A method for preparing a multilayer metal composite pipe includes steps of: internally and externally grinding blank pipes; cleaning oil stains; assembling a multilayer metal pipe; drawing to reduce a diameter; performing high-speed friction welding at the pipe ends; performing heat treatment; performing four-roller cross-rolling; straightening; performing two-roller cold-rolling; performing cold-drawing to reduce the diameter; performing cold-expansion to reduce the diameter; performing precise cold-rolling; degreasing; brightening; performing surface grinding; cleaning dust; detecting multilayer metal interface bonding; detecting flaws; testing metal structure performance; and sizing and packaging. By cycling the cold-drawing, the cold-expansion, and the precision cold-rolling, key indicators such as product dimensional accuracy, surface quality, material properties, and crystal grain size can be collaboratively controlled, so as to achieve higher accuracy, better performance, and more outstanding extreme specifications. The present invention solves the problem of inconsistent extension due to differences in metal properties.

A method for preparing a multilayer metal composite pipe includes steps of: internally and externally grinding blank pipes; cleaning oil stains; assembling a multilayer metal pipe; drawing to reduce a diameter; performing high-speed friction welding at the pipe ends; performing heat treatment; performing four-roller cross-rolling; straightening; performing two-roller cold-rolling; performing cold-drawing to reduce the diameter; performing cold-expansion to reduce the diameter; performing precise cold-rolling; degreasing; brightening; performing surface grinding; cleaning dust; detecting multilayer metal interface bonding; detecting flaws; testing metal structure performance; and sizing and packaging. By cycling the cold-drawing, the cold-expansion, and the precision cold-rolling, key indicators such as product dimensional accuracy, surface quality, material properties, and crystal grain size can be collaboratively controlled, so as to achieve higher accuracy, better performance, and more outstanding extreme specifications. The present invention solves the problem of inconsistent extension due to differences in metal properties.

The present invention provides a method of manufacturing a press-formed product. The method includes: a first process of preparing a material that is long in a first direction, and when viewed in a cross-section perpendicular to the first direction, the cross-section is a hollow cross-section that is long in a second direction perpendicular to the first direction; and a second process of bending the material in a direction intersecting the second direction when viewed from the first direction, by pressing the material along the second direction.

The present invention provides a method of manufacturing a press-formed product. The method includes: a first process of preparing a material that is long in a first direction, and when viewed in a cross-section perpendicular to the first direction, the cross-section is a hollow cross-section that is long in a second direction perpendicular to the first direction; and a second process of bending the material in a direction intersecting the second direction when viewed from the first direction, by pressing the material along the second direction.

A galvanized reinforcement beam is continuously formed by uncoiling a roll of galvanized sheet stock in a generally horizontal plane. Protrusions are formed at an upper surface of the sheet stock, which is then roll formed to form a tubular shape with the protrusions abutting a surface of the sheet stock to form venting gaps. The sheet stock is laser welded at the protrusions to continuously form a weld joint, where zinc oxide gas generated from the welding is permitted to escape an interior of the tubular shape through the venting gaps.

A galvanized reinforcement beam is continuously formed by uncoiling a roll of galvanized sheet stock in a generally horizontal plane. Protrusions are formed at an upper surface of the sheet stock, which is then roll formed to form a tubular shape with the protrusions abutting a surface of the sheet stock to form venting gaps. The sheet stock is laser welded at the protrusions to continuously form a weld joint, where zinc oxide gas generated from the welding is permitted to escape an interior of the tubular shape through the venting gaps.

A long steel pipe for reel-lay installation formed of electric resistance welded (ERW) steel pipes and having high buckling resistance and a method for producing the long steel pipe for reel-lay installation are provided. The long steel pipe is formed by successively butt-joining longitudinal ends of the ERW steel pipes by girth welding so that girth welds are formed. The ERW steel pipes are successively butt-joined in the pipe longitudinal direction such that the 0 o'clock cross-sectional position or the 6 o'clock cross-sectional position of one of adjacent ERW steel pipes faces an area from the 2 o'clock cross-sectional position to the 4 o'clock cross-sectional position or an area from the 8 o'clock cross-sectional position to the 10 o'clock cross-sectional position of the other of the adjacent ERW steel pipes.

Electric resistance welded steel pipe excellent in deformability and fatigue properties after quenching which enables working into complicated shapes without spheroidization and which improves the fatigue properties after cold working and quenching without carburization are provided. The electric resistance welded steel pipe is characterized by containing, by mass %, C: 0.15 to 0.55%, Si: 0.01 to 0.30%, Mn: 0.5 to 1.5%, Ca: 0.0010 to 0.0030%, S: 0.0005 to 0.0050%, and O: 0.0005 to 0.0050%, having contents of Ca, O, and S satisfying 0.10≦[Ca](1−124[O])/1.25[S]≦2.50, having Ca-based inclusions present at the base material and electric resistance weld zone with an average particle size of 1.0 to 10 μm and a density of 3 to 300/mm.sup.2, and having a difference ΔHv of the maximum hardness of the electric resistance weld zone and the average hardness of the base material part satisfying 100 to 500.

Electric resistance welded steel pipe excellent in deformability and fatigue properties after quenching which enables working into complicated shapes without spheroidization and which improves the fatigue properties after cold working and quenching without carburization are provided. The electric resistance welded steel pipe is characterized by containing, by mass %, C: 0.15 to 0.55%, Si: 0.01 to 0.30%, Mn: 0.5 to 1.5%, Ca: 0.0010 to 0.0030%, S: 0.0005 to 0.0050%, and O: 0.0005 to 0.0050%, having contents of Ca, O, and S satisfying 0.10≦[Ca](1−124[O])/1.25[S]≦2.50, having Ca-based inclusions present at the base material and electric resistance weld zone with an average particle size of 1.0 to 10 μm and a density of 3 to 300/mm.sup.2, and having a difference ΔHv of the maximum hardness of the electric resistance weld zone and the average hardness of the base material part satisfying 100 to 500.

A method for manufacturing a ring includes clamping a first region of a metal sheet against a mandrel, and, while the first region of the metal sheet is clamped against the mandrel, bending the metal sheet around the mandrel to join opposite end faces of the metal sheet and form the ring shaped to the mandrel. A system for manufacturing a ring from a metal sheet includes (a) a mandrel having a ring-shaped surface, (b) a clamp facing the ring-shaped surface and configured to clamp a first region of a metal sheet to the mandrel, and (c) a plurality of dies configured to bend the metal sheet around the mandrel, while the clamp clamps the first region to the mandrel, to join opposite end faces of the metal sheet and form a ring shaped to the ring-shaped surface.