JP2001150178A - Method and device for reducing residual welding stress - Google Patents

Abstract

PROBLEM TO BE SOLVED: To heat the whole periphery of piping uniformly and quickly with a simple device composition to reduce residual stress in the vicinity of the weld zone of a hollow body such as piping, etc. SOLUTION: When reducing residual tensile stress on the inside surface side of the hollow body, a ring-shaped arc generating ring is arranged on the outer peripheral side of the hollow body, a pair of ring coils for forming magnetic fields are arranged so that the ring is interposed between the coils, and the outer peripheral side of an annular weld zone is uniformly and quickly heated while an arc rotates at high speed in the circumferential direction. When reducing the residual tensile stress on the outside surface side of the hollow body, a disk-shaped arc generation plate is arranged on the inner peripheral side of the hollow body, a pair of ring coils for forming magnetic fields are arranged so that the generation plate is interposed between the coils, and the inner peripheral side of an annular weld zone is uniformly and quickly heated while the arc rotates at high speed in the circumferential direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for reducing residual stress in a pipe or a furnace in the vicinity of a welded part of a furnace equipment from stress corrosion cracking. The present invention relates to a method and an apparatus for reducing welding residual stress for reducing and improving tensile residual stress to a compression side.

[0002]

2. Description of the Related Art In a nuclear power plant, for example, a pipe made of austenitic stainless steel or a nickel base alloy, or a tubular container such as a furnace equipment is provided on the inner surface side with the pipe or equipment surface which comes into contact with high-temperature pure water. , A tensile residual stress exceeding the yield stress is generated, and stress corrosion cracking may occur. That is, to explain more specifically, on the inner surface near the protruding welded portion of a pipe such as a pipe or a tubular container, there is a tensile residual stress state in both the circumferential direction and the axial direction, and the existence of tensile residual stress on the inner surface is This leads to a reduction in stress corrosion cracking performance. For this reason, it is desired that the tensile residual stress is reduced or brought into a compressed state.

For this reason, various methods for reducing residual stress have been proposed. First, the prior art shown in FIG. 5 is called a water-cooled welding method, in which welding is performed while flowing cooling water 22 on the inner surface side of a welding joint 21 a of a pipe 21 to generate a temperature gradient in the thickness direction of the pipe 21, and welding is performed. In a method of reducing the residual tensile stress, the first layer 23 is subjected to underwater welding, and then the second or third layer 24 is subjected to water cooling welding. However, according to such a conventional technique, since it is necessary to flow water on the inner surface side of the pipe, the application is limited, and it is often difficult to apply the method particularly in the field.

[0006] The prior art shown in FIG. 6 is called a high-frequency induction heating method, in which the inner surface of the pipe 31 is water-cooled so that a predetermined temperature difference occurs in the thickness direction of the target portion of the welded portion 32 of the pipe 31. Is heated by induction heating using the high-frequency induction heating coil 33, the heating is stopped, and the inner surface of the pipe 31 is continuously cooled with water until the temperature in the plate thickness direction becomes substantially uniform, thereby pulling the inner surface of the pipe. This is a method for reducing residual stress.

[0005] In such prior art as well, it is necessary to water-cool the inner surface of the pipe, which not only limits the application but also makes the apparatus large-scale and difficult to implement locally. In addition, high-frequency induction heating is a heating method over the entire circumference of a pipe. If it is performed rapidly, the induction heating capacity becomes large, and uniformization over the entire circumference is difficult.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, the present invention provides a simple method of heating the entire circumference of a pipe in order to reduce residual stress in the vicinity of a welded portion of a hollow body such as a pipe or a tubular container. It is an object of the present invention to provide a method for reducing residual stress which can be performed uniformly and rapidly with a device configuration, and a device therefor.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for reducing the residual stress in a welded portion of a hollow body such as a pipe or a tubular container. Using the kinetic energy
High-speed rotation of the arc placed facing the vicinity of the annular weld of the hollow body and heating the vicinity of the annular weld from one side to reduce the temperature difference required to reduce the residual tensile stress on the inner or outer surface of the hollow body. It is characterized in that it is generated between the outer peripheral surfaces of the hollow body.

[0008] The second aspect of the present invention is the first aspect.
An invention relating to an apparatus for effectively achieving the described invention, wherein an arc generating means arranged in a face-to-face relationship with an annular welded portion of a hollow body, and an arc current generated between the arc generating means and a hollow body welded portion. Means for generating kinetic energy in the circumferential direction of the hollow body by lines of magnetic force generated in the axial direction of the hollow body.

