JP5910284B2 - Coating method for threaded joint for steel pipe and threaded joint product for steel pipe - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for forming a film of a threaded joint for steel pipes and a threaded joint product for steel pipes. More particularly, the present invention relates to an oil well tubular or OCTG (oil country tubular) that generally includes tubing and casing used for exploration and production of oil wells and gas wells. goods), a method for forming a film of a threaded joint for steel pipes, and a threaded joint for the threaded joints for connecting steel pipes such as riser pipes and line pipes, which have excellent galling resistance and sealability The present invention relates to a steel pipe threaded joint product.

  Threaded joints are widely used to connect steel pipes used in oil industry equipment such as oil well pipes. Conventionally, a standard threaded joint specified in the API (American Petroleum Institute) standard has been typically used for connecting steel pipes used for oil and gas exploration and production. However, in recent years, the wells for crude oil and natural gas have been deepened, and the number of vertical wells, horizontal wells, inclined wells, etc. has increased, and the drilling and production environment has become severe. In addition, the demand for screw joints such as compression resistance, bending resistance, and external pressure seal performance has been diversified due to the increasing development of wells in poor environments such as the ocean and polar regions. For this reason, the use of high-performance special threaded joints called premium joints is increasing, and the demands on the performance are also increasing.

  The premium joint usually has pins (male) 1 formed at both ends of each pipe and a box (female) 2 coupled to the pins 1 as shown in FIGS. 1 and 2, for example. . The pin 1 and the box 2 have a taper screw 3 as a mutually corresponding portion, a seal portion (specifically, a metal touch seal portion) 4 provided on a non-screw portion 9 connected thereto, and an end portion of the non-screw portion 9. A shoulder portion (specifically, a torque shoulder portion) 5 provided on the side is formed.

  The taper screw 3 is important for tightly fixing the threaded joint, and the seal portion 4 plays a role of ensuring sealing performance by the metal-metal contact between the box 2 and the pin 1, and the shoulder portion 5 is a screw The shoulder surface serves as a stopper during tightening of the joint. In addition, as shown in FIG. 1, the threaded joint designed so that the seal portion 4 seals the fluid by making a metal contact with the opposing surface in the radial direction at a part of the non-threaded portion 9 is a radial seal type screw. Called a joint. In the radial seal type threaded joint, as shown in FIG. 2, the seal portion 4 is a shape that simulates the state at the completion of tightening of the threaded joint by using the same scale drawings of the corresponding pin 1 and box 2. Is designed as a region where the male and female non-threaded portions 9 interfere with each other, and the seal contact length Ls is defined by the tube axis direction length Ls of the interfering regions. In the example of FIG. 2, the non-threaded portion 9 has a male-side outer peripheral surface having a curved shape and a female-side inner peripheral surface having a tapered shape. The seal taper angle θ is defined by the angle θ formed by the conical bus forming the taper shape and the tube axis direction 7. Further, when the threaded joint is tightened, the seal point SP is defined by the inner point of the outer peripheral surface of the male seal portion that first contacts the inner peripheral surface of the female side seal portion. Then, the seal radius R of the pin 1 is defined by the curvature radius R of the curve formed by the male outer peripheral surface (curved surface shape) of the non-threaded portion 9 in the cross section in the tube axis direction at the position corresponding to the seal point SP. Is done.

In the radial seal type threaded joint, there is a problem that goling (seizure) is likely to occur because the sliding distance of the seal portion 4 becomes long when the screw is tightened.
As a conventional technique that addresses the above problems, Cr ≧ 0 in order to ensure the hermeticity of the threaded joint for oil well pipes and to form a phosphate-based film with excellent galling resistance and wear resistance performance on the surface of the oil well pipe threads. For oil well pipes using Cr-Mo steel containing 0.08% by mass and Mo ≧ 0.02% by mass, a pin (male) screw or box (female ) The surface of either one of the screw joints is subjected to uneven processing with an average surface roughness Ra of 10 μm or less by shot blasting or the like (see Patent Document 1).

