Process for producing welded steel pipes with a high degree of strength, ductility and deformability

A process for producing welded steel pipes by the UGE-process, comprising the steps of:

• providing a steel sheet having a composition by wt. % of 0.02 to 0.20% carbon, 0.05 to 0.50% silicon, 0.50 to 2.50% manganese, and 0.003 to 0.06% aluminum, the remainder being iron containing production-related impurities;
• cold-forming, welding and sizing the sheet to a desired diameter to thereby form a pipe;
• subjecting the pipe to a heat treatment at a temperature in the range of 100-300° C., while holding the pipe at that temperature for a time suited to a wall thickness of the pipe;
• cooling the pipe with at least one of air cooling and forced cooling;
• and
• applying an insulation layer to an outside surface of the pipe, wherein the heat treatment is executed while the applying step is implemented.

A process for producing welded steel pipes by the UOE-process, comprising the steps of:

• providing a steel sheet having a composition by wt. % of 0.02 to 0.20% carbon, 0.05 to 0.50% silicon, 0.50 to 2.50% manganese, and 0.003 to 0.06% aluminum, the remainder being iron containing production-related impurities;
• cold-forming, welding and sizing the sheet to a desired diameter to thereby form a pipe;
• subjecting the pipe to a heat treatment at a temperature in the range of 100-300° C. while holding the pipe at that temperature for a time suited to a wall thickness of the pipe;
• cooling the pipe with at least one of air cooling and forced cooling;
• wherein the pipes are welded with a straight seam and presized before the heat treatment by a combined application of cold-expansion and cold-reduction.

A process for producing welded steel pipes by the UOE-process, comprising the steps of:

• providing a steel sheet having a composition by wt. % of 0.02 to 0.20% carbon, 0.05 to 0.50% silicon, 0.50 to 2.50% manganese, and 0.003 to 0.06% aluminum, the remainder being iron containing production-related impurities;
• cold-forming, welding and sizing the sheet to a desired diameter to thereby form a pipe;
• subjecting the pipe to a heat treatment at a temperature in the range of 100-300° C., while holding the pipe at that temperature for a time suited to a wall thickness of the ripe;
• cooling the pipe with at least one of air cooling and forced cooling to thereby realize a finished steel pipe;
• wherein the steel sheet has a 2.0% yield strength of Rp2.0≧640 MPa and a tensile strength of Rm≧770 MPa.