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Welded steel pipe for linepipe having high compressive strength and excellent sour gas resistance and manufacturing method thereof

  • US 9,181,609 B2
  • Filed: 11/25/2010
  • Issued: 11/10/2015
  • Est. Priority Date: 11/25/2009
  • Status: Active Grant
First Claim
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1. A welded steel pipe for a linepipe having the composition which contains by mass % 0.02 to 0.06% C, 0.01 to 0.5% Si, 0.8 to 1.6% Mn, 0.012% or less P, 0.0008% or less S, 0.01 to 0.08% Al, 0.005 to 0.050% Nb, 0.005 to 0.025% Ti, 0.0005 to 0.0035% Ca, 0.0020 to 0.0060% N, and Fe and unavoidable impurities as a balance, whereinC(%)−

  • 0.065Nb(%) is 0.025 or more,a CP value is 0.95 or less,a Ceq value is 0.28 or more,Ti/N is a value which falls within a range of 1.5 to 4.0, andthe steel pipe has metal microstructure where a fraction of bainite is 80% or more, a fraction of martensite-austenite constituent (MA) is 2% or less, and an average grain size of bainite is 5 μ

    m or less, wherein the CP value is expressed by the formula;


    CP=4.46C(%)+2.37Mn(%)/6+{1.18Cr(%)+1.95Mo(%)+1.74V(%)}/5+{1.74Cu(%)+1.7Ni(%)}/15+22.36P(%); and

    wherein the Ceq value is expressed by the formula;


    Ceq=C(%)+Mn(%)/6+{Cr(%)+Mo(%)+V(%)}/5+{Cu(%)+Ni(%)}/15.

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