JP4176412B2 - Method and apparatus for regenerating creep degraded part - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a portion deteriorated by creep damage in a thermal / nuclear power plant or chemical plant, particularly a welded part and a base material, for example, a high-temperature pressure-resistant welded part of a boiler or a turbine, a high-temperature pipe, a header, a nozzle or the like. The present invention relates to a method and an apparatus for regenerating a creep deteriorated portion of a material.
[0002]
[Prior art]
In recent years, for example, in thermal power plants, maintenance management that takes into account the deterioration of equipment due to long-term use, thermal fatigue due to frequent start / stop, rapid load fluctuations, etc. is becoming more and more important as the operation time becomes longer. It is becoming. For example, in large-diameter thick-walled pipes that use high-temperature pressure-resistant metal members, scratches such as cracks often occur inside the weld. In order to detect this wound early, nondestructive inspection such as tissue inspection and ultrasonic inspection is regularly performed.
[0003]
[Problems to be solved by the invention]
As a result of such periodic inspection, the remaining life of the creep deteriorated part is not until the next periodic inspection (usually 2 years, 4 years in the case of period extension) in welded parts and base materials that have deteriorated due to long-term use. If it is determined, the following measures will be taken.
[0004]
(1) For thick-walled large-diameter pipe welds a. The principle is replacement: replacement within the regular inspection period is difficult because the material arrangement takes a long time (eg several months). For this reason, the following emergency measures are taken.
b. Attaching the reinforcing plate: If the replacement is not possible, attach the reinforcing plate to the creep deteriorated part as soon as possible. However, a thick member such as the main steam pipe has a problem that the thickness of the reinforcing plate must be increased. Moreover, in order to attach a reinforcement board by welding, annealing after welding is required.
c. Repair welding: When repairing welds where creep has deteriorated, repair welding is carried out after removing the creep damage to some extent, but damage such as creep voids at the part cannot be completely removed. Since damage such as creep voids that could not be removed due to stress or the like may be accelerated, there is a problem that the practicality is poor. That is, since repair welding can generally be performed only at a depth of 0.2 t of the thickness t of the base material, damage such as creep voids at deeper portions cannot be completely removed. Then, due to the difference in strength (referred to as “mismatch”) between the repair weld (high strength) and the deteriorated part (weak strength) that could not be repair welded, the boundary between them was cracked. Since the crack was accelerated by thermal stress, it was not practical.
d. Crack progress monitoring: An electrode is attached to the creep-degraded part, and the progress of cracks is regularly monitored by the electric resistance method. In this case, it can be operated to the limit of the life, but the life cannot be extended.
[0005]
(2) In the case of a base material A damaged member, for example, a header of a header is replaced in principle. However, it is necessary to interrupt the operation of the equipment for the replacement, and the replacement requires a work period and a large cost. However, if the number of replacements is large and the material is not in stock, some of the members that have no lifetime remain until the next periodic inspection. In this case, refreshing (being welded after crack removal and R finishing, annealing) is performed. And it is necessary to monitor the life by the life inspection by the inspection at an appropriate time before the next periodic inspection.
[0006]
The present invention has been made in view of the circumstances described above, and an object of the present invention is to provide a method and an apparatus for regenerating a creep deteriorated part that can easily extend the life.
[0007]
[Means for Solving the Problems]
The present invention according to claim 1 is a method for regenerating a creep deteriorated portion, wherein after restraining thermal expansion of the creep deteriorated portion generated during heating before heating , the creep deteriorated portion to be regenerated is It is characterized in that after the A3 transformation point is repeatedly heated three times or more and then returned to room temperature, regenerative heat treatment is performed using pressure due to thermal expansion generated by heating the creep deteriorated portion.
[0008]
According to this means, in the state in which the expansion of the creep deteriorated portion is constrained, the internal pressure of the thermal expansion generated by heating the creep deteriorated portion is used to press the creep void / crack and repair and prolong the life. Can be achieved. A jig may be used to constrain the expansion of the creep deteriorated portion. However, if the creep deteriorated member itself is large, the expansion of the heated part is constrained by the unheated part. It can be unnecessary.
