JP2007118058A - Method and apparatus for improving residual stress in pipe body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for improving a residual stress in a pipe body, which method can surely improve the residual stress irrespective of an installed condition and a configured condition of the pipe body, and further to provide an apparatus therefor. <P>SOLUTION: When the outer peripheral surface of the weld zone of the cylindrical pipe body 2 is irradiated with a laser beam while turning the outer periphery of the pipe body 2, the heated width W in the peripheral direction caused by the irradiation with the laser beam and the circumferential moving speed V of the laser beam are set such that the circumferential stress of the inside surface of the pipe body 2 caused by the heating by the laser beam is larger than at least the yield stress of the material composing the pipe body 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tubular body residual stress improving method and a residual stress improving apparatus for improving a residual stress of a tubular body such as a pipe.

  When installing a pipe body such as a large pipe in a nuclear power plant, a large plant, etc., removal of stress remaining in the pipe when welding is a problem. When welding is performed, residual stress is generated in the pipe, and the residual stress may shorten the life of the pipe. Therefore, it is desirable to remove the residual stress generated by welding.

  As a method for removing stress remaining in the pipe, a high-frequency heating residual stress improvement method (hereinafter referred to as IHSI method) has been proposed. In this IHSI method, the outer surface of the pipe is forcedly cooled with running water so that a temperature gradient is created in the thickness direction near the portion that satisfies the stress corrosion cracking (SCC) conditions of the pipe. After raising the temperature by induction heating using a high frequency induction heating coil from the side, stop heating and continue cooling by flowing water on the inner surface until the thickness direction of the pipe reaches a substantially uniform temperature, resulting in welding The residual stress in the tensile state near the portion is reduced or compressed (Patent Documents 1 to 3).

  Further, as a method for removing the residual stress in the pipe, a method of reducing the residual stress on the back surface by using laser irradiation to heat or melt the surface of the pipe of stainless steel or the like at a solution temperature is proposed ( Patent Documents 4 to 6).

Japanese Unexamined Patent Publication No. 57-70095 JP 2001-150178 A Japanese Patent Laid-Open No. 10-272586 JP 2003-004890 A JP-A-8-5773 JP 2000-2547763 A

  In the IHSI method, a certain temperature difference is required between the outer peripheral surface of the tube and the inner peripheral surface of the tube at the end of heating. For this reason, it is easy to implement for a pipe that has already been installed and is capable of cooling the inside by a water flow, but is difficult to implement for a pipe body that cannot ensure a flowing water state inside the pipe. The IHSI method performs high-frequency induction heating in order to create a temperature gradient in the thickness direction of the tube. In the case of heating with a high-frequency induction coil, the depth at which heat is transferred depending on the material (dielectric constant) of the tube. And the range is different, and it is difficult to limit the heating range. In addition, the apparatus is large and consumes a large amount of energy. Further, when members with different dielectric constants such as dissimilar joints are mixed, it is difficult to provide a constant temperature gradient in the thickness direction.

  In addition, in the above-described method of reducing the residual stress on the back surface by heating or melting the surface of a pipe made of stainless steel or the like using laser irradiation, overheating or heating is insufficient. There is a possibility. If heated too much, an area exposed to the sensitization temperature is generated in the vicinity of the heating area, which adversely affects the material itself.For example, an oxide scale is formed on the heating surface, and the scale needs to be removed. In-house construction may increase exposure. In addition, in the case of insufficient heating, the residual stress cannot be sufficiently improved, and there is a possibility that SCC cannot be reliably prevented.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a residual stress improvement method and a residual stress improvement apparatus for a tubular body that can reliably improve the residual stress regardless of the installation state and the configuration state of the tubular body. To do.

The method for improving the residual stress of a tubular body according to the first invention for solving the above-mentioned problems is as follows.
When locally irradiating the outer peripheral surface of the welded portion of the cylindrical tube with laser light and rotating the irradiation region in the circumferential direction,
Setting the circumferential heating width by irradiation of the laser beam so that the circumferential stress of the inner surface of the tube generated by heating with the laser beam is at least greater than the yield stress of the material constituting the tube. It is characterized by.

The method for improving the residual stress of a tubular body according to the second invention for solving the above-mentioned problem is as follows.
In the method for improving residual stress of a tubular body according to the first invention,
The circumferential heating width is 0.15 times or more, preferably 0.4 times or more, the outer diameter of the tubular body.

A method for improving the residual stress of a tubular body according to a third invention for solving the above-mentioned problem is as follows.
When irradiating the outer peripheral surface of the welded portion of the cylindrical tube body with laser light while rotating around the outer periphery of the tube body,
The circumferential heating width by the irradiation of the laser beam and the laser beam so that the circumferential stress on the inner surface of the tube generated by the heating by the laser beam is at least larger than the yield stress of the material constituting the tube. The circumferential movement speed is set.

A method for improving the residual stress of a tubular body according to a fourth invention for solving the above-described problems is as follows.
In the method for improving residual stress of a tubular body according to the third invention,
Fourier number F = a × (W / V) / t ² where W is the circumferential heating width, V is the moving speed in the circumferential direction, a is the thermal diffusivity of the tube, and t is the thickness of the tube. And
The circumferential heating width W and the circumferential movement speed V are set so that the Fourier number F satisfies 0.05 ≦ F ≦ 1.4, and preferably 0.1 ≦ F ≦ 0.6. Is set.

