JP2001349982A - Method to suppress the progress of stress corrosion cracking - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To suppress the progress of stress corrosion cracking generated in a reactor material by a simple operation. SOLUTION: As a result of performing a nondestructive inspection on a reactor internal structure 1, when a stress corrosion crack 2 is found, a compressive residual stress region 3 which is a surface region including the stress corrosion crack 2 is found.
To apply a compressive residual stress to. The processing for adding the compressive residual stress includes, for example, peening processing or polishing finishing processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for suppressing the development of stress corrosion cracking occurring in a material used in an atomic coplant.

[0002]

2. Description of the Related Art Generally, austenitic stainless steel or Ni-based alloy having excellent corrosion resistance is used as a material of a reactor internal structure and piping. However, since these materials are used under severe conditions such as exposure to high-temperature water, so-called “stress corrosion cracking” may occur. Since such stress corrosion cracking may lead to serious accidents, these materials have conventionally been subjected to a peening treatment (for example, JP-A-7-266230, JP-A-8-174422, and JP-A-10-113871). ) Or laser surface heat treatment (for example, Japanese Patent Application Laid-Open No. 10-153682).
) Or heat treatment using a high-frequency induction coil (for example, Japanese Patent Application Laid-Open No. 5-281386).

[0003]

The above-mentioned various processes are performed only as preventive maintenance measures, and when stress corrosion cracking actually occurs, another process is performed. In other words, if stress corrosion cracking actually occurs after a certain period of time after the start of operation of the reactor and a crack or the like occurs, the crack is repaired by covering the Technology for joining plate materials (Japanese Patent Application No. 8-1344) and technology for applying compressive residual stress to cracks using a jig (Japanese Patent Application No. 7-1512)
95) had been adopted.

[0004] However, these techniques are not always easy to carry out, and have to spend a lot of man-hours. Further, these techniques have been difficult to apply to long cracks or cracks formed on the surface of a material having irregularities.

[0005] Safety standards for nuclear power plants in Japan now require that repair be performed whenever stress corrosion cracking occurs in materials. However, according to the standard to be revised in the near future, cracks evaluated as having no possibility of fracture as a result of evaluation of crack growth and fracture evaluation can be operated with these cracks as they are Becomes Therefore, if stress corrosion cracking is found in the reactor material, whether it is possible to continue operation as it is until the next periodic inspection, or how long is the life of this reactor material? Is greatly influenced by the technique for suppressing the rate of development of the stress corrosion cracking.

The present invention has been made in view of the above circumstances, and it is possible to suppress the progress of stress corrosion cracking generated in a reactor material by a simple construction technique. It is an object of the present invention to provide a method for suppressing the progress of stress corrosion cracking, which is capable of suppressing the progress of a material having a long surface or a material surface having unevenness on which stress corrosion cracking occurs.

[0007]

Means for Solving the Problems As means for solving the above-mentioned problems, the invention according to claim 1 has been developed in a reactor internal structure or piping formed of austenitic stainless steel or a Ni-based alloy. When the stress corrosion cracking is detected, the development of the stress corrosion cracking is suppressed by applying a compressive residual stress to the surface area of the structure or the pipe including the stress corrosion cracking. By adding such compressive residual stress, the material near the stress corrosion cracking is improved, and the progress of the stress corrosion cracking is suppressed.

The invention according to claim 2 is characterized in that when a stress corrosion crack generated in a reactor internal structure or piping formed of austenitic stainless steel or a Ni-based alloy is detected, the stress corrosion crack including the stress corrosion crack is included. The development of the stress corrosion cracking is suppressed by heat-treating the surface region of the structure or the pipe. Such heat treatment improves the material near the stress corrosion cracking and suppresses the progress of the stress corrosion cracking.

The invention according to claim 3 is characterized in that when a stress corrosion crack generated in a reactor internal structure or a pipe formed of austenitic stainless steel or a Ni-based alloy is detected, the stress corrosion crack is included. The development of the stress corrosion cracking is suppressed by overlaying the weld metal on the surface region of the structure or the pipe. Such a buildup of the weld metal improves the material near the stress corrosion cracking and suppresses the progress of the stress corrosion cracking.

According to a fourth aspect of the present invention, in the first aspect, the application of the compressive residual stress is performed by a peening process or a polishing finish process. These peening or polishing finishes are suitable for subsequent processing, and the processing operation can be easily performed.

According to a fifth aspect of the present invention, in the second aspect of the invention, the heat treatment is performed by a heat treatment using a laser beam;
It is one of a high-frequency heating treatment and a rotational friction heat treatment by pressing a disk member. These treatments can easily perform the work on site where stress corrosion cracking occurs.

A sixth aspect of the present invention is characterized in that, in the third aspect of the present invention, the welding metal is built up by arc welding or laser welding. These weldings are suitable for performing a welding operation on a specific narrow area such as a stress corrosion cracking part.