According to this means, the creep void / crack can be pressed and repaired more effectively by heating to the A3 transformation point or higher. That is, when the creep deteriorated part is a high-temperature pressure-resistant welded part, the hardened structure such as the HAZ part ( weld heat affected zone ) becomes a structure equivalent to the base material, and the damage progress rate is slow. Furthermore, precipitates and segregated impurities are confined in the new grain boundaries by the newly generated grain boundaries, and the crack propagation rate is slowed and the damage growth rate is slowed. On the other hand, in the case where the creep deteriorated part is the base bulge part of the header nozzle and the outer peripheral part of the pipe bent part, the deteriorated base material is heated to an appropriate temperature above the A3 transformation point. The structure of the part can be made the same structure as that of the unused material to extend the life. By repeating the heat treatment in the vicinity of the A3 transformation point, it is possible to more effectively confine precipitates and impurity segregates within new grain boundaries.
[0009]
According to a second aspect of the present invention, in the method of the first aspect, the creep deteriorated portion to be regenerated is a high temperature pressure resistant welded portion.
[0010]
According to this means, in particular, by using the internal pressure of thermal expansion generated by heating the high-temperature pressure-resistant welded part where the creep degradation has progressed the most, the creep voids and cracks are pressed and repaired to extend the life. Can do.
[0011]
According to a third aspect of the present invention, in the method according to the first aspect, the creep deteriorated portion to be regenerated is a root bulge portion of the nozzle head.
[0012]
According to this means, in particular, as with the high temperature pressure resistant welded portion, the creep void is utilized by utilizing the internal pressure of the thermal expansion generated by heating the root bulge portion of the header nozzle where the creep deterioration has progressed most.・ It is possible to prolong the life by pressure welding and repairing cracks.
[0013]
According to a fourth aspect of the present invention, in the method of the first aspect, the creep deteriorated portion to be regenerated is an outer peripheral portion of a pipe bending portion.
[0014]
According to this means, in particular, the internal pressure of the thermal expansion generated by heating the outer peripheral portion of the bent portion of the pipe where the creep degradation has progressed most, like the high-temperature pressure-resistant welded portion and the root bulging portion of the nozzle head. Can be used to press and repair creep voids and cracks to prolong life.
[0015]
According to a fifth aspect of the present invention, in the method according to the second aspect of the present invention, after repair welding the high temperature pressure resistant welded portion which is a creep deteriorated portion to be regenerated, the repaired welded portion is heated. And
[0016]
According to this means, a weld that is a creep deteriorated part to be regenerated can be pressed against a creep void that could not be removed by repair welding by a combination of repair welding and regenerative heat treatment by heating. Strength) and a deteriorated part (weak strength) that could not be repair welded can be reduced in strength difference (mismatch), and further life extension can be achieved.
[0017]
The present invention according to claim 6 is characterized in that in the method according to any one of claims 1 to 5, the heating is a high-frequency heating.
[0018]
According to this means, it is possible to heat locally and rapidly by using a high frequency. Then, by rapidly heating, heat diffusion can be prevented, and by locally heating, the thermal expansion force can be concentrated on the heating portion.
[0019]
The present invention according to claim 7 is characterized in that the creep deteriorated portion to be regenerated is pickled and then heated.
[0020]
According to this means, a crack that has been oxidized cannot be pressure-welded, but the crack can be pressure-welded by pickling the crack in advance.
[0021]
The present invention according to claim 8 is characterized in that, in the method according to claim 1 , the creep deteriorated portion to be regenerated is annealed after heating and then returned to room temperature.
[0022]
According to this means, if it is cooled rapidly after heating, it becomes martensite, and residual stress is generated locally, leading to damage development of creep voids, but it is the same as the base material by annealing after heating. It is possible to form a structure and to prevent the occurrence of residual stress.
[0023]
The present invention according to claim 9 is characterized in that, in the method according to claim 1 , the creep deteriorated portion to be regenerated is gradually cooled to the room temperature after heating.
[0024]
According to this means, if it is rapidly cooled after heating, it becomes martensite, and residual stress is generated locally, leading to damage development of creep voids. And the occurrence of residual stress can be prevented.
