JP6974984B2 - Remaining life evaluation method and maintenance management method - Google Patents

Description

The present disclosure relates to a remaining life evaluation method 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 (signal level) is the reflected echo height derived in advance. By querying the corresponding data with the creep void number density, the creep void number density corresponding to the detected reflected echo height is obtained, and further, the metal is based on the database in which the creep void number density and the creep damage amount are associated with each other. The amount of creep damage in the material is calculated.

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 has also been found that there may be no strict correspondence with the density, and methods and crack growth that can evaluate the internal state of the metal material in the early stages of the crack growth process inside the metal material. There is a need for a method for assessing the remaining life in the early stages of the process.

In view of the above circumstances, it is an object of the present invention to provide a method for evaluating the remaining life, which can evaluate the remaining life at an early stage of the crack growth process.
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 remaining life evaluation method according to at least one embodiment of the present invention is
A step of determining the size and position of a crack in the evaluation object by comparing the flaw detection signal obtained by the flaw detection of the evaluation object with the threshold for crack discrimination, and
A step of inputting the size and the position of the crack into the remaining life evaluation model and obtaining the remaining life of the evaluation object is provided.
The crack discrimination threshold is set so that at least a crack in a pseudo-crack state in which the local creep life consumption rate is X% or more and 90% or less (provided that 50 <X <90 is satisfied) can be discriminated. It is a feature.

The progress of creep damage (crack growth process) in the evaluation object is considered to be as follows. Creep voids occur at grain boundaries over time. Next, when the number of the creep voids increases, the creep voids coalesce and finally become a microscopic crack, and the macroscopic crack propagates and finally reaches penetration.
In the present specification, not only a clear crack that can be observed by visual observation of a cross section such as a macroscopic crack, but also a region that can be regarded as a crack in the crack growth process such as a set of creep voids (a dense region of creep voids) (a region that can be regarded as a crack (a dense region of creep voids). It is called a crack including the crack in the pseudo-crack state).

In the method (1) above, at least a crack in a pseudo-crack state in which the local creep life consumption rate is X% or more and 90% or less (provided that 50 <X <90 is satisfied) is set so as to be discriminable. Since the discriminant threshold is used, the size and size of the pseudo-cracked crack in the evaluated object even if the damaged state of the evaluated object is before the occurrence of cracks that can be observed by visual observation of the cross section such as macroscopic cracks. The position can be determined. Then, since the size and position of the crack thus obtained are input to the remaining life evaluation model to obtain the remaining life of the evaluation object, the damaged state of the evaluation object is observed by visual observation of the cross section like a macroscopic crack. The remaining life of the object to be evaluated can be evaluated even before the possible cracks occur.
In the method (1) above, the remaining life of the evaluation target can be obtained by inputting the size and position of the crack obtained from the flaw detection result of the evaluation target into the remaining life evaluation model. Life can be evaluated.

(2) In some embodiments, in the method of (1) above,
The crack discrimination threshold is
The time of the crack size predicted by inputting the crack size and position in the pseudo-crack state obtained from the flaw detection result of the sample material at the first time point using the crack discrimination threshold into the remaining life evaluation model. in variation curve, the prediction time t _2CAL said localized creep life consumption rate corresponds to the crack size Z ₂ after having reached 100%, the crack of the crack size Z ₂ is actually measured in the sample material It is characterized in that the ratio of time to the second time point t _{2ACT (t 2ACT} / t _2CAL ) is the threshold value verified to satisfy a predetermined range.

According to the method (2) above, _{it is verified that the above ratio (t 2ACT} / t _2CAL ) satisfies a predetermined range by using the threshold value for crack discrimination, and therefore it is used for the threshold value for crack discrimination and verification. By using the obtained remaining life evaluation model, the size and position of cracks in the evaluation target can be accurately obtained, and the accuracy of the remaining life of the evaluation target is improved.

(3) In some embodiments, in the method (2) above, the predetermined range may be set to 0.5 or more and 2.0 or less from a practical point of view.

(4) In some embodiments, in the method (3) above, the crack discrimination threshold is 0.5 × t _2CAL ≦ t before the step of determining the size and position of the crack in the evaluation object. It is characterized by comprising a step of verifying that _2ACT ≤ 2.0 × t _{2CAL is satisfied or confirming the verification result.}

_{According to the method (4) above, 0.5 × t 2CAL} ≦ t _2ACT ≦ 2.0 × t _2CAL is obtained by using the crack discrimination threshold value before determining the size and position of the crack in the evaluation object. Since the satisfaction is verified or the verification result is confirmed, it is not necessary to perform the above verification or confirm the verification result after performing the step of determining the size and position of the crack in the evaluation object.

(5) In some embodiments, in any of the above methods (1) to (4), the flaw detector used for the flaw detection device is used before the step of determining the size and position of the crack in the evaluation object. It is characterized by comprising a step of setting the measurement sensitivity to an amplification condition which is 10 dB to 30 dB higher than the reference condition of the flaw detector for detecting a visually observable crack.