Preferably, the arc generating means comprises a ring or a disk concentrically rotating with the hollow body, and the kinetic energy generating means is a ring-shaped coil disposed on both axial sides of the arc generating means. And a coil current is passed through the coil to form a magnetic field in the axial direction of the hollow body, and a DC power supply is applied between the arc generating means and the hollow body.

More specifically, in order to reduce the residual tensile stress on the inner surface of the hollow body, a ring-shaped arc generating ring is arranged on the outer peripheral side of the hollow body, and the ring is sandwiched between the arc generating rings for forming a magnetic field. A pair of ring coils may be arranged and the outer periphery of the annular weld may be rapidly and uniformly heated while the arc rotates in the circumferential direction at a high speed. In order to reduce the residual tensile stress on the outer surface of the hollow body, the hollow body may be used. A circular arc generating plate is arranged on the circumferential side, and a pair of ring coils for forming a magnetic field are arranged so as to sandwich the generating plate, and the arc rotates at high speed in the circumferential direction, so that the inner peripheral side of the annular welded portion is uniform. What is necessary is just to heat rapidly.

According to the present invention, an arc driving force (rotational force) acts in the circumferential direction of the hollow body by the coil magnetic field and the arc current,
Since the heating energy by the arc is extremely large and circulates at a high speed, for example, when reducing the tensile residual stress on the inner surface of the hollow body, the outer surface of the tube is rapidly heated without melting the welded portion, and the inner surface of the hollow body is heated. The temperature difference required to reduce the residual tensile stress on the side can be generated between the outer peripheral surfaces of the hollow body.

This makes it possible to redistribute the intrinsic strain within the thickness between the outer peripheral surfaces of the hollow body and to reduce the residual tensile stress on the inner surface, and to reduce the residual tensile stress in the vicinity of the welded portion on the inner surface of the pipe. It can be expected to improve the welded portion in terms of corrosion cracking resistance, fatigue resistance, brittleness resistance, fracture resistance, and the like.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to an embodiment shown in the drawings. However, unless otherwise specified, dimensions, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the invention, but are merely illustrative examples. FIG. 1 shows an apparatus for reducing residual stress in piping according to an embodiment of the present invention, and particularly relates to an apparatus for reducing tensile residual stress on the inner surface side. 1
Is a pipe made of stainless steel, and has an annular welded portion 1a formed at the center by butt welding. Reference numeral 3 denotes a ring-shaped electrode for arc generation, which is disposed concentrically with the pipe 1 on the outer peripheral side of the pipe 1 so as to face and bend in the vicinity of the annular welded portion 1a on the side of the pipe 1 and on the inner peripheral side. Is thinned like a knife edge so that the arc can easily fly toward the pipe 1. A DC power supply 4 is connected between the ring-shaped electrode 3 and the pipe 1 so that an arc 5 can be generated between the vicinity of the annular welded portion 1a and the ring-shaped electrode 3 (the arc 5 is generated at one point). I have. Reference numerals 2 and 2 denote a pair of ring coils for forming a magnetic field arranged so as to sandwich the ring-shaped electrode 3. Can be formed.

According to such a configuration, a DC power supply 4 is applied to the ring-shaped electrode 3 in a state where a coil current is applied to the magnetic field generating coils 2, 2, whereby a hollow body shaft is provided between the pair of coils 2, 2. A magnetic field is formed in the direction, while an arc 5 is generated between the annular weld 1a and the ring-shaped electrode 3 (the arc 5 is generated at one point), and the arc current flows to the annular weld 1a side. According to Faraday's law, kinetic energy is generated in the arc 5 in the circumferential direction, and the arc 5 is rotated at high speed circumferentially along the flow of the coil current of the arc magnetic field generating coils 2 and 2 generated by the ring-shaped electrode 3. Thereby, the annular welded portion 1a is uniformly heated.

