JP2006112594A - Metal covering steel pipe screw joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve both of the corrosion resistance and the sealing performance of a steel pipe screw joint. <P>SOLUTION: In the steel pipe screw joint comprising tubular pins 12, 22 formed in the end of steel pipes 10, 20 and a coupling 30 engaged to the pin, the tubular pins 12, 22 have male screw parts 13, 23 with screw grooves and pin seal parts 14, 24 to seal the leakage of the fluid flowing in the steel pipe interacting with the coupling 30. The coupling 30 provides a female screw part 33 that each male screw part 13, 23 of two pieces of steel pipes to be connected can be engaged and a coupling seal part 35 to seal the leakage of the liquid interacting with the pin seal parts 14, 24. The pin seal parts 14, 24 and the coupling seal part 35 are covered by layers 17, 27, 37 with 0.1 mm or more thickness of more excellent corrosion proof metal than the base material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a metal-coated steel pipe threaded joint having corrosion resistance and sealing properties.

Threaded joints of clad steel pipes used for oil well pipes and the like are required to have corrosion resistance and sealability. For this reason, there is a technique in which a Ni plating layer is coated to a thickness of 1 to 100 microns on a pipe end portion (including a coupling inner surface when a coupling is used) where the base material is directly exposed to a corrosive environment (for example, patents). Reference 1). In addition, in a threaded joint using a pin and a coupling, there is a technique of replacing the tip end portion of the pin and the central portion of the coupling with a corrosion-resistant metal material (for example, see Patent Document 2).
JP 57-92182 A (Claim 1, FIG. 1) WO99 / 43974 (page 7, line 16 to page 8, line 4, FIG. 1)

However, with a coating thickness of 1 to 100 microns, the fluid flowing inside the tube enters the inside of the coating surface, and the Ni plating layer covered by the pressure at the time of tightening and tightening is reduced, so that the corrosion resistance is maintained. It may not be possible. Furthermore, since it is not considered to cover the seal surfaces of both the pipe end portion and the coupling in the contact seal portion between the pipe end portion and the coupling used integrally therewith, corrosion at that portion is not considered. In some cases, the sealing performance may not be maintained.
In addition, in order to replace the tip of the pin and the center of the coupling with another metal material, it is necessary to use a material that has both strength and corrosion resistance, which increases the material cost considerably. It becomes difficult to obtain a high-strength seal part.

In order to solve the above problems, the present invention employs the following metal-coated steel pipe threaded joint.
(1) In a steel pipe threaded joint comprising a tubular pin formed at the tip of a steel pipe and a coupling fitted to the pin, the tubular pin cooperates with the male threaded portion having a thread groove and the coupling. A pin seal portion that seals leakage of a fluid flowing in the steel pipe, and the coupling includes two female screw portions that can be fitted to the male screw portions of the two steel pipes to be coupled, and the pin seal portion. And a coupling seal portion that seals leakage of the fluid, and the pin seal portion and the coupling seal portion have a thickness exceeding 0.1 mm of metal that is more corrosive than the base metal constituting them. It is characterized by being coated with a layer of
(2) The pin seal portion is formed as a cylinder projecting from the tip of the male screw portion, and the coupling seal portion includes a surface for receiving the tip surface and the outer peripheral surface of the cylinder body between the two female screw portions. It is characterized by being formed as an internal shoulder.
(3) The seal ring for sealing the leakage of the fluid is disposed between the cylindrical bodies of the left and right tubular pins to be connected.
(4) A seal ring that seals against leakage of the fluid is disposed between a front end surface of the cylindrical body and the internal shoulder.
(5) An intermediate shoulder that abuts the tubular pin and the coupling is provided at an intermediate portion of the male screw portion and an intermediate portion of the female screw portion.
(6) When compressive stress up to 95% tube YS is applied, the screw flank surface is also brought into contact, so that not only the internal shoulder but also the screw flank surface bears the compressive stress. .