According to the method (5) above, a crack in a pseudo-crack state is discriminated by performing a flaw detection of an evaluation object with a flaw detector set to an amplification condition in which the measurement sensitivity is 10 dB to 30 dB higher than that of the reference state. It becomes easier to do.

(6) In some embodiments, in the method of (5) above,
When the flaw detector used when the reference condition is set and the flaw detector used for flaw detection of the evaluation object are different, the measurement sensitivity is set to the amplification condition, and then the crack in the pseudo-crack state by both flaw detectors. It is characterized by further providing a step of comparing the flaw detection results of.

According to the method (6) above, even if the flaw detector used when the reference condition is set and the flaw detector used for flaw detection of the evaluation target are different, the remaining life of the evaluation target can be accurately evaluated.

(7) In some embodiments, in any of the methods (1) to (6) above, the local creep lifetime consumption rate is 100% at the time when locally visually observable cracks occur. It is characterized by being stipulated to be.

According to the method (7) above, it is possible to discriminate a crack in a pseudo-cracked state at a stage before the generation time of a local region where stress transmission is not performed, and before a local region where stress transmission is not generated occurs. The remaining life of the evaluation target can be evaluated even at the stage of.

(8) In some embodiments, in any of the methods (1) to (7) above, the quasi-cracked crack is a set of creep voids.

According to the method (8) above, the remaining life of the evaluation target can be evaluated even at the time when the set of creep voids occurs.

(9) In some embodiments, in any of the above methods (1) to (8),
The flaw detection is characterized by being an internal flaw detection capable of detecting at least a crack in the pseudo-crack state generated inside the evaluation object.

According to the method (9) above, the size and position of the crack in the pseudo-crack state generated inside the evaluation target can be detected, and the remaining life of the evaluation target is based on the size and position of the crack. Can be evaluated.

(10) In some embodiments, in any of the above methods (1) to (9), there is no portion in the flaw detection region of the evaluation target whose flaw detection signal is equal to or higher than the crack discrimination threshold. The case is characterized by comprising a step of predicting the ^{time Δt *} required for the flaw detection signal to reach the crack discrimination threshold value from the signal level of the flaw detection signal based on the known temporal change characteristics of the flaw detection signal. do.

According to the method (10) above, even if there is no portion in the flaw detection region of the evaluation target where the flaw detection signal is equal to or higher than the crack discrimination threshold, the flaw detection signal is based on the known tendency of time change of the flaw detection signal. It is possible to accurately determine the timing at which the above-mentioned pseudo-cracked cracks occur in the evaluation object.

(11) In some embodiments, in any of the methods (1) to (10), the crack discrimination threshold is individually set for the combination of the flaw detection method and the remaining life evaluation model. It is characterized by having a threshold value.

According to the method (11) above, the crack discrimination threshold is a value suitable for the combination of the flaw detection method and the remaining life evaluation model. Then, since the remaining life of the evaluation target is obtained by inputting the size and position of the crack obtained by using the crack discrimination threshold value into the remaining life evaluation model, the evaluation accuracy of the remaining life of the evaluation target is improved. ..

(12) In some embodiments, in any of the above methods (1) to (11), a plurality of the crack discrimination methods corresponding to a combination of the flaw detection method and the plurality of types of the remaining life evaluation model. From the threshold database in which the threshold is stored, the threshold for crack discrimination corresponding to the combination of the flaw detection method used for obtaining the flaw detection signal and the residual life evaluation model adopted in the step of obtaining the residual life is acquired. It is characterized by having a step to perform.

According to the method (12) above, a crack discrimination threshold suitable for the combination of the flaw detection method used for obtaining the flaw detection signal and the residual life evaluation model adopted in the step of obtaining the residual life can be obtained, and thus the evaluation target. The size and position of cracks in an object can be accurately determined, and the accuracy of the remaining life of the object to be evaluated is improved.

(13) In some embodiments, in any of the above methods (1) to (12), the crack generation site targeted for evaluation at the time of setting the crack discrimination threshold and the generation of cracks in the evaluation target object. When the conditions are different from those of the site, the step of resetting the crack discrimination threshold is provided.

According to the method (13) above, a crack discrimination threshold suitable for determining the size and position of a crack at the crack occurrence site in the evaluation object can be obtained, so that the crack at the crack generation site can be obtained. The size and position can be obtained with high accuracy, and the accuracy of the remaining life of the evaluation object is improved.

(14) In some embodiments, in any of the methods (1) to (13), the crack discrimination threshold is different from the first flaw detection method used to obtain the flaw detection signal. 2. It is characterized in that it is acquired based on a preset threshold value for the flaw detection method and a correlation between the flaw detection signal of the first flaw detection method and the flaw detection signal of the second flaw detection method.

According to the method (14) above, from the correlation between the flaw detection signal of the first flaw detection method and the flaw detection signal of the second flaw detection method, the threshold value for crack discrimination when the evaluation target is flawed by the first flaw detection method is determined. Since it can be estimated from the crack discrimination threshold value when the evaluation target is detected by the second flaw detection method, it is possible to simplify the preliminary preparation for acquiring the crack discrimination threshold value for the first flaw detection method.

