JP2000176652A - Method for joining metallic tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for joining a metallic tube, by which a joined body superior in strength, fatigue characteristic and corrosion resistance is obtained by reducing a difference in level that is generated in a weld zone. SOLUTION: The bore near the end of each metallic tube 30 is worked so that the difference in the bore after the expansion of each tube 30 is <=2 mm and desirably <=1 mm, the end face of these 30 with the bore so worked near the end is machined so as to have a prescribed surface roughness, and then, the tubes 30 are joined by diffusion welding. In this case, the working of the bore near the tube end may be either the one free from removal of the material such as expanding or the one requiring the removal such as grinding, or else it may be the combination of the two.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining metal pipes, and more particularly, to piping for plants and line pipes used in the chemical industry, petrochemical industry and the like, or casing tubes and production tubes used in oil wells. The present invention relates to a method for joining metal pipes suitable as a method for joining oil country tubular goods such as coiled tubes.

[0002]

2. Description of the Related Art Conventionally, in the fields of chemical industry, petrochemical industry, etc., a target product is obtained by utilizing a chemical reaction under various environments, or a starting material, an intermediate product, and a target product of a chemical reaction are obtained. Long metal tubes are used to transport corrosive fluids, such as objects, over long distances.

For example, when drilling an oil or gas well, a steel tube called a casing tube is buried in the tunnel to protect the tunnel excavated in the ground and prevent leakage of crude oil. Since an oil field is usually located several thousand meters underground, a casing tube having a length of several thousand meters is required. Crude oil, gas, and the like pumped from oil and gas wells are transported to a storage tank or a refinery via a separation device. In this case, a pipeline having a total length of several tens of kilometers is used.

On the other hand, a seamless steel pipe excellent in corrosion resistance is generally used for a metal pipe exposed to a corrosive environment. The length of a seamless steel pipe industrially mass-produced is 10 to 15 m. The upper limit of the length that can be manufactured is about 100 m. Therefore, a joined body in which a plurality of seamless steel pipes each having a length of 10 to 15 m are connected to an oil well pipe such as a line pipe or a casing.

[0005] As a joining method of a metal pipe used for such an application, a screw connection method (mechanical cup method), a welding method (orbital welding method), a friction welding method, a diffusion welding method, and the like are known.

[0006] The screw connection method is a method of connecting metal tubes by screwing screws formed at the ends of the metal tubes. The screw connection method requires a connection time of 5 joints.
10 to 10 minutes, has the advantage of high work efficiency,
There is a disadvantage that oil and gas leak easily from the fastening portion. For this reason, the screws formed on the metal tube require high precision, and the screwing operation requires a high degree of skill. Also, in order to avoid damage to the thread portion that has been machined with high precision, careful transportation is required. Furthermore, the fastening portion has a drawback in that although it is strong against tensile stress, it expands in the radial direction when compressive stress is applied, which promotes leakage of oil and gas.

[0007] On the other hand, the welding method is a method in which a groove is provided on an end face of a metal pipe and butted, and molten metal is built up on the groove to connect the metal pipes to each other. The welding method has the advantage that oil and gas do not leak from the welded portion and that it is resistant not only to tensile stress but also to compressive stress as long as there are no defects such as defective fusion or pinholes in the welded portion. However, the welding method has a limitation in welding efficiency, and in particular, in the case of welding a thick-walled pipe, since it is necessary to perform multilayer welding, the work time per joint requires 1-2 hours. . In addition, welding on site has the disadvantage that not only is it affected by the environment such as weather and wind speed, but it also requires skilled welding skills.

[0008] The friction welding method is a method in which, while applying pressure, butted metal pipes are relatively rotated with each other, and the ends of the metal pipes softened by the generated frictional heat are pressed. Compared to other joining methods, although there are advantages such as requiring no skill, being able to join in a short time, and being hardly affected by the working environment, the occurrence of burrs on the inner and outer surfaces of the metal tube pressure welding part is inevitable, There is a disadvantage that it takes a lot of time to remove.
As a method of solving the disadvantage, a ring having a wedge-shaped cross section is interposed between a pair of metal pipe end faces, and while the pair of metal pipes is fixed, the ring is pushed toward the center of the metal pipe while rotating the ring. A radial friction welding method for performing pressure welding has been developed, but the properties of the pressure-welded joint are not always sufficient.

[0009] On the other hand, in the diffusion bonding method, two metal tubes are abutted and heated to a temperature equal to or lower than the melting point of the metal tube while pressing the bonding surface, thereby diffusing elements at the bonding surface. This is a method of joining two metal tubes. In the diffusion bonding method, two metal tubes are directly joined to each other, and solid-phase diffusion bonding is performed, in which elements are diffused while maintaining a solid state, and an insert material is interposed at a bonding interface to melt the insert material. There is a liquid phase diffusion bonding method in which a part of the component is diffused to the metal tube side.

The diffusion bonding method is similar to the above-mentioned welding method in that oil and gas do not leak from the bonded portion and are resistant to compressive stress if the bonding is performed under appropriate conditions. Has an advantage that a high-quality joint can be manufactured with high efficiency, as short as about 1/3 to 1/2 of the welding method. Therefore, the diffusion joining method is particularly excellent as a joining method for oil country tubular goods, line pipes and the like.

[0011]

By the way, when joining metal tubes using the diffusion joining method, only the end face of the metal tube having a predetermined outer diameter and thickness is finished to a predetermined surface roughness, and the outer diameter and the outer diameter are reduced. In general, it is used for bonding without modifying the wall thickness.

However, industrially mass-produced metal tubes have a predetermined dimensional tolerance, and the outer diameter and wall thickness of each metal tube vary within the dimensional tolerance. Therefore, if diffusion bonding is performed using the mass-produced metal pipe as it is, a step may be generated on the outer peripheral surface side and / or the inner peripheral surface side of the joint.

When a joined body having a step on the outer peripheral surface side and / or the inner peripheral surface side of the joint portion is used as it is, stress concentrates on the stepped portion and the joint is broken from the stepped portion, or the stepped portion is a starting point of fatigue fracture. There is a problem that it is easy to become. Further, if there is a step on the inner peripheral surface side of the joint, the corrosive substance may stay at the step, which may adversely affect mechanical properties and corrosion resistance.

In this case, the step generated on the outer peripheral surface side of the joint can be easily removed by post-processing after the bonding, but it is difficult to remove the step generated on the inner peripheral surface after the bonding. is there.

The problem to be solved by the present invention is to provide a method for joining metal pipes, which can reduce a step generated at a joint portion, thereby obtaining a joined body having excellent strength, fatigue characteristics and corrosion resistance. It is in.

[0016]

In order to solve the above-mentioned problems, the present invention relates to a method for joining metal pipes in which metal pipes are butt-butted and diffusion-bonded to each other. Thus, the gist of the invention is to process the inner diameter of at least one of the metal pipes near the joint end before joining.

In this case, it is desirable that the processing is a diameter expansion processing without removing the material. Further, the processing may be a mechanical processing involving removal of a material. Alternatively, the processing may include a diameter-increasing processing without removing the material and a mechanical processing with the material being removed performed after the diameter-increasing processing.

According to the method for joining metal tubes according to the present invention having the above structure, before the metal tubes are diffusion-bonded to each other, the difference between the inner diameters of the respective metal tubes is reduced to a predetermined value or less.
An inner diameter near the end of each metal tube is machined. Therefore, the outer diameter and wall thickness of each metal pipe before processing vary, and even when there is a difference in the inner diameter of each metal pipe, a large step does not occur on the inner peripheral surface side of the joint. In addition, the strength, fatigue characteristics and corrosion resistance of the joined body are improved.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a process chart showing a method for joining metal tubes according to the first embodiment of the present invention. In FIG. 1, the metal pipe joining method according to the present invention includes a diameter expanding step, an end face processing step, and a diffusion joining step.

First, the diameter expanding step will be described. In the diameter increasing step, only the inner diameter of both ends of the cylindrical metal tube 30 as shown in FIG.
As shown in FIG. 1B, the inner diameter of the end of the metal tube 30 is set to d _0.
From a process of expanding to d _1.

