JP7788922B2 - Destructive evaluation device, method, and program - Google Patents

Description

Embodiments of the present invention relate to technology for assessing the damage caused to aging structures.

As nuclear power plants age, the importance of integrity assessments of structures is increasing. Stable operation and improved availability of nuclear equipment are extremely important in terms of the safety and economy of the entire plant. Typical aging phenomena in nuclear equipment include stress corrosion cracking (SCC) and the occurrence and progression of fatigue-induced cracks. In integrity assessments, a destructive assessment of crack progression is carried out based on fracture mechanics for equipment in which cracks have been detected during inspection or in which the presence of cracks is suspected.

Fracture assessment methods for structures require the appropriate method to be used depending on the fracture mode, and specific regulations have been established for this purpose. For example, fracture assessment methods for structures with cracks include linear fracture mechanics and elastic-plastic fracture mechanics. Linear fracture mechanics is applied to brittle materials, and stress intensity factors are generally used for fracture assessment. Elastic-plastic fracture mechanics is applied when large plastic deformation (large-scale yielding) occurs at the crack tip and ductile crack propagation is taken into account, and fracture resistance curves (hereinafter referred to as J-R curves) are generally used for fracture assessment.

Japanese Patent Application Laid-Open No. 2003-65921 Japanese Patent Application Laid-Open No. 2003-294880 Japanese Patent Application Laid-Open No. 2003-167925

Mechanical testing under conditions that correspond to the structure's operating environment, and material testing using test specimens placed in specific locations on the structure while it is in operation, allow changes in the structure's material properties to be understood and the structure to be subjected to destructive evaluation. However, the material property data obtained through such testing is representative data for the environment and specific location. The effects of the environment vary from part to part on the structure. For this reason, the above-mentioned tests pose challenges in understanding changes in material properties in the areas of interest and performing destructive evaluations that reflect the effects of these property changes.

The linear fracture mechanics evaluation method, one of the structural integrity evaluation methods, is an evaluation method that targets brittle fracture. According to this evaluation method, when the stress intensity factor K at the tip of a crack that has occurred in a structure exceeds the material's inherent fracture toughness value (K _Ic ), the structure is evaluated as undergoing unstable fracture. However, while the linear fracture mechanics evaluation method is appropriate for low-toughness materials or materials whose toughness has decreased due to aging, it is inappropriate for high-toughness materials whose toughness does not decrease.

For this reason, applying linear fracture mechanics evaluation methods to highly tough materials whose toughness does not decrease over their service life poses the problem of resulting in overly conservative or unconservative fracture assessment of the structure. Elastic-plastic fracture assessment methods should be applied to such highly tough materials, but if toughness decreases over time, there is a similar problem of resulting in overly conservative or unconservative fracture assessment of the structure.

Embodiments of the present invention have been made with these circumstances in mind, and aim to provide a fracture assessment technique for structures that does not result in overly conservative or unconservative assessments of structural integrity, even when the fracture mode (brittle fracture, elasto-plastic fracture) of the assessed area changes over time.

The destruction assessment device according to the embodiment includes a database that stores the action history of factors that promote aging deterioration for each part of a structure; a selection unit that selects an evaluation part of the structure based on design information; a discrimination unit that discriminates the type of failure from the perspective of at least elastic-plastic failure and brittle failure based on the structural mechanics information and action history of the evaluation part; an acquisition unit that acquires registered information on cracks present in the evaluation part; and an evaluation unit that evaluates the failure of the evaluation part by matching the type of failure to the existing cracks.

Embodiments of the present invention provide a fracture assessment technique for structures that does not result in overly conservative or unconservative assessment of structural integrity, even when the fracture mode (brittle fracture, elasto-plastic fracture) of the assessed area changes over time.

1 is a block diagram showing a destruction evaluation device according to a first embodiment of the present invention; 1 is a graph showing the relationship between the J integral value (J _app ) of a crack at stress σ (σ ₁ <σ ₂ <σ ₃ ) and the ductile crack growth resistance J _mat (J-R curve) when the fracture mode is elastic-plastic fracture. FIG. 10 is a block diagram showing a destruction evaluation device according to a second embodiment. 3 is a flowchart illustrating the steps of a destruction assessment method according to an embodiment and an algorithm of a destruction assessment program.

