阅读说明：本技术 油井管用螺纹接头及油井管用螺纹接头的制造方法 (Threaded joint for oil well pipe and method for manufacturing threaded joint for oil well pipe ) 是由 木本雅也 大岛真宏 于 2018-05-10 设计创作，主要内容包括：本发明提供具有优异的耐腐蚀性和耐烧结性的油井管用螺纹接头及其制造方法。特别是,油井管用螺纹接头的制造方法为具备公扣部(3)和母扣部(4)的油井管用螺纹接头的制造方法。制造方法具备：形成Zn-Ni合金镀层(100)的Zn-Ni合金镀层形成工序；以及,在Zn-Ni合金镀层形成工序后形成铬酸盐覆膜(200)的铬酸盐覆膜形成工序。铬酸盐覆膜形成工序具备铬酸盐处理工序和干燥工序。铬酸盐覆膜形成工序满足选自以下条件1～条件3中的1个或2个以上的条件。条件1：铬酸盐处理工序中的铬酸盐处理液的搅拌速度：以线速度计为0.5m/s以上；条件2：铬酸盐处理工序中的铬酸盐处理时间：不足50秒；条件3：干燥工序中的干燥温度：60℃以下。(The invention provides a threaded joint for an oil well pipe having excellent corrosion resistance and seizure resistance, and a method for manufacturing the same. In particular, the method for manufacturing a threaded joint for an oil well pipe is a method for manufacturing a threaded joint for an oil well pipe having a pin portion (3) and a box portion (4). The manufacturing method comprises: a Zn-Ni alloy plating layer forming step for forming a Zn-Ni alloy plating layer (100); and a chromate film forming step of forming a chromate film (200) after the Zn-Ni alloy plating layer forming step. The chromate coating forming step includes a chromate treatment step and a drying step. The chromate coating film forming step satisfies 1 or 2 or more conditions selected from the following conditions 1 to 3. Condition 1: stirring speed of chromate treatment liquid in chromate treatment step: the linear velocity is more than 0.5 m/s; condition 2: chromate treatment time in chromate treatment process: less than 50 seconds; condition 3: drying temperature in the drying step: below 60 ℃.)

1, A method for manufacturing a threaded joint for an oil well pipe,

the threaded joint for oil country tubular goods is provided with a pin portion having a pin portion side contact surface including a pin portion side threaded portion, and a box portion having a box portion side contact surface including a box portion side threaded portion,

the method for manufacturing the threaded joint for the oil well pipe comprises the following steps:

a Zn-Ni alloy plating layer forming step of immersing at least of the pin part side contact surface and the box part side contact surface in a plating solution containing zinc ions and nickel ions, and forming a Zn-Ni alloy plating layer composed of a Zn-Ni alloy and impurities on at least of the pin part side contact surface and the box part side contact surface by electroplating,

chromate film forming step: forming a chromate film on the Zn-Ni alloy plating layer after the Zn-Ni alloy plating layer forming step,

wherein the chromate coating film forming step includes the steps of:

chromate treatment process: immersing the pin part side contact surface and/or the box part side contact surface on which the Zn — Ni alloy plating layer is formed in a chromate treatment solution containing chromium ions, and performing chromate treatment; and the number of the first and second groups,

a drying procedure: after the chromate treatment step, drying the male part side contact surface and/or the female part side contact surface,

the chromate coating forming step satisfies 1 or 2 or more conditions selected from the following conditions 1 to 3,

condition 1: the stirring speed of the chromate treatment liquid in the chromate treatment step is as follows: the linear velocity is more than 0.5 m/s;

condition 2: chromate treatment time in the chromate treatment step: less than 50 seconds;

condition 3: drying temperature in the drying step: below 60 ℃.

2. The method of manufacturing a threaded joint for oil well pipes as set forth in claim 1,

the chromate coating film forming step satisfies at least the condition 1,

the chromate film forming step further includes a non-agitation dipping step of dipping the pin-side contact surface and/or the box-side contact surface in the chromate treatment liquid for hours in a state where the agitation of the chromate treatment liquid is stopped after the chromate treatment step and before the drying step.

3. The method of manufacturing a threaded joint for oil well pipes according to claim 1 or claim 2,

the pin part side contact surface includes a pin part side metal seal part and a pin part side shoulder part,

the box side contact surface further includes a box side metal seal and a box side shoulder.

A threaded joint for oil well pipes of types, comprising:

a pin portion having a pin portion side contact surface including a pin portion side threaded portion;

a box portion having a box portion side contact surface including a box portion side threaded portion;

a Zn-Ni alloy plating layer composed of a Zn-Ni alloy and impurities on at least of the pin part side contact surface and the box part side contact surface,

a chromate coating film on the Zn-Ni alloy plating layer,

wherein the chromate coating has a surface brightness L value of less than 65.

5. The threaded joint for oil well pipes as set forth in claim 4,

the amount of the chromate coating is 10 to 300mg/m in terms of chromium²。

6. The threaded joint for oil well pipes according to claim 4 or claim 5,

the pin part side contact surface includes a pin part side metal seal part and a pin part side shoulder part,

the box side contact surface further includes a box side metal seal and a box side shoulder.

Technical Field

The present invention relates to a threaded joint for an oil well pipe and a method for manufacturing the threaded joint for an oil well pipe.

Background

Oil well pipes are used for the production of oil and gas fields. An oil country tubular good is formed by connecting a plurality of steel pipes according to the depth of a well. The steel pipes are connected by tightly screwing pipe threaded joints formed at the ends of the steel pipes to each other. The oil country tubular goods are pulled up and loosened by inspection or the like, and are tightened again after inspection and reused.

The threaded joint for oil well pipes is provided with a male buckle part and a female buckle part. The male buckle portion includes a male thread portion formed on an outer peripheral surface of the distal end portion of the steel pipe. The female snap portion includes a female screw portion formed on an inner peripheral surface of a distal end portion of the steel pipe. The pin and box portions sometimes include unthreaded metal contact portions. The unthreaded metal contact portions each include a metal seal portion and a shoulder portion. When the steel pipes are screwed tightly with each other, the male screw portion and the female screw portion, the metal seal portion and the shoulder portion are in contact with each other.