The location of the ring electrode 3 is not particularly limited as long as the residual stress is to be reduced, and may be in the vicinity of the welded portion 1a. That is, in the present embodiment, an arc 5 is generated between the ring-shaped electrode 3 and the pipe 1, and at the same time, a coil current is applied to the coils 2 and 2 to create a magnetic field.
Is rotated at high speed in the circumferential direction of the pipe by electromagnetic force. Uniform and rapid heating is performed in the circumferential direction of the tube by the arc 5 rotated at a high speed to generate a predetermined temperature difference ΔT in the thickness direction of the tube. The temperature difference ΔT necessary for reducing the residual stress is equal to or more than the value obtained from the following equation (1). ΔT ≧ {4Vy (1-γ)} / E · α (1) where Vy: yield stress, E: Young's modulus, α: linear expansion coefficient, γ: Poisson's ratio.

Next, an example based on such an embodiment will be described. As test material, outer diameter 60mm, wall thickness 8.7mm
SUS316 welding pipe 1 was used. Ring-shaped electrode 3
Was used as a material for the above, and the distance from the outer surface of the pipe welded portion 1a was set to 1 to 2 mm. The magnetic field forming coils 2 and 2 arranged on the upper and lower sides of the ring-shaped electrode 3 have a wire diameter of 1,
A 2 mm conducting wire was used and the number of turns was 210 turns each. Assuming that the yield stress of the SUS316 pipe was about 205 N / mm, the temperature difference ΔT between the inside and outside of the pipe required for reducing the residual stress was calculated to be 200 ° C. or more from the equation (1).

The center of the weld bead was heated from the outer surface side under the conditions of a coil current of 20 A or more and an arc current of 50 to 100 A so that the temperature difference between the inner and outer surfaces of the welded portion 1a of the test welding pipe 1 became 200 ° C. or more. . When heated under these conditions,
FIG. 2 shows the temperature history on the inner and outer surfaces of the tube. From this, it can be understood that a temperature difference of 200 ° C. or more occurred about 40 seconds after the start of heating.

That is, the arc 5 is rotated at a high speed by the magnetic field of the coils 2 and 2 and the pipe welding portion 1a is uniformly and rapidly heated from the outer surface side. Temperature difference could be generated. FIG. 3A shows the result of measuring the residual stress in the vicinity of the welded portion 1a after the heat treatment according to the present embodiment, and FIG. 3B shows the result of measuring the residual stress of the untreated pipe welded portion 1a. 3 (A) and 3 (B), a maximum of 30 mm within a range of 10 mm from the welded portion 1a of FIG. 3 (B).
The tensile residual stress of about Kgf / mm ² is 10 A in FIG.
It can be seen that it has been reduced to Kgf / mm ² or less.

According to the present embodiment, the welded portion 1 on the inner surface of the pipe 1 is provided.
By reducing the tensile residual stress a, improvement in corrosion cracking resistance, fatigue resistance, brittle fracture resistance and the like can be expected. That is, FIG.
According to the embodiment, as shown in FIG.
By heating while rotating, the outer surface of the pipe 1 is rapidly heated, the intrinsic strain is redistributed within the plate thickness, and the tensile residual stress on the inner surface can be reduced.

FIG. 7 shows an apparatus for reducing residual stress in a pipe 1 according to an embodiment of the present invention, and particularly relates to an apparatus for reducing the residual tensile stress on the outer surface side of the pipe 1. In the present embodiment, in order to reduce the tensile residual stress on the outer surface side of the hollow body, a thin disk-shaped arc generating electrode 3 is arranged on the inner peripheral side of the pipe 1, and the arc generating electrode 3 for forming a magnetic field is sandwiched by the generating electrode 3. A pair of ring coils 2, 2 for generating a magnetic field are arranged in the vicinity.

In this embodiment as well, the arc 5 is rotated at a high speed in the circumferential direction of the tube between the disk-shaped electrode 3 and the pipe 1 by electromagnetic force, and the arc 5 rotated at a high speed is uniform and rapid in the circumferential direction of the tube. Heating is performed and a predetermined temperature difference Δ
Generate T. Note that a tensile residual stress is generated on the side of the general pipe 1 on which heat is applied. Therefore, the present embodiment is an application example in a case where a tensile residual stress is generated on the outer peripheral side of the pipe 1 by welding or overlaying from the inside.

In such a case, the piping 1 can be welded only from the inner surface (for example, in the case of the inner bone in a double configuration, or when other devices are present on the outer peripheral side) and in the corrosive environment on the outer peripheral side. In this case, the case of the pipe 1 to be placed is considered. In this embodiment, the inner diameter 102
A 304 stainless steel gold welding pipe 1 having a thickness of 6.0 mm and a thickness of 6.0 mm was used. Tungsten was used as the material of the disc-shaped electrode 3, and the distance was adjusted so that the distance from the inner surface of the pipe welded portion 1a was 1 to 2 mm.