(First embodiment)
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a block diagram showing a destruction assessment device 10A (10) according to a first embodiment of the present invention. The destruction assessment device 10A includes a database that stores action histories 11 of factors promoting aging deterioration for each portion of a structure, a selection unit 18 that selects an evaluation portion 20 of the structure based on design information 17, a discrimination unit 21 that discriminates a fracture mode 23 from the viewpoints of at least elastic-plastic fracture and brittle fracture based on structural mechanics information 12 and the action history 11 of the evaluation portion 20, an acquisition unit 22 that acquires registration information 25 of cracks present in the evaluation portion 20, and an evaluation unit 26 that evaluates the fracture of the evaluation portion 20 by matching the fracture mode 23 to the present cracks.

In addition to the action history 11 described above, the database (not shown) also stores structural mechanics information 12 and structure design information 17. In this embodiment, the evaluation portion 20 of the structure is assumed to be piping, vessels, equipment, welds, etc. made of metal components that become embrittled over time in the high-temperature, high-pressure, and high-radiation environment of a nuclear power plant.

The evaluation portion 20 is selected by the selection portion 18 based on the structure's design information 17 through user operation of the operation portion 16. Specifically, a list of the structure and its constituent parts is displayed on the screen based on the design information 17, and the user is prompted to select the location where they wish to perform destructive evaluation, which will be the evaluation portion 20. There are no particular restrictions on the evaluation portion 20 selected, and it can be any portion where there is a concern about deterioration over time, such as in reactor internal structures in a nuclear power plant.

The design information 17 is also linked to the action history 11 of factors that accelerate aging deterioration for each part of the structure, and both are stored in a database (not shown). The acceleration factors stored as the action history 11 are not limited to the temperature, pressure, and radiation dose mentioned above, but are applicable as long as they have the effect of accelerating the aging deterioration of the structure. In addition to the amount data detected by sensors 19 placed on the structure, these acceleration factors also include hypothetical data derived from operating conditions, which are stored as the action history 11.

It is also possible that no action history 11 or structural mechanics information 12 exists for the evaluation portion 20 selected by the selection unit 18. In this case, the failure mode 23 of the evaluation portion 20 can be determined directly from the observation results of a test piece placed near the evaluation portion 20. Alternatively, the action history 11 and structural mechanics information 12 of another portion with similar conditions may be applied to the evaluation portion 20.

Fracture modes 23 of structures can be broadly classified into three types: linear elastic fracture (brittle fracture), elastic-plastic fracture, and plastic collapse. Of these, linear elastic fracture (brittle fracture) occurs when plastic deformation is limited to the vicinity of the crack tip (small-scale yielding), causing the crack to rapidly propagate and lead to fracture. Linear elastic fracture (brittle fracture) is a fracture mode 23 observed in high-strength, low-toughness (low-ductility) metals.

In elastic-plastic fracture, the crack tip undergoes relatively large plastic deformation (large-scale yielding), followed by propagation of the crack and fracture. Elastic-plastic fracture is a fracture mode 23 observed in low-strength, high-toughness (high-ductility) metals. In plastic collapse, the crack does not propagate, the tip becomes blunt, and the entire cross section yields, resulting in fracture. Plastic collapse is a fracture mode 23 observed in extremely high-toughness (high-ductility) metals.

Structural mechanics information 12 is classified into stress data, structural data, and material property data, each of which is stored in a database (not shown). Stress data is information regarding the stress and allowable stress applied to the evaluation area 20.

The structural data is information relating to the dimensions of the structure that includes the evaluation portion 20. Specifically, it includes the shape and dimensions of the structure, the shape and dimensions of each part that makes up the structure, the shape and dimensions of the base materials, the shape and dimensions of the welds that connect the base materials, etc. The structural data may also include design information used when the structure was manufactured.

The material property data is information relating to the material properties of the constituent material of the evaluation portion 20. Specifically, the material property data includes the stress-strain curve, plane strain fracture toughness value (K _Ic ), elastic-plastic fracture toughness value (J _Ic ), fracture resistance curve (J-R curve), etc. of the constituent material.

