JP3146689B2 - Insulation tubing for preventing electrolytic corrosion with excellent coating adhesion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pipes of general pipes, especially oil well pipes, which prevents electric corrosion and crevice corrosion which occur when connecting pipes of different metals, and reduces the adhesiveness of the film material to be coated. The present invention relates to an improved insulating tubing for preventing electrolytic corrosion.

[0002]

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

[0003] In oil wells, these metal pipes for oil wells are plumbed several thousand meters underground at an angle perpendicular or nearly perpendicular to the surface of the ground for the extraction and production of crude oil and natural gas. In the present specification, all of these pipes are referred to as oil country tubular goods.

[0004] Generally, in an oil well, corrosiveness is high in a deep place due to high temperature, and conversely, it is low in a shallow place because the temperature is low. Therefore, in consideration of economy, the deep part of the well is made of, for example, various kinds of stainless steel, N
In many cases, a highly corrosion-resistant metal tube such as an i-base alloy, Ti, or a Ti alloy is used, and a low-corrosion-resistant metal tube such as carbon steel or a low-alloy metal is used in a shallow portion.

[0005] Therefore, a connection portion between the low-corrosion-resistant metal tube and the high-corrosion-resistant metal tube naturally occurs, but when the corrosion-resistant metal tube and the high-corrosion-resistant metal tube are simply connected, a potential difference is generated due to contact between different kinds of metal materials. Galvanic corrosion (electrolytic corrosion) occurs. Due to this galvanic corrosion, the corrosion proceeds on the low corrosion resistant metal pipe side at a rate of 2 to 10 times as fast as the corrosion of ordinary carbon steel pipe alone. On the other hand, hydrogen was generated on the high corrosion-resistant metal tube side, and this hydrogen entered into the inside to cause hydrogen embrittlement. Furthermore, crevice corrosion occurs in the gap between the joints, and the corrosion is promoted by electric corrosion.

In response to these problems, at present,
Do not directly connect the low-corrosion-resistant metal tube and the high-corrosion-resistant metal tube, and try to prevent corrosion by interposing a metal tube such as duplex stainless steel whose corrosion resistance is between the low-corrosion-resistant metal tube and the high-corrosion-resistant metal tube. I have. However, even when an intermediate metal pipe is interposed, it is impossible to completely prevent electrolytic corrosion and crevice corrosion between members, and the corrosion rate is only slightly reduced.

[0007] On the other hand, it is practically impossible to completely seal and seal the pipe members when they are connected to each other by the threaded joint structure. Inevitably, there is a gap open in a corrosive environment. Becomes If the above gap exists in the threaded joint structure, since there is almost no flow of liquid in this gap, hydrogen ions and the like generated by corrosion of metals such as iron easily accumulate at a high concentration, and the pH is extremely lowered, More severe corrosion occurs than the base metal. In other words, crevice corrosion occurs even under an environment that is weaker than the corrosion environment of the base material. When this crevice corrosion occurs, there is a danger of developing into stress corrosion cracking, and erosion of the seal surface results in impairing the sealability, which is an important function as a joint.

In order to solve the above problem, for example, Japanese Patent Application Laid-Open No. Hei 1-1199088 discloses a non-metallic layer of 1 to 100 μm in a threaded joint portion of an oil country tubular good of the same material containing 7.5% or more by weight of Cr. A joint that shields from corrosive environment and prevents crevice corrosion by covering the surface is proposed.

[0009]

However, when the non-metal layer is coated according to the technique disclosed in the above publication, the following inconvenience occurs. In other words, considering that the non-metal layer to be covered is divided into a conductor and an insulator, even if it is covered with a conductor,
It is virtually impossible to form a defect-free film without any through-holes, and since a considerable amount of through-holes is usually generated, it is impossible to prevent the corrosion of the film defects from being accelerated. On the other hand, even in the case of coating with an insulating material, crevice corrosion still occurs depending on the coverage of the coating, and in any case, the above gazette technology cannot sufficiently prevent crevice corrosion.

It is considered that the number of through-holes may be reduced by increasing the thickness of the coating in order to reduce such defective coatings. However, an increase in the thickness of the coating causes a decrease in adhesion to the base material, and At the time of fastening, the coating may be peeled off due to shear stress or the like caused by a difference in Young's modulus between the base material and the coating.

