JP6979307B2 - Crack evaluation standard formulation method, crack evaluation method by internal flaw detection inspection and maintenance management method - Google Patents

Description

This disclosure relates to a crack evaluation standard formulation method, a crack evaluation method by internal flaw detection inspection, and a maintenance management method.

In welded parts such as boiler pipes that are used for a long time in a high temperature and high pressure environment, cracks occur due to creep damage. Since cracks due to creep damage grow, it is necessary to repair the welded part in a timely manner according to the presence or absence of cracks and the length of the crack (crack height) in the thickness direction of the welded part. Therefore, a technique is being developed that can measure the presence or absence of cracks in the weld and the length of the cracks.

For example, in the damage evaluation method for a metal material disclosed in Patent Document 1, the reflected echo height of the phased array method is detected, and the detected reflected echo height is derived in advance from the reflected echo height and the creep void number density. By querying the corresponding data with, the creep void number density corresponding to the detected reflected echo height is obtained, and further, creep damage in the metal material is obtained based on the database in which the creep void number density and the creep damage amount are associated with each other. Seeking quantity.

Japanese Unexamined Patent Publication No. 2003-14705

The damage evaluation method for a metal material disclosed in Patent Document 1 uses the correspondence data between the reflected echo height and the creep void number density, but according to the findings of the present inventors, the reflected echo height and the number of creep voids are used. It is also becoming known that there may not be a strict correspondence with the density, and there is a need for a method that can evaluate the internal state of the metal material at the early stage of the crack growth process inside the metal material. ing.

In view of the above circumstances, at least one embodiment of the present invention provides a method for establishing a crack evaluation standard capable of evaluating the internal state of a metal material in an early stage of a crack growth process and a method for evaluating a crack by internal flaw detection inspection. The purpose is to do.
Further, at least one embodiment of the present invention aims to provide a maintenance management method capable of performing maintenance management in a wide range.

(1) The method for formulating a crack evaluation standard according to at least one embodiment of the present invention is
It ’s a way to formulate crack evaluation criteria.
The step of creeping and deforming the test piece to the first time point,
A step of performing an internal flaw detection inspection on the test piece at at least one second time point prior to the first time point and acquiring a flaw detection signal at at least one second time point.
By comparing the estimated size of the crack at the second time point obtained by tracing the crack growth process from the first time point to at least one second time point with the flaw detection signal at the second time point, the said Steps to determine crack evaluation criteria by internal flaw detection inspection,
It is characterized by having.

For example, the progress form (crack growth process) of creep damage in the weld is as follows. With aging, creep voids first occur at the grain boundaries of the heat-affected zone (HAZ portion) due to welding. Next, when the number of the creep voids increases, the creep voids are united and connected to form a microscopic crack, and the macroscopic crack propagates and finally reaches penetration.
In the present specification, not only a visually observable crack such as a macroscopic crack but also a crack in a pseudo-crack state, that is, a set of creep voids (a dense region of creep voids) can be regarded as a crack in the crack growth process. It will be called a crack including the area.

In the method (1) above, the estimated size of the crack at the second time point is obtained by tracing back the crack growth process from the first time point. That is, at the second time point, the size of the region that is a dense region of creep voids and can be regarded as a crack in the crack growth process can be obtained as the estimated size of the crack. Then, by comparing the estimated size of the crack at the second time point with the flaw detection signal at the second time point, it is possible to determine the crack evaluation standard by the internal flaw detection inspection, which can detect even a region that can be regarded as a crack in the crack growth process. Thereby, it is possible to provide a method for formulating a crack evaluation standard capable of evaluating the internal state of a metallic material in the early stage of the crack growth process.

(2) In some embodiments, in the method of (1) above,
In the step of acquiring the flaw detection signal, the flaw detection signal is acquired for each of the plurality of second time points prior to the first time point.
Further provided, a step of constructing a model of the crack growth process consistent with the change tendency of the flaw detection signal at each of the plurality of second time points.
The step of determining the evaluation criteria is characterized in that the model is used to trace the crack growth process back to one or more of the second time points to obtain the estimated size of the crack at the second time point.

According to the method (2) above, a model of the crack growth process for obtaining the estimated size of the crack at the second time point is constructed so as to match the change tendency of the flaw detection signal at each of the plurality of second time points. Therefore, the estimation accuracy of the estimated size of the crack at the second time point is improved. As a result, a crack evaluation standard suitable for detecting a region that can be regarded as a crack in the crack growth process can be obtained.

(3) In some embodiments, in the method (2) above, the model of the crack growth process becomes at least one of crack growth calculation, FEM, damage mechanical evaluation, void simulation method or microstructure simulation method. A based crack growth model may be used.

(4) In some embodiments, in any of the above methods (1) to (3),
A step of destructively inspecting the test piece subjected to the creep deformation up to the first time point and measuring the size of the crack at the first time point.
A step of obtaining the estimated size of the crack at the second time point based on the size of the crack at the first time point.
It is characterized by having.

According to the method (4) above, the estimated size of the crack at the second time point is obtained based on the measured size of the crack at the first time point, so that a crack evaluation standard more suitable for the evaluation of the crack by the internal flaw detection inspection can be obtained. Be done.

(5) In some embodiments, in any of the methods (1) to (4), in the step of determining the evaluation standard, the second evaluation standard of the crack by the internal flaw detection inspection is used. It is characterized in that a signal level threshold value capable of extracting a region corresponding to the estimated size of the crack at the second time point is obtained from the signal level distribution of the flaw detection signal at the time point.

According to the method (5) above, the range of cracks can be easily specified by using the evaluation criteria obtained as described above. That is, since the crack in the inspection target can be evaluated by comparing the flaw detection signal obtained by inspecting the inspection target by the internal flaw detection inspection with the signal level threshold value, it is easy to evaluate the crack in the inspection target. Become.

(6) In some embodiments, in any of the methods (1) to (5) above, the internal flaw detection inspection is a phased array method, an aperture synthesis method, a high frequency UT method, or an ultrasonic noise method. It may be at least one flaw detection test.

(7) The crack evaluation method by internal flaw detection inspection according to at least one embodiment of the present invention is
It is a method of evaluating a crack of an evaluation object by using the evaluation standard of the crack formulated by any one of the above methods (1) to (6).
The step of performing the internal flaw detection inspection on the evaluation target of the same material as the test piece and acquiring the flaw detection signal, and
A step of evaluating the presence or absence of a crack in the evaluation object based on the flaw detection signal acquired for the evaluation object according to the evaluation criteria of the crack.
It is characterized by having.

In the method (7) above, the evaluation criteria for cracks are determined by the method (1) above. In the method (1) above, as described above, the evaluation criterion of the crack is determined by comparing the estimated size of the crack at the second time point with the flaw detection signal at the second time point. Therefore, in the method (7) above, the presence or absence of cracks in the evaluation target is evaluated based on the flaw detection signal obtained by performing an internal flaw detection inspection on the evaluation target according to the crack evaluation criteria determined in this way. Therefore, the presence or absence of cracks in the evaluation object can be evaluated.

(8) In some embodiments, in the method of (7) above, in the step of evaluating the presence or absence of a crack, among the evaluation objects, the flaw detection signal acquired for the evaluation object sets the evaluation criteria. It is characterized in that the area to be filled is specified as a crack.

According to the method (8) above, the size of the region that can be regarded as a crack in the crack growth process can be specified.

(9) In some embodiments, the method (8) includes a step of evaluating the remaining life of the evaluation object from the specified size of the crack based on the model of the crack growth process. It is characterized by that.

According to the method (9) above, the remaining life of the evaluation target can be evaluated even at the stage where a region that can be regarded as a crack occurs in the crack growth process inside the evaluation target.

(10) In some embodiments, in the method (9) above, the model of the crack growth process was used to determine the estimated size of the crack at the second time point when formulating the evaluation criteria. It is characterized by being the same as the model showing the growth process.

According to the method (10) above, since an evaluation standard suitable for the model showing the crack growth process used for obtaining the estimated size of the crack at the second time point is obtained, the crack specified by the evaluation standard is obtained. By evaluating the remaining life of the evaluation target based on the model, the evaluation accuracy of the remaining life of the evaluation target is improved.

(11) In some embodiments, in any of the above methods (7) to (10), until a crack is generated in the evaluation object based on the flaw detection signal acquired for the evaluation object. It is characterized by including a step for obtaining the time Δt ^*.

According to the method (11) above, based on the flaw detection signal acquired for the evaluation target, the evaluation target is cracked even at the stage where the evaluation target does not have a region that can be regarded as a crack in the crack growth process. It is possible to grasp when a region that can be regarded as a crack occurs in the growth process.

(12) In some embodiments, in the method of (11) above, when the flaw detection signal acquired for the evaluation object does not meet the evaluation criteria, the known temporal change of the flaw detection signal of the internal flaw detection inspection is performed. It is characterized in that the ^{time Δt *} is obtained from the flaw detection signal acquired for the evaluation target based on the tendency.

According to the method (12) above, even if the flaw detection signal acquired for the evaluation target does not meet the evaluation criteria, the evaluation target can be evaluated based on the known tendency of the flaw detection signal of the internal flaw detection inspection to change with time. It is possible to accurately determine the time of occurrence of a region that can be regarded as a crack in the crack growth process.

