Abstract: A welded state monitoring system according to an aspect of the present invention is a welded state monitoring system used for plasma shielded electric resistance welding in which electric resistance welding is performed while irradiating a weld zone of a steel sheet with plasma, and is provided with a plasma irradiation device which irradiates the weld zone with plasma, a first image capturing device which captures an image of the weld zone from above and has an image sensor capable of detecting light having a wavelength of 850 nm or more, a first wavelength region limiting device which limits light incident on the first image capturing device to a wavelength region of 850 nm or more, and an image processing device which subjects the image captured by the first image capturing device to image processing and analyzes the welded state of the weld zone thereby being able to analyze the welded state without being affected by the plasma.

Abstract: A welded state monitoring system according to an aspect of the present invention is a welded state monitoring system used for plasma shielded electric resistance welding in which electric resistance welding is performed while irradiating a weld zone of a steel sheet with plasma, and is provided with a plasma irradiation device which irradiates the weld zone with plasma, a first image capturing device which captures an image of the weld zone from above and has an image sensor capable of detecting light having a wavelength of 850 nm or more, a first wavelength region limiting device which limits light incident on the first image capturing device to a wavelength region of 850 nm or more, and an image processing device which subjects the image captured by the first image capturing device to image processing and analyzes the welded state of the weld zone thereby being able to analyze the welded state without being affected by the plasma.

Abstract: This depression-provided steel pipe has plural depressions on an outer peripheral surface, the depressions being formed so as to form a line along an axial direction of the steel pipe, in which each of the depressed portions has, inside thereof, a columnar groove portion extending along the axial direction of the steel pipe and depressed deeper than a bottom surface of these depressed portions; 0.95?HA/HB?1.05 is satisfied, where HA is an average Vickers hardness in each of the depressed portions, and HB is a Vickers hardness at a portion between the depressed portions adjacent to each other in the axial direction of the steel pipe; and the outer peripheral surface is covered with a mill scale.

Abstract: This depression-provided steel pipe has plural depressions on an outer peripheral surface, the depressions being formed so as to form a line along an axial direction of the steel pipe, in which each of the depressed portions has, inside thereof, a columnar groove portion extending along the axial direction of the steel pipe and depressed deeper than a bottom surface of these depressed portions; 0.95?HA/HB?1.05 is satisfied, where HA is an average Vickers hardness in each of the depressed portions, and HB is a Vickers hardness at a portion between the depressed portions adjacent to each other in the axial direction of the steel pipe; and the outer peripheral surface is covered with a mill scale.

Abstract: The molybdenum foil coupling member is disclosed in which potassium (K) and silicon dioxide (SiO.sub.2) are respectively dispersed in the range from 200 to 800 ppm and from 200 to 2000 ppm so as to resist to fracturing upon exposed to high temperature. This coupling member is particularly well suited for used in electric lamps having quartz glass envelopes which are pinch sealed at either end.