The screw portions of the pin portion and the box portion and the unthreaded metal contact portion are repeatedly subjected to strong friction during tightening and loosening of the threads of the steel pipe. If these portions do not have sufficient durability against friction, galling (sintering that cannot be repaired) occurs when the screw is repeatedly tightened and loosened. Therefore, the threaded joint for oil country tubular goods is required to have sufficient durability against friction, that is, excellent seizure resistance.

Although the seizure resistance of a threaded joint for oil country tubular goods can be improved by applying the compound grease to the surface of the threaded joint for oil country tubular goods, the heavy metal such as Pb contained in the compound grease may affect the environment, and therefore, it is desired to develop a threaded joint for oil country tubular goods that does not use the compound grease.

types of threaded joints for oil well pipes using grease (referred to as green dope) containing no heavy metal in place of compound grease are proposed, and for example, threaded joints for oil well pipes excellent in seizure resistance even when grease containing no heavy metal is used are described in japanese patent laid-open nos. 2008-215473 (patent document 1) and 2003-074763 (patent document 2).

The threaded joint for oil well pipes described in patent document 1 is a threaded joint for oil well pipes comprising a pin portion and a box portion each having a contact surface having a threaded portion and an unthreaded metal contact portion, and is characterized in that the contact surface of at least of the pin portion and the box portion has a 1 st plating layer made of a Cu-Zn alloy, and patent document 1 describes that, by this means, sufficient leak resistance and seizure resistance are exhibited even in the case of applying a green paint or even in the case of no paint, and further, excellent corrosion resistance is exhibited, and even if a green paint or a lubricating coating is present on the plating layer, the occurrence of interstitial corrosion can be prevented.

In the technique disclosed in patent document 1, the specific alloy plating layer is formed on the contact surface, whereby the seizure resistance can be improved even when a green paint is used.

The joint for an oil well pipe described in patent document 2 is types of joints for an oil well steel pipe, each of which is formed of a male part having a male thread and a metal-to-metal seal part at the end of a steel pipe containing 9 mass% or more of Cr, and a coupling having a female thread and a metal-to-metal seal part at both ends, the joint for an oil well pipe being characterized in that a Cu — Sn alloy layer is provided on the surface of the female thread of the coupling and the metal-to-metal seal part at steps.

Disclosure of Invention

Problems to be solved by the invention

However, oil country tubular goods are shipped by ships or the like after manufacture and stored for hours before use, and the transportation and storage of oil country tubular goods may take a long time.

When the threaded joint for oil well pipes and the composition for forming a lubricating coating disclosed in patent documents 1 and 2 are stored outdoors for a long period of time, white rust may be generated in the threaded joint for oil well pipes, and corrosion resistance may be reduced. In this case, the gas tightness and seizure resistance of the threaded joint for oil country tubular goods may be reduced.

The purpose of the present invention is to provide a threaded joint for oil well pipes having excellent corrosion resistance and a method for manufacturing the same.

Means for solving the problems

A method for manufacturing a threaded joint for an oil well pipe, the threaded joint for an oil well pipe including a pin portion and a box portion, the pin portion having a pin portion side contact surface including a pin portion side threaded portion, the box portion having a box portion side contact surface including a box portion side threaded portion, the method for manufacturing a threaded joint for an oil well pipe including a Zn-Ni alloy plating layer forming step, and a chromate film forming step after the Zn-Ni alloy plating layer forming step, dipping at least of the pin portion side contact surface and the box portion side contact surface in a plating solution containing zinc ions and nickel ions, forming a Zn-Ni alloy plating layer by electroplating on at least of the pin portion side contact surface and the box portion side contact surface, the Zn-Ni alloy plating layer being composed of a Zn-Ni alloy and impurities, forming a chromate film on the Zn-Ni alloy plating layer in the chromate film forming step, forming the chromate film forming step including a chromate treatment step, a drying step after the chromate treatment step, forming a chromate film on the pin portion side contact surface having Zn-Ni alloy plating layer and a chromate treatment step, and performing chromate treatment on the box portion side contact surface, the chromate treatment step, the pin portion side contact surface, the chromate treatment step, and performing chromate treatment on the chromate treatment, the pin portion side contact surface, the chromate treatment, and the chromate treatment being.

Condition 1: stirring speed of chromate treatment liquid in chromate treatment step: the linear velocity is more than 0.5 m/s;

condition 2: chromate treatment time in chromate treatment process: less than 50 seconds;

condition 3: drying temperature in the drying step: below 60 ℃.

A threaded joint for an oil well pipe according to the present embodiment includes a pin portion, a box portion, a Zn-Ni alloy plating layer, and a chromate coating film, the pin portion having a pin portion side contact surface including a pin portion side threaded portion, the box portion having a box portion side contact surface including a box portion side threaded portion, the Zn-Ni alloy plating layer being provided on at least of the pin portion side contact surface and the box portion side contact surface, the Zn-Ni alloy plating layer being composed of a Zn-Ni alloy and impurities, the chromate coating film being provided on the Zn-Ni alloy plating layer, and the chromate coating film having a luminance L value of less than 65 on a surface thereof.

ADVANTAGEOUS EFFECTS OF INVENTION

The threaded joint for an oil well pipe according to the present embodiment has excellent corrosion resistance.

Drawings

Fig. 1 is a graph showing the relationship between the luminance L value of the chromate coating surface and the white rust generation area rate (%) after 300 hours of a Salt Spray Test (SST).

FIG. 2 is a graph showing the relationship between the stirring speed (m/s) of the chromate treating solution and the luminance L value of the chromate coating surface in the chromate treating step.

FIG. 3 is a graph showing the relationship between the chromate treatment time(s) in the chromate treatment step and the brightness L of the chromate coating surface.

FIG. 4 is a graph showing the relationship between the drying temperature (. degree. C.) in the drying step and the luminance L value of the chromate coating film surface.

Fig. 5 is a diagram showing the structure of the threaded joint for an oil well pipe of the collar type according to the present embodiment.

Fig. 6 is a diagram showing the structure of the integral threaded joint for oil country tubular goods according to the present embodiment.

Fig. 7 is a sectional view of the threaded joint for oil country tubular goods.

