JPH06192809A - Insulating pipe material for preventing electrolytic corrosion having excellent corrosion resistance - Google Patents

Abstract

PURPOSE:To provide the insulating pipe material which prevents electrolytic corrosion and crevice corrosion arising in the case of connection of different metallic pipes in an oil well, etc., and is excellent in the improvement of both the adhesion and corrosion resistance of films. CONSTITUTION:The low corrosion-resistant pipe material 1 and the highly corrosion-resistant pipe material 2 are screwed and connected directly or by means of a coupling 3. Amorphous insulating ceramics layers, at least the extreme surface layer parts of which are crystalline, are clad in a range L of >=60mm from the pipe end at the inside and outside surfaces of the pipe material of the low corrosion-resistant pipe material 1, in a range L of >=60mm from the pipe end at the inside and outside surfaces of the pipe material of the highly corrosion-resistant pipe material 2, in a range L of >=60mm from both pipe ends of the inside and outside surfaces of the coupling 3 and further in spacing parts A, B when these pipe materials are connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to general pipes, particularly oil well pipes, to prevent electrolytic corrosion and crevice corrosion that occur when pipes of dissimilar metals are spliced, and to improve the corrosion resistance of the film material to be coated. Insulation pipe material for preventing electrolytic corrosion.

[0002]

2. Description of the Related Art There are various types of metal tubes in oil wells. Tubing for transporting crude oil and natural gas from the underground production layer to the ground, casing provided around the tubing for protection of dug wells, steam injection pipes arranged to increase pressure in the oil layer And CO ₂ piping for secondary oil recovery.

In oil wells, these metal pipe materials for oil wells are piped up to several thousand meters underground at a vertical or nearly vertical angle to the surface of the ground for the extraction and production of crude oil and natural gas. In addition, in this specification, all of these pipes are called an oil country tubular good.

Generally, in an oil well, corrosiveness is large in a deep place because the temperature is high, and conversely, corrosiveness is small in a shallow place because the temperature is low. Therefore, in consideration of economy, deep stainless steel wells, such as stainless steel and N
A highly corrosion-resistant metal pipe material such as an i-based alloy, Ti, or a Ti alloy is used, and a low-corrosion resistance metal pipe material such as carbon steel or a low alloy metal is often used in the shallow portion.

Therefore, a connecting portion between the low corrosion resistant metal pipe material and the high corrosion resistant metal pipe material naturally occurs, but when the corrosion resistant metal pipe material and the high corrosion resistant metal pipe material are simply connected, a potential difference occurs due to contact between different metal materials, so-called Galvanic corrosion (electrolytic corrosion) occurs. Due to this galvanic corrosion, corrosion progresses at a rate of 2 to 10 times on the low corrosion resistant metal pipe side, for example, as compared with the corrosion of a normal carbon steel pipe alone. On the other hand, on the side of the highly corrosion-resistant metal pipe material, hydrogen was generated, and this hydrogen penetrated into the inside to cause hydrogen embrittlement. Furthermore, crevice corrosion occurs in the gap of the joint portion, and the corrosion is promoted by electrolytic corrosion.

With respect to these problems, under the present circumstances,
To prevent corrosion by directly connecting the low-corrosion-resistant metal pipe material and the high-corrosion-resistant metal pipe material, and by interposing a metal pipe material such as duplex stainless steel, which has corrosion resistance between the low-corrosion metal pipe material and the high-corrosion metal pipe material There is. However, even if an intermediate metal pipe material is interposed, it is impossible to completely prevent electrolytic corrosion and crevice corrosion between members, and it is only to moderate the corrosion rate.

On the other hand, it is virtually impossible to completely seal and seal the pipe materials when they are connected to each other by the screw joint structure, and unavoidably there is an open gap in the corrosive environment. Becomes When the above-mentioned gap exists in the screw joint structure portion, since there is almost no liquid flow in this gap portion, hydrogen ions and the like produced by corrosion of metals such as iron are likely to be accumulated at a high concentration, and the pH is extremely lowered, Corrosion occurs more severely than the base metal. That is, crevice corrosion occurs even in an environment weaker than the corrosive environment of the base material. When this crevice corrosion occurs, there is a risk of developing stress corrosion cracking, and as a result, the sealability, which is an important function as a joint, is impaired by eroding the sealing surface.

