JP2008095133A - Method for recovering strength in strength-deteriorated part and high-frequency induction heating apparatus used to method for recovering strength - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method with which the strength in a strength-deteriorated part can be recovered at the actual spot, and to provide a high-frequency induction heating apparatus which can suitably be used when the strength in the strength-deteriorated part is recovered. <P>SOLUTION: In order to recover the strength in the strength-deteriorated part in a facility constituted by using a steel-made member, this strength-deteriorated part can be held to heat to the temperature of the A<SB>3</SB>transporting point or higher of this steel-made member. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a strength recovery method for steel members used in thermal power plants, nuclear power plants, chemical plants, and the like, and in particular, creep strength such as a portion deteriorated in strength due to creep damage or a welded portion. The present invention relates to a technique for recovering the strength of a portion having a low strength, a portion in which strength is reduced due to embrittlement / fatigue, or a portion in which a structure having low strength exists in a structure having high strength.

  Equipment used in thermal power plants, nuclear power plants, chemical plants, etc. (for example, boilers and turbines) is often used for a long time at a high temperature of about 400 ° C. or higher and in a pressurized state. Of these facilities, steel members such as heated steam inlets and main steam inlet nozzles are often exposed to high temperatures and high pressures. When such a member is exposed to a high temperature and a high pressure and continues to be subjected to a constant load at a constant temperature, the strength of the material gradually decreases with the passage of time, and eventually breaks down. Such a phenomenon is called “creep”, and material deterioration and internal structure change due to creep are called “creep damage”. Further, when the steel member is exposed to a high temperature and a high pressure, the strength of the material is lowered due to embrittlement or fatigue depending on the use conditions and the material of the material, and the steel member is eventually destroyed.

  In this way, if a crack or other defect occurs due to creep damage or embrittlement or fatigue, the cracked part is now removed by a grinder, but if it is removed by a grinder, etc. Since the thickness of the member is reduced, it must be repair welded or replaced. However, when repair welding is performed, the crystal grains in the welded portion, particularly the heat-affected zone, become finer and the strength is lowered, so that cracks are likely to occur when exposed to high temperatures and high pressures. In addition, not only repair welding, but also when joining pipes to the nozzle or when joining pipes, the welding method is adopted. Becomes lower. On the other hand, it is also known that when the crystal grain size becomes too large, the retained austenite region increases and the fatigue limit decreases (see Non-Patent Document 1).

  With regard to the structure of the steel member, for example, when a high / medium pressure turbine casing material (Cr-Mo-V cast steel) is taken as an example, a bainite structure having a high creep strength is used. However, even if a low strength structure (for example, a ferrite structure) is mixed in a high strength structure such as bainite, the strength is lowered.

  As described above, the strength deterioration occurs in various cases, such as deterioration due to use, deterioration due to welding, deterioration due to organizational factors or the like due to manufacturing or repair. Therefore, in order to extend the life of the equipment, it is necessary to recover the strength of the portion where the strength has deteriorated (hereinafter, sometimes referred to as “strength deteriorated portion”).

  As a technique for recovering such strength, the technique of Patent Document 1 has been proposed. In this Patent Document 1, in a state in which the creep deteriorated portion is constrained, the creep deteriorated portion is heated to press the void or crack using the pressure due to expansion, and repaired by repairing the member damaged by creep. It is described that the life is extended.

  In Patent Document 2, a laser beam or an electron beam is used to heat a member that has undergone creep damage and has undergone systematic degradation or mechanical opening cracking to a remelting treatment or solution temperature range. Regeneration of mechanical defects or regeneration removal of systematic creep voids is described.

  Non-Patent Document 2, on the other hand, describes the relationship between creep strength deterioration and voids. When a member that has undergone creep damage is reheated, the minimum creep rate is almost as small as that of an unused material. It is described to show. This Non-Patent Document 2 also describes the relationship between creep strength deterioration and carbides, and shows that carbides on grain boundaries become coarse when exposed to high temperatures and high pressures for a long time. ing. Further, this Non-Patent Document 2 also shows that voids and cracks still remain even after reheating. Therefore, according to this non-patent document 2, the deterioration of creep strength is not directly related to the occurrence of voids or cracks, or the growth thereof, and in the vicinity of grain boundaries accompanying carbide precipitation or carbide coarsening. It can be seen that this is due to a local recovery phenomenon. Therefore, as described in Patent Document 1, it is considered that it is difficult to increase the creep strength even if heating is performed in a state where the creep deteriorated portion is constrained to reduce voids and cracks. Further, as described in Patent Document 2, it is considered that the creep strength cannot be increased by removing creep voids by heating with a laser beam or an electron beam.

  Moreover, as one of the causes of strength deterioration of members used at high temperatures, there is embrittlement, which is also known to be caused by carbide precipitation. This embrittlement also reduces the fatigue strength. Further, as described above, the fatigue limit varies depending on the crystal grain size (see Non-Patent Document 1).