Here, the material of the metal tube 30 to which the present invention is applied is not particularly limited, and stainless steel such as carbon steel, martensitic stainless steel, duplex stainless steel, and austenitic stainless steel is used. ,
Various materials such as a Ti alloy can be used.

In the present invention, the increment of the inner diameter of the metal tube 30 after the expansion with respect to the minimum value of the inner diameter before the expansion of each metal tube 30 is called an end diameter expansion ratio. Defined by

[0023]

## EQU1 ## Edge expansion ratio (%) = (d ₁ −d _{0 min} ) _{× 1}
00 / d _{0 min,} where d ₁ : the inner diameter of the end of the metal tube 30 after the expansion d _{0 min} : the minimum value of the inner diameter of the end of the metal tube 30 before the expansion.

In the case of the present invention, in the diameter expanding step, it is necessary to increase the inner diameter near the end of each metal tube 30 so that the difference between the inner diameters of the respective metal tubes 30 after the expansion is 2 mm or less. . If the difference between the inner diameters after the diameter expansion exceeds 2 mm, a step of 1 mm or more is generated on the inner peripheral surface side of the joining portion, and a joined body excellent in strength, fatigue characteristics and corrosion resistance cannot be obtained, which is not preferable. Preferably, the difference between the inner diameters of the metal tubes 30 is 1 mm or less.

For this reason, if the end portion diameter expansion ratio in the diameter expansion step is too small, a large step is generated on the inner peripheral surface side of the joint. Thus, determining if the maximum inner diameter of the front diameter of the metal pipe 30 and d _0max, the inner diameter d ₁ of each metal pipe 30 after expanded is to satisfy the following Expression 2, the end portion diameter ratio Good.

[0026]

[Number 2] _{d 0max -2 ≦ d 1 ≦ d} 0max ( Unit: mm)

In this case, the inner diameter d ₀ before the expansion is (d
_0max- 2) Only the metal tube 30 smaller than (mm)
It is expanded to inner diameter which corresponds to d _1, the inner diameter _{d 0} of the front diameter is about _{(d 0ma} x -2) metal tube 30 is (mm) or more, without the inner diameter in the vicinity of the end portion is expanded , And will be used for joining as it is.

Alternatively, the inner diameter d of each metal tube 30 after the diameter expansion
_The end diameter expansion ratio may be determined so that ₁ becomes larger than _d0max , and the diameter of each metal tube 30 may be expanded. In this case, all of the metal tube 30 is, will be expanded until the inner diameter corresponding to d _1.

[0029] As the minimum value d _0min and maximum value d _{0 max} inner diameter used in the calculation of the end portion diameter ratio, in terms of expected the safety factor is predicted from standards of the metal pipe used for joining Although it is desirable to use the minimum value and the maximum value, an actual measurement value may be used.

Further, the larger the end diameter expansion ratio is, the better in terms of reducing the step generated on the inner peripheral surface side of the joint, the better. What is necessary is just to select a diameter ratio.

The length of the expanded portion (hereinafter referred to as “expanded length” and indicated by “L ₁ ” in FIG. 1B) is the length of the processing of the metal tube 30. It may be arbitrarily selected in consideration of easiness, use of the obtained joined body, and the like.

Further, the diameter expansion method is not particularly limited, and various methods can be used. Normally,
A mandrel or a plug having an outer diameter corresponding to d1 shown in Equation ₁ may be inserted into the end of the metal tube 30 by a predetermined length to increase the inner diameter of the end.

Next, an end face processing step will be described. The end face processing step is a step of machining the end face of the metal pipe 30 whose end inner diameter has been expanded by the diameter expansion step to a predetermined surface roughness, as shown in FIG. This is because if the surface roughness of the end face of the metal tube 30 is rough, the bonding interface does not sufficiently adhere in the diffusion bonding step described later, and high bonding strength cannot be obtained.

The method for processing the end face is not particularly limited, and various methods such as grinding and lapping can be used. Further, if the surface roughness of the end face of the metal tube 30 is maintained in a predetermined range even after the diameter expansion, the end face processing step is not necessarily required, and can be omitted.

Next, the diffusion bonding step will be described. In the diffusion bonding step, the inner diameter of the end portion is expanded in the diameter expanding step,
Further, in an end face processing step, the metal pipes 30 whose end faces are processed to a predetermined surface roughness are abutted, and the metal pipes 30,
This is a step of performing diffusion bonding.

Here, in the diffusion bonding method, the metal pipes 30 are directly abutted to each other to diffuse elements while maintaining a solid state, and an insert material is interposed at a bonding interface to insert the insert material. There is liquid phase diffusion bonding in which elements are diffused while melting temporarily, but any method may be used.

In particular, liquid phase diffusion bonding is suitable as a bonding method since a bonded body having the same strength as the base material can be obtained in a shorter time than solid phase diffusion bonding. In FIG. 1 (d),
An insert material 36 is interposed at the joint interface between the metal tubes 30 and 30, and the metal tube joined body 32 joined by the liquid phase diffusion joining method
An example is shown below.

The optimum conditions for the diffusion bonding may be selected in accordance with the material of the metal tube 30 to be used. Specifically, it may be performed under the following conditions.

First, the surface roughness Rmax of the bonding surface is 50
μm or less is preferred. The surface roughness Rmax of the joint surface is 50
If it exceeds μm, the metal tubes 30 do not sufficiently adhere to each other on the bonding surface, and high bonding strength cannot be obtained, which is not preferable. In terms of obtaining high bonding strength, the surface roughness Rma
The smaller x is, the better.

The insert material 36 used is preferably a Ni-based alloy or a Fe-based alloy having a melting point of 1200 ° C. or less. If the melting point of the insert material 36 exceeds 1200 ° C., a high joining temperature is required, so that the base material is melted during joining or an unjoined portion is generated due to the unmelted insert material 36, which is not preferable. .

The thickness of the insert 36 used is preferably 100 μm or less. If the thickness of the insert material 36 exceeds 100 μm, the diffusion of elements at the bonding interface is not sufficiently performed, and the bonding strength is undesirably reduced.

The shape of the insert material 36 is not particularly limited, and a foil-shaped insert material 36 having a thickness of 100 μm or less may be interposed at the joining interface, or the thickness may be 100 μm or less. As described above, powdery or scaly insert material 36 is sprayed on the joining interface,
It may be applied in the form of a paste to the joint interface.

The bonding atmosphere is preferably a non-oxidizing atmosphere. Diffusion bonding in an oxidizing atmosphere is not preferred because the vicinity of the bonding interface is oxidized and the bonding strength is reduced.

The joining temperature is preferably in the range from 1250 ° C. to 1400 ° C. When the joining temperature is lower than 1250 ° C., the insert material 36 does not partially melt,
Alternatively, the diffusion of elements is not sufficiently performed, and the bonding strength is reduced, which is not preferable. On the other hand, if the joining temperature exceeds 1400 ° C., the base material may be undesirably melted.

The holding time at the joining temperature is preferably 30 seconds or more and 300 seconds or less. If the holding time is less than 30 seconds, the diffusion of elements at the bonding interface becomes insufficient, and the bonding strength decreases, which is not preferable. On the other hand, if the holding time exceeds 300 seconds, the working efficiency is undesirably reduced.

Further, the pressure applied to the bonding interface is:
1.5 MPa or more and 5 MPa or less are preferable. If the pressing force is less than 1.5 MPa, the adhesion at the bonding interface becomes insufficient, and the bonding strength decreases, which is not preferable. On the other hand, if the pressure exceeds 5 MPa, the vicinity of the joint is excessively deformed, which is not preferable.

As a heating method for performing diffusion bonding, various methods such as high-frequency induction heating, high-frequency direct current heating, and resistance heating can be used. Among them, high-frequency induction heating and high-frequency direct current heating are particularly suitable as a heating method because even relatively large materials to be joined can be easily heated, have high heating efficiency, and can be heated to the joining temperature in a very short time.

However, the high-frequency current used for high-frequency induction heating or high-frequency direct current heating has a frequency of 100 k
Hz or less is preferably used. Frequency 100
When the frequency exceeds kHz, only the surface is heated by the skin effect, and the entire joint surface is not uniformly heated, which is not preferable.