In order to solve the above problem, for example, in Japanese Patent Laid-Open No. 1-199088, a non-metallic layer of 1 to 100 μm is formed on a threaded joint portion of an oil country tubular goods of the same material containing Cr by 7.5% or more by weight. We have proposed a joint that prevents crevice corrosion by blocking the corrosive environment.

[0009]

The technique disclosed in the above publication exemplifies a method for forming a non-metal layer. Among the exemplified methods, the method used for coating by ion plating, sputtering or plasma CVD is used. It is difficult to obtain a thermodynamically stable crystalline material with a plasma output or electric energy for sputtering, so that only an amorphous film formed with low energy is formed. On the other hand, when coating is performed using thermal CVD or thermal spraying, a crystalline film is formed because the coating energy is high.

Therefore, the technique described in this publication discloses a method of forming only one of an amorphous film and a crystalline film.

However, when the coated non-metal layer is an amorphous layer, the coefficient of thermal expansion is closer to that of a metal than that of a crystalline layer of the same kind of material, and the anisotropy is small. Shows relatively good adhesion. However, this amorphous layer is
Since it is a metastable state, in a special corrosive environment such as an oil well environment, metal ions in the coating elute and the coating thickness decreases, resulting in deterioration of insulation resistance and sufficient electrolytic corrosion prevention effect. I can't get it.

On the other hand, in the case of a crystalline layer, although it exhibits good corrosion resistance, it is difficult to obtain good adhesion due to the difference in thermal expansion from the base metal and the anisotropy of the coating. .

On the other hand, when a crystalline layer film is formed by using thermal CVD, the film itself has good corrosion resistance, but since a high temperature treatment at a coating temperature of 1000 ° C. or higher is usually required, the oil country tubular good It is difficult to apply it in practice, because the strength required for it will deteriorate and the threaded part of the oil well pipe joint including the premium joint will be deformed.

Further, when a crystalline coating film is obtained by thermal spraying, since the coating film contains a large number of pores, the corrosive liquid reaches the pipe surface through the coating film and does not exert a corrosion preventing effect.

[0015] Therefore, an object of the present invention is to provide an insulating pipe material for preventing electrolytic corrosion, which is capable of preventing electrolytic corrosion that occurs when connecting dissimilar metal pipe joints in oil wells and the like, and which is excellent in adhesion and corrosion resistance to the metal pipe material. It is in.

[0016]

Means for Solving the Problems As a result of intensive studies on the electrolytic corrosion preventing joint, the present inventors have found that after coating the surface of the base metal tube of the joint with an amorphous insulating ceramics layer, its outermost layer It was found that by crystallizing only the above, an insulating tubing material for preventing electrolytic corrosion, which is excellent in both corrosion resistance and insulation resistance, can be obtained.

According to the present invention based on such knowledge, in a metal pipe material having a threaded screw portion for connection formed on a pipe end portion: the screw engagement on at least one of an inner surface and an outer surface exposed when the pipe material is connected. At least one of a region extending from the inner surface end or the outer surface end excluding the threaded portion to a range of 60 mm or more and the threaded threaded portion area where a gap is formed when connected; an amorphous insulating material having a crystalline outermost layer portion It is characterized in that it is covered with a ceramics layer.

In this case, the insulating ceramics layer preferably has a specific resistance of 10 ⁸ Ωcm or more, a thickness of 0.4 μm or more, and a coverage of 90% or more and less than 100%. Further, a single layer or a composite layer of a metal or its oxide, nitride or carbide having an expansion coefficient intermediate between that of the insulating ceramic layer and the pipe material, between the amorphous insulating ceramic layer and the tube metal. Those having

[0019]

[Function] Galvanic corrosion that occurs when dissimilar metals come into contact with each other is
This is due to the fact that the reaction on the anode side is promoted by using a metal that is easily corroded as an anode. That is, the voltaic battery is assembled by the potential between different metals. Therefore, in order to prevent electrolytic corrosion, it is sufficient to cover different metals with an insulating ceramic layer and increase the liquid resistance by separating them from each other so that no corrosion current flows. The present inventors have found that, and confirmed that this aspect is actually effective.

