JPS61136087A - Pipe joint for oil well pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pipe joint for oil country tubular goods that are vertically inserted deep underground to extract natural gas and crude oil produced underground. .

[Background of the invention]

The depth of wells that produce crude oil is several thousand meters, and in recent years the depth has been increasing further to reach 10,000 meters. A huge number of oil country tubular goods are inserted vertically into such wells, and they are all connected in series by pipe joints. Various severe forces act on such pipe joints. Firstly, the tensile force in the axial direction due to the accumulated weight of the pipe and pipe fitting itself, and secondly the compressive force on the outer circumferential surface due to Tonosho,
The third factor is the pressure exerted by the internal fluid on the inner circumferential surface.

Needless to say, these forces become even more severe as the well deepens. For pipe joints that can be used under these increasingly severe conditions, it is very important that they can withstand enormous tensile loads and maintain reliable airtight sealing. Therefore, many proposals have been made to meet these demands.

[Conventional technology and its drawbacks]

Below, conventional proposed techniques will be considered. Satisfactory results have been achieved by improving the shape, pitch, etc. of the threaded portion of the joint in order to develop technology that can withstand enormous tensile loads. Regarding airtight sealing performance, in addition to the sealing at the threaded portion, a tapered lip portion is formed to provide a metal-to-metal sealing portion, thereby ensuring a certain degree of sealing performance.

However, metal-to-metal seals have a problem of galling (seizure) during tightening.

Usually, the seal part of oil country tubular goods and joints has a weight of 100 to 150 k.
A high surface pressure of g/w' is applied, and galling is likely to occur if there is insufficient lubrication of the seal part during fastening. When this galling occurs, it causes a seal failure, leading to a loss of confidence in the airtight sealing performance of the pipe joint as a whole, which may lead to accidents such as oil or gas leaks.

Therefore, as one of the countermeasures, conventionally, a chemical conversion coating such as a zinc phosphate coating or an iron oxalate coating and Zn plating are applied to the metal-to-metal seal portion. In addition, when high lubrication is particularly required or when forming a chemical conversion film (for high alloy materials, Cu plating or MoS2 paste is used. However, in the case of the chemical conversion film and Zn plating, lubrication is Cu plating had the disadvantage that galling resistance was poor due to insufficient galling resistance, and galling occurred after only a few uses.Also, in the case of Cu plating, it corrodes significantly in environments such as hydrogen sulfide, so it has been developed in recent years. It was inappropriate to use it with high alloy materials that can withstand use in the corrosive environment that is currently used.Furthermore, when Mo32 paste is used, it is easy to peel off due to weak adhesion to the other material, and the seal There was a problem in that it was difficult to supply and adhere MoS2 paste to the parts, and high lubricity could not be obtained.

Table 1 shows the test methods for evaluating galling resistance.
This figure shows the test results of the prior art in which iron oxalate and Cu plating were applied to the metal-to-metal seal portion of the base material using the tight test and Bowden friction test. The base material is a duplex stainless steel shown in Table 3. It should be noted that the tight test is a test in which the actual joint is repeatedly tightened and untightened, and the number of repetitions until galling occurs is evaluated as galling resistance. In addition, the Bowden friction test evaluates the number of sliding movements until galling occurs using a Bowden friction tester as galling resistance. The test conditions for the Bauden friction test are as follows.

Bowden friction test conditions.

Shape of tip of test piece on bottle side: Hemisphere with diameter of 3/16 inch Surface roughness:
0.5p mRmax or less Test piece shape on plate side = 3cm x 15m x 100tm Surface roughness = 2 to 35μmRmax Sliding conditions Pressing load: 3kgf Sliding length: 10n+ Sliding speed variation: 4tx/see Temperature = 200 °C Lubricant Varnish Red Compound Log/rrf.