[0011] Accordingly, an object of the present invention is to provide an insulating tube for preventing electrolytic corrosion which is excellent in adhesion to the metal tube while preventing electrolytic corrosion and crevice corrosion occurring when connecting different types of metal tubes in an oil well or the like. It is in.

[0012]

SUMMARY OF THE INVENTION The object of the present invention is to form a screw thread for connection at the end of a pipe, and to have a Cr content of 13% by weight or more.
Stainless steel or Ni having a Ni content of 20 wt% or more
In the base alloy pipe material, the screw which forms a gap over a range of 60 mm or more from the inner surface end or outer surface end excluding the screwed screw portion on at least one of the inner surface and the outer surface exposed when the tube material is connected, and when the tube material is connected. After forming a single layer or a composite layer of Cr or its oxides, nitrides, carbides, Ni or its oxides on the combined screw portion, the upper layer has a thickness of 0.4 μm or more and a specific resistance of 10 ⁸ Ωcm or more. Can be achieved by forming the insulating inorganic compound coating of the above at a coverage of 90% or more and less than 100%.
Further, in this case, a synthetic resin film for protecting the insulating inorganic compound film is preferably laminated on the surface of the insulating inorganic compound film.

Here, Cr or its oxide, nitride, carbide, Ni used as a lower layer of the insulating film is used.
Alternatively, the oxide thereof may have a content of Cr of 13% or more and Ni
The present inventors have found that since the content is similar to the composition of the stainless steel or the Ni-based alloy tube or the surface coating of 20% or more, it can contribute to the improvement of mutual adhesion.

Therefore, the present inventors have found that by forming this layer between the above-mentioned tube material and the insulating film, the layer has excellent resistance to peeling under stress in an oil well environment. Further, the Cr or its oxide, nitride, and carbide layers may be multi-layered or different metal compound layers may be composited (in the present invention, these multi-layers and composites are collectively referred to as composite layers). It has been found that it has excellent resistance to delamination under stress in an oil well environment of equal or higher level.

The insulating film has a specific resistance of 10 ^8.
Ωcm or more _{Al 2 O 3, Si 3 N} 4, Ta 2 O 5, SiO 2, AlN, assumes the BN, be determined in accordance with the environment used in the film type selection to be used desirable.

The total film thickness of the Cr or its oxide, nitride, carbide, Ni or its oxide layer and the insulating inorganic compound film is desirably 100 μm or less. If the total thickness exceeds 100 μm, the dimensional accuracy of the threaded portion and the seal portion may be adversely affected, and peeling due to internal stress of the film may be caused. The Cr or its oxide, nitride, carbide, Ni or its oxide is intended to improve the adhesion between the tube and the insulating inorganic compound film, and is thinner than the insulating inorganic compound film. Is desired. The preferred total thickness of Cr or its oxide, nitride, carbide, Ni or its oxide layer is
The range is from 0.1 μm to 5 μm. Thickness 0.1μm
If it is less than 5, the effect is hardly obtained, and if it exceeds 5 μm, the effect is almost lost.

On the other hand, the coverage is determined by an electrochemical method. That is, in a liquid in which only the base material can be dissolved, the current is monitored by constant potential polarization, and the coverage (%) = [(current density of base material without coating) − (base material with coating) Current density)] / (current density without coating)
× 100.

In the present invention, the pipe is not limited to an oil well pipe, and may be applied to a case where different kinds of metals are connected in, for example, a pipeline for transporting seawater and soil, a pipeline for a plant, and the like.

[0019]

[Action] Galvanic corrosion that occurs when dissimilar metals come into contact is as follows.
This is because the reaction on the anode side is promoted by using a readily corrosive metal 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 necessary to cover the insulating inorganic compound film between different metals and increase the inter-liquid resistance by increasing the distance between them to prevent corrosion current from flowing. The present inventors have found that this is good, and have confirmed that this embodiment is actually effective.
Here, the specific resistance of the insulating inorganic compound used in the present invention is 1
0 ⁸ [Omega] cm to define the above, the generally complete insulation is obtained, a case specific resistance of more than 10 ⁸ [Omega] cm, when the specific resistance is less than 10 ⁸ [Omega] cm becomes semiconductive, this In the case of a semiconductive film, as in the case of a conductive film,
This is because there is an extremely high risk of electrolytic corrosion occurring with the low corrosion resistant pipe. The presence or absence of the electrolytic corrosion prevention effect is determined by the coverage of the insulating inorganic compound film and the size of the coating region. This will be clarified by the following examples. Further, the reason why the coverage is set to less than 100% is that pinhole defects (defects of the film penetrating to the base material) at present.
This is because it is known that it is difficult to coat a film having no particles.