Fig. 8 is a diagram showing the structure of a threaded joint for an oil well pipe that does not have the metal seal portion and the shoulder portion of the present embodiment.

Fig. 9 is a cross-sectional view of examples of the contact surface of the threaded joint for an oil country tubular good according to the present embodiment.

Detailed Description

Hereinafter, the present embodiment will be described in detail with reference to the drawings. The same or corresponding portions in the drawings are denoted by the same reference numerals, and description thereof will not be repeated.

The present inventors have conducted various studies on surface treatment and corrosion resistance on a contact surface of a threaded joint for oil country tubular goods. As a result, the following findings were obtained.

Zinc (Zn) has lower hardness and melting point than copper (Cu) used in conventional plating. However, a Zn — Ni alloy as a Zn alloy has sufficiently high hardness and high melting point. Therefore, if the plating layer is formed of a Zn — Ni alloy, the seizure resistance of the threaded joint for oil country tubular goods can be improved. In this specification, a plating layer composed of a Zn-Ni alloy and impurities is referred to as a Zn-Ni alloy plating layer.

As a technique for suppressing the generation of white rust, chromate treatment is known. Conventionally, chromate treatment liquids contain 6-valent chromium. Chromium 6 may have environmental impact. Therefore, it is desired to develop a so-called 3-valent chromate treatment that does not contain 6-valent chromium. The 3-valent CHROMATE treatment is carried out using DAIN CHROMATE TR-02 (trade name) manufactured by Daihu chemical Co., Ltd., which is a commercially available product. Hereinafter, in the present specification, unless otherwise specified, chromate treatment means 3-valent chromate treatment.

However, it has been found that white rust may be generated in a shorter time than expected in a threaded joint for oil country tubular goods even if the Zn — Ni alloy plating layer is subjected to chromate treatment.

The present inventors have found, as a result of their studies, that the luminance L value of the surface of a chromate coating film can be used as an index of corrosion resistance.

The corrosion resistance of the threaded joint for oil country tubular goods can be determined from the area ratio of white rust generated on the surface of the threaded joint for oil country tubular goods (hereinafter referred to as "white rust generation area ratio"). In the present embodiment, when the white rust generation area ratio after 300 hours in the salt water spray test (SST) is less than 50%, it is judged that the corrosion resistance is excellent. The salt spray test and the white rust generation area ratio will be described in detail in examples described later. Hereinafter, in the present specification, unless otherwise specified, "white rust generation area ratio" means "white rust generation area ratio after 300 hours of a salt water spray test (SST)".

The present inventors have found that the white rust generation area ratio is correlated with the luminance L value of the chromate coating surface. Fig. 1 is a graph showing the relationship between the luminance L value of the chromate coating surface and the white rust generation area rate (%) after 300 hours of a Salt Spray Test (SST). FIG. 1 is a diagram obtained by the examples described later.

The vertical axis of fig. 1 represents the white rust occurrence area ratio (%). The horizontal axis of FIG. 1 represents the luminance L value of the chromate film surface. Referring to fig. 1, the white rust occurrence area ratio and the luminance L value of the chromate film surface are in a roughly correlated relationship, and the white rust occurrence area ratio tends to decrease as the luminance L value of the chromate film surface decreases. If the brightness L value of the surface of the chromate coating is less than 65, the white rust generation area ratio is less than 50%.

That is, if the brightness L value of the surface of the chromate coating is less than 65, the threaded joint for oil well pipes has excellent corrosion resistance. Further, the lower the brightness L value of the surface of the chromate film, the higher the corrosion resistance tends to be.

Next, the present inventors have found the following chromate treatment conditions for obtaining excellent corrosion resistance in a threaded joint for an oil well pipe.

The chromate film forming step for forming a chromate film usually includes a chromate treatment step and a drying step. Conventionally, in a chromate treatment process, a material to be treated is immersed in a chromate treatment solution. In the drying step, the material to be treated is dried after the chromate treatment step.

[ stirring speed of chromate treatment liquid in chromate treatment Process ]

The chromate treatment is generally carried out by immersing the material to be treated in a treatment solution, and the method recommended by manufacturers of commercially available products for the chromate treatment of valence 3 is also the immersion treatment.

In addition, , a male thread portion and a female thread portion of a threaded joint for an oil well pipe are complex shapes in which a plurality of projections and depressions having a height of several mm are formed on thread crests and roots and are continuously formed at intervals of several mm, and further, a male thread portion of a threaded joint for an oil well pipe is located at an end portion of a pipe having a length of several meters or more.

FIG. 2 is a graph showing the relationship between the stirring speed (m/s) of the chromate treating solution and the luminance L value of the chromate coating surface in the chromate treating step. Fig. 2 is obtained by the examples described later. In fig. 2, test numbers under the same conditions except for the stirring speed of the chromate treatment liquid are compared. Test numbers 4 to 6, 8 to 9 and 13 are shown in FIG. 2.

Referring to FIG. 2, when the stirring speed of the chromate treatment liquid is 0.5m/s or more in terms of linear velocity, the brightness L value of the chromate coating surface is less than 65. That is, the threaded joint for oil well pipes has excellent corrosion resistance.

[ chromate treatment time in chromate treatment Process ]

It has been considered that the greater the amount of chromate film deposited, the higher the corrosion resistance of the material to be treated. It is therefore envisioned that: the longer the chromate treatment time, the higher the corrosion resistance of the threaded joint for oil well pipes. However, as a result of studies by the present inventors, it has been found that shortening the chromate treatment time to some extent is effective for improving the corrosion resistance of a threaded joint for an oil well pipe.

FIG. 3 is a graph showing the relationship between the chromate treatment time(s) in the chromate treatment step and the brightness L of the chromate coating surface. Fig. 3 is obtained by the examples described later. In FIG. 3, test numbers under the same conditions except for the chromate treatment time are compared. Fig. 3 shows test numbers 1 and 4 to 7.

Referring to fig. 3, when the chromate treatment time in the chromate treatment process is less than 50 seconds, the brightness L value of the chromate coating surface is less than 65. That is, the threaded joint for oil well pipes has excellent corrosion resistance.

