JPH05231569A - Dissimilar metal pipe joint - Google Patents

Abstract

PURPOSE:To prevent galvanic corrosion by specifying the curvature radius of the round part of each portion of the surface of a joint fitting part, and by forming a ceramic film on the fitted surface of either a pin or a box. CONSTITUTION:The curvature radius of round parts R1-R4 of each portion of the surface of joint fitting parts is set no less than 0.3mm, while an insulating coating layer 7 consisting of ceramic film is formed on one fitted surfaces of a pin and a box 3 that are made of dissimilar metals. For the insulating ceramic, Al2O3, MgO, CaO, Si3N4, and BN, for example, can be used. Dissimilar metal pipes can be connected to each other while electric insulation is ensured, and galvanic corrosion can thus be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe joint used for connecting casing pipes or tubing pipes of dissimilar metals in oil and gas wells and geothermal wells, which does not cause corrosion of dissimilar metals.

[0002]

2. Description of the Related Art Casing pipes or tubing strings in oil and gas wells and geothermal wells are usually made of pipes made of the same metal and connected by screw joints made of the same metal. However, it is costly to construct the casing or tubing at all depths from corrosion-resistant materials in wells where corrosion is concentrated only in a specific depth area and severe corrosion does not occur in other depth areas. Not desirable. That is, in such a well, it is cost and corrosion resistance to place a corrosion resistant material such as stainless steel only in a portion where severe corrosion damage is concerned, and to place a cheap material such as carbon steel in the other portions. It is a basic idea to satisfy both conflicting conditions. An example of forming a casing or tubing strings based on this idea is shown in FIG. That is, FIG. 4 is an example of tubing strings made of different metals, 1 is a carbon steel pin, 2 is a stainless steel box, 3 is a carbon steel box, 4 is a stainless steel pin, 5 is stainless steel / It is a joint part of carbon steel.

FIG. 5 schematically shows a cross section of a stainless steel / carbon steel joint portion. 1 is a carbon steel pin, 2 is a stainless steel box, 4 is a stainless steel pin, and 6 is a stainless steel pin. Indicates galvanic corrosion. In this case, carbon steel (1, 3 in Fig. 4) and stainless steel (2 in Fig. 4) are inevitable.
As described above, metals having different corrosion resistance must be connected to each other. Therefore, in this joint part, the carbon steel part (1 in FIG. 5), which should be originally usable, is corroded in a short period of time because it is connected to the stainless steel (2 in FIG. 5), so-called galvanic corrosion 6. Will occur.

Based on the principle of galvanic corrosion, the most reliable method for preventing this is to electrically insulate different metals from each other. However, in the conventional threaded joint, no research and development has been done from this point of view, and the problem of galvanic corrosion is avoided by exclusively connecting the pipes of the same metal material with the threaded joint of the same metal material. Is the actual situation.

[0005]

SUMMARY OF THE INVENTION In view of the background described above, an object of the present invention is to provide a threaded joint for connecting dissimilar metals to each other without causing galvanic corrosion.

[0006]

The inventors of the present invention have conducted research and development based on the principle of galvanic corrosion that the most reliable method for preventing galvanic corrosion is to electrically insulate different metals from each other. As a result, it was found that this object can be achieved by a screw joint consisting of a pin or a box in which a ceramic insulating coating layer is applied to the surface of the fitting portion of a specific shape.

That is, the gist of the present invention is to provide a metal pipe joint portion composed of pins and boxes of dissimilar metals, in which the radius of curvature of the R portion of each portion on the surface of the joint fitting portion is 0.3 mm or more, and the pin or A dissimilar metal pipe joint joint characterized in that a ceramic film is formed on at least one fitting surface of the box.

The present invention will be described in detail below. First, the insulating coating must be applied to at least the fitting portion of either the pin or the box. The term “fitting portion” as used herein is a generic term for a portion where the surfaces of the pin and the box come into contact with each other when the pin and the box are screwed together to show electrical conduction, and includes so-called screw portion, shoulder portion, and seal portion. It is a waste.

Next, it goes without saying that the material of the coating must be an insulator. As the insulating substance, there are polymeric materials as well as ceramics, but polymeric materials are not sufficient and ceramics are appropriate because the film is not damaged by screwing. As insulating ceramics, A
There are various types such as l ₂ O ₃ , MgO, CaO, Si ₃ N ₄ and BN. These must be applied alone or in combination by a thermal spraying method or a vapor deposition method without exposing the base metal to the fitting surface.

Third, the fitting surface to which the insulating coating is applied should not include a portion having a shape with a radius of curvature R of less than 0.3 mm. The reason for this is that it is difficult to form a thick insulating coating layer where R <0.3 mm and the coating layer that is formed is easily damaged when screws are screwed in. This is because the electrical insulation cannot be achieved.

