JP2004211187A - Method and apparatus for heat treatment of piping system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment method of a piping system whereby the residual stress in a welded metal zone and a heat affected zone on the inside surface is converted into compressive stress; and a heat treatment apparatus used therefor. <P>SOLUTION: After a piping system is constructed, a heating coil is wound at least twice around the outer surface of a pipeline 1a, and a cooling fluid is caused to flow through the pipeline with a cooling water circulation device 19. A high-frequency heating device equipped with the heating coil, an electric source 17, and a transformer 16 causes the temperature difference between the inner surface and outer surface of the pipeline. Based on the temperature of a heated zone detected by a thermocouple 22, a control unit 18 controls the temperature distributions in the peripheral and axial directions of the pipeline. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat treatment method and a heat treatment apparatus for a piping system, and more particularly to a heat treatment method and a heat treatment apparatus for a piping system suitable for piping used in a nuclear power plant.
[0002]
[Prior art]
Japanese Patent Publication No. 53-38246 discloses an example of reducing the tensile residual stress in a region exposed to a corrosive environment in order to suppress the occurrence of stress corrosion cracking in a structural material. In this publication, in order to reduce the residual tensile stress on the inner surface of the pipe at the existing pipe welding site, after assembling the piping system of the plant, a cooling fluid is supplied to the inside of the piping of the piping system, and the outside of the piping is heated. A temperature difference is generated between the inner surface of the pipe and the outer surface of the pipe. The inner surface is tensile-yielded and the outer surface is compressive-yield to prevent stress corrosion cracking.
[0003]
Japanese Patent Application Laid-Open No. 2001-262235 discloses a method for removing a residual stress in a welded portion of a container by using a personal computer or the like to configure a pipe and container local heat treatment apparatus, setting up the apparatus according to instructions from a personal computer, and setting up a heat treatment program. It describes that an automatic operation is performed according to a pattern. Further, Japanese Patent Application Laid-Open No. 2001-3120 discloses that a short pipe of the same steel type as a mother pipe can be easily welded and welded between a heat-resistant steel and a branch pipe in order to increase the strength of a welded joint and improve reliability. Is connected to the mother pipe using a welding material of the same composition as the heat-resistant steel, heat-treated at the normalization temperature and tempering temperature of the heat-resistant steel after welding, and then the branch pipe is welded to the tip of the short pipe. ing.
[Patent Document 1]
JP-B-53-38246
[Patent Document 2]
JP 2001-262235 A
[Patent Document 3]
JP 2001-3120 A
[0004]
[Problems to be solved by the invention]
In each of the above publications, stress corrosion cracking that may occur in a weld metal site is not sufficiently considered. Generally, a weld metal has a higher yield stress than a pipe base metal, and therefore, the tensile residual stress generated by welding is likely to be about the yield stress. Therefore, in order to cause tensile yield, it is necessary to sufficiently increase the tensile stress generated on the inner surface.
[0005]
The present invention has been made in view of the above-mentioned disadvantages of the related art, and has as its object to improve the reliability of a connection portion of a piping system used in a nuclear power plant or the like by heat treatment. Another object is to realize heat treatment with a simple configuration.
[0006]
[Means for Solving the Problems]
A feature of the present invention that achieves the above object is that after assembling a piping system having a piping, a cooling fluid is caused to flow inside the piping, and then the piping is heated using a high-frequency heating device having a heating coil, and the inner surface of the piping and the piping are heated. In the heat treatment method for generating a temperature difference between the outer surfaces of the pipes, the temperature distribution in the circumferential and axial directions of the pipe is controlled by a heating coil.
[0007]
In this aspect, the cooling fluid may be pure water, the piping system may be a reactor piping, and the cooling fluid may be reactor water. Further, it is preferable to change the distance from the outer surface of the pipe to the inner surface of the heating coil in the longitudinal direction of the heating coil. By eccentricizing the center of the heating coil from the center of the pipe, the distance between the heating coil and the outer surface of the pipe can be improved. The distance may be changed in the circumferential direction.
[0008]
Preferably, the gap between the pipe and the heating coil is made substantially constant in the circumferential direction to prevent the flow of air in the formed gap, or the number of turns of the heating coil exceeds at least two turns. To change. Preferably, at least two heating coils are provided, and the current can be controlled for each heating coil.
[0009]
Then, the frequency of the high-frequency current supplied to the heating coil may be changed with time, the temperature of the pipe surface heated by the heating coil is measured, and the current supplied to the heating coil is controlled based on the measured temperature. If at least one of the strength and the material of the pipe to be heated by the heating coil changes along the pipe axis, the heating coil is arranged according to the strength or the material of the pipe to reduce the degree of heating. It may be changed.
[0010]
Also preferably, the heating coil detects at least one of the current or voltage on the surface of the pipe to be heated, and controls the current supplied to the heating coil based on the detected value, and before installing the coil to be heated, The presence or absence of a defect on the inner surface of the piping system is confirmed by a non-destructive inspection, and when a defect is detected, it is preferable to use a heating coil to perform heating different from the case where no defect is detected near the defect.
