A 500 MPa grade longitudinally welded steel pipe with a low yield ratio and a manufacturing method therefor, the components thereof by weight percentages being as follows: C 0.11%-0.16%, Si 0.15%-0.35%, Mn 0.8%-1.5%, V 0.06%-0.15%, Al 0.002%-0.04%, Ti 0%-0.05%, Nb 0%-0.05%, the balance being Fe and inevitable impurities, and the carbon equivalent Ceq being not more than 0.4%. According to the above component design, molten steel is subjected to smelting in a converter or electric furnace, and is cast into a slab; the slab is heated at 1,200 C.-1,300 C. and rolled into a plate strip, with the finished rolling temperature of the plate strip being between 840 C.-940 C.; the rolled plate strip is subjected to laminar flow cooling with a water curtain, the laminar flow cooling adopting the manner of rear-section cooling, and is coiled into a plate roll when being cooled to the temperature interval of 500 C.-560 C.; and after welding formation, a heat treatment on the welding seams is carried out at a heating temperature of 950 C.50 C. The steel pipe of the present invention has the characteristics of an excellent welding property, a high strength and toughness, a low yield ratio and the like, and the yield strength thereof is greater than 500 MPa and the yield ratio thereof is less than 0.85.

An object is to prolong the life of a ring tool, and improve the productivity of a welded pipe. A ring tool unit is held in a downstream-side end portion of a mandrel to be inserted into a welded pipe currently being manufactured from the upstream side of a welding position, and is used as a cutting tool for continuously cutting a bead produced on the inner surface of the welded pipe, wherein the ring tool unit is formed by fitting a ring tool having a ring-like blade in a sleeve having a circular hole for holding the outer circumference of the ring tool.

A position detection apparatus for a seam portion and a heating portion of a welded steel pipe, the position detection apparatus includes: a light source configured to irradiate the seam portion and the heating portion with light in a first wavelength range; an imaging unit having a plurality of different channels and configured to capture an image of each of the seam portion and the heating portion irradiated with the light by the light source; and an image processing unit configured to process the image captured by the imaging unit and to detect the position of each of the seam portion and the heating portion, wherein the imaging unit includes: a first channel capable of receiving the light in the first wavelength range; and a second channel capable of receiving light in a second wavelength range corresponding to radiation light from the heating portion.

A method of making a heat exchanger that includes providing a plurality of tubes. Each of the plurality of tubes has exterior cladding on an exterior surface, interior cladding on an interior surface, and a weld seam extending along the length of the plurality of tubes. The method further includes arranging the plurality of tubes such that each of the plurality of tubes is inserted into a corresponding header slot with the weld seams of each of the plurality of tubes oriented downward with respect to gravity, and brazing each of the plurality of tubes and the header after each tube has been inserted into a corresponding header slot. The brazing causes the interior cladding to melt and pool inside the plurality of tubes and along an interior side of the weld seams to form a clad cover portion encases debris generated while forming the weld seams.