By the way, depending on the position and size of the strength deteriorated part, it is conceivable to stop the operation of the equipment and temporarily remove the strength-reduced steel member from the equipment to recover the strength. However, if the operation of the equipment is stopped, productivity is lowered. Therefore, it is necessary to perform the maintenance of the equipment while the equipment is in operation or to shorten the time as much as possible even if the equipment is stopped. Therefore, it is desirable to recover the strength of the strength-degraded portion at the site and in a short time. In addition, although the non-patent document 2 described above describes re-heat treatment of a member that has been damaged by creep, it does not describe a specific method for performing this re-heat treatment on site.
JP 2003-253337 A JP-A-6-88120 Takeo Yokobori Translation supervision, “Fundamental and Fracture Mechanics of Metal Fatigue”, Hyundai Engineering Co., p. 301-309 Kazuhiro Kimura et al., “Research Report on the Refractory Metal Materials 123rd Committee”, Vol. 23, no. 2, Sections 1 and 2 p. 53-61

  This invention is made | formed in view of such a condition, The objective provides the method which can recover the intensity | strength of an intensity degradation part from a viewpoint different from the technique described in the said patent document 1. FIG. There is to do. Another object of the present invention is to provide a high-frequency induction heating apparatus that can be suitably used when the strength of the strength-degraded portion is recovered on site.

The intensity recovery method strength deteriorated part according to the present invention that has solved the above problems, the strength deterioration of the equipment that is constructed using a steel member at A ₃ transformation point or above the temperature of the steel member It has a gist in that it is heated and held.

  The heating of the strength deterioration portion is preferably performed using a high frequency induction heating device. Examples of the strength-degraded part include a welded part between steel materials and a heat-affected part thereof.

  The high-frequency induction heating device of the present invention that can be suitably used for the strength recovery method has a configuration for keeping the relative relationship between the induction heating coil and the strength deteriorated portion to be heated, in addition to the induction heating coil. It has a gist in that it has.

  The high-frequency induction heating apparatus includes at least two induction heating coils, and one induction heating coil and the other induction heating coil that are adjacent to each other are inductive while maintaining a relative relationship between the strength deterioration portion to be heated. You may connect so that the relative relationship between heating coils can be adjusted. It is preferable that the at least two induction heating coils are arranged with a current-carrying polarity in which the current-carrying directions of the conductors located on the side close to the adjacent coil are the same direction.

  According to the present invention, on-site repair is possible by heating the strength-degraded portion to a predetermined temperature or higher using a heating device such as a high-frequency induction heating device. In addition, by maintaining for a certain period of time in the heated state, the precipitated carbide can be re-dissolved, the refined crystal grains can be recovered, or the coarsened crystal grains can be recovered, or the strength is low. For example, it is possible to increase the strength of the ferrite structure, for example, by changing the ferrite structure to a bainite structure having high strength, and to recover the strength of the strength-degraded portion.

  When heating the strength-degraded part, for example, a high-frequency induction heating device can be used. In particular, the high-frequency induction heating device of the present invention has a configuration for keeping the relative relationship between the induction heating coil and the strength deteriorated portion to be heated constant, so that the strength deteriorated portion is heated intensively and uniformly. And the strength of the strength-degraded portion can be reliably recovered.

  As described above, the strength deterioration of steel members is caused by precipitation of carbides by exposure to high temperature and high pressure, or by coarsening and softening of carbides, or by refinement of crystal grains when repair welding is performed. appear. In addition, depending on the cooling rate at the time of manufacture, a ferrite structure having a low strength is generated in the bainite structure, so that there is a portion where the strength of the member is originally low.

Therefore the present inventors have studied how to recover the strength of the strength deteriorated part, if heated and held at A ₃ transformation point or above the temperature of the steel member, precipitation (or precipitated coarsening) the carbides solid Can be melted, or the refined crystal grains can be recovered (or the coarsened crystal grains can be recovered), or the ferrite structure can be bainite, and the strength of the strength-deteriorated portion can be reduced before deterioration (ie, It was found to recover to the same level as the strength of the new material.

The temperature at which the strength-degraded part is heated is a solid solution of carbide precipitated (or precipitated and coarsened) in the strength-degraded part, or recovery of refined crystal grains (or recovery of coarse crystal grains). if the temperature at which it is better, specifically, it is preferable to more a ₃ transformation point of the steel material to be heated. It is preferably “A ₃ transformation point + 50 ° C.” or more, more preferably “A ₃ transformation point + 100 ° C.” or more. The upper limit of the heating temperature is not particularly limited, but is about 1200 ° C. As the temperature of the A ₃ transformation point may be based on the temperature of A _c3 transformation point.

The A ₃ transformation point of a steel material can be obtained from the heating-expansion curve of a heated sample using, for example, a diameter change following He-Ne gas laser attached to a hot working reproduction apparatus (machining for master). Good.

  When the strength deteriorated portion is heated and held, the carbide precipitated (or precipitated and coarsened) in the strength deteriorated portion can be dissolved, or the refined crystal grains are recovered (or coarsened crystal grains). For example, a ferrite structure having a low strength such as a ferrite structure may be converted into a high strength such as a bainite structure. As one guideline, the crystal grain size number may be set appropriately so as to be comparable to that of the new material. However, the specific holding time cannot be uniformly defined because it depends on the type (composition) of the steel material to be heated, the degree of strength deterioration, or how much the strength is recovered. It should be noted that the heating temperature and holding time have a great influence on the solid solution of carbides, recovery of crystal grains, and structure control. When the heating temperature is increased, solid solution of carbides, growth of crystal grains, or transformation of the structure occurs. Because it is promoted, the holding time can be shortened.

