Patent ID: 7770428

Claim:
A hot bend pipe for line pipe and having a strength of at least API X70 which is manufactured by carrying out bending of a welded steel pipe after heating to a temperature of at least 900° C. to at most 1100° C. and which has a quenched and tempered structure obtained by cooling after the bending at a cooling rate of at least 3° C. per second to a temperature range of 300° C. or lower followed by tempering in a temperature range of 300-500° C., characterized in that the base metal has a composition comprising, in mass percent, C: 0.03-0.12%, Si: 0.05-0.50%, Mn: 1.4-2.2%, S: at most 0.0050%, Al: at most 0.06%, N: at most 0.0070%, and a remainder of Fe and impurities, with the carbon equivalent (Ceq) defined by Equation (1) being at least 0.36% and the weld cracking parameter (Pcm) defined by Equation (2) being at most 0.22%, and that the weld metal has a weld cracking parameter (Pcm) defined by Equation (2) of at most 0.30%, a B content of at most 5 ppm, and an oxygen content of at most 300 ppm: Ceq = C + Mn 6 + Cr + Mo + V 5 + Cu + Ni 15 ( 1 ) Pcm = C + Si 30 + Mn 20 + Cu 20 + Ni 60 + Cr 20 + Mo 15 + V 10 + B . ( 2 )