JPH0972467A - Threaded joint with excellent seizure resistance under no grease lubrication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of galling due to repeated tightening and loosening without need for use of fluid lubrication such as grease, by forming roughness in the contact surface of a box or a pin, and smoothing the roughness surface with a resin coating layer formed by dispersively-mixing molybdenum disulfide or tungsten disulfide with resin. SOLUTION: In a box 1 and a pin 2 which are joint members, roughness of 5-40μm is formed at only the box 1 or a contact surface between the box 1 and the pin 2 for a threaded part 3 and a metal-to-metal contact part 4 which constitute the joint members respectively. Molybdenum disulfide or tungsten disulfide which is a solid lubricant is dispersively-mixed with a resin binder (polyamide imido, epoxy, furan, phenol). The roughness surface is covered completely, and a resin coating surface is constituted so as to be smoothed. At the time of assembling, the box 1 and the pin 2 are fitted, and high pressure is applied to the threaded part 3 and the metal-to-metal contact part 4 respectively to slide them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oil well pipe threaded joint used for crude oil mining, and a line pipe threaded joint for transporting mined crude oil, in which repeated make-up (tightening) and breakout (no tightening) without applying grease. Loosen)
Also, the present invention relates to a screw joint that can be repeatedly used without seizing the joint.

[0002]

2. Description of the Related Art Threaded joints are generally used for tubing and casings used for oil well excavation. Since the screw joint is subjected to a combination of internal and external pressure, axial force, bending, etc. under the use environment, it is required that the joint does not leak even under these combined loads and the joint is not damaged. On the other hand, when lowering the casing or tubing, the joints that have been tightened may be loosened once.
API (American Petroleum Institute) that the joint can be used without seizure even when tightening and loosening three times with the casing
But it is desired. To meet the above performance requirements
Until now, it has become common sense to apply the compound grease described in API BUL5A2 and tighten the joint. Here, the role of compound grease is to secure seizure resistance and improve sealing performance.

After that, as an invention for further improving the sealing property, a special screw joint having a metal-to-metal contact portion, that is, a premium joint has been actively developed, and a premium joint having seal portions of various shapes (Japanese Patent Publication No. 59-
No. 44552 and Japanese Patent Publication No. 5-41876) have been invented. With such an invention, the gas sealability of the joint has been improved to a level equal to or higher than the yield strength of the tubular body.
However, in order to obtain a better sealing property, it is necessary to apply a higher surface pressure to the metal contact part so as to exceed the yield point of the base material. , Research to prevent galling has become popular.

As a measure for preventing galling, development of grease in which compound metal grease appropriately contains heavy metal powder such as zinc, lead, copper, or inorganic substances such as mica, and reduction of local surface pressure by devising the shape of the seal portion Research (JP-A-62-209291, JP-A-4-277392)
No. gazette) and research on controlling the properties of the seal surface (Actual fair 6
No. 713), and research for improving the goring property by surface treatment (Japanese Patent Publication No. 3-78517, Japanese Patent Laid-Open No. Hei 5 (1993) -78517).
-117870, JP-A-62-258283, JP-A-60-26695, and JP-A-58-31.
097, JP-A-58-17285, JP-A-61-124792, JP-A-61-136087.
Issue gazette) etc. With such research results, seizure resistance has been improved to a practically sufficient range by using an appropriate surface treatment and compound grease.

[0005] In particular, Japanese Patent Publication No. 3-78517 is known as a known example of forming a resin coating in which molybdenum disulfide is dispersed and mixed in an oil well pipe threaded joint. It is formed to a roughness or less. Since this is an invention with compound grease application in mind, it aims at the effect that grease is enclosed in the unevenness of the final surface, and it is a base for tightening and loosening under grease-free lubrication, which is the purpose of the present invention. Stable seizure resistance cannot be obtained due to selective contact due to the surface roughness of.

As a known example in which the relationship between the maximum surface roughness before surface treatment and the surface treatment film thickness is specified, there is JP-A-6-10154. Although there is a common point with the present patent only when looking at the relationship between the base surface roughness and the film thickness, such a known example aims to improve the sealability by reducing the gap of the metal contact portion, and, Although the effect of compound grease is mentioned, the seizure resistance without lubrication is not mentioned at all.