A copper wire having a wire diameter of 1 mm was used for a pair of magnetic field generating coils 2 and 2 located on both sides of the disk-shaped electrode 3, and the number of turns was 210 turns. On the inner and outer surfaces of the welded portion 1a of the test welding pipe 1, the center of the weld bead was heated from the inner surface side under the conditions of a coil current of 20A or more and an arc current of 50 to 150A so as to generate a temperature difference ΔT required for residual stress reduction. The same effect as in the above embodiment was obtained.

[0024]

As described above, according to the present invention, the arc 5 is rotated at a high speed by the magnetic field of the coils 2 and 2 to uniformly and rapidly heat the pipe weld 1a from the inner surface side. The temperature difference required to reduce the tensile residual stress on the outer surface could be generated. By reducing the tensile residual stress of the welded portion 1a on the outer surface side of the pipe 1, improvement in corrosion cracking resistance, fatigue resistance, brittle breakage resistance and the like on the outer peripheral side of the pipe 1 can be expected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a pipe residual stress reducing device according to an embodiment of the present invention, particularly, a device that reduces tensile residual stress on an inner surface side.

FIG. 2 is a graph showing a temperature history of the inner and outer surfaces of the tube by arc heating according to the present invention.

3A is a distribution diagram of a residual stress in a weld after the heat treatment according to the present invention, and FIG. 3B is a distribution map of a residual stress in a weld of an untreated pipe.

FIG. 4 shows a heating process and a cooling process of the temperature distribution between the inner and outer surfaces of the pipe, the intrinsic strain distribution within the plate thickness, and the tensile residual stress distribution when the arc is heated while being driven to rotate by magnetism.

FIG. 5 is a schematic view showing a conventional residual stress reducing device called a water-cooled welding method.

FIG. 6 is a schematic view showing a conventional residual stress reducing device called a high-frequency induction heating method.

FIG. 7 is an apparatus configuration diagram for reducing a tensile residual stress on the outer surface side of the pipe in the pipe residual stress reducing apparatus according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piping 1a Annular weld part 2 A pair of ring coils for forming a magnetic field 3 Ring-shaped or disk-shaped electrode for generation 4 DC power supply 5 Arc

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C21D 9/50 102 C21D 9/50 102A G21D 1/00 B23K 101: 04 // B23K 101: 04 G21D 1/00 X ( 72) Inventor Shoji Kushimoto 2-1-1 Shinama, Arai-machi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Masahiko 2-1-1 Shinama, Arai-machi, Takasago City, Hyogo Prefecture Takasago Mitsubishi Heavy Industries, Ltd. Inside the research institute (72) Inventor Hozumi Nakura 2-1-1, Shinhama, Arai-machi, Takasago-shi, Hyogo F-term in the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. (reference) 4E081 YS01 YX20 4K042 AA24 DB01 DB03 DF02 EA03

Claims (3)

[Claims] In a method for reducing residual stress in a welded portion of a hollow body such as a pipe or a tubular container, a kinetic energy generated in a circumferential direction of the hollow body by a magnetic field and an arc current is used to make a vicinity of an annular welded portion of the hollow body. High-speed rotation of the arc disposed facing the surface, heating the vicinity of the annular weld from one side, the temperature difference required to reduce the tensile residual stress on the inner surface of the hollow body or the outer surface side between the outer peripheral surface of the hollow body. Method of reducing welding residual stress characterized by having generated 2. A method for reducing a residual stress in the vicinity of a welded portion of a hollow body such as a pipe or a tubular container, comprising: an arc generating means arranged near the annular welded portion of the hollow body and facing the welded portion of the arc generating means and the hollow body. Means for generating kinetic energy in the circumferential direction of the hollow body by means of the arc current generated between the magnetic field lines and the magnetic force lines generated in the axial direction of the hollow body. 3. The arc generating means is a ring or a disk concentrically circling with the hollow body, and the kinetic energy generating means is a ring-shaped coil arranged on both axial sides of the arc generating means. 2. A welding residual stress reducing apparatus according to claim 1, wherein a coil current is passed through said coil to form a magnetic field in the axial direction of the hollow body, and a DC power is applied between said arc generating means and said hollow body. .