[0011]
In addition, a heating section is formed in the axial direction of the cooling section that cools the outer surface of the pipe over the entire circumference, and this heating section is heated over the entire circumference of the pipe by a heating coil, or the outer surface of the pipe is heated over the entire circumference. A cooling unit that cools the entire circumference of the pipe in the axial front-rear direction of the heating unit heated by the coil may be formed.
[0012]
Another feature of the present invention to achieve the above object is that a heat treatment apparatus is provided with a heating coil for high-frequency induction heating arranged on the outer surface side of a piping system, and a predetermined gap between the surface of the piping system and the heating coil. , A cooling water pipe attached to the heating coil and circulating cooling water inside, means for supplying high-frequency current to the heating coil, and temperature measurement to detect the temperature of the outer surface of the piping system heated by the heating coil An apparatus and a control device for controlling the heating coil based on the temperature detected by the temperature measuring device, wherein the heating coil heats the piping system to generate a compressive residual stress on the inner surface of the piping system. In this feature, at least two sets of heating coils may be provided so that a high-frequency current can be supplied to each heating coil independently.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, some embodiments of the present invention will be described with reference to the drawings. 1 to 5 are views of an embodiment of a piping heat treatment apparatus according to the present invention. FIG. 1 schematically shows a state in which a heat treatment apparatus is attached to an outer peripheral portion of a pipe. A straight pipe 1a and a straight pipe 1b, which are installed so that the center axis of the pipe is horizontal, are welded at a welding portion 2 to generate a compressive residual stress on the inner surface of the welded portion. A thermocouple 22 for measuring the temperature of the surface of the weld is attached to the weld metal site on the outer surface of the pipe. The thermocouple 22 is connected to a temperature measuring device 21a via a cable 23. The temperature measuring device 21 a converts a voltage based on the thermoelectromotive force of the thermocouple 22 into a digital value by an AD converter (not shown) and sends the digital value to the control device 18.
[0014]
A heating coil 11 is spirally attached to the pipe via a spacer 12. A high-frequency current is supplied from a high-frequency transmitter 17 to the heating coil ends 10 a and 10 b of the heating coil 11 via a transformer 16 and a cable 14. A current detector 20 for detecting a secondary current is attached in the middle of the cable 14, and sends the current to the control device 18 via a secondary current measuring device 21b and an AD converter (not shown). The control device 18 has control means (not shown) for controlling the effective value and frequency of the high-frequency current generated by the transformer. Further, cooling water is supplied from the cooling water circulation mechanism 19 to the heating coil 11, the transformer 16, and the high-frequency oscillator 17 via the hose 15.
[0015]
Next, the heating coil 11 as a component to be mounted, the spacer 12 supporting the heating coil, and the spacer circumferential direction mounting jig will be sequentially described.
[0016]
FIG. 2 shows the details of the structure of the heating coil 11. The heating coil includes a strip-shaped copper plate 11a through which a high-frequency current flows, and a tube 11b for cooling the copper plate 11a.
[0017]
FIG. 3 shows a cross-section when virtually cut on a plane having the center axis of the pipe 1 as a normal line. The spacers 12 are mounted on the spacer circumferential mounting jigs 13a and 13b at approximately 45 ° intervals. Further, the spacer 12 is set such that the space on the lower side is smaller when comparing the upper side in the circumferential direction of the pipe with the lower side in the circumferential direction of the pipe. The two parts of the spacer circumferential mounting jigs 13a and 13b are fixed with bolts and nuts 24 and mounted on the pipe 1.
[0018]
FIG. 4 shows a separated state in which the heat treatment apparatus is installed in a pipe. The spacer 12 is mounted on the circumference of the semicircular spacers 13a and 13b. The radius of curvature of the spacer mounting jigs 13a and 13b is set to be equal to the radius of curvature of the outer surface of the pipe 1. Therefore, at the time of installation, a gap between the pipe surface and the heating coil can be appropriately provided only by mounting the spacer circumferential mounting jig on the semicircular arc in accordance with the pipe surface. A heat insulating material 25 is provided between the spacers 12.
[0019]
If the tube surface is exposed to air during heating, the tube surface will not be heated due to heat transfer with the air. On the other hand, by reducing the heat transfer from the pipe surface to the surroundings by the heat insulating material 25, the pipe can be efficiently heated. Moreover, since the heat insulating material is integrated with the spacer and the heating coil, the heat insulating material can be installed in a short time without increasing the number of steps. As the heat insulating material 25, any material can be used as long as it reduces heat transfer to the surrounding air. For example, a cotton-like material made of non-combustible fibers having electrical insulation properties is used.