A method for improving the residual stress of a tubular body according to a fifth aspect of the present invention for solving the above problem is as follows.
In the method for improving residual stress of a tubular body according to the third invention,
When forcibly cooling the inner peripheral surface of the tube,
Fourier number F = a × (W / V) / t ² where W is the circumferential heating width, V is the moving speed in the circumferential direction, a is the thermal diffusivity of the tube, and t is the thickness of the tube. And
The circumferential heating width W and the circumferential movement speed V are set so that the Fourier number F is 0.05 ≦ F, preferably 0.1 ≦ F. .

A method for improving the residual stress of a tubular body according to a sixth aspect of the present invention for solving the above problem is as follows.
In the method for improving residual stress of a tubular body according to the fifth aspect of the invention,
When the tube is arranged in a horizontal direction,
The irradiation start position of the laser beam is a position shifted near the uppermost point of the tubular body and on the rear side in the traveling direction of the laser beam.

A method for improving the residual stress of a tubular body according to a seventh invention for solving the above-described problems is as follows.
In the method for improving residual stress of a tubular body according to the first to sixth inventions,
A plurality of laser beams are used, and a heating region by irradiation with the plurality of laser beams is made uniform in the axial direction of the tube body.

A method for improving the residual stress of a tubular body according to an eighth invention for solving the above-described problems is as follows.
In the method for improving residual stress of a tubular body according to the seventh aspect of the invention,
When the thickness of the tubular body is t and the radius of the tubular body is r,
The heating region has an axial length of 3√ (rt) or more, preferably 4√ (rt) or more.

A method for improving the residual stress of a tubular body according to a ninth invention for solving the above-mentioned problems is as follows.
In the method for improving residual stress of a tubular body according to the first to eighth inventions,
When a tube is constructed by welding different materials, and the laser beam is irradiated to the welded portion of the tube,
The circumferential heating width is set for each material of the tubular body.

A method for improving the residual stress of a tubular body according to a tenth aspect of the present invention for solving the above problems is as follows.
In the method for improving residual stress of a tubular body according to the first to ninth inventions,
When a tube is constructed by welding different thicknesses, and the laser beam is irradiated to the welded portion of the tube,
The circumferential heating width is set for each thickness of the tubular body.

An apparatus for improving a residual stress of a tubular body according to an eleventh invention for solving the above-mentioned problems is as follows.
An optical head capable of locally irradiating a laser beam on the outer peripheral surface of a welded portion of a cylindrical tube and adjusting an irradiation area;
The circumferential heating width by irradiation with the laser beam is set so that the circumferential stress on the inner surface of the tube generated by heating with the laser beam is at least greater than the yield stress of the material constituting the tube. It is characterized by being set by adjusting.

A tubular body residual stress improving apparatus according to a twelfth invention for solving the above-mentioned problems is
In the tubular body residual stress improving apparatus according to the eleventh aspect,
The circumferential heating width is 0.15 times or more, preferably 0.4 times or more, the outer diameter of the tubular body.

A tubular body residual stress improving apparatus according to a thirteenth aspect of the present invention for solving the above problems is as follows.
A rotational driving means capable of revolving around the outer circumference of the cylindrical tube body and controlling the circumferential movement speed;
An optical head that is held by the rotation driving means and irradiates the outer peripheral surface of the welded portion of the tube body with a laser beam and can adjust the irradiation region;
The circumferential heating width by irradiation with the laser beam is set so that the circumferential stress on the inner surface of the tube generated by heating with the laser beam is at least greater than the yield stress of the material constituting the tube. And the circumferential moving speed of the optical head is set by the control of the rotation driving means.

A tubular body residual stress improving apparatus according to a fourteenth aspect of the present invention for solving the above-mentioned problems is
In the tubular body residual stress improving apparatus according to the thirteenth aspect,
Fourier number F = a × (W / V) / t ² where W is the circumferential heating width, V is the moving speed in the circumferential direction, a is the thermal diffusivity of the tube, and t is the thickness of the tube. And
The circumferential heating width W and the circumferential movement speed V are set so that the Fourier number F satisfies 0.05 ≦ F ≦ 1.4, and preferably 0.1 ≦ F ≦ 0.6. Is set.

A tubular body residual stress improving apparatus according to a fifteenth aspect of the present invention for solving the above problems is as follows.
In the tubular body residual stress improving apparatus according to the thirteenth aspect,
A cooling means for forcibly cooling the inner peripheral surface of the tubular body;
Fourier number F = a × (W / V) / t ² where W is the circumferential heating width, V is the moving speed in the circumferential direction, a is the thermal diffusivity of the tube, and t is the thickness of the tube. And
The circumferential heating width W and the circumferential movement speed V are set so that the Fourier number F is 0.05 ≦ F, preferably 0.1 ≦ F. .

A tubular body residual stress improving apparatus according to a sixteenth aspect of the present invention for solving the above problems is as follows.
In the tubular body residual stress improving apparatus according to the fifteenth aspect,
When the tube is arranged in a horizontal direction,
The rotation driving means is characterized in that the irradiation start position of the laser beam is shifted to a position near the uppermost point of the tubular body and to the rear side in the traveling direction of the laser beam.

