolling rate at a temperature of less than 950.degree.C. The steel exhibits absorption energy of at least 10kg-m at -20.degree.C and a .sub.D T.sub.C transition temperature of lower than -40.degree.C, if necessary, may be tempered at a temperature of 500.degree. to 680.degree.C to improve the properties.

Growing community of inventors

Fukuyama, Japan

Hiroyoshi Matsubara