[0020]
Next, the procedure of the heat treatment will be described. In FIG. 1, after preparing the device in the state shown in the figure, the insides of the pipes 1a and 1b joined by the welding joint 2 are filled with a cooling fluid, and the cooling water circulating device 19 is started to activate the heating coils 11 and After supplying the cooling water to the transformer 16 and the high-frequency transmitter 17, a high-frequency current is supplied to the heating coil 11. The induction current is induced on the outer surface of the pipe by the high-frequency current flowing through the heating coil 11, thereby generating heat due to the electric resistance of the pipe. The temperature of the pipe surface is measured by the thermocouple 22, and the controller 18 controls the current supplied to the heating coil when the outer surface reaches a predetermined temperature. On the other hand, since the inner surface of the pipe is in contact with the coolant, the temperature is lower than that of the outer surface. Therefore, a temperature difference occurs between the outer surface and the inner surface of the pipe.
[0021]
The welding residual stress generated in the welded portion of the pipe is substantially constant regardless of the position on the circumference. Therefore, in order to generate a compressive residual stress on the inner surface of the pipe over the entire circumference, it is preferable that the temperature difference between the outer surface and the inner surface of the pipe be constant over the entire circumference of the pipe regardless of the position on the circumference. . Therefore, a difference in temperature between the outer surface and the inner surface of the pipe will be described.
[0022]
The temperature distribution in the pipe thickness direction suitable for reducing the welding residual stress on the inner surface of the pipe is, for example, the maximum temperature is 550 ° C. or less for type 304 stainless steel in which material sensitization occurs, and the temperature difference between the inner and outer surfaces is 220 It is said to be above ℃. The values of these maximum temperatures and the temperature difference between the inner and outer surfaces are obtained from the presence or absence of sensitization of the material and the physical properties of the material (Young's modulus, Poisson's ratio, yield stress, linear expansion coefficient). is there. In the case of type 316L stainless steel, the material is hardly sensitized, so that there is no problem even if the maximum temperature is set to a temperature higher than 550 ° C.
[0023]
FIG. 5 shows a temperature distribution from the inner surface to the outer surface while the outer surface of the pipe is being heated. Regarding the condition where the distance between the outer surface of the pipe 1 and the heating coil 11 is constant in the circumferential direction, and the case where the distance between the outer surface of the pipe 1 and the heating coil 11 is small on the lower side and larger on the upper side, An evaluation line (41a or 42a in the figure), an evaluation line at an intermediate position (41b or 42b in the figure), and an upper evaluation line (41c or 42c in the figure) are shown.
[0024]
In the graph shown in FIG. 5, the distance from the inner surface of the pipe is plotted on the horizontal axis. The origin O represents the inner surface of the tube, and the position indicated by the broken line 43 represents the outer surface of the tube. In piping installed in a horizontal direction, water inside causes convection by heating. Therefore, assuming that the heating coil is installed at the same distance from the pipe surface over the entire circumference of the pipe, the amount of heat generated by high-frequency induction heating is equal over the entire circumference, whereas water as a coolant causes convection on the inner surface of the pipe. As a result, the temperature at the bottom of the tube is less likely to rise as compared with the top of the tube. Therefore, when the temperature distribution along the lower evaluation line 41a, the intermediate evaluation line 41b, and the upper evaluation line 41c is shown as curves 44a, 44b and 44c, in the circumferential direction of the pipe, The temperature difference between the inner surface and the outer surface becomes smaller as it goes down below the upper side.
[0025]
On the other hand, if the distance between the heating coil and the pipe surface is set to be smaller on the lower side than on the upper side of the pipe, the calorific value is larger on the lower side. Therefore, even if the coolant filled in the pipe causes convection, the lower side has a larger calorific value than the upper side, so the lower evaluation line 42a of the pipe, the evaluation line 42b at the intermediate position, and When the temperature distribution along the upper evaluation line 42c is shown, a curve 45 is obtained in any of the evaluation lines, and the temperature difference between the inner surface and the outer surface can be made uniform over the entire circumferential direction of the pipe.
[0026]
In this way, in the spacer circumferential direction mounting jig shown in FIG. 4 which is divided into two in the circumferential direction, the gap between the outer surface of the pipe and the coil becomes smaller as the position in the circumferential direction of the pipe becomes lower than the upper side. By installing such a spacer and installing the heating coil on the spacer, it becomes easy to accurately set the gap between the outer surface of the pipe and the heating coil in a short time when installing the heating coil on the pipe. . Further, it is possible to heat the pipe so that the temperature difference between the inner surface and the outer surface becomes uniform over the entire circumference of the pipe. By using this heating method, the tensile residual stress on the inner surface of the pipe can be converted to a compressive stress.
[0027]
In the present embodiment, the spacing between the spacers supporting the heating coil in the circumferential direction is set to about 45 ° C., and a heat insulating material is provided between the spacers to prevent the flow of the air in the gaps. The surface was kept hot. Instead of providing a heat insulating material, the number of spacers may be increased and the spacing in the circumferential direction of the spacers may be increased to prevent the flow of air in the gap.