A tubular body residual stress improving apparatus according to a seventeenth aspect of the present invention for solving the above problems is as follows.
In the residual stress improving apparatus for a tubular body according to the above 11th to 16th inventions,
A plurality of the optical heads are arranged in the axial direction of the tubular body, and a heating region by irradiation of laser light from the plurality of optical heads is made uniform in the axial direction of the tubular body.

An apparatus for improving a residual stress of a tubular body according to an eighteenth aspect of the invention for solving the above-mentioned problem is as follows.
In the tubular body residual stress improving apparatus according to the seventeenth aspect,
When the thickness of the tubular body is t and the radius of the tubular body is r,
The axial length of the heating region is set to 3√ (rt) or more, preferably 4√ (rt) or more.

A tubular body residual stress improving apparatus according to a nineteenth aspect of the present invention for solving the above-mentioned problems is provided.
In the residual stress improving apparatus for a tubular body according to the above 11th to 18th inventions,
When a tube is constructed by welding different materials, and the laser beam is irradiated to the welded portion of the tube,
The circumferential heating width is set for each material of the tubular body by adjusting the optical head.

A tubular body residual stress improving apparatus according to a twentieth invention for solving the above-mentioned problems is
In the tubular body residual stress improving apparatus according to the eleventh to nineteenth aspects of the invention,
When a tube is constructed by welding different thicknesses, and the laser beam is irradiated to the welded portion of the tube,
The circumferential heating width is set for each thickness of the tubular body by adjusting the optical head.

  According to the present invention, the circumferential heating width and the circumferential movement speed are set so that the circumferential stress on the inner surface of the tube generated by heating with the laser beam is at least greater than the yield stress of the material constituting the tube. Therefore, the welding residual stress (tensile stress) on the inner surface of the tube can be reliably improved by laser heating without depending on the installation state of the tube. Therefore, SCC generated in piping installed in a nuclear power plant or the like can be reliably prevented.

  Further, when laser heating is performed while forcibly cooling the inner surface of the tube body, the setting range of the circumferential heating width and the circumferential moving speed is widened, and the residual stress can be improved more reliably. Furthermore, since the circumferential heating width is set according to the material constituting the tube and the plate thickness of the tube, the residual stress can be improved more reliably without depending on the configuration state of the tube itself. .

  Since the present invention is based on the LSIP method, in principle, the residual stress can be improved by a locally heated moving heat source and can be constructed using a small-capacity laser oscillator. . Therefore, the use of a compact laser oscillator makes preparation work easier than high-frequency heating by the IHSI method. In addition, since it is surface heat input, it is easy to obtain a temperature difference within the plate thickness even with a thin-walled tube, and because the inner and outer surface temperature difference that occurs during heating of the outer surface is used, forced cooling of the inner surface is not required, which is a conventional method. Compared to the IHSI method, the application range is wide.

  The tubular body residual stress improving method and residual stress improving apparatus according to the present invention will be described in detail with reference to FIGS.

FIG. 1 is a schematic diagram showing a tubular body residual stress improving apparatus according to the present invention.
As shown in FIG. 1, the residual stress improving apparatus 1 is arranged so as to be able to move around the outer periphery of a pipe 2 that is a cylindrical tube body, and can be controlled in rotational speed in the circumferential direction. And an arm part 4 supported by the rotation drive device 3 and extending in the axial direction of the pipe 2, and capable of rotating around the pipe 2 coaxially with the pipe 2, and held by the arm part 4, and welding of the pipe 2 A plurality of optical heads 5 that irradiate a predetermined region of the outer peripheral surface of the part C with laser light 5 a and a plurality of optical fibers 6 are connected to the optical head 5, and laser light is supplied to the optical head 5 through the optical fibers 6. The apparatus includes a laser oscillator 7 and a control unit 8 that controls the rotation driving device 3, the laser oscillator 7, and the like.

  The rotation drive device 3 can be attached to and detached from the outer periphery of the pipe 2 and can be freely installed around a place where the residual stress is to be improved, for example, around the welded portion c. The rotary drive device 3 may have any configuration as long as the inner peripheral side holds the pipe 2 and the outer peripheral side that supports the arm portion 4 can circulate. For example, the rotary drive device 3 holds the pipe 2 on the inner peripheral side. It may be configured to have a fixed portion that becomes the fixed side and a circulating portion that supports the arm portion 4 and rotates around the pipe 2 coaxially with the pipe 2 on the outer peripheral side.

  The optical head 5, the optical fiber 6, and the laser oscillator 7 constitute a heating optical system, and a plurality of laser beams 5 a are received by the plurality of optical heads 5 arranged on the arm portion 4 along the axial direction of the pipe 2. The predetermined area on the outer peripheral surface of the pipe 2 is irradiated to uniformly heat the predetermined area. In the optical head 5, the optical head 5 itself, or a lens, a mirror, or the like constituting the optical head 5 is attached to, for example, a slide mechanism whose position can be changed, and the position thereof is changed to change the circumferential direction. The heating area is adjusted by adjusting the irradiation width and the axial irradiation width.