  When the type of steel material to be heated is, for example, Cr—Mo—V cast steel generally used as a casing material for a high and medium pressure turbine of a thermal power plant, the holding time may be at least 5 seconds. The holding time may be, for example, 1 minute or longer, or 10 minutes or longer. The upper limit of the holding time is not particularly limited, but is about 8 hours (particularly about 5 hours), for example, because the strength recovery effect such as growing crystal grains is saturated even when heated for a long time.

  It is a well-known fact that tempering after heating and holding. In the case of tempering, for example, it is recommended to temper by holding at about 690 ° C. for about 5 to 8 hours, or at about 710 ° C. for about 3 hours.

  As a result of heating and holding the strength deteriorated portion as described above, the crystal grain size is preferably within ± 40% with respect to the crystal grain size of the new material. If the crystal grain size is within ± 40%, it can be considered that the strength has recovered to almost the same level as the new material. The crystal grain size is preferably within ± 20%.

  The crystal grain size may be compared by the crystal grain size number. The crystal grain size number can be measured, for example, by a method defined in “Method for testing austenite grain size of steel” in JIS G0551.

  In the present invention, unlike the Patent Document 1 introduced above, it is not necessary to constrain the strength degradation portion. In the present invention, the strength of the strength deteriorated portion is recovered by increasing the strength of the structure such as solid solution of the carbide in the strength deteriorated portion, growth / control of crystal grains, or bainite of the ferrite structure. This is because, for example, as described in Patent Document 1, it is not a technique for pressing a void or a crack by constraining a strength-degraded portion.

  The strength deterioration portion may be heated and held at a predetermined temperature using a heating device. As the heating device, for example, a sheath heater or a high-frequency induction heating device can be used. By using a sheath heater or a high-frequency induction heating device, on-site repair is possible, and it is possible to recover the strength in a very short time without stopping the equipment to be repaired or even if the equipment is stopped. Because it becomes. For example, it is possible to remove the strength deteriorated part from the equipment and repair it by heating and holding it with an electric furnace, etc., and then repairing it by welding to the original equipment. become longer. In addition, when the equipment is renewed, much more cost and time are required, but if the strength deteriorated part is heated and recovered using a sheath heater or a high frequency induction heating device, the cost can be reduced. Become. By using a sheath heater or a high-frequency induction heating device, it is possible to select only the strength-deteriorated portion and perform pinpoint repair, thereby improving the repair efficiency. That is, if a sheath heater or a high-frequency induction heating device is attached to the strength deterioration portion and heated and held, only the strength deterioration portion can be locally heated. As the heating device, it is preferable to use a high-frequency induction heating device.

  In the present invention, the strength deteriorated part is, for example, a welded part (particularly, a heat affected part), a high temperature / It means a part that has been used under high pressure for a long time and has been damaged by creep, a part that has become brittle, or a part that has been fatigued. In addition, the strength of the repair welded portion of these portions and the heat-affected zone are also reduced and included in the strength-degraded portion of the present invention. Further, a structure having a low strength is generated in a structure having a high strength due to a cooling rate at the time of manufacture, and a portion where the strength is lowered is also included in the strength deteriorated portion of the present invention.

  The strength deterioration portion can be detected by, for example, measuring the hardness of a steel member or observing the structure by a replica method.

  Regarding the relationship between the hardness and the strength deteriorated portion, it is known that there is a relatively good correlation between the hardness and strength of the material, and when the strength decreases, the hardness decreases. Therefore, in the method of measuring the hardness of the material and detecting the strength-degraded portion, the Vickers hardness of the steel member is measured in the field, and if it is lower than the initial Vickers hardness of the member, the strength is deteriorated. It can be judged. At this time, if a calibration curve showing the relationship between hardness and strength is obtained in advance, the degree of strength reduction can be obtained by measuring the hardness, and the remaining life of the steel member can be predicted.

  On the other hand, in the method of detecting the strength degradation portion by observation of the structure by the replica method, the remaining life of the steel member can be predicted by transferring the metal structure to a film and observing the precipitation state of carbides and the occurrence of voids.

  Next, among the heating devices that can be used to recover the strength of the strength-degraded portion, a high-frequency induction heating device will be described as a heating device that can be suitably used. The high-frequency induction heating device of the present invention is characterized in that, in addition to the induction heating coil, a structure for keeping the relative relationship between the induction heating coil and the strength deteriorated portion to be heated constant is provided. . By providing a configuration for keeping the relative relationship between the induction heating coil and the strength deterioration portion to be heated constant, the strength deterioration portion can be heated and held at a predetermined temperature for a predetermined time.

