Patent ID: 10480043

Abstract:
A seamless steel pipe for line pipe has a chemical composition consisting, by mass percent, of C: 0.03-0.15%, Si: ≤0.50%, Mn: 1.0-2.0%, P: ≤0.050%, S: ≤0.005%, Cr: 0.1-1.0%, Al: 0.001-0.10%, N: ≤0.01%, Ni: 0.05-2.0%, B: 0.0003-0.0015%, Ca: 0.0002-0.0050%, Mo: 0.10-0.50%, Ti: 0.001-0.05%, Cu: 0-2.0%, Nb: 0-0.05%, V: 0-0.10%, the balance: Fe and impurities, and satisfying the conditions of 2Nb+4V+Mo≤0.50, wherein a metal micro-structure of the steel pipe contains 50% or more of bainite, in an area fraction, a wall thickness of the steel pipe is 25 mm or larger, and in a scale formed on the surface of the steel pipe, metal particles consisting mainly of Ni or Cu having an average circle-equivalent diameter of 0.1-5 mm exist. A distance from a boundary between the base metal of the steel pipe and the scale to a region in which the metal particles do not exist is 20 mm or longer.