(Margins below, continued on next page) Table 1 As is clear from Table 1, the conventional technology for forming iron oxalate coatings on metal-to-metal seals has failed in both the tight test and Bowden test. Galling resistance is insufficient. In addition, in the case of Cu plating, although it exhibits sufficient galling resistance, it cannot withstand use in a corrosive environment, as described above.

Furthermore, conventionally, by applying noble metal plating such as Au plating, some products can withstand use in corrosive environments and at the same time improve galling resistance. However, in this case, there was a problem in that the base material itself corroded due to the action of the local battery.

In short, conventional pipe joints for oil country tubular goods have not been sufficiently satisfactory in terms of galling resistance, corrosion resistance, and range of use of materials as base materials.

[Means for Solving the Problems] The present invention improves and eliminates the above-mentioned drawbacks of conventional pipe joints for oil country tubular goods, and can be used for a wide range of materials from general materials to high-alloy materials. It is an object of the present invention to provide a pipe joint for oil country tubular goods which has excellent galling resistance and is free from corrosion and has a high slip resistance of 12I, which is higher than that of Cu plating.

The gist of the present invention is therefore a pipe joint for oil country tubular goods having a metal-to-metal seal portion, the surface roughness of at least one side of the metal-to-metal seal portion being 5 to 25 μm.
This is a pipe joint for oil country tubular goods, characterized in that the surface roughness is equal to or less than the surface roughness, and a synthetic resin coating is formed on the surface of the synthetic resin in which MoS2 powder with a particle size of 10 μm or less is dispersed and mixed at a ratio of 20 to 90 wt%.

The configuration of the present invention will be explained in more detail below with reference to the drawings.

11th! I is a half-longitudinal cross-sectional view showing a coupling type oil country tubular pipe joint part. In the figure, 1 is an oil country pipe, 2 is a coupling, 3 is a male thread formed in the oil country country pipe 1, and 4 is a female thread formed in the coupling 2. A tapered lip portion 5 without a threaded portion is formed at the tip of the male thread 3 of the oil country tubular goods 1. Also coupling 2
A tapered screw heating portion 6 corresponding to the lip portion 5 is formed at the inner part of the female thread 3 . Said lip portion 5
The tube end 5a, the screw heat section 6, and the stepped section 6a constitute a metal-to-metal seal section 7. The present invention aims to form a resin coating on the metal-to-metal seal portion 7, which has excellent galling resistance and corrosion resistance, and can be used with a wide range of materials.

By the way, in general, resin coatings are non-conductive and do not form local batteries even when they come into contact with metal, and do not affect the corrosion of the base material to which they are applied, and since the resin itself is a polymer, It has the property of being resistant to decomposition and deterioration. This property is most suitable as a lubricating base material for oil country tubular pipe joints, which is the object of the present invention. As a result of repeated experiments to impart galling resistance to resin coatings, the present inventors found that resin coatings exhibit sufficient galling resistance equivalent to or better than Cu plating under the following conditions. .

That is, (1) The particle size of the MoS2 powder added to the resin forming the coating must be 10 μm or less.

(2) The resin used to form the film is MoS2 powder at 20 to 90%
It must include the revised percentage.

(2) The metal-to-metal seal portion 7 of the base material has a surface roughness of a maximum height of 5 to 25 μmRmax.

(2) The thickness of the resin coating shall be less than or equal to the maximum height of the surface roughness.

It is.

FIG. 2 is an enlarged sectional view when the resin liquid lIw8 is formed on the lip portion 5 of the metal-to-metal seal portion 7 under the above conditions.

Next, the experimental method used to discover the reason for limiting the conditions and the reason for fixing them will be explained with reference to FIGS. 3 to 5. In both cases, the material used for the Bauden friction test is duplex stainless steel shown in Table 3 (same as in the conventional case shown in Table 1). In the case of Figures 3 and 4, the surface roughness of the plate used for the Bauden friction test is 15μaR+sax, and the coating thickness is 10μm.
It is. The surface roughness may be formed by sandblasting, shotblasting, or the like.

