A high-strength steel pipe excellent in formability and burst resistance wherein, when a high-strength steel pipe exceeding 850 N/mm2 in tensile strength is produced by a UOE method, a ratio (R/r) of an average radius of curvature in a range of 120 mm in a circumferential direction including a weld of the steel pipe before pipe expansion in a pipe expansion process (R) to the radius of the steel pipe after pipe expansion (r) is 0.65 to 2.0, and preferably the ratio (R/r) is 0.90 to 2.0. Preferably, Vickers hardness of the base metal Hv, the minimum Vickers hardness at the HAZ Hz, pipe wall thickness t, and a peaking amount at the weld of the steel pipe before pipe expansion in a pipe expansion process δ satisfy the following expression, (1+0.005t|δ|)Hz<0.03584Hv 2−25.34Hv+4712.

High-strength steel pipe excellent in formability and burst resistance

A method for producing slit hollow profiles from a cut blank is provided, in which the hollow profile is produced from the essentially flat blank using rolling-up technology or using U-O-forming, so that the hollow profile has a slit in the axial direction along the abutting edges of the formed blank. Highly dimensionally stable, slit hollow profiles can be produced which can be easily joined to form closed hollow profiles, is achieved by the cut blank providing a circumferential length in the locally provided cross-sectional areas which is greater than the required forming length, so that when the cut blank is formed into a closed hollow profile the opposite edges of the formed cut blank abut on one another and when it is formed into the final shape at least the areas of the hollow profile abutting on the edge joint are at least partly compressed in the circumferential direction.

Method for producing slit hollow profiles

A method which, in attaching a stiffening ring ( 3 b ), a lock ring ( 11 ), and a stop ring ( 15 ) to the outer surfaces of steel pipes, corrects peaking which occurs in the pipe joint and these rings; a method which, in attaching a joint ring ( 2 ) to the inner surface of a steel pipe, correct speaking which occurs in the joint ring ( 2 ), a method of producing a stiffening ring ( 3 a ) utilized in the above-mentioned joint; a construction for a packing ( 6 ) used in the joint; a method of laying steel pipes having the joint; and a seal surface construction for the joint. According to the pipe joint thus produced, manufacture of pipe joints in a factory can be unmanned and the field operation can be simplified.

Pipe joining method

PROBLEM TO BE SOLVED: To make it possible to process both side edge parts of a steel plate as a steel tube stock into a joint geometry which reduces a gap in a beveling part of an open tube.SOLUTION: On the basis of a steel material condition exhibiting a property of a steel plate which is formed into an open tube by press molding and a press condition exhibiting press molding, a peaking quantity such that both side edge parts of the steel plate forming a beveling part of the open tube project from a perfect circular outer peripheral surface is predicted. Each rout face angle, which is formed by a root face part of both the side edge parts, which are confronted with each other when the open tube is formed, and each end face of both the side edge parts before beveling is so set that respective root face parts of both the side edge parts of a predicted peaking quantity rightly face with each other and are confronted. Both the side edge parts of the steel plate are respectively processed into each joint geometry having each root face part having a set root face angle.

Beveling device and beveling method

The invention discloses a system and a method for preparing longitudinal submerged arc welding (LSAW), and belongs to the technology field of petroleum and natural gas pipe The system comprises an expending-ratio relation module, which establishes a function relation between the expending-ratio and the yield strength according to the yield strength of steel board, the yield strength of welding pipe, and the expending-ratio of welding pipe; a function judge module, which is used for comparing the yield strength of steel board to the given yield strength threshold of steel board, comparing the yield strength of welding pipe to the given yield strength threshold of welding pipe, and obtaining the comparative result of yield strength of steel board and comparative result of yield strength of welding pipe; and a board width adjusting module, which adjusts expending-ratio through adjusting the board width of welding pipe according to the comparative result of yield strength of steel board, comparative result of yield strength of welding pipe, and the function relation The system and the method for preparing longitudinal submerged arc welding (LSAW) realize accurate control of stretch performance of steel pipe, raise the qualified rate, and reduce the fluctuating range

System and method for preparing longitudinal submerged arc welding (LSAW)

PURPOSE:To manufacture an UOE-system steel pipe by a small press duty by U- forming a blank plate having properly bent ends and further, O-forming it by regulating an acting angle of forming force within a range of giving no circumferential compression, before welding, expanding, and straightening a formed plate. CONSTITUTION:A blank plate 10 is U-formed after subjecting the ends of plate 10 to an end bending by regulating a bending radius (rc) at the end parts within an allowable range of peaking between the end parts of plate 10 at the time of O-forming, or regulating it preferably to the degree of (rc)/R=0.62-0.75 with respect to the radius R of a desired steel pipe. Next, a welding is performed by restricting the O-forming within a range, where an acting angle of forming force with respect to the plate 10 is >=-45 deg. and gives no circumferential compression. Next, the out of roundness of a welded pipe is straightened while expanding it with a small expanding rate to obtain a steel pipe having a desired radius, thus a duty of forming press necessary for performing the O-forming in a UOE-system steel-pipe manufacturing is remarkably reduced.

Kenji Aoyanagi

Papers

Manufacture of steel pipe by uoe-system