JP2007063642A - Method for improving remaining stress and coil for high-frequency induction heating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for improving the remaining stress in a welded part and a coil for high-frequency induction heating which can efficiently apply to various pipings having different shapes and sizes. <P>SOLUTION: As the heating coil for improving the remaining stress in the piping 1 joining straight pipes 1a, 1b having different sizes at a welding part 2, two or more of the partial heating coils 10A, 10B having different diameters are used and these coils are combined and these are disposed at one side and the other side of the welding part 2, respectively so as to be possible to efficiently generate the temperature difference to the piping 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a residual stress improving method by high frequency induction heating and a coil used for high frequency induction heating, and more particularly to a residual stress improving method and a high frequency induction heating coil suitable for heat treatment of a welded joint portion of a pipe member.

  Residual stress is generated in the weld zone. If this is left untreated, stress corrosion cracking may occur, and as a countermeasure for this, various methods for improving the residual stress by heat treatment have been proposed. As a method for reducing the tensile residual stress on the inner surface of the pipe, there is a stress improvement method (IHSI: Induction Heating Stress Improvement) by high frequency induction heating (see, for example, Patent Document 1).

And in this stress improvement method by this prior art, a cooling fluid is made to flow in the piping installed in the plant and the outer surface is heated by high frequency induction, thereby giving a temperature difference between the inner surface and the outer surface of the piping. After yielding by tensile stress and yielding by compressive stress on the outer peripheral surface, compressive stress remains on the inner surface of the pipe by reversing the stress state of the inner and outer surfaces in the subsequent cooling process. The tensile residual stress on the inner surface of the pipe at the site is reduced to prevent stress corrosion cracking.
Japanese Examined Patent Publication No. 53-38246

  The above prior art does not give consideration to the fact that there are pipes that have different shapes and dimensions for the stress improvement target, and the high frequency induction heating coil requires diversity, which increases the construction cost. There was a problem that.

  In the high-frequency induction heating stress improvement method, a high-frequency induction heating coil is arranged outside the part that improves the residual stress in the pipe, and a high-frequency current is passed through the pipe to induce a current in the pipe, which is heated by the resistance heat. Therefore, for pipes with different pipe outer diameters within the coil mounting range, such as stepped pipes, and pipes with a non-straight central axis, such as elbows, a dedicated coil must be manufactured for each pipe. Therefore, the construction cost will increase.

  The present invention has been made in view of the above-described conventional situation, and its object is to provide a residual stress improving method and a high-frequency induction heating coil that can be efficiently applied to various pipes having different shapes and dimensions. It is to provide.

  The object is to improve the residual stress of the pipe member welded portion by high-frequency induction heating of the pipe member, in which the high-frequency induction heating for improving the residual stress is performed on the pipe member welded portion. This is achieved by changing the operating conditions on one side and the other side. At this time, the pipe member may be a pipe of a nuclear reactor.

  The object is a high-frequency induction heating coil used in the residual stress improving method, wherein the high-frequency induction heating coil is composed of two or more partial heating coils having different diameters on one side and the other side. The high-frequency induction heating coil is also configured by two or more partial heating coils having different winding pitches on one and the other, and further, the high-frequency induction The heating coil is also achieved by being a coil that is flexible and at least one of the diameter and the winding pitch can be changed on one side and the other side in the length direction.

  According to the present invention, the tensile residual stress remaining in the pipe member can be efficiently transferred to the compression side, so that an increase in the construction cost can be suppressed and stress corrosion cracking of the pipe can be prevented, and has become a target. Installation of the heating coil to the tube member can be easily obtained.

  Hereinafter, the method for improving the residual stress of the welded portion and the high frequency induction heating coil according to the present invention will be described. First, an example of an apparatus used for carrying out the present invention will be described with reference to FIGS. To do.

  In the case of this apparatus, as shown in FIG. 4, the processing target for residual stress improvement is a pipe 1 in which a straight pipe 1 a and a straight pipe 1 b are joined by a welded portion 2, and a heating coil 10 is set in the pipe 1. It has become. As shown in FIG. 5 (a), the heating coil 10 is composed of a coil conductor 12 made of a copper strip of 5 turns, and a pipe 13 is joined to the coil conductor 12. The heating coil 10 is configured together with the coil conductor 12.