  The relative relationship between the induction heating coil and the strength deteriorated portion to be heated means both the position and the distance between the induction heating coil and the strength deteriorated portion to be heated. That is, the relative relationship is that the induction heating coil is disposed at a relative position where the strength deterioration portion can be appropriately heated, and the strength deterioration portion can be heated at an appropriate temperature when the induction heating coil is energized. And adjusting the relative distance between the strength deteriorated portion to be heated. The relative position at which the strength-degraded part can be heated appropriately means that the position to be heated is included in the projected image of the induction heating coil when the shape of the induction heating coil is projected onto the member to be heated. means. As for the position of the induction heating coil and the strength deteriorated portion to be heated, the induction heating coil may be disposed above the strength deteriorated portion so as to cover the strength deteriorated portion. The distance to the part cannot be defined uniformly. This is because the distance must be adjusted depending on the temperature to be heated and the shape of the object to be heated.

  As a configuration for keeping the relative relationship between the induction heating coil and the strength deteriorated portion to be heated constant, for example, a member (jig) that can keep the distance from the strength deteriorated portion constant is used as the induction heating coil. You should prepare for.

  Hereinafter, the high-frequency induction heating apparatus of the present invention having a configuration for keeping the relative relationship between the induction heating coil and the strength deterioration portion to be heated constant will be described more specifically with reference to the drawings. However, the drawings shown below are not intended to limit the present invention, and can be appropriately changed in design within a range that can be adapted to the gist of the preceding and following descriptions, both of which are within the technical scope of the present invention. include.

  Fig.1 (a) is a schematic explanatory drawing which shows the example of 1 structure of the high frequency induction heating apparatus of this invention, (b) is the figure which expanded a part of said (a). In the high-frequency induction heating apparatus shown in FIG. 1 (a), when the form of the material 2 to be heated is mainly flat (for example, when it is flat like the wall or bottom of equipment, it is curved) This is a device that can be suitably used for a part of the above. The form of the material to be processed 2 may be a curved surface having a curved surface.

  In FIG. 1, reference numeral 1 denotes a high-frequency induction heating device, 2 denotes a material to be heated, and the high-frequency induction heating device 1 is held so as to cover the strength deterioration portion 21. The high-frequency induction heating apparatus 1 includes a rectangular induction heating coil 11 and a jig 12 for keeping a constant distance between the induction heating coil 11 and the strength deterioration portion 21 to be heated.

  An enlarged view of the jig 12 is shown in FIG. The jig 12 includes a spacer 12a for keeping the distance between the induction heating coil 11 and the workpiece 2 to be heated constant, a connecting member 12b for connecting the spacer 12a and the induction heating coil 11, It is comprised from the volt | bolt 12c for fixing the spacer 12a and the connection member 12b, and the jig | tool 12 is connected to the induction heating coil 11 with the volt | bolt etc. which are not shown in figure.

  As shown in FIG. 1A, the jig 12 and the material to be processed 2 are brought into close contact with each other, so that the distance between the induction heating coil 11 and the material to be processed 2 can be fixed and kept for a long time. It becomes possible to do. Therefore, by supplying a current to the induction heating coil 11 from a power source (not shown), the workpiece 2 can be heated locally and stably for a long time.

  You may comprise the said jig | tool 12 so that the length can be changed. This is because the distance between the induction heating coil 11 and the workpiece 2 is changed as necessary. The material of the spacer 12a may be a material that is not heated by the induction heating coil 11, that is, a non-conductive material. For example, ceramic can be used. A heat resistant resin may also be incorporated.

  FIG. 2A is a schematic explanatory view showing another configuration example of the high-frequency induction heating device of the present invention, and FIG. 2B is a cross-sectional view of the above-described (a) when viewed from the AA ′ direction. . The same parts as those in FIG.

  The high-frequency induction heating apparatus 1 shown in FIG. 2A has a configuration in which the material to be treated 3 to be heated is mainly tubular (for example, piping provided in equipment) and has a particularly large diameter. It can be used suitably. In FIG. 2, reference numeral 1 denotes a high-frequency induction heating device, 3 denotes a material to be heated, and the high-frequency induction heating device 1 has a strength detected on the wall surface of the tubular material 3 that extends in the lateral direction. It is held so as to surround a deteriorated portion (not shown). As this strength deterioration part, the part (circumferential direction welding part) etc. which welded and joined the tubular steel members mutually are mentioned, for example.

  The high-frequency induction heating apparatus 1 includes a semicircular induction heating coil 11a and a semicircular induction heating coil 11b (collectively referred to as the induction heating coil 11) so as to surround the large-diameter tubular workpiece 3. Are arranged so as to be substantially circular. In addition, the semicircular induction heating coil 11a and the semicircular induction heating coil 11b are deteriorated in strength to be heated in the direction of the central axis of the substantially circular induction heating coil 11 configured by combining them. A jig 12 is provided for maintaining a constant distance from the part.

  The induction heating coil is connected via an insulating material 13 so that the feeding-side ends of the induction heating coil 11a and the induction heating coil 11b do not contact and short-circuit. Moreover, the high frequency induction heating apparatus 1 is fixed to an equipment main body (not shown) using a fixing base 5 in order to securely fix it in the vicinity of the strength deterioration portion.

  As shown in FIG. 2 (a), the induction heating coil 11 can be fixed while keeping the distance between the induction heating coil 11 and the material to be processed 3 constant by bringing the jig 12 and the material to be processed 3 into close contact with each other. It can be held for a long time. Therefore, by supplying a current to the induction heating coil 11 from a power source (not shown), the material 3 can be heated locally and stably for a long time.