(13) In some embodiments, in any of the methods (7) to (12) above, the evaluation object is a high-strength ferritic steel including a welded portion.

According to the findings of the present inventors, in the case of a welded portion formed by welding a member made of high-strength ferritic steel, there is no correlation between the degree of creep damage on the outer surface and the degree of creep damage on the inner surface, and welding is performed. It is desirable to evaluate the degree of creep damage inside the part.
In this regard, the crack evaluation method by the internal flaw detection inspection described in (7) above is a flaw detection signal obtained by performing an internal flaw detection inspection on the evaluation target in accordance with the crack evaluation criteria determined by the method (1) above. Since the cracks in the evaluation target are evaluated based on, the cracks in the evaluation target can be evaluated. Therefore, the method (13) above is suitable for evaluating cracks in a member made of high-strength ferritic steel.

(14) The maintenance management method according to at least one embodiment of the present invention is
A step of evaluating a crack in the evaluation object by any of the above methods (7) to (13), and a step of evaluating the crack.
It is characterized by comprising a step of performing maintenance management of the evaluation target based on the evaluation result of the crack of the evaluation target.

According to the method (14) above, since the region that can be regarded as a crack in the crack growth process can be evaluated, the maintenance and management of the evaluation target can be performed widely.

(15) In some embodiments, in the method of (14) above, the maintenance is characterized by comprising at least one of the replacement, repair or life extension measures of the evaluation object.

According to the method (15) above, since the region that can be regarded as a crack in the crack growth process can be evaluated, it is possible to widely carry out replacement, repair or life extension measures of the evaluation target.

According to at least one embodiment of the present invention, it is possible to provide a method for establishing a crack evaluation standard and a method for evaluating a crack by an internal flaw detection inspection, which can evaluate the internal state of a metal material in an early stage of a crack growth process.
Further, according to at least one embodiment of the present invention, maintenance management can be carried out extensively.

It is a figure which shows each process in the maintenance management method which concerns on some Embodiments. It is a flowchart which showed the step performed in an inspection process. It is a figure for demonstrating the intensity distribution of the reflected wave of an ultrasonic wave obtained from the welded part of the evaluation object in this flaw detection process. It is a flowchart which showed the procedure in the crack evaluation standard establishment process. It is a flowchart which showed the procedure in the data collection process for the evaluation standard establishment. It is a flowchart which showed the procedure in the evaluation standard determination process. It is a figure for demonstrating the intensity distribution of the reflected wave of ultrasonic waves obtained from the welded part of the test piece in the flaw detection signal acquisition process of the data collection process for evaluation standard establishment. FIG. 7 is a diagram schematically showing the correlation between the intensity of the reflected wave (echo height) and the position in the vertical direction in the region where the intensity of the reflected wave is large in the intensity distribution of FIG. 7, and FIG. 7A is a diagram. The two-dimensional strength distribution in the cross section including the thickness direction of the welded portion, and (b) shows the one-dimensional strength distribution along the thickness direction of the welded portion. It is a figure which showed schematically the cut surface of the welded part of the test piece after executing the data acquisition process for the evaluation standard establishment. It is a graph of the master curve showing the relationship between time and crack length. It is a graph which shows the one-dimensional strength distribution along the thickness direction of the welded part about the flaw detection signal at the 2nd time point. It is a flowchart which shows the schematic procedure of the crack growth calculation applicable to the estimated size acquisition process. It is a graph which shows the relationship between the remaining life and the crack length. It is a flowchart which shows the schematic procedure of the crack growth calculation applicable to the remaining life evaluation process. It is a graph showing the tendency of crack growth due to creep damage, (a) shows the relationship between time and crack length, and (b) shows the relationship between initial crack length and penetration time. It is a figure for exemplifying the groove shape of the member to be welded by a weld part. It is a figure for demonstrating the outer diameter and the thickness of the pipe to be welded by a weld part. It is a figure which shows the reflected wave intensity curve and the correction curve obtained in the preliminary preparation process. It is a figure which shows one Embodiment of the advance preparation process. An example of the reflected wave intensity curve obtained in the preparatory step is shown. It is a figure which shows the calculation process for finding the threshold value arrival time of the weld part of the evaluation target part by the Larson mirror parameter method.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present invention to this, but are merely explanatory examples. No.
For example, expressions that represent relative or absolute arrangements such as "in one direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial" are exact. Not only does it represent such an arrangement, but it also represents a tolerance or a state of relative displacement at an angle or distance to the extent that the same function can be obtained.
For example, expressions such as "same", "equal", and "homogeneous" that indicate that things are in the same state not only represent exactly the same state, but also have tolerances or differences to the extent that the same function can be obtained. It shall also represent the existing state.
For example, the expression representing a shape such as a quadrangular shape or a cylindrical shape not only represents a shape such as a quadrangular shape or a cylindrical shape in a geometrically strict sense, but also an uneven portion or a chamfer within the range where the same effect can be obtained. It shall also represent the shape including the part and the like.
On the other hand, the expressions "equipped", "equipped", "equipped", "included", or "have" one component are not exclusive expressions excluding the existence of other components.

(Overview of maintenance management method)
First, with reference to FIG. 1, the outline of the maintenance management method according to some embodiments will be described.
FIG. 1 is a diagram showing each process in the maintenance management method according to some embodiments. The maintenance management method according to some embodiments includes an inspection / evaluation necessity determination process S1, a target site selection process S2, an inspection means selection process S3, an inspection process S4, a remaining life evaluation process S5, and a remaining life. It includes a reference value resetting process S6, a countermeasure determination process S7, a monitoring determination process S8, a maintenance plan planning process S9, a countermeasure / monitoring implementation process S10, and a crack evaluation standard formulation process S100.
The maintenance management method according to some embodiments is a maintenance management method applied to the maintenance management of a metal member used for a long time in an environment where a large load is applied at a high temperature, and is, for example, a boiler in a thermal power generation facility. It is applied to the maintenance management of welded parts such as steam pipes that connect between the steam turbine and the steam turbine.

Hereinafter, the outline of each process in the maintenance management method according to some embodiments will be described. It should be noted that the steps in the maintenance management method according to some embodiments are not necessarily performed sequentially in the order shown in FIG. 1, and some steps may not be performed, and the steps are different from the order shown in FIG. There may be steps to be performed. In particular, the crack evaluation standard formulation step S100, which will be described later, does not need to be repeatedly performed in the subsequent maintenance management once the crack evaluation standard is determined.

(Inspection / evaluation necessity determination step S1)
The inspection / evaluation necessity determination step S1 is a step of determining which of the plurality of objects to which the maintenance management method according to some embodiments is applied is subjected to the flaw detection inspection and the evaluation of the remaining life. Is. In the inspection / evaluation necessity determination step S1, if the object that can be inspected is, for example, a plurality of steam pipes connecting between a boiler and a steam turbine in a thermal power generation facility, the steam pipes having a plurality of systems exist. Of these, it is determined which system of piping is to be inspected and the remaining life is evaluated.

In the inspection / evaluation necessity determination step S1, for example, for the part of the object whose remaining life is estimated to be the shortest by experience, the remaining life is simply extended based on information such as operation data and design values. An evaluation may be performed, and based on the evaluation result, it may be determined whether or not to perform a more detailed inspection or an evaluation of the remaining life.
For example, if the object to be inspected is the above-mentioned multiple steam pipes, the pipe system for determining the necessity of detailed inspection and evaluation of the remaining life is selected from the steam pipes having a plurality of systems. In this case, all piping systems may be selected, or only some piping systems may be selected. Then, for each of the selected piping systems, the remaining life is simply evaluated for the portion of the piping system that is empirically estimated to have the shortest remaining life.
In the simple evaluation of the remaining life performed in the inspection / evaluation necessity determination step S1, the evaluation method of the remaining life described later may be used.

(Target part selection step S2)
The target site selection step S2 selects which part of the object is judged to be subjected to the flaw detection inspection and the evaluation of the remaining life in the inspection / evaluation necessity determination step S1. It is a process to do.
For example, for example, a plurality of steam pipes connecting a boiler and a steam turbine in a thermal power generation facility will be described. In the piping system that is determined to be performed, select which part to perform the flaw detection inspection and the evaluation of the remaining life. Specifically, for example, among a plurality of welded portions in the piping system, which welded portion is to be subjected to flaw detection inspection and evaluation of remaining life is selected.

(Inspection means selection process S3)
The inspection means selection step S3 is a step of selecting a method for performing a flaw detection inspection and an evaluation of the remaining life of the selected portion for performing a flaw detection inspection and an evaluation of the remaining life in the target site selection step S2. In some embodiments, first, a method for evaluating the remaining life is selected, and then a flaw detection inspection method suitable for the selected method for evaluating the remaining life is selected.
For the evaluation of the remaining life, for example, crack growth calculation, FEM, damage mechanical evaluation, void simulation method, microstructure simulation method and the like can be used.
Further, the phased array method, the aperture synthesis method, the high frequency UT method, or the ultrasonic noise method can be used for the flaw detection inspection. Here, the high-frequency UT method refers to a flaw detection inspection using ultrasonic waves having a frequency of 20 MHz or higher.

