Patent ID: 9737962
Date: 2017-08-22
CPC Classifications: B23K,C22C,F16L,Y10T

Claim:
1. A pipeline comprising a plurality of weld zones where ends of a plurality of steel pipes are joined by welding, wherein the plurality of the steel pipes are produced from a plurality of charges of molten steel having one or more steel compositions, by mass %, a yield point elongation is not present on a stress-strain curve that is obtained when stress is applied in a longitudinal direction of each of the steel pipes; t which is a thickness of each of the steel pipes in units of mm and D which is an average pipe outside-diameter in units of mm satisfy a following Expression 1; ΔYS which is a yield strength difference between one steel pipe and the other steel pipe that are welded to each other in units of MPa, and YR which represents a yield ratio that is a ratio of the yield strength to a tensile strength of a pipe having a low yield strength out of the one steel pipe and the other steel pipe, satisfy a following Expression 2: wherein a ΔCeq value which is an absolute value of a difference of Ceq values expressed by a following Expression 4 between the one steel pipe and the other steel pipe is 0.045% or less, and the tensile strength of the plurality of the steel pipes is 450 MPa to 850 MPa or less, wherein [C], [Mn], [Ni], [Cu], [Cr], [Mo], and [V]represent amounts of C, Mn, Ni, Cu, Cr, Mo, and V by mass %.