[0025]
The present invention is defined in claim 10, in the apparatus for reproducing the creep deteriorated part includes a clamp that restrains the thermal expansion of the creep deteriorated part to be reproduced, and a heating means for heating the creep deteriorated part, heating The means is generated when the creep deteriorated portion is heated by the heating means by heating the creep deteriorated portion by repeating the A3 transformation point of the base material three times or more and constraining the creep deteriorated portion by the clamp. Regeneration heat treatment is performed using a pressure due to thermal expansion.
[0026]
According to this means, with the expansion of the creep deteriorated portion to be regenerated restrained by the clamp, the internal pressure of the thermal expansion generated by heating the creep deteriorated portion is used to press the creep void / crack. Can be repaired to prolong life.
[0027]
The present invention of claim 11 is the device in accordance with claim 10, wherein said heating means is a high-frequency heating coil.
[0028]
According to this means, it is possible to heat locally and rapidly by using a high frequency. Then, the diffusion of heat can be prevented by rapid heating, and the expansion tension can be concentrated on the heated portion by locally heating.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0030]
FIG. 1 shows an embodiment of the present invention, in which a regenerator 1 is detachably attached to a pipe 2 having a high-temperature pressure-resistant welded part that is a creep deteriorated part. The pipe 2 is a high-temperature pipe made of a low alloy steel pipe or the like, and a welded portion is formed at a portion covered with the high-frequency heating coil 10. FIG. 2 shows a cross section of the pipe welded portion. Reference numeral 3 denotes a high-temperature pressure-resistant welded portion, and reference numeral 4 denotes a HAZ portion.
[0031]
The reproducing apparatus 1 includes clamps 5 and 6 on the left and right. The restraint pressure by these clamps 5 and 6 can be adjusted by the pressurizing force adjusting unit 7, and further, a pressurizing measuring instrument 8 for measuring the pressure is provided, but it is not always necessary to pressurize the pipe 2, It may be simply grasped. A high-frequency heating coil 10 is provided between the clamps 5 and 6. The high frequency heating coil 10 is positioned facing the welded portion 3 of the pipe 2. The high-frequency heating coil 10 has an annular shape surrounding the pipe 2. However, when the pipe 2 has a large diameter, a plurality of arc-shaped coils may be used. Further, a water cooling pipe 11 for coil cooling, a thermometer 12 for detecting the pipe temperature, and a power cable 13 are provided.
[0032]
Next, an example of a procedure for regenerating the high-temperature pressure-resistant welded portion 3 of the pipe 2 using the regenerator 1 will be described.
[0033]
(1) Reduction of creep voids First, it is preferable to pickle the pipe welded portion 3 in advance so that the crack can be pressed. Thereby, it is possible to reliably remove the oxide film and press the crack.
[0034]
Next, the pipe 2 is restrained by the clamps 5 and 6, and the welding portion 3 is heated by the high-frequency heating coil 10. At this time, the high frequency heating coil 10 heats only the local part (welded part 3) of the pipe 2. Since the pipe 2 is fixed by the clamps 5 and 6, and the high-frequency heating coil 10 heats only the local part (welded part 3) of the pipe 2, the pressure due to the thermal expansion force of the heated part is Acts on itself. As a result, creep voids and cracks are pressed and repaired in a shorter period of time than emergency measures such as welding. Moreover, since it can heat rapidly, it can prevent the spreading | diffusion of a heat | fever and can make a thermal expansion force act on a heating part effectively.
[0035]
Moreover, it is preferable that heating temperature is higher than the transformation point of material, for example, A3 transformation point (transformation point of (alpha) iron and (gamma) iron). FIG. 3 shows a photograph of the tissue. (A) is the case where the heating temperature is set to the A3 transformation point or higher, and (b) is the case where the heating temperature is set to the A3 transformation point or lower. In any case, it can be seen that creep voids can be reduced, but the effect of reducing creep voids is higher when the heating temperature is higher than the A3 transformation point.
[0036]
Since creep voids and cracks can be reduced in this way, the life of the pipe 2 can be extended. Thereby, for example, by extending the life until the next periodic inspection, materials may be arranged by then and the piping 2 may be replaced at the next periodic inspection.