(7) In a steel pipe threaded joint comprising a tubular pin formed at the tip of a steel pipe and a tubular box fitted to the pin formed at the tip of the steel pipe, the tubular pin has a male screw part having a thread groove, the box, The box includes a pin seal portion that seals leakage of fluid flowing in the steel pipe, and the box cooperates with the pin seal portion to engage with the male screw portion, and to leak the fluid. And the pin seal portion and the box seal portion are covered with a layer having a thickness exceeding 0.1 mm of a metal having better corrosion resistance than the base material constituting the pin seal portion and the box seal portion. And
(8) The pin seal part is formed as a cylinder projecting from the tip of the male screw part, and the box seal part is formed as an internal shoulder having a surface for receiving the tip surface and the outer peripheral surface of the cylinder. Features.
(9) A seal ring that seals against leakage of the fluid is disposed between a front end surface of the cylindrical body and the internal shoulder.
(10) An intermediate shoulder that abuts the tubular pin and the tubular box is provided at an intermediate portion of the male screw portion and an intermediate portion of the female screw portion.
(11) When compressive stress up to 95% tubular body YS is applied, the screw flank surface is brought into contact with each other, so that not only the internal shoulder but also the screw flank surface bears the compressive stress. .

(12) Further, each of the above metal coatings is formed by welding.
(13) Furthermore, the internal stress can be released by heat treatment to maintain the mechanical properties of the steel pipe.

  The metal-coated steel pipe threaded joint of the present invention has a structure in which the inner surface of the joint and the seal portion are covered with a layer having a thickness exceeding 0.1 mm of a corrosion-resistant metal superior in corrosion resistance to those base materials. This makes it possible to take low-cost anti-corrosion measures that take advantage of the strength of the material. Further, since the corrosion-resistant metal layer is coated with a thickness exceeding 0.1 mm, the corrosion resistance and sealability of the joint inner surface and the seal portion can be maintained for a longer period of time.

  FIG. 1 is an assembly configuration diagram showing an example of the threaded joint of the present invention. The steel pipes 10 and 20 to be connected are clad steel pipes whose inner surfaces exposed to a passing fluid are coated with corrosion-resistant metals 11 and 21 having excellent corrosion resistance, and their tips are tubular pins for connection. 12 and 22. The tubular pins 12 and 22 are composed of male threaded portions 13 and 23 in which thread grooves are formed, and pin seal portions 14 and 24 that are cylindrical bodies having smooth outer peripheral surfaces at their tips. The thread groove contacts at the thread flank surface 70 to form a thread. The pin seal portions 14 and 24 are portions that cooperate with the coupling seal portion of the coupling 30 fastened to the tubular pins 12 and 22 to seal the leakage of fluid flowing in the steel pipe. And the front end surface and outer peripheral surface of the pin seal parts 14 and 24 are coat | covered with corrosion-resistant metals, such as Ni which were excellent in corrosion resistance rather than the base material which comprises them, like a steel pipe inner surface. Note that the metal coating on the outer peripheral surfaces of the pin seal portions 14 and 24 is not necessarily applied to the entire surface, and the seal is actually performed from the front end surfaces of the pin seal portions 14 and 24 by a synergistic action with the coupling seal portion of the coupling 30. The outer peripheral surface portion where the action is performed may only be covered.

  The coupling 30 for connecting and fixing the two steel pipes 10 and 20 is formed with female screw portions 33 fitted to the male screw portions 13 and 23 of the tubular pins 12 and 22 at both ends thereof, respectively. Between 33, a coupling seal portion is formed which cooperates with the pin seal portions 14 and 24 to seal leakage of fluid flowing in the steel pipe. Specifically, the coupling seal portion is formed as an internal shoulder 35 having a surface for receiving the distal end surface and the outer peripheral surface of the pin seal portions 14 and 24. Then, the peripheral surfaces (side wall surface 35a, upper surface 35b, and bottom surface 35c) of the internal shoulder 35 are covered with a corrosion-resistant metal such as Ni, which has better corrosion resistance than the base material constituting them.

  Note that the corresponding surfaces of the tip surfaces of the pin seal portions 14 and 24 and the internal shoulder 35 only have to be structured such that they are abutted with each other when the tubular pins 12 and 22 are inserted into the coupling 30. That is, it is not always necessary to form the front end face of the cylindrical body, which is the pin seal portions 14 and 24, and the receiving face of the internal shoulder 35 corresponding thereto as an upright surface as shown in the figure, and they are inclined so as to face each other. It may be a surface.

  The thickness of the metal coating layer of the internal shoulder 35 of the tubular pins 12 and 22 and the coupling 30 is more than 0.1 mm, particularly preferably 0.5 mm or more. The reason for this is that if the thickness of the coating layer is smaller than these values, the fluid easily enters the coating layer and deteriorates the steel pipe, and the reduction of the coating layer due to tightening and tightening is considered. .