(Inspection step S4)
The inspection step S4 is a step of performing a flaw detection inspection on the portion selected in the target site selection step S2 by the inspection method selected in the inspection means selection step S3 and evaluating a crack. In the following description, the part where the flaw detection inspection and the evaluation of the crack are performed is also referred to as an inspection target part or an evaluation target part. In addition, the object including the evaluation target portion is also referred to as an evaluation target.
In the inspection step S4, the crack is evaluated based on the crack evaluation standard determined in the crack evaluation standard formulation step S100.
Details of the inspection step S4 and the crack evaluation standard formulation step S100 will be described later.

(Remaining life evaluation step S5)
The remaining life evaluation step S5 is a step of estimating (evaluating) the remaining life by the remaining life evaluation method selected in the inspection means selection step S3 for the evaluation target portion for which the flaw detection inspection and the crack evaluation were performed in the inspection step S4. be.
The details of the remaining life evaluation step S5 will be described later.

(Remaining life reference value resetting step S6)
In the remaining life reference value resetting step S6, as a result of evaluating the remaining life in the remaining life evaluation step S5, when it becomes necessary to review the factor values in the remaining life evaluation, etc., the factor values, etc. Is the process of resetting. Specifically, for example, when the remaining life is evaluated in the remaining life evaluation step S5, the value used as the temperature condition is the design value of the evaluation target portion, and this design value is a value in which a sufficient safety factor is expected. If this is the case, the remaining life estimated in the remaining life evaluation step S5 may be shorter than necessary. For example, in such a case, it is conceivable that a reasonable result can be obtained by estimating the remaining life using the measured value as the temperature condition. Therefore, if necessary, the value of the factor in the remaining life evaluation is reviewed in the remaining life reference value resetting step S6.
When the factor value is reviewed in the remaining life reference value resetting step S6, the remaining life is evaluated again in the remaining life evaluation step S5 based on the revised factor value. Further, if it is determined that it is not necessary to review the value of the factor in the remaining life evaluation as a result of evaluating the remaining life in the remaining life evaluation step S5, the remaining life reference value resetting step S6 is carried out. Not done.

(Countermeasure determination step S7)
The countermeasure determination step S7 determines, for example, whether or not to take measures such as replacement, repair, and life extension measures for the evaluation target portion based on the evaluation result of the remaining life in the remaining life evaluation process S5, and measures are required. If it is determined, it is a process of deciding what kind of measures to take.
Specifically, from the evaluation result of the remaining life in the remaining life evaluation step S5, it was found that the evaluation target portion reaches the life in the period from the scheduled repair time to the next repair time, for example. Occasionally, in the countermeasure determination step S7, countermeasures such as replacement, repair, and life extension measures for the evaluation target portion are determined. In the countermeasure determination step S7, whether to replace the evaluation target part, repair it, what kind of repair is to be performed if it is repaired, whether to take life-prolonging measures, and what kind of measures should be taken if life-prolonging measures are taken. It will be decided whether to take it.

It should be noted that, for example, in the inspection / evaluation necessity determination step S1, the inspection step S4 or the remaining life evaluation step is performed, as in the case where it is determined that replacement or repair is necessary without performing a detailed flaw detection inspection in the inspection step S4. The countermeasure determination step S7 may be carried out without going through S5.

(Monitoring determination step S8)
The monitoring determination step S8 is a step of determining the presence / absence of a portion that needs to be monitored and the monitoring method in the operation of the equipment in the future. In the monitoring determination step S8, for example, it is determined whether or not monitoring is necessary for the evaluation target portion determined to take measures such as repair in the countermeasure determination process S7, and if so, how to monitor. do. Further, in the monitoring determination step S8, for example, the evaluation target portion determined to be unnecessary for replacement or repair in the countermeasure determination step S7 from the evaluation result of the remaining life in the remaining life evaluation process S5 was monitored just in case. Determine if it is better and, if so, how to monitor it.
In addition, for example, even if it is determined in the inspection / evaluation necessity determination step S1 that it is not necessary to perform a more detailed inspection or evaluation of the remaining life, in the monitoring determination step S8, it should be noted in future operation of the equipment. Therefore, the monitoring determination step S8 may be performed without going through the countermeasure determination step S7, as in the case of determining to monitor.

(Maintenance planning process S9)
The maintenance plan planning process S9 is a process of examining what kind of measures should be taken at what time for each object. If a maintenance plan is not required for the time being, for example, a part where it is determined to be replaced in the countermeasure determination step S7 and a sufficient remaining life is secured by the replacement, the maintenance plan planning step S9 may not be carried out. be.

(Countermeasure / monitoring implementation process S10)
The countermeasure / monitoring implementation step S10 is a step of carrying out replacement or repair determined to be necessary in the countermeasure determination step S7, or monitoring a portion determined to be necessary to be monitored in the monitoring determination step S8.
The process from the countermeasure determination process S7 to the countermeasure / monitoring implementation process S10 described above is referred to as a maintenance management process S11.

(About the object)
The object to which the maintenance management method according to some embodiments is applied is, for example, a steam pipe connecting between a boiler and a steam turbine in a thermal power generation facility, as described above. There are multiple types of welds in such steam pipes. For example, the steam pipe has a circumferential welded portion for connecting the pipes and a pedestal welded portion for connecting the pipe and the branch pipe. Further, when the pipe is manufactured from a plate-shaped member, there is a longitudinal welded portion extending in the pipe axial direction in order to connect the end portions of the plates.

A member that is used for a long time in a high temperature and high pressure environment, such as a steam pipe used in a boiler or the like, may have cracks due to creep damage at the welded portion.
For example, the progress form (crack growth process) of creep damage in the weld is as follows. With aging, creep voids first occur at the grain boundaries of the heat-affected zone (HAZ portion) due to welding. Next, when the number of the creep voids increases, the creep voids are united and connected to form a microscopic crack, and the macroscopic crack propagates and finally reaches penetration.
In the present specification, not only a visually observable crack such as a macroscopic crack but also a crack in a pseudo-crack state, that is, a set of creep voids (a dense region of creep voids) can be regarded as a crack in the crack growth process. It will be called a crack including the area.

For example, in the piping of equipment such as steam pipes that connect between the boiler and the steam turbine, flaw detection inspections, etc. cannot be performed while the equipment is in operation, so periodic inspections, etc. are performed when the equipment is stopped. It will be. In addition, since it is difficult to stop the equipment frequently due to the demand for long-term continuous operation and cost, the periodic inspection is often performed for a long period such as a year. Therefore, regarding creep damage as described above, it is desired to detect the crack at the earliest possible stage in the process of crack growth and predict the remaining life.
Therefore, in some embodiments, the inspection step S4 and the remaining life evaluation step S5 are carried out as described below.

(Detailed explanation of inspection process S4)
Hereinafter, the inspection step S4 will be described in detail.
In some embodiments described below, it is assumed that the evaluation target portion in the inspection step S4 is, for example, the welded portion of the steam pipe described above. Further, in some embodiments described below, the internal flaw detection inspection in the inspection step S4 is assumed to be, for example, an internal flaw detection inspection by a phased array method using ultrasonic waves. In addition to the phased array method, the internal flaw detection inspection may be performed by an aperture synthesis method, a high frequency UT method, or an ultrasonic noise method.
FIG. 2 is a flowchart showing the steps carried out in the inspection step S4.
The inspection step S4 performs an internal flaw detection inspection on the evaluation target portion of the evaluation target, and obtains a flaw detection signal according to the main flaw detection step S41 and the crack evaluation criteria determined in the crack evaluation standard formulation step S100 described later. A crack evaluation step S42 for evaluating the presence or absence of cracks in the evaluation target portion based on the flaw detection signal acquired for the evaluation target portion is provided.

In this flaw detection step S41, as shown in FIG. 3, the phased array ultrasonic flaw detector 2 irradiates the inside of the welded portion 4a, which is the evaluation target portion, while scanning ultrasonic waves, and the reflected wave (echo) of the ultrasonic waves. ) Is received. Note that FIG. 3 is a diagram for explaining the intensity (echo height) distribution of the reflected wave of the ultrasonic wave obtained from the welded portion 4a of the evaluation target in the flaw detection step S41.
The welded portion 4a, which is the evaluation target portion, is a welded portion 4a such as a pipe of a device (actual machine) actually used such as a boiler.

It should be noted that scanning the ultrasonic wave means that the convergence position of the ultrasonic wave is changed every moment, and the ultrasonic wave is at least in a two-dimensional plane including the thickness direction of the welded portion 4a or in a three-dimensional space. Is to change the convergence position of. The phased array ultrasonic flaw detector 2 can irradiate while scanning the ultrasonic wave, and can measure the intensity (echo height) of the reflected wave of the ultrasonic wave at each convergence position. Therefore, according to the phased array ultrasonic flaw detector 2, it is possible to acquire the intensity distribution (echo height distribution) of the reflected wave as shown in FIG. FIG. 3 shows the intensity distribution of the reflected wave by a contour diagram (contour diagram).
Since the intensity of the reflected wave also changes depending on the intensity of the ultrasonic wave to be irradiated, the intensity of the reflected wave may be the ratio of the intensity of the reflected wave to the intensity of the ultrasonic wave to be irradiated in the present specification.

