Method for producing hot-rolled seamless pipes from transformable steel, in particular for pipelines for deep-water applications, and corresponding pipes

Abstract

The invention relates to a method for producing hot-rolled seamless pipes (1) from transformable steel, in particular for pipelines for deep-water applications. The pipe ends (3) are hot-upsetted in order to achieve a thickened wall portion after a final rolling process of the pipes (1). The aim of the invention is to produce pipes with excellent fatigue, corrosion, and welding properties. This is achieved in that a pre-selected ratio between a wall thickness of the pipe end (3) and a wall thickness of a wall body (2) adjoining the pipe end (3) is set by the hot-upsetting process such that a pipe (1) is achieved with a pipe end (3) which has a lower strength than the pipe body (2) after a uniform tempering process of the entire pipe (1) following the hot-upsetting process by using a previously ascertained wall thickness-dependent cooling rate during the tempering process.

Description

technical field [0001] The present invention relates to a method of producing hot-rolled seamless pipes from deformable steels, in particular pipes for deepwater applications, wherein the pipe ends are hot-upsetted after the final rolling process of the pipes in order to achieve Thickened wall. [0002] The present invention also relates to a seamless pipe made of deformable steel having a minimum yield point of 415 MPa, said seamless pipe being formed by hot rolling, followed by hot upsetting of the pipe ends to produce a thickened wall portion, and This is followed by a uniform quenching and tempering treatment (homogeneous tempering) of the entire tube, followed by a machining step for the thickened tube ends. [0003] In particular, the invention relates to pipes produced according to the method described above and welded together at their pipe ends to produce pipes. Background technique [0004] It is generally known to transport oil and gas using pipelines, where ind...

AI Technical Summary

Problems solved by technology

[0019] - The use of steel pipes manufactured from high-strength grades such as X80 pipeline steel according to American Petroleum Institute standard API5L is still restricted because weldability cannot be sufficiently ensured in a given case

Studies have shown that with these high-strength grades the required mechanical properties of welded joints in the quenched and tempered In welds on pipe ends, more particularly when sour gases are used, these steels have a tendency to increase hardness, form cracks and increase corrosion susceptibility

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