[ drying temperature in drying step ]

Conventionally, in order to improve the productivity, it has been attempted to increase the drying temperature in the drying step after the chromate treatment, and if the drying temperature is slightly high, the time required until the completion of drying is shortened, and the productivity is improved.

FIG. 4 is a graph showing the relationship between the drying temperature (. degree. C.) in the drying step and the luminance L value of the chromate coating film surface. Fig. 4 is obtained by the examples described later. In fig. 4, test numbers under the same conditions except for the drying temperature are compared. Fig. 4 shows test nos. 2 to 6.

Referring to fig. 4, when the drying temperature in the several drying steps is 60 ℃ or lower, the luminance L value of the surface of the chromate coating film is less than 65. That is, the threaded joint for oil well pipes has excellent corrosion resistance.

As described above, in the chromate film forming step of the present embodiment, if the conditions of 1 or 2 or more selected from the stirring speed of the chromate treatment liquid, the chromate treatment time, and the drying temperature of the chromate treatment liquid are satisfied, the threaded joint for oil country tubular goods has excellent corrosion resistance.

The method for manufacturing a threaded joint for an oil well pipe according to the present embodiment, which is completed based on the above findings, includes a pin portion and a box portion, the pin portion having a pin portion side contact surface including a pin portion side threaded portion, the box portion having a box portion side contact surface including a box portion side threaded portion, the method for manufacturing a threaded joint for an oil well pipe includes a Zn-Ni alloy plating layer forming step, and a chromate film forming step after the Zn-Ni alloy plating layer forming step, in which at least of the pin portion side contact surface and the box portion side contact surface are immersed in a plating solution containing zinc ions and nickel ions, and a Zn-Ni alloy plating layer is formed by electroplating on at least of the pin portion side contact surface and the box portion side contact surface, the Zn-Ni alloy plating layer is composed of a Zn-Ni alloy and impurities, in the chromate film forming step, a chromate film is formed on the Zn-Ni alloy plating layer, the chromate film forming step includes a chromate treatment step, a drying step, a chromate treatment is performed on the pin portion side contact surface, and a chromate treatment step, wherein the chromate treatment is performed on the pin portion side contact surface is performed, and a chromate treatment condition is 1 or 2.

Condition 1: stirring speed of chromate treatment liquid in chromate treatment step: the linear velocity is more than 0.5 m/s;

condition 2: chromate treatment time in chromate treatment process: less than 50 seconds;

condition 3: drying temperature in the drying step: below 60 ℃.

In the method of manufacturing a threaded joint for an oil well pipe according to the present embodiment, the conditions of the chromate coating film forming step can be appropriately adjusted. Therefore, a threaded joint for oil country tubular goods having a chromate coating film with a low surface brightness L value can be manufactured. The threaded joint for oil well pipes exhibits excellent corrosion resistance.

In the above production method, the chromate film forming step satisfies at least condition 1, and the chromate film forming step may further include steps including a non-stirring dipping step, the non-stirring dipping step being performed after the chromate treatment step and before the drying step, and the non-stirring dipping step dipping the pin-side contact surface and/or the box-side contact surface in the chromate treatment liquid for hours while stirring of the chromate treatment liquid is stopped.

In the above manufacturing method, the pin side contact surface may further comprise the pin side metal seal and the pin side shoulder, and the box side contact surface may further comprise the box side metal seal and the box side shoulder.

A threaded joint for an oil well pipe according to the present embodiment has a pin portion, a box portion, a Zn-Ni alloy plating layer, and a chromate coating, the pin portion having a pin portion side contact surface including a pin portion side threaded portion, the box portion having a box portion side contact surface including a box portion side threaded portion, the Zn-Ni alloy plating layer being provided on at least of the pin portion side contact surface and the box portion side contact surface, the Zn-Ni alloy plating layer being composed of a Zn-Ni alloy and impurities, the chromate coating being provided on the Zn-Ni alloy plating layer, the chromate coating having a luminance L value of less than 65.

The brightness L value of the chromate film coated surface of the threaded joint for an oil well pipe according to the present embodiment is less than 65. Therefore, the threaded joint for oil well pipes exhibits excellent corrosion resistance.

The amount of the chromate film deposited on the threaded joint for an oil well pipe may be 10 to 300mg/m in terms of chromium²。

When the amount of the chromate film deposited is in the above range, the corrosion resistance of the threaded joint for oil country tubular goods is stably improved.

In the threaded joint for oil country tubular goods described above, the pin side contact surface may further include a pin side metal seal portion and a pin side shoulder portion and the box side contact surface may further include a box side metal seal portion and a box side shoulder portion.

The threaded joint for an oil well pipe and the method for manufacturing the same according to the present embodiment will be described in detail below.

[ threaded joint for oil well pipe ]

The threaded joint for oil well pipes is provided with a male buckle part and a female buckle part. Fig. 5 is a diagram showing the structure of the threaded joint for an oil well pipe of the collar type according to the present embodiment. Referring to fig. 5, the threaded joint for oil well pipes includes a steel pipe 1 and a coupling 2. Both ends of the steel pipe 1 are formed into a male snap part 3 having a male screw part on the outer surface. Female thread portions 4 having female thread portions on the inner surfaces are formed at both ends of the coupling 2. The coupling 2 is attached to the end of the steel pipe 1 by screwing the pin portion 3 and the box portion 4. Although not shown, in order to protect each threaded portion, a protector may be attached to the pin portion 3 of the steel pipe 1 and the box portion 4 of the coupling 2 to which the corresponding member is not attached.

alternatively, a threaded joint for oil country tubular goods may be used in which the end of the steel pipe 1 is the pin 3 and the end is the box 4 without using the coupling 2. fig. 6 is a view showing the structure of the integral threaded joint for oil country tubular goods of the present embodiment, and referring to fig. 6, the threaded joint for oil country tubular goods comprises the steel pipe 1, the end of the steel pipe 1 is formed at the pin 3 having the male thread on the outer surface, the end of the steel pipe 1 is formed at the box 4 having the female thread on the inner surface, the pin 3 and the box 4 are screwed together, whereby the steel pipes 1 can be connected to each other, and the threaded joint for oil country tubular goods of the present embodiment can be used in both of the coupling method and the integral threaded joint for oil country tubular goods.