In the crack evaluation step S42, the intensity of the reflected wave received in the flaw detection step S41 is compared with the signal level threshold value th, and a crack 6a is generated in a region where the intensity of the reflected wave in the evaluation target portion is equal to or higher than the signal level threshold value th. It is determined that there is. This signal level threshold value th is an evaluation standard for cracks determined in the crack evaluation standard formulation step S100, which will be described later.
For example, in the case of FIG. 3, a crack 6a is generated inside the heat-affected zone 8a in the welded portion 4a. The length ax of the crack 6a in the thickness direction of the welded portion 4a is 10 mm, and the distance from the crack 6a to the surface of the welded portion 4a is 7 mm.
In the present specification, the crack length means the length of the crack in the thickness direction of the welded portion, for example, the wall thickness direction of the pipe, unless otherwise specified.

The flaw detection step S41 itself is a non-destructive inspection, and in FIG. 3, the cross-sectional shape of the welded portion 4a to be evaluated is shown superimposed on the intensity distribution of the reflected wave for reference. The welded portion 4a is a portion where two members are welded to each other, or a portion where different portions of one member are welded to each other, and is located around the welded portion (weld) 10a and the welded portion 10a. It includes a heat-affected zone 8a. For example, when the member to be welded is, for example, two pipes, the welded portion 4a extends in the circumferential direction of these pipes. Alternatively, when the plate is bent and the side edges of the plate are welded to each other to form a pipe, the welded portion 4a extends in the axial direction of the pipe formed by welding. Creep damage is particularly problematic in the cracks (creep cracks) 6a in the heat-affected zone 8a.

(Regarding the crack evaluation standard formulation process S100 and the crack evaluation standard)
Hereinafter, the crack evaluation standard formulation step S100 and the crack evaluation standard will be described.
The crack evaluation standard is a reference value used when evaluating the presence or absence of a crack in the evaluation target portion in the present flaw detection step S41, and as described above, is the above-mentioned signal level threshold value th in some embodiments. This signal level threshold value th is predetermined by the crack evaluation standard formulation step S100 described below.
FIG. 4 is a flowchart showing the procedure in the crack evaluation standard formulation process S100. The crack evaluation standard formulation step S100 includes an evaluation standard formulation data collection step S110 and an evaluation standard determination step S120. FIG. 5 is a flowchart showing a procedure in the evaluation standard establishment data collection process S110. FIG. 6 is a flowchart showing the procedure in the evaluation standard determination step S120.
Hereinafter, the crack evaluation standard formulation step S100 will be described with reference to the flowcharts of FIGS. 4 to 6.

(Data collection process S110 for formulating evaluation criteria)
In the crack evaluation standard formulation step S100, first, the evaluation standard formulation data collection step S110 is carried out.
As shown in FIG. 5, the data acquisition step S110 for establishing evaluation criteria is internal to the creep deformation step S111 that creep-deforms the test piece to the first time point and the test piece at the second time point before the first time point. It includes a flaw detection signal acquisition step S112 of performing a flaw detection inspection and acquiring a flaw detection signal at a second time point.

In the data collection step S110 for formulating the evaluation criteria, a test piece for obtaining the evaluation criteria for cracks is prepared, and a load is applied to the test piece while being heated for a predetermined time in the creep deformation step S111 as shown in FIG. Hang and creep deform.

After the test piece is creep-deformed for a predetermined time in the creep deformation step S111, an internal flaw detection inspection is performed on the test piece in the flaw detection signal acquisition step S112 to acquire the flaw detection signal.
FIG. 7 is an example of a contour diagram of the intensity distribution of the reflected wave obtained by the internal flaw detection inspection of the test piece 12, and for reference, the cross-sectional shape of the welded portion 4b of the test piece 12 is superimposed on the intensity distribution of the reflected wave. It is also shown. The test piece 12 is a metal piece made of the same material as the object to be evaluated in the inspection step S4, and has a welded portion 4b. The welded portion 4b also includes a welded portion 10b and a heat-affected zone 8b located around the welded portion 10b.
The internal flaw detection inspection in the flaw detection signal acquisition step S112 is performed by the same method as the internal flaw detection inspection in the inspection step S4, and is, for example, an internal flaw detection inspection by a phased array method using ultrasonic waves.

That is, in the flaw detection signal acquisition step S112, as shown in FIG. 7, the phased array ultrasonic flaw detector 2 irradiates the inside of the welded portion 4b of the test piece 12 while scanning ultrasonic waves to reflect the ultrasonic waves. Receive waves. As a result, the intensity distribution of the reflected wave at the time of performing the flaw detection signal acquisition step S112 can be obtained. The time of implementation is the second time, which will be described later.

FIG. 8 is a diagram schematically showing the correlation between the intensity of the reflected wave (echo height) and the position in the vertical direction in the region where the intensity of the reflected wave is large in the intensity distribution of FIG. 7. (A) shows a two-dimensional strength distribution in a cross section including the thickness direction of the welded portion, and (b) shows a one-dimensional strength distribution along the thickness direction of the welded portion.

The creep deformation step S111 and the flaw detection signal acquisition step S112 are repeated until the cracks generated inside the test piece 12 are sufficiently grown, that is, at least until a microscopic crack is generated.
Specifically, for example, when it is determined that the growth of cracks inside the test piece 12 is insufficient based on the flaw detection signal acquired in the flaw detection signal acquisition step S112, the flaw detection signal acquisition step S112 is carried out. After that, step S101 is negatively determined, and the process returns to the creep deformation step S111, and a load is applied while heating to creep-deform the test piece 12 for a predetermined time.
Further, for example, when it is determined based on the flaw detection signal acquired in the flaw detection signal acquisition step S112 that the crack inside the test piece 12 has grown into a macroscopic crack having a size larger than, for example, a predetermined size. After the flaw detection signal acquisition step S112 is performed, step S101 is affirmatively determined, and the evaluation standard formulation data collection step S110 is terminated. When it is determined that the crack inside the test piece 12 has reached the surface of the test piece 12, the evaluation standard establishment data acquisition step S110 may be terminated.

In the following description, when the creep deformation step S111 and the flaw detection signal acquisition step S112 are repeatedly executed as described above, the time point at which the final creep deformation step S111 is completed is referred to as a first time point. That is, the first time point corresponds to the time when the crack inside the test piece 12 reaches, for example, a size larger than a predetermined size, or the time when the crack reaches the surface of the test piece 12.
Further, the time point at which the flaw detection signal acquisition step S112 is performed is referred to as a second time point. The second time point is a time point before the first time point, and there is at least one second time point. That is, at the second time point, there are as many times as the number of times the flaw detection signal acquisition step S112 is performed.

In the process of repeatedly executing the creep deformation step S111, a creep void is generated in the heat-affected zone 8b of the test piece 12. Then, the number of creep voids gradually increases, and as shown in FIG. 7, a region that is a dense region of creep voids and can be regarded as a crack in the crack growth process, that is, a crack 6b in the present specification appears. Note that FIG. 7 is a contour diagram of a relatively early stage in the crack growth process at any of the plurality of second time points, before the microscopic crack occurs.
After that, when the number of creep voids increases, the creep voids are united and connected to form a microscopic crack, and the macroscopic crack propagates to penetrate.

(Evaluation Criteria Determination Step S120)
As shown in FIG. 4, after executing the evaluation standard formulation data collection step S110 in the crack evaluation standard formulation step S100, the evaluation standard determination step S120 is executed. As shown in FIG. 6, the evaluation standard determination step S120 includes a size measurement step S121, a model construction step S123, an estimated size acquisition step S125, and a threshold value acquisition step S127.

The size measurement step S121 is a step of measuring the size of the crack at the first time point. In the size measurement step S121, as shown in FIG. 9, the welded portion 4c of the test piece 12 after the data acquisition step S110 for establishing the evaluation standard is executed is cut. Note that FIG. 9 is a diagram schematically showing the cut surface of the welded portion 4c of the test piece 12 after the data acquisition step S110 for establishing the evaluation standard is executed.
Then, in the size measuring step S121, for example, the length a1 of the crack 6c in the cut welded portion 4c is measured. The measurement of the length a1 of the crack 6c in the size measurement step S121 is a direct visual measurement and can be performed using a ruler, a caliper, or the like, but depending on the size of the crack 6c, a microscope is used. May be good.

The model building step S123 is a step of building a model of the crack growth process that matches the changing tendency of the flaw detection signal at a plurality of second time points. Examples of the model used in the model construction step S123 include crack growth calculation, FEM, damage mechanical evaluation, void simulation method, structure simulation method, and the like. In the following description, it is assumed that the model used in the model construction step S123 is based on the crack growth calculation.

That is, in the model construction step S123, factors such as the physical property values of the material in the crack growth calculation are adjusted in order to construct a model of the crack growth process that matches the change tendency of the flaw detection signals at a plurality of second time points by the crack growth calculation. do. As a result, as a model of the crack growth process consistent with the change tendency of the flaw detection signal at the plurality of second time points, a master curve 14 showing the relationship between time and the crack length is obtained, for example, as shown in FIG.