First, the reason for limiting the particle size of the MoS2 powder is as shown in FIG. By the way, M in this case
The amount of oS2 powder added was 70-t%, and the base resin was a low molecular weight epoxy resin. Other conditions are as described above.

What is clear from FIG. 3 is that as the particle size increases beyond 10 μm, the galling resistance rapidly decreases, and the amount of particles peeled off during friction increases rapidly. Therefore, the particle size of the MO32 powder is preferably 10 μm or less.

Next, the reason for limiting the mixing ratio of MO32$5) powder will be explained with reference to FIG. In FIG. 4, silicone resin (molecular weight approximately 2000), low molecular weight epoxy resin (molecular weight approximately 20,000), and polyether sulfone are used as base resins. The test method was to use an average particle size of 6 μm (particle size distribution width of 3 to 10 μm) for each resin.
[mu]m) MoS2 powder was added in a range of 10 to 115 wt% as appropriate, and a Bowden friction test was conducted for each content to compare galling resistance. Other test conditions were as described above. What is clear from the results shown in Figure 4 is that for any resin, MoS
If the content of the two powders is 15 wt% or less, the galling resistance is low. In addition, the galling resistance is 20-
It rises sharply after reaching t%, and then drops sharply again above 90-t%. In particular, in the case of polyether sulfone and low molecular weight epoxy resin, the content of MoS2 powder is within the range of 20 to 90 iv t%, and the galling resistance is higher than that of Cu plating (150).

In addition, when MoS2 powder is added in this way, the galling resistance improves rapidly, and epoxy phenol resin (molecular weight 1
000-3000), acrylic resin (molecular weight 2000
~5000), urethanized part (molecular weight 3000~10
000), ferrule resin (molecular weight 2000-50
00).

Resorcinol epoxy resin (molecular weight 20,000-5,000
Resins such as 0), polyamide resin (nylon 66), polyoxybenzoyl (Econol), polyimide resin, and isocyanate resin were confirmed. Moreover, even with these resins, the content of MO52 powder required to obtain galling resistance equivalent to or higher than that of Cu plating was common to all resins, and was approximately 20 to 90 wt%.

By the way, MoS2 is known as a solid lubricant with good lubricity, and it is considered as a matter of course that when the amount added increases, the lubricity improves. However, according to the experiment shown in Figure 4, M
When the oS2 content exceeds 90-t%, the galling resistance is extremely low. This is because the adhesion of the resin coating containing MoS2 powder was low in both cases, and peeling occurred during the friction test.

Therefore, 1 synthetic resin made by mixing this MO52 powder
It is clear that the technology used as fJif agent alone cannot achieve the objective.

Next, the reason for limiting the surface roughness of the base material (lip portion 5) and the thickness of the resin coating will be explained with reference to FIG.

In this case, the amount of MoS2 powder added was 70-t%, and the average particle size was 6 μm (distribution width 3 to 10 μl11).

The resin used as the base material is a low molecular weight epoxy resin.

The test is a Bauden friction test, and the surface roughness of the duplex stainless steel plate as the base material is 2 to 35 μmRm.
ax, and each resin was coated with the above-mentioned mixing ratio to a film thickness of 3 to 30 μm.

What is clear from FIG. 5 is that when the coating thickness is 3 μm, the galling resistance is low regardless of the surface roughness. This is due to lack of lubrication. Also, the coating thickness is 5
In μm, the surface roughness of the base material is 5 to 25 μm Rmax
Within this range, the galling resistance is equal to or higher than that of Cu plating. What should be noted is that when the coating thickness is 10 μm and the surface roughness is 10 μm or more, the coating thickness is 20 μm. In cIm, when the surface roughness is 20 μm or more, it is equivalent to or better than Cu plating. In other words, when the surface roughness is larger than the coating thickness (when the coating thickness is smaller than the surface roughness), it exhibits galling resistance equal to or higher than that of Cu plating. This shows that the thickness of the resin coating and the surface roughness are closely related, and at the same time, by making the thickness of the resin coating thinner than the surface roughness of the base material, the effect of the surface roughness of the base material on the coating surface is reduced. This indicates that it is better to keep small and gentle unevenness to a certain extent.