[0007]

Against this background, as a recent research, the grease applied has a high pressure during makeup and deteriorates the use performance (JP-A-63-2104).
87, JP-A-6-11078) and environmental pollution problems caused by heavy metal components contained in compound grease, etc., and compound grease such as commercialization of compound grease not containing heavy metal components is involved. Problems started to arise. AP established in 1991
I RP5 C5 is also a program that evaluates the problems of grease amount and grease pressure that affect the joint performance. Moreover, the application of compound grease not only deteriorates the work environment but also reduces the work efficiency.
Therefore, an epoch-making threaded joint which can eliminate the above-mentioned problems if the conventional performance, especially the goring property can be secured without using such compound grease at all. Nevertheless, the reason why compound grease had to be used was that the galling property was deteriorated by several steps with the conventional technique under completely grease-free lubrication.

In order to solve the above-mentioned problems, the inventors have conducted extensive research and as a result, repeated tightening and loosening without using any liquid lubricant such as compound grease which has been conventionally applied before making up the joint. In contrast, it has come to satisfy the use performance such as sealing property without causing galling. The gist of the invention is (1) In a threaded joint of a pipe composed of a pin consisting of a male screw and a metal contact part without a screw and a box consisting of a female screw and a contact part without a screw, the contact surface of the box or the pin is 5 to 40 μm. A pin or box screwing characterized in that unevenness is provided, a resin film layer in which molybdenum disulfide or tungsten disulfide powder is dispersed and mixed in a resin is formed on the surface, and the uneven surface is smoothed with the resin film layer. Sometimes a threaded joint with excellent seizure resistance under no lubrication without grease or liquid lubricant.

(2) In a threaded joint of a pipe composed of a pin consisting of a male screw and a metal contact part without a screw, and a box consisting of a female screw and a contact part without a screw, the contact surface of either the box or the pin is 5 to 5. An unevenness of 40 μm is provided, a resin coating layer in which molybdenum disulfide or tungsten disulfide powder is dispersed and mixed is formed on the surface, and the uneven surface is smoothed by the resin coating layer, and at the same time, the sliding surface A threaded joint excellent in seizure resistance without lubrication without grease and liquid lubricant when screwing a pin and a box, characterized in that the surface roughness is formed to be less than the surface roughness of the uneven surface.

(3) In a threaded joint of a pipe composed of a pin consisting of a male screw and a metal contact part without a screw, and a box consisting of a female screw and a contact part without a screw, the contact surface of the box or the pin has irregularities of 5 to 40 μm. The shape of the resin coating layer is a resin coating layer in which molybdenum disulfide powder is dispersed and mixed in the resin, and the uneven surface is smoothed by the resin coating layer. The proportion of molybdenum disulfide is 30 to 90 wt.
%, And the resin is selected from polyamide-imide resin, epoxy resin, furan resin, and phenol resin, to prevent seizure without lubrication without grease and liquid lubricant when screwing in a pin or box. With excellent screw fittings.

[0011]

The present invention will be described in detail below with reference to the drawings. FIG. 1 shows a schematic part of a constituent member of a joint part applied to the present invention. As shown in FIG. 1, a box 1 which is a joint member
And pin (steel pipe tip joint portion) 2 are provided with predetermined irregularities on only the box 1 or on the contact interface between the box 1 and the pin 2 with respect to the screw portion 3 and the metal-to-metal contact portion 4 constituting the joint member, respectively. , Cover this with a resin coating layer,
The surface of the base material facing the surface-treated layer during screwing of the joint slides. FIG. 2 is a diagram showing an assembly configuration of each joint component member. As shown in FIG. 2, fit the box 1 and the pin 2 together,
The screw portion 3 and the metal-to-metal contact portion 4 are slid while applying high surface pressure. Therefore, for example, an evaluation test of seizure resistance was performed on a premium joint having a metal-to-metal contact portion of φ178 mm, which is the maximum diameter of tubing size that is required to prevent galling when tightening and loosening 10 times. .

Table 1 shows zinc plating, copper plating, tin plating, phosphate treatment among existing surface treatments effective for seizure resistance.
The number of times seizure occurs when the sandblasted box and the machined pin are tightened and loosened without applying a lubricant. Even with copper plating, which is said to have the best seizure property, galling occurs at the third time,
It shows how difficult it is to secure galling resistance without lubrication. This is because, in order to perform a gas seal, a premium joint usually generates a high surface pressure at the metal-to-metal contact portion that exceeds the yield point of the base metal itself of up to 600 MPa, and during joint make-up and breakout. This is because the metals slide with each other under such a high surface pressure.