The estimated size acquisition step S125 is a step of tracing back to the second time point and obtaining the estimated size of the crack at the second time point based on the model built in the model building step S123. In the estimated size acquisition step S125, the estimated size of the crack at the second time point is obtained as follows.
As shown in FIG. 10, in the master curve 14 obtained in the model building step S123, the time corresponding to the length a1 of the crack 6c measured in the size measuring step S121 is set as the time t1. The time t1 corresponds to the first time point described above.
Then, starting from the time t1, the time on the horizontal axis of the graph of FIG. 10 corresponding to the plurality of second time points is obtained.

Next, of the plurality of times corresponding to the plurality of second time points, the time is later than _{the time t L} corresponding to the lower limit of the detection of the phased array ultrasonic flaw detector 2 used in the evaluation standard establishment data collection step S110. , The time _{t2 closest to the time t L} is specified based on the master curve 14. Then, the estimated length a2 of the crack at the specified time t2 is read from the master curve 14. The estimated length a2 of this crack is the estimated size of the crack acquired in the estimated size acquisition step S125.

The threshold value acquisition step S127 is a step of obtaining a signal level threshold value th that can extract a region corresponding to the estimated size of the crack at the second time point corresponding to the time t2 specified as described above.
In the threshold value acquisition step S127, as shown in FIG. 11, the position of the crack whose size was measured in the size measurement step S121 from the intensity distribution (signal level distribution) of the flaw detection signal (reflected wave) at the second time point corresponding to the time t2. The intensity of the reflected wave corresponding to the estimated crack length a2 is obtained at the position corresponding to. FIG. 11 is a graph showing a one-dimensional intensity distribution of the flaw detection signal, that is, the reflected wave at the second time point corresponding to the time t2, along the thickness direction of the welded portion. As shown in FIG. 11, the intensity of the reflected wave corresponding to the estimated crack length a2 can be obtained from the intensity distribution of FIG. 11, that is, the graph of the echo height. As a result, the intensity of the reflected wave from which the estimated length a2 of the crack is obtained can be known, and the intensity of the reflected wave is used as the crack evaluation standard, that is, the signal level threshold th.

The time t2 is not only set in consideration of the lower limit of detection of the phased array ultrasonic flaw detector 2 as described above, but may be another method. That is, with respect to the signal level distribution at the time when it becomes a candidate for time t2, a temporary signal level threshold value th'is obtained, and the position and the number of regions having the obtained temporary signal level threshold value th' or more are the size measurement steps. It may be confirmed as follows whether or not it matches the position of the macroscopic cracks observed in S121 and the number of macroscopic cracks.
For example, a case where the number of microscopic cracks observed in the size measurement step S121 is one will be described. Regarding the signal level distribution at the time when it becomes a candidate at time t2, the number of regions that are equal to or greater than the provisional signal level threshold value th'is 1, and the position of the region is the position of the macroscopic crack observed in the size measurement step S121. In the case of, the position and the number of regions having the provisional signal level threshold value th'or or higher are matched with the position of the macroscopic cracks and the number of macroscopic cracks observed in the size measurement step S121. That is, in this case, the region where the temporary signal level threshold value th'or or higher at the time of being a candidate for time t2 is the same as the model constructed in the model construction step S123, for example, the crack 6c having a length a1 at the first time point. Therefore, there is no contradiction.
In this case, since it can be determined that the provisional signal level threshold value th'is appropriate as an evaluation criterion for cracks, the provisional signal level threshold value th'is set as the signal level threshold value th.

On the other hand, for example, the number of macroscopic cracks observed in the size measurement step S121 is 1, but the number of regions having a tentative signal level threshold value th'or more than 2 with respect to the signal level distribution at the time of being a candidate at time t2. If this is the case, the number of regions that are equal to or greater than the provisional signal level threshold value th'and the number of macroscopic cracks observed in the size measurement step S121 do not match. That is, in this case, the microscopic crack that should have occurred at the first time point based on the model constructed in the model construction step S123 is not actually generated. Therefore, there is a contradiction between the region that is equal to or higher than the temporary signal level threshold value th'at the time t2 candidate and the microscopic crack at the first time point, so that the temporary signal level threshold value th'is cracked. It turns out that it is inappropriate as an evaluation standard for. Therefore, in such a case, it is determined that the provisional signal level threshold value th'is inappropriate as the signal level threshold value th.
Further, even if both the number of regions that are equal to or higher than the temporary signal level threshold value th'and the number of macroscopic cracks observed in the size measurement step S121 are matched at 1, if the positions of the two are different. , It is determined that the provisional signal level threshold value th'is inappropriate as the signal level threshold value th.

For example, even when the number of microscopic cracks observed in the size measurement step S121 is 2 or more, it is possible to confirm whether or not the provisional signal level threshold value th'is appropriate as a crack evaluation standard based on the same idea. can.

If it is determined that the provisional signal level threshold value th'is inappropriate as an evaluation criterion for cracks, the process returns to the estimated size acquisition step S125, and among the plurality of times corresponding to the plurality of second time points, the above-mentioned time The time t2α, which is later than t2 and is closest to the time t2, is specified based on the master curve 14. Then, the estimated length a2α of the crack at the specified time t2α is read from the master curve 14. Then, in the threshold value acquisition step S127, the estimated length a2α of the crack corresponds to the position corresponding to the position of the crack whose size was measured in the size measurement step S121 from the signal level distribution of the flaw detection signal at the second time point corresponding to the time t2α. Find the intensity of the reflected wave. Using the intensity of this reflected wave as a new temporary signal level threshold value th', it is confirmed again whether or not the new temporary signal level threshold value th'is appropriate as a crack evaluation criterion as described above.

If it is determined that the new provisional signal level threshold value th'is appropriate as an evaluation criterion for cracks, the new provisional signal level threshold value th'is set as the signal level threshold value th.
If it is determined that the new temporary signal level threshold value th'is inappropriate as an evaluation criterion for cracks, the process returns to the estimated size acquisition step S125 again, and the above-mentioned process is repeated.

Here, a schematic procedure of crack growth calculation applicable to the estimated size acquisition step S125 will be described. FIG. 12 is a flowchart showing a schematic procedure of crack growth calculation applicable to the estimated size acquisition step S125.
In the crack growth calculation described below, the crack length is calculated retroactively in time, so the crack growth calculation described below is also referred to as a crack growth inverse analysis.

In the crack growth reverse analysis, first, the data necessary for the analysis is acquired (S200). The acquired data are the length a1 of the crack 6c at the above time t1, the depth of the crack 6c (distance from the surface of the weld 4c to the tip of the crack 6c), stress, temperature, creep rate, creep crack growth rate data. And the material.
Next, in step S202, the length a1 is assigned to the variable a, and in step S204, 1 is assigned to the variable n. Then, in the C ^* calculation step S206, the C ^* parameter (corrected J integral J') is calculated based on the acquired data.

In the crack growth rate acquisition step S208, the crack growth rate (da / dt) is acquired based on ^{the C *} parameter calculated in the ^{C * calculation step S206.} The logarithm of the C ^* parameter and the logarithm of the crack growth rate (da / dt) have a proportional relationship with the coefficient m according to the material, and the crack growth rate (da / dt) is calculated from ^{the C * parameter.} Can be asked.
^{Alternatively, the relationship between the crack growth rate (da / dt) and the C *} parameter is obtained in advance for each material, and the crack growth rate (da / dt) is ^{obtained from the calculated C *} parameter based on the relationship. May be.

In the crack reduction calculation step S210, the crack growth rate (da / dt) obtained in the crack growth rate acquisition step S208 is multiplied by a minute time Δt to obtain the crack reduction Δa.
In the crack dimension update step S212, the variable a is updated by subtracting the crack reduction amount Δa from the variable a.

Then, in the time determination step S214, it is confirmed whether or not the time t1 is traced back to the time t2. If the determination result in the time determination step S214 is negative, 1 is added to the variable n ^{to return to the C *} calculation step S206.
On the other hand, when the determination result in the time determination step S214 is positive, that is, when the time t2 is traced back, the variable a at that time is the length a2 of the crack 6b to be obtained.

The reverse crack growth analysis is not limited to the method shown in FIG. 12, and is obtained in advance by an experiment for each combination of the material and dimensions of the member to be welded, the groove shape of the weld, and the like. It may be performed using the crack growth rate (da / dt). That is, the length a2 of the crack 6 b at the time t2 may be estimated using the crack growth rate (da / dt) previously obtained by the experiment regardless of ^{the C * parameter.} In other words, the crack growth inverse analysis may be performed as long as the master curve 14 can be prepared.

(Detailed explanation of remaining life evaluation step S5)
Hereinafter, the remaining life evaluation step S5 will be described in detail.
In some embodiments, the remaining life evaluation step S5 is a step of evaluating the remaining life of the evaluation target portion from the size of the crack specified in the inspection step S4 based on the model of the crack growth process.
That is, in the remaining life evaluation step S5, from the length ax of the crack 6a inside the welded portion 4a of the evaluation target portion determined in the inspection step S4, the remaining life of the welded portion 4a of the evaluation target portion is as follows. To evaluate.

