JPH08285153A - Sealing ring to be used in oil well pipe joint - Google Patents

Abstract

PURPOSE: To enhance collapse resistance of an anticorrosive ring by incorporating a metallic reinforcing strip into the inside or the outer periphery of an anticorrosive resin ring to prevent infiltration of a corrosive fluid from an impactively contacting part of a pin tip box central part at joint fitting time. CONSTITUTION: An anticorrosive resin ring 7 is inserted to hold sealing performance of a place where a male screw pin 2 of a joint and a female screw box impactively contact with each other to completely coat an inside surface of an oil well pipe. A steel wire 9 being a metallic reinforcing strip is incorporated into the inside or the outer periphery of this anticorrosive resin ring 7. Therefore, at using time, collapse resistance of the anticorrosive ring 7 can be enhanced to an (n)-ring phenomenon of pushing out the anticorrosive ring 7 inside by a difference between a pressure drop in a pipe inside surface and back pressure of the anticorrosive ring 7. Even if large groove bottom pressure is applied to the anticorrosive ring 7, it can be reliably housed in a groove without being permanently deformed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oil well pipe threaded joint applied to a well producing corrosive gas and oil.

[0002]

2. Description of the Related Art In a corrosive environment, it is usual to use oil country tubular goods to which a large amount of expensive alloy having excellent corrosion resistance is added. However, the cost of these alloy steel oil country tubular goods is higher than that of the carbon steel oil country tubular goods which are usually used, and the total oil well development cost is being pressed.
In particular, as in recent years, in a situation where international cost competition is intensifying, a substitute for a high alloy is desired.

The oil country tubular good shown in FIG. 1 is an example of a joint developed in consideration of such market conditions. By protecting the inner surface of the oil country tubular goods from a corrosive environment with a resin coating, the carbon steel oil country tubular goods can be used even in a corrosive environment. here,
The object of the present invention is to insert, as known from JP-A-63-13992 and JP-A-63-167188, to fill a gap between both pipes when a screw joint is fastened. It is a ring. As shown in FIG. 1, in an oil well pipe joint including a coupling (box) 1 having an internal coating 6 and an internal thread inside, and a pipe (pin) 2 having an external thread and an internal coating 5 at the inside, a box By inserting the joint anticorrosion resin ring 7 between the pin and the tip of the pin, it becomes possible to completely cover the inner surface of the steel pipe with the resin. Incidentally, 3 is the center of the tube axis, 4 is the metal contact seal portion, and 8 is the groove bottom.

However, the practical performance test conducted by us revealed that there were unexpected problems. That is, a phenomenon in which the ring 7 jumps inward (referred to as looping; see FIG. 2) occurs due to a sudden drop in the pipe pressure. If the looping occurs in the actual use environment, the protrusion of the inner surface of the pipe makes it impossible to insert the measuring device for inspecting the inner surface of the pipe and the oil layer. In addition, the role of the inner surface coating at the corner is also impaired. Presuming the cause, the pressure accumulated between the ring and the bottom of the ring mounting groove and the pressure difference inside the pipe are problems, and this seems to act as back pressure on the ring and push it out ((a) in FIG. 2). reference). Of course, it would be best to completely prevent the internal fluid from entering with a resin ring so that back pressure is not generated, but it is actually difficult to stop a minute leak, and internal fluid pressure accumulates at the groove bottom. Will result. However, since this internal fluid is not supplied one after another, it is considered to be acceptable from the viewpoint of corrosion resistance. However, it is a problem if the exchange with the internal fluid becomes free like looping.

An object of the present invention is to provide an anticorrosion ring which does not cause looping by reinforcing the ring with a steel wire to enhance the crush strength against back pressure. Until now, practical tests that predicted the possibility of differential pressure generation have not been conducted, and it seems that precise design has not been done so far, and the resin ring of the current product is made of a single material. There is.

[0006]

In view of the above background, the present invention focuses on a resin / steel composite ring having high looping resistance, and provides an inexpensive corrosion resistant oil well pipe joint using the ring. The purpose is to provide.

[0007]

A seal ring used in an oil well pipe joint according to the present invention is a pipe (pin) having a female thread on the inner surface and a male thread on the outer surface and having an inner surface coated. ) Is an anti-corrosion resin ring that prevents intrusion of corrosive fluid from the contact part at the center of the pin tip box at the time of fitting with a joint made of It is characterized by

Further, according to the present invention, a steel wire is enclosed in the resin ring in the circumferential direction, or a strip-shaped steel plate is combined with the outer circumference of the resin ring, or a groove is formed on the outer circumference of the resin ring. Can be formed, and a strip-shaped steel plate can be embedded in the groove.

[0009]

EXAMPLE First, the resin ring of the present invention has a metal reinforcing strip incorporated inside or on the outer periphery thereof. The metal reinforcing strip is, for example, a steel wire and is a steel plate or the like that is slit into a strip shape. As a form of this assembling, three types of structures are possible as shown in FIG. FIG. 3A shows a resin-containing corrosion-resistant ring 7 in which a steel wire 9 is wrapped with resin. In the design, the crush strength of the ring needs to be larger than the differential pressure. Since steel has overwhelmingly higher rigidity than resin, the crush strength of this composite material can be regarded as the crush strength of steel. Since the crushing strength of the steel wire occurs when the circumferential stress σ shown in FIG. 3 (b) reaches the yield stress σy, the wire diameter t can be designed based on the following equation. t = 2 × D × P / (π · σy)

Here, the expected differential pressure is put into the pressure P, and D
Is the outer diameter of the applicable joint, and σy is the proof stress of the steel wire. For example, P = 3 kg / mm ² , D = 150 mm, σy = 100 kg
/ Mm ² , the wire diameter is about 2.9 mm. The cross-sectional shape of the resin can be determined by determining the wire diameter. It is desirable to secure the resin thickness with a sufficient margin for the tightening margins from both pipes. Practically, considering the size of the ring and the size of the ring mounting groove, the composite width with the steel wire is 5 to 5.
About 8 mm is preferable, and in this case, the resin thickness is 1 mm to 2.5 mm on each side in the above example. The cross-sectional shape of the ring is basically rectangular, and has a corner R, a groove bottom having a semicircular shape, or the like, which matches the groove shape design of the fitting to be mounted.