[0013]

[Table 1]

Therefore, the inventors focused on molybdenum disulfide and tungsten disulfide, which are excellent in the lubricating function under high surface pressure, and worked on the research on the solid lubricating coating for the oil well pipe threaded joint. It is also known that the lubrication effect of a lubricant greatly varies depending on use conditions, that is, surface pressure, sliding speed, type of lubricant, presence / absence, surface texture, temperature, and the like. It is known that molybdenum disulfide may exhibit extremely excellent seizure resistance or may be inferior to ordinary grease lubrication depending on the method of use. In particular, in the case of molybdenum disulfide, it is no exaggeration to say that the surface treatment and the binder (binder) determine the lubricity.

Table 2 shows the number of times of tightening and loosening when a galling occurs when a resin coating is applied to a φ178 mm premium joint. Polyamideimide was used as the resin, and molybdenum disulfide having a mean particle size of 5 μm or more by the Fischer method was used. The content rate of molybdenum disulfide was 80 wt%. No grease or liquid lubricant was used on the contact surfaces. The surface irregularities were formed by, for example, sandblasting. The film thickness is based on the sandblasted surface as a reference value measured by an electromagnetic film thickness meter. From this, when the resin film thickness is significantly thinner than the roughness of the sandblasted surface, galling occurs 10 times before. Therefore, in order to elucidate the goring mechanism in the absence of grease lubrication, the inventors analyzed the cross-section of the coating before and after the test with CMA.
(Computer Aided Micro-ana
It was observed by a lyzer).

[0016]

[Table 2]

FIG. 3 shows sample No. The cross section before the test having the same structure as the cross section after the test of FIG. 4 is a cross section before the test having the same structure as the cross section after the test of FIG. 6
FIG. 3 is a schematic view of each of a pre-test cross section having the same configuration as the post-test cross section of FIG. FIG. 3 shows an example of the present invention in which unevenness is provided on the surface of the base material 5,
A solid lubricant molybdenum disulfide or tungsten disulfide 7 is dispersed and mixed in the resin-based binder 6 so that the uneven surface is completely covered and the surface of the resin coating is smooth. In FIG. 3, after tightening and loosening 10 times, the film thickness was reduced as a whole, but the surface of the base material was not significantly exposed and no galling occurred.

On the other hand, even if the surface roughness is the same, as shown in FIG. 4, when the coating thickness is significantly smaller than the base material surface roughness, the cross section before the test is concave and the coating film thickness is thick and convex. Unevenness remains on the coating surface while being thin and reflecting the unevenness on the base material surface. As a result of the test on the surface, since the convex portions selectively contact and slide, it is possible to assume a mechanism in which the solid lubricant does not sufficiently spread and leads to galling. Sample No. Similar results are exhibited in 7, 8 and 9. This is equivalent to the technique described in Japanese Examined Patent Publication No. 3-78517, but it has been found that when grease is not used, sufficient seizure resistance is not exhibited.

Even when the surface of the coating film is relatively smooth, as shown in FIG. 5, if the surface roughness of the base material is insufficient, galling still occurs. In this case, unlike the above mechanism, the adhesion between the resin and the surface of the base material becomes insufficient, and the resin is peeled off by sliding, so it is presumed that galling occurs. Sample No. When the surface roughness of the base material is as small as 3 μm as shown in 11, the adhesiveness between the resin and the base material surface is insufficient even if the coating film thickness is increased to smooth the coating surface, causing galling.

When the surface roughness of the base material was 50 μm, there were problems from the following two points. One is that the seizure resistance is less than 10 times even though the coating film thickness is made smooth. The other is that the coating of about 50 μm adheres to the threaded portion as well, so that the fitting of the screw becomes tight and the torque required for make-up becomes unnecessarily large. For the above reasons, the film thickness on the surface of the base material is set to R _max.
The thickness is 5 to 40 μm, and the resin having molybdenum disulfide dispersed therein is used to smooth the irregularities, whereby excellent lubricity can be obtained even when not coated with grease.

Table 3 shows the number of times of tightening and loosening when a galling occurred when a resin coating in which polyamideimide was used as a binder and tungsten disulfide was dispersed and mixed was applied to a premium joint of φ178 mm. Tungsten disulfide having a mean particle size of 5 μm or more as measured by the Fischer method was used. Content of tungsten disulfide is 80w
It was set to t%. No grease or liquid lubricant was used on the contact surfaces. The surface irregularities were formed by sandblasting. Similarly to molybdenum disulfide, when the solid lubricant is tungsten disulfide, the film thickness of the base material surface is 5 to 4 at R _max .
By setting the thickness to 0 μm and smoothing the irregularities with a resin coating, excellent lubricity can be obtained even when not applied with grease.