Specifically, as shown in FIG. 13, the length ax of the crack 6a inside the welded portion 4a at the implementation time tx at the time of implementation of the main flaw detection step S41 in the inspection step S4 is calculated by crack growth calculation. The penetration time tr at which the length ax of the crack 6a becomes the length ar penetrating the welded portion 4a is obtained. The difference between the penetration time tr and the implementation time tx corresponds to the remaining life.
Note that FIG. 13 is a graph showing the relationship between the remaining life and the crack length.
That is, in some embodiments, the model of the crack growth process (crack growth calculation) used for evaluating the remaining life in the remaining life evaluation step S5 is the second time point in the model construction step S123 of the crack evaluation standard formulation step S100. It is the same as the model showing the crack growth process (crack growth calculation) used to obtain the estimated size of the crack in.

Here, a schematic procedure for calculating crack growth applicable to the remaining life evaluation step S5 will be described. FIG. 14 is a flowchart showing a schematic procedure of crack growth calculation applicable to the remaining life evaluation step S5.
The crack growth calculation described below is also referred to as crack growth analysis.

In the crack growth analysis, first, the data necessary for the analysis is acquired (S300). The acquired data include the length ax of the crack 6a at time tx, the depth of the crack 6a (distance from the surface of the weld 4a to the tip of the crack 6a), stress, temperature, creep rate, creep crack growth rate data and The material.
Next, in step S302, the length ax is assigned to the variable a, and in step S304, 1 is assigned to the variable n. Then, in the C ^* calculation step S306, the C ^* parameter (corrected J integral J') is calculated based on the acquired data.

In the crack growth rate acquisition step S308, the crack growth rate (da / dt) is acquired based on ^{the C *} parameter calculated in the ^{C * calculation step S306.} The logarithm of the C ^* parameter and the logarithm of the crack growth rate (da / dt) have a proportional relationship with the coefficient m according to the material, and the crack growth rate (da / dt) is calculated from ^{the C * parameter.} Can be asked.
^{Alternatively, the relationship between the crack growth rate (da / dt) and the C *} parameter is obtained in advance for each material, and the crack growth rate (da / dt) is ^{obtained from the calculated C *} parameter based on the relationship. May be.

In the crack increment calculation step S310, the crack growth rate (da / dt) obtained in the crack growth rate acquisition step S308 is multiplied by a minute time Δt to obtain the crack growth rate Δa.
In the crack dimension update step S312, the variable a is updated by adding the crack increment Δa to the variable a.

Then, in the penetration determination step S314, it is determined whether or not the length of the variable a, that is, the crack 6a is equal to or greater than the penetration length ar penetrating the welded portion 4a. If the determination result in the penetration determination step S314 is negative, 1 is added to the variable n ^{to return to the C *} calculation step S306.
On the other hand, when the determination result of the penetration determination step S314 is positive, that is, when the length of the crack 6a is equal to or greater than the penetration length ar penetrating the welded portion 4a, the remaining life calculation step S318 is executed. To. In the remaining life calculation step S318, the remaining life, that is, the remaining life (tr-tx) is obtained as the product of the variable n and the minute time Δt.

The crack growth analysis is not limited to the method shown in FIG. 14, and the cracks obtained in advance by experiments for each combination of the material and dimensions of the member to be welded, the groove shape of the weld, and the like. It may be performed using the progress rate (da / dt). That is, the time tr may be estimated from the length ax of the crack 6a at the time tx by using the crack growth rate (da / dt) previously obtained by the experiment regardless of ^{the C * parameter.} In other words, the crack growth analysis may be performed as long as the master curve 14 can be prepared. The same master curve 14 can be used in the crack growth reverse analysis and the crack growth analysis.

Here, FIG. 15 is a graph showing the tendency of crack growth due to creep damage, (a) shows the relationship between time and crack length, and (b) shows the relationship between initial crack length and penetration time. Shows the relationship. When a crack penetrates a weld, it means that the crack reaches the surface. In FIGS. 15A and 15B, the horizontal axis is the logarithmic axis. As is clear from FIGS. 15 (a) and 15 (b), the longer the length of the initial crack, the earlier the time when the crack growth rate rapidly increases and the shorter the penetration time.

In some embodiments, the member welded by the weld 4a is made of high-strength ferritic steel.
In the case of the welded portion 4a of a member made of high-strength ferritic steel, there is no correlation between the degree of creep damage on the outer surface and the degree of creep damage on the inside, and welding is performed regardless of the degree of creep damage on the outer surface of the welded portion 4a. It is necessary to evaluate the degree of creep damage inside the part 4a.
In this regard, in some of the above-described embodiments, the length ax of the crack 6a inside the welded portion 4a can be accurately evaluated, and the creep damage degree of the welded portion 4a of the member made of high-strength ferritic steel can be accurately evaluated. Suitable for evaluation.

The high-strength ferritic steel is, for example, Gr. Equivalent material of 91 series steel (Tue SCMV28, Tue STPA28, Tue SFVAF28, Tue STBA28), Gr. Equivalent material of 92 series steel (Tue STPA29, Tue SFVAF29, Tue STBA29), Tue Gr. Equivalent material of 122 series steel (Tue SUS410J3, Tue SUS410J3TP, Tue SUSF410J3, Tue SUS410J3TB, Tue SUS410J3DTB) or Gr. It is an equivalent material of 23 series steel (fire STPA24J1, fire SFVAF22AJ1, fire STBA24J1, fire SCMV4J1).

The material of the member to be welded by the welded portion 4a is not limited to high-strength ferritic steel, and may be, for example, low alloy steel or stainless steel.
The low alloy steel is, for example, an equivalent material of STBA12, an equivalent material of STBA13, an equivalent material of STPA20, an equivalent material of fire STPA21, an equivalent material of STPA22, an equivalent material of STPA23, or an equivalent material of STPA24.
The stainless steel is, for example, SUS304TP equivalent material, SUS304LTP equivalent material, SUS304HTP equivalent material, fire SUS304J1HTB equivalent material, SUS321TP equivalent material, SUS321HTP equivalent material, SUS316HTP equivalent material, SUS347HPP equivalent material, or It is an equivalent material of Tue SUS310J1TB.

FIG. 16 is a diagram for exemplifying the groove shape of the member to be welded by the welded portion 4a. For example, the groove is a V-shaped groove, an X-shaped groove, a U-shaped groove, and a narrow groove.
FIG. 17 is a diagram for explaining the outer diameter D and the thickness t of the pipe to be welded by the welded portion 4a.

In some embodiments, the crack growth rate da / dt is obtained in advance by an experiment for each combination of the material of the pipe to be welded by the welded portion 4a, the groove shape, the outer diameter D, the thickness t, and the material of the welding rod. Then, the crack growth reverse analysis and the crack growth analysis may be performed. By obtaining the crack growth rate da / dt in advance for each combination, the crack growth rate da / dt, in other words, the master curve 14, can be accurately obtained, the signal level threshold value th can be accurately determined, and the remaining life is also long. It can be evaluated accurately.

In some embodiments, the crack growth rate da / dt is obtained in advance by an experiment for each combination of the material of the pipe to be welded by the welded portion 4a, the groove shape, the outer diameter D, the thickness t, and the material of the welding rod. At that time, the crack growth rate da / dt is obtained by using the equipment (actual machine) actually used. By obtaining the crack growth rate da / dt using an actual machine, the crack growth rate da / dt, in other words, the master curve 14, can be obtained more accurately, and the signal level threshold value th can be accurately determined. , The remaining life can also be evaluated accurately.

(About the prediction of the occurrence time of the area that can be regarded as a crack in the crack growth process)
In the above description, a region that can be regarded as a crack in the crack growth process, that is, a technique for detecting the crack 6b in the present specification and an evaluation of the remaining life of the evaluation target portion in which the crack 6b is present have been described.
On the other hand, in the embodiment described below, the prediction of the time when the above-mentioned region that can be regarded as a crack is generated before the above-mentioned region that can be regarded as a crack is generated will be described.

In this embodiment, a preliminary preparation step is performed in advance.
In the preparatory step, a sample for acquiring an intensity curve having a welded portion is prepared, and as shown in FIG. 18, a reflected wave intensity curve 16 showing a change over time in the intensity of the reflected wave of ultrasonic waves with respect to the sample for acquiring the intensity curve is obtained in advance. create. The details of the preparatory process will be described later.

As shown in FIG. 18, when the intensity (echo height) of the reflected wave of the welded portion 4a of the evaluation target portion obtained in the main flaw detection step S41 of the inspection step S4 ^{is H * less than the signal level threshold, the reflected wave. Based on the intensity curve 16, the time Δt * from the intensity H * of the} reflected wave received in the flaw detection step S41 until the intensity of the reflected wave with respect to the welded portion 4a of the evaluation target portion reaches the signal level threshold th is obtained. This process is called a threshold reaching life estimation process. The threshold reaching life estimation step is performed in the crack evaluation step S42 described above when the intensity of the reflected wave of the welded portion 4a of the evaluation target portion obtained in the main flaw detection step S41 is H ^{* less than the signal level threshold value.}

By using the reflected wave intensity curve 16 created in advance in the threshold reaching life estimation step, the time until the signal level threshold th is reached at the stage where no crack is generated in the welded portion 4a to be evaluated Δt ^* ( That is, the time from the time when the inspection step S4 is performed to the time when the crack is generated) can be obtained.