[0028]
Another embodiment of the heat treatment apparatus according to the present invention will be described with reference to FIG. The heat treatment apparatus according to the present embodiment is applied to a straight pipe installed such that the center axis of the pipe is vertical, and a welded portion between the straight pipes. The shape of the spacer 12 is different from that of the embodiment shown in FIG. 1, and the distance between the heating coil 11 and the outer surface of the pipe 1 is smaller in the lower part along the central axis of the pipe than in the upper part. It has a shape.
[0029]
In FIG. 6, a spacer 12 and a heating coil 11 fixed thereto are installed at a position sandwiching the pipe welding portion 2 in the axial direction, and cooling water is supplied to the heating coil by the cooling water circulating device as in the embodiment shown in FIG. A high frequency voltage is applied to the heating coil while circulating. When a high-frequency current is supplied to the heating coil, an induced current is induced on the outer surface of the pipe, and heat is generated by electric resistance of the pipe. The heating coil is provided so that the distance between the outer surface of the pipe and the heating coil is smaller in the lower part of the pipe than in the upper part. Therefore, the calorific value is relatively larger in the lower part than in the upper part.
[0030]
When the temperature of the pipe rises due to the high-frequency induction heating and the temperature of the water inside the pipe rises, the water whose temperature has risen moves upward. That is, convection occurs. Due to the convection, a part of the heat generated from the high-frequency induction heating, which is transmitted from the inner surface of the pipe to the water, moves upward.
[0031]
If the distance between the heating coil and the outer surface of the pipe is uniform over the entire axial direction of the pipe, the amount of heat generated in the pipe by the high-frequency induction loaded from the heating coil becomes uniform in the axial direction. In addition, since the amount of heat transferred from the pipe to the water on the inner surface of the pipe is larger in the lower part than in the upper part, the temperature distribution in the cross section differs between the upper part and the lower part of the pipe. There is a possibility that the residual tensile stress cannot be reduced uniformly.
[0032]
On the other hand, as shown in the present embodiment, when the distance between the outer surface of the tube and the heating coil is set smaller in the lower part than in the upper part, the lower part generates a larger amount of heat, so the inner part of the pipe in the lower part When the amount of heat transferred from the surface to the water is greater than above, the temperature difference between the inner and outer surfaces can be uniform at any position in the axial direction of the entire pipe. As a result, a compressive residual stress can be generated at the welded portion on the inner surface of the pipe.
[0033]
Note that, similarly to the embodiment shown in FIG. 1, in this embodiment, a heat insulating material is inserted between the spacers so that the pipe can be efficiently heated. It is good also as composition.
[0034]
Also, the distance between the heating coil held by the spacer and the surface of the pipe is made constant in the axial direction, and the interval between the heating coils is made denser on the lower side to increase the amount of heat generated on the lower side. The temperature distribution in the axial direction may be controlled.
[0035]
In each of the above embodiments, in order to prevent the water in contact with the inner surface of the pipe from boiling and reducing heat transfer and convection, the cooling fluid flowing inside the pipe is pressurized, The pressurized fluid may be cooled by flowing into the inside of the pipe.
[0036]
In each of the above embodiments, the frequency of the high-frequency current supplied to the heating coil was constant regardless of time. Next, a method for changing the frequency of the high-frequency current with time as shown in FIG. 7 will be described.
[0037]
The relationship between the frequency of the high-frequency current supplied to the heating coil and the depth at which the induced current is generated on the outer surface of the pipe decreases as the frequency increases. FIG. 8 shows the temperature distribution along the evaluation line 41b of the pipe when the heating coil 11 is installed around the pipe 1 and heated at the frequencies fh and fl (fh> fl). The horizontal axis of the graph in the figure indicates the distance from the inner surface of the pipe, the origin O indicates the inner face of the pipe, and the position indicated by a broken line 43 indicates the outer face of the pipe. Comparing the case where the frequency is fh and the case where the frequency is fl, the region where heat is generated is deeper in the region where the frequency is low. Therefore, the distribution along the evaluation line 41b is as indicated by curves 51a and 51b when the frequency is relatively high and the frequency is low. As shown in FIG. 7, the time of the frequency fh is set to th and the time of the frequency fl is set to tl, as shown in FIG. The case is superimposed, and the temperature distribution is indicated by a solid line 52 in FIG. The gradient of the temperature distribution in the vicinity of the inner surface of the pipe is larger at 52 as compared with 51a or 51b where the frequency is fh or fl alone. When the thickness is large, the thermal stress generated on the inner surface increases depending on the gradient of the temperature distribution. Therefore, by alternately using fh and fl as the applied frequency, the thermal stress generated on the inner surface of the pipe can be increased on the tensile side, and as a result, the residual stress on the inner surface of the pipe can be compressed.