Fig. 7 is a sectional view of the threaded joint for oil country tubular goods. In fig. 7, the pin 3 includes a pin side threaded portion 31, a pin side metal seal portion 32, and a pin side shoulder portion 33. In fig. 7, the box 4 includes a box side screw portion 41, a box side metal seal portion 42, and a box side shoulder portion 43. The portions that the pin part 3 and the box part 4 contact when they are screwed tightly are referred to as contact surfaces 34, 44. Specifically, when the pin 3 and the box 4 are screwed tightly, the screw portions (the pin-side screw portion 31 and the box-side screw portion 41), the metal seal portions (the pin-side metal seal portion 32 and the box-side metal seal portion 42), and the shoulder portions (the pin-side shoulder portion 33 and the box-side shoulder portion 43) contact each other. In fig. 7, the pin part side contact surface 34 includes the pin part side threaded part 31, the pin part side metal seal part 32, and the pin part side shoulder part 33. In fig. 7, the box portion side contact surface 44 includes the box portion side threaded portion 41, the box portion side metal seal portion 42, and the box portion side shoulder portion 43.

In fig. 7, the pin 3 is arranged in the order of the pin side shoulder portion 33, the pin side metal seal portion 32, and the pin side screw portion 31 from the end of the steel pipe 1. In the box 4, the box-side threaded portion 41, the box-side metal seal portion 42, and the box-side shoulder portion 43 are arranged in this order from the end of the steel pipe 1 or the coupling 2. However, the arrangement of the pin-side threaded portion 31 and the box-side threaded portion 41, the pin-side metal seal portion 32 and the box-side metal seal portion 42, and the pin-side shoulder portion 33 and the box-side shoulder portion 43 is not limited to the arrangement of fig. 7, and may be changed as appropriate. For example, as shown in fig. 6, the pin 3 may be arranged in the order of the pin side metal seal portion 32, the pin side screw portion 31, the pin side metal seal portion 32, the pin side shoulder portion 33, the pin side metal seal portion 32, and the pin side screw portion 31 from the end of the steel pipe 1. In the box 4, the box side metal seal portion 42, the box side screw portion 41, the box side metal seal portion 42, the box side shoulder portion 43, the box side metal seal portion 42, and the box side screw portion 41 may be arranged in this order from the end of the steel pipe 1 or the coupling 2.

Fig. 5 to 7 show a so-called special button having metal seal portions (a pin-side metal seal portion 32 and a box-side metal seal portion 42) and shoulder portions (a pin-side shoulder portion 33 and a box-side shoulder portion 43). However, the metal seal portions (the pin-side metal seal portion 32 and the box-side metal seal portion 42) and the shoulder portions (the pin-side shoulder portion 33 and the box-side shoulder portion 43) may be omitted. Fig. 8 shows a threaded joint for an oil well pipe that does not have the metal seal portions 32 and 42 and the shoulder portions 33 and 43. The threaded joint for oil well pipes of the present embodiment can also be suitably used for threaded joints for oil well pipes that do not have the metal seal portions 32, 42 and the shoulder portions 33, 43. Without the metal seal portions 32, 42 and the shoulder portions 33, 43, the pin portion side contact surface 34 includes the pin portion side threaded portion 31. Without the metal seal portions 32, 42 and the shoulder portions 33, 43, the box-side contact surface 44 includes the box-side threaded portion 41.

Fig. 9 is a cross-sectional view of examples of the contact surfaces 34, 44 of the threaded joint for oil country tubular goods according to the present embodiment, the threaded joint for oil country tubular goods is provided with a Zn — Ni alloy plating layer 100 on at least of the pin-side contact surface 34 and the box-side contact surface 44, the threaded joint for oil country tubular goods is provided with a chromate coating 200 on the Zn — Ni alloy plating layer 100 in step , and the threaded joint for oil country tubular goods may be provided with the Zn — Ni alloy plating layer 100 and the chromate coating 200 on both the pin-side contact surface 34 and the box-side contact surface 44.

The threaded joint for an oil well pipe may be provided with the Zn — Ni alloy plating layer 100 and the chromate coating 200 on the pin-side contact surface 34 and only the Zn — Ni alloy plating layer 100 on the box-side contact surface 44. The threaded joint for an oil well pipe may have the Zn — Ni alloy plating layer 100 and the chromate coating 200 on the pin-side contact surface 34 and only the chromate coating 200 on the box-side contact surface 44.

The threaded joint for oil country tubular goods may be provided with the Zn — Ni alloy plating layer 100 and the chromate coating 200 on the box-side contact surface 44, and with only the Zn — Ni alloy plating layer 100 on the pin-side contact surface 34. The threaded joint for an oil well pipe may have the Zn — Ni alloy plating layer 100 and the chromate coating 200 on the box-side contact surface 44 and only the chromate coating 200 on the pin-side contact surface 34.

[ Zn-Ni alloy plating layer ]

The Zn-Ni alloy plating layer 100 is provided on at least of the pin part side contact surface 34 and the box part side contact surface 44, the Zn-Ni alloy plating layer 100 may be directly connected to the pin part side contact surface 34 and/or the box part side contact surface 44, another plating layer may be provided between the Zn-Ni alloy plating layer 100 and the pin part side contact surface 34, and another plating layer may be provided between the Zn-Ni alloy plating layer 100 and the box part side contact surface 44.

The Zn-Ni alloy plating layer 100 is composed of a Zn-Ni alloy and impurities. The Zn — Ni alloy contains zinc (Zn) and nickel (Ni). The Zn-Ni alloy sometimes contains impurities. The impurities of the Zn — Ni alloy plating layer 100 and the impurities of the Zn — Ni alloy mean substances other than Zn and Ni, and include substances that are contained in the Zn — Ni alloy plating layer 100 in the range that does not affect the effect of the present invention, such as in the production of a threaded joint for an oil well pipe. The Zn-Ni alloy plating layer 100 has a composition in which the ratio of Ni is 10 to 20 mass% when the total of Zn and Ni is 100 mass%. The lower limit of the Ni content of the Zn — Ni alloy plating layer 100 is preferably 11 mass%, and more preferably 12 mass%. The upper limit of the Ni content of the Zn — Ni alloy plating layer 100 is preferably 18 mass%, and more preferably 16 mass%.

