Patent ID: 8653400

Claim:
A method of production of a high strength welded steel pipe superior in hydrogen embrittlement cracking resistance of weld metal comprising shaping a steel sheet of a tensile strength of 850 MPa or more into a tubular form, seam welding an abutting part from the inner surface and then the outer surface of the steel sheet, using a dehydrogenation treatment to reduce the hydrogen concentration of the inner surface weld metal to 0.2 cc or less per 100 g at a temperature of 100° C. or less, then expanding or reducing the size of the pipe for correction, wherein said dehydrogenation treatment comprises heating to a heating temperature T [° C.] in the range of 150 to 500° C. for a heating time t[s] found from the following formula from the weld metal thickness h [mm] and heating temperature T up to a heating time of 1200 seconds t =( h/ 16) 2 /exp (−957/273+T)) .