  The material of the insulating material 13 may be a material that is not heated by the induction heating coil 11, that is, a non-conductive material, and may be a material similar to the jig 12.

  In FIG. 2, the fixed base 5 is used to fix the high-frequency induction heating device 1, but a wheel or the like may be attached to the fixed base 5 and movable along the tubular workpiece 3. If the high-frequency induction heating device 1 placed on the fixed base 5 is moved at a constant speed, a wide range of heat treatment can be performed.

  FIG. 3A is a schematic explanatory view showing another configuration example of the high-frequency induction heating device of the present invention, and FIG. 3B is a cross-sectional view of the above-mentioned (a) when viewed from the BB ′ direction. . The same parts as those in FIG. In FIG. 3, reference numeral 1 denotes a high-frequency induction heating device, 6 denotes a material to be heated, and the high-frequency induction heating device 1 is detected on the wall surface of a tubular material to be processed 6 extending in the vertical direction. It is held so as to surround a deteriorated portion (not shown). As this strength deterioration part, the part (circumferential direction welding part) etc. which welded and joined the tubular steel members mutually are mentioned, for example.

  The high-frequency induction heating apparatus 1 shown in FIG. 3A is suitable when the form of the material to be treated 6 to be heated is mainly tubular (for example, piping provided in equipment) and particularly has a small diameter. Can be used.

  The high-frequency induction heating apparatus 1 includes a semicircular induction heating coil 11a and a semicircular induction heating coil 11b (collectively referred to as the induction heating coil 11) in order to surround the small diameter tubular workpiece 6. Are arranged so as to be substantially circular. Further, the semicircular induction heating coil 11a and the semicircular induction heating coil 11b are circumferentially heated in the direction of the central axis of the substantially circular induction heating coil 11 configured by combining them. A jig 12 is provided for maintaining a constant distance from the strength deteriorated part such as a welded part.

  The high-frequency induction heating device 1 is connected to a clamp 7 provided below the high-frequency induction heating device 1 via a connection member 8 in order to reliably fix the high-frequency induction heating device 1 in the vicinity of the strength deterioration portion.

  As shown in FIG. 3A, the jig 12 and the material to be processed 6 are brought into close contact with each other, so that the distance between the induction heating coil 11 and the material to be processed 6 can be fixed and kept for a long time. It becomes possible to do. Therefore, by supplying a current to the induction heating coil 11 from a power source (not shown), the workpiece 6 can be heated locally and stably for a long time.

  The material of the connecting member 8 that fixes the induction heating coil 11 to the clamp 7 may be a material that is not heated by the induction heating coil 11, that is, a non-conductive material, and may be a material similar to the jig 12.

  In FIG. 3, the clamp 7 is used to fix the high-frequency induction heating device 1, but the clamp 7 may be configured to move along the tubular workpiece 6. A wide range can be heat-treated by moving the high-frequency induction heating device 1 at a constant speed.

  The high-frequency induction heating device may include two or more induction heating coils. When two or more induction heating coils are provided, the adjacent one of the induction heating coil and the other induction heating coil maintain a relative relationship with the strength deterioration portion to be heated, while maintaining a relative relationship between the induction heating coils. It is preferable to be connected so that the relationship can be adjusted. The relative relationship between the induction heating coils means the distance between the induction heating coils and the displacement with respect to the strength deterioration portion. That is, when two or more induction heating coils are provided, the distance between the induction heating coils is appropriate so that heating unevenness does not occur when the strength deteriorated portion is heated, and the strength deteriorated portion can be heated at a uniform temperature. It is necessary to adjust to. In addition, when the induction heating coil has a planar shape as shown in FIG. 4 to be described later, for example, when the strength deterioration portion to be heated has a curved surface, so as to follow the shape of the strength deterioration portion, What is necessary is just to adjust the displacement of each induction heating coil so that the relative relationship between the induction heating coil and the strength deterioration portion becomes constant.

  Below, the example of a structure when two or more induction heating coils are connected is demonstrated. FIG. 4 is a schematic explanatory view showing another configuration example of the high-frequency induction heating device of the present invention, in which a rectangular induction heating coil 11 c and a rectangular induction heating coil 11 d are connected using a connecting member 14. Yes. FIG. 4 does not show a jig for keeping the distance between the induction heating coil and the strength deteriorated portion to be heated constant. In addition, the rectangular induction heating coils 11c and 11d have a configuration in which a core material is interposed between the reciprocating circuit conductors constituting these coils. By arranging the core material with the magnetic flux converging function, the magnetic flux generated around the reciprocating circuit conductor is focused on the core material with the same polarity, thereby preventing induction heating heat input from being reduced due to cancellation of the magnetic flux. it can. As the core material, for example, a solid body of an iron-based oxide commonly called ferrite, or a ferromagnetic material such as a silicon steel plate can be used.

  The rectangular induction heating coils 11c and 11d are fixed to the connecting member 14 with bolts. The connecting member 14 is provided with a slit 14a, and the distance between the rectangular induction heating coils 11c and 11d and the like. The inclination between coils can be adjusted freely.