[ method for measuring chemical composition of Zn-Ni alloy plating layer ]

The chemical composition of the Zn — Ni alloy plating layer 100 was measured by the following method. A desktop fluorescent X-RAY analyzer (FISCROPE X-RAY XDAL manufactured by Fisher Instruments, Ltd.) was used for the measurement. A calibration curve was prepared using a commercially available Zn-Ni alloy-coated steel plate standard plate. In the measurement, the Ni content (mass%) was measured at 4 points on the surface of the Zn — Ni alloy plating layer 100 (4 points of 0 °, 90 °, 180 °, and 270 ° in the circumferential direction of the oil well pipe threaded joint), and the arithmetic mean of the measurement results at these 4 points was taken as the Ni content (mass%) of the Zn — Ni alloy plating layer 100.

[ thickness of Zn-Ni alloy plating layer ]

The thickness of the Zn-Ni alloy plating layer 100 is not particularly limited. The thickness of the Zn-Ni alloy plating layer 100 is, for example, 1 to 20 μm. When the thickness of the Zn-Ni alloy plating layer 100 is 1 μm or more, sufficient seizure resistance can be obtained. The above effect is saturated even if the thickness of the Zn — Ni alloy plating layer 100 exceeds 20 μm. The lower limit of the thickness of the Zn-Ni alloy plating layer 100 is preferably 3 μm, and more preferably 5 μm. The upper limit of the thickness of the Zn-Ni alloy plating layer 100 is preferably 18 μm, and more preferably 15 μm.

The thickness of the Zn — Ni alloy plating layer 100 is measured by the following method. A probe of an eddy current phase type film thickness measuring instrument based on ISO (International Organization for standardization)21968(2005) was brought into contact with the Zn-Ni alloy plating layer 100. The phase difference between the high-frequency magnetic field on the probe input side and the eddy current on the Zn — Ni alloy plating layer 100 excited thereby was measured. The phase difference is converted into the thickness of the Zn — Ni alloy plating layer 100.

The Zn-Ni alloy plating layers 100 may be disposed locally on the contact surfaces 34, 44 or entirely, and the metallic seal portions 32, 42 are particularly increased in surface pressure in the final stage of the thread tightening, so that when the Zn-Ni alloy plating layers 100 are disposed locally on the contact surfaces 34, 44, it is preferable to dispose at least the metallic seal portions 32, 42, and , the production efficiency of the threaded joint for oil country tubular goods is improved when the Zn-Ni alloy plating layers 100 are disposed entirely on the contact surfaces 34, 44.

The hardness and melting point of the Zn — Ni alloy plating layer 100 are higher than those of the Cu plating layer conventionally used as a plating layer for a threaded joint for an oil well pipe, and the melting point is also as high as that of the Cu plating layer. Therefore, even if the screwing and unscrewing are repeated, the damage of the Zn — Ni alloy plating layer 100 can be suppressed. As a result, even if the screw tightening and the screw loosening are repeated, the seizure resistance can be maintained.

Further, zinc (Zn) contained in the Zn — Ni alloy plating layer 100 is a base metal compared to iron (Fe) which is a main component of the steel pipe. Therefore, the effect of sacrificial corrosion prevention is exhibited, and the corrosion resistance of the threaded joint for oil country tubular goods is improved.

[ chromate coating ]

The threaded joint for an oil well pipe of the present embodiment includes a chromate coating 200 on the Zn — Ni alloy plating layer 100. As described above, the threaded joint for an oil well pipe may be stored outdoors for a long period of time until it is actually used. At this time, when the chromate coating 200 is formed, the corrosion resistance of the pin part 3 and the box part 4 is improved.

The chromate coating 200 is a coating containing chromate of chromium having a valence of 3. The chromate coating 200 is formed by a chromate coating forming step described later.

[ L value of chromate coating ]

The luminance L value of the surface of the chromate coating film 200 is less than 65. When the brightness L value of the surface of the chromate coating 200 is 65 or more, the white rust occurrence area ratio (%) exceeds 50%. In this case, the corrosion resistance of the threaded joint for oil country tubular goods is reduced. The brightness L value of the surface of the chromate coating is preferably 45 or more from the viewpoint of aesthetic appearance. The upper limit of the luminance L value of the surface of the chromate coating 200 is preferably 63, and more preferably 60. The lower limit of the luminance L value of the surface of the chromate coating 200 is preferably 48, and more preferably 50.

Specifically, the average value of n is calculated as 2 times using CR-300 manufactured by KONICA MINOLTA corporation, the measurement position is preferably the metal seal portion 32, 42 or the land portion 33, 43, the measurement area is represented by Φ 10mm, and the L value (luminance L value) indicating the luminance is used as an index using a color system of L ＊ a ＊ b ＊.

[ amount of chromate film deposited ]

The thickness, i.e., the amount of adhesion, of the chromate coating film 200 is not particularly limited. The amount of the chromate coating 200 adhering may be 10 to 300mg/m in terms of chromium². If the amount of the chromate coating 200 adhered is 10mg/m in terms of chromium²As described above, the corrosion resistance of the threaded joint for oil country tubular goods is stably improved. If the amount of the chromate coating 200 adhered is 300mg/m in terms of chromium²The generation of defects such as voids in the structure of the chromate coating 200 can be suppressed as follows. Therefore, the corrosion resistance of the threaded joint for oil country tubular goods is stably improved. The lower limit of the amount of the chromate coating 200 deposited (in terms of chromium) is more preferably 20mg/m²The step is preferably 50mg/m². The upper limit of the amount of the chromate coating 200 deposited (in terms of chromium) is more preferably 250mg/m²The step is preferably 200mg/m²。

The amount of the chromate coating 200 adhering was measured by the following method. A test piece of 5 mm. times.20 mm was cut out from the male part 3 or the female part 4 provided with the chromate coating 200. The test piece was immersed in an aqueous solution prepared by dissolving 50g of sodium cyanide and 5g of sodium hydroxide in 1L of pure water. At 15A/dm²The cathodic electrolysis was carried out by applying electricity for 1 minute to dissolve the chromate coating 200 on the test piece. The solution of the chromate coating 200 was analyzed by an inductively coupled plasma mass spectrometer (ICPMS-2030) manufactured by shimadzu corporation.