Next, the operation of the metal pipe joining method according to the present invention will be described. Metal tubes that are mass-produced industrially have a predetermined dimensional tolerance, and the required dimensional accuracy varies depending on the application. Above all, oil well pipes such as casing tubes, production tubes, and coiled tubes, and metal pipes used for line pipes are known to require higher accuracy than other uses.

The standard for determining the dimensional tolerance of the line pipe is, for example, the American Petroleum Institute (hereinafter referred to as “AP”).
I ") standard 5LC (second edition, August 1, 1991)
Days). Further, as a standard for determining the dimensional tolerance of the casing and the tubing, for example, API standard 5CT
(First edition, April 1, 1995).

According to the API standard 5LC, for example, in the case of a line pipe having an outer diameter of 4 to 18 inches (101.6 to 457.2 mm), the outer diameter of the pipe main body is ± 0.
A range of 75% is acceptable. The wall thickness of the pipe is acceptable if it is in the range of + 15% to -12.5% of the standard value.

Thus, for example, an outside diameter of 12.75 inches (323.85 mm) and a wall thickness of 0.375 inches (9.
In the case of an API grade X52 line pipe (525 mm), the maximum value of the outer diameter is 326.279 mm, and the minimum value is 321.421 mm. The maximum value of the thickness is 10.954 mm, and the minimum value is 8.334 mm.

Therefore, the line pipe is cut at the center,
Assuming the case of rejoining, it is necessary to join the metal tube 41 having the maximum outer diameter and the minimum thickness within the dimensional tolerance and the metal tube 42 having the minimum outer diameter and the maximum thickness.
At this time, assuming that the two axes are abutted and diffusion bonded so that they coincide with each other, as shown in FIG.
A step of 5.049 mm at the maximum occurs on the inner peripheral surface side of 1, 42.

Therefore, in this case, the minimum value d of the inner diameter is
_{Since 0 min} is 299.513 mm, the metal pipes 41 and 42 may be expanded so that the inner diameter d ₁ after the expansion is 307.611 mm or more, that is, the end diameter expansion ratio is 2.70% or more. In calculation, the step generated on the inner peripheral surface side is 1 mm
It can be:

Similarly, the inner diameter d ₁ after the expansion is 308.61.
If the metal pipes 41 and 42 are expanded so that the end diameter expansion ratio becomes 3.04% or more, that is, 1 mm or more, the step generated on the inner peripheral surface side is calculated to be 0.5 mm or less. Can be. Further, the inner diameter _{d 1} after diameter expansion is 309.611mm
When the metal pipes 41 and 42 are expanded so that the end diameter expansion ratio becomes 3.37% or more, the calculation is generated on the inner peripheral surface side as shown in FIG. 2B. Steps can be completely eliminated.

According to the API standard 5CT, for example, in the case of a casing or tubing having an outer diameter of 41/2 inches (114.3 mm) or more, the outer diameter of the pipe main body is from -1.00% of the standard value to- A range of 0.50% is acceptable. The thickness of the pipe is ± 12.5 of the standard value.
% Is acceptable.

Therefore, for example, an outer diameter of 7 inches (177.
8 mm) and 0.54 inch wall thickness (13.716 mm)
For an API grade H40 casing of inches, the maximum outer diameter is 179.578 mm and the minimum is 17
9.911 mm. The maximum value of the wall thickness is 15.4.
31 mm, and the minimum value is 12.002 mm.

For this reason, the metal pipe 51 having the maximum outer diameter and the minimum thickness within the dimensional tolerance and the metal pipe 52 having the minimum outer diameter and the maximum thickness are abutted and diffusion bonded so that their axes are coincident. Then, as shown in FIG.
A maximum step of 4.763 mm occurs on the inner peripheral surface side of the metal tubes 51 and 52.

Therefore, in this case, the minimum value of the inner diameter d
_{Since 0 min} is 146.049 mm, if the metal pipes 51 and 52 are expanded so that the inner diameter d ₁ after the expansion is 153.574 mm or more, that is, the end diameter expansion rate is 5.15% or more. In calculation, the step generated on the inner peripheral surface side is 1 mm
It can be:

[0060] Similarly, the inner diameter _{d 1} after the diameter is 154.54
If the metal pipes 51 and 52 are expanded so that the diameter of the metal pipes 51 and 52 becomes 7 mm or more, that is, the end diameter expansion ratio becomes 5.84% or more, the step generated on the inner peripheral surface side is calculated to be 0.5 mm or less. Can be. Further, the inner diameter _{d 1} after diameter expansion is 155.574mm
When the metal pipes 51 and 52 are expanded so that the end diameter expansion rate becomes 6.52% or more, the calculation is generated on the inner peripheral surface side as shown in FIG. 3B. Steps can be completely eliminated.

In the above estimation, it is assumed that the inner diameter of the metal pipe used for joining varies within the range of the maximum and minimum allowable dimensional tolerances. Therefore, when the inner diameter of the metal tube used for joining varies within a narrower range than the allowable dimensional tolerance, the end expansion ratio is smaller than the end expansion ratio obtained by the above calculation. Even if there is a step on the inner peripheral surface side, 1mm
It can be:

Next, a metal pipe diffusion bonding method according to a second embodiment of the present invention will be described. In the metal pipe diffusion bonding method according to the present embodiment, the inner diameter difference near the end of the metal pipe before bonding is reduced by 2 mm by the diameter expansion processing without removing the material.
Instead of making the diameter less than or equal to mm, the difference in inner diameter near the end is made to be 2 mm or less by machining with the removal of material.

Here, when machining the vicinity of the end of the metal pipe, when the machined metal pipes are butted, an acute angle notch is not formed at the joint interface.
It is desirable to remove the material on the inner peripheral surface side near the end of the metal tube continuously and smoothly. Specifically, as shown in FIG. 4A, the inner peripheral surfaces near the ends of both metal tubes 61 and 62 are removed in a tapered shape with a large base angle, or
As shown in FIG. 4B, it may be removed in an elliptical shape. Although not shown, the material on the inner peripheral surface side may be removed from only one of the metal tubes having a small inner diameter.

Examples of the mechanical processing involving the removal of material include, specifically, grinding processing and cutting processing, but are not particularly limited thereto. Also, after removing the material near the end of the metal tube 30 by machining, the end face may be worked as necessary and then diffusion bonded, as in the first embodiment.

Next, a metal pipe diffusion bonding method according to a third embodiment of the present invention will be described. The diffusion joining method for a metal tube according to the present embodiment involves enlarging the inner diameter near the end of the metal tube by a diameter-enlarging process without removing the material, and further involves removing the material near the end. Machine processing is performed, and a difference in inner diameter in the vicinity of the end of the metal tube abutted by this is set to 2 mm or less.

In addition, after performing the diameter-enlarging process near the end of the metal tube and performing the machining with the removal of the material, when the machined metal tubes are abutted, a sharp notch is formed in the joining interface. As in the second embodiment, it is desirable to continuously and smoothly remove the material on the inner peripheral surface side near the end of the metal tube so that no is formed.

That is, as shown in FIG. 5A, the inner peripheral surface near the end of one of the metal pipes 71 subjected to the diameter expansion processing is removed in a tapered shape having a large base angle. FIG.
As shown in (b), it may be removed in an elliptical shape. Also,
Although not shown, both the metal tubes 7 subjected to the diameter expansion processing are
The material in the vicinity of the end faces of the metal tubes 71 and 72 is removed in a tapered shape with a large base angle or in an elliptical shape so that the difference in inner diameter between the end portions of the metal tubes 71 and 72 is 2 mm or less. Is also good.

The method of machining is not particularly limited. The diameter of the vicinity of the end of the metal tube 30 may be increased and machined, then the end face may be machined if necessary, and then diffusion bonding may be performed. This is also the same as in the second embodiment.

As described above, according to the method for joining metal tubes according to the present invention, even when using metal tubes having variations in outer diameter and wall thickness, the end portions of each metal tube are required before joining. Since a process involving the removal of the material such as a diameter expanding process and / or a cutting process without removing the material is performed in the vicinity, the inner diameters of the metal pipes can be easily made uniform.

