JPH07127770A - High alloy fitting excellent in protection against corrosion, wear resistance and seizure resistance - Google Patents

Abstract

PURPOSE:To restrain occurrence of crevice corrosion, and to improve wear resistance and seisure resistance by coating the pipe end part which includes a seal surface of a fitting and is exposed to corrosive environment with an alloy layer of a specified thickness, which contains a specified quantity of Cr and Mo. CONSTITUTION:A fitting, for example, a coupling 2 where a box part 4 is formed puts a pipe 1 where a pin part 3 is formed in the connecting state. A coupling base material for forming the pipe 1 and the coupling 2 at least contains 7.5wt% or more Cr. In this case, an alloy layer 0.1-5mum thick is formed on a part including a seal surface of a fitting, which is exposed to a corrosive environment, the is, a coating part 10. That is, the alloy layer contains Cr more than Cr content of the coupling base material by 1-10%, and contains Mo more than Mo content of the coupling base material by 0.3-3%. Thus, the occurrence of crevice corrosion is restrained, and wear resistance and seizure resistance are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a pipe joint for oil well pipes used for the production of crude oil and natural gas, in which the occurrence of crevice corrosion is suppressed and, in addition, the wear resistance and seizure resistance are improved. The present invention relates to an excellent high alloy pipe joint.

[0002]

2. Description of the Related Art Recently, with the decrease of crude oil and natural gas resources, in wells for collecting and producing crude oil and natural gas (hereinafter referred to as "oil wells"), oil well pipes are perpendicular to the surface of the ground. Or, it is piped at an angle close to vertical and extending several thousand meters underground.

In these wells, tubing for transporting crude oil and natural gas from an underground production layer to the ground, a casing provided around the tubing to protect a dug well, and the pressure of the oil layer are increased. Pipe materials such as steam injection pipes and CO ₂ pipes for secondary oil recovery are installed to improve the efficiency of extraction. Hereinafter, in the present specification, these pipe materials are collectively referred to as “oil well pipe”. Usage conditions are taken into consideration when selecting the steel type for oil country tubular goods. Generally, in deep oil wells, the operating temperature is high and the environment is highly corrosive,
The operating temperature is low and the corrosivity is low in shallow areas. Therefore, when using it in a deep oil well, select a high corrosion resistant pipe material such as duplex stainless steel, Ni-based alloy and Ti and Ti alloy. When using it in a shallow oil well, for example, carbon steel etc. Low corrosion resistant pipes are often selected and used.

As a technique for connecting oil country tubular goods, a pipe material having a screw joint structure is widely used. However, when the oil country tubular goods are connected to each other by the screw joint, there is a gap at the tip of the joint due to the joint structure. Therefore, there arises a problem that so-called crevice corrosion occurs. That is,
In the gap of this joint, the flow of the solution with the outside is hindered, and the metal ions eluted from the joint metal and the Cl ⁻ ions in the solution concentrate and react, so that the pH inside the gap
Is decreased, the passivation film on the joint metal part is broken, and corrosion occurs and grows.

When crevice corrosion occurs, there is a risk of developing stress corrosion cracking, and by eroding the sealing surface that constitutes the metal seal of the joint, the sealability which is an important function required for the joint is improved. It will damage.
As a measure to prevent this crevice corrosion, it has been proposed to coat the threaded joint portion of the oil country tubular good with a non-metallic layer of carbide and nitride of 1 to 100 μm (JP-A-1-199088).
(See the official gazette). By coating with a non-metal layer, the threaded joint is shielded from the corrosive environment and crevice corrosion is attempted to be suppressed.

[0006] The threaded joint has a problem that measures must be taken in addition to the measures for preventing crevice corrosion. For example,
Since crude oil flows at a high-speed flow of over 10 m / s on the inner surface of the oil country tubular goods, uneven flow occurs in the flow of crude oil in the clearance created in the threaded joint, causing erosion wear in the clearance of the fitting, especially at the edges. Occurs. When this erosion wear occurs, the sealability of the joint is impaired by eroding the seal surface. As a countermeasure against such erosion damage, thermal spraying of a high hardness coating containing carbide ceramics is generally performed.

