JP2002364786A - Film-forming method for threaded joint for oil well pipe and threaded joint product for oil well pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure airtight performance of a threaded joint for an oil well pipe and to form a phosphorate based film with excellent anti-seizing property and abrasion-resistant property on a screw surface of the oil well pipe. SOLUTION: In this method, the phosphorate based film is formed on a surface of the threaded joint provided on the oil well pipe using Cr-Mo steel in which 0.08 mass% or higher of Cr and 0.02 mass% or higher of Mo are contained in the steel. A recess/projection treatment with an average surface roughness Ra of 10 μm or lower is previously applied onto the surface of any one of threaded joint of a pin (male) screw or a box (female) screw prior to a series of chemical conversion treatment, anti-seizing property and abrasion- resistant property can be formed, a high performance special threaded joint having both airtight performance and watertight performance can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a phosphate-based film having excellent seizure resistance and abrasion resistance on the surface of a thread for oil country tubular goods, while securing the airtightness of a threaded joint for oil country tubular goods. The present invention relates to a pipe threaded joint product.

[0002]

2. Description of the Related Art As shown in FIG. 1 (a), an oil country tubular good used for drilling and producing oil has a pin (male) screw 1a formed on the outer surface of both ends of a pipe 1 and an inner surface of both ends of a coupling 2. Box (female) screw 2a formed, or FIG.
As shown in (b), a pin (male) screw 1a formed on the outer surface of one end of the pipe 1 and a box (female) screw 1b formed on the inner surface of the other end are fitted and tightened. Is connected while maintaining airtightness and watertightness.

Further, recently, even in a deeply harsh environment of an oil well, in order to secure high airtightness and watertightness, as shown in FIG. ) Special threaded joints with 3a have been developed and sold.

[0004] However, when these screw joints are tightened, a large torque is applied, so that "galling" called "galling" is generated on the screw surface. As a method for preventing this galling, for example, Japanese Patent Application Laid-Open No. 1-2191
As in No. 73, there is a method of forming a film of phosphate, for example, zinc phosphate or manganese phosphate on the surface of a threaded joint.

However, in the film forming method proposed in Japanese Patent Application Laid-Open No. 1-219173, a material using steel containing Cr or Mo has a sufficient thickness due to the influence of a passive film formed on the surface. There is a disadvantage that a phosphate film is difficult to form. Therefore, as a method of forming a thick phosphate film on such steel containing Cr or Mo,
Japanese Patent Application Laid-Open No. 5-117870 proposes a method in which a concavo-convex processing of 20 to 60 μm is performed before performing a chemical conversion treatment.

[0006]

The problem to be solved by the present invention is disclosed in Japanese Patent Laid-Open No. 5-117.
According to the method proposed in No. 870, a thick phosphate film is formed on the screw surface, and galling resistance (seizure resistance)
Is improved, but minute gaps are formed in the metal joint due to the effect of the uneven surface processed before the chemical conversion treatment, and the higher airtightness and watertightness recently required by customers such as oil companies using oil well pipes There was a problem that the nature could not be secured.

Further, as a method of obtaining a thick chemical conversion film, there is a method of extending the chemical conversion treatment time. However, this method has a problem that the chemical conversion treatment efficiency of phosphate decreases and the productivity of the threaded joint decreases. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is intended to secure the airtightness of a threaded joint for oil country tubular goods and to have a seizure resistance on the surface of a thread for oil country tubular goods.
An object of the present invention is to provide a method for forming a phosphate-based film having excellent wear resistance and a threaded joint product.

[0009]

In order to achieve the above-mentioned object, a method for forming a film of a threaded joint for an oil country tubular good according to the present invention comprises, before a series of chemical conversion treatments, a pin (male) screw or a box (female). Either one of the screws is subjected to unevenness with an average surface roughness Ra of 10 μm or less on the surface of the threaded joint, or both a pin (male) screw and a box (female) screw before a series of chemical conversion treatments The joint surface is subjected to unevenness processing in which the sum of both average surface roughnesses Ra is 7.3 μm or less.

[0010] In the threaded joint product for oil country tubular goods according to the present invention, the surface of either the pin (male) screw or the box (female) screw is previously subjected to unevenness processing with an average surface roughness Ra of 10 µm or less. Alternatively, on the surface of a threaded joint in which the sum of the average surface roughness Ra of both the pin (male) screw and the box (female) screw has been previously subjected to unevenness processing of 7.3 μm or less, A phosphate-based film was formed.