For this reason, when the metal pipes are joined so that their axes coincide, the step on the inner peripheral surface side can be made substantially zero. In addition, even if the axis of each metal pipe is slightly displaced at the time of joining due to force majeure, the step generated on the inner peripheral surface side is small compared to the case where the processing near the end is not performed. Becomes

In particular, the process of expanding the diameter of the end of a metal tube using a tool such as a mandrel does not involve the removal of material, and therefore can be performed more easily than machining such as grinding or cutting. it can. Therefore, the step on the inner peripheral surface side of the joining portion can be reduced without increasing the joining cost, and a joined body having excellent strength and fatigue characteristics can be obtained.

Further, in the case of a metal pipe having a large dimensional tolerance, the step on the inner peripheral surface side near the end portion may not be able to be sufficiently reduced only by the diameter expansion processing. However, if the inner peripheral surface near the end of the metal tube is machined with the removal of material, or if the mechanical processing is performed after the diameter expansion, the step on the inner peripheral surface is reduced. The size can be reliably reduced.

Next, an example of a method of using the joined metal pipe obtained by the method according to the present invention will be described. The metal pipe joined body obtained by the method as described above can be used as it is as piping for various plants, etc., but is used after being subjected to a pipe expanding process for almost uniformly expanding the inner diameter of the entire metal pipe joined body. May be. In this case, it is desirable to perform the pipe expansion process so that the pipe expansion ratio E (%) of the joined metal pipe satisfies the following equation (3).

[0074]

E (%) ≦ 30−T (%) where, E = ((inner diameter after expansion / inner diameter before expansion of non-joined portion) −1) × 100 T = (step on inner peripheral surface side of joined portion) / Thickness of metal tube before expansion)
× 100

When the ratio of the step generated on the inner peripheral surface side of the joint to the plate thickness of the metal pipe before expansion (hereinafter referred to as “T value”) is not 0, that is, the step is formed on the inner peripheral surface side of the joint. If this occurs, it is not preferable that the pipe expansion ratio E is larger than (30-T), since stress concentrates on the stepped portion at the time of pipe expansion and a defect may occur at the joint.

In the equation (3), the upper limit of the expansion ratio is set to 30%. This is because the heat-affected zone is generated in the vicinity of the joint, and when the pipe expansion ratio exceeds 30%, regardless of whether a step is generated on the inner peripheral surface side of the joint,
This is because a defect may be generated in the vicinity of the joint.

The metal pipe joined body obtained by the method according to the present invention has an inner peripheral surface near the joint end before joining so that the inner diameter difference between the joined end faces of the two butted metal pipes is 2 mm or less. Therefore, the T value is small. Therefore, compared with the case where the inner peripheral surface side near the joining end is not machined in advance, the tube can be expanded at a high pipe expansion ratio E, and the generation of defects near the joining interface can be suppressed.

Example 1 Diffusion bonding of a metal tube was performed according to the following procedure. That is, as a metal pipe, American Petroleum Institute grade X52 (hereinafter referred to as “API X5
2 ") and an outer diameter of 12.75 inches (32
3.9 mm), a 0.375 inch (9.5 mm) thick steel pipe was used, and the inner diameter of the end of the steel pipe was 3%.
The diameter was expanded so that

Next, the end face of the expanded metal tube is finished so as to have a surface roughness Rmax of 25 μm or less, and a joining interface of the metal tube has a melting point of 1050 ° C. having a composition equivalent to JIS BNi-3 and a thickness of 1050 ° C. Insert a 50 μm Ni-based alloy foil,
Liquid phase diffusion bonding was performed.

The method of heating the joint portion includes a frequency of 3 k
A high frequency induction heating method using a high frequency current of Hz was used.
The bonding conditions were a bonding temperature of 1300 ° C. and a holding time of 18
The bonding was performed in an Ar atmosphere with 0 seconds at a pressure of 4.5 MPa.

(Examples 2 and 3, Comparative Examples 1 and 2) Metal Tube 3
The end diameter expansion ratios of 0 are 0% (Comparative Example 1) and 1%, respectively.
(Comparative Example 2) Diffusion bonding of a metal tube was performed according to the same procedure as in Example 1 except that 5% (Example 2) and 10% (Example 3) were used.

For the joined bodies obtained in Examples 1 to 3 and Comparative Examples 1 and 2, the maximum value of the step generated on the inner peripheral surface side of the joint (hereinafter, this is simply referred to as “maximum step”) is shown. It was measured. Further, only a step generated on the outer peripheral surface side of the obtained joined body was ground with a grinder to 0.5 mm or less, and then a JIS Z 3124 No. test piece was cut out from the joined body and subjected to a tensile test. Furthermore, J
A fatigue test is performed by cutting out a test piece conforming to the IS Z3103 non-finished butt welded joint test method, and a fatigue strength ratio (ratio of the fatigue limit of the joint to the fatigue limit of the base material)
Was measured. Table 1 shows the results.

[0083]

[Table 1]

In Comparative Example 1 in which the end portion diameter expansion ratio was 0%, the maximum step reached 5 mm. Tensile strength is 450MPa
, Which was slightly lower than the strength of the base material. The test piece broke from the joint interface. Furthermore, the fatigue strength ratio is
It showed a low value of 0.4. This is presumably because stress was concentrated on the step generated on the inner peripheral surface side of the joint, and the step became the starting point of fatigue fracture.

In Comparative Example 2 in which the end diameter expansion rate was 1%, the maximum step was reduced to 3.5 mm. However, the tensile strength was 466 MPa, and the test piece broke from the joint interface. Further, the fatigue strength ratio was 0.5, which was almost the same as that of Comparative Example 1.

On the other hand, the end diameter expansion ratio was set to 3
%, 5%, and 10% in Examples 1, 2 and 3,
The maximum steps were all reduced to 1.0 mm. The tensile strength was 500 MPa or more, which is equivalent to the base material, and the test piece was broken from the base material side. Further, the fatigue strength ratio was 0.9, showing fatigue characteristics almost equal to those of the base metal.

From the above results, before joining the metal tubes,
It was found that when the inside diameter of the end portion of the metal tube was expanded at a predetermined end portion expansion rate or more, the maximum step became 1 mm or less. Also, it was found that when the maximum step was reduced, a joined body having high joining strength and high fatigue strength was obtained.

Example 4 Diffusion bonding of a metal tube was performed according to the following procedure. That is, as a metal tube, API
X75 outer diameter 12.75 inches (323.9m
m), a steel pipe having a wall thickness of 0.375 inch (9.5 mm) was used, and the inner diameter of the end of the steel pipe was expanded such that the end expansion ratio was 5%.

Next, the end surface of the expanded metal tube is finished so that the surface roughness Rmax is 15 μm or less, and Fe-3 having a melting point of 1200 ° C. and a thickness of 50 μm is formed on the joining interface of the metal tube.
Liquid phase diffusion bonding was performed with a B-3Si-1C alloy foil interposed.

The heating method of the bonding portion includes a frequency of 3 k
A high frequency induction heating method using a high frequency current of Hz was used.
The bonding conditions are a bonding temperature of 1250 ° C. and a holding time of 60.
The bonding was performed in an Ar atmosphere at a pressure of 4.5 MPa for seconds.

(Example 5) As an insert material, JIS
Using a Ni-based alloy foil having a composition equivalent to BNi-5 and having a melting point of 1140 ° C. and a thickness of 50 μm, a joining temperature of 1300
Diffusion bonding of a metal tube was performed according to the same procedure as in Example 4 except that the temperature and the holding time were changed to 180 seconds.

(Example 6) JIS was used as the insert material.
Using a Ni-based alloy foil having a composition equivalent to BNi-5 and having a melting point of 1140 ° C. and a thickness of 100 μm, a joining temperature of 1300
Diffusion bonding of a metal tube was performed according to the same procedure as in Example 4 except that the temperature and the holding time were changed to 180 seconds.