[0038]
Another embodiment of the present invention will be described with reference to FIG. In each of the above embodiments, one heating coil is disposed at a portion where the residual stress on the inner surface of the pipe is improved. In this embodiment, the heating is performed using a plurality of heating coils 111, 112, and 113 at the positions in the axial direction of the nozzle 101 and the pipe 102. In each of the heating coils, the temperature of the outer surface of the pipe facing the heating coil is measured. Measured by thermocouples 131, 132, 133 attached to the outer surface, the electromotive force of a thermocouple not shown in the figure is transmitted to a temperature measuring device via a cable, and then sent to a control device via an AD converter. The method is characterized in that the pipe is heated while controlling the current applied to the heating coil.
[0039]
Units 141, 142, and 143 shown in FIG. 9 collectively show a control device, a power supply, a transformer, and a cooling water circulation device for applying a current to each of the heating coils 111, 112, and 113.
[0040]
The present embodiment is an example in which the present invention is applied to a pipe in which the pipe thickness of the pipe at the welding portion changes near the welding portion. Referring to FIG. 10, a description will be given of a temperature distribution in a case where a portion where the thickness of the surrounding tube changes greatly is heated by a set of heating coils 110 when comparing the thickness of the tube with the surrounding portion of the welding portion. This is a case where the pipe 102 is joined to the nozzle 101 at the welding portion 2, and a case where the nozzle 102 is heated by a set of heating coils 110. The isotherms at 100 ° C., 300 ° C., and 500 ° C. are shown as solid lines 151, 152, and 153 in the figure. The heat generated in the vicinity of the welding portion moves to a region where the pipe thickness is large due to heat conduction. For this reason, a predetermined temperature difference cannot be generated at the welding site. Although not shown, if a predetermined temperature difference is to be generated at a portion where the pipe thickness is large, the temperature at the welding portion becomes excessively high. Therefore, it is not possible to generate a compressive residual stress at the welding site.
[0041]
On the other hand, a temperature distribution when heating is performed by a heating coil having three independent control systems as shown in FIG. 9 will be described with reference to FIG. The heating coil 111 and 112 heat the welding site 2 and its vicinity and the pipe 102. Further, the portion of the nozzle 101 whose thickness is larger than that of the pipe 102 is heated by the heating coil 113 with a higher output than the heating coils 111 and 112. Therefore, unlike the case of FIG. 10, the shape of the solid lines 151, 152, and 153, which are the isotherms of 100 ° C., 300 ° C., and 500 ° C., in the region of the nozzle 101 can be extended to a high temperature range. As a result, a compressive residual stress having a larger absolute value can be generated on the inner surface of the pipe when heating is performed with three sets of heating coils than when heating is performed with one set of heating coils.
[0042]
In this embodiment, a power supply and a transformer are provided for each set of coils. However, a power supply and a transformer are used as one set, and a control panel having a set of power supply and a transformer and a relay mechanism between each coil is provided. A configuration may be adopted.
[0043]
In this embodiment, the temperature of the pipe surface is measured by a thermocouple in order to control the current supplied to the heating coil, but the induced current or voltage induced on the pipe surface is measured, and the value is measured. And the current supplied to the heating coil may be controlled, or one coil may be moved in the axial direction of the pipe, and the heat value may be changed for each moved portion.
[0044]
Next, a case where the material characteristics of the pipe changes in a direction along the central axis of the pipe will be described. FIG. 9 shows a case where the strength of the welding portion 2 is larger than the strength of the pipe 102. The material of the pipe is type 304 stainless steel. Comparing the weld metal part and the base material of the pipe, the strength is higher at the weld part. When heating is performed so that the temperature difference generated between the inner surface and the outer surface of the pipe is equal to the region where the material strengths are different, the strength on the pipe side is smaller than that on the weld metal side. When a tensile heat load is applied from the weld metal part, it yields and tensile plastic strain is generated. Tensile plastic strain also occurs in the weld metal part, but it is small compared to the pipe side. At the time when the heating is stopped and the whole temperature becomes uniform, the plastic strain generated on the inner surface of the pipe is larger on the pipe side than on the weld metal part. Therefore, at the boundary between the weld metal part and the pipe, a tensile residual stress is applied to the weld metal part. As shown in FIG. 9, in order to prevent the occurrence of tensile residual stress in the weld metal portion, the heating coil 132 is installed at the welding site 2 in a configuration in which the high-frequency current can be controlled independently in FIG. The heating coil 131 may be installed on the pipe side and set so that the temperature difference between the inner and outer surfaces generated at the welding portion 2 is smaller than the temperature difference between the inner and outer surfaces generated at the pipe side. The ratio of reducing the generated temperature difference may be estimated from the ratio between the strength of the pipe and the strength of the welded portion. In type 304 stainless steel, the strength of the base material is 270 MPa, and the welding site is 400 MPa, so it may be adjusted to be about 0.67 times. As described above, when the material characteristics of the pipe differ depending on the range on the pipe, a heating coil may be provided for each range having different material characteristics, and the high-frequency current may be controlled in each area.