JP 2002-364786 A

However, the inventors examined the prior art and found that there were the following problems.
That is, for example, as shown in FIG. 3, a phosphate-based film (for example, Mn phosphate) has poor wear resistance when used alone (mode 1), while a base material (mode 3) that is the base material of the film. Is poor in galling resistance, but in the mixed region of the film and the base material (mode 2), Mn phosphate contributes to improvement of lubricity, and the base material contributes to wear resistance. Both galling resistance is good, and the larger the thickness of the mode 2, the better the galling resistance is maintained. However, when surface roughness (Ra ≦ 10 μm) is imparted to the base material by shot blasting prior to film formation according to the conventional technique, a large number of dot-like convex portions 20 are dispersed as shown in FIG. A point contact state is formed, and a leak path 21 is likely to be formed by sewing between such a large number of dispersed point contact locations, and the sealing performance is likely to deteriorate. Under the condition that the surface roughness after shot blasting is made small in order to suppress the deterioration of the sealing property, the thickness of the mode 2 becomes thin and the galling resistance is lowered.

  In other words, the conventional technique for improving wear resistance and galling resistance (Ra (≦ 10 μm) imparted by shot blasting to either male or female → imparting a phosphate-based film) is likely to cause deterioration of the sealing performance. There was a problem.

In order to solve the above-mentioned problems, the inventors have devised means for improving wear resistance and galling resistance while ensuring sufficient sealing performance, and have made the present invention. That is, the present invention is as follows.
(1) A shoulder portion provided on both males and males at the time of tightening the screw joint, comprising male and female pins and female side boxes of male and female males and females having corresponding male and female taper screws. The pin and the box abut on each other in the axial direction, and the pin and the box make a metal contact in the radial direction to seal the fluid at a seal portion provided between the shoulder portion and the taper screw. a structure has been the pin or film-forming method of a threaded joint for steel pipes subjected to the outermost layer coating treatment of phosphate-based on the box tubular threaded joint, prior to the outermost layer coating process, the most A circumferential groove with an average surface roughness Ra in the tube axis direction of 1.0 μm or more and 5.0 μm or less is given to the seal portion on the pin side or the box side, which is the side subjected to the surface film treatment, by cutting. Or even more Small irregularities so as not to crush roughening at shot blasting, then the and performs outermost layer film treatment, and improved wear resistance, galling resistance while securing sealing performance, a steel pipe A method of forming a film on a threaded joint.
(2) A point cut tool is used for the cutting, and the circumferential groove is provided by controlling a tip shape of the point cut tool, a pipe radial direction cutting amount, and a pipe axis direction feed. The film formation method of the threaded joint for steel pipes as described in said (1).
(3) The tube axis direction feed per rotation of the point cut tool is set to Ls / 10 or less with respect to the seal contact length Ls which is the length in the tube axis direction of the region in which the metal is brought into contact. The film formation method of the threaded joint for steel pipes as described in (2).
(4) A pin having a male taper screw and a box having a female taper screw of males and females forming a threaded joint correspondingly, and a box having a female taper screw are mounted on the shoulder portion provided to both the male and female when tightening the threaded joint. The pin and the box are in contact with each other in the axial direction, and the pin and the box are in metal contact in the radial direction at the seal portion in the non-threaded portion between the shoulder portion and the taper screw portion provided on both the male and female. A steel pipe threaded joint product having a structure for sealing a fluid, wherein a phosphate-based film is formed by the film forming method for a steel pipe threaded joint according to any one of (1) to (3) above. A threaded joint product for steel pipes, characterized in that the average surface roughness Ra in the pipe axis direction at the interface between the phosphate-based film and the base material that is the base material is 1.0 to 5.0 μm.
(5) The seal portion in the outer surface of the pin has an arc shape with a seal radius R of the pin being 1.0 inch or more in the cross section in the tube axis direction, and the seal portion in the inner surface of the box is the seal of the box in the cross section in the tube axis direction. The threaded joint product for steel pipes according to (4) above, which has a linear shape with a taper angle θ of 3.0 to 10.0 degrees.