When the oil country tubular goods are connected to each other by the screw joint structure, a metal seal is formed, so that the screw portion and the metal seal portion of the joint are required to have a high degree of airtightness. Therefore, at the time of connection, a high surface pressure must be applied to the screw portion and the metal seal portion, and seizure or peeling of the metal seal portion cannot be avoided during repeated use.
As a countermeasure against these problems, it has been conventionally known to apply a surface treatment to the metal seal portion of the oil country tubular goods joint. That is, in the joint of carbon steel or Cr-Mo steel, the surface of the metal seal portion is subjected to chemical conversion treatment by phosphate treatment or oxalic acid treatment, and the chemical conversion treatment film obtained relaxes the contact of the metal seal portion. . However, in a joint in which the base material is high Cr steel, the reactivity of the chemical conversion treatment becomes poor, and therefore sufficient film formation cannot be obtained by the phosphate treatment or oxalic acid treatment. Therefore, in high Cr steel joints, a metal or Zn or Cu coating that is a soft metal is formed on the metal seal by electroplating to prevent contact with similar metals and prevent seizure or peeling. .

[0008]

The above-mentioned measures have been taken against crevice corrosion, erosion wear and seizure which occur in threaded joints for oil country tubular goods, but these measures also have the following problems. Yes, it cannot be said that the measures are applied effectively.

Even with a joint in which crevice corrosion is suppressed by coating with a non-metal layer (a joint proposed by JP-A-1-199088), it is practically impossible to form a defect-free coating film having no through holes. Therefore, there are usually a large number of through holes. Corrosion cannot be completely prevented at a film defect portion having such a through hole. Therefore, the technique proposed in the above publication cannot be a sufficient countermeasure against crevice corrosion.

If crevice corrosion is caused by film defects, it is considered that crevice corrosion can be suppressed by increasing the thickness of the film to reduce the number of through holes in order to reduce such film defects. However, increasing the thickness of the coating leads to a decrease in adhesion to the base material, and when the joint is connected, due to shear stress due to the difference in Young's modulus between the base material and the coating, cracks may occur in the coating, The coating may peel off.

The sprayed coating, which is taken as a measure against erosion wear, necessarily contains pores in the coating, and therefore there is a problem that sufficient adhesion to the base material cannot be ensured. Furthermore, in order to form the sprayed coating uniformly on the surface of the base material, a coating having a thickness of at least 100 μm or more is required. However, if such a thick sprayed coating is formed on the seal portion of the oil country tubular goods joint, the sealing performance of the joint is impaired.

As a measure for preventing seizure, when a Zn or Cu coating is formed on the joint portion of a high alloy oil country tubular good by electroplating, hydrogen (H ₂ ) is generated in the plating solution during the process, Contact between the base metal of the joint and hydrogen is unavoidable. In oil country tubular goods pipe joints that require high strength, hydrogen cracking due to hydrogen intrusion is feared, and dehydrogenation treatment such as baking is necessary to avoid this.

An object of the present invention is to solve the problems of the prior art, suppress the occurrence of crevice corrosion, and provide a high alloy pipe joint excellent in wear resistance and seizure resistance.

[0014]

The present invention provides the following (1)-
The main point is the high alloy pipe joint of (2).

(1) A pipe joint containing 7.5% by weight or more of Cr, in which a pipe end portion exposed to a corrosive environment including a sealing surface has a thickness of 0.1 to 5 μm and Cr is used as a joint base material. 1 to 10% more than the Cr content of
A high alloy pipe joint excellent in corrosion resistance, wear resistance and seizure resistance, characterized by being coated with an alloy layer containing 0.3 to 3% more.