(15) In some embodiments, in any of the above methods (1) to (14),
The crack discrimination threshold is
Creep deform the test piece to the third time point,
The flaw detection was performed on the test piece at the fourth time point prior to the third time point, and the flaw detection signal at the fourth time point was acquired.
It was preset by comparing the estimated size of the crack at the fourth time point obtained by tracing the crack growth process from the third time point to the fourth time point with the flaw detection signal at the fourth time point. It is characterized by.

In the method (15) above, the estimated size of the crack at the fourth time point is obtained by tracing back the crack growth process from the third time point. That is, the size of the region that is a quasi-cracked crack at the fourth time point can be obtained as the estimated size of the crack. Then, by comparing the estimated size of the crack at the fourth time point with the flaw detection signal at the fourth time point, a crack discrimination threshold that can detect a crack in a pseudo-crack state can be determined. As a result, the size and position of the crack in the pseudo-crack state in the evaluation object can be obtained by using the crack discrimination threshold value, so that the evaluation object can be evaluated even when the crack in the pseudo-crack state occurs. The remaining life of the can be evaluated.

(16) In some embodiments, in any of the methods (1) to (15) above, the remaining life evaluation model is a crack growth calculation, FEM, damage mechanical evaluation, void simulation or microstructure simulation method. A model based on at least one may be used.

(17) In some embodiments, in any of the methods (1) to (16) above, the flaw detection is at least one of a phased array method, an aperture synthesis method, a high frequency UT method, or an ultrasonic noise method. It may be one flaw detection.

(18) In some embodiments, in any of the above methods (1) to (17),
In the step of determining the size and position of the crack,
Among the evaluation objects, a region in which the signal level of the flaw detection signal acquired for the evaluation object is equal to or higher than the crack discrimination threshold value is specified as the crack.

In the method (18) above, the size of a crack in a pseudo-crack state can be specified.

(19) In some embodiments, in any of the methods (1) to (18) 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 respect, in the above method (19), at least a crack in a pseudo-crack state in which the local creep life consumption rate is X% or more and 90% or less (however, 50 <X <90 is satisfied) can be discriminated. The size and position of the crack in the evaluation target are obtained using the crack discrimination threshold value, and the obtained crack size and position are input to the remaining life evaluation model to obtain the remaining life of the evaluation target. Therefore, the method (19) above is suitable for evaluating the remaining life of a member made of high-strength ferritic steel.

(20) The maintenance management method according to at least one embodiment of the present invention is
The step of evaluating the remaining life of the evaluation object by any of the above methods (1) to (19), and
It is characterized by comprising a step of performing maintenance management of the evaluation target based on the evaluation result of the remaining life of the evaluation target.

According to the method (20) above, the remaining life of the evaluation object is evaluated even if the damage state of the evaluation object is before the occurrence of a clear crack observable by visual observation of the cross section such as a microscopic crack. Since it can be done, it is possible to carry out maintenance management of the evaluation target in a wide range.

(21) In some embodiments, in the method of (20) 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 (21) above, the remaining life of the evaluation object can be evaluated even if the damaged state of the evaluation object is before the occurrence of a crack that can be observed by visual observation of the cross section such as a microscopic crack. , Exchange, repair or life extension measures for the object to be evaluated can be widely implemented.

According to at least one embodiment of the present invention, it is possible to provide a remaining life evaluation method capable of evaluating the remaining life at an early stage of the 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 a crack evaluation process. It is a figure which shows an example of the result of having examined the validity of a signal level threshold value. 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. 9 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. 9, and FIG. 9A 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 a welded part about the flaw detection signal at the 4th 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 figure which shows the local creep life consumption rate in the region where the value becomes more than a signal level threshold value. 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. It is a table explaining another embodiment of a sensitivity setting / confirmation process.

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, for the flaw detection inspection, a phased array method, a UT method, an aperture synthesis method, a high frequency UT method, or an ultrasonic noise method can be used. 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.
As described above, in some embodiments, the remaining life evaluation step S5 and the maintenance management step S11 for performing maintenance management of the evaluation target based on the evaluation result of the remaining life of the evaluation target are provided.
As a result, the remaining life of the evaluation target can be evaluated even if the damage state of the evaluation target is before the occurrence of cracks that can be observed by visual observation such as macroscopic cracks. Maintenance management can be performed.
Also, in some embodiments, the measures for the evaluation target include at least one of replacement, repair or life extension measures for the evaluation target.
As a result, the remaining life of the evaluation target can be evaluated even if the damage state of the evaluation target is before the occurrence of cracks that can be observed by visual observation such as microscopic cracks, so that the evaluation target can be replaced or repaired. Alternatively, life extension measures can be widely implemented.