Generally, crevice corrosion is a phenomenon in which metal ions, hydrogen ions, chlorine ions and the like generated by the corrosion are accumulated in the crevices, the pH is extremely lowered, and remarkable corrosion occurs. Normally, the oil country tubular goods are connected using a screw joint, but there is a clearance as shown at the connection boundaries A and B between the inner surface and the outer surface of the screw portion 20 in FIGS. 1 and 2, and crevice corrosion occurs here. . Furthermore, this crevice corrosion is promoted by electrolytic corrosion. This crevice corrosion can also be prevented by forming an insulating ceramic layer under the preferred and preferred embodiment of the present invention.

However, in forming the insulating ceramic layer, when the coating non-metal layer is an amorphous layer as described above, good adhesion to the base metal is exhibited, but the oil well environment In such a special corrosive environment, a sufficient electrolytic corrosion preventing effect cannot be obtained. On the other hand, when it is crystalline, it exhibits good corrosion resistance, but it is difficult to obtain good adhesion with the base metal.

Therefore, in the present invention, by making only the surface of the non-crystalline layer crystalline, excellent corrosion resistance under a corrosive environment is exhibited, and by leaving the lower layer side amorphous, the pipe material Good adhesion is exhibited against.

In the present invention, Al ₂ O ₃ , Si ₃ N ₄ , Ta ₂ O
₅ , the insulating ceramics such as SiO ₂ , ZrO _{2 and the} like, as described above, by coating the surface of the pipe base material by a method such as sputtering, ion plating, plasma CVD, MO (Metal Organic) -CVD, After forming the amorphous layer, the surface portion of the amorphous layer is crystallized.

As a method for crystallizing the surface portion of the amorphous layer, in addition to the heating method, plasma is generated in an oxidizing gas such as oxygen and carbon dioxide, or a mixed gas thereof, and the amorphous layer surface is crystallized. On the other hand, a method of performing plasma treatment can be mentioned.

As a means for forming an amorphous insulating ceramics layer having a crystalline outermost layer, the above-mentioned sputtering method, ion plating method, plasma C are used.
An amorphous insulating ceramics layer is formed on the surface of the pipe base material by VD, MO-CVD, or the like, and then a crystalline insulating ceramics layer is formed on the surface by a thermal CVD method, a thermal spraying method, or the like. Of course, it is also good.

On the other hand, examples of the base material of the pipe material used in the present invention include ferritic high chromium steel, austenitic stainless steel, Ni-based alloys having a Ni content of 20 wt% or less and a Cr content of 13 wt% or more, titanium, titanium alloys and the like. To be

In general, complete insulation is obtained when the specific resistance is 10 ⁸ Ωcm or more, and when the specific resistance is less than 10 ⁸ Ωcm, it becomes semiconductive. As in the case of the conductive coating, the risk of electrolytic corrosion with the low corrosion resistant pipe material is extremely high. Therefore, the specific resistance of the insulating ceramic layer covering the pipe material is 1
Preferably in the 0 ⁸ Ωcm or more.

According to a preferred aspect of the present invention, the coverage of the insulating ceramic layer is 90% or more and less than 100%. This coverage is determined by an electrochemical method.
That is, in a liquid in which only the base material can be dissolved,
The current was monitored by potentiostatic polarization, and the coverage (%) = [(current density of base material without coating)-(current density of base material with coating)] / (current density without coating)
The value is defined by × 100.

Further, the presence or absence of the effect of preventing electrolytic corrosion is determined by the coverage of the insulating ceramics layer and the size of the coating region, and this point will be clarified by Examples described later. Furthermore, the coverage is set to less than 100% at present, because of pinhole defects (defects of the film penetrating to the base material).
This is because it is known that it is difficult to coat a film without a coating.

Further, under the insulating ceramic layer,
A metal having an expansion coefficient intermediate between those of the tube material and the insulating ceramic layer, as shown in Table 3 below, or an oxide thereof,
By forming the stress relaxation layer composed of a single layer or a composite layer of nitride or carbide, it is effective in improving the peeling resistance of the insulating coating particularly in an oil well environment under stress.
The thickness of this stress relaxation layer is preferably 0.1 μm to 5 μm. This is because if the film thickness is less than 0.1 μm, the effect is hardly obtained, and if it exceeds 5 μm, the effect is almost lost.