[0011]

EXAMPLES Next, the present invention will be further explained based on examples. A carbon steel box and a duplex stainless steel pin (outer diameter 244.5 mm × wall thickness 10.03 mm) were screwed together to evaluate electrical insulation. In the present embodiment, the API (American Petroleum Institute) standard round screw joint: A and buttress screw joint: B were mainly used, but a special screw joint having a metal-to-metal seal portion and a screw portion having a buttress screw: C Was also tested. The cross-sectional shapes of a duplex stainless steel pin having a round screw: A, a buttress screw: B, and a special screw: C and a carbon steel box are shown in FIGS.

That is, in FIG. 1, FIG. 1 shows an outline of a cross-sectional shape of a round screw pin used in the embodiment. 4 is a stainless steel pin, 3 is a carbon steel box, 7 is a coating layer, 8 is an outer surface of the pin tube body, 9 is a chamfered surface, 1
0 indicates a pin end, and R _{1 to} R ₄ indicate points where the radius of curvature changes.

FIG. 2 shows an outline of the sectional shape of the pin of the buttress screw used in the embodiment. 11 is a pin end, 12 is a stabbing flank surface, 13 is a road flank surface, 14
Indicates a crest surface, and R _{1 to} R ₅ indicate points where the radius of curvature changes.
FIG. 3 shows an outline of the cross-sectional shape of the pin of the special screw used in the example. 15 is the first shoulder surface, 16 is the sealing surface, 1
Reference numeral 7 indicates the second shoulder surface, and R _{1 to} R ₇ indicate points where the radius of curvature changes.

The radius of curvature was changed by changing the positions of R _{1 to} R _{7 in} each figure, and threading was performed. That is, in the round screw, the angle formed by the chamfered surface at the tip of the pin and the threaded surface is R ₁ , the angle formed by the pin end and the chamfered surface is R ₂ , and the outer surface of the tubular body has a thread in the incomplete threaded portion. Of the angle between the outer surface of the tubular body and the threaded surface, the tip end side of the pin is R ₃ , the rear end side of the pin is R ₄ , and the others are according to the API standard.

In the buttress screw, the angle formed by the chamfered surface at the tip of the pin and the threaded surface is R ₁ , the angle formed by the pin end and the chamfered surface is R ₂ , and the crest surface and the load at the screw thread of the complete screw portion. The angle formed by the flank surface is R ₃ , the stubbing flank surface side R ₄ and the load flank surface side are R ₅ among the angles formed by the outer surface of the tubular body and the threaded surface in the incomplete threaded portion, and the others are the same as the API standard. did.

In the special screw, the angle formed by the first shoulder surface and the seal surface is R ₁ , the angle formed by the seal surface and the second shoulder surface is R ₂ , and the angle formed by the second shoulder surface and the threading start surface. the R _3, the crest of the first thread R _4, the angle crest surface and the load flank at full thread R _5, of the angle of the tube external surface and threaded working surface in incomplete thread portion The stubbing flank surface side was R ₆ , the load flank surface side was R ₇ , and the others were the same as the API standard buttress screw.

The surface of the fitting portion of the duplex stainless steel pin was coated with an Al ₂ O ₃ film by the post spraying method of shot blasting. The target coating thickness is 80 μm. Carbon steel box is threaded and Zn plated 1
It was applied to a thickness of 0 μm. 20 g of API standard compound grease was applied to the pin fitting portion and screwed together, and in that state, electrical insulation between the pin and the box was evaluated by a tester. The results are shown in Table 1.

[0018]

[Table 1]

From Table 1, in the comparative example, if a pin or box having a minimum radius of curvature of less than 0.3 mm is used regardless of the screw type, the alumina coating is damaged during screwing, and the electrical insulation is not maintained. However, according to the present invention, it is apparent that electrical insulation can be secured in a screwed state regardless of the screw type. Although alumina is used in this embodiment, the same effect can be expected with other insulating ceramics.

[0020]

As described above, according to the present invention, it is possible to connect dissimilar metal pipes to each other while ensuring electrical insulation.
As a result, galvanic corrosion can be prevented.

[Brief description of drawings]

FIG. 1 shows an outline of a cross-sectional shape of a pin of a round screw used in an example.

FIG. 2 shows an outline of a cross-sectional shape of a pin of a buttress screw used in an example.

FIG. 3 shows an outline of a sectional shape of a pin of a special screw used in an example.

FIG. 4 is an example of tubing strings formed of dissimilar metal tubes.

FIG. 5 is a schematic view showing an outline of a cross section of a stainless steel / carbon steel joint portion in FIG. 1.

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

Claims (1)

[Claims] 1. In a metal pipe joint part composed of pins and boxes of dissimilar metals, the radius of curvature of the R part on each surface of the joint fitting part is 0.3 mm or more, and at least one of the pin and the box is fitted. A dissimilar metal pipe joint characterized in that a ceramic film is formed on the mating surface.