The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the addition of the compressive residual stress, the heat treatment, and the buildup of the weld metal are caused by the edge of the stress corrosion crack. It is characterized in that it is performed only on the surface area near the part. By performing the treatment only on the vicinity of the end of the stress corrosion cracking as described above, a sufficient effect of suppressing the progress can be obtained, so that the treatment operation can be simplified.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for suppressing the progress of stress corrosion cracking according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing the vicinity of a surface of a reactor material to which a method according to an embodiment of the first invention is applied,
(A) is a perspective view showing an external shape, and (b) is a cross-sectional view.

The worker, with respect to the reactor internal structure 1,
It is assumed that a nondestructive inspection such as a penetrant inspection, an ultrasonic inspection, or a visual inspection is performed, and as a result of the inspection, a stress corrosion crack 2 as shown in FIG. 1 is found. In such a case, the worker performs a process of adding a compressive residual stress to a compressive residual stress region 3 which is a surface region including the stress corrosion crack 2.

The processing for applying the compressive residual stress includes, for example, peening or polishing. There are various types of peening such as shot peening, laser peening, and water jet peening, and any type of peening may be performed.
There are various types of polishing finishes such as a rotary brush finish and an emery finish.

FIG. 2 is a characteristic diagram showing the effect of the above-described process of applying a compressive residual stress, wherein the horizontal axis represents time and the vertical axis represents the length of stress corrosion crack 2. . In this figure, the curve A shows the characteristics of the case where the above-described processing for applying the compressive residual stress is performed, and the curve B shows the characteristics of the case where such a processing is not performed. As shown in this figure, in the characteristic curve B, the crack length gradually increases after the crack discovery time t1, whereas in the characteristic curve A, the crack discovery time t1
Since then, the crack length has hardly changed, and there is a remarkable difference between the two in the crack growth rate.

The peening process and the polishing finishing process are as follows.
Conventionally, it was only performed as a preventive maintenance measure,
As described above, even when the stress corrosion crack 2 is found after a certain period of time after the start of the reactor operation, the stress corrosion crack 2
Can be greatly suppressed. Therefore, according to the safety regulations of the nuclear power plant, which is scheduled to be revised recently, the treatment for adding the compressive residual stress to the stress corrosion cracking 2 of this degree as described above is carried out as it is. The internal structure 1 can be used continuously. That is, it is possible to substantially extend the life of the reactor internal structure 1 substantially. Such peening treatment and polishing finishing treatment are suitable for post-treatment, and are performed when the length of the stress corrosion crack 2 is long or the surface of the reactor internal structure 1 where the stress corrosion crack 2 has occurred. Even if there are irregularities on the surface, the processing operation can be easily performed.

FIGS. 3A and 3B are explanatory views showing the vicinity of the surface of a reactor material to which the method according to the second embodiment of the present invention is applied, wherein FIG. 3A is a perspective view showing an external shape, and FIG. It is. FIG. 3 differs from FIG. 1 in that the compressive residual stress region 3 is changed to a heat treatment region 4.

The worker performs a nondestructive inspection such as a penetrant inspection, an ultrasonic inspection or a visual inspection on the reactor internal structure 1 in the same manner as in the above case. Suppose that a stress corrosion crack 2 as shown in FIG. In such a case, the worker performs a heat treatment on the heat treatment region 4 which is the surface region including the stress corrosion crack 2.

As the heat treatment, there are various heat treatments such as a heat treatment by a laser beam, a high-frequency heat treatment, and a rotational friction heat treatment by pressing a disk member. Even when such processing is performed, it is possible to obtain substantially the same characteristics as the curve A in FIG.

FIGS. 4A and 4B are explanatory views showing the vicinity of the surface of a reactor material to which the method according to the third embodiment of the present invention is applied, wherein FIG. It is. FIG. 4 differs from FIG. 1 in that the compressive residual stress region 3 has a compressive residual stress region 3 a near both ends of the stress corrosion crack 2.
3b.

The reason why the stress corrosion cracking 2 is prevented from expanding by the treatment described with reference to FIG. 1 is that the material of the reactor internal structure 1 in the entire vicinity of the stress corrosion cracking 2 is improved and the length of the stress corrosion cracking 2 is improved. This is because the length is restricted in the length direction. However, if only the extension in the longitudinal direction of the stress corrosion crack 2 is to be restrained, the treatment near the middle of the stress corrosion crack 2 may be omitted and the material only near both ends may be improved. Should be able to restrain the lengthwise extension sufficiently. The third invention is based on such an idea, and intends to apply a compressive residual stress to only the compressive residual stress areas 3a and 3b near both ends of the stress corrosion crack 2 by peening or polishing. It is.

And, in fact, such stress corrosion cracking 2
By performing only the above-described processing only on the compressive residual stress regions 3a and 3b near both ends of the above, characteristics similar to those of the curve A in FIG. Therefore, the processing work by the worker can be simplified, and the number of work steps can be reduced. In particular, when the length of the stress corrosion cracks 2 is considerably long, or when many stress corrosion cracks 2 are generated, it is difficult to homogenize the processing contents. If the treatment is performed with emphasis on at least the vicinity of both ends of the stress corrosion crack 2, the development of the stress corrosion crack 2 can be sufficiently suppressed.