[0031] The thickness of the insulating ceramic layer definitive present invention is preferably not less than 0.4 .mu.m, as the total thickness of the stress relaxation layer, it is desirable to within 100 [mu] m. This is because if the total film thickness exceeds 100 μm, the dimensional accuracy of the screw part forming part and the seal part may be adversely affected, and peeling due to internal stress of the film may occur.

[0032]

EXAMPLES Hereinafter, specific examples in which the present invention is mainly applied to oil country tubular goods will be described in detail. In addition, in the present invention, the pipe is not limited to the oil well pipe, for example, in the pipeline for transporting seawater and soil, the pipeline for plants, etc., it can be applied to the case where different metals are spliced. On the street.

FIGS. 1 and 2 are views showing an insulating coating according to the present invention, more specifically a connecting portion of an oil country tubular good coated with insulating ceramics. 1 shows the case of the connection type using a coupling, and FIG. 2 shows the case of the direct connection type.

In FIG. 1, the low-corrosion-resistant pipe material 1 and the high-corrosion-resistant pipe material 2 are screwed together by a coupling 3. These constitute the connecting element referred to in the present invention. The coupling 3 is usually made of the same material as or substantially the same material as the highly corrosion resistant pipe material 2.

In this embodiment, the low corrosion resistance pipe material 1 is used.
60 from the pipe end excluding the threaded portion 20 on the inner and outer surfaces of the pipe material
Over the range of mm or more (the range indicated by the reference symbol L, the same applies hereinafter), and the connection boundaries A and B of the screw portion 20 (the A portion is shown in FIG. 7 and the B portion is shown schematically in FIG. 8). On the other hand, a layer composed of an amorphous insulating ceramics layer as a lower layer and a crystalline ceramics film laminated on the upper layer (hereinafter, this multilayer film is referred to as an adhesive insulating film) according to the present invention is 4, 5 , 21 and 22 parts.

In the coupling 3, the adhesive insulating coating is formed at 6, 7, 23, and 24 portions over the entire area including the A and B portions of the threaded portion 20 on the inner and outer surfaces of the pipe material.

On the other hand, in the high corrosion resistance pipe material 2, as in the low corrosion resistance pipe material 1, the threaded portion 2 is formed on the inner and outer surfaces of the pipe material.
Over the range of 60 mm or more from the end of the pipe except 0, the adhesive insulating coating according to the present invention is formed on the connecting boundaries A and B of the screw portion 20 at the portions 8, 9, 21, and 22. ing.

In the case of the above-mentioned specific example, the low-corrosion-resistant tubing 1, the high-corrosion-resistant tubing 2 and the coupling 3 were all provided with the adhesive insulating coating at 4 to 9 and 21 to 26 parts. From the viewpoint of preventing electrolytic corrosion, the adhesive insulating coating may be formed on any one or two of the low corrosion resistance pipe material 1, the high corrosion resistance pipe material 2 and the coupling 3. It is desirable to form 6 or 7 parts. In short, the application location of the adhesive insulating coating and the combination thereof can be appropriately selected depending on the application and the expected degree of corrosion.

On the other hand, in the case of FIG. 2, the low-corrosion resistant pipe material 1 and the high-corrosion resistant pipe material 2 are directly screwed and connected without using a coupling. In the case of the specific example of FIG. 2 as well as the specific example of FIG. 1, over the range of 60 mm from the pipe end excluding the threaded portion 20 and the connection boundaries A, B of the threaded portion 20 on the inner and outer surfaces of the pipe material of the low corrosion resistance tubular material 1. Part (A part in FIG. 9, FIG. 1)
No. 0 is shown by enlarging the B portion), the adhesive insulating coating according to the present invention is formed in 4,5, 21, 22 parts. Further, also in the high corrosion resistance pipe material 2, as in the low corrosion resistance pipe material 1, the threaded portion 20 is formed on the inner and outer surfaces of the pipe material.
The adhesive insulating coating is formed at the portions 8, 9, 25, and 26 over the range of 60 mm or more from the pipe end portion except for and the connection boundaries A and B of the screw portion 20.