(Comparative Example 3) As an insert material, a melting point of 1
A metal was prepared according to the same procedure as in Example 4 except that a joining temperature was set to 1400 ° C., a holding time was set to 300 seconds, and a pressing force was set to 5.0 MPa. The tubes were diffusion bonded.

With respect to the joined bodies obtained in Examples 4 to 6 and Comparative Example 3, the maximum step, the tensile strength and the fatigue strength ratio were measured in the same procedure as in Example 1. Table 2 shows the results.

[0095]

[Table 2]

In Comparative Example 3 using an insert material having a melting point of 1290 ° C., the tensile strength was 428 MPa, and the test piece broke from the joint interface, despite the holding time being 300 seconds. The fatigue strength ratio was 0.7, and the fatigue limit was slightly lower than that of the base metal. This is presumably because the insert material had a high melting point, and the elements were not sufficiently diffused at the bonding interface.

On the other hand, the tensile strengths of Example 4 using an insert material having a melting point of 1200 ° C. and Examples 5 and 6 using an insert material having a melting point of 1140 ° C. were equal to those of the base material. The test piece broke from the base material side. Further, the fatigue strength ratios were all 0.9.

[0098] In Examples 4 to 6 and Comparative Example 3, the end step diameter expansion ratio of the metal tube was 5%, and the maximum step was 1.0 mm.

From the above results, in the case where the metal pipe is subjected to liquid phase diffusion bonding, the metal pipe is expanded at a predetermined end diameter expansion rate and diffusion bonded using an insert material having a melting point of 1200 ° C. or less. It was found that a joined body having high joining strength and high fatigue strength was obtained.

Example 7 Diffusion bonding of a metal tube was performed according to the following procedure. That is, as a metal tube, API
X75 outer diameter 12.75 inches (323.9m
m), a steel pipe having a wall thickness of 0.375 inch (9.5 mm) was used, and the inner diameter of the end of the steel pipe was expanded such that the end expansion ratio was 5%.

Next, the end face of the expanded metal tube is finished so as to have a surface roughness Rmax of 15 μm or less, and a powdery material having a composition equivalent to JIS BNi-5 and having a melting point of 1140 ° C. is formed on the joining interface of the metal tube. A Ni-based alloy was inserted so as to have a thickness of 30 μm, and liquid phase diffusion bonding was performed.

The heating method of the bonding portion includes a frequency of 3 k
A high frequency induction heating method using a high frequency current of Hz was used.
The bonding conditions are as follows: bonding temperature 1300 ° C., holding time 60
The bonding was performed in an Ar atmosphere at a pressure of 3.0 MPa for 2 seconds.

(Embodiment 8) As an insert material, JIS
The same as Example 7 except that a flaky Ni-based alloy having a composition equivalent to BNi-5 was used, inserted into the joining interface of the metal tube so as to have a thickness of 50 μm, and kept at the joining temperature for 30 seconds. Diffusion bonding of the metal tube was performed according to the procedure.

(Comparative Example 4) JIS was used as the insert material.
200 μm thick Ni having a composition equivalent to BNi-5
Using a system alloy foil, the holding time at the joining temperature is 300
Diffusion bonding of a metal tube was performed according to the same procedure as in Example 7, except that the pressing force was set to 4.5 MPa for seconds.

(Comparative Example 5) JIS was used as the insert material.
Using a Ni-based alloy foil having a composition equivalent to BNi-5 and a thickness of 50 μm, a joining temperature of 1400 ° C. and a holding time of 10
Diffusion bonding of the metal tube was performed according to the same procedure as in Example 7, except that the pressing force was set to 5.0 MPa for seconds.

(Comparative Example 6) JIS was used as the insert material.
Diffusion bonding of a metal tube was performed according to the same procedure as in Example 7, except that a Ni-based alloy foil having a composition equivalent to BNi-5 and having a thickness of 50 µm was used and the holding time at the bonding temperature was set to 600 seconds.

For the joined bodies obtained in Examples 7 to 8 and Comparative Examples 4 to 6, the maximum step, the tensile strength, and the fatigue strength ratio were measured in the same procedure as in Example 1. Table 3 shows the results.

[0108]

[Table 3]

In Comparative Example 4 in which the thickness of the insert material was 200 μm, the holding time was 300 seconds and the pressing force was 4.5.
Despite the MPa, the tensile strength was 455MPa
a, and the test piece broke from the joint interface. The fatigue strength ratio was 0.7, and the fatigue limit was slightly lower than that of the base metal. This is because the insert material is thick
This is probably because the elements contained in the insert material were not sufficiently diffused.

Further, in Comparative Example 5 in which the holding time was 10 seconds, the tensile strength was 421 MPa, and the test piece broke from the bonding interface, even though the bonding temperature was 1400 ° C. The fatigue strength ratio was 0.7, and the fatigue limit was slightly lower than that of the base metal. This is presumably because the holding time was short and the diffusion of elements at the bonding interface was not sufficiently performed.

Further, in Comparative Example 6 in which the holding time was 600 seconds, the bonding strength was 522 MPa, which is equivalent to that of the base material, and the test piece broke from the bonding interface, but the fatigue strength ratio was 0.8. The fatigue limit was slightly lower than that of the base metal. This is considered to be because the holding time was long and the vicinity of the joint was excessively deformed, and the deformed portion became the starting point of fatigue failure.

On the other hand, when the thickness of the insert material is 30 to
50 μm, and the holding time at the bonding temperature is 10 to
In Examples 7 and 8 where the time was 60 seconds, the bonding strength was 500 MPa or more, which is equivalent to that of the base material, and the test piece was broken from the base material side. Further, the fatigue strength ratio was 0.9 in each case.

In Examples 7 and 8 and Comparative Examples 4 and 6, the end step diameter expansion rate of the metal tube was 5%, so that the maximum step was 1.0 mm.

From the above results, in the case where the metal pipe is subjected to liquid phase diffusion bonding, when the end of the metal pipe is expanded at a predetermined end expansion ratio and the thickness of the insert material is set to 100 μm or less, the bonding strength is reduced. It was also found that a metal pipe joint having high fatigue strength was obtained. Further, it has been found that the holding time is preferably in the range of 30 to 300 seconds in order to sufficiently diffuse the elements at the bonding interface and suppress excessive deformation of the bonding portion.

Example 9 Diffusion bonding of a metal tube was performed according to the following procedure. That is, as a metal tube, API
X75 outer diameter 12.75 inches (323.9m
m), a steel pipe having a wall thickness of 0.375 inch (9.5 mm) was used, and the inner diameter of the end of the steel pipe was expanded such that the end expansion ratio was 5%.

Next, the end face of the expanded metal tube is finished so that the surface roughness Rmax is 15 μm or less, and the joining interface of the metal tube has a melting point of 1140 ° C. having a composition equivalent to JIS BNi-5 and a thickness of 1140 ° C. Insert a 50 μm Ni-based alloy foil,
Liquid phase diffusion bonding was performed.

[0117] The method of heating the bonding portion includes a frequency of 3 k.
A high frequency induction heating method using a high frequency current of Hz was used.
The joining conditions were a joining temperature of 1350 ° C. and a holding time of 24 hours.
Bonding was performed in an Ar atmosphere at 0 MPa for 1.5 seconds under a pressure of 1.5 MPa.

(Example 10) The pressing force at the time of joining was 5.0 M
Diffusion bonding of the metal tube was performed according to the same procedure as in Example 9 except that the pressure was changed to Pa.

Comparative Example 7 Diffusion bonding of a metal tube was performed according to the same procedure as in Example 9 except that the joining temperature was 1450 ° C., the holding time was 60 seconds, and the pressure was 4.0 MPa.

(Comparative Example 8) Except that the joining temperature was 1400 ° C, the holding time was 300 seconds, and the pressing force was 1.0 MPa,
In accordance with the same procedure as in Example 9, diffusion bonding of the metal tube was performed.

(Comparative Example 9) Except that the joining temperature was 1300 ° C, the holding time was 300 seconds, and the pressing force was 7.0 MPa,
In accordance with the same procedure as in Example 9, diffusion bonding of the metal tube was performed.