  Although FIG. 4 shows an example in which two rectangular induction heating coils are connected, the present invention is not limited to this configuration, and three or more rectangular induction heating coils may be connected. FIG. 5 shows a configuration example when three rectangular induction heating coils (11c to 11e) are connected. Note that FIG. 5 does not show a jig for keeping the distance between the induction heating coil and the strength deterioration portion to be heated constant.

  As shown in FIG. 4 and FIG. 5, when two or more induction heating coils are connected, it is preferable that the magnetic fluxes formed by the respective induction heating coils are arranged in the same direction and energized. . For example, a current may be passed in the direction of the arrow attached to the induction heating coil in the figure. This is because by making the magnetic flux formed by energization the same direction, the cancellation of the magnetic flux can be reduced and the heating efficiency can be increased. This will be described in more detail with reference to the drawings.

  FIG. 6 shows a cross-sectional view of the induction heating coil when rectangular induction heating coils 15A and 15B are arranged adjacent to each other as shown in FIG. In FIG. 6, arrows indicate the magnetic flux generated when the induction heating coil is energized and the direction thereof.

  When the induction heating coil itself is not provided with a core material, the magnetic fluxes generated when the induction heating coils 15a and 15b are energized cancel each other as shown in 15A of FIG. If the core material 15f is provided in itself, the cancellation of the magnetic flux can be prevented as shown by 15B in FIG.

  As described above, the rectangular induction heating coil itself can be configured by arranging the core material 15f between the reciprocating circuit conductors. However, in order to arbitrarily adjust the positioning between the rectangular induction heating coils. In addition, the core material cannot be interposed. Therefore, when adjacent rectangular induction heating coils are passed through the two conductors constituting the electric circuit on the side close to the adjacent coil so that the currents are in opposite directions, FIG. As shown, the magnetic flux around the conductors generated by energization cancels each other, and as a result, induction heating heat input is reduced.

  Therefore, when two or more induction heating coils are connected, as shown by arrows in the induction heating coils shown in FIGS. 4 and 5, the energization polarity to adjacent rectangular induction heating coils (ie, For each coil, it may be set so that the currents flowing in the two conductors constituting the electric circuit near the adjacent coil are in the same direction. That is, as shown in FIG. 6 (c), if the currents flowing through the induction heating coils 15b and 15c constituting the electric circuit close to the adjacent coil are set to be in the same direction, the circumference of the conductor generated by energization Are added together, and as a result, induction heating heat input is increased.

  FIG. 7 shows an example of an embodiment of the present invention, and shows an example applied to a header 9 such as a boiler. 7A is a schematic explanatory view, and FIG. 7B is a cross-sectional view of FIG. 7A viewed from the C-C ′ direction. In FIG. 7, a jig for keeping the distance between the induction heating coils 11f and 11g and the strength deterioration portion 92 to be heated constant is not shown. The header 9 illustrated in FIG. 7 has a circular cross section, but may have a rectangular cross section.

  In FIG. 7, a header 9 is a container that collects a large number of pipes and distributes the flow or merges the flows, and a nozzle 91 for attaching the pipes is attached by welding. The welded portion 92 at the base portion of the nozzle 91 and the heat-affected zone have finer crystal grains and lower strength. In addition, there are portions where the crystal grains are coarsened, and depending on how the stress is applied, there are cases in which damage occurs. Therefore, in the present invention, as shown in FIG. 7, induction heating coils 11 f and 11 g are provided in the vicinity of the welded portion 92 and its heat-affected zone so as to keep the relative relationship with the welded portion 92 constant. What is necessary is just to heat the vicinity.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

Example 1
A simulation experiment was conducted using a high-temperature reduction reactor instead of a high-frequency induction heating device to determine how much the crystal grains grow when the strength deteriorated portion is heated and held.

  In a thermal power generation facility, a sample cut out from a high and medium pressure turbine used for about 20 years in an environment of about 400 ° C. or higher (hereinafter sometimes referred to as casing waste) is heated and held using a high temperature reduction reactor, The change in crystal grain size before and after heating was measured. Further, the hardness was measured in order to examine the change in strength before and after heating.

  In the above sample, C is 0.15% by mass, Si is 0.47% by mass, Mn is 0.62% by mass, P is 0.009% by mass, S is 0.009% by mass, and Cr is 1.15% by mass. Cr-Mo-V cast steel containing 1.0% by mass, Mo by 1.02% by mass, V by 0.08% by mass, Ni by 0.13% by mass and Cu by 0.14% by mass with the balance being iron and inevitable impurities This sample was processed into a test piece having a shape of φ8 mm × 12 mm and heat-treated under the conditions shown in Table 1 below using a hot processing reproduction device (processing for master). Table 1 also shows the heating rate from room temperature to heating temperature and the cooling rate from heating temperature to room temperature.

A ₃ transformation point of the sample is hot-working reproduction apparatus heated with a diameter change-following He-Ne gas laser that comes with (working Foamaster) - seeking expansion curve, the steel material from this curve Ac ₃ transformation point was determined. In addition, No. 1 in Table 1 below. In 3 to 8, the heating temperature was too low, so the Ac ₃ transformation point could not be measured.

  After the heating and holding, the steel was held at 690 ° C. for 5 hours in an argon gas atmosphere, and was subjected to stress removal annealing, and then cooled to room temperature.