In the case of the concrete example of FIG. 2 as well as in FIG. 1, both the low corrosion resistant pipe material 1 and the high corrosion resistant pipe material 2, that is, the adhesive insulating coatings have the reference numerals 4, 5, 8, 9, 21, 21, 22. Two
Although it is formed in 5, 26 parts, from the viewpoint of preventing electrolytic corrosion, it is possible to form only 8, 9 parts on the highly corrosion resistant pipe material 2 side.

The surface on which the adhesive insulating coating is applied is the same as in 2 above.
In the case of one specific example, both the inner and outer surfaces of the pipe materials 1 and 2 are used, but it is not always necessary to apply it to both the inner and outer surfaces, and at least the surface exposed to the corrosive environment in the oil well is sufficient. Specifically, both inner and outer surfaces can be used in the case of tubing, and only the inner surface can be used in the case of a casing.

When there is a possibility that the surface of the pipe materials 1 and 2 may be damaged by the suspending and conveying operation using a wire rope, the surface of the adhesive insulating coating is protected by fluorine in order to prevent its peeling or destruction. It is preferable to apply an organic coating of a resin or polypropylene.

On the other hand, in each of the above examples, the formation range L of the adhesive insulating coating is specified to be 60 mm or more with reference to the end of the connecting element, but when forming the film layer with the connecting boundary of the connecting element sandwiched, For example, one connecting element may be formed over a length of 30 mm or more, and the other connecting element may be formed over a length of 30 mm or more, so that the total length range may be 60 mm or more. Therefore, the present invention also includes this example.

However, in each of the above-mentioned examples, in consideration of the fact that electric corrosion and crevice corrosion overlap at the place where a gap is formed when they are connected, they are exposed to the minimum corrosive environment.
It is necessary to form the adhesive insulating coating in the gaps 21 to 26 in 10 to 10. In addition, when forming the adhesive insulating coating on 4 to 9 parts, it is needless to say that when the adhesive insulating coating is formed with the connecting boundary interposed, it is desirable that both film layers be continuous as much as possible. Yes. Therefore, as shown in FIG. 1 or FIG. 2, when there is a step between the metal pipe materials 1 and 2 and the coupling 3, it is practically necessary to form the adhesive insulating coating on the wall surface of the step. Often.

The reasons for limiting the numerical values of the present invention and the effects of the present invention will be clarified by showing examples below. (Example 1) In the electrolytic corrosion test, assuming the connection structure of the example of FIG. 1, between the low corrosion resistance material 10 having a bare upper surface and the high corrosion resistance material 11 having a bare upper surface, as shown in FIG. The joint material 12 provided with the adhesive insulating coating 13 was connected in series, and each part was connected with a bolt 14 to examine the electrolytic corrosion condition. Both L _{1 and} L _{3 were} 100 mm, and the side surface and the back surface of each member were coated with fluorine. On the other hand, in the crevice corrosion test, as shown in FIG.
A plate-shaped low-corrosion-resistant material 10 and high-corrosion-resistant material 11 having a thickness of 30 mm × 30 mm and a thickness of 3 mm is provided with an adhesive insulating coating 13, and the adhesive insulating coatings 13 of both are laminated to face each other and bolted. It fastened by 14 and used for the test.

Further, in the peeling resistance test, the joint material 1
A tensile test piece having the shape shown in FIG. The test piece has a total length L ₄ : 120 mm, an intermediate small diameter portion length L ₅ : 50 mm, large diameter portions at both ends of φ ₁ ; 20 mm, and an intermediate small diameter portion of φ ₂ : 10 ± 0.05 mm. Then, the adhesive insulating coating was formed on the entire test piece, a tensile strain of 0.3% was applied, and the test piece was subjected to a corrosion test to examine the presence or absence of peeling.

Low corrosion resistance material 10 used in the above test
As the material, medium carbon steel for API-L80 grade was used. On the other hand, as the high corrosion resistance material 11, UNSNO.S31803 (two-phase stainless steel) was used. Further, as the joint material 12, UNSNO.S3 is used.
1803 was used with an adhesive insulating coating.

As the adhesive insulating coating, as shown in Table 1, after coating the above-mentioned stress relaxation coating on the underlayer, amorphous Al ₂ O ₃ , Si ₃ N ₄ , Ta ₂ O ₅ , SiO ₂ , ZrO ₂ was coated by the ion plating method or the plasma CVD method. The coating conditions are also shown in Table 1.

