| 摘要 |
PURPOSE: A super-high-strength line pipe is provided which is excellent in low temperature toughness, is field welded easily, and has a tensile strength of at least 900 MPa (exceeding X100 of the API standard). CONSTITUTION: A super-high-strength line pipe is 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 - 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. |