(2) 7.5% or more Cr and 3.0% by weight
A pipe joint containing Ni as described above, in which the pipe end portion exposed to the corrosive environment including the sealing surface has a thickness of 0.1 to 5 μm, and the amount of Cr is 1 to 10% more than the Cr content of the base metal joint. , Mo by 0.3 to 3% more than the Mo content of the joint base metal, and
High alloy pipe joint with excellent corrosion resistance, wear resistance and seizure resistance, which is characterized by coating Ni with an alloy layer containing Ni in the same amount as the joint base material or in an amount up to 5%.

On the surface of the alloy layer described in (1) and (2) above
It is preferable to coat a Cr oxide layer having a thickness of 0.1 to 5 μm, and to coat the surface of the Cr oxide layer with a Ni sulfide layer having a thickness of 0.1 to 5 μm.

[0018]

[Function] The inventors of the present invention have proposed the corrosion generated in the joint for oil country tubular goods,
As a result of earnest studies on the phenomenon of wear and seizure and a method of preventing it, the following new knowledge was obtained.

Coating the surface of the base material of the joint with an alloy layer having a specific composition is extremely effective in preventing crevice corrosion, and can also improve wear resistance and seizure resistance. Furthermore, by forming an oxide layer on the surface of the coated alloy layer, not only corrosion resistance but also wear resistance and seizure resistance are significantly improved, which is preferable for improving the characteristics of the joint.

When the alloy layer to be coated is a conductive and highly corrosion-resistant material, it is necessary to accelerate the corrosion of the base material by galvanic corrosion in the coating defect portion, that is, the portion where the through hole is formed as described above. Become. In this case, in order not to accelerate the corrosion of the base metal, C contained in the base metal and alloy layer
It is necessary to reduce the difference in r, Mo, or Ni content so as not to impair the corrosion resistance.

The present invention has been completed based on the above findings, and will be described below in detail with reference to the drawings.

The pipe joint of the present invention contains Cr among the chemical components of the base metal.
It is essential that the content be 7.5% or more. This is because when the Cr content is less than 7.5%, the passivation film due to Cr is not formed. Further, in the case of containing Ni, in order to stably form NiS that is effective for improving the corrosion resistance in an environment containing H ₂ S, 3.0% or more, to further secure the film stability. Is preferably
The content is 5.0% or more.

1 and 2 are axial sectional views showing two examples of a pipe joint for oil country tubular goods. FIG. 1 shows a pipe 1 in which a pin portion 3 is formed by a coupling 2 in which a box portion 4 is formed.
It is an example of a coupling type joint that connects
(A) is sectional drawing which shows the basic structure, (b) is the figure which expanded the A section of (a) figure, (c) is the figure which expanded the B section of (a) figure.

FIG. 2 shows an example of an ingral type joint in which the pin portion 3 is formed at one end of the pipe 1 and the box portion 4 is formed at the other end to connect the pipes to each other. ) Is a cross-sectional view showing the basic configuration thereof, (b) is an enlarged view of a C portion, and (c) is an enlarged view of a D portion.

The joint base material is a material forming the pipe 1 and the coupling 2 in the example of FIG. 1, and a material forming both pipes 1 and 1 in the example of FIG.

In the pipe joint of the present invention, the portion including the sealing surface which is exposed to the corrosive environment, that is, (b) in both figures,
The coated portion 10 indicated by (c) is coated with an alloy layer having a thickness of 0.1-5 μm. Although the illustrated coated portion 10 is on both the inner and outer surfaces of the pipe joint, it is not necessary to apply it to both inner and outer surfaces, and it may be appropriately selected depending on the severeness of the corrosive environment and the use of the oil country tubular good to be used. For example, in the case of tubing, both the inner and outer surfaces can be coated, and in the case of a casing, only the inner surface can be coated. However, since the inner surface of the tubing is harsh as a corrosive environment, the coating of the alloy layer is essential.

In order to prevent the corrosion of the joint from being promoted, it is necessary to reduce the difference in the content of the components contained in the joint base material and the alloy layer to be coated. It is naturally determined by the material of the material.