  In this joint, two steel pipes are connected by tightening fitting of the male screw portions 13 and 23 of the tubular pins 12 and 22 and the female screw portion 33 of the coupling 30, and the pin seal portions 14 and 22 of the tubular pins 12 and 22 are connected. The leakage of the fluid flowing in the steel pipe is sealed by the contact surface pressure between 24 and the internal shoulder 35 of the coupling 30.

  FIG. 2 is a modification of the threaded joint shown in FIG. 1 and is different from FIG. 1 in that the tubular pins 12 and 22 and the cup are connected between the fitting pins of the tubular pins 12 and 22 and the coupling 30. The intermediate shoulders 16, 36 and 26, 36 that abut the ring 30 are provided. When the tubular pins 12 and 22 and the coupling 30 are connected, the intermediate shoulders 16 and 36 and 26 and 36 serve to limit an entry pressure of the tubular pins 12 and 22 into the coupling 30. Thereby, compared with the case where only the pin seal portions 14 and 24 and the internal shoulder 35 are used to limit the pressure of entry of the tubular pins 12 and 22 into the coupling 30, the reliability of the threaded joint strength and the like is improved. Will improve.

  The intermediate shoulders 16 and 36 and the intermediate shoulders 26 and 36 are not inserted when the tubular pins 12 and 22 are inserted into the coupling 30 as in the case of the internal shoulder 35 corresponding to the pin seal portions 14 and 24 described above. What is necessary is just to become a structure mutually faced. That is, the abutting surfaces do not necessarily have to be formed as upright surfaces as shown in the drawing, and may be inclined surfaces facing each other.

  Next, the pin seal portions 14 and 24 of the tubular pins 12 and 22 and the internal shoulder 35 of the coupling 30 will be described in more detail. FIG. 3 is an enlarged view of the pin seal portion 14. The pin seal portion 14 has a cylindrical shape, and the tip end surface 14a, the outer peripheral surface 14b, and the inner peripheral surface 14c are more resistant to corrosion than the base material. The metal film layer 17 is covered (the hatched portion is the covered portion). In addition, although not shown in figure, the other pin seal part 24 is comprised similarly.

  On the other hand, FIG. 4 is a partially enlarged view showing the internal shoulder 35 of the coupling 30 in detail. The internal shoulder 35 has a protruding portion that protrudes between the left and right female screw portions 33, and includes a side wall surface 35a and an upper surface 35b that receive the distal end surface 14a and the outer peripheral surface 14b of the pin seal portion 14, and a protruding portion. A bottom surface 35c of the internal shoulder 35 is provided. And the surrounding surface (side wall surface 35a, upper surface 35b, and bottom surface 35c) of this internal shoulder 35 is coat | covered with the metal film layer 17 excellent in corrosion resistance from the base material (a point aggregate part is a coating part). .

  The screw joint having the pin seal portion 14 and the internal shoulder 35 shown in FIGS. 3 and 4 has the contact surface pressure of the seal all or partly due to the tightening torque between the tubular pins 12 and 22 and the coupling 30 when the tightening is completed. It can be applied to a so-called butt-type metal-to-metal seal screw joint to be formed. Further, the basic structure of the threaded joint having the pin seal portion 14 and the internal shoulder 35 shown in FIGS. 3 and 4 is that when the tightening is completed, the contact surface pressure between the tubular pins 12 and 22 and the coupling 30 is not a tightening torque. The present invention can also be applied to other metal-to-metal seal screw joints determined by the seal tightening length.

  FIG. 5 is an explanatory diagram of a screw joint of a metal-to-metal seal of the type in which the contact surface pressure between the tubular pins 12 and 22 and the coupling 30 is determined by their seal tightening allowance. In the case of this joint, the outer peripheral surface 24b of the cylinder that is the pin seal portion 24 is formed to have a curved surface that bulges outward, and the outer diameter S of the tangent point corresponds to the upper surface 35b of the internal shoulder 35. It is larger than the inner diameter G of the tangent point. As a result, when the fastening of the tubular pin 22 and the coupling 30 is completed, the contact surface pressure between the pin seal portion outer peripheral surface 14b and the internal shoulder upper surface 35b at these tangent points is determined by the seal fastening allowance of both. A joint independent of torque can be obtained.

