Nippon Steel Corporation

Kunio Koyama

Kyoichi Nagano

Toshihiko Takami

Takuya Hara

Hitoshi Asahi

Hiroshi Tamehiro

Yoshio Terada

Shigeru Ohkita

To provide a super-high strength line pipe that is excellent in low temperature toughness, can be field welded easily, and has a tensile strength of at least 900 MPa (exceeding &times;100 of the API standard), and a production method thereof. The present invention relates to a super-high strength line pipe produced by shaping a steel plate into a pipe shape and arc welding seam portions, the strength of a base steel portion is 900 to 1,100 MPa and the strength of the weld metal is higher than the base steel strength &minus;100 MPa. In the steel pipe, the Ni content of the weld metal is higher by at least 1% than that of the base steel. The combination of the chemical components of the steel plate with those of the weld metal, for accomplishing these steel pipes by a U&O step is shown concretely. A production method of the steel plate and the welding method for achieving the steel pipe are also described. Furthermore, a method of reducing the strength of the inner surface of the weld metal to restrict cracking at the time of pipe expansion is also shown.

Super-high-strength line pipe excellent in low temperature toughness and production method thereof

In a low hydrogen type covered arc-electrode, the sources of diffusible hydrogen are kept to a low level by selecting kind of the ingredients for producing the electrodes or by baking the ingredients. In the process of the present invention, the covered arc-electrode is baked at a high temperature so as to extremely reduce the amount of the sources of diffusible hydrogen of the weld metal, while decomposition of limestone, which is one of the covering components, is prevented due to a novel baking atmosphere containing CO.sub.2. The weight ratio of Na.sub.2 O/K.sub.2 O in the covering is adjusted to be 1 or more, so as to keep amount of fumes.

Process for production of a low hydrogen type covered arc-electrode

Non-Fused flux composition particularly suitable for horizontal submerged-arc welding in production of welded structures such as storage tanks and pressure vessels, comprising 13 to 30% TiO.sub.2, 5 to 50% CaF.sub.2, 20 to 40% MgO, 12 to 30% Al.sub.2 O.sub.3, 2 to [20-(% CaF.sub.2).div.3]% SiO.sub.2, 0.1 to 1.0% B.sub.2 O.sub.3, and providing good low temperature fracture toughness of weld metal.

Non-fused flux composition for submerged-arc welding

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Machida, Japan

Kunio Koyama