JPH06109173A - Oil well fitting - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an oil country tubular goods joint for connecting a pin and a pin box made of dissimilar metals that do not cause galvanic corrosion. [Structure] In a mechanical joint composed of a pin and a box of dissimilar metals, an insulating layer of ceramics, synthetic resin, or the like is formed on each of the pin side and the box side of each portion of the joint fitting surface, and the space between these pins and box A cured layer of adhesive was interposed in the gap. As a result, the electrical insulation state between different kinds of metals can be reliably maintained, galvanic corrosion can be prevented, and in addition, joint strength and sealability, which are functions as a mechanical joint, can be secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a dissimilar metal pin (male) and a box (female), respectively, used for connecting dissimilar metal casing pipes or tubing pipes in oil or gas wells and geothermal wells. Regarding mechanical joints.

[0002]

BACKGROUND OF THE INVENTION Casing pipes or tubing strings in oil or gas and geothermal wells are made of pipes of the same metal and are connected by threaded joints of the same metal, the properties of which are the strength of the joint, water and gas. It is customary to demand performance such as sealing properties and seizure resistance to withstand repeated use.

However, in a specific depth region of a well, for example, corrosion is intensively generated in a flushing zone where water vapor is transformed into warm water, and in other depth regions,
In wells where severe corrosion does not occur, it is cost prohibitive to construct the casing or tubing with a corrosion resistant material.

Therefore, in such a well, as shown in FIG.
As shown in, the coupling 2 and the pin 1 made of a corrosion resistant material such as stainless steel are arranged only in the portion 3 where severe corrosion is concerned, and the inexpensive portion such as carbon steel is arranged in the other portion 4. Is a basic idea that balances the contradictory conditions of cost and corrosion resistance.

However, stainless steel contains Cr, Ni and Mo.
Since it is a steel containing, for example, a potential different from that of carbon steel composed exclusively of iron, when stainless steel and carbon steel come into direct contact with each other, as shown by the arrow in FIG. There is a problem that a galvanic current is generated between the pin 1 and the stainless steel coupling 2, and a corroded portion 3 is suddenly generated in a short period on the inner surface of the carbon steel serving as an anode, causing so-called galvanic corrosion.

In order to insulate the different materials 1 and 2,
As shown in FIG. 5, a sprayed film 6 of ceramic material is formed on a plain steel pin 1, and the pin 1 is fitted with a stainless steel coupling 2 having a Teflon coating 7 on a screw surface. It is conceivable that a damaged portion 5 is generated at each tip of the screw thread, and the insulation is easily broken, and electricity is conducted and corroded.

[0007]

SUMMARY OF THE INVENTION In view of the background described above, an object of the present invention is to provide a joint for oil country tubular goods for connecting a pin made of a dissimilar metal that does not cause galvanic corrosion and a pin box.

[0008]

The present invention has been studied from the viewpoint that the most reliable method for preventing galvanic corrosion is to electrically insulate different metals.
Completed based on the finding that a screw joint that does not cause galvanic corrosion can be obtained by avoiding mechanical contact between screws as much as possible and forming an insulating coating such as ceramics in order to achieve reliable electrical insulation. did.

That is, according to the present invention, in a mechanical joint comprising a pin (male) and a box (female) of dissimilar metals, a resin or an insulating ceramic is sprayed on each of the pin side and the box side of each portion of the joint fitting surface. , Vapor deposition or coating, and (1) to prevent the interference between the pin / box by making a large gap between the pin / box,
(2) To widen the clearance between the screws at the front end and the rear end of the fastening start so as to alleviate the contact between the screws at the time of fitting, (3)
By inserting an insulating resin ring into the shoulder part, the contact of the shoulder part is mitigated, and further,
The combination of (1), (2), and (3) prevents damage to the insulating ceramic or resin that occurs during screw fastening, and evenly applies a curable adhesive just before mating to make the pin / A box is fitted, or a curable adhesive is injected into the gap between the pin and the box after fitting to completely fill the gap and then cure.

The oil country tubular goods joint of the present invention is manufactured in the following manner.

First, the insulating coating is applied to at least the fitting portion of either the pin or the box.
The fitting portion mentioned here includes a screw portion, a shoulder portion, and a seal portion. The other box or pin is then uniformly coated with a relatively soft polymeric material, such as Teflon, to prevent exposure of the base metal to prevent ceramic damage during fitting. However, it is necessary to consider the following points in practice in these joint structures. When mating, pin /
In order to make the fitting force between the boxes as small as possible, it is important to take a large clearance (clearance) between the screws to reduce the so-called screw interference amount (the fitting deformation amount between the screws), or to eliminate them altogether.