Based on the action history 11 and structural mechanics information 12, the discrimination unit 21 discriminates the fracture mode 23 of the evaluation area 20 from two options: elastic-plastic fracture and brittle fracture, or in some cases, three options including plastic collapse, and transfers the results to the evaluation unit 26. Note that the discrimination unit 21 is not limited to the above two or three options, and may also have four or more options.

The discrimination of the fracture mode 23 in the discrimination unit 21 is performed, for example, using a two-parameter evaluation method. Here, the two-parameter evaluation method is a method for discriminating fracture modes using a fracture assessment diagram (FAC) consisting of linear fracture mechanics parameters and plastic collapse parameters. The information required for this two-parameter evaluation method is provided from the action history 11 and structural mechanics information 12.

Registered crack information 25 is information on the shape and dimensions of cracks detected in flaw detection tests conducted during pre-service inspections (SPIs) and in-service inspections (ISIs) in the case of nuclear power plants. Examples of flaw detection tests include surface inspections such as penetrant inspections and magnetic particle inspections, and volumetric inspections such as radiography and ultrasonic inspections. Registered information 25 also includes information based on actual measurements regarding the classification of cracks (planar cracks, linear cracks, lamination cracks, etc.), the position and direction of cracks in the structure, and the dimensions of cracks (length, depth, etc.).

The acquisition unit 22 acquires registration information 25 of cracks present in the evaluation area 20 selected by the selection unit 18 and transfers it to the evaluation unit 26. The evaluation unit 26 evaluates the damage of this evaluation area 20 based on the damage form 23 corresponding to the crack present in the evaluation area 20, and outputs the evaluation results from the output unit 27.

For evaluation areas 20 determined to have brittle fracture, the evaluation unit 26 applies a crack propagation simulation corresponding to brittle fracture and performs a fracture evaluation. Similarly, for cracks in evaluation areas 20 determined to have elastic-plastic fracture or plastic collapse, the evaluation unit 26 applies a crack propagation simulation corresponding to either elastic-plastic fracture or plastic collapse, and performs a fracture evaluation. Note that the parameters required for each simulation are provided from the structural mechanics information 12, and it is also possible to apply an evaluation formula 15 corresponding to each simulation.

If the fracture mode 23 is determined to be brittle fracture, the evaluation unit 26 determines the stress intensity factor K of the crack contained in the evaluation area 20 based on the structural mechanics information 12. If this stress intensity factor K exceeds the fracture toughness K _Ic , the evaluation unit 26 also determines the crack growth rate (da/dt). Then, the size of the crack in the future (at the next inspection time) can be estimated and the result can be output from the output unit 27.

Furthermore, when the fracture mode 23 is determined to be an elastic-plastic fracture, the evaluation unit 26 further determines the J-integral value of the crack included in the evaluation region 20 based on the stress intensity factor K and the structural mechanics information 12. Then, based on whether or not this J-integral value exceeds the fracture toughness J _Ic , the evaluation unit 26 determines whether or not the crack propagation will continue in the future, and outputs the result from the output unit 27.

Furthermore, the evaluation unit 26 can correct the discrimination parameters of the fracture mode 23 in the discrimination unit 21 and the determination parameters of the stress intensity factor K and the propagation rate (da/dt) so as to eliminate the difference between the crack size estimated in the past (at the previous inspection time) and the crack size actually measured at the present time. Note that the fracture evaluation in the evaluation unit 26 can also be performed using Weibull stress instead of fracture toughness K _Ic .

2 is a graph showing the relationship between the J integral value (J _app ) of a crack at stress σ (σ ₁ <σ ₂ <σ ₃ ) and the ductile crack propagation resistance J _mat (J-R curve) when the fracture mode 23 is elastic-plastic fracture. As shown, as the load (stress σ) on the evaluation portion 20 increases, the J integral value (J _app ) increases, and elastic-plastic fracture begins at stress σ ₁ that exceeds the elastic-plastic fracture toughness value (J _Ic ).