  At this time, the heating coil 10 is composed of two ring members 4A and 4B and four lateral members 5A, 5B, 5C and 5D, as particularly shown in detail in FIG. A circumferential mounting jig is provided so that it can be mounted on the pipe 1.

  First, the ring members 4A and 4B are assembled by the four transverse members 5A, 5B, 5C, and 5D so as to be separated from each other in the length direction of the heating coil 10 and to be positioned at both ends of the heating coil 10, respectively. However, at this time, the transverse members 5A, 5B, 5C, and 5D are arranged at substantially equal intervals in the circumferential direction of the ring members 4A and 4B, and the coil conductor 12 of the heating coil 10 is held inside them. It is like that.

  At this time, as shown in the figure, bolts 6 are screwed into the ring members 4A and 4B from the outer peripheral side toward the center, whereby positioning with respect to the pipe 1 can be performed, and the heating coil 10 is connected to the pipe 1 It can be held at a predetermined position.

  Returning to FIG. 4, the coil conductor 12 of the heating coil 10 is supplied with a high-frequency current from the high-frequency oscillator 18 through the cable 16, thereby inducing an induced current on the surface of the pipe 1, thereby obtaining heating by Joule heat. Like that. For this reason, the coil conductor 12 is connected to the high-frequency oscillator 18 via the cable 16.

  The high-frequency oscillator 18 is supplied with power from a power transformer 19 via a cable 21A. At this time, the pipe 13 of the heating coil 10, the high-frequency oscillator 18, and the power transformer 19 are cooled. Cooling water is supplied from the water circulation device 17 via the hose 15 so that the temperature rise is suppressed.

  Here, a control device 20 is further connected to the high-frequency oscillator 18 via a cable 21B. And the thermocouple 22 is connected to this control apparatus 20 via the cable 21C. Here, this thermocouple 22 is attached in the vicinity of the welded portion 2 on the outer surface of the pipe 1 as shown in the figure, and functions to measure the temperature of the surface of the welded portion 2.

  Next, the operation of this apparatus will be described. At this time, first, the heating coil 10 is brought into the state shown in FIG. That is, the heating coil 10 is installed in the pipe 1 so that the welded portion 2 that is a joint portion between the straight pipe 1a and the straight pipe 1b is substantially in the center. After that, cooling water is passed through the pipe 1 so that the temperature rise on the inner surface of the pipe is suppressed, and then a high frequency current is supplied to the heating coil 10 to induce an induced current in the pipe 1. Heat is generated on the outer surface due to the electrical resistance of the material.

  At this time, the outer surface temperature of the pipe 1 to be heat-treated is measured by the thermocouple 22. Therefore, the control device 20 controls the output of the high-frequency oscillator 18 based on the measurement result of the outer surface temperature, thereby controlling the high-frequency current value supplied to the heating coil 10 and heat-treating the outer surface of the pipe 1. An operation for obtaining the required predetermined temperature is obtained.

  By the way, the welding residual stress generated in the vicinity of the welded portion 2 in the pipe 1 at this time is substantially constant regardless of the position on the circumference of the pipe 1. Therefore, in order to generate compressive residual stress on the inner surface of the pipe 1 over the entire circumference, the temperature difference between the outer surface and the inner surface of the pipe 1 is always constant regardless of the position on the circumference. Need to be heated.

  Moreover, at this time, it is desirable that a temperature difference between the outer surface and the inner surface of the pipe 1 is sufficiently ensured so that compressive residual stress can be efficiently generated on the inner surface of the pipe 1. It is necessary to match the shape and size to the shape and size of the pipe 1 as much as possible.

  Therefore, hereinafter, an embodiment of the present invention will be described. First, FIG. 1 is an embodiment in which a pipe 1 in which a straight pipe 1c and a straight pipe 1d having different diameters are joined by a welded portion 2 is a processing target. Accordingly, in this embodiment, two or more partial heating coils 10 </ b> A and 10 </ b> B are used as heating coils, and these are arranged on both sides of the welded portion 2.

  At this time, the straight pipe 1c and the straight pipe 1d have the same inner diameter, but when the diameter of the straight pipe 1c is D1 and the diameter of the straight pipe 1d is D2, as shown in the drawing, these have a relationship of D1 <D2. It is in. Accordingly, in accordance with this, in this embodiment, the inner diameter of the partial heating coil 10A is DA, and the inner diameter of the partial heating coil 10B is DB, so that the relationship of DA <DB is established.