On the other hand, crevice corrosion is a phenomenon in which metal ions, hydrogen ions, chlorine ions, and the like generated by corrosion accumulate in gaps, causing a significant drop in pH and significant corrosion. Normally, the oil country tubular goods are connected using a threaded joint, but there are gaps as shown at the connection boundaries A and B between the inner surface and the outer surface of the threaded portion 20 in FIGS. 1 and 2, where crevice corrosion occurs. . Furthermore, this crevice corrosion is promoted by electrolytic corrosion.

The present inventors have found that crevice corrosion can be prevented by coating the gap with an insulating film, and have confirmed that this embodiment is actually effective. Further, when the electrolytic corrosion and crevice corrosion are prevented by the above means, the intrusion of hydrogen on the high corrosion resistant tube side is suppressed, which is also effective in preventing hydrogen embrittlement.

Further, an insulating inorganic compound film used in the above-described method for preventing electrolytic corrosion and crevice corrosion, and a Cr content of 1
By forming a single layer or a composite layer of Cr or its oxides, nitrides, carbides, Ni or its oxides between stainless steel or Ni-based alloy tubing having a Ni content of 3 wt% or more and a Ni content of 20 wt% or more, It is effective for improving the peeling resistance of the insulating inorganic compound film in an oil well environment under stress.

The Cr or its oxide, nitride, carbide, Ni or its oxide layer formed in the lower layer,
Al ₂ O ₃ formed on the upper _{layer, Si 3 N 4, Ta 2} O 5, SiO 2, AlN, the method for forming a BN insulator layer, oxidation using an ion (plasma), nitriding, carburizing, Ion plating, sputtering, plasma CVD, thermal CVD, MO (MetalOrg)
anic)-A method such as CVD or thermal spraying is adopted, and a method suitable for the substance may be appropriately selected. However, among the oxide, nitride, and carbide layers of Cr formed in the lower layer, the oxidation, nitridation, and carburization treatments using ions (plasma) have a Cr content of 13 wt% and a Ni content of 20 wt% or more. This is an effective method for improving adhesion since Cr diffusion from stainless steel or Ni-based alloy occurs preferentially and a diffusion layer composed of an oxide, nitride or carburized layer of Cr is formed.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific example in which the present invention is mainly applied to an oil country tubular good will be described in detail. FIGS. 1 and 2 are views showing a connecting portion of an oil country tubular good coated with an insulating coating according to the present invention, more specifically, an insulating inorganic compound coating. FIG. 1 shows the case of a coupling type using a coupling, and FIG. 2 shows the case of a direct coupling type.

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

In this specific example, the low corrosion resistant tubing 1
60 mm from the pipe end except for the thread 20 on the inner and outer surfaces of the pipe material
mm or more (the range indicated by the symbol L, the same applies hereinafter), and the connection boundaries A and B of the screw portion 20 (A portion in FIG. 7 and B portion in FIG. 8 are schematically enlarged). On the other hand, a lower layer according to the present invention comprises a Cr layer or a layer composed of oxides, nitrides, carbides, Ni or oxides thereof, and a layer composed of an insulating inorganic compound film laminated on the upper layer (hereinafter referred to as the The multilayer film is referred to as an adhesive insulating film) at 4, 5, 21, and 22 parts. In the coupling 3, the adhesive insulating coatings are denoted by reference numerals 6, 7, 2 over the entire area including the A and B portions of the threaded portion 20 on the inner and outer surfaces of the tube.
3, 24 parts.

On the other hand, in the high corrosion resistant tubing 2 as well, similarly to the low corrosion resistant tubing 1, the screw portion 2 is formed on the inner and outer surfaces of the tube.
The adhesive insulating coating according to the present invention is formed on portions 8, 9, 21, and 22 of the connection boundaries A and B of the screw portion 20 over a range of 60 mm or more from the pipe end excluding 0. ing.