[0037]
(2) Recrystallization of HAZ part Moreover, the damage progress rate of the HAZ part 4 can be reduced especially by performing heating temperature control as shown in FIG. That is, the welding part 3 of the pipe 2 is heated by the high-frequency heating coil 10 in the same manner as described above, but is first heated beyond the A3 transformation point, then lowered from the A3 transformation point, and the A3 transformation point is set again. Be overheated. Thus, it repeats, Preferably it heats exceeding the A3 transformation point 3 to 5 times. Thereafter, the temperature is lowered to some extent and annealing is performed. Or you may make it cool gradually instead of annealing.
[0038]
By doing in this way, the HAZ part 4 which was a martensite structure can be made into the ferrite pearlite structure equivalent to a base material. Accordingly, the ductility is provided, and the damage progress rate can be reduced.
Further, as shown in FIG. 5, precipitates 21 and grain boundary segregation 22 generated along grain boundaries 20 as welded are confined in new grain boundaries 23 formed by the above-described treatment. For this reason, the crack propagation speed becomes slow, and the damage propagation speed can be lowered. As described above, the life of the pipe welded portion can be extended also in the HAZ portion 4.
[0039]
In the above-described embodiment, the welded part 3 is heated by the regenerator 1. However, in the case of a large structure, the expansion of the heated part is restricted by the unheated part. Even if 1 is not used, the welded part can be regenerated only by heating the welded part.
[0040]
Moreover, although the high frequency heating coil was mentioned and demonstrated as a heating means, it cannot be overemphasized that it is not limited to a high frequency heating coil if it is a heating means which can be heated locally rapidly.
[0041]
Next, FIG. 6 shows an example in which regeneration is performed using the regeneration apparatus 1 after repair welding of the high temperature pressure resistant weld 3 of the pipe 2.
[0042]
That is, as described above, since repair welding can generally be performed only at a depth portion of 0.2 t of the plate thickness t of the pipe 2, damage such as creep voids at deeper portions cannot be completely removed. Is. A crack occurs at the boundary portion due to a difference in strength (mismatch) between the repair weld 30 (high strength) and a deteriorated portion (weak strength) that could not be repair welded, and these cracks are accelerated by thermal stress. Therefore, it was poor in practicality.
[0043]
Therefore, in this example, in the high-temperature pressure-resistant welded portion 3 which is a creep deteriorated portion, a portion (a depth portion of 0.2 t of the plate thickness t of the pipe 2) where damage such as creep voids can be removed is indicated by reference numeral 30. After that, the entire welded portion 3 including the repair welded portion 30 is heated by the high-frequency heating coil 10, whereby the strength difference (mismatch) between the repaired welded portion 30 and the deteriorated portion that could not be repaired welded. This is to improve the life prolonging effect.
[0044]
Next, FIG. 7 shows other embodiment of this invention, and shows the case where it applies to the header 40, such as a boiler. A header 40 (the header shown in the figure has a circular cross-section, but a rectangular cross-section) is a container that collects a large number of pipes and distributes the flow, and has a nozzle 41 for attaching each pipe. It is attached by welding. In such a configuration, the base portion of the nozzle 41 swells as indicated by reference numeral 42 due to insufficient strength due to material defects, corrosion, wear, or overheating, that is, bulges, and the wall thickness becomes thin, resulting in creep degradation. Is the easiest to progress. Accordingly, the creeping bulging portion 42 at the base of the tube base is heated locally above the transformation point at a high frequency by the regenerator 1 ′ so as to make the structure equivalent to that of the unused material to extend the life. can do.
[0045]
That is, in the regenerator 1 ′, the high-frequency heating coil 10 and the clamp 16 are attached to the nozzle 41 by the joining device 17 in the bulging portion 42 that has creep-degraded at the base of the nozzle. The other end (not shown) of the joining device 17 is rigidly attached to the header 40 or other structure. As a result, when the high-frequency heating coil 10 heats the bulged portion 42 having creep deteriorated at the base of the tube base, expansion of the bulged portion 42 having creep deteriorated at the base of the tube base is restrained by the clamp 16 and the joining device 17. Therefore, the pressure due to the thermal expansion force acts on the heating part itself. As a result, the creep voids / cracks are pressed and repaired as described above.
