High-strength thick-walled electric resistance welded steel pipe for conductor casing for deep well, production method therefor, and high-strength thick-walled conductor casing for deep well

Abstract

Provided is an electric resistance welded steel pipe that has high strength, high toughness, and excellent post-welding heat treatment resistance. A hot-rolled steel sheet comprising the following is used as a starting material: a composition containing 0.01-0.12% of C, 0.05-0.50% of Si, 1.0-2.2% of Mn, 0.03% or less of P, 0.005% or less of S, 0.001-0.10% of Al, 0.006% or less of N, 0.010-0.100% of Nb, and 0.001-0.050% of Ti; and a structure that comprises 90% or more by volume of a main phase that is a bainitic ferrite phase and 10% or less (including 0%) by volume of a second phase, in which the average particle size of the bainitic ferrite phase is 10(mu)m or less and extremely fine Nb deposits having a particle size of less than 20 nm are dispersed at a rate that, when calculated in terms of Nb, surpasses 75% by ratio (%) of the total amount of Nb. The starting material is formed to have a substantially circular cross section by roll forming and subsequently subjected to electric resistance welding in order to obtain an electric resistance welded pipe, the electric resistance welded section of the electric resistance welded pipe is subjected to inline heat treatment, and the result is subjected to diameter reduction rolling so that the deviation from roundness of a steel pipe end section is 0.6% or less.

Description

technical field [0001] The present invention relates to an electric resistance welded steel pipe suitable for use as a conductor casing for the earth retaining wall of a well during the excavation of an oil well or a natural gas well, and particularly relates to an electric resistance welded steel pipe suitable for use in the development of a deep-sea oil field or a deep-sea gas field existing in a water depth of 3000 m or more A high-strength thick-walled electric resistance welded steel pipe used for conductor casings for wells (hereinafter also referred to as deep wells) and a manufacturing method thereof. Background technique [0002] Conductor casings are used as retaining walls of wells to protect oil well pipes from external pressure at the initial stage of excavation operations for oil wells and natural gas wells. Conventionally, conductor bushings have been manufactured by joining UOE steel pipes to connectors (threaded forged parts). [0003] When the conductor ca...

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Problems solved by technology

In order to use the steel pipe manufactured by the technology described in Patent Document 1 as a conductor casing for deep wells, it is necessary to further add a process of cutting and straightening to improve the roundness of the end of the steel pipe. In the technology described in Patent Document 1, there is a Problems such as drop in productivity during casing

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