In the case of the above-mentioned specific example, the adhesive insulating coatings were formed on all of the low-corrosion-resistant tubing 1, the high-corrosion-resistant tubing 2 and the coupling 3 in 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-resistant tubing 1, the high-corrosion-resistant tubing 2, and the coupling 3. It is desirable to form it in 6 or 7 parts. In short, the application site 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 tube 1 and the high corrosion resistant tube 2 are directly screwed together without using a coupling. In the case of the specific example of FIG. 2 as well as the specific example of FIG. Portion (portion A in FIG. 9, FIG. 1
(Part B is schematically enlarged to 0), and the adhesive insulating coating according to the present invention is formed in 4, 5, 21 and 22 parts. Also, in the high corrosion resistant tubing 2, similarly to the low corrosion resistant tubing 1, the screw portion 20 is formed on the inner and outer surfaces of the tube.
The adhesive insulating coatings are formed at portions 8, 9, 25, and 26 over a range of 60 mm or more from the end of the pipe except for the portion along the connection boundaries A and B of the screw portion 20.

In the specific example of FIG. 2, as in FIG. 1, the low-corrosion-resistant tube 1 and the high-corrosion-resistant tube 2 are coated with the adhesive insulating coatings 4, 5, 8, 9, 21, 22, and 22, respectively. 2
Although formed in 5, 26 parts, from the viewpoint of preventing electrolytic corrosion, it is also possible to use only 8, 9 parts on the high corrosion resistant tube 2 side. In FIGS. 1 and 2, when the above-mentioned adhesive insulating film is formed also in four parts, the underlying Cr or its oxide, nitride, carbide, Ni or its oxide layer is a conductive film. In some cases, there is a fear that electrolytic corrosion will occur between this film and the low corrosion resistant tubing 1. In that case, the covering region of the upper insulating film may be longer than the lower layer.

Further, the surface on which the adhesive insulating film is to be provided
In the case of one specific example, both the inner and outer surfaces of the pipe materials 1 and 2 are used. However, it is not always necessary to apply both to the inner and outer surfaces, and at least the surface exposed to the corrosive environment in the oil well may be used. Specifically, in the case of tubing, both inner and outer surfaces can be used, and in the case of a casing, only the inner surface can be used.

When there is a possibility that the surfaces of the tubular members 1 and 2 may be damaged by the hanging and transporting operation using a wire rope, the surface of the insulating inorganic compound film is prevented from being peeled or broken. It is preferable to apply an organic coating such as a fluorine resin or a polypropylene resin.

On the other hand, in each of the above examples, the forming range L of the adhesive film is defined as 60 mm or more based on the end of the connecting element. However, when the film layer is formed across the connecting boundary of the connecting element, for example, Over a length of 30 mm or more for one connecting element, 30 mm for the other connecting element
It may be formed over the above length, and the total length may be 60 mm or more.

However, in each of the above-mentioned examples, considering that the electrolytic corrosion and the crevice corrosion are superimposed at the places where the gaps are formed when they are connected, FIG.
It is necessary to form the above-mentioned adhesive insulating coating in the gaps 21 to 26 in the range from 10 to 10. In forming the adhesive insulating coating in 4 to 9 parts, it is needless to say that when the adhesive insulating coating is formed across the connection boundary, it is desirable that both film layers be as continuous as possible. No. Therefore, as shown in FIG. 1 or FIG. 2, when there is a step between the metal pipes 1 and 2 and the coupling 3, it is practically essential to form the adhesive insulating film 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 with reference to the following examples. (Embodiment 1) In the electrolytic corrosion test, assuming the connection structure of the example of FIG. 1, as shown in FIG. 3, between the low-corrosion-resistant material 10 having a bare upper surface and the high-corrosion-resistant material 11 having a bare upper surface as shown in FIG. The joining material 12 provided with the adhesive insulating coating 13 was connected in series, and the respective parts were connected with bolts 14 to examine the state of electrolytic corrosion. Incidentally, the L _1, L ₃ both 100 mm, sides and back of each member to form a fluorine coating. On the other hand, in the crevice corrosion test, as shown in FIG.
A 30 mm × 30 mm, 3 mm-thick plate-shaped low corrosion-resistant material 10 and a high corrosion-resistant material 11 each having an adhesive insulating film 13 formed thereon, and the two adhesive insulating films 13 are laminated with the adhesive insulating films 13 facing each other. No. 14 was used for the test.