Next, there is a ring having a basic structure in which resin and steel are doubled. As shown in FIG. 3 (c), this is made by completely making steel as the backup ring 10 and considering the contact of the pipes from both sides, FIG.
As the concave resin shown in (d), the one in which a strip-shaped steel plate is filled in the groove can be applied. In designing the ring shape, the crush strength of the steel is first designed as in the above. First, the width h is determined in relation to the size of the groove. If the thickness is 5 mm, the wall thickness t is determined by the following relational expression. t = D · P / (2 · σy)

Here, the ring diameter is 150 mm and the pressure is 3 kg / mm.
² and material strength of 100 kg / mm ² , 2.2 mm. The thickness of the resin depends on the groove depth and varies depending on the joint, but considering that steel is used as a backup ring, it is preferable to secure the original resin thickness of about twice that of steel. In this case, the width and depth of the composite are 5 each.
It will be mm x 6.6 mm. Also, in the case of a concave shape, if the width increase is 1 mm to 2.5 mm on one side like the internal type,
The width is 7 mm to 10 mm.

As described above, the ring rectangular cross-sectional shape can be designed to be about 5 mm to 10 mm regardless of whether it is the internal type or the double structure type, and it can be used without changing the shape significantly with the conventional resin homogeneous ring. Moreover, its crushing rigidity can be secured at least 20 times in proportion to the material strength.

[0014]

The function of the ring of the present invention when it is used will be described below in comparison with the case of the conventional ring. Taking the above-mentioned internal ring as an example, consider a resin having a similar shape and no steel core. If the resin strength is 5 kg / mm ² , it is 0.1
It will be crushed at 5 kg / mm ² (15 atm). Actually, the resistance to outflow to the inside of the ring due to friction with the ring groove seems to be higher, but considering that the production fluid pressure is several hundred atmospheric pressure, if back pressure acts on the resin homogeneous ring. It can be easily released. Also, in the case of a resin homogeneous ring, once it is permanently deformed inward,
The adhesion with the ring groove cannot be maintained and a gap is easily formed. As a result, the corrosive fluid is allowed to enter the joint and the function as the inner surface coated steel pipe is lost. In that respect, in the composite ring with steel, since steel is an elastic body, not only can permanent deformation of the ring be prevented, but also
Since the ring is returned to its original position when the internal pressure load returns to the normal use state from the back pressure state, it has a stable sealing function against the internal fluid.

[0015]

As described above, in the anticorrosion ring of the present invention, the steel wire is included in the resin ring, or the steel ring is combined with the outer circumference of the resin as a backup ring, so that the pressure drop on the inner surface of the pipe is reduced during use. It is possible to increase the crush resistance of the anticorrosion ring against the looping phenomenon that pushes the anticorrosion ring inward due to the difference in back pressure of the anticorrosion ring, and even if a large groove bottom pressure acts on the anticorrosion ring, it does not permanently deform inside the groove. Therefore, it is possible to obtain the oil-proof pipe fitting equipped with the anticorrosion ring and the anticorrosion ring without causing any trouble to the logging equipment.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view in which an anticorrosion ring is attached to an oil well pipe joint having an inner resin coating.

FIG. 2 is a schematic diagram of a looping phenomenon.

FIG. 3 (a) is an anticorrosion ring in which a steel wire is embedded inside to increase the crush strength of a resin ring, (b) is a supplementary explanatory diagram for estimating the crush strength of a steel wire, and (c) is a steel plate on the outside. Anticorrosion ring with improved crush strength of resin ring, (d)
Is an illustration of a concave composite resin ring.

[Explanation of symbols]

 1 Female screw box 2 Male screw pin 3 Pipe axis center line 4 Metal contact seal part 5 Pin inner surface resin coating 6 Box inner surface resin coating 7 Anticorrosion resin ring 8 Resin ring storage groove bottom 9 Resin ring reinforcing steel wire 10 Backup ring P Back pressure D Ring outer diameter t Steel wire ring thickness or steel plate wall thickness h Steel plate width

Claims (4)

[Claims] 1. A pin tip box center at the time of fitting using a coupling (box) having a female thread on the inner surface and a pipe (pin) having a male thread on the outer surface and having an inner coating. A seal ring for use in an oil country tubular goods joint, which is a corrosion-resistant resin ring for preventing invasion of a corrosive fluid from an abutting portion of a portion, wherein a metal reinforcing strip is incorporated into or inside the resin ring. 2. A seal ring used for an oil country tubular goods joint according to claim 1, wherein a steel wire is enclosed in a resin ring in a circumferential direction. 3. The seal ring used for an oil country tubular goods joint according to claim 1, wherein a strip-shaped steel plate is combined with the outer periphery of the resin ring. 4. A seal ring used for an oil country tubular goods joint according to claim 1, wherein a groove portion is formed on the outer periphery of the resin ring, and a strip-shaped steel plate is filled in the groove.