[0045]
Still another embodiment of the present invention will be described with reference to FIG. This embodiment is an effective method for reducing the residual tensile stress in the axial direction on the inner surface of the pipe at the butt welding portion. Two sets of the heating coil 211 and the heating coil 212 are installed in a region sandwiching the welded portion 2. Further, on the outer surface of the welded portion 2 of the pipe, a cooling mechanism including a nozzle 221 for water injection and a water recovery mechanism 222 for cooling the outer surface of the welded portion 2 of the pipe during heating is provided. In such an arrangement, after the heating coil 211, the heating coil 212, and the cooling mechanism are installed around the welded portion, the water recovery mechanism 222 of the cooling mechanism is operated, and then the cooling water is injected from the nozzle 221 for water injection. Let it. A high-frequency current is applied to each of the two sets of heating coils provided with the cooling mechanism sandwiched in the axial direction of the pipe.
[0046]
FIG. 13 shows the deformation and isotherm of the cross section of the pipe when cooling the surface of the welding portion by the cooling mechanism and heating by two sets of heating coils. In FIG. 13, solid line 251, solid line 252, solid line 253, and solid line 254 indicate isotherms at 100 ° C., 200 ° C., 300 ° C., and 400 ° C., respectively. The temperature of the area facing the coil rises due to the induction current induced from the heating coil 211 and the heating coil 212 near the outer surface of the pipe, and the high temperature area spreads inside the pipe by heat conduction. Further, since the welded portion is water-cooled, the temperature rise is small compared to the heated region. At this time, the heating region undergoes a deformation that expands in the radial direction due to a rise in temperature. On the other hand, since the welding portion is cooled by the cooling leg mechanism, the deformation in the radial direction is smaller than that in the heating region. For this reason, the welded portion undergoes a convex deformation on both the inner and outer surfaces. In such a variant, the axial stress of the pipe is tensile on the inner surface and compressive on the outer surface. Further, the circumferential stress is compressed on both the inner surface and the outer surface.
[0047]
When the thermal stress as described above is applied to the pipe where the welding residual stress is generated, and then the heating is stopped and the temperature of the entire pipe reaches a uniform temperature, the axis on the inner surface of the welded part of the pipe is Directional stress becomes compression.
[0048]
Another embodiment of the present invention will be described with reference to FIG. This embodiment is an effective method for reducing the tensile residual stress in the circumferential direction on the inner surface of the pipe at the butt welding portion. Two sets of quenching mechanisms composed of a nozzle 221 for water injection and a water recovery mechanism 222 are installed in a region sandwiching the weld 2. A heating coil 211 for heating the outer surface of the welded portion 2 of the pipe is provided on the outer surface of the welded portion 2 of the pipe 201. In such an arrangement, after the cooling mechanism and the heating coil 211 are installed around the welded portion, the water recovery mechanism of the cooling mechanism is operated, and then the cooling water is injected from the water injection nozzle. A high-frequency current is applied to the heating coil 211 installed in an arrangement sandwiched between two sets of cooling mechanisms in the axial direction.
[0049]
FIG. 15 shows the deformation and isotherm of the cross section of the pipe when cooling the surface of the welding portion by two sets of cooling mechanisms and heating by the heating coil. In FIG. 15, a solid line 251, a solid line 252, a solid line 253, and a solid line 254 indicate isotherms of 100 ° C., 200 ° C., 300 ° C., and 400 ° C., respectively. The temperature of the area facing the coil rises due to the induced current induced from the heating coil 211 near the outer surface of the pipe, and the high temperature area spreads inside the pipe by heat conduction. Further, since the surroundings are water-cooled by the cooling mechanism, the temperature rise is small as compared with the heating area. At this time, the heating region undergoes a deformation that expands in the radial direction due to a rise in temperature. On the other hand, since the welding portion is cooled by the cooling leg mechanism, the deformation in the radial direction is smaller than that in the heating region. For this reason, the welded portion undergoes outwardly convex deformation on both the inner and outer surfaces. In such a variant, the axial stress of the pipe is compression on the inner surface and tension on the outer surface. Further, the circumferential stress becomes tensile on the inner and outer surfaces.
[0050]
When the thermal stress as described above is applied to the pipe where the welding residual stress is generated, and then the heating is stopped and the temperature of the entire pipe reaches a uniform temperature, the circumference of the welded area on the inner surface of the pipe is Directional stress becomes compression.
[0051]
A further embodiment of the present invention will be described with reference to FIGS. The present embodiment is a case of a joint having a crack at a weld site on the inner surface of a pipe. In the present embodiment, first, the presence or absence of cracks in the weld metal and the weld heat-affected zone of the pipe weld is inspected. The inspection method uses ultrasonic flaw detection because it is necessary to detect a defect on the inner surface of the existing pipe.