(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 aged use, 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 coalesce and finally become a microscopic crack, and the macroscopic crack propagates and finally reaches penetration.
In the present specification, not only cracks that can be observed by visual observation of a cross section such as macroscopic cracks, but also regions that can be regarded as cracks in the crack growth process (pseudo-cracks) such as a set of creep voids (dense region of creep voids). It will be called a crack including the crack in the state).

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. In the following description, the result obtained by the flaw detection inspection is referred to as a flaw detection signal, a signal level, a reflected wave, a reflected echo, or simply an echo.
FIG. 2 is a flowchart showing the steps carried out in the inspection step S4.
The inspection step S4 includes a sensitivity setting / confirmation step S41 for setting or confirming the measurement sensitivity of the flaw detection device, and a main flaw detection step S42 for performing an internal flaw detection inspection on the evaluation target portion of the evaluation target and acquiring a flaw detection signal. A crack evaluation step S43 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 according to the crack evaluation criteria determined in the crack evaluation standard formulation step S100 described later.

In the sensitivity setting / confirmation step S41, prior to the main flaw detection step S42, the measurement sensitivity of the flaw detector used in the main flaw detection step S42 is set to the amplification condition that can detect the crack in the pseudo-crack state described above, or the amplification condition. It is a process to confirm that it is set to.

In the sensitivity setting / confirmation step S41, the measurement sensitivity of the flaw detector is set to an amplification condition that is 10 dB to 30 dB higher than the reference condition described later of the flaw detector for detecting a visually observable crack. This makes it easier to identify cracks in the pseudo-cracked state in some embodiments.

The reference conditions of the flaw detector for detecting visually observable cracks will be described.
The reference condition is the sensitivity of the flaw detector set to detect a predetermined localized defect uniquely defined by JIS or the like. With this setting, for example, it is possible to detect creepy cracks grown to about several mm. The sensitivity of the flaw detector under the reference conditions is specifically adjusted by using the comparison test piece described in JIS Z 3060: 2015 “Ultrasonic flaw detection test method for steel welds”.
Although not shown, a standard hole is installed in the comparison test piece, and the sensitivity (measurement sensitivity) of the flaw detector is adjusted so that the maximum echo of the reflected wave from the standard hole is 80%. The sensitivity obtained as a result is defined as the reference sensitivity (sensitivity under the reference condition). Note that 80% means that 80% of echoes are observed when the echo of the maximum measurement limit of the flaw detector is set to 100%.

For defects or flaws such as planar defects (for example, clear cracks) targeted by the general ultrasonic flaw detection method, the evaluation targets according to some embodiments are based on analysis methods such as crack growth calculation. It is a flaw that can be regarded as a crack (a crack in a pseudo-crack state, in fact, a density of voids), and it is necessary to judge a signal at a lower level than a clear crack detection signal.
Therefore, in some embodiments, the sensitivity is increased by 10 dB to 30 dB from the reference sensitivity, and the echo height, which is the signal level threshold value th, is set in consideration of the legibility at the time of flaw detection in the flaw detection step S42 described below. The sensitivity may be adjusted to 20-80%.
Here, increasing the sensitivity by 10 dB means amplifying the signal about 3.2 times. If the echo height, which is the signal level threshold value, is set to 20% under the condition that the sensitivity is increased by 10 dB, the echo height corresponding to about 6.3% (≈20% / 3.2) under the condition of the reference sensitivity. Will be used for judgment.

In this flaw detection step S42, flaw detection is performed after setting the sensitivity of the amplification conditions set in the sensitivity setting / confirmation step S41. Here, if the flaw detection device used in the flaw detection step S42 is different from the flaw detection device used when calculating the signal level threshold value th described later, calibration described later is performed.
When the main flaw detection step S42 is repeatedly carried out, if the sensitivity setting / confirmation step S41 has already been carried out, it is not necessary to repeatedly carry out the sensitivity setting / confirmation step S41 each time the main flaw detection step S42 is carried out. ..
In this flaw detection step S42, 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 S42.
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 S43, the intensity of the reflected wave received in the flaw detection step S42 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 the crack evaluation standard (crack discrimination threshold) determined in the crack evaluation standard formulation step S100, which will be described later.
Thus, in some embodiments, the flaw detection is an internal flaw detection that can detect at least a pseudo-cracked crack that occurs inside the evaluation object, so that a pseudo-cracked crack that occurs inside the evaluation object. The remaining life of the object to be evaluated can be evaluated based on the size and position of the object.

FIG. 4 is a flowchart showing the procedure in the crack evaluation step S43.
As shown in FIG. 4, the crack evaluation step S43 includes a crack determination threshold acquisition step S431, a comparison step S432, a crack identification step S434, and a threshold arrival life estimation step S435.

In the crack discrimination threshold acquisition step S431, from the threshold database created as described later, the flaw detection method carried out in the main flaw detection step S42 and the remaining life of the evaluation target portion as described later in the remaining life evaluation step S5. This is a step of acquiring a signal level threshold value th (threshold value for crack discrimination) corresponding to a combination with a crack growth process model (remaining life evaluation model) used in the evaluation.