Furthermore, the structure which adds a seal ring to the joint structure demonstrated until now can also be employ | adopted. For example, in FIG. 6, the height of the side wall surface of the internal shoulder 35 of the coupling 30 is made shorter than what has been described so far, and the gap between the tip surfaces of the two pin seal portions 14 and 24 formed thereby is shown. A seal ring 40 is arranged. In this case, the seal ring 40 is disposed in close contact with both front end surfaces of the pin seal portions 14 and 24 and the bottom surface of the internal shoulder 35. Thereby, the clearance gap between the front end surface of the pin seal parts 14 and 24 and the internal shoulder 35 is closed, and the fluid leakage is sealed.
As shown in FIG. 7, the same effects as described above can be obtained by arranging the seal rings 41 and 42 between the tip surfaces of the pin seal portions 14 and 24 and the side wall surfaces of the internal shoulder 35. can get.

  Next, a so-called integral type threaded joint is shown in which the tip of a steel pipe is thickened to form a pin and a box, and the steel pipe is connected using the pin and the box. FIG. 8 is an assembly configuration diagram showing an example of the joint. The steel pipes 50 and 60 are clad steel pipes whose inner surfaces exposed to the passing fluid are covered with corrosion-resistant metals 51 and 61, the steel pipe 50 is a tubular pin 52 whose tip is increased in thickness, and the steel pipe 60 is Each has a tubular box 62 whose tip is increased in thickness.

  The tubular pin 52 includes a male screw portion 53 in which a thread groove is formed, and a pin seal portion 54 that is a cylindrical body having a smooth outer peripheral surface at the tip thereof. The pin seal portion 54 cooperates with the pin box 62 to seal leakage of fluid flowing inside the steel pipe. And the front end surface and outer peripheral surface of the pin seal part 54 are coat | covered with corrosion-resistant metal 57, such as Ni which is excellent in corrosion resistance from the base material which comprises them. The metal coating on the outer peripheral surface of the pin seal portion 54 is not necessarily applied to all of them, and the portion from the front end surface of the pin seal portion 54 to the portion where the seal action actually works in cooperation with the pin box 62 is covered. Just have it.

  The tubular box 62 has a female screw portion 63 fitted to the male screw portion 53, a side wall surface and an upper surface receiving the tip surface and the outer peripheral surface of the pin seal portion 54, and the fluid flowing inside the steel pipe leaks in cooperation with them. And an internal shoulder 65 for sealing. Then, the peripheral surfaces (side wall surface 65a and upper surface 65b) of the internal shoulder 65 are covered with a corrosion-resistant metal 67 such as Ni, which has better corrosion resistance than the base material constituting them. In addition, the thickness of the metal coating layer of the tubular pin 52 and the tubular box 62 is also set to a thickness exceeding 0.1 mm, particularly preferably a thickness of 0.5 mm or more for the reason described above.

  In the threaded joint shown in FIG. 8, when the tubular pin 52 and the tubular box 62 are connected, contact surface pressure is generated between the distal end surface and the outer peripheral surface of the pin seal portion 54 and the side wall surface and the upper surface of the internal shoulder 65. This seals the fluid flowing in the pipe from leaking out of the pipe.

  Also in the case of the threaded joint using the tubular pin 52 and the tubular box 62, the tubular pin 52 and the tubular box 62 are pushed into the corresponding simplified portions of the male threaded portion 53 and the female threaded portion 63 as in FIG. An intermediate shoulder can be provided to serve as a so-called torque stop that limits the pressure of entry of the tubular pin 52 into the tubular box 62. Further, a metal-to-metal seal screw joint of a type using so-called tightening allowance as shown in FIG. Furthermore, as shown in FIG. 9, it is possible to employ a configuration in which a seal ring 43 is disposed between the pin seal portion 54 of the tubular pin 52 and the internal shoulder 65 of the tubular box 62 to further improve the sealing performance.

  By the way, when the strength of the metal cover is weaker than the base metal strength, and when the joint is subjected to compressive stress up to 95% YS of the tube strength, it is an interface that receives the tip surface and the outer peripheral surface of the cylindrical body. Narshoulder alone cannot bear the compressive stress. However, in the case of a joint of a type in which the screw flank surfaces 70 of the mutually engaged screw portions are in contact, the flank surface 70 can bear a compressive stress. On the other hand, a joint of a type in which the screw flank surface does not contact cannot bear compressive stress on the flank surface. In view of this, it is preferable that the screw flank of the threaded portion of the screw joint of the present invention is in contact with the threaded joint.