  According to the present invention, an average surface roughness Ra in the tube axis direction is 1.0 μm or more and 5.0 μm by cutting the pin or the seal portion of the box on the side subjected to the film treatment before the film treatment. Since the following circumferential grooves are provided and then the film treatment is performed, it is possible to improve wear resistance and galling resistance while ensuring sufficient sealing performance.

It is a cross-sectional schematic diagram which shows the example of a radial seal type premium joint. It is the A section enlarged view of FIG. It is a schematic diagram which shows the cross-section of a phosphoric acid Mn film formation part. 1A and 1B are a schematic cross-sectional view (a) and a schematic plan view (b) showing an example of an embodiment of the present invention. It is a plane schematic diagram which shows the problem of a prior art.

  In the present invention, as shown in FIG. 1 and FIG. 2, a male pin 1 and a female box 2 of male and female males and females having corresponding male and female taper screws 3 are formed. The pin 1 and the box 2 are in axial contact with each other at a shoulder portion 5 provided on both the male and female when the threaded joint is tightened, and is provided between the shoulder portion 5 and the taper screw 3. The pin 1 and the box 2 of the threaded joint for steel pipes are structured such that the pin 1 and the box 2 are in metal contact with each other in the radial direction at the seal portion 4 to seal the fluid. The point of applying is the same as in the prior art.

However, in the present invention, before the coating treatment, the case where the coating treatment is applied to the seal portion 4 on the pin 1 side or the box 2 side, for example, on the box 2 side is shown. Similarly, the circumferential groove 8 having an average surface roughness Ra in the tube axis direction of 1.0 μm or more and 5.0 μm or less is provided by cutting, and then the coating treatment is performed.
When the point cut tool 10 is used for the cutting as shown in FIG. 4 and the tip shape of the point cut tool 10, the amount of cutting in the radial direction of the pipe and the feed in the pipe axis direction are controlled, the circumferential groove 8 is provided. Since the surface roughness can be made simultaneously with the sealing shape processing, it is efficient.

  By forming the circumferential grooves 8 in this way by cutting, periodic irregularities are formed in the tube axis direction as shown in FIG. 4, and the groove edges 8A of the grooves 8 that are the cutting traces are irregularities of the irregularities. The groove edge 8A has a very long line contact that spirally circulates around the circumferential surface over both ends of the seal contact length Ls part when the threaded joint is tightened after subsequent formation of the phosphate film. Therefore, the leak path 21 as shown in FIG. 5 is extremely difficult to form.

If the Ra applied by circumferential groove processing by cutting is less than 1.0 μm, the thickness of the mode 2 becomes insufficient and sufficient galling resistance cannot be obtained. On the other hand, when Ra is more than 5.0 μm, the area of the line contact region is insufficient, the contact surface pressure becomes excessive, and wear is promoted, so that the galling resistance and the sealing performance are deteriorated. Therefore, Ra is set to 1.0 to 5.0 μm.
In addition, it is preferable to provide shot-blasting with small unevenness that does not crush the unevenness of the groove on the surface to be processed after the cutting, because galling resistance is further improved.

Further, from the viewpoint of further improving the sealing performance, in the cutting process, it is preferable that the feed in the tube axis direction per rotation of the point cut tool 10 is Ls / 10 or less.
Moreover, from the point of the obviousness of the effect by application of the film forming method of the present invention, the target threaded joint is a special threaded joint (premium joint) of the form shown in FIGS. A special threaded joint with a pin side that has a circular arc shape with a pin seal radius R of 1.0 inch or more, and a box side that has a linear shape with a seal taper angle θ of the box of 3.0 to 10.0 degrees. It is preferable that

  Pins with special screw machining in the form of Fig. 1 and Fig. 2 on the seamless pipe material of carbon steel P110 (specified in ISO11960) of outer diameter 9-5 / 8inch x wall thickness 0.545inch at multiple experimental levels A make & break (abbreviated as M & B) test described in ISO 13679 was performed using the corresponding box to evaluate galling resistance. For each level, for the seal part of the box, cut it in a spiral shape with a point cut tool to form a circumferential groove, or apply shot blasting to give surface roughness, and then treat with Mn phosphate To form a Mn phosphate coating. Table 1 shows experimental conditions and experimental results. From Table 1, it was shown that by passing Ra of the box before the treatment with Mn phosphate to 1.0 μm or more, M & B was passed 4 times and excellent galling resistance was exhibited.