By doing so, C is contained in the steel.
Phosphoric acid with excellent airtightness, seizure resistance and abrasion resistance is provided on the surface of a threaded joint for oil country tubular goods using a Cr-Mo steel containing r of 0.08% by mass or more and Mo of 0.02% by mass or more. A salt-based film can be formed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors have found that Cr
Cr containing at least 0.02% by mass of Mo
-When forming a phosphate-based film on the surface of a threaded joint provided in an oil country tubular goods using Mo steel, the unevenness of the surface of the threaded joint that is pre-processed before the chemical conversion treatment, and after the chemical conversion treatment with phosphate The following findings were obtained as a result of studying the relationship between seizure resistance, airtightness, and watertightness of the threaded joint.

[0013] Regarding the seizure resistance, which is the first problem, the numerical value of the average surface roughness Ra of the concavo-convex processing applied to the surface of the threaded joint pre-processed before the chemical conversion treatment is large, that is, the surface of the threaded joint has a large surface roughness. The coarser one has higher seizure resistance,
The inventor has found that galling is unlikely to occur.

Next, regarding the airtightness and watertightness, which are the second problems, the numerical value of the average surface roughness Ra of the unevenness processing performed on the surface of the threaded joint which is processed before the chemical conversion treatment is small, that is, The inventor has found that a smooth surface of the threaded joint has higher airtightness and watertightness.

As a result of further research based on the above research results and findings, the inventor has found that in order to overcome both the first and second problems, a pin (male) screw is required before a series of chemical conversion treatments. Or, when the surface roughness of one of the box (female) screws is given an average surface roughness Ra of 10 μm or less, or a pin (male) screw and a box (female) before a series of chemical conversion treatments The sum of the average surface roughnesses Ra of both the screws when the unevenness processing is performed is 7.3 μm.
Learned that it was necessary to:
We succeeded in obtaining a threaded joint with excellent seizure resistance, airtightness and watertightness.

In the method for forming a film of a threaded joint for oil country tubular goods according to the present invention, the steel contains 0.08% by mass or more of Cr and 0.1% by mass of Mo.
When forming a phosphate-based coating on the surface of a threaded joint provided in an oil country tubular good using Cr-Mo steel containing not less than 02% by mass, a pin (male) screw or a box is required before a series of chemical conversion treatments. The surface of one of the (female) screws is subjected to unevenness with an average surface roughness Ra of 10 μm or less, or a pin (male) screw and a box (female) screw are subjected to a series of chemical conversion treatments beforehand. The gist of the present invention is to provide both the threaded joint surfaces with unevenness with a sum of the average surface roughnesses Ra of 7.3 μm or less.

In the threaded joint product for oil country tubular goods according to the present invention, the steel contains 0.08% by mass or more of Cr and 0.02% by mass of Mo.
A threaded joint product provided in an oil country tubular good using Cr-Mo steel containing at least 10 mass%, wherein a surface of either a pin (male) screw or a box (female) screw has an average surface roughness Ra in advance. Or the surface of both the pin (male) screw and the box (female) screw has a sum of the average surface roughness Ra of 7.3 in advance.
The gist of the present invention is that a phosphate-based film is formed on the surface of the threaded joint on which the unevenness processing of μm or less has been performed.

According to the present invention, before the chemical conversion treatment with a phosphate, either the pin (male) screw or the box screw (female) has an average surface roughness Ra of 10 μm or less or a pin (male). Both the screw and the box (female) screw are previously subjected to unevenness processing in which the sum of their average surface roughnesses Ra is 7.3 μm or less. The passivation film near the screw surface, which is an obstacle to formation, is removed, and at the same time, the screw surface is activated.In the next chemical conversion treatment with phosphate, a thick and dense phosphate film is formed. Has improved seizure resistance. At the same time, by preventing the screw surface from being excessively roughened, it is possible to reduce minute gaps in the metal joint portion and to secure airtightness and watertightness of the screw joint.