[0046]
In the header 40 shown in FIG. 7, each nozzle 41 is attached to the header 40 by welding. Therefore, even when these welds are creep-degraded, the above-mentioned regeneration device 1 ′ is used. In the same manner as described above, creep voids and cracks can be pressed and repaired.
[0047]
Further, as a portion where creep deterioration is most likely to proceed in a boiler, a turbine, or the like, as shown in FIG. 8, for example, an outer peripheral portion 52 of a bent portion 51 of a pipe such as a U-shaped pipe (boiler pipe, heating pipe, etc.) 50. There is. That is, since such a U-shaped pipe 50 is made by bending a single pipe, the outer peripheral portion 52 of the bent portion 51 extends from the inner peripheral portion 53, and the outer peripheral portion 52 is shown as illustrated in FIG. Since the thickness is made thinner than the portion 53 and bending is performed, creep degradation is most likely to proceed. Accordingly, the outer peripheral portion 52 of the pipe bent portion 51 which has been creep-degraded is also heated to the transformation point or higher locally at a high frequency by the above-described reproducing device, so that the life can be extended to the same structure as that of the unused material. it can.
[0048]
In the above-described regeneration of the header and the pipe bent portion, when the base material is 9Cr or 12Cr, the heat treatment is preferably performed by heating, that is, preferably repeatedly over the A3 transformation point three times or more. After that, it is necessary to temper. For example, tempering of about 1 hour per inch (25.4 mm) is required at a heating temperature of 650 to 800 ° C., about 9 minutes for 9Cr with a thickness of 7 mm, and about 3 hours with 9Cr with a thickness of 80 mm. Like that.
[0049]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
[0050]
The present invention according to claim 1 is a method for regenerating a creep deteriorated portion , wherein thermal expansion generated by heating the creep deteriorated portion after constraining the thermal expansion of the creep deteriorated portion generated during heating before heating. By using the internal pressure, creep voids and cracks can be welded and repaired to prolong life. As a result, the service life can be extended until the next periodic inspection (after 2 years), the reliability of the equipment is improved, and the part that can extend the service life to 4 years is changed from 2 years to 4 years. It can be extended and maintenance costs can be greatly reduced.
By heating the creep deteriorated part to be regenerated to the A3 transformation point or higher of the base material, the creep void / crack can be more effectively pressed and repaired. The hardened structure such as the HAZ part has the same structure as that of the base material, and the root bulge part of the nozzle head and the bent outer periphery of the U-shaped pipe have the same structure as that of the unused material. Further, precipitates and segregated impurities are confined in the new grain boundaries by the newly generated grain boundaries, and the crack propagation rate can be slowed. This can also extend the life. Further, by repeating the heat treatment in the vicinity of the A3 transformation point, it is possible to more effectively confine precipitates and impurity segregated substances in new grain boundaries.
[0051]
The present invention described in claims 2, 3, and 4 is particularly generated by heating the high-temperature pressure-resistant welded portion where creep deterioration has progressed most, the root bulging portion of the nozzle head, and the pipe bending outer peripheral portion. Using the internal pressure of thermal expansion, creep voids and cracks can be pressed and repaired to prolong life.
[0052]
According to the fifth aspect of the present invention, the welded portion which is the creep deteriorated portion to be regenerated can be welded with a creep void that could not be removed by repair welding by a combination of repair welding and regenerative heat treatment by heating, and repaired. It is possible to reduce the difference in strength (mismatch) between the welded portion (strong strength) and the deteriorated portion (weak strength) that could not be repair welded, thereby further extending the life.
[0053]
The present invention according to claim 6 can be heated locally and rapidly by using a high frequency for heating. By rapidly heating, heat diffusion is prevented, and by locally heating. The thermal expansion force can be concentrated on the heating unit.
[0054]
According to the seventh aspect of the present invention, although the crack that has been oxidized cannot be pressed, the crack can be pressed by pickling the crack in advance.