[ lubricating coating ]

Referring to fig. 9, the threaded joint for oil country tubular goods may be provided with a lubricating coating 300 on the chromate coating 200 at step , and when the threaded joint for oil country tubular goods is provided with the lubricating coating 300, the lubricity of the threaded joint for oil country tubular goods is improved.

The lubricating film 300 may be solid, semisolid, or liquid. The lubricating coating 300 may be a commercially available lubricant. The lubricating coating 300 contains, for example, lubricating particles and a binder. The lubricating coating 300 may contain solvents and other ingredients as desired.

The lubricating particles are not particularly limited as long as they have lubricity. The lubricating particles are selected from graphite and MoS₂(molybdenum disulfide), WS₂(tungsten disulfide), BN (boron nitride), PTFE (polytetrafluoroethylene), CFx (graphite fluoride) and CaCO₃(calcium carbonate) 1 or more than 2 of the group.

The binder is, for example, 1 or 2 selected from the group consisting of organic binders and inorganic binders. The organic binder is, for example, 1 or 2 selected from the group consisting of thermosetting resins and thermoplastic resins. The thermosetting resin is, for example, 1 or 2 or more selected from the group consisting of polyethylene resin, polyimide resin, and polyamideimide resin. The inorganic binder is, for example, 1 or 2 selected from the group consisting of an alkoxysilane and a compound having a siloxane bond.

Examples of commercially available lubricants include SEAL-GUARD ECF (trade name) manufactured by JET-LUBE corporation. The other lubricating film 300 is, for example, a lubricating film 300 containing rosin, metal soap, wax, and lubricating powder. The chemical composition of the lubricating coating 300 formed on the pin portion 3 side and the chemical composition of the lubricating coating 300 formed on the box portion 4 side may be the same or different.

The thickness of the lubricating coating 300 is not particularly limited. The thickness of the lubricating film 300 is, for example, 10 to 100 μm. If the thickness of the lubricating coating 300 is 10 μm or more, the lubricity of the threaded joint for an oil well pipe is stably improved. Even if the thickness of the lubricating coating 300 exceeds 100 μm, the above effect is saturated because excessive lubricating coating 300 is removed when the thread is tightened.

The thickness of the lubricating film 300 was measured by the following method. A male part 3 or a female part 4 provided with a lubricating film 300 is prepared. The male snap portion 3 or the female snap portion 4 is cut so as to be perpendicular to the axial direction of the pipe. The cross section including the lubricating film 300 was observed with a microscope. The magnification for microscopic observation was 500 times. The film thickness of the lubricating film 300 is thus determined.

[ base Material of threaded Joint for oil well pipe ]

The chemical composition of the base material of the threaded joint for oil country tubular goods is not particularly limited. The base material is, for example, carbon steel, stainless steel, alloy steel, or the like. Among the alloy steels, duplex stainless steels containing alloying elements such as Cr, Ni, and Mo, and high alloy steels such as Ni alloys have high corrosion resistance. Therefore, when these high alloy steels are used as the base material, the corrosion resistance of the threaded joint for oil country tubular goods is improved.

[ production method ]

The method of manufacturing a threaded joint for an oil well pipe according to the present embodiment includes a Zn — Ni alloy plating layer forming step and a chromate film forming step. The chromate coating forming step is performed after the Zn — Ni alloy plating layer forming step.

As described above, the oil country tubular good threaded joint is provided with the pin portion 3 and the box portion 4, the pin portion 3 has the pin portion side contact surface 34 including the pin portion side threaded portion 31, the box portion 4 has the box portion side contact surface 44 including the box portion side threaded portion 41, the pin portion side contact surface 34 may further include the pin portion side metal seal portion 32 and the pin portion side shoulder portion 33, the box portion side contact surface 44 may further include the box portion side metal seal portion 42 and the box portion side shoulder portion 43.

[ Zn-Ni alloy plating layer formation step ]

In the Zn-Ni alloy plating layer forming step, a Zn-Ni alloy plating layer 100 composed of a Zn-Ni alloy and impurities is formed on at least of the pin-side contact surface 34 and the box-side contact surface 44, the Zn-Ni alloy plating layer 100 is formed by electroplating, electroplating is performed by immersing at least of the pin-side contact surface 34 and the box-side contact surface 44 in a plating solution containing zinc ions and nickel ions, and conditions for electroplating are appropriately set, wherein the plating solution preferably contains 1 to 100g/L of zinc ions and 1 to 50g/L of nickel ions, and the conditions for electroplating are, for example, a bath pH of 1 to 10, a plating solution temperature of 10 to 60 ℃, and a current density of 1 to 100A/dm²And processing time: 0.1-30 minutes.

[ chromate coating film formation Process ]

In the chromate film forming step, a chromate film 200 is formed on the Zn — Ni alloy plating layer 100. In the present embodiment, the chromate treatment is a treatment of forming a coating film (chromate coating film 200) containing chromate of 3-valent chromium. The chromate coating 200 formed by the chromate treatment suppresses white rust on the surface of the Zn — Ni alloy plating layer 100. This improves the corrosion resistance of the threaded joint for oil country tubular goods.

The chromate coating forming step includes a chromate treatment step and a drying step. The drying step is performed after the chromate treatment step.

[ chromate treatment Process ]

In the chromate treatment step, chromate treatment is performed. The chromate treatment immerses the pin part side contact surface 34 and/or the box part side contact surface 44 on which the Zn — Ni alloy plating layer 100 is formed in a chromate treatment liquid. The chromate treatment liquid contains chromium ions having a valence of 3. For example, chromium (III) chloride and chromium (III) sulfate may be dissolved to contain chromium ions having a valence of 3. As the chromate treatment liquid, commercially available chromate treatment liquids may be used. The commercially available CHROMATE treatment liquid is, for example, DAIN CHROMATE TR-02 (trade name) manufactured by Daihe chemical Co. The temperature of the chromate treatment liquid is, for example, normal temperature.