For the joined bodies obtained in Examples 9 to 10 and Comparative Examples 7 to 9, the maximum step, the tensile strength and the fatigue strength ratio were measured in the same procedure as in Example 1. Table 4 shows the results.

[0123]

[Table 4]

In Comparative Example 7 in which the joining temperature was 1450 ° C., the tensile strength was 525 MPa, which was equivalent to that of the base material, and the test piece broke from the base material side. However, the fatigue strength ratio was 0.8, and the fatigue limit was slightly lower than that of the base metal. This is presumably because the high joining temperature caused erosion near the joining interface, and the eroded portion became the starting point of fatigue failure.

In Comparative Example 8 in which the pressing force was 1 MPa, the tensile strength was 418 MPa despite the joining temperature of 1400 ° C. and the holding time of 300 seconds. Broke. The fatigue strength ratio was 0.6, and the fatigue limit was lower than that of the base metal. This is considered to be because the bonding interface did not adhere sufficiently due to the low pressing force, and an unbonded portion was partially generated.

Comparative Example 9 where the pressure was 7 MPa
In this example, the tensile strength was 424 MPa even though the joining temperature was 1300 ° C., and the test piece broke from the joint interface. Further, the fatigue strength ratio was 0.7, and the fatigue limit was lower than that of the base metal. This is considered to be because the applied pressure was high and the joint was excessively deformed, and the deformed portion became a starting point of fatigue failure.

On the other hand, the joining temperature was set to 1350 ° C.
In Example 9 in which the pressing force was 1.5 MPa and Example 10 in which the pressing force was 5.0 MPa, the bonding strength was 500 MPa or more, which is equivalent to the base material, and the test piece was on the base material side. Broke from Further, the fatigue strength ratio was 0.9 in each case, indicating a fatigue limit equivalent to that of the base metal.

Examples 10 to 11 and Comparative Examples 6 to 8
In each of the examples, since the diameter expansion ratio at the end of the metal tube was 5%, the maximum step was 1.0 mm in each case.

From the above results, in the case where the metal pipe is subjected to liquid phase diffusion bonding, if the metal pipe is expanded at a predetermined end expansion rate and the bonding temperature is set to 1400 ° C. or less, the erosion near the bonded part is reduced. Was suppressed, and a joined body having high joining strength and fatigue strength was obtained. Also, the pressing force is 1.5M
It was found that when the pressure was Pa or more and 5 MPa or less, occurrence of unjoined portions and excessive deformation of the joined portions were suppressed, and a joined body having high joining strength and fatigue strength was obtained.

(Example 11) Diffusion bonding of a metal tube was performed by the following procedure. That is, as a metal tube, American Petroleum Institute grade H40 (hereinafter referred to as “API H
40 ". ) Of 7.00 inch (1
77.8mm), wall thickness 0.54 inch (13.7mm)
The inner diameter of the end of the steel pipe is set to 5
%.

Next, the end face of the expanded metal tube is finished so that the surface roughness Rmax is 50 μm or less, and the joining interface of the metal tube has a melting point of 1140 ° C. having a composition equivalent to JIS BNi-5 and a thickness of 1140 ° C. Insert a 30 μm Ni-based alloy foil,
Liquid phase diffusion bonding was performed.

[0132] The method of heating the bonding portion includes a frequency of 3 k.
A high frequency induction heating method using a high frequency current of Hz was used.
The bonding conditions are as follows: bonding temperature 1300 ° C., holding time 15
Bonding was performed in an Ar atmosphere with 0 seconds at a pressure of 3.5 MPa.

Example 12 The procedure was the same as that of Example 11 except that the joining temperature was 1350 ° C., the holding time was 240 seconds, the pressure was 4.0 MPa, and the frequency of the high-frequency current flowing through the induction coil was 100 kHz. , Diffusion bonding of the metal tube was performed.

(Example 13) A bonding temperature was 1350 ° C, a holding time was 240 seconds, a pressing force was 4.0 MPa, and the bonding was performed by a high-frequency direct current heating method using a high-frequency current of 50 kHz. According to the same procedure as in Example 11, diffusion bonding of the metal tube was performed.

(Comparative Example 10) Surface roughness Rmax of bonding surface
Was set to 100 μm, the joining temperature was set to 1400 ° C., the holding time was set to 300 seconds, and the pressing force was set to 5.0 MPa.

Comparative Example 11 The procedure was the same as that of Example 11 except that the joining temperature was 1400 ° C., the holding time was 300 seconds, the pressing force was 4.0 MPa, and the frequency of the high-frequency current passed through the induction coil was 400 kHz. , Diffusion bonding of the metal tube was performed.

Examples 11 to 13 and Comparative Examples 10 to 11
With respect to the joined body obtained in the above, the maximum step, the tensile strength, and the fatigue strength ratio were measured according to the same procedure as in Example 1.
Table 5 shows the results.

[0138]

[Table 5]

The surface roughness Rmax of the bonding interface is 100 μm
In Comparative Example 10, the tensile strength was 598 MPa, and the test piece broke from the joint interface, even though diffusion bonding was performed at relatively high temperature, high pressure and for a long time. The fatigue strength ratio was 0.6, and the fatigue limit was lower than that of the base metal. This is considered to be because the pores present at the bonding interface could not be completely eliminated by the diffusion of elements due to the rough surface roughness.

Similarly, in Comparative Example 11 in which induction heating was performed using a high-frequency current having a frequency of 400 MPa, tensile strength was similarly obtained despite diffusion bonding under relatively high temperature, high pressure, and long time conditions. 564 MPa, and the test piece broke from the joint interface. Further, the fatigue strength ratio is 0.1.
6, indicating that the fatigue limit was lower than that of the base metal. This is presumably because, due to the high frequency, the entire joint interface was not uniformly heated, and an unjoined portion was generated on the inner peripheral surface side of the metal tube.

On the other hand, the surface roughness Rmax of the bonding interface
Is 50 μm or less, and in Examples 11 and 12 in which induction heating is performed using a high-frequency current having a frequency of 100 kHz or less,
The tensile strength was 700 MPa or more, which is equivalent to that of the base material, and the test piece was broken from the base material side. Further, the fatigue strength ratio was 0.9, showing a fatigue limit equivalent to that of the base metal.

Similarly, in Example 13 joined by a high-frequency direct current heating method using a high-frequency current having a frequency of 50 kHz, the tensile strength was 700 MPa or more, which is equivalent to that of the base material, and the test piece was Broke from Further, the fatigue strength ratio was 0.9, showing a fatigue limit equivalent to that of the base metal.

Examples 11 to 13 and Comparative Examples 10 to
In No. 11, the end step diameter expansion rates of the metal tubes were all 5%, so that the maximum steps were all 1.0 mm.

From the above results, when performing liquid phase diffusion bonding of a metal pipe, the end of the metal pipe is expanded at a predetermined end expansion rate, and the surface roughness Rmax of the bonding interface is set to 50 μm.
It was found that when the following conditions were satisfied, a joined body having high joining strength and fatigue strength could be obtained. Further, when the bonding interface is subjected to high-frequency induction heating or high-frequency direct current heating, if the frequency of the high-frequency current is 100 kHz or less, the entire bonding surface can be uniformly heated, and a bonded body having high bonding strength and fatigue strength can be obtained. I knew it could be done.

Example 14 Diffusion bonding of a metal tube was performed according to the following procedure. That is, as a metal pipe, an outer diameter of 139.8 mm, a wall thickness of 6.6 mm, and a length of 1 m made of carbon steel pipe for pressure piping (JIS G3454) STPG410.
4A, the inner peripheral surface near the end was cut into a tapered shape (hereinafter, such a process is referred to as “type A”). The outer peripheral surface was left unprocessed.

Next, the end surface of the metal tube whose inner peripheral surface near the end was machined was finished so that the surface roughness Rmax was 20 μm or less, and BNi-3 (JI
Liquid phase diffusion bonding was performed by interposing a Ni-based alloy foil having a composition equivalent to SZ3265) having a melting point of 1050 ° C. and a thickness of 40 μm.