The comparison step S432 is a step of comparing the intensity (signal level S) of the reflected wave received in the flaw detection step S42 with the signal level threshold value th acquired in the crack discrimination threshold acquisition step S431.

As a result of comparing the signal level S and the signal level threshold value th in the comparison step S432, if the intensity of the signal level S is equal to or higher than the signal level threshold value th, step S433 is positively determined and the crack identification step S434 is carried out.

The crack identification step S434 is a step of determining the size and position of a crack in the evaluation target by comparing the flaw detection signal obtained by the flaw detection of the evaluation target with the threshold for crack discrimination. That is, in the crack identification step S434, the size and position of the region where the signal level S is equal to or higher than the signal level threshold value th in the evaluation target portion are specified and specified based on the information of the reflected wave received in the flaw detection step S42. The size and position of the region shall be the size and position of the crack in the evaluation target portion.
This makes it possible to specify the size of the crack in the pseudo-crack state in the evaluation object.

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. Thus, in some embodiments, the size and location of the crack in the object to be evaluated can be determined.
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 S42 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.

As a result of comparing the signal level S and the signal level threshold value th in the comparison step S432, if the intensity of the signal level S is less than the signal level threshold value th, step S433 is negatively determined and the threshold value reaching life estimation step S435 is performed. Is also good . The threshold reaching life estimation step S435 will be described in detail later.

When the crack specifying step S434 or the threshold reaching life estimation step S435 is carried out, the process proceeds to step S436, and the crack specifying step S434 or the threshold reaching life estimation step S435 is carried out for all the evaluation target portions for which internal flaw detection was performed in the main flaw detection step S42. Determine if it was done.
If the crack identification step S434 or the threshold value reaching life estimation step S435 is carried out for all the evaluation target portions subjected to internal flaw detection in the main flaw detection step S42, step S436 is affirmatively determined and the process in the crack evaluation step S43 is completed. do.
If there is an evaluation target portion for which the crack identification step S434 or the threshold value reaching life estimation step S435 has not been performed among the evaluation target portions for which internal flaw detection has been performed in the main flaw detection step S42, step S436 is negatively determined and the process returns to the comparison step S432. ..

(Regarding the validity of the signal level threshold th)
In the crack specifying step S434, the size and position of the region where the signal level S is equal to or higher than the signal level threshold value th are specified in the evaluation target portion, and the size and position of the specified region are determined by the size and position of the crack in the evaluation target portion. And the position.
As described above, the signal level threshold value th is used as a criterion for detecting a crack in a pseudo-crack state, and it is desirable to verify whether this criterion is appropriate.

FIG. 5 is a diagram showing an example of the result of examining the validity of the signal level threshold value th. In FIG. 5, the horizontal axis is the logarithmic axis with respect to the test time.
In FIG. 5, the time point (first time point) when creep damage is applied to the test material by the creep test and the internal flaw detection inspection is performed is the starting point of the horizontal axis, and the crack Ca in the pseudo-cracked state detected at the first time point is found. Subsequent creep tests show the results of an evaluation of how it progresses.
In FIG. 5, the solid line graph shows the crack growth process obtained by the same remaining life evaluation model as the remaining life evaluation model used for evaluating the remaining life in the remaining life evaluation step S5, and the broken line graph is a solid line. It shows the range of 1/2 times and 2 times of the above graph showing the growth process of the shown crack.
In FIG. 5, the point Ca1 is a plot showing the size of the crack Ca in the pseudo-cracked state obtained based on the result of the internal flaw detection inspection performed at the first time point and the signal level threshold value th, and the point Ca2 is the first. It is a plot which shows the size of the crack Ca measured by the cutting investigation from the 1st time point to the 2nd time point after a predetermined time elapse.

As shown in FIG. 5, the result of performing the crack growth calculation with the size of the crack Ca in the pseudo-crack state at the first time point as the initial defect size is the measured value, that is, the crack Ca measured by the cutting investigation at the second time point. It was found to show a good match with the size of.

That is, the signal level threshold value th determined as described later is the size of the crack in the pseudo-crack state obtained by using the signal level threshold value th (crack discrimination threshold) from the flaw detection result of the test material at the first time point. In the crack size over time curve predicted by inputting the threshold and position into the remaining life evaluation model, the predicted time point corresponding to _{the crack size Z 2 after the local creep life consumption rate described later reaches 100%.} It has been found that the time ratio (t _2ACT / t _{2CAL ) between t 2CAL and the second time point t 2ACT in} which a crack of crack size Z ₂ is actually measured in the test material meets a predetermined range.
As described above, a crack in a pseudo-crack state refers to a set of creep voids (a dense region of creep voids), and the boundary with a healthy portion is unclear. Therefore, it is difficult to unconditionally determine the signal level threshold value th from the observation results such as the density of creep voids.
On the other hand, the most important thing in the remaining life evaluation is to accurately predict the growth of cracks after the local creep life consumption rate reaches 100%. Here, the accuracy of predicting crack growth by the remaining life evaluation model is greatly affected by the crack length and position (depth) of the initial input values.
Therefore, the present inventors have a remainder with respect to the size and position of the crack in the pseudo-crack state obtained by using the signal level threshold value th in the test material different from the test material in which the signal level threshold value th is determined. We thought that the validity of the life evaluation model as an initial input value should be verified. Based on this idea, the size and position of the crack in the pseudo-crack state are input to the remaining life evaluation model, and if the prediction accuracy of the crack growth is within the predetermined range, it is appropriate as the initial input value, in other words, the signal level threshold. Th is evaluated as appropriate. Here, the predetermined range is arbitrarily set, but it is practically preferable to set it to 0.5 or more and 2.0 or less.
When the remaining life evaluation model changes, the signal level threshold value th may change accordingly. Therefore, it is important that the remaining life evaluation model used for verification is the same as the remaining life evaluation model used for evaluating the remaining life in the remaining life evaluation step S5.