FIG. 19 shows an embodiment of the preparatory process.
The preparatory step may be carried out at the same time in the crack evaluation standard formulation step S100 of FIG. 4 described above.
In FIG. 19, first, one or more strength curve acquisition samples are prepared (sample preparation step S400). In the following description, it is assumed that the sample for acquiring the strength curve is the test piece 12 in the crack evaluation standard establishment step S100 described above.
For the prepared test piece 12, the intensity of the reflected wave of the ultrasonic wave is measured at each of the two or more time points where the elapsed time is different (reflected wave intensity acquisition step S402). Next, based on this measurement result, the reflected wave intensity curve for the test piece 12 is identified (identification step S404).
Thereby, the reflected wave intensity curve can be easily obtained by the measurement in the test stage using the test piece 12.

FIG. 20 shows an example of the reflected wave intensity curve obtained in the preparatory step. The reflected wave intensity curves 16a and 16b are identified and obtained from two measurement points u1, u2, v1 and v2 at different time points.

In one embodiment, the following general formula (1) is selected as an approximate curve for the two test pieces 12.
General formula y = p · e ^qx (1)
However, y; echo height, x; elapsed time, p, q; coefficient Next, by performing flaw detection twice at different elapsed times and substituting these measured values into equation (1), the coefficients p, q. Ask for. In this way, the reflected wave intensity curves 16a and 16b can be obtained from the two test pieces 12.

In the threshold reaching life estimation step, one embodiment is used as a method of obtaining ^{the time Δt * from the intensity H *} of the reflected wave of the welded portion 4a of the evaluation target portion obtained in the main flaw detection step S41 until the signal level threshold th is reached. Then, as shown in FIG. 18, using the reflected wave intensity curve 16, ^{the time Δt *} _sample for the reflected wave intensity to reach the signal level threshold value th from the ^{reflected wave intensity H * is obtained for the test piece 12.} ..
Next, in the step of determining the time Delta] t ^*, the Larson-Miller parameter method, converting the time Delta] t ^* _sample time Delta] t ^{*.
According to this embodiment, the threshold arrival time Δt *} of the welded portion 4a of the evaluation target portion can be easily ^{obtained from the time Δt *} _sample obtained by using the test piece 12 by the calculation using the Larson mirror parameter method. can. ^{That is, when the intensity H * of the} reflected wave acquired for the evaluation target portion does not reach the signal level threshold value th, the reflected wave acquired for the evaluation target portion is based on the known tendency of the temporal change of the flaw detection signal of the internal flaw detection inspection. The time Δt ^* can be obtained.

In one embodiment, as shown in FIG. 21, the entire life of the test piece 12 (penetration time in FIG. 13) _{under test conditions (temperature T 1} , load stress σ ₁ ) in a creep test or the like using the Larson mirror parameter method is used. (Until the arrival of tr) From tr ₁ and the time before the intensity of the reflected wave reaches the signal level threshold th Δt ^* _sample , the change amount ΔD ₁ of the life consumption rate is calculated by the equation (2).
Next, from the total lifetime tr _{2 under the operating conditions (temperature T 2} , load stress σ ₂ ) of the welded portion 4a of the evaluation target portion, ^{and the time Δt *} until the intensity of the reflected wave reaches the signal level threshold th, the equation ( In 3), the change amount ΔD ₂ of the life consumption rate is calculated.

Next, the total life span tr1 and tr2 are obtained from the equations (4) and (5). In the formulas (4) and (5), when the materials of the welded portions are the same, the coefficients a0, a1, a2, a3 and C have the same values.
Since ΔD ₁ and ΔD ₂ are considered to be equivalent, the equation (6) holds, and therefore, from the ratio of the _{total lifetime tr 1 obtained by the equation (4) to the total lifetime tr 2} obtained by the equation (5). ^{, As shown in the equation (7), the time Δt *} until the intensity of the reflected wave of the welded portion 4a to be evaluated reaches the signal level threshold value th can be obtained.
In FIG. 18, t ^* _sample indicates the time when the intensity of the reflected wave of the test piece 12 ^{becomes H *.}

Another method for determining the time Delta] t ^* from the intensity of the reflected wave obtained in this flaw step S41 H ^* to reach the signal level threshold, in one embodiment, as shown in FIG. 18, the reflected wave intensity curve 16 Is corrected by the Larson mirror parameter method, and a correction curve 18 showing a change over time in the intensity of the reflected wave with respect to the welded portion 4a of the evaluation target portion is obtained.
In the step of obtaining the time Δt ^* in this embodiment, the correction curve 18 is used to obtain ^{the time Δt *.}

According to this embodiment, by obtaining the correction curve 18, the threshold value arrival time Δt ^* with respect to the welded portion 4a of the evaluation target portion can be easily obtained.
In FIG. 18, t ^* indicates the time when the intensity of the reflected wave of the welded portion 4a to be evaluated ^{becomes H *} , and t3 indicates the time when the crack occurs.

In some of the above-described embodiments, the following effects are exhibited.
(1) The method for formulating a crack evaluation standard according to at least one embodiment is a method for formulating a crack evaluation standard.
Creep deformation step S111, which creep-deforms the test piece 12 to the first time point,
A flaw detection signal acquisition step S112 for performing an internal flaw detection inspection on the test piece 12 at at least one second time point prior to the first time point and acquiring a flaw detection signal at at least one second time point.
By comparing the estimated size of the crack at the second time point obtained by tracing the crack growth process from the first time point to at least one second time point with the flaw detection signal at the second time point, the crack by the internal flaw detection inspection The evaluation standard determination step S120 for determining the evaluation standard of the above is provided.

As a result, the estimated size of the crack at the second time point is obtained by tracing back the crack growth process from the first time point. That is, at the second time point, the size of the region that is a dense region of creep voids and can be regarded as a crack in the crack growth process can be obtained as the estimated size of the crack. Then, by comparing the estimated size of the crack at the second time point with the flaw detection signal at the second time point, it is possible to determine the crack evaluation standard by the internal flaw detection inspection, which can detect even a region that can be regarded as a crack in the crack growth process. Thereby, it is possible to provide a method for formulating a crack evaluation standard capable of evaluating the internal state of a metallic material in the early stage of the crack growth process.

(2) In some embodiments, in the flaw detection signal acquisition step S112, flaw detection signals are acquired for each of the plurality of second time points prior to the first time point.
In some embodiments, the model building step S123 is further provided to build a model of the crack growth process that matches the changing tendency of the flaw detection signal at each of the plurality of second time points.
In the evaluation standard determination step S120, the crack growth process is traced back to one or more second time points using the above model to obtain the estimated size of the crack at the second time point (estimated size acquisition step S125).

As a result, the model of the crack growth process for obtaining the estimated size of the crack at the second time point is constructed so as to match the change tendency of the flaw detection signal at each of the plurality of second time points. The estimation accuracy of the estimated size of is improved. As a result, a crack evaluation standard suitable for detecting a region that can be regarded as a crack in the crack growth process can be obtained.

(3) In some embodiments, the above model of the crack growth process may also use a crack growth model based on at least one of crack growth calculation, FEM, damage mechanics evaluation, void simulation method or microstructure simulation method. good.

(4) In some embodiments, a size measuring step S121 is provided in which the test piece 12 that has been creep-deformed up to the first time point is subjected to destructive inspection and the size of the crack at the first time point is measured.
Some embodiments include an estimated size acquisition step S125 that obtains an estimated size of the crack at the second time point based on the size of the crack at the first time point.

As a result, since the estimated size of the crack at the second time point is obtained based on the measured size of the crack at the first time point, a crack evaluation standard more suitable for the evaluation of the crack by the internal flaw detection inspection can be obtained.

(5) In some embodiments, in the threshold value acquisition step S127, as a crack evaluation standard by the internal flaw detection inspection, a region corresponding to the estimated size of the crack at the second time point is obtained from the signal level distribution of the flaw detection signal at the second time point. The extractable signal level threshold value th is obtained.

By using the evaluation criteria thus obtained, the range of cracks can be easily specified. That is, since the crack in the inspection target can be evaluated by comparing the flaw detection signal obtained by inspecting the evaluation target portion of the inspection target by the internal flaw detection inspection with the signal level threshold value th, the crack in the inspection target can be evaluated. Is easy to evaluate.

(6) In some embodiments, the internal flaw detection inspection may be at least one flaw detection inspection of a phased array method, an aperture synthesis method, a high frequency UT method, or an ultrasonic noise method.

(7) The crack evaluation method by the internal flaw detection inspection according to at least one embodiment is a method of performing a crack evaluation of an evaluation object using the crack evaluation criteria formulated as described above.
The crack evaluation method by the internal flaw detection inspection according to at least one embodiment includes the main flaw detection step S41 in which the internal flaw detection inspection is performed on the evaluation target of the same material as the test piece 12 and the flaw detection signal is acquired.
A crack evaluation step S42 for evaluating the presence or absence of cracks in the evaluation target based on the flaw detection signal acquired for the evaluation target according to the crack evaluation criteria is provided.

