Method for producing seamless tube

Abstract

A method for producing a seamless tube while reducing the inner surface scratches comprising a piercing step, in which the relations shown by expressions (1)-(3) are simultaneously satisfied if the diameter of a billet is R(m), the crack length in the axially central portion of the billet is r(m), and two times of the amount of rotation of the billet during the time from when the billet touches arolling roll until the billet reaches a boring plug is N. 0=r / R=0.13...(1), r / R=-0.13N+0.13...(2), r / R=-0.065N+0.39...(3). Even if a cast piece of wide ferrite temperature range is used, poor piercing and inner surface scratches of the tube are prevented from occurring and a high-quality seamless tube can be produced inexpensively.

Description

technical field The present invention relates to a method for manufacturing a seamless steel pipe including a piercing-rolling process, and more particularly, to a method for manufacturing a seamless steel pipe free from inner surface defects by the piercing-rolling method. Background technique Affected by the increasing demand for energy sources such as crude oil and natural gas, the development of oil and gas wells is booming. In recent years, both oil wells and gas wells have been transferred from land to seabed, and the environment inside oil wells and gas wells has of course become harsher with the existence of oil wells and gas wells. Pipelines for transporting crude oil and natural gas from oil wells and gas wells tend to be designed with larger diameters and thicker walls in consideration of the workability for mass transportation and the laying environment including pressure resistance in deep seas. Furthermore, from the viewpoint of steel material properties, str...

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Problems solved by technology

In order to solve the above-mentioned problems, the inventors of the present invention studied the following methods of manufacturing seamless steel pipes based on conventional problems, obtained the following findings (a) to (e), and completed the present invention. The manufacturing method is to properly combine the casting conditions and piercing and rolling conditions of the slab, which can prevent piercing defects in advance, prevent the occurrence of inner surface defects, and can improve the manufacturing yield

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