In addition, the metal coating | cover with respect to the pin seal part and internal shoulder demonstrated by the said embodiment can be performed by plasma powder welding (same also with powder plasma welding), overlay welding, or those combinations. Moreover, the metal coating | cover with respect to the inner peripheral surface (a tubular pin and the inner peripheral surface of a tubular box) of a steel pipe can be performed by build-up welding, mechanical bonding, billet hot rolling diffusion bonding at the time of steel pipe assembly, etc.
In plasma powder welding, the welding material powder is supplied to a plasma column formed between the electrode in the plasma torch and the surface of the base material to form droplets, which are then applied to the surface of the base material. Welding and overlay welding.

A metal-coated steel pipe threaded joint according to the present invention was manufactured, and a galling test, an airtight test, and a corrosion resistance test were performed. The experimental method and results are shown below.
1. Threaded joint structure for testing The joint of the present invention: the threaded joint shown in FIG. 1 of the present specification.
Comparative joint: a threaded joint of the shape shown in FIG. 1, wherein the coated metal layers 17, 27, 37
Nothing.

2. Manufacture introduction of threaded joint of the present invention (1) Introduction of metal pipe Size of clad metal tube base material and steel grade: 1 level ・ Size: Outer diameter 177.8 mm x Thickness 10.36 mm
-Steel type: Carbon steel (Fe-0.3C-0.2Si-1.4Mn-0.2Cu)
I. Base metal inner surface coating metal and forming method ... 1 level ・ Coating metal: Ni-based corrosion resistant alloy (Ni-17Cr-17Mo-6Fe-4W)
・ Coating method: overlay welding by plasma powder welding (PPW) ・ Coating metal overlay thickness: 2.3 ± 0.7 mm
・ Machining: None (in the state of overlay welding)
C. Cover metal of tip end surface 14a and outer peripheral surface 14b of pin seal part 14 ... 2 levels The end part of the clad metal tube produced in the above steps A to A is subjected to groove machining for screw formation, and the pin seal part The following two levels of coating metals were prepared on the 14 tip surfaces 14a and the outer peripheral surface 14b.
・ First level (A): Ni-based corrosion-resistant alloy (Ni-17Cr-17Mo-6Fe-4W): Same as the inner surface coating alloy of the mother pipe.
・ Second level (B): Co-based corrosion-resistant wear-resistant alloy (Co-27Cr-5Mo-3Ni-0.25C)
D. Metal coating method of the tip surface 14a and the outer peripheral surface 14b of the pin seal portion 14 ... 1 level-Coating method: overlay welding by plasma powder welding (PPW)-Coated metal overlay thickness: 2.3 ± 0.7 mm
E. Heat treatment (heat treatment of the entire metal tube after the above metal coating) 3 levels-First level (none): no heat treatment.
・ Second level (SR): Residual stress removal treatment (620 ° C. × 1 h → air cooling)
The purpose was to release only the internal stress generated by welding overlay.
Third level (QT): quenching and tempering treatment (900 ° C. × 1 h → water cooling + 620 ° C. × 0.5
h → air cooling)
The base material structure of L80 in the vicinity of the overlay layer is rough due to the heat applied by the weld overlay.
Since it is large and annealed, the original structure and softness of the base metal
The purpose was to recover the strength by crystallization.
F. Machining of pin-sill part 14 ... 1 level ・ After heat treatment (without heat treatment), inner peripheral surface 14c of pin seal part 14, tip surface
14a and outer peripheral surface 14b were machined (cut).
・ Coated metal layer thickness after machining: 1.5 ± 0.5 mm
G. Others ・ The method of forming the threaded portion was the same as that of a well-known conventional pipe.
(2) Introduction of production of coupling 30 a. Coupling 30 base metal size and steel grade 1 level ・ Size: Outer diameter 194.5 mm x Thickness 30.0 mm
-Steel type: Carbon steel (Fe-0.3C-0.2Si-1.4Mn-0.2Cu) ... Same as clad tube base material.
I. Coated metal for internal shoulder of coupling 30 ... 2 levels (same as clad tube)
First level (A): Ni-based corrosion resistant alloy (Ni-17Cr-17Mo-6Fe-4W)
Second level (B): Co-based corrosion-resistant wear-resistant alloy (Co-27Cr-5Mo-3Ni-0.25C)
C. Metal coating method for internal shoulder part 1 level ・ Coating method: Overlay welding by plasma powder welding method (PPW) ・ Coated metal overlay thickness: 2.3 ± 0.7 mm
D. Heat treatment (heat treatment of the entire coupling after the above metal coating) ... 3 levels-First level (none): no heat treatment.
Second level (SR): Residual stress removal process (620 ° C. × 1 h → air cooling).
The purpose was to release only the internal stress generated by welding overlay.
Third level (QT): quenching and tempering treatment (900 ° C. × 1 h → water cooling + 620 ° C. × 0.5
h → air cooling).
Is the base metal structure near the overlay layer coarsened by the heat applied during weld overlay?
Because it is in an annealed state, it is due to the original structure and softening of the base material.
The purpose was to restore strength.
E. Machining of internal shoulder coating alloy layer: 1 level ・ After heat treatment (those not subjected to heat treatment), the internal shoulder coating metal layer was machined (cut).
・ Coated metal layer thickness after machining: 1.5 ± 0.5 mm
F. Others • The thread forming method was performed by a well-known conventional method.