FIGS. 5A and 5B are explanatory views of the vicinity of the surface of a reactor material to which the method according to the fourth embodiment of the present invention is applied, wherein FIG. 5A is a perspective view showing an external shape, and FIG. It is. FIG. 5 differs from FIG. 4 in that the compressive residual stress regions 3a and 3b are changed to heat treatment regions 4a and 4b. Therefore, for the same reason as described with reference to FIG. 4, in this case, substantially the same characteristics as the curve A in FIG. 2 can be obtained.

FIGS. 6A and 6B are explanatory views of the vicinity of the surface of a reactor material to which the method according to the fifth embodiment of the present invention is applied, wherein FIG. 6A is a perspective view showing an external shape, and FIG. It is. The fifth aspect of the present invention is to suppress the development of stress corrosion cracking by overlaying a weld metal on a region of the reactor material including the stress corrosion cracking. Therefore, the weld metal may be overlaid over the entire length of the stress corrosion crack 2, but in this embodiment, the weld metal is overlaid only near both ends.

That is, as shown in the figure, the build-up weld metals 5 a and 5 b are formed at both ends of the stress corrosion crack 2. As a type of welding in this case, for example, there is arc welding or laser welding suitable for performing a welding operation on a specific narrow portion. Thus, by forming the overlay welding metals 5a and 5b at both ends of the stress corrosion crack 2, it is possible to obtain substantially the same characteristics as the curve A in FIG.

[0028]

As described above, according to the present invention, it is possible to suppress the progress of stress corrosion cracking generated in a reactor material by a simple operation. In addition, it is possible to suppress the progress even on the surface of the material having the unevenness in the portion where the stress corrosion cracking occurs. That is, while maintaining the soundness after the construction of the nuclear power plant, it is possible to reduce the labor for maintaining the soundness.

[Brief description of the drawings]

FIGS. 1A and 1B are explanatory views of the vicinity of a surface of a reactor material to which a method according to an embodiment of the first invention is applied, wherein FIG. 1A is a perspective view showing an external shape, and FIG.

FIG. 2 is a characteristic diagram showing an effect when a process according to the present invention is performed.

FIGS. 3A and 3B are explanatory views of the vicinity of a surface of a reactor material to which a method according to an embodiment of the second invention is applied, wherein FIG. 3A is a perspective view showing an external shape, and FIG.

FIGS. 4A and 4B are explanatory views of the vicinity of a surface of a reactor material to which a method according to an embodiment of the third invention is applied, wherein FIG. 4A is a perspective view showing an external shape, and FIG.

FIGS. 5A and 5B are explanatory views showing the vicinity of a surface of a reactor material to which a method according to an embodiment of the fourth invention is applied, wherein FIG. 5A is a perspective view showing an external shape, and FIG.

FIGS. 6A and 6B are explanatory views showing the vicinity of a surface of a reactor material to which a method according to an embodiment of the fifth invention is applied, wherein FIG. 6A is a perspective view showing an external shape, and FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactor internal structure 2 Stress corrosion cracking 3, 3a, 3b Compressive residual stress area 4, 4a, 4b Heat treatment area 5a, 5b Overlay weld metal

Claims (7)

[Claims] When a stress corrosion crack generated in a reactor internal structure or piping formed of austenitic stainless steel or a Ni-based alloy is detected, the surface of the structure or piping including the stress corrosion crack is detected. A method for suppressing the development of stress corrosion cracking, characterized by suppressing the development of stress corrosion cracking by applying compressive residual stress to a region. 2. When a stress corrosion crack generated in a reactor internal structure or a pipe formed of austenitic stainless steel or a Ni-based alloy is detected, the surface of the structure or the pipe including the stress corrosion crack is detected. A method for suppressing the growth of stress corrosion cracking, comprising suppressing the growth of stress corrosion cracking by heat treating a region. 3. When a stress corrosion crack generated in a reactor internal structure or piping formed of austenitic stainless steel or a Ni-based alloy is detected, the surface of the structure or piping including the stress corrosion crack is detected. A method for suppressing the development of stress corrosion cracking, characterized by suppressing the development of stress corrosion cracking by overlaying a weld metal in a region. 4. The method according to claim 1, wherein said compressive residual stress is applied by peening or polishing. 5. The heat treatment according to claim 1, wherein the heat treatment is a heat treatment using a laser beam.
3. The method according to claim 2, wherein the method is one of a high-frequency heating treatment and a rotational friction heat treatment by pressing a disk member. 6. The method according to claim 3, wherein the build-up of the weld metal is performed by arc welding or laser welding. 7. The method according to claim 1, wherein the application of the compressive residual stress, the heat treatment, and the build-up of the weld metal are performed only on a surface region near an end of the stress corrosion cracking. The method for suppressing the progress of stress corrosion cracking according to any one of the above.