In this crack evaluation method, the crack evaluation criteria are determined as described above. That is, as shown in FIG. 11, the crack evaluation criterion is determined by comparing the estimated crack size a2 at the second time point with the flaw detection signal at the second time point. Therefore, in this crack evaluation method, the presence or absence of cracks in the evaluation target is evaluated based on the flaw detection signal obtained by performing an internal flaw detection inspection on the evaluation target according to the crack evaluation criteria determined in this way. , The presence or absence of cracks in the evaluation object can be evaluated.

(8) In some embodiments, in the crack evaluation step S42 for evaluating the presence or absence of a crack, a region of the evaluation target to which the flaw detection signal acquired for the evaluation target satisfies the evaluation criteria is specified as a crack.

This makes it possible to specify the size of the region that can be regarded as a crack in the crack growth process.

(9) In some embodiments, the remaining life evaluation step S5 for evaluating the remaining life of the evaluation object from the specified crack size based on the model of the crack growth process is provided.

As a result, the remaining life of the evaluation target can be evaluated even at the stage where a region that can be regarded as a crack in the crack growth process is generated inside the evaluation target.

(10) In some embodiments, the model of the crack growth process is the same as the model showing the crack growth process used to determine the estimated size of the crack at the second time point when formulating the evaluation criteria.

Since the evaluation criteria suitable for the model showing the crack growth process used to obtain the estimated size of the crack at the second time point have been obtained, the crack size specified by the evaluation criteria is used based on the model. By evaluating the remaining life of the evaluation target, the evaluation accuracy of the remaining life of the evaluation target is improved.

(11) In some embodiments, a threshold value reaching life estimation step is provided ^{in which the time Δt *} until a crack is generated in the evaluation target is obtained based on the flaw detection signal acquired for the evaluation target.

As a result, based on the flaw detection signal acquired for the evaluation target, even if the evaluation target does not have a region that can be regarded as a crack in the crack growth process, the region that can be regarded as a crack in the crack growth process in the evaluation target. Can be grasped when will occur.

(12) In some embodiments, if the flaw detection signal acquired for the evaluation target does not meet the evaluation criteria, the flaw detection acquired for the evaluation target is based on the known tendency of the flaw detection signal of the internal flaw detection inspection to change with time. The time Δt ^* is obtained from the signal.

As a result, even when the flaw detection signal acquired for the evaluation target does not satisfy the evaluation criteria, that is, the intensity of the reflected wave of the welded portion 4a of the evaluation target portion obtained in the main flaw detection step S41 of the inspection step S4 is increased. ^{Even if the H *} is less than the signal level threshold value th, it is possible to accurately determine the time of occurrence of a region that can be regarded as a crack in the crack growth process in the evaluation object based on the known tendency of the time-dependent change of the flaw detection signal in the internal flaw detection inspection. can.

(13) In some embodiments, the evaluation object is a high-strength ferritic steel including a welded portion.

According to the findings of the present inventors, in the case of a welded portion formed by welding a member made of high-strength ferritic steel, there is no correlation between the degree of creep damage on the outer surface and the degree of creep damage on the inner surface, and welding is performed. It is desirable to evaluate the degree of creep damage inside the part.
In this regard, the above-mentioned crack evaluation method evaluates cracks in the evaluation target based on the flaw detection signal obtained by performing an internal flaw detection inspection on the evaluation target in accordance with the crack evaluation criteria determined as described above. Therefore, the crack in the evaluation object can be evaluated. Therefore, the above crack evaluation method is suitable for evaluating cracks in a member made of high-strength ferritic steel.

(14) The maintenance management method according to at least one embodiment is based on the inspection step S4 for evaluating the crack of the evaluation target by the crack evaluation method by the internal flaw detection inspection described above and the evaluation result of the crack of the evaluation target. A maintenance management step S11 for performing maintenance management of the evaluation target is provided.

As a result, the region that can be regarded as a crack in the crack growth process can be evaluated, so that the maintenance and management of the evaluation target can be performed widely.

(15) In some embodiments, the maintenance management in the maintenance management step S11 includes at least one of replacement, repair or life extension measures of the evaluation object.

As a result, the area that can be regarded as a crack in the crack growth process can be evaluated, so that the replacement, repair, or life extension measure of the evaluation target can be widely implemented.

The present invention is not limited to the above-described embodiment, and includes a modification of the above-mentioned embodiment and a combination of these embodiments as appropriate.
For example, in some of the above-described embodiments, the evaluation target portion is a welded portion in a plurality of steam pipes connecting between a boiler and a steam turbine in a thermal power generation facility, but the welded portion to be evaluated is a boiler. The crack evaluation standard formulation method, the crack evaluation method by internal flaw detection inspection, and the maintenance management method according to the present invention are applicable to various welds exposed to high temperature and high pressure. ..

2 Phased array ultrasonic flaw detector 4a, 4b, 4c Welded part 6a, 6b, 6c Crack 8a, 8b, 8c Heat-affected zone 10a, 10b, 10c Welded part 12 Test piece 14 Master curve 16 Reflected wave intensity curve 18 Correction curve

Claims (15)

It ’s a way to formulate crack evaluation criteria.
The step of creeping and deforming the test piece to the first time point,
A step of performing an internal flaw detection inspection on the test piece at at least one second time point prior to the first time point and acquiring a flaw detection signal at at least one second time point.
Of the estimated crack sizes at the second time point obtained by tracing the crack growth process from the first time point to at least one second time point, the time is later than the time corresponding to the lower limit of detection of the flaw detector. By comparing the estimated size of the crack at the second time point corresponding to the time closest to the time with the flaw detection signal at the second time point, the step of determining the evaluation criteria of the crack by the internal flaw detection inspection. ,
A method for formulating crack evaluation criteria, which is characterized by being equipped with. In the step of acquiring the flaw detection signal, the flaw detection signal is acquired for each of the plurality of second time points prior to the first time point.
Further provided, a step of constructing a model of the crack growth process consistent with the change tendency of the flaw detection signal at each of the plurality of second time points.
Claim 1 is characterized in that in the step of determining the evaluation criteria, the model is used to trace the crack growth process back to one or more of the second time points to obtain the estimated size of the crack at the second time point. How to formulate crack evaluation criteria described in. The crack according to claim 2, wherein the model of the crack growth process is a crack growth model based on at least one of crack growth calculation, FEM, damage mechanics evaluation, void simulation method or microstructure simulation method. Evaluation standard formulation method. A step of destructively inspecting the test piece subjected to the creep deformation up to the first time point and measuring the size of the crack at the first time point.
A step of obtaining the estimated size of the crack at the second time point based on the size of the crack at the first time point.
The crack evaluation standard formulation method according to any one of claims 1 to 3, wherein the method is provided with. In the step of determining the evaluation criterion, as the evaluation criterion of the crack by the internal flaw detection inspection, a region corresponding to the estimated size of the crack at the second time point from the signal level distribution of the flaw detection signal at the second time point. The crack evaluation standard formulation method according to any one of claims 1 to 4, wherein the signal level threshold value that can be extracted is obtained. The one according to any one of claims 1 to 5, wherein the internal flaw detection inspection includes at least one flaw detection inspection of a phased array method, an aperture synthesis method, a high frequency UT method, or an ultrasonic noise method. How to formulate crack evaluation criteria. A method for evaluating a crack in an object to be evaluated by using the evaluation standard for the crack formulated by the method according to any one of claims 1 to 6.
The step of performing the internal flaw detection inspection on the evaluation target of the same material as the test piece and acquiring the flaw detection signal, and
A step of evaluating the presence or absence of a crack in the evaluation object based on the flaw detection signal acquired for the evaluation object according to the evaluation criteria of the crack.
A crack evaluation method by internal flaw detection inspection, which comprises. The seventh aspect of claim 7, wherein in the step of evaluating the presence or absence of a crack, a region of the evaluation target in which the flaw detection signal acquired for the evaluation target satisfies the evaluation criteria is specified as a crack. Crack evaluation method by internal flaw detection inspection. The crack evaluation method by internal flaw detection inspection according to claim 8, further comprising a step of evaluating the remaining life of the evaluation object from the specified size of the crack based on the model of the crack growth process. .. 9. The model of the crack growth process is the same as the model showing the crack growth process used to obtain the estimated size of the crack at the second time point when formulating the evaluation criteria. Rhagades evaluation method by the described internal flaw detection inspection. The invention according to any one of claims 7 to 10, further comprising a step ^{of obtaining a time Δt *} until a crack is generated in the evaluation object based on the flaw detection signal acquired for the evaluation object. Crack evaluation method by internal flaw detection inspection. When the flaw detection signal acquired for the evaluation object does not meet the evaluation criteria, the time from the flaw detection signal acquired for the evaluation object is based on the known tendency of the flaw detection signal of the internal flaw detection inspection to change with time. The crack evaluation method by internal flaw detection inspection according to claim 11, wherein ^{Δt * is obtained.} The crack evaluation method by internal flaw detection inspection according to any one of claims 7 to 12, wherein the evaluation object is a high-strength ferritic steel including a welded portion. A step of evaluating a crack in the evaluation object by the method according to any one of claims 7 to 13.
Based on the evaluation result of the crack of the evaluation target, the step of performing maintenance management of the evaluation target and
A maintenance management method characterized by being equipped with. The maintenance management method according to claim 14, wherein the maintenance management includes at least one of replacement, repair, or life extension measures of the evaluation object.

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