This disclosure relates to a method for manufacturing a double pipe, including: a primary roll forming step of forming bending portions on both sides of a strip for an external pipe in a longitudinal direction; a stacking step of stacking a strip for an internal pipe on the strip for the external pipe; a secondary roll forming step of mechanically coupling the strip for the external pipe and the strip for the internal pipe; a forming step of forming the strip for the external pipe and the strip for the internal pipe, mechanically coupled to each other, into a pipe shape; a welding step of bonding the bending portions on both sides of the strip for the external pipe, and the strip for the internal pipe, which are formed into the pipe shape; and a heat treatment step of heat-treating bonded portions of the strip.

A method for producing a multilayer large pipe having an outer support layer and at least one inner liner layer. Advantages with regard to productivity and the properties of the multilayer large pipe are achieved by the sequence of method steps wherein production of a support sheet is pre-bent to a predetermined initial bending radius for the support layer and at least one liner sheet is pre-bent to a predetermined initial bending radius for the liner layer, placement of the at least one pre-bent liner sheet against the inside of the pre-bent support sheet, with a positioning and parallel alignment of its longitudinal edges extending in the direction of the bending axis in order to form the support layer and the at least one liner layer, there is integral joining of at least one of two longitudinal edges of the at least one liner sheet to the support sheet, shaping of the composite of the integrally joined support layer and at least one liner layer to form a slit multilayer large pipe by a bending machine, with nonpositive, frictional engagement in liner regions that are not integrally joined, and there is closing of the remaining gap of the slit multilayer large pipe with a longitudinal seam by welding.

Disclosed is a welded structural member production method comprises: a first preparation step of preparing a cross-sectionally hat-shaped first metal workpiece which has a first base wall, a pair of first standing walls and a pair of flanges; a second preparation step of preparing a cross-sectionally U-shaped second metal workpiece which has a second base wall, and a pair of second standing walls; a positioning step of positioning the first metal workpiece and the metal workpiece in such a manner that each of two pairs of distal edges of the second standing walls and inner edge regions of the flanges are butted against each other; and a joining step of externally welding a butted region of each of the pairs of the distal edges of the second standing walls and the inner edge regions of the flanges to thereby join the first and second metal workpieces together.

A method for producing a composite filter tube and filter element made of a multilayer metal mesh and metal powders, including: knitting to obtain metal meshes of different mesh numbers, obtaining a layered structure by means of a lamination method, then putting the layered structure in a vacuum furnace for sintering processing, sintering a metal composite layer to obtain a composite filter sheet and tube made of a multilayer metal mesh and metal powders with a multilayer metal mesh as a structure support layer and a metal powder sinter structure as a filter layer, then rolling the composite filter sheet and tube into a tubular filter element by using a shaping machine, and welding to obtain a composite filter tube and filter element product made of a multilayer metal mesh and metal powders.

A method for limiting fitting distortion when welding a fitting to an in-service pipelinewhere the fitting includes a thick, longitudinally extending, seam located between fitting halvesinvolves welding, on each side of the fitting, a middle third section of the seam in a pyramid-like fashion using an inward progression starting from an end of the middle third section along a profile of a seam bevel, and welding outer third sections of the seam using an outward progression from an end adjacent to the middle third section along a profile of the seam bevel. The welding of each of the three sections per side includes a temper bead welding technique of at least two layers to provide stress relief in lieu of traditional post weld heat treatment.

The present disclosure relates to electro-conduction devices and methods for submerged arc welding of straight-seam steel pipes and in particular to a lateral electro-conduction device and method for multi-wire submerged arc inner/outer welding of a straight-seam steel pipe. The present disclosure aims to overcome the problem of poor closing of the electromagnetic field resulting from the existing negative-pole electro-conduction mechanism and the problem of unstable welding process resulting from bending deformation in the steel pipe welding process. The device includes: a floating surface contact electro-conduction device, capable of forming a surface contact with an outer surface of the straight-seam steel pipe; a lateral electro-conduction brush device, including multiple electro-conduction brushes and electrically connected with the floating surface contact electro-conduction device; a lateral electro-conduction metal plate. electrically connected with a negative-pole wire harness of a welding machine and electrically connected with the lateral electro-conduction brush device.

A method of preparing a pipe-section for welding to another pipe-section to form a pipeline comprising a plurality of said pipe-sections, the method comprising at least the steps of: (i) providing a pipe-section having first and second pipe-ends; (ii) defining a first portion L1 of the longitudinal length of the pipe-section from the first pipe-end being in the range 3% to 40% of the overall length of the pipe-section; (iii) defining a second portion L2 of the longitudinal length of the pipe-section from the end of the first portion L1 towards the second pipe-end; (iv) heating at least the first portion L1 to at least a first temperature T1 of at least 500 C. for at least 2 minutes; (v) maintaining a second temperature T2 of the second portion L2 during step (iv) below the first temperature T1. The invention is able to reduce the strain capacity during reel-laying of a pipeline formed from a plurality of pipe sections formed by the invention.