When the environment in which the oil country tubular goods are used is a corrosive environment containing CO ₂ , high Cr steel or high Cr-Mo steel is mainly used as the material of the base material. In such an environment, the passivation film made of Cr oxide (Cr ₂ O ₃ ) exhibits good corrosion resistance, and Mo is indispensable for stable formation of the passivation film. The coating of the alloy layer to be contained is required. In this case, if the Cr content of the alloy layer to be coated is less than 1% of the Cr content of the base metal, the effect of improving crevice corrosion is not recognized, so the Cr content of the alloy layer is less than that of the base metal. You have to increase more than%. Further, if the Cr content of the alloy layer exceeds the Cr content of the base metal by more than 10%, galvanic corrosion may occur in a portion coated with the alloy layer and a portion not coated with the alloy layer. For example, when the Cr content of the base material is 10%, the Cr content of the coating alloy layer is 11 to
It is in the range of 20%. On the other hand, if the Mo content in the alloy layer to be coated is less than 0.3% of the Mo content in the base metal, no crevice corrosion improvement effect is observed, and if it exceeds 3%, galvanic corrosion may occur, so the Mo content in the alloy layer may be The content is more than the Mo content of the base metal
It was decided to increase in the range of 0.3 to 3%. Therefore, when the Mo content of the base material is 3.0%, the Cr content of the coating alloy layer is in the range of 3.3 to 6.0%.

When H ₂ S is contained in the environment in which the oil country tubular good is used, the base material is mainly made of high Cr-Ni steel or high Cr steel.
Cr-Ni-Mo steel is used. In such environments, since the passive film made of Cr oxide has no corrosion resistance against H ₂ S, thereby forming a Ni sulfide (NiS) coating that prevents penetration of H ₂ S on the upper layer thereof Becomes essential, Cr, Mo
An alloy layer consisting of Ni and Ni is required to be coated. The Cr and Mo contents of the coated alloy layer are 1 to 10% more than the Cr content of the base metal for the same reason as described above, and the Mo content is 0.3 to more than the Mo content of the base metal. It is necessary to increase by 3%.
On the other hand, if the Ni content of the alloy layer is lower than the Ni content of the base material, the surface of the alloy layer may also be corroded, so the Ni content of the base material should be at least the same. Further, if the Ni content of the alloy layer exceeds 5% of the Ni content of the base metal, galvanic corrosion may occur in the portion coated with the alloy layer and the portion not coated with the alloy layer. Was increased to 5% or less.

The thickness of the alloy layer is set to be 0.1 to 5 μm. This is because when the film thickness is less than 0.1 μm, sufficient effect of preventing crevice corrosion cannot be obtained, and even when the film thickness exceeds 5 μm, the effect of preventing crevice corrosion is almost saturated.

In the joint of the present invention, in order to further improve not only corrosion resistance but also wear resistance and seizure resistance, an oxide layer and further a Ni sulfide layer are formed on the surface of the coated alloy layer. Is desirable. It is naturally on the surface of the alloy layer
The passivation film made of Cr oxide and the Ni sulfide film are extremely thin and easily disappear after repeated screw fastening, but by forming them as independent layers, their life can be extended. Is. In addition, Cr oxide and Ni
Since the sulfide coating itself has extremely high hardness as compared with the pipe base material and the alloy layer, it has excellent erosion resistance and therefore can not only further improve the corrosion resistance, but also between the alloy layers or between the alloy layer and the mother layer. This is because direct contact with the material metal is prevented and seizure is prevented. As a mode of forming an oxide, the surface of the alloy layer is coated with a Cr oxide layer, and the surface of the Cr oxide layer is further coated with a Ni sulfide layer.

The thicknesses of the Cr oxide layer and the Ni sulfide layer were both 0.1 to 5 μm. For both Cr oxide and Ni sulfide, if the layer thickness is less than 0.1 μm, the effect of sufficiently preventing crevice corrosion cannot be obtained, and no improvement in wear resistance and seizure resistance can be observed. This is because the effect of preventing crevice corrosion and the effects of wear resistance and seizure resistance are almost saturated even if the coating exceeds the range.