  When the residual stress is improved, in the residual stress improving apparatus 1 according to the present invention, the heating region is adjusted in advance by adjusting the optical head 5, the output of the laser oscillator 7 is controlled by the control unit 8, and the rotational drive is performed. By rotating the device 3 at a predetermined moving speed, the laser beam 5a irradiated from the optical head 5 is irradiated to a predetermined region on the outer peripheral surface of the pipe 2 while moving around the outer periphery of the pipe 2. A predetermined area on the outer peripheral surface of the pipe 2 is heated. At this time, the residual stress on the inner surface after cooling is reduced or improved to compressive stress by utilizing the temperature difference between the inner and outer surfaces of the pipe 2 generated during heating and causing the inner surface to yield. The heating temperature is preferably less than the solution temperature. In the case of the present invention, the inner surface side of the pipe 2 is not necessarily forcedly cooled.

  The residual stress improving method will be further described. When heating is performed so that a predetermined temperature difference is generated between the outer surface and the inner surface in a predetermined region of the tubular body where the residual stress is to be improved, the outer surface is in a compressive stress state, and the inner surface is In the tensile stress state, the inner surface is in a tensile yield state. When the inner surface and the outer surface of the predetermined region are cooled after heating, the outer surface becomes a tensile stress state, the inner surface becomes a compressive stress state, and the residual stress of the inner surface can be improved from the tensile stress state to the compressive stress state. . In this way, it is possible to prevent stress corrosion cracking on the inner surface of the tubular body by improving the residual stress generated on the inner surface of the tubular body from the tensile state to the compressed state.

  In the residual stress improvement method, the amount of stress that can be improved can be controlled according to the amount of strain (stress) applied during heating. This will be described with reference to stress-strain curves shown in FIGS.

  FIG. 2A shows the yield stress (corresponding strain amount = εy) of the material constituting the target pipe when the strain amount applied during heating is εy, that is, the generated stress during heating is the yield stress. It is a figure explaining the stress change of object piping when it is considered equivalent. As shown in FIG. 2 (a), if the stress generated during heating is equivalent to the yield stress, the internal stress generated during heating (strain) causes the residual stress after heating (after construction) and through the cooling process. The initial stress (tensile residual stress) can be reduced.

  FIG. 2 (b) shows the case where the strain applied during heating is 2εy with respect to the yield stress (strain = εy), that is, the generated stress during heating is double the yield stress. It is a figure explaining the stress change of object piping. As shown in FIG. 2 (b), assuming that the stress generated during heating is twice the yield stress, the residual stress after heating (after construction) and after cooling due to the internal tensile stress (strain amount) generated during heating The stress can be improved from the initial stress (tensile residual stress) to the compressive stress.

  Thus, the residual stress can be improved to a desired stress depending on the magnitude (strain amount) of the stress generated during heating, and at least a strain corresponding to the yield stress is desirably at least twice the yield stress. It can be seen that the strain may be generated during heating. Therefore, when the outer peripheral surface of the pipe 2 is heated using the residual stress improving apparatus 1 according to the present invention, the circumferential stress generated during the heating is at least a strain equivalent to the yield stress, preferably twice the yield stress. What is necessary is just to set the conditions at the time of laser heating so that it may become the above distortion | strain.

Here, the conditions at the time of laser heating were examined. In the present invention, the irradiation region where the energy density of the laser beam is 1 / e ² is used as the heating region.

  When the outer peripheral surface of the welded portion of the cylindrical pipe 2 is laser-heated, it is considered that there is a difference in the stress generated during heating due to the difference in the circumferential heating width, that is, the reduction amount of the residual stress changes. There is a need. For example, if the circumferential heating width is narrow, the effect of improving the residual stress is hindered by the influence of local bending. This is because when the heating width is narrow, bending occurs in the heated portion due to local thermal expansion during heating, compressive stress is generated, and residual stress is not reduced after cooling. Conversely, when the heating width is wide, local bending occurs during heating, but there is no effect in the highest temperature range, tensile stress is generated on the inner surface due to the temperature difference between the inner and outer surfaces, and the residual stress is reduced after cooling. .

  FIG. 3 shows the result of studying this by numerical analysis, which is a relationship between the circumferentially generated stress and [circumferential heating width / outer diameter]. As shown in FIG. 3, it can be seen that the circumferentially generated stress increases monotonously with [circumferential heating width / outer diameter] and then becomes constant when [circumferential heating width / outer diameter] is approximately 1.0. . Here, when the material of the target pipe is stainless steel, an appropriate range of [circumferential heating width / outer diameter] is 0, if the stress generated by laser heating is equal to or higher than the yield stress (250 MPa) of stainless steel. 15 or more. Further, if the stress generated by laser heating is twice or more (500 MPa) of the yield stress of stainless steel, the appropriate range of [circumferential heating width / outer diameter] is 0.4 or more. That is, as a result of investigation by numerical analysis, it was confirmed that the effect of improving the desired residual stress can be obtained by making the circumferential heating width 0.15 times or more of the outer diameter in stainless steel.

Further, the present invention irradiates the outer peripheral surface of the welded portion of the cylindrical pipe 2 with laser light while circling the outer periphery of the pipe 2 to generate a temperature difference within the plate thickness of the pipe. Since the residual stress is improved by using the generated stress, the temperature distribution within the plate thickness in an unsteady state is important. That is, in order to obtain an appropriate temperature distribution within the plate thickness (in order to obtain an appropriate generated stress in the circumferential direction), it is necessary to examine conditions during laser heating from the viewpoint of heating time. Therefore, a dimensionless Fourier number F (= a × τ) indicating a temperature distribution, where the thermal diffusivity of the pipe is a (mm ² / sec), the thickness of the pipe is t (mm), and the heating time is τ (sec). / T ² ) and numerical analysis using the Fourier number F was used to examine the optimum laser heating conditions.