[0052]
With reference to FIG. 16, a description will be given of a preferable temperature distribution for suppressing the progress of the crack when the crack is detected as a result of the inspection. FIG. 16 shows a temperature distribution preferable for suppressing the development of cracks along an evaluation line 371 from the tip of the defect at the welded portion to the outer surface of the pipe and an evaluation line 372 from the inner surface to the outer surface of the pipe where there is no defect. It is. The horizontal axis of the graph in the figure indicates the distance from the inner surface of the pipe, and the broken line 381 indicates the position of the tip of the defect with reference to the inner surface of the pipe. The broken line 382 is the position of the outer surface of the pipe.
[0053]
In order to generate the above-mentioned temperature distribution, it is necessary to adjust the heating of the outer surface of the defective portion of the pipe so that it becomes shallower than the surroundings. A heating method for providing such a temperature distribution will be described with reference to FIG. In FIG. 17, heating is performed using three sets of heating coils. The heating of the weld where the crack has been detected raises the frequency and generates a temperature distribution. By applying a predetermined temperature distribution to the tip of the crack by such a construction device, it is possible to generate a compressive residual stress at the tip of the crack that has occurred, thereby slowing the progress of the crack. It is possible to do.
[0054]
In this embodiment, the case where three sets of heating coils are used is shown. However, with one set of heating coils, only the space between the heating coil at the portion where the crack is detected and the winding interval of the heating coil is increased. It is also possible to widen only the part where is detected.
[0055]
Another embodiment of the present invention will be described with reference to FIG. This embodiment is a case of a boiling water reactor power plant. A pipe 710 attached to the reactor pressure vessel 700, a circulation pump 720, and a riser pipe 730 constitute a recirculation system, which is one pipe system of the boiling water reactor power plant. By joining a large number of bent pipes, straight pipes, and the like by welding, a recirculation system pipe is assembled.
[0056]
After the assembly of the reactor pressure vessel 700 and the recirculation system piping is completed, the outer surface of the piping is heated by the heating coil while flowing water through the recirculation system piping. It can be applied to the welded joint 741 shown in FIG. 18 as a welded portion between straight pipes, a welded joint 742 as a nozzle-shaped portion, a welded joint 743 as a portion where the shape of a pipe changes, and the like.
[0057]
As shown in FIG. 6, the residual stress on the inner surface of the pipe can be converted into a compressive stress for the joint 741 between the straight pipes in which the central axis of the pipe is vertical. Further, the residual stress on the inner surface of the pipe can be compressed by the illustrated method for the welded joint 742 that is a nozzle-shaped portion. For the welded joint 743, a spacer and a spacer jig along the shape of the pipe surface are manufactured in advance, and a heating coil unit in which a heating coil is attached to the spacer is manufactured in advance. By attaching to a part and filling the pipe with reactor water and heating the outer surface with a heating coil, a compressive residual stress can be generated on the inner surface of the pipe.
[0058]
When the method of this embodiment is applied to the recirculation system piping of a boiling water reactor power plant, since the reactor water is filled in the piping, it is not necessary to newly prepare a coolant on the inner surface of the piping. . In the above description, a boiling water reactor plant is taken as an example, but the same applies to piping systems of other nuclear power plants such as a pressurized water reactor plant and a heavy water reactor plant, thermal power plants and chemical plants. The invention can be applied.
[0059]
【The invention's effect】
As described above, according to the present invention, after assembling a piping system of a plant, a compressive residual stress can be generated on the inner surface of the piping of the piping system, so that stress corrosion cracking of the piping system can be prevented. . Further, a heating coil required for heat treatment can be easily installed. Further, a compressive residual stress can be generated in a weld metal portion on the inner surface of the pipe, and the reliability of the pipe system is improved.
[Brief description of the drawings]
FIG. 1 is a schematic view of one embodiment of a heat treatment apparatus according to the present invention.
FIG. 2 is a partial perspective view of one embodiment of a heating coil according to the present invention.
FIG. 3 is a cross-sectional view of one embodiment of the heating device according to the present invention.
FIG. 4 is a cross-sectional view of one embodiment of the heating device according to the present invention.
FIG. 5 is a diagram illustrating a temperature distribution of a pipe in a pipe thickness direction.
FIG. 6 is a schematic view of another embodiment of the heat treatment apparatus according to the present invention.
FIG. 7 is a diagram illustrating an example of a high-frequency current applied to a heating coil.
FIG. 8 is a diagram illustrating a temperature distribution by a heating coil.
FIG. 9 is a schematic view of still another embodiment of the heat treatment apparatus according to the present invention.
FIG. 10 is a diagram illustrating a conventional pipe heat treatment.
FIG. 11 is a diagram illustrating a pipe heat treatment according to the present invention.
FIG. 12 is a schematic view of still another embodiment of the pipe heat treatment apparatus according to the present invention.
FIG. 13 is a diagram illustrating deformation of a pipe.
FIG. 14 is a schematic view of still another embodiment of the heat treatment apparatus according to the present invention.
FIG. 15 is a diagram illustrating deformation of a pipe.