The method for forming these coating films including the alloy layer is not particularly limited, but examples thereof include ion plating, sputtering, and plasma CVD. A method suitable for the layer to be coated may be appropriately selected. It is also possible to improve the seizure resistance by forming a soft metal such as Zn or Cu on the surface of the Cr oxide layer or the Ni sulfide layer by electroplating. In this case, the Cr on the surface of the alloy layer
Oxide layer and Ni sulfide layer generated in plating solution
The effect of preventing the invasion of H ₂ was also recognized.

[0034]

EXAMPLES The pipe joint of the present invention will be described in detail based on the results of the corrosion test in Example 1 and the wear test and seizure test in Example 2.

(Example 1) Table 1 shows the chemical compositions of steel types A to I of the high alloy oil country tubular goods subjected to the corrosion test.

[0036]

[Table 1]

These oil well pipes are used as the base material on the surface of the pipe.
An alloy layer containing Cr, Ni, and Mo, or a Cr ₂ O ₃ layer as an oxide layer on top of this, or Cr ₂ O ₃ and Ni sulfide (Ni
S) layer was applied. Here, the alloy layer and Cr ₂ O ₃ were formed by sputtering, and the Ni sulfide layer was formed by ion plating. Tables 2 (1) to (3) show the relationship between the steel type of the oil country tubular goods, the composition of the alloy coating layer, and the layer thickness, which are classified into the inventive example and the comparative example.

FIG. 3 is a view showing the structure of the test piece used in the corrosion test. The base material 5 provided with the coated portion 10 was fixed with a gap using bolts 6 to obtain a corrosion test piece. The corrosion test conditions were set assuming the environment in which the high alloy well tubular as the base material is used, and the test time was 720 hours. Corrosion test conditions and results are summarized in Table 2 (1) to (3).

[0039]

[Table 2 (1)]

[0040]

[Table 2 (2)]

[0041]

[Table 2 (3)]

As is clear from the results shown in Table 2, neither crevice corrosion nor galvanic corrosion occurred in any of the examples of the present invention satisfying all the conditions specified in the present invention. In particular, as in Test Nos. 24 to 26, those having a Cr ₂ O ₃ layer or a Cr ₂ O ₃ and Ni sulfide layer formed on the alloy layer have excellent corrosion resistance even in a severe corrosive environment. Was confirmed.

Test Nos. 27 and 3 in which Cr, Mo or Ni of the coating layer in the comparative examples had a lower concentration than the conditions specified in the present invention
Crevice corrosion occurred at 0, 32-34, 37, 39, 40, 42, 44, 47 and 49. On the other hand, test No. 28, 2 in which Cr, Mo or Ni of the coating layer has a higher concentration than the conditions specified in the present invention
Galvanic corrosion occurred at 9, 31, 36, 38, 40, 41, 43, 45, 46, 48 and 50. In Test Nos. 32 and 40 in which the film thickness of the coating layer is thinner than the conditions specified in the present invention, crevice corrosion occurs, and in Test Nos. 35 and 38 in which the film thickness of the coating layer is thicker than the conditions specified in the present invention, The corrosive property is almost saturated, and especially in test No. 38, galvanic corrosion occurs.

(Example 2) In the same manner as in Example 1, the steel types A to I of the high alloy oil country tubular goods shown in Table 1 were used, or the alloy layer containing Cr, Ni and Mo, or the Cr ₂ O ₃ layer or Cr was formed on the alloy layer. ₂ O ₃ and Ni
After applying the sulfide layer, it was subjected to a wear test and a seizure test.

FIG. 4 is a diagram showing a schematic structure of the wear test apparatus. As the abrasion test, an alumina suspension 21 containing alumina having a particle diameter of 200 μm was used, and after increasing the pressure by a pump 23, a blast erosion test was carried out in which the high pressure suspension collided with the abrasion test piece 22. The test conditions were that the concentration of alumina was 100 g / liter, the flow rate was 20 m / s, and the collision angle was 30.
The test time was 2 hours. The wear resistance is evaluated by measuring the erosion thinning depth as the wear amount, calculating the ratio of each wear depth (the erosion depth of the coating material / the erosion depth of the base material), and evaluating from the results. There is.

