Patent ID: 8795450

Claim:
A manufacturing method for a steel pipe for fuel injection pipe having a tensile strength of not lower than 900 N/mm 2 , the inner surface of which is repeatedly subjected to pressures created by fuel injection, having an increased critical internal pressure defined as a highest internal pressure at which fracture does not occur even when the pressure is applied under a load condition of sinusoidal wave with respect to time and the repeating cycle reaches 10 7 cycles in the fatigue test wherein the lowest internal pressure is set at 18 MPa, comprising the steps of: providing a steel pipe that has a chemical composition comprising, by mass percent, C: 0.12 to 0.27%, Si: 0.05 to 0.40%, and Mn: 0.8 to 2.0%, with the balance being Fe and impurities, in which the impurities contain Ca: 0.001% or less, P: 0.02% or less, and S: 0.01% or less, and wherein the maximum diameter of non-metallic inclusions within 20 μm in depth from the inner surface is not larger than 20 μm, quenching the steel pipe at a temperature of not lower than the Ac 3 transformation point, and tempering the quenched steel pipe at a temperature of not higher than the Ac 1 transformation point.