[ drying Process ]

In the drying process, the pin part side contact surface 34 and/or the box part side contact surface 44 are subjected to a drying process. In the drying treatment, the male part side contact surface 34 and/or the female part side contact surface 44 after the chromate treatment are immediately subjected to water washing and dried. The drying may be performed by a hot-air furnace or the like. The drying time is, for example, 1 to 100 minutes.

The treatment conditions in the chromate film forming step satisfy 1 or 2 or more conditions selected from the following conditions 1 to 3, and in the present embodiment, a threaded joint for oil well pipes has excellent corrosion resistance as long as any conditions are satisfied.

Condition 1: stirring speed of chromate treatment liquid in chromate treatment step: the linear velocity is more than 0.5 m/s;

condition 2: chromate treatment time in chromate treatment process: less than 50 seconds;

condition 3: drying temperature in the drying step: below 60 ℃.

[ Condition 1: stirring speed of chromate treatment liquid in chromate treatment step: at a linear velocity of 0.5m/s or more

Referring to fig. 2, the threaded joint for oil country tubular goods is preferably stirred so that a liquid flow is generated as much as possible in the cutting direction of the thread of the threaded joint for oil country tubular goods, and in this case, the retention of reaction gas during chromate treatment can be further suppressed at step .

The lower limit of the stirring speed is preferably 0.6m/s, more preferably 0.7m/s, and the upper limit of the stirring speed in the step is preferably 0.8m/s, but is preferably 2.0m/s, more preferably 1.5m/s, and the upper limit of the stirring speed in the step is preferably 1.2 m/s.

[ Condition 2: chromate treatment time in chromate treatment process: less than 50 seconds)

Referring to fig. 3, if the chromate treatment time in the chromate treatment step is less than 50 seconds, the corrosion resistance is excellent. It has been considered that the greater the amount of chromate coating 200 deposited, the higher the corrosion resistance of the material to be treated. It is therefore expected that the longer the chromate treatment time, the higher the corrosion resistance of the threaded joint for oil country tubular goods. However, the chromate treatment time is effective as short as less than 50 seconds for improving the corrosion resistance of the threaded joint for oil country tubular goods.

The upper limit of the chromate treatment time is preferably 48 seconds, more preferably 45 seconds, and further steps are preferably 40 seconds, and the lower limit of the chromate treatment time is not particularly limited, but is preferably 5 seconds, more preferably 8 seconds, and further steps are preferably 10 seconds.

[ Condition 3: drying temperature in the drying step: below 60℃)

Referring to fig. 4, in the drying step, if the drying temperature is 60 ℃ or lower, the threaded joint for oil country tubular goods has excellent corrosion resistance. Therefore, the drying temperature in the drying step is 60 ℃ or lower. Conventionally, in order to improve the productivity, it has been attempted to increase the drying temperature in the drying step after the chromate treatment step. When the drying temperature is high, the time required until the drying is completed is shortened, and the production efficiency is improved. However, in order to improve the corrosion resistance of a threaded joint for an oil well pipe, it is effective to lower the drying temperature in the drying step to 60 ℃ or lower.

The upper limit of the drying temperature is preferably 58 ℃, more preferably 55 ℃, and further steps is preferably 50 ℃, and the lower limit of the drying temperature is not particularly limited, but is preferably 20 ℃, more preferably 25 ℃, and further steps is preferably 30 ℃.

Through the above steps, the threaded joint for an oil well pipe according to the present embodiment can be manufactured.

[ non-agitated dipping Process ]

The chromate film forming step of the above-described manufacturing method satisfies at least the above-described condition 1, and stages of the method may further include a non-agitation dipping step, and the non-agitation dipping step is performed after the chromate treatment step and before the drying step.

The chromate coating 200 is formed by dipping the material to be treated in the chromate treating solution, however, a step of stirring the chromate treating solution and then dipping the material in a state where stirring is stopped may be provided, whereby the fine-particle chromate coating 200 is formed at the initial stage of stirring, the coating rate of the chromate coating 200 is improved, and then dipping the material without stirring makes it possible to efficiently obtain a sufficient amount of the chromate coating 200 adhered while maintaining a high coating rate.

The chromate film forming step satisfies the above condition 1, and therefore, the stirring speed of the chromate treatment liquid in the chromate treatment step is 0.5m/s or more, the agitation-free dipping step is performed after the chromate treatment step, the pin-side contact surface 34 and/or the box-side contact surface 44 is dipped in the chromate treatment liquid for hours in the agitation-free dipping step in a state where the agitation of the chromate treatment liquid is stopped, and for the agitation-free dipping step, the pin-side contact surface 34 and/or the box-side contact surface 44 may be dipped directly in the same chromate treatment liquid after the chromate treatment step.

In the non-agitation dipping step, the pin-side contact surface 34 and/or the box-side contact surface 44 are dipped times, wherein times is an arbitrary time, the dipping time in the non-agitation dipping step is, for example, 10 to 100 seconds, the lower limit of the dipping time in the non-agitation dipping step is preferably 15 seconds, more preferably 20 seconds, and further times is preferably 30 seconds, and the upper limit of the dipping time in the non-agitation dipping step is preferably 80 seconds, more preferably 70 seconds, and further times is preferably 60 seconds.

[ substrate treating Process ]

The production method of the present embodiment may be provided with a base treatment step, such as acid washing and alkali degreasing, as necessary before the Zn — Ni alloy plating layer 100 formation step, and the base treatment step may be carried out by cleaning oil adhered to the contact surface and the like, and the base treatment step may be further provided with grinding processes such as sand blasting and mechanical lapping, and these base treatments may be carried out by only 1 kind or by a combination of plural kinds.

[ film Forming Process ]

After the chromate coating 200 is formed, a film forming step may be performed. In the film forming step, the lubricating film 300 is formed on the chromate film 200.

The lubricating coating 300 can be formed by applying a composition containing the components of the lubricating coating 300 or a lubricant to the chromate coating 200, the application method is not particularly limited, for example, spraying, brushing, and dipping, in the case of spraying, the composition or the lubricant can be heated and sprayed in a state in which the fluidity is improved, the lubricating coating 300 can be formed locally on the contact surfaces 34 and 44, but is preferably formed uniformly on the entire contact surfaces 34 and 44, and the film forming step can be performed on both the pin part 3 and the box part 4, or only .