FIG. 5 is a diagram showing a schematic structure of a seizure test device. In the seizure test, the test piece 32 is heated to 50 ° C.,
The load applied to the indenter 31 is set to 3 kg, and the coated portion of the test piece 10
Was slid for a length of 5 cm, and the number of times the coefficient of friction increased was defined as the number of seizures until seizure occurred. The seizure property (number of seizures of coating material / number of seizures of base material) is calculated and evaluated. The larger this value, the better the seizure resistance.
Here, the indenter 31 was made of the same material as the steel type of the oil country tubular goods as the base material.

The composition, thickness, abrasion test and seizure test results of the coating layer are summarized in Table 3.

[0048]

[Table 3]

It can be seen from Table 3 that the examples of the present invention exhibit better wear resistance and seizure resistance than the comparative examples.

[0050]

According to the present invention, it is possible to provide a pipe joint for oil well pipes in which crevice corrosion is less likely to occur even in a corrosive environment, corrosion resistance is improved, and wear resistance and seizure resistance are also excellent. You can This can significantly extend the life of the pipe joint.

[Brief description of drawings]

FIG. 1 (a) is an axial cross-sectional view showing the basic structure of a coupling type pipe joint, FIG. 1 (b) is an enlarged view of part A thereof, and FIG. 1 (c) is an enlarged view of part B thereof. It is a figure.

FIG. 2A is an axial cross-sectional view showing a basic structure of an Inglel type pipe joint, FIG. 2B is an enlarged view of a C portion thereof, and FIG. 2C is an enlarged view of a D portion thereof. Is.

FIG. 3 is a diagram showing a configuration of a test piece used in a corrosion test.

FIG. 4 is a diagram showing a schematic configuration of a wear test apparatus.

FIG. 5 is a diagram showing a schematic configuration of a seizure test device.

[Explanation of symbols]

1 ... Tube, 2 ... Coupling, 3 ... Pin part, 4 ... Box part, 5 ... Base material 6 ... Bolt, 10 ... Coated part 21 ... Alumina suspension, 22 ... Wear test piece, 23 ... Pump 31 ... Indenter , 32 ... Seizure test piece

Claims (4)

[Claims] 1. A pipe joint containing 7.5% by weight or more of Cr, in which the pipe end portion exposed to a corrosive environment including the sealing surface has a thickness of 0.1 to 5 μm and Cr is contained in the joint base metal. 1 to 10% more than the Cr content, and Mo is 0.3 to more than the Mo content of the joint base metal.
A high alloy pipe joint excellent in corrosion resistance, wear resistance and seizure resistance, characterized by being coated with an alloy layer containing 3% more. 2. A pipe joint containing Cr in an amount of 7.5% or more by weight and Ni in an amount of 3.0% or more, the pipe end portion exposed to a corrosive environment including a sealing surface having a thickness of 0.1 to 5 μm, Cr
1 to 10% more than the Cr content of the joint base metal, Mo is 0.3 to 3% more than the Mo content of the joint base metal, and Ni is the same or 5% as the Ni content of the base metal joint. A high alloy pipe joint with excellent corrosion resistance, wear resistance and seizure resistance, characterized by being coated with an alloy layer containing a large amount. 3. The excellent corrosion resistance, wear resistance and seizure resistance according to claim 1 or 2, wherein the surface of the alloy layer is coated with a Cr oxide layer having a thickness of 0.1 to 5 μm. High alloy pipe fitting. 4. The surface of the Cr oxide layer further has a thickness of 0.1 to 5 μm.
The high alloy pipe joint excellent in corrosion resistance, wear resistance and seizure resistance according to claim 3, characterized by being coated with a Ni sulfide layer.