Hereinafter, in the present invention, before the chemical conversion treatment with a phosphate, the average surface roughness Ra of the unevenness previously processed on either a pin (male) screw or a box (female) screw.
Is set to 10 μm or less because of the average surface roughness R of the irregularities.
When a is larger than 10 μm, the airtightness and watertightness of the threaded joint are reduced due to minute gaps in the metal joint of the threaded joint caused by large irregularities on the thread surface after the chemical conversion treatment with phosphate. It is.

On the other hand, if the average surface roughness Ra of either the pin (male) screw or the box (female) screw is 10 μm or less, the above-described passivation film is removed and the screw surface is removed. By the activation, a thick and dense phosphate film can secure the seizure resistance of the threaded joint enough to withstand ten times of tightening and loosening, and both airtightness and watertightness.

In the present invention, before the chemical conversion treatment with a phosphate, the sum of the average surface roughness Ra of the irregularities previously formed on both the pin (male) screw and the box (female) screw is 7.3 μm or less. The reason is that the average surface roughness R
When the sum of a is greater than 7.3 μm, the airtightness and watertightness of the threaded joint are reduced due to the minute gap in the metal joint of the threaded joint caused by the large unevenness of the thread surface after the chemical conversion treatment with phosphate. It is because it falls.

On the other hand, the average surface roughness R of the unevenness formed on both the pin (male) screw and the box (female) screw is
If the sum of a is not more than 7.3 μm, the above-mentioned passivation film is removed and the screw surface is activated, and a thick and dense phosphate film is used. It is possible to secure seizure resistance, airtightness, and watertightness of both.

In order to carry out the present invention, the surface of the threaded joint may be previously subjected to a concavo-convex processing before the chemical conversion treatment. Examples of the method include a shot blasting method using sand-alumina and ceramics, and a resin-made resin containing hard particles. And a method using a metallic brush.

In actual threading, the average surface roughness Ra before the concavo-convex processing before the chemical conversion treatment with phosphate is about 0.1 due to the influence of the vibration of the workpiece during the cutting at the time of threading. Many are 3 μm or more. However, in these cases, the surface roughness is different from that in which the average surface roughness Ra satisfies a predetermined range by performing unevenness processing by the shot blast method or the like described above. It is needless to say that the operation and effect of the present invention cannot be obtained even if the above-mentioned range of the present invention is partially satisfied, since the activation is not obtained.

[0025]

EXAMPLES The results of experiments conducted to confirm the effects of the present invention will be described below. Outside diameter 273mm, wall thickness 2
Either a pin (male) screw or a box (female) screw, or a pin (male) screw and a box of a steel pipe obtained by processing a special threaded joint to a material using 4.4 mm Cr-Mo steel for sour resistance The surface of both the threaded part of the (female) screw and the metal joint is processed to various roughness by sandblasting before the phosphate conversion treatment, and then the threaded joint is subjected to the phosphate conversion treatment. The results of comparing the seizure resistance, airtightness and watertightness are shown in Table 1 below.

[0026]

[Table 1]

As is clear from Table 1, before the chemical conversion treatment with a series of phosphates, either the pin (male) screw or the box (female) screw has an average surface roughness Ra of 10 or less.
μm or less (Nos. 3 to 8 and N
o. In Nos. 12 to 17), they had seizure resistance enough to withstand the ten times of tightening and loosening, and also had good airtightness and watertightness.

Next, when the surface roughness before the chemical conversion treatment with phosphate is larger than 10 μm in average surface roughness Ra (No. 9, 10, 18, 19), the number of times of tightening and loosening is 10 times. Although the threaded joint has a sufficient seizure resistance, it can leak in a test in which gas pressure is applied to the inner surface of the threaded joint under tensile stress, resulting in sufficient airtightness and watertightness. Had no properties.

From the above results, when either the pin (male) screw or the box (female) screw was previously subjected to unevenness processing before a series of chemical conversion treatment with phosphate, the seizure resistance of the threaded joint was improved. In order to obtain a threaded joint having both air-tightness and water-tightness, it is found that the surface roughness before the chemical conversion treatment with phosphate is appropriate to have an average surface roughness Ra of 10 μm or less.

3 to 6 show the test results described above. FIG. FIG. 4 shows the number of times of tightening and loosening in Nos. 1 to 10, and FIG. 5 shows the results of the airtightness test in Nos. 1 to 10, and FIG. 2
And No. FIG. 6 shows the number of times of tightening and loosening in Nos. 11 to 19, and FIG. 2 and No. 11-1
9 shows the results of an airtightness test in Example 9.