  The cross section is exposed by dividing into two in the longitudinal direction so as to pass through the central axis of the obtained test piece, one of which is polished and etched with a 3% by mass nital solution, and then the microstructure is observed 400 times with an optical microscope did. A photograph of the microstructure was taken, and the grain size number was measured in comparison with the grain size standard chart defined in “Method for testing austenite grain size of steel” in JIS G0551. In addition, it measured similarly about the particle size number of a new material (No. 1), and the particle size number of the casing waste material before heat processing (No. 2). The measurement results are also shown in Table 1 below.

  Moreover, the graph which shows the relationship between heating temperature and a particle size number is shown as FIG. In FIG. 8, ◇ indicates an example in which the holding time is 6 seconds, □ indicates an example in which the holding time is 60 seconds, and Δ indicates an example in which the holding time is 600 seconds.

  Moreover, the hardness of the obtained test piece was measured using the Vickers hardness meter. The hardness was measured at three locations, and the results were averaged. In addition, it measured similarly about the particle size number of the casing waste material before heat processing, and the particle size number of a new material. The measurement results are also shown in Table 1 below. Moreover, the graph which shows the relationship between heating temperature and Vickers hardness is shown as FIG. In FIG. 9, ◇ indicates an example in which the holding time is 6 seconds, □ indicates an example in which the holding time is 60 seconds, and Δ indicates an example in which the holding time is 600 seconds.

  As is apparent from Table 1 and FIG. 8, the higher the heating temperature or the longer the holding time, the more the crystal grains grow and the particle size number becomes smaller. Further, as apparent from Table 1 and FIG. 9, the higher the heating temperature or the longer the holding time, the harder it is, indicating that the hardness has been recovered by heating and holding. This is considered to be because the higher the heating temperature or the longer the holding time, the more the transformation to austenite proceeds, and the more the transformation amount from austenite to bainite or martensite increases during cooling. Note that there is a correlation between the hardness of the material and the creep strength, and it is generally known that the higher the hardness, the higher the creep strength.

Example 2
A creep test was performed using a test piece cut out from the casing waste material used in Example 1 above. As a test piece, No. shown in Table 2 below. 21-30 were used.

  No. 21 is data calculated by calculating the average creep strength at each test stress from the creep test data of the new material shown in FIG. No. In Nos. 22 to 26, a creep test was performed using a heat-treated test piece cut out from the casing waste material. The heat treatment is performed by heating to 1100 ° C. in a high-temperature reduction reactor and holding at this temperature for 8 hours or 10 minutes, and then cooling to room temperature (AC; cooling rate is about 1000 ° C./hour) or holding 350 After gradually cooling to 0 ° C. (cooling rate is about 200 ° C./hour), it was air-cooled and then tempered by heating at 690 ° C. for 8 hours (No. 22, 23, 25, 26). In addition, after heating to 1100 ° C. with a high-frequency induction heating device and holding at this temperature for 4 minutes or 1 hour, air cooling to room temperature (AC; cooling rate is about 1000 ° C./hour) or holding, then 350 ° C. (Cooling rate is about 200 ° C./hour), then air-cooled, and then tempered by heating at 690 ° C. for 8 hours (No. 24, 27).

  No. 28, the casing waste material is heated to 1100 ° C. with a high-frequency induction heating device, held at this temperature for 1 hour, then gradually cooled to 350 ° C. (cooling rate is about 200 ° C./hour), then air-cooled, For a sample tempered by heating at 690 ° C. for 8 hours, when the shape of the high-frequency induction heating coil is projected onto the casing waste material, it includes the boundary between the portion where the shape of the high-frequency induction heating coil is projected and the portion where it is not projected A creep test was carried out using what was cut out as described above. No. In 29, the above-mentioned casing waste materials were welded together, and a creep test was performed using a sample cut out so as to include a welded joint and a heat-affected zone. No. In No. 30, a creep test was performed using a sample in which the casing waste material was heat-treated and the crystal grain size was adjusted to about 10 to 30 μm in order to simulate the structure in the weld heat affected zone (fine grain region reproduction material).

The test stress in the creep test was 8 kgf / mm ² , 12 kgf / mm ² or 20 kgf / mm ² . From the result of the creep test, the Larson-Miller parameter (LMP) was calculated using the following formula (1). The calculation results are shown in Table 2 below. The relationship between LMP and stress is shown in FIGS. FIG. 21 and no. As a result of Nos. 22 to 24, FIG. 21 and no. As a result of 25-27, FIG. 21 and no. The results of 28 to 30 are shown respectively. In the following formula (1), T is a test temperature (° C.), tr is a fracture time (h), and 20 is a material constant.
LMP = (T + 273) × (logtr + 20) (1)

  In addition, the creep test was performed using various new materials, the Larson-Miller parameter was calculated, and the relationship with the stress was plotted. 25 and No. A graph in which the results of 26 are plotted is shown in FIG. In FIG. 25 (1100 ° C., 8 hr, slow cooling). 26 results (1100 ° C., 10 min, slow cooling) are shown.

  As is apparent from Table 2 and FIGS. 10 to 13, it can be seen that the creep strength of the casing waste material is restored to the level of the new material in the case of heating and holding (No. 22 to 27).