In other words, if the coating thickness is made thinner than the surface roughness and fine irregularities are provided on the coating surface, the lubricant (thread comparand) normally used during actual fastening work will be filled into the recesses, and the lubricant will This means that good lubricity is obtained due to the synergistic effect of the coating and the lubricant because the friction surfaces come into contact with each other through the . In addition, when the film thickness is thicker than the surface roughness (see the chain line in Figure 2), the surface of the film becomes smooth, the lubricant is easily squeezed out, and good lubricity is obtained due to the synergistic effect with the lubricant. This means that not only does it disappear, but the coating becomes more prone to wear and peeling, making it difficult to maintain its lubricating effect.

By the way, it is known that airtight sealability is impaired if the surface roughness of the base material exceeds 25 μmRmax. Therefore, the surface roughness of the base material (lip portion 5) is 5 to 25 μm.
Rmax is appropriate, and the thickness of the resin coating is 5 to 25μ.
-1) <Appropriate.

From the above study results, it is clear that in order to achieve the object of the present invention, it is necessary to satisfy the conditions described in items 1 to 0 above.

〔Example〕

Next, specific examples will be described based on Tables 2 and 3. Table 2 compares the case of the present invention and the case of the prior art, and Table 3 shows the materials of the base materials in Table 2. The galling resistance was evaluated using the Bowden friction test, and the galling resistance was 150% compared to conventional Cu plating.
was taken as the average index, and if it was higher than that, it was determined to be good, and if it was lower than that, it was determined to be poor.

As is clear from Table 2 above, the galling resistance of the present invention exceeds the galling resistance of 150 for conventional Cu plating, and is extremely excellent. ing.

By the way, the present invention is not limited to the above-described embodiments, and can be modified as appropriate. For example, the joint may be of a coupling type or an integral type joint that directly connects oil country tubular goods and oil country country tubular goods. In addition, the formation of surface roughness on the base material and the formation of a resin film added with MoS2 powder on this uneven surface can be performed even if the lip part 5 is not carved with a male thread, and the thread heat on the female thread side can be formed. Of course, it may be part 6.

〔Effect of the invention〕

As explained above, the present invention can be used for a wide range of materials from general materials to high-alloy materials, has no fear of corrosion in corrosive environments, and has high lubricity superior to that of Cu plating. It is possible to provide oil country tubular goods with excellent galling resistance.

[Brief explanation of the drawing]

The drawings are all related to the present invention; Fig. 1 is a half-longitudinal cross-sectional view of a coupling-type pipe joint, Fig. 2 is an enlarged view of the lip portion thereof, and Fig. 3 is a particle size of MoS2 powder and galling resistance. FIG. 4 is a drawing showing the relationship between MoS2 powder content and galling resistance, and FIG. 5 is a drawing showing the relationship between base material surface roughness and galling resistance. 7...Metal-to-metal seal portion l...Oil country tubular goods 2...Coupling patent applicant Sumitomo Metal Industries Co., Ltd. Representative Patent attorney Toshihiko Uchida 3rd page=:::Kakudaku page 5

Claims (1)

[Claims] 1. A pipe joint for oil country tubular goods having a metal-to-metal seal, wherein the surface roughness of at least one side of the metal-to-metal seal is 5 to 25 μmRmax, and 20 μm of MoS_2 powder with a particle size of 10 μm or less is applied to the surface. ~90W
1. A pipe joint for oil country tubular goods, characterized in that a coating of synthetic resin dispersed and mixed at a ratio of t% is formed with a thickness equal to or less than the surface roughness.