3. Method for Producing Threaded Joint for Comparison (Comparative Example) Using the base material for metal pipe and the base material for coupling used in the above threaded joint of the present invention, FIG.
A threaded joint with the shape shown in Fig. 1 was manufactured by the conventional method.

4). Test joint Six joints (Example) of the present invention manufactured according to the introduction shown in the above item 2 and one conventional joint (comparative example) manufactured according to the introduction described in the above item 3. (Class) Prepared. Table 1 shows the types of coating metals and heat treatment methods for these pin seal portions and internal shoulder portions.

5. Test item (1) Scratch test Ten tightening / unfastening tests were performed and evaluated by the presence or absence of scuffing (burn-in).
(2) Airtight test The airtight test was evaluated based on the presence or absence of leakage by tests at 70% VME, 80% VME, 85% VME and 90% VME levels. (Pressure: 80ksi)
(3) Corrosion resistance test A test piece having the same composition as that of the inner surface coated metal was prepared by dissolution, and stress was applied for 30 days in a 20% NaCl aqueous solution in which 1 bar H ₂ S at 200 ° C and 10 bar CO ₂ at 200 ° C were juxtaposed. It was held and evaluated by the presence or absence of corrosion and cracking.

6). Test result The test result of the said 5th term is shown in Table 2.

From the above results, the following (a) to (d) can be considered.
(A) The comparative example (conventional joint) was good in both the galling test and the airtight test, but corrosion occurred in the corrosion test. It can be seen that the conventional example cannot withstand use in a highly corrosive environment.
(B) In all of Examples 1 to 6 (the joints of the present invention), corrosion and cracking did not occur. It can be seen that the joint of the present invention can sufficiently withstand use in a highly corrosive environment.
(C) In Example 1 in which heat treatment was not performed, leakage occurred in the 80% VME airtight test. In Examples 2 and 3 in which the residual stress removing heat treatment was performed, no leak occurred up to 85% VME, but leak occurred at 90% VME. In Examples 4 to 6 that were subjected to quenching and tempering heat treatment, no leak occurred even at 90% VME, and the same airtightness as that of the conventional example could be secured.
The joint of the present invention, in particular, the covering method such as overlay welding with heat input above the transformation temperature (about 400 ° C. or higher) to the base metal removes internal stress of the base metal or recovers softening (insufficient strength). Therefore, it can be seen that it is effective to perform metal heat treatment after the coating process of the coated metal and before the machining of the coated metal in order to ensure airtightness. As this heat treatment, the quenching and tempering heat treatment is more effective than the residual stress removing heat treatment.
(D) This galling test is a test conducted to confirm the occurrence of galling when the metal pipe of the joint of the present invention and the coated metal of the coupling are the same.
No galling was observed in any of the examples, including those in which the metal tube and the coating metal of the coupling were the same metal. In the coated metal of the example, no galling occurred even if both (“coated metal of metal tube” and “coated metal of coupling”) were the same. However, in the case of a coated metal in which galling occurs, it seems that it is effective to suppress galling by making the two different metals.