[0055]
In the present invention according to claims 8 and 9 , respectively, the creep deteriorated part to be regenerated is annealed or gradually cooled to return to room temperature to return to room temperature, thereby preventing the occurrence of residual stress. be able to.
[0056]
According to a tenth aspect of the present invention, there is provided an apparatus for regenerating a creep deteriorated portion, wherein the expansion of the creep deteriorated portion to be regenerated is restrained by a clamp and the thermal expansion generated by heating the creep deteriorated portion is restrained. Using internal pressure, creep voids and cracks can be pressed and repaired to prolong life.
[0057]
The present invention according to claim 11 can be heated locally and rapidly by using a high frequency for heating. By rapidly heating, diffusion of heat is prevented, and by locally heating. The thermal expansion force can be concentrated on the heating unit.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example in which a high-temperature pressure-resistant welded portion of a pipe is regenerated by a regenerating apparatus according to the present invention.
FIG. 2 is a cross-sectional view showing a high-temperature pressure-resistant welded portion of the pipe.
FIG. 3 is a photograph showing the structure of a welded part before reproduction and reproduced by the above-described reproducing apparatus, where (a) is heated to a temperature higher than the A3 transformation point, and (b) is heated to a temperature lower than the A3 transformation point. This is the case.
FIG. 4 is a diagram showing an example of a heating / cooling process by the regenerator.
FIG. 5 is a schematic view showing a grain boundary of a welded portion regenerated by the regenerating apparatus.
FIG. 6 is a view similar to FIG. 2, showing another example of regenerating a high temperature pressure resistant weld of piping according to the present invention.
FIG. 7 is a perspective view showing a case in which a modified example of the reproducing apparatus is applied to a nozzle head.
8A is a view showing a U-shaped pipe to be regenerated according to the present invention, and FIG. 8B is a cross-sectional view taken along the line bb of FIG. 8A.
[Explanation of symbols]
1, 1 'Regenerator 2 Piping 3 High-temperature pressure-resistant welding part 4 HAZ part 5, 6 Clamp 10 High frequency heating coil (heating means)
16 Clamp 30 Repair welding part 40 Header 41 Tubular 42 Swelling part 50 U-shaped piping 51 Bending part 52 Outer part 53 Inner part

Claims (11)

In the method of regenerating the creep deteriorated portion, after restraining the thermal expansion of the creep deteriorated portion generated during heating before heating , the creep deteriorated portion to be regenerated is repeatedly exceeded three times or more by the A3 transformation point of the base material. A method characterized by regenerating heat treatment using a pressure due to thermal expansion generated by heating the creep-deteriorated portion by heating to a room temperature after heating .   2. The method according to claim 1, wherein the creep deteriorated portion to be regenerated is a high temperature pressure resistant welded portion.   2. The method according to claim 1, wherein the creep deteriorated portion to be regenerated is a root bulge portion of the nozzle head.   2. The method according to claim 1, wherein the creep deteriorated portion to be regenerated is an outer peripheral portion of a pipe bent portion.   3. The method according to claim 2, wherein after repairing and welding the high-temperature pressure-resistant welded part which is a creep deteriorated part to be regenerated, the repaired welded part is heated.   The method according to any one of claims 1 to 5, wherein the heating is high-frequency heating.   The method according to any one of claims 1 to 6, wherein the creep deteriorated portion to be regenerated is heated after pickling. 2. The method according to claim 1 , wherein the creep deteriorated portion to be regenerated is annealed after heating and then returned to room temperature. 2. The method according to claim 1 , wherein the creep deteriorated portion to be regenerated is gradually cooled to the room temperature after heating. An apparatus for regenerating a creep deteriorated portion includes a clamp for restraining thermal expansion of the creep deteriorated portion to be regenerated and a heating means for heating the creep deteriorated portion, the heating means including the creep deteriorated portion as a mother Reheating heat treatment using the pressure due to thermal expansion generated when the creep deteriorated portion is heated by the heating means by repeatedly heating the A3 transformation point of the material three times or more and constraining the creep deteriorated portion by the clamp. A device characterized by that. 11. The apparatus according to claim 10 , wherein the heating means is a high frequency heating coil.

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