  Here, the two or more partial heating coils 10A and 10B are not shown in the figure, but each has the bolt 6 independently as in the heating coil 10 described in FIGS. Thus, the partial heating coil 10A is set on the straight pipe 1c side from the welded portion 2, and the partial heating coil 10B is set on the straight pipe 1d side from the welded portion 2.

  At this time, the coil conductors 12 of the partial heating coil 10 </ b> A and the partial heating coil 10 </ b> B are connected in series, and a high frequency current is supplied to the coil conductor 12 from the high frequency oscillator 18. At this time, the pipe 13 is also connected in series, and the cooling water is circulated from the cooling water circulation device 17.

  Therefore, if a high frequency current is supplied from the high frequency oscillator 18 to the partial heating coil 10A and the partial heating coil 10B, the diameter of the partial heating coil 10A is determined in accordance with the diameter of the straight pipe 1c. Since the diameter of 10B is determined in accordance with the diameter of the straight pipe 1d, these have the same positional relationship.

  Therefore, in this case, since the operating condition of induction heating can be changed between the straight pipe 1c and the straight pipe 1d, even if the diameters of the straight pipe 1c and the straight pipe 1d are different, uniform heating can be achieved. Since there is no possibility that the distance between the coil and the object to be processed increases in any of the straight pipe 1c portion and the straight pipe 1d portion, as a result, uniform heating is obtained in the entire welded portion 2, And since a power loss is reduced, a compressive residual stress can be efficiently generated in the piping 1.

  In the apparatus described with reference to FIGS. 4 and 5, the pipe 1 to be processed is the same diameter and the same material made by joining the straight pipe 1 a and the straight pipe 1 b with the welded portion 2. Therefore, in this case, As shown in the figure, there was no particular problem even when the coil conductor 12 was wound with the same diameter and the same hitch as the heating coil 10.

  Next, FIG. 2 shows an embodiment in which a pipe 1 in which a straight pipe 1e and a straight pipe 1f made of different materials are joined by a welded portion 2 is a processing target. In this case as well, two partial heating coils 10C and 10D are used as heating coils, and these are arranged on both sides of the welded portion 2, but in this embodiment, the partial heating coil 10C and the partial coil are arranged. Although the diameter of the heating coil 10D is the same, the pitch (interval between adjacent conductors) P of the coil conductor 12 is changed so that the number of turns (number of turns) is different between the partial heating coil 10C and the partial heating coil 10D. It is a thing.

  Here, first, it is assumed that the straight pipe 1e is made of stainless steel and the straight pipe 1f is carbon steel. Next, the pitch of the partial heating coil 10C is P1, the pitch of the partial heating coil 10D is P2, and P1 <P2, so that the number of turns of the partial heating coil 10C is as a whole as shown in the figure. 3 and the number of turns of the partial heating coil 10D is 2.

  In general, in the case of high-frequency induction heating, the heating condition varies depending on the material of the target member, and when the target member is stainless steel and carbon steel, the temperature of carbon steel tends to rise faster. On the other hand, since the electric power induced per unit length of the target member by the heating coil increases as the pitch P of the coil is narrower, the temperature rise can be controlled by changing the pitch P.

  Therefore, in the case of the pipe 1 in which the stainless steel straight pipe 1e and the carbon steel straight pipe 1f shown in FIG. The temperature of the straight pipe 1f side of steel rises quickly, and uniform heating cannot be obtained.

  Therefore, in this embodiment, the pitch P2 of the partial heating coil 10D arranged on the carbon steel straight pipe 1f side is made larger than the pitch P1 of the partial heating coil 10C on the stainless steel straight pipe 1e side, thereby induction. The operating condition of heating is different between the straight pipe 1e side of the stainless steel and the straight pipe 1f side of the carbon steel, the temperature rise on the straight pipe 1f side of the carbon steel is moderated, and the heating is made uniform. Therefore, according to this embodiment, the compressive residual stress can be efficiently generated in the pipe 1.

  At this time, since the electric power induced per unit length of the target member is controlled even if the diameter of the heating coil is changed, instead of changing the coil pitch, the straight pipe 1e side is changed as in the embodiment of FIG. Even if heating coils having different diameters are applied to the straight pipe 1f, the induction heating operation conditions can be changed in accordance with the heating coils, and similar effects can be obtained.