In the peeling resistance test, the joint material 1
A tensile test piece having the shape shown in FIG. The test strip has an overall length L _4: 120 mm, intermediate diameter Director L _5: 50 mm, the large-diameter portion is phi ₁ at both ends; at 20 mm, ₂ small diameter portion of the intermediate phi: a 10 ± 0.05 mm. And
The adhesive insulating film was formed on the entire test piece,
% Tensile strain was applied and subjected to a corrosion test to examine the presence or absence of peeling.

The low corrosion resistant material 10 used in the above test
The medium carbon steel for API-L80 grade was used. On the other hand, as the high corrosion resistance material 11, UNSNO.N08825 (22Cr-42Ni-3M
o) and UNSNO.N10276 (16Cr-56Ni-16Mo)
One having an adhesive insulating film was used. Also, as the joining material 12, UNSNO.N08825 (22Cr-42Ni-3Mo) and UNSNO.
Two types of N10276 (16Cr-56Ni-16Mo) were used, which were provided with an adhesive insulating coating.

Cr, Cr ₂ O ₃ , Cr
N, Cr ₇ C ₃ , Ni, NiO is coated on the upper insulating inorganic compound coating layer 1
The 3, specific resistance 10 ⁸ [Omega] cm or more _{Al 2 O 3, Si 3 N} 4, Ta
₂ O ₅ , SiO ₂ , AlN, BN were used. For comparison, semiconductive TiO ₂ having a specific resistance of 10 ⁷ Ωcm was also used. Here, CrN is nitriding treatment using ions, Cr ₇ C ₃ is carburizing treatment using ions, Al ₂ O ₃ , Ta ₂ O _5, TiO ₂ is a sputtering method, and Si ₃ N ₄ , BN is a plasma CVD method. , Cr, Cr ₂ O ₃ , Ni, NiO, Si
O ₂ and AlN were formed by using an ion plating method. Further, for protecting the insulating inorganic compound coating layer, a similar test was performed on a layer in which a fluorine-based resin was laminated thereon.

[0039] The electrolytic corrosion, the corrosive environment in the crevice corrosion and peeling resistance test, carbon dioxide gas environment: 1 atm CO ₂ and hydrogen sulfide gas environment: with 1 atm H ₂ S, the temperature 60
C, the solution was 5% -NaCl, and the test time was 720 hours. The adhesion insulation 50mm length L ₂ of the joint member 12 having been subjected to coating 13 or in place of the 60mm measured coverage, the corrosion rate and the gap existence requires the coating thickness from the environment, the length, the coating The rate was determined.

Further, in order to examine the erosion / corrosion properties of the insulating inorganic compound film 13, 5
% -NaCl boiling solution in a 5 mm radius hemisphere
It was continuously rubbed at a rate of 5 times / min with a force of g / mm ² for 24 hours, and the presence or absence of peeling was examined. At this time,
The laminating effect of the fluororesin was also examined.

The results of the above tests are shown in Tables 1, 2 and 3.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

As is clear from Tables 1, 2 and 3, out of the 48 test cases, test No. 42-4
In the case of 4,48, the corrosion rate of the low corrosion resistant material 10 is 1.
0 (g / m ² ) / h, which resulted in poor corrosion resistance. On the other hand, the specific resistance was 10 ⁸ Ωcm or more, the insulating inorganic compound coating film thickness was 0.4 μm or more, and the insulating inorganic compound coating length was 60 m.
test N with a coverage of 90% or more and 99.999% or less
o. In the case of Nos. 1 to 41 and 45, it was found that the corrosion rate was low, electric corrosion and crevice corrosion were prevented, and peeling resistance was good.

No. It was confirmed that the case where the fluorine-based resin was applied was particularly effective in preventing peeling and the like, as compared with the case where the organic film was not formed.

Further, when the thickness of the lower layer film was out of the range of 0.1 to 5 μm, In 46 and 47, only the peeling was observed.

(Example 2) Next, results of a test on hydrogen embrittlement will be described. A test was performed using a steel material having the shape shown in FIG. Among them, medium carbon steel for API-L80 grade was used as the low corrosion resistant material 10. On the other hand, UNSNO.N10276 (16Cr-56Ni-16Mo) was used as the high corrosion resistance material 11. In addition, UNSNO.10276 (16Cr-56N
i-16Mo), and the underlying film is a 0.5 μm thick Ni
And 5 μm of Al ₂ O ₃ , Si ₃ N ₄ , Ta ₂ O ₅ , SiO ₂ , AlN, B
The one with the N coating 13 was used.