As the stress further increases to σ ₂ , stable fracture begins, but as the crack progresses (Δa), J _mat (J-R curve) also increases, so crack progress stops at a _2. If the load on the evaluation portion 20 increases further and exceeds stress σ ₃ , which satisfies the following equations (1) and (2), unstable fracture occurs, and the crack continues to progress even if the stress σ is a constant value.
J _app ≧ J _mat (1)
∂J _app /∂a=dJ _mat /da (2)

Second Embodiment
Next, a second embodiment of the present invention will be described with reference to Fig. 3. Fig. 3 is a block diagram showing a destruction assessment device 10B (10) according to the second embodiment. In addition to the configuration of the destruction assessment device 10A of the first embodiment, the destruction assessment device 10B of the second embodiment further includes a virtual crack estimation unit 32, a convergence calculation unit 28, and a soundness determination unit 29. In Fig. 3, parts having the same configuration or function as those in Fig. 1 are designated by the same reference numerals, and duplicated explanations will be omitted.

When the registered crack information 25 for the evaluation area 20 is unknown, the estimation unit 32 estimates the presence of a virtual crack based on the existing information 31. Here, when the registered crack information 25 is unknown, it means that a flaw detection test has not been conducted on the evaluation area 20 of interest, or that the crack has not been detected due to suspected omission. Furthermore, the existing information 31 may be registered information 25 for a crack detected in another area that shares the same action history 11 and structural mechanics information 12, or information on a crack detected in a corresponding area of another nuclear power plant.

The convergence calculation unit 28 calculates the parameters used to perform the fracture assessment based on at least one of statistical methods and numerical analysis. For example, the parameters that make up the Weibull stress calculation formula must be determined using statistical methods, but the convergence calculation unit 28 can automatically determine the optimal parameters.

The judgment unit 29 judges the soundness of the structure based on the results of the evaluation of damage at the evaluation portion 20 performed by the evaluation unit 26, and outputs the judgment result to the output unit 27. Based on this soundness judgment result, a maintenance plan for the structure during future inspection periods can be formulated. Alternatively, the soundness of the structure against the expected strength of a disaster such as a major earthquake can be judged.

The steps of the destruction assessment method according to the embodiment and the algorithm of the destruction assessment program will be explained based on the flowchart in Figure 4. First, the action history 11 of factors promoting aging deterioration is stored in a database for each part of the structure (S11). Then, the evaluation part 20 of the structure is selected based on the design information 17 (S12).

If structural mechanics information 12 and action history 11 corresponding to the selected evaluation area 20 are available (S13, No), the fracture mode 23 of the evaluation area 20 is determined from the perspective of elastic-plastic fracture and brittle fracture based on this structural mechanics information 12 and action history 11 (S15).

On the other hand, if there is no structural mechanics information 12 or action history 11 corresponding to the selected evaluation area 20 (S13, Yes), analogous information such as the action history 11 and structural mechanics information 12 of other areas with similar conditions or test specimen results is obtained (S14), and the failure mode 23 of the evaluation area 20 is determined (S15).

Next, if there is registered information 25 for a crack present in the selected evaluation area 20 (S16, No), the registered information 25 for this crack is obtained, and the fracture form 23 is matched to this crack to evaluate the fracture of the evaluation area 20 (S18), and information on future crack growth, etc. is output as a result.

On the other hand, if there is no registered information 25 for cracks present in the selected evaluation area 20 (S16, Yes), analogous information such as crack information for other areas with similar conditions is obtained (S17), and the fracture form 23 is matched to this crack to evaluate the fracture of the evaluation area 20 (S18), and information on future crack growth, etc. is output as the evaluation result.

Then, the soundness of the structure is judged based on the results of the evaluation of damage in the evaluation areas 20 (S19), and the judgment result is output to the output unit 27. The flow from (S12) to (S19) is then repeated until all evaluation areas 20 have been selected (S20 No, Yes, END).

By using at least one of the embodiments of the destruction assessment device described above, the destruction mode of the evaluation area, which changes over time, can be evaluated from the perspective of brittle destruction and elastic-plastic destruction, making it possible to avoid overly conservative or unconservative evaluation of the soundness of the structure.

While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments may be embodied in a variety of other forms, and various omissions, substitutions, modifications, and combinations may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope of the invention and its equivalents as defined in the claims, as well as the scope and spirit of the invention.