The verification of the validity of the signal level threshold value th described above is performed in advance after the signal level threshold value th is determined in the crack evaluation standard formulation step S100 described later and before the inspection step S4 is performed.
If the validity of the signal level threshold value is verified in advance, it is not necessary to verify the validity of the signal level threshold value th again before the inspection step S4, and the verification result showing the validity of the signal level threshold value th. Just check.
Further, for example, to explain the validity of the signal level threshold value th and the validity of the evaluation result of the remaining life to the other party who presents the evaluation result of the remaining life of the evaluation target, such as the owner of the evaluation target. In addition, the above-mentioned verification result may be explained to the other party.

As described above, in some embodiments, _{it is verified that the above ratio (t 2ACT} / t _2CAL ) satisfies a predetermined range, so that the signal level threshold value th and the remaining life evaluation model used for the verification are used. As a result, the size and position of cracks in the evaluation target can be obtained with high accuracy, and the accuracy of the remaining life of the evaluation target is improved.

Further, in some embodiments, the remaining life of the evaluation target can be evaluated even at the time when the set of creep voids occurs.

(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 S42, and as described above, in some embodiments, the above signal level threshold value th (for crack discrimination). Threshold). This signal level threshold value th is predetermined by the crack evaluation standard formulation step S100 described below.
FIG. 6 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. 7 is a flowchart showing a procedure in the evaluation standard formulation data collection process S110. FIG. 8 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. 6 to 8.

(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. 7, 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 third time point and the test piece at the fourth time point prior to the third 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 fourth 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 heating the test piece in the creep deformation step S111 for a predetermined time 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. 9 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.
In the flaw detection signal acquisition step S112, the measurement sensitivity of the flaw detection device was increased by 10 dB to 30 dB compared to the above-mentioned reference conditions for detecting cracks after the local creep life consumption rate reached 100%. Set to amplification conditions.

In the flaw detection signal acquisition step S112, as shown in FIG. 9, the phased array ultrasonic flaw detector 2 irradiates the inside of the welded portion 4b of the test piece 12 while scanning ultrasonic waves, and the reflected waves of the ultrasonic waves are emitted. Receive. 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 fourth time, which will be described later.

FIG. 10 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. (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 third time point. That is, the third 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 fourth time point as described above. The fourth time point is a time point before the third time point, and there is at least one fourth time point. That is, at the fourth 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. 9, 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. 9 is a contour diagram of a relatively early stage in the process of crack growth at any of the plurality of fourth time points, before the microscopic crack occurs.
After that, when the number of creep voids increases, the creep voids coalesce into a microscopic crack, and the microscopic crack propagates to penetrate.

(Evaluation Criteria Determination Step S120)
As shown in FIG. 6, in the crack evaluation standard establishment process S100, the evaluation standard determination data collection step S110 is executed, and then the evaluation standard determination step S120 is executed. As shown in FIG. 8, 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 third time point. In the size measurement step S121, as shown in FIG. 11, 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. 11 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 fourth 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 some embodiments, the model used in the model building step S123 is the same model as the remaining life evaluation model used to evaluate the remaining life in the remaining life evaluation step S5.
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 fourth 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 fourth 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 going back to the fourth time point and obtaining the estimated size of the crack at the fourth 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 fourth time point is obtained as follows.
As shown in FIG. 12, 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 t3. The time t3 corresponds to the above-mentioned third time point.
Then, starting from the time t3, the time on the horizontal axis of the graph of FIG. 12 corresponding to the plurality of fourth time points is obtained.