Specifically, as shown in FIG. 4, the Fourier number F, which is an optimum condition for laser heating, is obtained from the relationship between the Fourier number F and the calculated value of the thermal stress of the cylindrical pipe. Here, the heating time τ is defined by [circumferential heating width W / laser beam moving speed V], and accordingly, the Fourier number F is [a × (W / V) / t ² ]. As can be seen from FIG. 4, regardless of the plate thickness, when the Fourier number F is about 0.2, the circumferentially generated stress (stress in the circumferential direction generated on the inner surface of the pipe) is maximized, and the Fourier number F is larger than that. As it becomes, it gets smaller gradually. Here, when the material of the target pipe is stainless steel, if the stress generated by laser heating is equal to or higher than the yield stress (250 MPa) of stainless steel, the appropriate range of the Fourier number F is about 0.05 to 1.4. It becomes. Moreover, if the stress generated by laser heating is twice or more (500 MPa) of the yield stress of stainless steel, the appropriate range of the Fourier number F is about 0.05 to 0.6. Accordingly, since the thermal diffusivity a of the pipe and the plate thickness t of the pipe are constant, if the circumferential heating width W and the circumferential moving speed V are controlled to appropriate values, the range of the appropriate Fourier number is obtained. be able to.

Based on the above knowledge, when controlling the residual stress improving apparatus 1 according to the present invention, the predetermined region S on the outer peripheral surface of the pipe is irradiated with laser light while moving around, and when the predetermined region S is heated, circumferential heating is performed. The width W needs to be 0.15 times or more, preferably 0.4 times or more of the outer diameter D. Further, a relationship of [0.05 × t ² /a<W/V<1.4×t ² / a] between the circumferential heating width W and the circumferential movement speed V is preferably [0 It is necessary to satisfy the relationship of 1 × t ² /a<W/V<0.6×t ² / a] (see FIG. 5).

  As described above, in the present invention, in order to reliably reduce the residual stress or to reliably improve the compressive residual stress, the circumferential heating width W and the circumferential movement speed V are limited. In addition, as a restriction | limiting of a heating condition, it is desirable to restrict | limit not only the circumferential direction heating width W but the axial direction heating width L (refer FIG. 5).

  Therefore, the circumferential heating width W was set to a constant value satisfying the above conditions, and the axial heating width L was changed to confirm the improved stress. The results are shown in FIG. 6. FIGS. 6 (a), (b), and (c) show changes in axial stress, and FIGS. 6 (d), (e), and (f) show circumferential stress. 6 (a) and 6 (d) show the axial heating width L = 5 × √ (rt) and FIG. 6 (d), where r (= D / 2) is the radius of the pipe. b) and (e) are axial heating widths L = 4 × √ (rt), and FIGS. 6C and 6F are axial heating widths L = 3 × √ (rt). .

  As can be seen from FIG. 6, the circumferential stress does not depend on the axial heating width L, but the stress improvement is greater than the desired stress, and the axial stress changes depending on the axial heating width L. In any case, the residual stress is improved, and the axial length of the predetermined region is preferably 3√ (rt) or more, preferably 4√ (rt) or more. . Therefore, the plurality of optical heads 5 are arranged on the arm portion 4 along the axial direction of the pipe 2 so that a desired axial heating width L can be uniformly heated.

  When welding pipe bodies, such as piping, the same material is not necessarily welded, and different materials may be welded. When applying the residual stress improving apparatus 1 according to the present invention shown in FIG. 1 to such a dissimilar tube, in order to obtain an appropriate temperature difference within the plate thickness, physical property values for each material, for example, for each material In consideration of the thermal diffusivity, it is desirable to change the circumferential heating width W for each material.

  For example, as shown in FIG. 7, when the residual stress improving apparatus 1 according to the present invention is used to perform laser heating on a dissimilar pipe body obtained by welding stainless steel 2A and low alloy steel 2B with a Ni-base alloy weld metal 2C. Since stainless steel 2A and weld metal 2C have a low thermal diffusivity and a slow heat transfer, it is necessary to increase the circumferential heating width W, that is, to increase the substantial heating time. On the other hand, the low alloy steel 2B has a large thermal diffusivity and quick heat transfer, so it is necessary to narrow the circumferential heating width W, that is, to shorten the substantial heating time.

Here, the influence of the heating time (construction speed) in a dissimilar material pipe was examined.
FIG. 8A is a graph showing the circumferentially generated stress in each material with respect to the Fourier number. As shown in FIG. 8A, it can be seen that even when the materials are different, the stress generated during heating tends to be the same when normalized by the Fourier number. As described above, the Fourier number F is represented by [(thermal diffusivity a) × {(circumferential heating width W) / (circumferential movement speed V)} / (plate thickness t) ² ]. By changing the circumferential heating width W according to the material, substantially the same generated stress can be obtained in each material at the time of heating at a constant circumferential moving speed V (circumferential speed).

