Metal working – Method of mechanical manufacture – With testing or indicating
Reexamination Certificate
2000-03-27
2002-05-14
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
With testing or indicating
C029S240000, C029S407030, C073S862210, C073S862230, C285S333000, C285S355000
Reexamination Certificate
active
06385837
ABSTRACT:
This application is based on Japanese Patent Application No. 11-98046 filed Apr. 5, 1999, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for fixedly connecting together an externally threaded tube and an internally threaded tube by tight engagement of an externally threaded portion and an internally threaded portion provided on the externally and internally threaded tubes, respectively. The present invention is applicable to operations to connect any threaded tubes, but is preferably applicable to operations to connect tubes having comparatively large lengths and diameters, for obtaining pipes used to support earth drilling tools for drilling or boring the earth in oil fields, and fluid transporting pipes used for transporting oils, natural gases and other fluids.
2. Discussion of the Related Art
As a method of fixedly connecting together two tubes, there is known a method wherein an externally threaded portion of an externally threaded tube and an internally threaded portion of an internally threaded tube are first brought into engagement with each other, and are then rotated relative to each other so that the two tubes are fastened or fixedly connected to each other. Three typical examples of this method are as follows:
1) The threaded surfaces (hereinafter referred to as “contacting thread surfaces” of the externally and internally threaded portions of the two tubes are held in meshing engagement with each other, with an axial tightening force acting between the contacting threaded surfaces, while shoulder surfaces of the two tubes are held in contact with each other at their contacting portions (hereinafter referred to “contacting shoulder surfaces”);
2) The contacting thread surfaces of the two tubes are held in meshing engagement with each other, with an axial tightening force acting between the contacting thread surfaces, and a non-threaded tapered outer circumferential surface (a radial sealing surface) of the externally threaded tube and a non-threaded tapered inner circumferential surface (radial sealing surface) of the internally threaded tube are held in engagement with each other, with a radial tightening force acting between the tapered outer and inner circumferential surfaces, while the contacting shoulder surfaces are held in contact with each other; and
3) The externally and internally threaded surfaces of the two tubes which are both tapered are held in meshing engagement with each other, with a radial tightening force acting between the contacting thread surfaces of the two tubes, without the contacting shoulder surfaces being provided on the two tubes.
Where the two tubes are fixedly connected together by the method 1) indicated above, a fluid-tight sealing is provided between the contacting shoulder surfaces of the two tubes. Where the two tubes are fixedly connected together by the method 2) indicated above, a fluid-tight sealing is provided both between the contacting shoulder surfaces, and between the radial sealing surfaces. In view of these facts, a tube assembly obtained by connecting the two tubes by the method 1) is suitably usable as a drill pipe for supporting earth drilling or boring tools, and a tube assembly obtained by connecting the two tubes by the method 2) is suitably usable as a fluid transporting pipe. The tube assembly obtained according to the method 2) wherein the sealing is provided between the radial sealing surfaces exhibits higher degrees of fluid tightness and fluid leakage resistance, than the tube assembly obtained according to the method 1) wherein the sealing is provided between the contacting shoulder surfaces.
Where the method 2) is applied to two tubes each of which has two shoulder surfaces that are spaced apart from each other in the axial direction, the axially corresponding shoulder surfaces of the two tubes are usually held in contact with each other. Of the four shoulder surfaces of the two tubes, one of the two shoulder surfaces of the internally threaded tube which is located at the outer or distal end of the internally threaded portion, and one of the two shoulder surfaces of the externally threaded tube which is located at the inner or proximal end of the externally threaded portion are referred to as “torque shoulder surfaces”. Each of the two tubes has a radial sealing surface in the form of a non-threaded tapered inner or outer circumferential surface between the two shoulder surfaces. When the two tubes each having the two shoulder surfaces and the radial sealing surface are connected together according to the method 2), the axial tightening force acts on the tubes at two axial positions corresponding to the two sets of contacting shoulder surfaces, and the radial tightening force acts on the tubes between the contacting radial sealing surfaces. Since the fluid-tight sealing is provided primarily by the contacting radial sealing surfaces, the method is called a radial sealing method [Method 2)-1]. Depending upon the dimensional relationships of the radial sealing surfaces and the shoulder surfaces of the two tubes, it is possible that only the torque shoulder surfaces of the two tubes are held in contact with each other, with the other shoulder surfaces being held in an axially spaced-apart relationship with each other.
Where the two tubes are not provided with the torque shoulder surfaces, it is possible that the axial tightening force acts between the contacting shoulder surfaces, while the radial tightening force acts between the radial sealing surfaces. In this case, the fluid-tight sealing is provided primarily by the contacting shoulder surfaces, and therefore the method is called a shoulder sealing method. Tube assemblies obtained according to this shoulder sealing method and the above-indicated radial sealing method are referred to as premium joints, and these methods are called a premium joint method [Method 2)-2].
The specific method that can be suitably used for fixedly connecting together the two tubes depends upon the configurations of the threaded portions of the two tubes and the configurational and dimensional relationships of the threaded portions and the shoulder surfaces. Not only the method 3) but also the methods 1) and 2) may be used where the threaded portions of the tubes are tapered. Usually, the method 1) is used for the tubes whose threaded portions have trapezoidal or triangular threads, and the methods 2) and 3) are used for the tubes whose threaded portions have trapezoidal threads. The externally and internally threaded tubes may be called a “pin” and a “box”, respectively.
Although an operation to fixedly connect together two threaded tubes is desirably controlled on the basis of the axial and radial tightening forces, this control is difficult. Conventionally, therefore, the tube connecting operation is controlled on the basis of a wrenching torque applied to rotate the two tubes relative to each other, or both the torque and a speed of the relative rotation.
Where the tube connecting operation is controlled on the basis of the wrenching torque, the relative rotation (wrenching operation) is terminated when the actual wrenching torque (torque equal to a resistance to the relative rotation) has become equal to a desired or target value. In this case, the desired wrenching torque value corresponding to a desired tightening force of the two tubes is calculated on the basis of a measured or estimated coefficient of friction at the contacting portions (contacting thread surfaces and contacting shoulder surfaces) of the two tubes. However, the friction coefficient greatly varies depending upon the physical conditions (e.g., roughness) of the contacting surfaces as machined, the lubricating conditions of those contacting surfaces, and other conditions, which vary under different machining conditions and under different environments in which the tube connecting operation is carried out. Accordingly, the actual tightening force tends to h
Hashimura Shinji
Mori Kazuya
Murakami Yukitaka
Central Motor Wheel Co., Ltd.
Hughes S. Thomas
Oliff & Berridg,e PLC
Omgba Essama
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