Pipe thread joint

Abstract

A threaded joint which economically imparts effective sealing properties to a metal-to-metal seal portion and which can prevent seizing at the time of make-up comprises a steel pipe 1 having at its tip a male thread 1 b and an unthreaded sealing surface 1 a, and a coupling 2 having on its inner surface a female thread 2 b and an unthreaded sealing surface 2 a. With the yield pressure of the inner surface of the pipe being Py, (1) the average pressure Pm of the annular contact portion satisfies Pm / Py>=3, and the width in the axial direction of the portion which receives a pressure Ps which satisfies Ps / Py>=1 in the annular contact portion is at least 1 mm (or at least 2 mm), and the surface roughness Ry of both unthreaded sealing surfaces is at most 25 mum (or at most 30 mum), or (2) the relationship between the average pressure Pm of the annular contact portion and the surface roughness Ry (mum) of the unthreaded sealing surface satisfies Pm / Py>=0.0032xRy2+1.0, and the width in the axial direction of the portion which receives a pressure Ps which satisfies Ps / Py>=1 in the annular contact portion is at least 1 mm.

Description

technical field [0001] The present invention relates to a threaded joint for pipes having a metal-to-metal sealing portion and used in oil well pipes such as development, production and transportation of oil and gas. Background technique [0002] As oil wells and gas wells get deeper and deeper, the conditions of use of joints connecting oil well pipes used in the development and production of oil and gas are becoming more and more severe. A higher level of performance. [0003] In such wells, conventionally used threaded tubular joints such as buttress joints or circular threaded joints, in which thread engagement of API standard threads alone performs engagement, cannot provide sufficient strength and sealing performance. [0004] Therefore, special tubular joints have been proposed, which have metal-to-metal sealing portions, have sufficient joint strength and excellent air-tightness, and these have been put into practical use. [0005] For example, US Patent No. 4,732,...

AI Technical Summary

Problems solved by technology

However, the reduction of surface roughness requires high work precision, and the work time becomes longer, and the loss of work efficiency and cost become larger

On the other hand, when the contact force applied to the sealing part increases, if the width of the contact part is narrow, the pressure becomes high, and abrasion tends to occur, resulting in damage to the joint

[0014] However, none of the above-mentioned threaded joints having a metal-to-metal sealing portion considers the relationship between surface roughness and applied pressure on sealing performance

[0015] For example, U.S. Patent Nos. 4,732,416, 4,623,173, 5,137,310, and 5,423,579 propose tubular joints for pipes without mentioning the surface roughness of the sealing surface and the applied pressure

[0016] On the other hand, for each of the threaded joints for pipes described in JP A 61-124792, JP A 06-10154, JP A 07-217777 and JP A08-145248, the surface roughness is specified in relation to the surface treatment , without mentioning the relationship between surface roughness and applied pressure and the width of the contact part, and the relationship between these and sealing performance

[0017] Therefore, for the special threaded joints having the metal-to-metal sealing portion proposed so far, it is difficult to definitely prevent leakage such as abrasion or fluid.

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