The destruction assessment device described above includes a control device with a highly integrated processor, such as a dedicated chip, FPGA (Field Programmable Gate Array), GPU (Graphics Processing Unit), or CPU (Central Processing Unit), a storage device such as ROM (Read Only Memory) or RAM (Random Access Memory), an external storage device such as HDD (Hard Disk Drive) or SSD (Solid State Drive), a display device, an input device such as a mouse or keyboard, and a communications interface. This allows for hardware configuration using a standard computer. Therefore, the components of the destruction assessment device can also be implemented using a computer processor and run by a destruction assessment program.

The destruction assessment program may also be provided pre-installed in a ROM or the like. Alternatively, the program may be provided stored in an installable or executable file format on a computer-readable storage medium such as a CD-ROM, CD-R, memory card, DVD, or flexible disk (FD).

The destruction assessment program according to this embodiment may also be stored on a computer connected to a network such as the Internet and provided by downloading it via the network. The destruction assessment device may also be configured by combining separate modules that independently perform the functions of their constituent elements, interconnected via a network or dedicated lines.

10 (10A, 10B)...Failure evaluation device, 11...Action history, 12...Structural mechanics information, 15...Evaluation formula, 16...Operation unit, 17...Design information, 18...Selection unit, 19...Sensor, 20...Evaluation area, 21...Discrimination unit, 22...Acquisition unit, 23...Failure mode, 25...Crack registration information, 26...Evaluation unit, 27...Output unit, 28...Convergence calculation unit, 29...Determination unit, 31...Existing information, 32...Estimation unit.

Claims (11)

A database that stores the history of factors that accelerate deterioration over time for each part of a structure, and
a selection unit that selects an evaluation portion of the structure based on design information;
a discrimination unit that discriminates the fracture mode from the viewpoint of at least elastic-plastic fracture and brittle fracture based on the structural mechanics information of the evaluation portion and the action history;
an acquisition unit that acquires registration information of cracks present in the evaluation portion;
and an evaluation unit that evaluates the destruction of the evaluation portion by matching the destruction form to the existing crack. 2. The destructive evaluation device according to claim 1,
A destruction evaluation device including an estimation unit that estimates an existing virtual crack based on existing information when registered information of the crack in the evaluation portion is unknown. 3. The destructive evaluation device according to claim 1 or 2,
A destruction evaluation device including a convergence calculation unit that calculates a parameter for evaluating destruction of the evaluation portion based on at least one of a statistical method and a numerical analysis. 3. The destructive evaluation device according to claim 1 or 2,
A destruction evaluation device in which the destruction of the evaluation portion is evaluated based on an evaluation formula corresponding to the destruction mode. 3. The destructive evaluation device according to claim 1 or 2,
The destructive evaluation device, wherein the action history is a detected amount of at least one of temperature and neutrons based on a sensor output. 3. The destructive evaluation device according to claim 1 or 2,
The action history is obtained from the observation results of a test piece placed near the evaluation location. 3. The destructive evaluation device according to claim 1 or 2,
The structural mechanics information includes at least one of stress data, structural data, and material property data of the structure. 3. The destructive evaluation device according to claim 1 or 2,
The fracture evaluation device distinguishes the fracture mode from the viewpoint of plastic collapse in addition to the elastic-plastic fracture and the brittle fracture. 3. The destructive evaluation device according to claim 1 or 2,
A destruction assessment device comprising a judging unit that judges the soundness of the structure based on the assessment result of the destruction at the assessment portion. A step of accumulating the action history of factors that accelerate aging deterioration in a database for each part of the structure;
selecting an evaluation portion of the structure based on design information;
A step of determining a fracture mode from the viewpoint of at least elastic-plastic fracture and brittle fracture based on the structural mechanics information of the evaluation portion and the action history;
acquiring registration information of cracks present in the evaluation portion;
and evaluating the failure of the evaluation portion by matching the failure form to the existing crack. On the computer,
A step of storing the action history of factors that accelerate aging deterioration in a database for each part of the structure;
selecting an evaluation portion of the structure based on design information;
a step of determining a fracture mode from the viewpoint of at least elastic-plastic fracture and brittle fracture based on the structural mechanics information of the evaluation portion and the action history; and a step of acquiring registration information of cracks present in the evaluation portion.
a destruction evaluation program that executes a step of evaluating destruction of the evaluation portion by matching the destruction form to the existing cracks.