[0147] The method of heating the bonding portion includes a frequency of 3 k.
A high frequency induction heating method using a high frequency current of Hz was used.
The bonding conditions were as follows: bonding temperature 1290 ° C., holding time 12
The bonding was performed in an Ar atmosphere with 0 seconds and a pressure of 3.0 MPa.

(Embodiment 15) As shown in FIG. 4B, the inner peripheral surface near the end of the metal pipe is cut into an elliptical shape (hereinafter, such a process is referred to as "type B"). ), Diffusion bonding of the metal tube was performed in the same manner as in Example 14.

(Example 16) A metal pipe was cut in the same manner as in Example 14 except that the inner peripheral surface near the end of the metal tube was cut into a type A and the outer peripheral surface was cut into a type B. The tubes were diffusion bonded.

(Comparative Example 12) Diffusion bonding of a metal tube was performed according to the same procedure as in Example 14, except that the inner peripheral surface and the outer peripheral surface near the end of the metal tube were not machined. .

(Comparative Example 13) Diffusion bonding of a metal tube was performed according to the same procedure as in Example 14, except that only the outer peripheral surface near the end of the metal tube was cut to type A.

Examples 14 to 16 and Comparative Examples 12 to 13
For the metal pipe joined body obtained in the above, the maximum step generated on the inner peripheral surface side and the outer peripheral surface side of the joint was measured. Also, 20
A tensile test was performed using a 0Tonf universal testing machine in the state of a carbon steel pipe joint for pressure piping having a total length of 2 m, and the tensile strength was determined. Further, both ends of a carbon steel pipe joint for pressure piping having a total length of 2 m were sealed, and a fatigue test was performed in which a tensile / compression load was repeatedly applied while an internal pressure of 6 MPa was applied to determine a fatigue limit. Further, the fatigue strength ratio was evaluated by the ratio with the fatigue limit of the carbon steel pipe for pressure piping obtained by the same method. Table 6 shows the results.

[0153]

[Table 6]

In Comparative Example 12 in which no machining was performed near the end, the maximum steps on the inner peripheral surface side and the outer peripheral surface side were 1.2 mm and 1.5 mm, respectively. The tensile strength is
497 MPa, slightly lower than the strength of the base material, and the test piece broke from the joint interface. Furthermore, the fatigue strength ratio is
It showed a low value of 0.5. This is presumably because stress was concentrated on the step generated at the joint, and the step became the starting point of fatigue failure.

In Comparative Example 13 in which only the outer peripheral surface near the end was machined, the maximum step on the outer peripheral surface was 0.1 m.
m or less, but the maximum step on the inner peripheral surface side is 0.5 mm
Met. Also, the tensile strength is almost the same as the base material,
Although the test piece broke from the heat-affected zone, the fatigue strength ratio was 0.
It was 7.

On the other hand, in Examples 14 to 16 in which the inner peripheral surface near the end was machined, the maximum step generated on the inner peripheral surface was 0.1 mm or less. Further, the tensile strength was about 510 MPa in each case, and the test piece broke from the heat-affected zone. Further, the fatigue strength ratio was 0.9 in each case, indicating substantially the same fatigue characteristics as the base metal.

From the above results, it was found that when the material on the inner peripheral surface side of the end portion of the metal tube was removed and the maximum step on the inner peripheral surface was reduced, the fatigue characteristics of the joint were improved.

Example 17 Diffusion bonding of a metal tube was performed according to the following procedure. That is, as a metal pipe, an outer diameter of 139.8 mm, a wall thickness of 6.6 mm, and a length of 1 m made of carbon steel pipe for pressure piping (JIS G3454) STPG410.
As shown in FIG. 5 (a), the inner peripheral surface side near the end was expanded at an end enlarging rate of 5%, and the inner peripheral surface side was cut into type B. The outer peripheral surface was left unprocessed.

Next, the end face of the metal pipe in the vicinity of the end, which has been subjected to the diameter expansion processing and the mechanical processing, is finished so that the surface roughness Rmax is 20 μm or less.
Melting point 11 having composition equivalent to 5 (JIS Z3265)
Liquid phase diffusion bonding was performed by inserting a Ni-based alloy foil having a thickness of 40 μC and a thickness of 35 μm.

[0160] The method of heating the bonding portion includes a frequency of 3 k.
A high frequency induction heating method using a high frequency current of Hz was used.
The bonding conditions are as follows: bonding temperature 1300 ° C., holding time 60
The bonding was performed in an Ar atmosphere at a pressure of 3.0 MPa for 2 seconds.

(Example 18) The same procedure as in Example 17 was carried out except that the vicinity of the end of the metal tube was expanded at an end expansion ratio of 10%, and then the inner peripheral surface was cut into type A. Follow the steps,
Diffusion bonding of the metal tube was performed.

(Example 19) After expanding the vicinity of the end of a metal tube at an end expansion ratio of 10%, the inner peripheral surface and the outer peripheral surface were cut into type B and type A, respectively. Except for the above, the metal tube was subjected to diffusion bonding according to the same procedure as in Example 17.

(Comparative Example 14) Diffusion bonding of a metal tube was performed according to the same procedure as in Example 17, except that the inner peripheral surface and the outer peripheral surface near the end of the metal tube were not machined. .

(Comparative Example 15) Diffusion bonding of a metal tube was performed according to the same procedure as in Example 17, except that only the outer peripheral surface near the end of the metal tube was cut into type B.

Examples 17 to 19 and Comparative Examples 14 to 15
According to the same procedure as in Example 14, the measurement of the maximum level difference generated on the inner peripheral surface side and the outer peripheral surface side of the joint, a tensile test, and a fatigue test were performed on the joined metal pipe obtained in the above. Table 7 shows the results.

[0166]

[Table 7]

In Comparative Example 14 in which no machining was performed near the end, the maximum steps on the inner peripheral surface side and the outer peripheral surface side were 1.5 mm and 1.6 mm, respectively. The tensile strength is
497 MPa, slightly lower than the strength of the base material, and the test piece broke from the joint interface. Furthermore, the fatigue strength ratio is
It showed a low value of 0.4.

In Comparative Example 13 in which only the outer peripheral surface near the end was machined, the maximum step on the outer peripheral surface was 0.1 m.
m or less, but the maximum step on the inner peripheral surface side is 0.3 mm
Met. Also, the tensile strength is almost the same as the base material,
Although the test piece broke from the heat-affected zone, the fatigue strength ratio was 0.
It was 7.

On the other hand, in Examples 17 to 19 in which the inner peripheral surface side near the end was subjected to the diameter expansion processing and the mechanical processing, the maximum step generated on the inner peripheral surface side was 0.1 mm or less. there were. Further, the tensile strength was about 510 MPa in each case, and the test piece broke from the heat-affected zone. Further, the fatigue strength ratio was 0.9 in each case, indicating substantially the same fatigue characteristics as the base metal.

From the above results, it was found that when the material on the inner peripheral surface side of the end portion of the metal pipe was removed and the maximum step on the inner peripheral surface was reduced, the fatigue characteristics of the joint were improved.

Example 20 Diffusion bonding of a metal tube was performed according to the following procedure. That is, as a metal pipe, an outer diameter of 139.8 mm, a wall thickness of 6.6 mm, and a length of 1 m made of carbon steel pipe for pressure piping (JIS G3454) STPG410.
As shown in FIG. 5B, the inner peripheral surface side near the end was expanded at an end diameter expansion ratio of 5%, and then the inner peripheral surface was cut into a type B. The outer peripheral surface was left unprocessed.

Next, the end face of the metal pipe in the vicinity of the end, which has been subjected to the diameter expansion processing and the mechanical processing, is finished so that the surface roughness Rmax is 20 μm or less, and the BNi-
Melting point 11 having composition equivalent to 5 (JIS Z3265)
Liquid phase diffusion bonding was performed by inserting a Ni-based alloy foil having a thickness of 40 μC and a thickness of 35 μm.

The heating method of the bonding portion includes a
A high frequency induction heating method using a high frequency current of Hz was used.
The bonding conditions are as follows: bonding temperature 1300 ° C., holding time 15
The bonding was performed in an Ar atmosphere with 0 seconds and a pressure of 3.0 MPa.