FIG. 16 is a diagram illustrating a temperature distribution of a pipe.
FIG. 17 is a schematic view of still another embodiment of the heat treatment apparatus according to the present invention.
FIG. 18 is a perspective view of an application example of the heat treatment apparatus according to the present invention.
[Explanation of symbols]
1, 1a, 1b: piping, 2: welded part, 11: heating coil, 12: spacer, 13: spacer circumferential mounting jig, 14: current cable, 15: cooling water circulation hose, 16: transformer, 17: power supply, Reference numeral 18: Control device, 19: Cooling water circulation device, 20: Current detector, 21a: Temperature measuring device, 21b: Secondary current measuring device, 22: Thermocouple, 23: Cable, 24: Bolt, 25: Heat insulating material, 101 ... Nozzle thick part, 102 pipe, 110 heating coil, 120 spacer, 131 thermocouple for temperature measurement, 141 power supply / cooling water circulation device / control device, 151 isothermal line, 201 pipe, 211 heating Coil, 221: water shower mechanism, 222: water recovery mechanism, 360: crack, 700: boiling water reactor pressure vessel, 720: circulation pump, 730: riser pipe.

Claims (18)

After assembling a piping system having a piping, a cooling fluid is flowed into the piping, and then heat treatment is performed using a high-frequency heating device having a heating coil to heat the piping to generate a temperature difference between the inner surface of the piping and the outer surface of the piping. In the method, a temperature distribution in a circumferential direction and an axial direction of the pipe is controlled by a heating coil. The method according to claim 1, wherein the cooling fluid is pure water. The heat treatment method for a piping system according to claim 1, wherein the piping system is a reactor piping, and the cooling fluid is a reactor water that can be supplied by a nuclear reactor. The method according to any one of claims 1 to 3, wherein a distance from an outer surface of the pipe to an inner surface of the heating coil is changed in a longitudinal direction of the heating coil. The heat treatment method for a piping system according to claim 4, wherein a distance between the heating coil and the outer surface of the pipe is changed in a circumferential direction by decentering a center of the heating coil from a center of the pipe. The piping system according to any one of claims 1 to 4, wherein a gap between the pipe and the heating coil is made substantially constant in a circumferential direction to prevent air flow in the formed gap. Heat treatment method. The heat treatment method for a piping system according to any one of claims 1 to 6, wherein the number of turns of the heating coil exceeds at least two turns, and the winding interval is changed. 8. The heat treatment method for a piping system according to claim 1, wherein at least two heating coils are provided, and a current can be controlled for each heating coil. The method according to any one of claims 1 to 8, wherein the frequency of the high-frequency current supplied to the heating coil is changed with time. 9. The heat treatment method for a piping system according to claim 8, wherein a temperature of a pipe surface heated by the heating coil is measured, and a current supplied to the heating coil is controlled based on the measured temperature. 9. The heat treatment method for a piping system according to claim 8, wherein at least one of a current and a voltage on a pipe surface heated by the heating coil is detected and a current supplied to the heating coil is controlled based on the detected value. . Before installing the coil to be heated, check the presence or absence of defects on the inner surface of the piping system by non-destructive inspection, and if a defect is detected, apply heating different from the case where no defect is detected using a heating coil near the defect The method for heat treating a pipe according to any one of claims 1 to 11, characterized in that: 13. A heating section is formed in an axial front-back direction of a cooling section for cooling the outer surface of the pipe over the entire circumference, and the heating section is heated by a heating coil over the entire circumference of the pipe. The method for heat treating a pipe according to any one of the above. 14. The cooling unit according to claim 1, wherein a cooling unit that cools the entire outer circumference of the pipe is formed in the axial front-rear direction of the heating unit that heats the outer surface of the pipe by the heating coil over the entire circumference. The heat treatment method of the pipe described. A heating coil for high-frequency induction heating arranged on the outer surface side of the piping system, a spacer for maintaining a predetermined gap between the surface of the piping system and the heating coil, and a cooling water circulating inside the heating coil attached to the heating coil. A cooling water pipe, means for supplying a high-frequency current to the heating coil, a temperature measuring device for detecting a temperature of an outer surface of a piping system heated by the heating coil, and a temperature measuring device based on the temperature detected by the temperature measuring device. A control device for controlling a heating coil, wherein the heating coil heats a piping system to generate a compressive residual stress on an inner surface of the piping system. The heat treatment apparatus for a piping system according to claim 15, wherein at least two sets of the heating coils are provided, and a high-frequency current can be supplied to each heating coil independently. In the pipe, at least one of the strength and the material of the portion heated by the heating coil changes along the pipe axis, and the heating coil is arranged according to the strength or the material of the pipe to change the degree of heating. The heat treatment method for a piping system according to claim 8, wherein The pipe heat treatment method according to any one of claims 1 to 14, wherein the cooling fluid introduced into the pipe is pressurized, and the pipe is filled with water to flow the cooling fluid. .

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