The assembly | attachment block diagram of the screw coupling which shows embodiment of this invention. The assembly | attachment block diagram in case the screw coupling shown in FIG. 1 is equipped with the intermediate shoulder. The pin seal part enlarged view of a tubular pin. Coupling internal shoulder enlarged view. Explanatory drawing of the screw joint of a metal-to-metal seal. The assembly block diagram which shows the example which has arrange | positioned the seal ring to the front-end | tip of a pin seal part. The assembly block diagram which shows another example which has arrange | positioned the seal ring to the front-end | tip of a pin seal part. The assembly block diagram of the integral type screw joint which concerns on embodiment of this invention. The assembly block diagram which shows the example which has arrange | positioned the seal ring to the front-end | tip of the pin seal part in an integral type threaded joint.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20: Steel pipe 11,21: Corrosion-resistant metal of steel pipe inner surface 12,22: Tubular pin 13,23: Male thread part 14,24: Pin seal part 17,27: Metal layer superior in corrosion resistance than base material 30: Coupling 33: Female thread part 35: Internal shoulder (coupling seal part)
16, 26, 36: Intermediate shoulder 37: Metal layer having better corrosion resistance than the base material 40, 41, 42, 43: Seal ring 50, 60: Steel pipe 52: Tubular pin 53: Male thread part 54: Pin seal part 62 : Tubular box 63: Male thread part 65: Internal shoulder 70: Frank surface

Claims (13)

In a steel pipe threaded joint comprising a tubular pin formed at the tip of a steel pipe and a coupling fitted to the pin,
The tubular pin includes a male screw part having a thread groove, and a pin seal part that cooperates with the coupling to seal leakage of fluid flowing in the steel pipe,
The coupling includes two female screw portions that can be fitted with male screw portions of two steel pipes to be connected, and a coupling seal portion that cooperates with the pin seal portion to seal leakage of the fluid. Prepared,
A metal-coated steel pipe threaded joint characterized in that the pin seal part and the coupling seal part are covered with a layer having a thickness exceeding 0.1 mm of metal that is more corrosive than the base metal constituting them. The pin seal part is formed as a cylindrical body protruding from the tip of the male screw part,
2. The metal-coated steel pipe screw according to claim 1, wherein the coupling seal portion is formed as an internal shoulder having a surface for receiving a distal end surface and an outer peripheral surface of the cylindrical body between the two female screw portions. Fittings.   The metal-coated steel pipe threaded joint according to claim 2, wherein a seal ring that seals leakage of the fluid is disposed between the cylindrical bodies of the left and right tubular pins to be connected.   The metal-coated steel pipe threaded joint according to claim 2, wherein a seal ring that seals the leakage of the fluid is disposed between a distal end surface of the cylindrical body and the internal shoulder.   The metal coating according to any one of claims 1 to 4, wherein an intermediate shoulder for abutting the tubular pin and the coupling is provided at an intermediate portion of the male screw portion and an intermediate portion of the female screw portion. Steel pipe threaded joint.   The metal-coated steel pipe threaded joint according to any one of claims 1 to 5, wherein the thread flank surfaces of the threaded portions that are engaged with each other are brought into contact with each other. In a steel pipe threaded joint comprising a tubular pin formed at the tip of a steel pipe and a tubular box fitted to the pin formed at the tip of the steel pipe,
The tubular pin includes a male screw part having a thread groove, and a pin seal part that cooperates with the box to seal leakage of fluid flowing in the steel pipe,
The box includes a female screw part into which the male screw part can be fitted, and a box seal part that cooperates with the pin seal part to seal leakage of the fluid,
A metal-coated steel pipe threaded joint, wherein the pin seal part and the box seal part are covered with a layer having a thickness exceeding 0.1 mm of a metal superior in corrosion resistance to the base material constituting them. The pin seal part is formed as a cylindrical body protruding from the tip of the male screw part,
The metal-coated steel pipe threaded joint according to claim 7, wherein the box seal portion is formed as an internal shoulder having a surface for receiving the tip surface and the outer peripheral surface of the cylindrical body.   The metal-coated steel pipe threaded joint according to claim 8, wherein a seal ring that seals leakage of the fluid is disposed between a distal end surface of the cylindrical body and the internal shoulder.   The metal sheath according to any one of claims 7 to 9, wherein an intermediate shoulder for abutting the tubular pin and the tubular box is provided at an intermediate portion of the male screw portion and an intermediate portion of the female screw portion. Steel pipe threaded joint.   The metal-coated steel pipe threaded joint according to any one of claims 7 to 10, wherein the thread flank surfaces of the threaded portions engaged with each other are brought into contact with each other.   The metal-coated steel pipe threaded joint according to any one of claims 1 to 11, wherein the metal coating is formed by welding. The metal-coated steel pipe threaded joint according to any one of claims 1 to 12, wherein the threaded joint is heat-treated.

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