Electric resistance welded steel pipe securing the high strength and high toughness demanded from oil well pipe in recent years. The metal structure in a region having a width of 0.5 mm in both the thickness directions from a reference point, when using a point defined as a point of the thickness in the thickness direction from the surface in the base material part of the steel pipe as the reference point, consists of polygonal ferrite: 10 area % or less and a balance: bainitic ferrite. The thickness is 15 mm or more.

A pair of upper and lower pressure rollers 3, 4 is disposed so that their axes 15, 16 are tilted in a horizontal plane in respective directions opposite to each other with respect to a straight line perpendicular to a welding line of a joint portion J. The pressure rollers 3, 4 are positively driven by corresponding electric motors 63, 64 to thereby roll the joint portion. Thus, steps defined at the joint portion can be smoothed and a step gradient can be reduced to ensure a high degree of joint strength. Thus, it is possible to prevent a step portion from being interfolded into the base material of the meal plates 5, 6.

A pair of upper and lower pressure rollers 3, 4 is disposed so that their axes 15, 16 are tilted in a horizontal plane in respective directions opposite to each other with respect to a straight line perpendicular to a welding line of a joint portion J. The pressure rollers 3, 4 are positively driven by corresponding electric motors 63, 64 to thereby roll the joint portion. Thus, steps defined at the joint portion can be smoothed and a step gradient can be reduced to ensure a high degree of joint strength. Thus, it is possible to prevent a step portion from being interfolded into the base material of the meal plates 5, 6.

A joining apparatus for panel sheets and a joining method for panel sheets using the same are provided. The joining apparatus includes an element punching device which stores and supplies elements according to a specification of a panel sheet and inserts the element into a first panel sheet among different types of panel sheets. Additionally, a welding device resistively welds a part of the first panel sheet into which the element is inserted by the element punching device.

A joining apparatus for panel sheets and a joining method for panel sheets using the same are provided. The joining apparatus includes an element punching device which stores and supplies elements according to a specification of a panel sheet and inserts the element into a first panel sheet among different types of panel sheets. Additionally, a welding device resistively welds a part of the first panel sheet into which the element is inserted by the element punching device.

An electric resistance welded steel pipe having an identifiable seam portion and a method for manufacturing the same. The electric resistance welded steel pipe includes a steel pipe portion with a seam portion, which is formed by electric resistance welding, and a coating portion of zinc phosphate. The coating portion covers at least an outer surface side of the steel pipe portion. A part of the coating portion that is immediately above the seam portion forms a color difference portion that has a width W along a pipe circumferential direction of greater than or equal to 0.1 times a wall thickness of the pipe and less than or equal to the wall thickness of the pipe. The color difference portion has a visually identifiable color difference from the other parts of the coating portion.

Electric resistance welded steel pipes or steel tubes with a tensile property TS of not less than 434 MPa which have electric resistance welded parts exhibiting both excellent HIC resistance and excellent low-temperature toughness, and methods for manufacturing such steel pipes or steel tubes.

A side impact protective structure is provided for a vehicle floor pan. Right and left rear rails are attached, respectively, to right and left lateral sides of the floor pan. A kick-up cross member extends transversely between the right and left rocker assemblies. A right reinforcement is welded to the floor pan, the right rear rail, and the kick-up cross member. A left reinforcement is welded to the left rear rail, to the floor pan and the kick-up cross member. An assembly method includes the steps of selecting a thin mild steel floor pan between a thicker HSLA steel structural member and a thicker corner reinforcement and welding the components together with three thickness welds.

A side impact protective structure is provided for a vehicle floor pan. Right and left rear rails are attached, respectively, to right and left lateral sides of the floor pan. A kick-up cross member extends transversely between the right and left rocker assemblies. A right reinforcement is welded to the floor pan, the right rear rail, and the kick-up cross member. A left reinforcement is welded to the left rear rail, to the floor pan and the kick-up cross member. An assembly method includes the steps of selecting a thin mild steel floor pan between a thicker HSLA steel structural member and a thicker corner reinforcement and welding the components together with three thickness welds.

A second joining flange formed along an edge of a second panel and a third joining flange formed along an edge of a third panel are superimposed on a first joining flange formed along an edge of a first panel, a seam weld is made in a section in which the first joining flange and the second joining flange form two layers and a section in which the first joining flange and the third joining flange form two layers, and a spot weld is made in a section in which the first joining flange, the second joining flange and the third joining flange form three layers. Such structure enhances production efficiency by increasing welding speed, and facilitates spot welding in the section having three layers, for which seam welding is difficult due to the large number of superimposed sheets, thereby enhancing strength against peel-off.