  For example, when the tube thickness is about 22 mm, the heating width W1 of stainless steel (SUS316) 2A and weld metal (600 alloy) 2C is 120 mm, and the heating width W2 of low alloy steel 2B is 60 mm, the moving speed V When the circumferential direction generated stress in each material is shown in the graph of FIG. 8B, substantially the same generated stress can be obtained in each material during heating by changing the circumferential heating width W. At this time, it was confirmed that the variation in the effect of improving the residual stress (stress generated during heating) was small by performing the circumferential movement speed at a speed of about 5 to 8 mm / s.

  A pipe body such as a welded pipe does not necessarily have the same plate thickness, and may have a different plate thickness depending on the location. When applying the residual stress improving apparatus 1 according to the present invention shown in FIG. 1 to a pipe body having a different plate thickness (stepped pipe body), in order to obtain an appropriate temperature difference within the plate thickness, It is desirable to change the circumferential heating width W according to the thickness of the plate.

  For example, as shown in FIGS. 9A and 9B, a pipe 2D having an average plate thickness t1 and a pipe 2E having an average plate thickness t2 (> t1) and gradually increasing from the plate thickness t1 to the plate thickness t3. And the pipe 2D and the weld metal 2F have the same thickness when the tube is welded with the weld metal 2F having the average plate thickness t1 using the residual stress improving apparatus 1 according to the present invention. Therefore, the pipe 2E has an average plate thickness t2 larger than the average plate thickness t1 of the pipe 2D and the weld metal 2F. It is necessary to increase the substantial heating time, that is, to change the circumferential heating width according to the representative plate thickness at each location. This is because, when the present invention is applied to a place where the plate thickness of the tube body is different, the temperature difference in the plate thickness at each location may be different, so select the circumferential heating width according to the plate thickness. This is to keep the temperature difference uniform.

  Note that the pipe body shown in FIG. 9 is an application target of a spray nozzle of a pressurizer in a PWR (Pressurized Water Reactor) as an example. In practice, the pipe 2D is made of stainless steel ( SUS316), the pipe 2E is made of low alloy steel, and the weld metal 2F is made of a Ni alloy weld metal. Therefore, it is necessary to determine the circumferential heating width in consideration of the material thickness (thermal diffusivity) of the tube as well as the thickness of the tube. In the case of such a tubular body, W1 ′ = k1 × W1, W2 ′ = k2 × W2 (k1 and k2 are coefficients in consideration of the thermal diffusivity), and the pipe 2E has a large thermal diffusivity. In a), W2 ′ is narrower than W1 ′. For example, if the diameter of the pipe is D, the circumferential heating width is set to 0.8D for the pipe 2D and the weld metal 2F, and the circumferential heating width is set to 0.4D for the pipe 2E.

  When the tube shown in FIG. 9 is subjected to laser heating under the above conditions, FIG. 10 is a graph that examines the effect of improving the residual stress using numerical analysis of a three-dimensional moving heat source thermal elastic-plastic model. As is apparent from FIG. 10, it was confirmed that the region of the weld metal 2F simulating the welding residual stress (tensile stress) on the inner surface can be improved to the compressive stress by the laser heating according to the present invention.

  When the residual stress improving apparatus 1 according to the present invention shown in FIG. 1 is applied, it is not always necessary to forcibly cool the inner surface of the pipe. However, the inner surface of the pipe is forcedly cooled by a cooling means such as running water or stored water. In this case, there are advantages that the restrictions on the circumferential heating width W and the circumferential speed V are wider and the degree of freedom of the control value is greater than in the first embodiment.

When the inner surface of a pipe is forcibly cooled, the circumferentially generated stress and the Fourier number have a relationship as shown in FIG. 11, and if the Fourier number is 0.2 or more, the circumferentially generated stress is stable at a constant magnitude. It becomes. Therefore, when the inner surface of the pipe is water-cooled, the laser heating condition is limited as follows. When the material of the target pipe is stainless steel, the stress generated by laser heating is set to be equal to or higher than the yield stress (250 MPa) of stainless steel. The proper Fourier number is 0.05 or more, and the proper Fourier number for making the yield stress (500 MPa) or more twice that of stainless steel is 0.1 or more. In other words, when the residual stress improving apparatus 1 according to the present invention is controlled by forcibly cooling the inner surface of the pipe, the predetermined area on the outer peripheral surface of the pipe is irradiated while moving around the laser beam to heat the predetermined area. At this time, between the circumferential heating width W and the moving speed V of the light source, [0.05 × t ² / a <W / V], preferably [0.1 × t ² / a <W / V]. The relationship is established. In addition, the cooling water which performs forced cooling does not need to be flowing water, and may be stored water.

  In particular, as shown in FIG. 12, in a pipe body 10 in which a pipe 11 and a double pipe 13 having a thermal sleeve 12 therein are welded at a welded portion C, the pipe body 10 is installed in the vertical direction and is thermally This embodiment can be suitably applied when the opening 12a of the sleeve 12 is on the upper side. In the case of such a tubular body 10, since the cooling water 14 exists on the inner surface side of the tubular body 10, the temperature of the heated portion only rises for a short time, and nucleate boiling can be maintained. For this reason, even if the cooling water 14 is stored water, the effect of internal water cooling can be acquired. In this case, since the inner surface is water-cooled, the circumferential movement speed can be reduced and the laser output can be reduced. In addition, since the tube body 10 is installed in the vertical direction and the opening 12a of the thermal sleeve 12 is on the upper side, the steam generated by heating does not stay on the inner surface of the tube body 10, so that the water cooling effect is achieved. There is no inhibition.

