Pipe joints or couplings – Particular interface – Tapered
Reexamination Certificate
1999-06-04
2001-05-29
Nicholson, Eric K. (Department: 3629)
Pipe joints or couplings
Particular interface
Tapered
C285S390000
Reexamination Certificate
active
06237967
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a threaded connection for oil country tubular goods and its method of manufacturing, used in exploration and production of natural gas or crude oil, and particularly, to a threaded connection for oil country tubular goods, suitable for use at very deep oil wells, and the like, in highly corrosive environments.
2. Related Art
Threaded connections are in widespread use today as a technical means of connecting oil country tubular goods used in exploration for and production in natural gas fields and oil fields at depths of several thousands meters. There are two types of the threaded connections. One is an integral type wherein a pipe is provided with a pin section at one end and a box section at the other end, the pin section of the pipe being connected with the box section of another pipe. The other is a coupling type wherein two pipes, each provided with a pin section at opposite ends, are connected via a coupling provided with a box section at opposite ends. Performances required of these threaded connections include; 1) capability to withstand axial tensile force caused by the weights of connected pipes themselves, 2) capability to withstand an internal pressure caused by an internal fluid flowing inside of the pipes, and 3) corrosion resistance against the internal fluid. The performances mentioned above are more strictly required lately because of recent trends of an increasing number of oil wells being worked in harsh environments containing corrosive components such as hydrogen sulfide, and the like.
As a result of increase of depth of oil wells, the diameter of each oil well has become major factor of the cost of drilling, and the requirement for reduction in the diameter of oil well has led to requirements for the smaller outer diameter of a threaded connection, which in turn, has resulted in requirements for reduction in the wall thickness of the box section.
In order to cope with such requirement, many proposals relating to a threaded connection, which provide with a seal section and a torque shoulder section, have been made. An integral type threaded connection disclosed, as a typical example, in Japanese Patent Laid-Open No. Sho 60-26878 is described hereafter.
FIG. 8
shows a cross sectional view of an integral type threaded connection “along a plane of the axis of a pipe“. The above connection provides with grooves on the internal surface of both a pin section and a box section thereof to prevent turbulence in flow of an internal fluid so that corrosion resistance is enhanced (hereafter the term “along a plane of the axis of a pipe” is omitted). A seal forming threadless section
13
provided on the external surface of the pin section
11
which includes a thread section
12
and a seal forming threadless section
23
provided on the surface of the box section
21
on the farther inner side thereof than a female thread section
22
provided on the surface of the box section are brought into contact with each other, forming a seal section. The above seal section ensures gas tightness against an internal pressure caused by the internal fluid.
In general threaded connections including the threaded connection shown in
FIG. 8
are provided with a make-up force reinforcement mechanism, called “interference”, whereby the pitch diameter of the male thread section of the pin section is rendered larger than that of the female thread section of the box section.
Hereinafter, in this specification, the term “a pipe” means to include “the pin section at the extremity of the pipe and, in the case of the integral type, the box section as well”. The term “a pipe proper” means to include “neither the pin section nor the box section”.
When a torque shoulder forming a threadless face
14
disposed at the extremity of the pin section
11
is butted against a torque shoulder forming a threadless face
24
disposed in the innermost part of the surface of the box section
21
, a torque shoulder is formed. The torque shoulder is provided so as to control a torque for making up the threaded connection such that an appropriate pressure is developed at a contact face of the seal section.
In
FIG. 8
, a smooth groove
30
is additionally provided on the internal surface of the threaded connection in close vicinity of the torque shoulder such that turbulence in flow of the fluid along the internal surface is prevented, avoiding inducement of local corrosion.
However, the threaded connection constituted as above has problems described hereafter.
Occasionally oil country tubular goods are subjected to a compressive force in the axial direction and bending load, although not so frequently. In the event that the threaded connection is loaded thereafter with a tensile force due to pipes' own weight, the contact pressure degreases at the seal section and at the torque shoulder, and in an extreme case, openings are formed. As a result, there arise such problems as leakage of the internal fluid due to deterioration in gas tightness against the internal pressure and initiation of intense local corrosion due to turbulence in flow of the internal fluid caused by the openings formed as above.
When a twisting torque acts on the threaded connection in a loosening direction for any reason in a state when the contact pressure is lowered or openings are present, the threaded connection will be at a risk of being disconnected, and the pipes drop down into an oil well. Since it is very difficult to connect again the pipes in a oil well, the worst case may occur to abandon the oil well still under development or already in production. There is an increasing tendency of such incidents to occur because of an increase in tensile stress due to the pipe's own weight according as the depth of oil wells increases.
The objective of the invention is to provide a threaded connection capable of preventing from the contact pressure decrease and formation of openings at the seal section and/or at the torque shoulder when a tensile stress is imposed on the threaded connection after a compressive force in the axial direction or bending load is applied thereto, and to ensure corrosion resistance as well.
SUMMARY OF THE INVENTION
FIG. 1
is a sectional view showing an embodiment of a coupling type threaded connection according to the invention. In this type of the threaded connection, the pin section
11
provided at each end of a pipe
10
is connected to the pin section
11
provided at another end of pipe
10
via a coupling
20
provided with the box section
21
at both ends thereof.
FIG. 2
is an expanded sectional view of a part (part A in
FIG. 1
) in the vicinity of the extremity of the pin section of the typical threaded connection according to the invention. In
FIG. 2
, a seal forming threadless face
13
and a torque shoulder forming threadless face
14
of the pin section
11
are disposed to a seal forming threadless face
23
and a torque shoulder forming threadless face
24
of the box section
21
and they are brought into contact with and butted each other forming a metal-to-metal seal and a torque shoulder similarly to the case of the threaded connection shown in FIG.
8
. In
FIG. 2
, a portion of the internal surface of the pin section, having inside diameter of dx
1
extends from the extremity of the pin section toward the vicinity of the end of the pipe proper beyond the seal forming section corresponding length. Normally, a thick walled portion has a constant wall thickness as shown in FIG.
2
. However, a thick walled portion may have a varying wall thickness rather than a constant wall thickness. For example, a portion having the varying diameter of dx
2
shown in
FIG. 2
where the diameter gradually increases up to the inside diameter of the pipe proper, may overlap to the length of the seal section. In such a case, the length from the extremity of the pin section to the position where the inside diameter becomes equal to that of the pipe proper (that is, the length of the thick walled portion
Sugino Masaaki
Yamamoto Miyuki
Burns Doane , Swecker, Mathis LLP
Nicholson Eric K.
Sumitomo Metal Industries Ltd.
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