The welding operation monitoring system includes an image capturing device that is disposed on a side opposite to a side to which the plasma flow is supplied out of a pipe inside and a pipe outside of the strip-shaped steel sheet formed in a tubular shape, and is configured to capture a color image including a plasma flow over the V-shaped region; and a welding operation monitoring device that is configured to generate a specific color component image obtained by extracting a specific color component from the color image, and specifies a V-shaped display region, which is a region corresponding to the V-shaped region within the color image, on the basis of the V-shaped region shown in the specific color component image, thereby analyzing a state of the welding operation.

A method for manufacturing an electric resistance welded metal pipe by butting side ends of a metal strip against each other and then welding the side ends by high frequency heating to manufacture an electric resistance welded metal pipe, each side end being provided with an inner surface side corner portion located on an inner surface side of the electric resistance welded metal pipe, the method includes a step of forming an inclined surface at the inner surface side corner portion before butting the side ends of the metal strip, and wherein the side ends are butted and welded to each other such that the inclined surface remains on an excess metal of the metal pipe after electric resistance welding and a discharged metal is not welded to the excess metal.

An electric-resistance-welded stainless clad steel pipe or tube that is excellent in both the fracture property of the weld and the corrosion resistance of the pipe or tube inner surface as electric resistance welded without additional welding treatment such as weld overlaying after electric resistance welding is provided. An electric-resistance-welded stainless clad steel pipe or tube comprises: an outer layer of carbon steel or low-alloy steel; and an inner layer of austenitic stainless steel having a predetermined chemical composition, wherein a flatness value h/D in a 90 flattening test in accordance with JIS G 3445 is less than 0.3, and a pipe or tube inner surface has no crack in a sulfuric acid-copper sulfate corrosion test in accordance with ASTM A262-10, Practice E, where h is a flattening crack height (mm), and D is a pipe or tube outer diameter (mm).

An electric-resistance-welded stainless clad steel pipe or tube that is excellent in both the fracture property of the weld and the corrosion resistance of the pipe or tube inner surface as electric resistance welded without additional welding treatment such as weld overlaying after electric resistance welding is provided. An electric-resistance-welded stainless clad steel pipe or tube comprises: an outer layer of carbon steel or low-alloy steel; and an inner layer of austenitic stainless steel having a predetermined chemical composition, wherein a flatness value h/D in a 90 flattening test in accordance with JIS G 3445 is less than 0.3, and a pipe or tube inner surface has no crack in a sulfuric acid-copper sulfate corrosion test in accordance with ASTM A262-10, Practice E, where h is a flattening crack height (mm), and D is a pipe or tube outer diameter (mm).

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 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 resistance welded steel pipe is provided. A hot-rolled steel sheet having a composition containing, in mass %, C: 0.025 to 0.168%, Si: 0.10 to 0.30%, Mn: 0.60 to 1.90%, and one or at least two selected from Ca, Nb, V, and Ti such that Pcm is 0.20 or less is subjected to continuous cold roll forming to obtain a pipe-shaped body. Tapered grooves are formed in the steel sheet such that the ratio of the tapered portions to the wall thickness of the steel sheet is 10 to 80%. Then end surfaces of the pipe-shaped body are butted against each other and subjected to electric resistance welding. Ultrasonic waves are transmitted toward the electric resistance weld surface such that a beam width is within the range of 0.1 to 4.0 mm, and the reflected waves are used for ultrasonic flaw detection using an ultrasonic flaw detector.

The objective of the present invention is to enable accurate detection of a mismatch during electric resistance welding. This operation monitoring device for high-frequency resistance welding and induction heated welding of an electric resistance welded steel pipe, in which a strip-shaped metal sheet is continuously formed into a cylindrical shape by means of a group of rollers while being conveyed from an upstream side to a downstream side, and in which the two edge portions, in the circumferential direction, of the metal sheet, which are caused to converge into a V-shape, are caused to melt by the application of heat and are caused to abut one another, is characterized by being provided with a means for detecting a mismatch by recognizing a non-uniformity between light-emitting regions of a metal part, on both sides, in the circumferential direction, of the abutting position on an outer surface or an inner surface of the metal plate, on the basis of an image of a region including a V-convergence location, which is a location at which the two edge portions in the circumferential direction converge into said V-shape, and said metal part which is caused to flow out onto the surface of the metal plate by means of an electromagnetic force downstream of the V-convergence location, wherein said image is captured by means of an image capturing device from an outer surface side or an inner surface side of the metal plate that has been formed into said cylindrical shape.

The present invention relates to an air conditioner. The air conditioner according to the present embodiment has a refrigeration capacity of 7 kW to 11 kW, inclusive, and uses a refrigerant R32 as a refrigerant, and since a refrigerant pipe therein is made of a ductile stainless steel material having 1% or less of a delta-ferrite matrix structure with respect to the grain size area thereof, and includes a suction pipe guiding the suction of the refrigerant into a compressor and having an outer diameter of 15.88 mm, the refrigerant pipe can maintain strength and hardness as good as or better than those of a copper pipe, while also maintaining good processability.

The present invention relates to an air conditioner. The air conditioner according to the present embodiment has a refrigeration capacity of 11 kW to 16 kW, inclusive, and uses R32 as a refrigerant circulating therein, and since a refrigerant pipe therein is made of a ductile stainless steel material having 1% or less of a delta-ferrite matrix structure with respect to the grain size area thereof, the refrigerant pipe can maintain strength and hardness as good as or better than those of a copper pipe, while also maintaining good processability.

Provided is a method for manufacturing an electric resistance welded metal pipe by butting side ends of a metal strip against each other and then welding the side ends by high frequency heating to manufacture an electric resistance welded metal pipe, each side end being provided with an inner surface side corner portion located on an inner surface side of the electric resistance welded metal pipe, wherein the method comprises a step of forming an inclined surface at the inner surface side corner portion before butting the side ends of the metal strip; and wherein the side ends are butted and welded to each other such that the inclined surface remains on an excess metal of the metal pipe after electric resistance welding and a discharged metal is not welded to the excess metal.