  In the case where the inner surface has accumulated water and is applied to a pipe installed in the horizontal direction, in addition to the above control, it is necessary to consider the heating start position (laser beam irradiation start position). As shown in FIG. 13, when the pipe 21 installed in the horizontal direction is heated in a state in which the inner surface of the pipe 21 has the accumulated water 22, the boiled steam is stopped vertically above the inner surface of the pipe 21. This is because the cooling efficiency may decrease. Therefore, in the present embodiment, in order to reliably perform the heating before the vapor stops on the vertically upper side, the start position (end position) of the laser beam 23 is in the vicinity of the uppermost point P2 on the vertically upper side, and By setting the position P1 shifted to the rear side in the traveling direction, uniform heating can be performed over the entire circumference. The position P1 shifted backward in the traveling direction is preferably a position where the uppermost point P2 is 100 ° C. or lower when the laser beam 23 passes through the uppermost point P2 of the pipe 21. Such control is the same in the case of a double pipe having a thermal sleeve.

  In the present invention, as an example of implementation, a cylindrical pipe is an object of residual stress improvement. However, the present invention is not limited to a cylindrical pipe, and any welded curved member is applicable.

It is a schematic diagram of the residual stress improvement apparatus of the tubular body concerning the present invention. It is a figure explaining the residual stress improvement in this invention, (a) shows the case where the distortion | strain equivalent to a yield stress is provided, (b) shows the case where the distortion 2 times the yield stress is provided. In this invention, it is a graph which shows the relationship between the circumferential direction generated stress and the circumferential heating width / outer diameter. In this invention, it is a graph which shows the relationship between the circumferential direction generated stress and a Fourier number. It is a figure explaining the circumferential direction heating width and circumferential direction moving speed which are controlled in the residual stress improvement apparatus which concerns on this invention. It is a graph explaining the axial direction heating width controlled in the residual stress improvement apparatus which concerns on this invention. It is a figure explaining the case where the residual-stress improving apparatus which concerns on this invention is applied to the tubular body comprised from a several different material. (A) is a graph which shows the relationship between the circumferential direction generated stress and Fourier number in a different material in this invention, (b) is a graph which shows the relationship between the circumferential direction generated stress and the circumferential direction moving speed in a different material. is there. It is a figure explaining the case where the residual stress improvement apparatus which concerns on this invention is applied to the pipe body from which plate | board thickness differs, (a) is an external view, (b) is sectional drawing. It is the graph which verified the improvement effect of the residual stress in this invention. In this invention, it is a graph which shows the relationship of the circumferential direction generated stress at the time of performing forced cooling, and a Fourier number. It is a figure explaining the case where the residual stress improvement apparatus which concerns on this invention is applied to the pipe body which is arrange | positioned at a perpendicular direction and the inner surface is forcedly cooled. It is a figure explaining the case where the residual stress improvement apparatus which concerns on this invention is applied to the tubular body arrange | positioned in a horizontal direction and forcedly cooling the inner surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Residual stress improvement apparatus 2 Piping 3 Rotation drive apparatus 4 Arm part 5 Optical head 6 Optical fiber 7 Laser oscillator 8 Control part 10 Piping 11 Piping 12 Thermal sleeve 13 Piping 14 Cooling water 21 Piping 22 Cooling water 23 Laser beam C Welding part D Piping outer diameter S Heating area V Circumferential movement speed W Circumferential heating width

Claims (20)