Subsequently, when both the pin (male) screw and the box (female) screw have been subjected to concavo-convex processing before a series of chemical conversion treatment with phosphate, both the pin (male) screw and the box (female) screw are required. If the sum of both surface roughnesses before the chemical conversion treatment with phosphate is 7.3 μm or less in average surface roughness Ra (No. 20 to 23, No. 25 to 27, N
o. 29, 30; 32, no. 35 and no. 3
7) While maintaining airtightness and watertightness, it was able to withstand 10 tightening and loosening times.

Next, when the sum of both surface roughnesses before the chemical conversion treatment with phosphate is larger than 7.3 μm in average surface roughness Ra (No. 24, 28, 31, 33, 34,
36, 38) Although it can withstand 10 tightening and loosening times and the threaded joint has sufficient seizure resistance, gas pressure was applied to the inner surface of the threaded joint under tensile stress. Leakage occurred in the test and did not have sufficient airtightness and watertightness.

Table 1 shows that both the pin (male) screw and the box (female) screw were not subjected to any concavo-convex processing and were cut (N)
o. 1, 2, 11) were also shown, but as it was, the airtightness and the watertightness were satisfactory, but it was not able to withstand 10 tightening and loosening times.

[0034]

As described above, according to the present invention,
As well as ensuring the airtightness of the oil country tubular goods threaded joint, a phosphate-based coating with excellent seizure resistance and abrasion resistance can be formed on the surface of the oil country pipe thread, so that seizure resistance, airtightness and watertightness can be achieved. A high performance special threaded joint having both performances can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a threaded joint formed in an oil country tubular good;
(A) is a pin (male) screw formed on the outer surface of both ends of the pipe and a box (female) screw formed on the inner surface of both ends of the coupling. (B) is a pin (male) screw formed on the outer surface of one end of the pipe. And a box (female) screw formed on the inner surface of the other end.

FIG. 2 is a sectional view showing a main part of a special threaded joint for connecting an oil country tubular good;

FIG. It is the figure which showed the number of times of tightening and loosening back in 1-10.

FIG. It is the figure which showed the result of the airtightness test in 1-10.

FIG. 2 and No. It is the figure which showed the number of times of tightening and loosening back in 11-19.

FIG. 2 and No. It is the figure which showed the result of the airtightness test in 11-19.

Claims (4)

[Claims] 1. The steel according to claim 1, wherein said steel contains 0.08% by mass or more of Cr,
When forming a phosphate-based coating on the surface of a threaded joint provided in an oil country tubular good using a Cr-Mo steel containing 0.02% by mass or more, a pin (male) is previously formed before a series of chemical conversion treatments. A method for forming a film for a threaded joint for oil country tubular goods, wherein an uneven surface with an average surface roughness Ra of 10 μm or less is applied to either one of a threaded joint and a box (female) threaded joint surface. 2. The steel according to claim 1, wherein said steel contains 0.08% by mass or more of Cr,
Is a threaded joint product provided in an oil country tubular good using Cr-Mo steel containing 0.02% by mass or more, and an average of a surface of one of a pin (male) screw and a box (female) screw is previously determined. A threaded joint product for oil country tubular goods, wherein a phosphate-based coating is formed on the surface of a threaded joint having a surface roughness Ra of 10 μm or less. 3. The steel according to claim 1, wherein said steel contains 0.08% by mass or more of Mo,
When forming a phosphate-based coating on the surface of a threaded joint provided in an oil country tubular good using a Cr-Mo steel containing 0.02% by mass or more, a pin (male) is previously formed before a series of chemical conversion treatments. A method for forming a film for a threaded joint for oil country tubular goods, characterized in that the surface of both threaded joints of a screw and a box (female) thread is subjected to a concavo-convex processing in which the sum of the average surface roughnesses Ra of both is 7.3 μm or less. 4. The steel according to claim 1, wherein said steel contains 0.08% by mass or more of Mo,
Is a threaded joint product provided in an oil country tubular good using Cr-Mo steel containing 0.02% by mass or more, wherein both a pin (male) screw and a box (female) screw are provided on both screw surfaces in advance. A threaded joint product for oil country tubular goods, characterized in that a phosphate-based film is formed on the surface of a threaded joint having an average surface roughness Ra of 7.3 μm or less.