  In particular, as is apparent from FIGS. 10 and 13, the creep strength when the casing waste is heated and held for 4 minutes (No. 24) and when heated and held for 10 minutes (No. 23) is the lower limit of the creep strength of the new material. It turns out that it recovers to the extent. On the other hand, it can be seen that the creep strength when the casing waste material is heated and held for 8 hours (No. 22) recovers to the upper limit of the creep strength of the new material.

  As can be seen from FIGS. 11 and 13, the creep strength when the casing waste material is heated and held for 10 minutes (No. 26) is restored to the lower limit of the creep strength of the new material. On the other hand, it can be seen that the creep strength when the casing waste material is heated and held for 1 hour (No. 27) and when it is heated and held for 8 hours (No. 25) recovers to the upper limit of the creep strength of the new material.

  Comparing FIG. 10 and FIG. 11, it can be seen that the creep strength is higher in the case of slow cooling than in the case of air cooling after heating and holding. This is thought to be due to the formation of an upper bainite structure having a high creep strength, although a ferrite structure having a low creep strength is formed in part when the cooling is performed while air cooling results in a structure close to martensite.

  As is apparent from FIGS. 11 to 13, the creep strength of the high-frequency heat treatment boundary (No. 28) is similar to the creep strength when the casing waste material is heated and held for 10 minutes (No. 26). It can be seen that the creep strength recovers to the lower limit. On the other hand, the creep strength of the welding material (No. 29) and the fine grain region reproduction material (No. 30) are comparable and are found to be remarkably low.

  No. above. 25 and No. FIG. 13 shows the result of the creep strength of 26 and the result of the individual creep strength of the new material. As is apparent from FIG. 13, the creep strength when the casing waste is heated and held for 8 hours (No. 25) has recovered to the upper limit of the creep strength of the new material, and the casing waste is heated and held for 10 minutes. It can be seen that the creep strength of (No. 26) has recovered to the lower limit of the creep strength of the new material.

(A) of FIG. 1 is a schematic explanatory drawing which shows one structural example of the high frequency induction heating apparatus of this invention, (b) is the figure which expanded a part of (a). FIG. 2A is a schematic explanatory view showing another configuration example of the high-frequency induction heating device of the present invention, and FIG. 2B is a cross-sectional view of FIG. 2A when viewed from the AA ′ direction. . FIG. 3A is a schematic explanatory view showing another configuration example of the high-frequency induction heating device of the present invention, and FIG. 3B is a cross-sectional view of the above-described (a) when viewed from the BB ′ direction. is there. FIG. 4 is a schematic explanatory view showing another configuration example of the high-frequency induction heating device of the present invention. FIG. 5 is a schematic explanatory view showing another configuration example of the high-frequency induction heating device of the present invention. FIG. 6 is a diagram schematically illustrating a magnetic flux generated when two rectangular induction heating coils are arranged adjacent to each other and energized. FIG. 7A is a schematic explanatory view showing an example of an embodiment of the present invention, and FIG. 7B is a cross-sectional view of FIG. 7A viewed from the C-C ′ direction. FIG. 8 is a graph showing the relationship between the heating temperature and the particle number. FIG. 9 is a graph showing the relationship between the heating temperature and the Vickers hardness. FIG. 10 is a graph showing the results of the creep test. FIG. 11 is a graph showing the results of a creep test. FIG. 12 is a graph showing the results of a creep test. FIG. 13 is a graph showing the results of a creep test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High frequency induction heating apparatus 11 Induction heating coil 12 Jig 12a Spacer 12b Connection member 12c Bolt 13 Insulation material 14 Connection member 14a Slit 2 Material to be processed 21 Strength degradation part 3 Material to be processed (large diameter) Tubular material to be treated)
5 Fixing base 6 Material to be heated (tubular material with small diameter)
7 Clamp 8 Connection member 9

Claims (6)

It is a method of recovering the strength of the strength deterioration part of the equipment configured using steel members,
Strength recovery method of the intensity degradation unit for the said intensity deteriorated part, characterized in that to restore the strength by heating maintained at A ₃ transformation point or above the temperature of the steel member.   The strength recovery method according to claim 1, wherein the strength deterioration portion is heated using a high frequency induction heating device.   The strength recovery method according to claim 1 or 2, wherein the strength deteriorated portion is a portion including a welded portion between steel materials and a heat affected zone thereof.   It is a high frequency induction heating apparatus used for the strength recovery method according to any one of claims 1 to 3, wherein the apparatus is provided with a relative relationship between the induction heating coil and the strength deterioration portion to be heated, in addition to the induction heating coil. A high frequency induction heating apparatus comprising a configuration for maintaining a constant relationship.   The high-frequency induction heating apparatus includes at least two induction heating coils, and one induction heating coil and the other induction heating coil that are adjacent to each other are inducted while maintaining a constant relative relationship with a strength deterioration portion to be heated. The high frequency induction heating device according to claim 4, wherein the relative relationship between the heating coils is connected to be adjustable.   The high-frequency induction heating device according to claim 5, wherein the at least two induction heating coils are arranged with a current-carrying polarity in which the current-carrying directions of conductors located on the side close to the adjacent coil are the same direction.

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