Next, among the plurality of times corresponding to the plurality of fourth 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 _{t4 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 t4 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 fourth time point corresponding to the time t4 specified as described above.
In the threshold value acquisition step S127, as shown in FIG. 13, 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 fourth time point corresponding to the time t4. The intensity of the reflected wave corresponding to the estimated crack length a2 is obtained at the position corresponding to. FIG. 13 is a graph showing a one-dimensional intensity distribution of the flaw detection signal, that is, the reflected wave at the fourth time point corresponding to the time t4, along the thickness direction of the welded portion. As shown in FIG. 13, the intensity of the reflected wave corresponding to the estimated crack length a2 can be obtained from the intensity distribution of FIG. 13, 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 t4 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 at time t4, 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 point t4 candidate, 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 t4 is the same as the model constructed in the model building step S123, for example, the crack 6c having a length a1 at the third time point. Therefore, there is no contradiction.
In this case, since it can be determined that the temporary signal level threshold value th'is appropriate as an evaluation criterion for cracks, the temporary 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 t4. 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 third 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 t4 candidate and the microscopic crack at the third 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 fourth time points, the above-mentioned time The time t4α, which is later than t4 and is closest to the time t4, is specified based on the master curve 14. Then, the estimated length a2α of the crack at the specified time t4α 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 fourth time point corresponding to the time t4α. 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.

As described above, in some embodiments, the test piece 12 is creep-deformed to the third time point, and the test piece 12 at the fourth time point prior to the third time point is subjected to flaw detection, and the flaw detection at the fourth time point is performed. The signal level threshold th is obtained by comparing the estimated size of the crack at the 4th time point obtained by acquiring the signal and tracing the crack growth process from the 3rd time point to the 4th time point with the flaw detection signal at the 4th time point. (Rhagades discrimination threshold) is set in advance.
In this method, the estimated size of the crack at the fourth time point is obtained by tracing back the crack growth process from the third time point. That is, the size of the region that is a quasi-cracked crack at the fourth time point can be obtained as the estimated size of the crack. Then, by comparing the estimated size of the crack at the fourth time point with the flaw detection signal at the fourth time point, a crack discrimination threshold that can detect a crack in a pseudo-crack state can be determined. As a result, the size and position of the crack in the pseudo-crack state in the evaluation object can be obtained by using the crack discrimination threshold value, so that the evaluation object can be evaluated even when the crack in the pseudo-crack state occurs. The remaining life of the can be evaluated.

Here, a schematic procedure of crack growth calculation applicable to the estimated size acquisition step S125 will be described. FIG. 14 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 time t3, 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, and 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 t3 is traced back to the time t4. 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 t4 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. 14, 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 t4 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.

The signal level threshold value th (threshold value for crack discrimination) thus obtained is individually set for the combination of the flaw detection method in the flaw detection step S42 and the residual life evaluation model described later in the residual life evaluation step S5. It is a threshold value that has been set. That is, in some embodiments, data for establishing evaluation criteria is collected in the flaw detection signal acquisition step S112 by the same method as the internal flaw detection inspection in the inspection step S4, and the remaining life is determined in the remaining life evaluation step S5 in the model construction step S123. The signal level threshold value th (threshold value for crack discrimination) is set by constructing a model using the same model as the remaining life evaluation model used for evaluation.
As a result, the threshold value for crack discrimination becomes a value suitable for the combination of the flaw detection method and the remaining life evaluation model. Then, since the remaining life of the evaluation target is obtained by inputting the size and position of the crack obtained by using the crack discrimination threshold value into the remaining life evaluation model, the evaluation accuracy of the remaining life of the evaluation target is improved. ..
In some embodiments, the signal level threshold value th (crack discrimination threshold value) is set for each combination of the flaw detection method in the flaw detection step S42 and the residual life evaluation model in the residual life evaluation step S5.

In some embodiments, a plurality of signal level threshold values (crack discrimination thresholds) set for each combination of the flaw detection method in the flaw detection step S42 and the residual life evaluation model in the residual life evaluation step S5 are set. A threshold database to be stored has been created. The plurality of signal level threshold values th (thresholds for discriminating cracks) determined by carrying out the evaluation standard establishment data collection step S110 are stored in the threshold database.
As a result, a crack discrimination threshold suitable for the combination of the flaw detection method used to obtain the flaw detection signal and the residual life evaluation model adopted in the residual life evaluation step S5 can be obtained, so that the size of the crack in the evaluation target and the crack size can be obtained. The position can be obtained with high accuracy, and the accuracy of the remaining life of the evaluation target is improved.

The signal level threshold value th obtained in this way makes it possible to discriminate at least a crack in a pseudo-crack state in which the local creep life consumption rate is X% or more and 90% or less (however, 50 <X <90 is satisfied). It is known to be the set threshold.

In addition to the signal level threshold value th used in the internal flaw detection inspection by the phased array method, the inventors have described the signal level threshold value th used in the internal flaw detection inspection by the high frequency UT method and the signal level threshold value th used in the internal flaw detection inspection by the aperture synthesis method. Also, the local creep life consumption rate in the region where the value is equal to or higher than the signal level threshold value th was investigated.

The result is shown in FIG. As shown in FIG. 15, the inventor has a local creep life consumption rate of X% or more and 90% or less (provided that 50 <X <90 is satisfied) in the region where the value is equal to or more than the signal level threshold value th. It became clear by these investigations.

In FIG. 15, the three-point plot indicated by the white circle is a plot for each of the three test materials TP1, and the three-point plot indicated by the black circle is the plot of the three test materials TP2. It is a plot for each. The difference between the test material TP1 and the test material TP2 is the difference in the material.