[0022]

[Table 3]

Next, the necessity of making the roughness of the opposing sliding surfaces smaller than the roughness of the uneven surface provided on the coating base will be described. Table 4 shows the test results of the premium joint with the nominal outer diameter of φ178 mm. Here, the box is anti-seizure treated, and the one corresponding to the opposite sliding surface is not resin-coated at the pin seal portion. Sample N
o. As shown in Nos. 21 and 24, when the roughness of the opposing sliding surfaces exceeds the roughness of the base treatment, galling occurs. The reason for this is that the roughness of the opposing sliding surfaces has the effect of sweeping out the solid lubricant that is present in the concave surface in the base treatment.
It is speculated that it is more prone to goring. Therefore, in this case, the roughness of the opposing sliding surfaces is smaller than the surface treatment roughness of the box, which is effective in extending the seizure resistance.

[0024]

[Table 4]

Next, the content of molybdenum disulfide is set to 30-9.
The reason for specifying 0 wt% will be described. Table 5 shows the test results when a resin coating having a different molybdenum disulfide content was applied to a premium joint having a nominal outer diameter of φ178 mm. From this, it was found that when the molybdenum disulfide content was less than 30%, galling occurred. The reason for setting the upper limit to 90% is that if the amount is more than 90%, the binding force of molybdenum disulfide by the resin is expected to decrease.

[0026]

[Table 5]

Next, the resin binder is polyamide imide,
The reason for specifying epoxy, furan, and phenol is that the tensile strength and impact value are relatively high, and the bonding strength with molybdenum disulfide is also strong. Further, when considering the swelling property, the polyamide-imide is the most preferable, and when considering the mixed use with the compound grease, the polyamide-imide is the most preferable. When polyamide imide was used, excellent seizure resistance was exhibited regardless of whether or not grease was applied.

[0028]

As described above, according to the present invention, without using liquid lubrication such as grease at all, seizure resistance is excellent under non-lubrication without causing galling in repeated tightening and loosening. Located in the screw joint.

[Brief description of drawings]

FIG. 1 is a schematic view of a joint component member to which the present invention is applied,

FIG. 2 is a diagram showing an assembly configuration of each joint component member;

FIG. 3 shows the relationship between the resin coating according to the present invention and the surface roughness, and the coating cross section after the test.

FIG. 4 is a schematic view of a cross section of a resin coating of a known example before and after the test,

FIG. 5 is a schematic diagram before and after the test when the surface roughness is insufficient.

[Explanation of symbols]

 1 Box 2 Pin 3 Screw Part 4 Metal Contact Part 5 Base Material Surface 6 Resin 7 Solid Lubricant

Claims (3)

[Claims] 1. A threaded joint for a pipe, which comprises a pin consisting of a male screw and a metal contact part without a screw and a box consisting of a female screw and a contact part without a screw, wherein the contact surface of the box or the pin is provided with irregularities of 5 to 40 μm. , A molybdenum disulfide powder or a tungsten disulfide powder dispersed and mixed in a resin to form a resin coating layer on the surface, and the uneven surface is smoothed with the resin coating layer. A screw joint with excellent seizure resistance under no lubrication without liquid lubricant. 2. A threaded joint for a pipe comprising a pin consisting of a male screw and a metal contact without a screw and a box consisting of a female screw and a contact without a screw, wherein the contact surface of either the box or the pin is 5 to 40 μm. The surface of the opposite sliding surface is formed at the same time as forming a resin coating layer in which molybdenum disulfide or tungsten disulfide powder is dispersed and mixed in a resin on the surface, and the uneven surface is smoothed by the resin coating layer. A threaded joint excellent in seizure resistance without lubrication without grease and liquid lubricant when screwing a pin and a box, characterized in that the roughness is formed to be less than the surface roughness of the uneven surface. 3. A threaded joint for a pipe, which comprises a pin consisting of a male screw and a metal contact part without a screw and a box consisting of a female screw and a contact part without a screw, wherein the contact surface of the box or the pin is provided with irregularities of 5 to 40 μm. , A resin coating layer in which molybdenum disulfide powder is dispersed and mixed is formed on the surface, and the uneven surface is smoothed by the resin coating layer, which is a characteristic feature, and the proportion of molybdenum disulfide is 30 to 90 wt%.
The resin is selected from polyamide-imide resin, epoxy resin, furan resin, and phenol resin, and has excellent seizure resistance under no lubrication without grease and liquid lubricant when screwed into a pin or box. Screwed joints.