When locally irradiating the outer peripheral surface of the welded portion of the cylindrical tube with laser light and rotating the irradiation region in the circumferential direction,
Setting the circumferential heating width by irradiation of the laser beam so that the circumferential stress of the inner surface of the tube generated by heating with the laser beam is at least greater than the yield stress of the material constituting the tube. A method for improving the residual stress of a tubular body characterized by the following. The method for improving residual stress in a tubular body according to claim 1,
The method for improving residual stress of a tubular body, wherein the circumferential heating width is 0.15 times or more, preferably 0.4 or more times the outer diameter of the tubular body. When irradiating the outer peripheral surface of the welded portion of the cylindrical tube body with laser light while rotating around the outer periphery of the tube body,
The circumferential heating width by the irradiation of the laser beam and the laser beam so that the circumferential stress on the inner surface of the tube generated by the heating by the laser beam is at least larger than the yield stress of the material constituting the tube. A method for improving the residual stress of a tubular body, characterized by setting a circumferential moving speed of the tube. In the method for improving residual stress of a tubular body according to claim 3,
Fourier number F = a × (W / V) / t ² where W is the circumferential heating width, V is the moving speed in the circumferential direction, a is the thermal diffusivity of the tube, and t is the thickness of the tube. And
The circumferential heating width W and the circumferential movement speed V are set so that the Fourier number F satisfies 0.05 ≦ F ≦ 1.4, and preferably 0.1 ≦ F ≦ 0.6. A method for improving the residual stress of a tubular body, characterized in that: In the method for improving residual stress of a tubular body according to claim 3,
When forcibly cooling the inner peripheral surface of the tube,
Fourier number F = a × (W / V) / t ² where W is the circumferential heating width, V is the moving speed in the circumferential direction, a is the thermal diffusivity of the tube, and t is the thickness of the tube. And
The circumferential heating width W and the circumferential movement speed V are set so that the Fourier number F is 0.05 ≦ F, preferably 0.1 ≦ F. A method for improving the residual stress of pipes. In the method for improving residual stress of a tubular body according to claim 5,
When the tube is arranged in a horizontal direction,
A method for improving residual stress of a tubular body, wherein the irradiation start position of the laser light is shifted to a position near the uppermost point of the tubular body and to the rear side in the traveling direction of the laser light. The residual stress improvement method for a tubular body according to any one of claims 1 to 6,
A method for improving residual stress of a tubular body, wherein a plurality of laser beams are used, and a heating region by irradiation of the plurality of laser beams is made uniform in an axial direction of the tubular body. The method for improving residual stress in a tubular body according to claim 7,
When the thickness of the tubular body is t and the radius of the tubular body is r,
A method for improving a residual stress of a tubular body, wherein the axial length of the heating region is 3√ (rt) or more, preferably 4√ (rt) or more. The residual stress improvement method for a tubular body according to any one of claims 1 to 8,
When a tube is constructed by welding different materials, and the laser beam is irradiated to the welded portion of the tube,
The method for improving residual stress in a tubular body, wherein the circumferential heating width is set for each material of the tubular body. In the residual stress improvement method of the tubular body according to any one of claims 1 to 9,
When a tube is constructed by welding different thicknesses, and the laser beam is irradiated to the welded portion of the tube,
The method for improving the residual stress of a tubular body, wherein the circumferential heating width is set for each thickness of the tubular body. An optical head capable of locally irradiating a laser beam on the outer peripheral surface of a welded portion of a cylindrical tube and adjusting an irradiation area;
The circumferential heating width by irradiation with the laser beam is set so that the circumferential stress on the inner surface of the tube generated by heating with the laser beam is at least greater than the yield stress of the material constituting the tube. An apparatus for improving residual stress in a tubular body, characterized in that it is set by adjusting the angle. In the tubular-body residual-stress improving apparatus of Claim 11,
The apparatus for improving residual stress of a tubular body, wherein the circumferential heating width is 0.15 times or more, preferably 0.4 times or more, the outer diameter of the tubular body. A rotational driving means capable of revolving around the outer circumference of the cylindrical tube body and controlling the circumferential movement speed;
An optical head that is held by the rotation driving means and irradiates the outer peripheral surface of the welded portion of the tube body with a laser beam and can adjust the irradiation region;
The circumferential heating width by irradiation with the laser beam is set so that the circumferential stress on the inner surface of the tube generated by heating with the laser beam is at least greater than the yield stress of the material constituting the tube. The apparatus for adjusting residual stress of a tubular body, characterized in that the circumferential moving speed of the optical head is set by the control of the rotation driving means. The tubular body residual stress improving apparatus according to claim 13,
Fourier number F = a × (W / V) / t ² where W is the circumferential heating width, V is the moving speed in the circumferential direction, a is the thermal diffusivity of the tube, and t is the thickness of the tube. And
The circumferential heating width W and the circumferential movement speed V are set so that the Fourier number F satisfies 0.05 ≦ F ≦ 1.4, and preferably 0.1 ≦ F ≦ 0.6. An apparatus for improving residual stress in a tubular body, characterized in that The tubular body residual stress improving apparatus according to claim 13,
A cooling means for forcibly cooling the inner peripheral surface of the tubular body;
Fourier number F = a × (W / V) / t ² where W is the circumferential heating width, V is the moving speed in the circumferential direction, a is the thermal diffusivity of the tube, and t is the thickness of the tube. And
The circumferential heating width W and the circumferential movement speed V are set so that the Fourier number F is 0.05 ≦ F, preferably 0.1 ≦ F. Equipment for improving residual stress in pipes. In the tubular-body residual-stress improving apparatus of Claim 15,
When the tube is arranged in a horizontal direction,
The apparatus for residual stress improvement of a tubular body characterized in that the rotation driving means sets the irradiation start position of the laser light to a position near the uppermost point of the tubular body and to the rear side in the traveling direction of the laser light. . In the residual stress improvement apparatus of the pipe body in any one of Claims 11 thru | or 16,
A plurality of the optical heads are arranged in the axial direction of the tubular body, and a heating region by irradiation of laser light from the plurality of optical heads is made uniform in the axial direction of the tubular body. Stress improvement device. The residual stress-improving device for a tubular body according to claim 17,
When the thickness of the tubular body is t and the radius of the tubular body is r,
The residual stress improving apparatus, wherein the axial length of the heating region is set to 3√ (rt) or more, preferably 4√ (rt) or more. In the residual stress improvement apparatus of the pipe body in any one of Claims 11 thru | or 18,
When a tube is constructed by welding different materials, and the laser beam is irradiated to the welded portion of the tube,
The apparatus for improving residual stress in a tubular body, wherein the circumferential heating width is set for each material of the tubular body. In the residual stress improvement apparatus of the pipe body in any one of Claim 11 thru | or 19,
When a tube is constructed by welding different thicknesses, and the laser beam is irradiated to the welded portion of the tube,
The apparatus for improving residual stress in a tubular body, wherein the circumferential heating width is set for each thickness of the tubular body.

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