[0049]

[Table 1]

Next, crystallization treatment was carried out by heating only the surface layer of each amorphous layer with a gas burner. At this time, as a comparative material, an amorphous single coating material not subjected to crystallization treatment and a material obtained by coating the surface of the crystalline single coating material with a fluorine resin were also tested.

As the corrosive environment in the electrolytic corrosion, corrosion and peeling resistance test, carbon dioxide gas environment: 1 atm CO ₂ and hydrogen sulfide gas environment: 1 atm H ₂ S were used, the temperature was 60 ° C., the solution was 5% NaCl, The test time was 720 hours. The length L ₂ of the joint material 12 having the adhesive insulating coating 13 is set to 60 mm,
The corrosion rate, the presence or absence of crevice corrosion, and the film thickness after the test were examined. Table 2 shows the above test results.

[0052]

[Table 2]

[0053]

[Table 3]

As can be seen from Table 2, in Test Nos. 1 to 3 which are examples of the present invention, peeling occurred due to tensile strain, but the electrolytic corrosion preventing effect and the crevice corrosion preventing effect were sufficiently observed. Further, it was found that Nos. 4 to 9 had good corrosion resistance.

On the other hand, in Test Nos. 10 to 14 as comparative examples, good electrolytic corrosion preventing effect and crevice corrosion preventing effect were recognized, but elution of the coating film itself was confirmed. Further, Comparative Examples No. 15 to 20 did not show a sufficient electrolytic corrosion preventing effect.

[0056]

As described above, according to the present invention, it is possible to prevent electrolytic corrosion that occurs when connecting dissimilar metal pipe joints in oil wells and the like, and to obtain one having both excellent adhesion to metal pipe materials and corrosion resistance. .

[Brief description of drawings]

FIG. 1 is a view showing a coupling portion of an oil country tubular good and a coupling which are subjected to electrolytic corrosion prevention according to the present invention.

FIG. 2 is a view showing a connecting portion of an oil country tubular good having electrolytic corrosion prevention according to the present invention.

FIG. 3 is a view showing a specimen for a corrosion resistance test in Example 1.

FIG. 4 is a diagram showing a specimen for a crevice corrosion test in Example 1.

FIG. 5 is a view showing a specimen for a peel resistance test in Example 1.

FIG. 6 is a view showing a specimen for a hydrogen embrittlement test in Example 2.

FIG. 7 is an enlarged view of a portion A in FIG.

FIG. 8 is an enlarged view of portion B in FIG.

FIG. 9 is an enlarged view of a portion A in FIG.

FIG. 10 is an enlarged view of portion B in FIG.

[Explanation of symbols]

1 ... Low corrosion resistance pipe material, 2 ... High corrosion resistance pipe material, 3 ... Coupling, 4-9 ... Insulating film, 10 ... Low corrosion resistance material, 11 ...
High corrosion resistance material, 12 ... Joint material.

Claims (3)

[Claims] 1. A metal pipe material having a screw thread portion for connection formed on a pipe end portion: an inner surface end of the metal pipe material excluding the screw thread portion on at least one of an inner surface and an outer surface exposed when the pipe material is connected. Alternatively, at least one of a region extending from the outer surface end to a range of 60 mm or more and the screwed screw portion region where a gap is formed when connected is covered with an amorphous insulating ceramic layer whose outermost layer is crystalline. Insulation pipe material with excellent corrosion resistance for preventing electrolytic corrosion. 2. The insulating ceramic layer has a specific resistance of 10 ⁸
Ωcm or more, thickness 0.4 μm or more, coverage rate 90%
The insulating tubing for preventing electrolytic corrosion, which is excellent in corrosion resistance, according to claim 1, which is coated with 100% or more and less than 100%. 3. A single layer or a composite layer of a metal or its oxide, nitride or carbide having an expansion coefficient intermediate between that of the insulating ceramic layer and the pipe material is provided between the insulating ceramic layer and the insulating ceramic layer. Alternatively, the metal pipe material for preventing electrolytic corrosion having excellent corrosion resistance according to claim 2.