  Next, the series A test described in ISO 13679 was performed to evaluate the sealing performance. The results are shown in Table 1. From Table 1, leakage occurred under the condition that Ra was increased by shot blasting to improve galling resistance. On the other hand, even when Ra was increased by cutting, leakage occurred when Ra of the box before the Mn phosphate treatment was excessively increased. On the other hand, it became clear that the examples of the present invention have excellent sealing properties. In particular, the ratio of the feed amount of the point cut tool to the contact length Ls of the seal portion is set to 1/10 or less, and the seal radius R of the pin is set to 1.0 inch or more. It was shown that sealability can be secured even under high compressibility conditions.

1 pin 2 box 3 taper screw 4 seal part 5 shoulder part 6 tube axis 7 pipe axis direction 8 circumferential groove 8A groove edge 9 non-threaded part 10 point cut tool 20 point-like convex part 21 leak path
Ls: Seal contact length θ: Seal taper angle R: Pin seal radius
SP: Seal point

Claims (5)

A male and female pin having male and female taper screws having corresponding tapers and a box on the female side are provided, and at the time of tightening the screw joint, The pin and the box are in contact with each other in the axial direction, and the pin and the box are in metal contact in the radial direction to seal the fluid at a seal portion provided between the shoulder portion and the taper screw. and the pin or the box tubular threaded joint comprising a film-forming method for a threaded joint for steel pipes subjected to the outermost layer coating treatment of phosphate-based, said before the outermost layer film treatment, the outermost layer film treatment A circumferential groove that gives an average surface roughness Ra in the tube axis direction of 1.0 μm or more to 5.0 μm or less by cutting is given to the seal portion on the pin side or the box side, which is the side to be processed, or further Unevenness of the groove Grant by small irregularities shot blasting as not crushed, then the and performs outermost layer film treatment, and improved wear resistance, galling resistance while securing sealing performance, tubular threaded joint Film forming method.
  The point cutting tool is used for the cutting, and the circumferential groove is provided by controlling a tip shape of the point cutting tool, a pipe radial direction cutting amount, and a pipe axial direction feed. The film formation method of the threaded joint for steel pipes as described in any one of.   The tube axis direction feed per one rotation of the point cut tool is set to Ls / 10 or less with respect to a seal contact length Ls which is a length in the tube axis direction of the region in which the metal is contacted. The film formation method of the threaded joint for steel pipes of description.   A pin having a male side taper screw and a box having a female side taper screw of a male and female that form a screw joint correspondingly, and a box provided with both male and female when tightening the screw joint, The box and the box are in contact with each other in the axial direction, and the pin and the box are in metal contact with each other in the radial direction at the seal portion in the non-threaded portion between the shoulder portion and the taper screw portion provided on both the male and female. A threaded joint product for steel pipes having a structure to be sealed, wherein a phosphate-based film is formed by the film forming method for a threaded joint for steel pipes according to any one of claims 1 to 3, and the phosphate A threaded joint product for steel pipes, characterized in that the average surface roughness Ra in the pipe axis direction at the interface between the base film and the base material which is the base material is 1.0 to 5.0 μm.   The seal portion in the outer surface of the pin has an arc shape with a pin seal radius R of 1.0 inch or more in the cross section in the tube axis direction, and the seal portion in the inner surface of the box has a seal taper angle θ of the box in the cross section in the tube axis direction. 5 is a linear shape of 3.0 to 10.0 degrees, the threaded joint product for steel pipes according to claim 4.

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