The dimensions of the test piece were such that the low-corrosion-resistant material 10 was a plate-shaped band having a width of 10 mm and a length of 100 mm, while the high-corrosion-resistant material 11 was formed of a width of 100 mm and a length of 100 mm by hydrogen erosion effectively. What was bent in a U-shape was used in order to perform it. The joining material 12 has a width of 10 mm
And the length is 40 mm, 60 mm, 80 mm
3 types were prepared. At the time of connection, the low-corrosion-resistant material 10 and the joining material 12 are fixed with bolts 14, while the joining material 12 and the high-corrosion-resistant material 11 are fixed in series with long bolts 15, and the long bolts 15 are connected with high-corrosion resistance. By penetrating through a through hole formed at the other end of the material 11 and tightening with a nut 16, the separation distance at the U-shaped tip portion was narrowed by 5 mm to apply a restraining stress.

The coverage was 90% or more for the joint material 12 of any length. The brittleness due to hydrogen generated on the cathode side (high corrosion resistant material side) is most absorbed at room temperature and the sensitivity is high.
2 were performed.

<Step 1> Carbon dioxide gas environment (1 atm CO ₂ )
, The temperature was 150 ° C, the solution was 5% -NaCl, and the test time was 720 hours.

<Step 2> Carbon dioxide gas environment (1 atm CO ₂ )
, The temperature was 25 ° C, the solution was 5% -NaCl, and the test time was 720 hours.

With respect to the test material having passed through the above steps 1 and 2, the presence or absence of cracks in the U-bend portion was examined. Table 4 shows the results.

[0054]

[Table 4]

As is apparent from Table 4, the length of the joining material 12 (the length of the insulating coating) is 60 mm or more and 80 mm or more.
mm (Case Nos. 2 and 3), it was found that cracks did not occur and the generation of hydrogen on the high corrosion resistant material 11 side was suppressed.

[0056]

As is evident from the above description, according to the present invention, in an oil well or the like, electric corrosion and crevice corrosion that occur when connecting dissimilar intermetallic materials can be reliably prevented, and even under stress. It is possible to obtain a metal pipe material having good peelability.

[Brief description of the drawings]

FIG. 1 is a view showing a connection part of an oil country tubular good and a coupling in which electrolytic corrosion prevention is performed according to the present invention.

FIG. 2 is a diagram showing a connecting portion of an oil country tubular good according to the present invention, in which electrolytic corrosion prevention is performed.

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

FIG. 4 is a view 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 a portion B in FIG. 1;

FIG. 9 is an enlarged view of a portion A in FIG. 2;

FIG. 10 is an enlarged view of a portion B in FIG. 2;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Low corrosion resistant tubing, 2 ... High corrosion resistant tubing, 3 ... Coupling, 4-9 ... Insulating coating, 10 ... Low corrosion resistant material, 11 ...
High corrosion resistance material, 12 ... joint material, insulating coating.

Continuation of the front page (56) References JP-A-1-199088 (JP, A) JP-A-5-149486 (JP, A) JP-A-60-205091 (JP, A) JP-A-60-121385 (JP, A) , A) JP-A-1-147081 (JP, A) JP-A-53-45362 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23F 15/00 C23C 28/00 F16L 15/04

Claims (2)

(57) [Claims] 1. A threaded screw portion for connection is formed at a pipe end,
In a stainless steel or Ni-based alloy tube material having a Cr content of 13 wt% or more and a Ni content of 20 wt% or more, an inner surface end excluding the screwed screw portion on at least one of an inner surface and an outer surface exposed when the tube material is connected. Alternatively, over a range of 60 mm or more from the outer surface end, and in the screwing screw portion where a gap occurs when connected, Cr
Alternatively, after forming a single layer or a composite layer of oxide, nitride, carbide, Ni or its oxide, an insulating inorganic compound film having a thickness of 0.4 μm or more and a specific resistance of 10 ⁸ Ωcm or more. Is formed at a coverage of 90% or more and less than 100%. 2. The insulating tubing according to claim 1, wherein a synthetic resin film for protecting the insulating inorganic compound film is laminated on the surface of the insulating inorganic compound film.