Next, a 100-tonf universal testing machine was used to insert a pipe-expansion tool from one end of the obtained metal-pipe joint to expand the metal-pipe joint. In addition, in the case of this example, the pipe expansion ratio E was set to 20%.

Example 21 The same procedure as in Example 20 was carried out except that the vicinity of the end of the metal tube was expanded at an end expansion ratio of 10%, and then the inner peripheral surface was cut to type A. Follow the steps,
Diffusion bonding of the metal tube was performed. The obtained metal pipe joint was expanded at a pipe expansion rate of 25%.

(Example 22) After expanding the vicinity of the end of a metal tube at an end expansion ratio of 10%, the inner peripheral surface side and the outer peripheral surface side were cut into type B and type A, respectively. Except for the above, the metal tube was subjected to diffusion bonding according to the same procedure as in Example 20. About the obtained metal-pipe joint, the expansion rate was 25.
The pipe was expanded in%.

(Comparative Example 16) Diffusion bonding of a metal tube was performed according to the same procedure as in Example 17 except that machining was not performed on the inner peripheral surface side and the outer peripheral surface side near the end of the metal tube. . Further, with respect to the obtained metal pipe joined body, a pipe expansion rate of 10
% Pipe expansion was performed.

(Comparative Example 17) Diffusion bonding of a metal tube was performed in the same procedure as in Example 20, except that only the outer peripheral surface near the end of the metal tube was cut into type B. Also,
The obtained metal pipe joint was expanded at a pipe expansion ratio of 20%.

Examples 20 to 22 and Comparative Examples 16 to 17
In accordance with the same procedure as in Example 14, the measurement of the maximum step generated on the inner peripheral surface side and the outer peripheral surface side of the joint and the tensile test were performed on the joined metal pipe assembly obtained in the above. Further, the metal pipe joined body after the tube expansion was subjected to an ultrasonic flaw detection test, and the presence or absence of a defect at the joint interface was examined. Table 8 shows the results.

[0180]

[Table 8]

In Comparative Example 16 in which no machining was performed near the end, the maximum steps on the inner peripheral surface side and the outer peripheral surface side were 2.0 mm and 0.5 mm, respectively. In addition, a defect was detected at the joint interface after the pipe expansion, and accordingly, the tensile strength was significantly lower than the strength of the base material, and became 388 MPa.

In Comparative Example 13 in which only the outer peripheral surface near the end was machined, the maximum step on the outer peripheral surface was 0.1 m.
m, but the maximum step on the inner peripheral side is 0.8 mm
Met. In addition, a micro defect was detected at the joint interface after pipe expansion, and the tensile strength was 492 MPa accordingly,
The strength was slightly lower than the strength of the base material. This is presumably because the pipe expansion was performed at a pipe expansion ratio E relatively higher than the T value described above.

On the other hand, in the second embodiment, the pipe expansion was performed after the diameter expansion and the machining were performed on the inner peripheral surface side near the end.
In the case of 0 to 22, the maximum steps generated on the inner peripheral surface side were all 0.1 mm or less. No defects were observed at the joint interface, and the tensile strength was 560 MPa or more in each case.

From the above results, when the maximum step on the inner peripheral surface side of the joint is reduced, the T value is reduced, and it is possible to perform pipe expansion at a high pipe expansion rate without causing defects in the joint. all right.

As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. It is.

For example, in the above-described embodiments, the liquid-phase diffusion bonding method is used as a means for bonding the metal tubes, but the metal tubes may be bonded using the solid-phase diffusion bonding method.

Further, the method for joining metal tubes according to the present invention comprises:
It is particularly suitable as a method for joining an oil well pipe such as a casing tube buried underground, but the application of the present invention is not limited to oil well pipes, and gas wells, geothermal wells,
Casing tubes used for hot spring wells, water wells, etc.
Alternatively, it can also be used as a method for joining a line pipe laid on the ground surface or a pipe for a plant, whereby the same effect as in the above embodiment can be obtained.

[0188]

According to the present invention, there is provided a method of joining metal pipes in which metal pipes are butt-bonded to each other by diffusion joining. At least one of the metal pipes has a joint end face having a difference in inner diameter of 2 mm or less. Since the nearby inner diameter is processed before joining, even if the outer diameter and / or thickness of each metal pipe varies, the step generated on the inner peripheral surface side of the joined portion can be reduced. . Therefore, there is an effect that stress concentration occurring at the joint is reduced, and a joined body having excellent strength and fatigue characteristics can be obtained. In addition, since the step on the inner peripheral surface side of the joint is reduced, the retention of corrosive substances is reduced, so that the corrosion resistance and mechanical properties of the joint are not adversely affected.

[0189] Further, in the case where the processing is a diameter expansion processing without removing the material, the processing can be easily performed as compared with other processing methods such as cutting. Therefore, there is an effect that a joined body excellent in strength, fatigue characteristics and corrosion resistance can be obtained without increasing joining cost.

In the case where the above-mentioned processing is mechanical processing involving the removal of material, even if the dimensional tolerance of the inner diameter and wall thickness of the metal pipe is large, the step formed on the inner peripheral surface side is surely formed. Has the effect of being able to reduce.

Further, in the case where the above-mentioned processing includes a diameter-increasing processing without removing the material and a mechanical processing in which the material is removed after the diameter-increasing processing, the step generated on the inner peripheral surface side is reduced. There is an effect that the size can be reliably reduced.
Moreover, by this, about the obtained metal pipe joint,
There is an effect that pipe expansion can be performed at a relatively large pipe expansion rate.

As described above, according to the method for joining metal tubes according to the present invention, a joined body having excellent strength, fatigue characteristics and corrosion resistance can be obtained at low cost. If applied to pipes and the like, it greatly contributes to cost reduction of oil drilling work and pipe laying work and improvement of reliability, and is an industrially extremely effective invention.

[Brief description of the drawings]

FIG. 1 is a process diagram showing a method for joining metal tubes according to an embodiment of the present invention.

FIG. 2 is a view for explaining the relationship between the dimensional accuracy of a metal tube mass-produced industrially and a step generated at a joint.

FIG. 3 is a view for explaining the relationship between the dimensional accuracy of a metal tube mass-produced industrially and a step generated at a joint.

FIG. 4 (a) is a diagram showing a state where a metal pipe whose inner peripheral surface side is machined into a tapered shape at the end is joined, and FIG. 4 (b) is an inner peripheral surface of the end; It is a figure which shows the state which joined the metal pipe machined to the elliptical side.

FIG. 5 (a) is a view showing a state where a metal pipe whose inner peripheral surface side is machined into a tapered shape is joined after an end portion is subjected to a diameter expanding process, and FIG. FIG. 7 is a view showing a state in which a metal pipe whose inner peripheral surface side is machined into an elliptical shape is joined after an end portion is subjected to a diameter expanding process.

[Explanation of symbols]

 Reference Signs List 30 metal pipe 32 metal pipe joint 36 insert material 41, 42 metal pipe 51, 52 metal pipe

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) B23K 101: 06 (72) Inventor Shigeyuki Inagaki 3-9-111 Tenpakucho, Minami-ku, Nagoya City, Aichi Prefecture Daido Special Steel Tempakuso 205 F term (reference) 4E067 AA02 AB02 AB05 AD02 AD03 AD04 BA03 BA05 BB02 BH01 BH03 DA00 DA09 DB02 DC03 DC06 DC07 EC06

Claims (4)

[Claims] 1. A method for joining metal pipes in which metal pipes are butt-butted and diffusion-bonded to each other, wherein an inner diameter near at least one of the metal pipes is reduced so that a difference between inner diameters of two metal pipes at the joining end faces is 2 mm or less. A method for joining metal tubes, which is performed before joining. 2. The metal pipe joining method according to claim 1, wherein the processing is a diameter expansion processing without removing a material. 3. The metal pipe joining method according to claim 1, wherein the processing is machining involving removal of a material. 4. The metal pipe according to claim 1, wherein the processing includes a diameter expansion processing without removing the material and a machining processing with removal of the material performed after the diameter expansion processing. Joining method.