[0012] As a result, the insulated pin and the box can be easily fitted together without making contact with each other at a high surface pressure. Note that with this alone, the screws may not be tightly fitted and may be loosely joined.Therefore, a hardening type adhesive such as resin should be evenly applied immediately before fitting, or press fit into the screw gap after fitting. By doing so, it is important to completely fill the gap.

[0013]

As described above, in the oil country tubular goods joint of the present invention, galvanic corrosion can be prevented by reliably maintaining the electrical insulation state between different kinds of metals.

[0014]

EXAMPLE As an example of the present invention, an example in which the present invention is applied to an oil country tubular goods joint comprising a carbon steel pin and a stainless steel coupling will be shown.

Embodiment 1 FIG. 1 shows an example in which the present invention is applied to a thread portion of a pin 1 and a coupling 2 of an oil well pipe joint.

In the figure, a carbon steel pin 1 is coated with an alumina sprayed film 6 to a thickness of 20 to 150 μm, fitted into a stainless steel coupling 2 coated with a Teflon coating 7, and a resin adhesive 9 is injected into the gap. After that, the pin 1 and the coupling 2 are moved to confirm that the insulation is completely realized, and the adhesive is cured.

Embodiment 2 FIG. 2 shows an example in which the present invention is applied to a metal seal portion 11 of a pin 1 and a coupling 2 of an oil well pipe joint.

In the figure, similar to the case of the first embodiment, the alumina sprayed film 6 of 20 to 150 is formed on the carbon steel pin 1.
It is applied to the stainless steel coupling 2 coated with the Teflon coating 7 to a thickness of μm, and the resin adhesive 9
After the resin adhesive 9 is injected into the metal seal portion 11 instead of the compound grease, the metal seal portion 11 is fitted with the resin adhesive 9.

Table 1 shows the result of conducting the continuity test of the oil country tubular goods joint thus assembled. In the table, PJ is a premium joint having a metal seal portion, API is a round screw of API standard, alumina is sprayed on the pin, Teflon is applied on the box,
Experiments were carried out using samples in which the threads were appropriately shaved to eliminate interference in the circumferential and axial directions and samples with interference in the circumferential and axial directions.

As a result, in the case of the API round screw, the insulating property was ensured only in the joint having the structure in which the interference amount not only in the circumferential direction but also in the axial direction was completely eliminated and the contact of the coating was prevented. It was found that a Teflon ring can be attached to the premium joint to protect the film on the shoulder.

Furthermore, a series of API round screws (B
1 series) was fitted with a sample with or without interference using an adhesive, and the sealability and joint strength were tested as a performance test. The results are shown in Table 2, and it can be seen that even in a joint without interference, by filling the gap with an adhesive and curing the joint, both the joint strength and the sealing performance can be secured while maintaining the insulating property.

[0022]

[Table 1]

[Table 2]

[0023]

INDUSTRIAL APPLICABILITY The oil country tubular goods joint of the present invention can reliably maintain the electrical insulation state between different kinds of metals to prevent galvanic corrosion, and moreover, the joint strength and the seal which are functions as a mechanical joint. It is possible to secure the property.

[Brief description of drawings]

FIG. 1 shows an example applied to a round screw as a first embodiment of the present invention.

FIG. 2 shows an example in which the present invention is applied to a premium joint as a second embodiment.

FIG. 3 shows an aspect of an oil country tubular good string in a well.

FIG. 4 shows a mode of galvanic corrosion and connection between stainless steel and carbon steel.

FIG. 5 shows a schematic diagram of damage to the coating on the tip of the screw.

[Explanation of symbols]

 1 pin 2 Coupling 3 Corrosion part 4 Non-corrosion part 5 Damaged part 6 Alumina sprayed film 7 Teflon coating 8 Corrosion part 9 Resin adhesive 11 Metal seal part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiji Tsuru 1-1-1, Toibata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture New Nippon Steel Corporation Yawata Steel Works

Claims (1)

[Claims] 1. In a mechanical joint comprising pins (male) and box (female) of different kinds of metals, one surface of the joint is a insulating layer of ceramic or resin on the pin side, and the other side of the box is insulated on the box side. An oil country tubular goods joint characterized in that another coating layer of ceramic or resin is formed, and a hardened adhesive layer is interposed in a relatively large gap provided between these pins and the box.