  Therefore, according to the embodiment of FIGS. 1 and 2, the heating coil 10 is composed of two or more partial heating coils 10A and 10B, or two or more partial heating coils 10C and 10D. By preparing coils 10A, 10B, 10C, 10D, etc. having different diameters and pitches, and using them in combination, the outer diameter of the pipe 1 is different within the target range of high frequency induction heating. Even in this case, it can be handled as it is.

  And as a result, according to the embodiment, even when the outer diameter of the pipe 1 is different within the target range of the high frequency induction heating, it is not necessary to manufacture a dedicated coil for the pipe each time. Construction costs can be reduced.

  By the way, in the embodiment described with reference to FIGS. 1 and 2, the pipe 13 is joined to the coil conductor 12 in order to allow the cooling water to flow. At this time, as shown in the embodiment of FIG. Instead of the coil conductor 12, a rectangular copper tube 120 may be used.

  In the case of the heating coil shown in FIGS. 1 and 2, since the pipe 13 has to be joined to the coil conductor 12 made of a copper strip, it is relatively difficult to manufacture. However, in the embodiment of FIG. In this case, since the coil conductor is a copper tube 120 and there is a passage 23 therein, this passage 23 can be used as a cooling water passage, and in this case, it can be manufactured relatively easily.

  In the above embodiment, the heating coil is water-cooled. Alternatively, a similar cooling can be performed by using a blower or the like to air-cool the entire coil. In the case of the embodiment, the construction cost is reduced and the weight can be reduced, so that the workability during construction is also improved.

  Furthermore, in the case of this air-cooled embodiment, the rigidity of the heating coil itself can be reduced, so that a flexible heating coil that can be arbitrarily changed in shape can be obtained. That is, in this case, the high-frequency induction heating coil can be configured by a coil that is flexible and can change at least one of the diameter and the winding pitch between one and the other in the length direction.

  Therefore, according to this embodiment, even when the outer diameter of the pipe 1 is different within the target range of the high frequency induction heating, it is possible to cope with the change in the shape of the heating coil itself without using a plurality of heating coils. .

  At this time, it is only necessary to provide the coil with the necessary flexibility, and therefore air cooling is not necessarily a necessary requirement.

It is a schematic diagram which shows 1st Embodiment of the coil for high frequency induction heating by this invention. It is a schematic diagram which shows 2nd Embodiment of the high frequency induction heating coil by this invention. It is a schematic diagram which shows 3rd Embodiment of the high frequency induction heating coil by this invention. It is a block block diagram which shows an example of the apparatus used for implementation of the residual stress improvement method of the welding part by this invention. It is explanatory drawing which shows one Embodiment of the heating coil which concerns on this invention.

Explanation of symbols

1: Piping (target for residual stress improvement)
1a, 1b, 1c, 1d, 1e, 1f: straight pipe 2: welded portion 4A, 4B: ring member 5A, 5B, 5C, 5D: transverse member 6: bolt 10: heating coil 10A, 10B, 10C, 10D: part Heating coil 12: Coil conductor 13: Pipe (for cooling water flow)
15: Hose (for cooling water circulation)
16: Cable (for power supply)
17: Cooling water circulation device 18: High frequency oscillator 19: Power transformer 20: Control devices 21A, 21B, 21C: Cable 22: Thermocouple (for temperature measurement)
23: Passage (for cooling water flow)
120: Copper tube (rectangular copper tube)

Claims (5)

In the residual stress improvement method in which the residual stress improvement of the pipe member weld is performed by high frequency induction heating of the pipe member,
A method for improving residual stress, comprising performing high-frequency induction heating for improving the residual stress by changing operating conditions on one side and the other side of the welded portion of the pipe member. In the residual stress improvement method of Claim 1,
The method for improving residual stress, wherein the pipe member is a piping of a nuclear reactor. A high-frequency induction heating coil used in the method for improving residual stress according to claim 1,
The high-frequency induction heating coil is composed of two or more partial heating coils having different diameters on one side and the other side. A high-frequency induction heating coil used in the method for improving residual stress according to claim 1,
The high frequency induction heating coil is composed of two or more partial heating coils having different winding pitches on one side and the other side. A high-frequency induction heating coil used in the method for improving residual stress according to claim 1,
The high-frequency induction heating coil is a high-frequency induction heating coil that is flexible and includes at least one of a diameter and a winding pitch that can be changed between one and the other in the length direction.

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