(Regarding local creep life consumption rate)
The local creep life consumption rate in FIG. 15 was performed by the following procedure.
First, a creep test was performed on a plurality of small test pieces (about Φ6 mm) by changing the test time, and the void number density was obtained for each small test piece. The creep life consumption rate was calculated from the ratio with each test time based on the time when the small test piece broke, and the relationship with the previously obtained void number density was obtained (not shown).
Next, creep damage was given to the test material prepared separately, and a region having a value equal to or higher than the signal level threshold value th was specified based on the signal level threshold value th obtained as described above. Then, the region was cut and the local creep life consumption rate in the region was obtained. Specifically, the number of voids on the cut surface of the region is measured, and the local creep lifetime consumption rate of the region is determined from the relationship between the number of voids density obtained in advance and the creep lifetime consumption rate as described above. I asked.
Here, the creep life consumption rate is calculated based on the breakage of the small test piece (100%), and then the creep life consumption rate is evaluated by applying it to the local damage of the specimen (thick wall material). ing. This is because the small test material has a size of about Φ6 mm, so it can be considered to be almost homogeneous with the condition of the cut surface related to the measurement of the void number density of the test piece. In other words, 100% of the local creep life consumption rate can be regarded as a state in which a locally observable microscopic crack is generated (a state in which stress transfer is no longer performed).

As described above, in some embodiments, at least the cracks in the pseudo-crack state in which the local creep life consumption rate is X% or more and 90% or less (provided that 50 <X <90 is satisfied) can be discriminated. Since the crack discrimination threshold is used, even if the damaged state of the evaluation target is before the occurrence of cracks that can be observed by visual observation of the cross section, such as macroscopic cracks, the cracks in the pseudo-crack state in the evaluation target The size and position can be determined. Then, since the size and position of the crack thus obtained are input to the remaining life evaluation model to obtain the remaining life of the evaluation object, the damaged state of the evaluation object is observed by visual observation of the cross section like a macroscopic crack. The remaining life of the object to be evaluated can be evaluated even before the possible cracks occur.
In the above method, the remaining life of the evaluation target is obtained by inputting the size and position of the crack obtained from the flaw detection result of the evaluation target into the remaining life evaluation model, so that the remaining life is quickly evaluated. can.

Also, in some embodiments, the local creep lifetime consumption rate is specified to be 100% at the time of locally visually observable cracks. Therefore, it is possible to discriminate a quasi-cracked crack in a stage before the occurrence of a local region where stress transmission is not performed, and it is an evaluation target even in a stage before the occurrence of a local region where stress transmission is not performed. You can evaluate the remaining life of an object.

(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 inputting the size and position of the crack specified in the inspection step S4 into the remaining life evaluation model and obtaining the remaining life of the evaluation object.
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 and its position determined in the inspection step S4, the welded portion 4a of the evaluation target portion is as follows. Evaluate the remaining life of the.

Specifically, as shown in FIG. 16, from 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 S42 in the inspection step S4, the crack growth calculation is performed. The penetration time tr at which the length ax of the crack 6a becomes the penetration 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. The penetration length ar has a different value depending on the position of the crack 6a.
Note that FIG. 16 is a graph showing the relationship between the remaining life and the crack length.
That is, in some embodiments, the remaining life evaluation model (crack extension calculation) used for evaluating the remaining life in the remaining life evaluation step S5 is the fourth 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.

Here, a schematic procedure for calculating crack growth applicable to the remaining life evaluation step S5 will be described. FIG. 17 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. The length ax of the crack 6a at time tx is the size of the crack input to the remaining life evaluation model, and the depth of the crack 6a (distance from the surface of the welded portion 4a to the tip of the crack 6a) is the remaining life evaluation model. The position of the crack entered in.
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 variable a, that is, the length of the crack 6a obtained by the crack growth calculation 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. NS. 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. 17, and the cracks obtained in advance by experiments are obtained 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. 18 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. 18A and 18B, the horizontal axis is the logarithmic axis. As is clear from FIGS. 18 (a) and 18 (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. 19 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. 20 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. 21, 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. 21, 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 S42 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 S42 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 step is the threshold value reaching life estimation step S435 shown in FIG. The threshold reaching life estimation step S435 is performed in the crack evaluation step S43 as 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 S42 is H ^{* less than the signal level threshold value.} Will be done.

By using the reflected wave intensity curve 16 created in advance in the threshold value reaching life estimation step S435, the time until the signal level threshold value th is reached at the stage where the welded portion 4a to be evaluated is not cracked 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. 22 shows an embodiment of the preparatory step.
The preparatory step may be carried out at the same time in the crack evaluation standard formulation step S100 of FIG. 6 described above.
In FIG. 22, 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. 23 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 S435, one implementation is performed 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 S42 until the signal level threshold th is reached. In the embodiment, as shown in FIG. 21, the reflected wave intensity curve 16 is used, and for the test piece 12, ^{the time Δt *} _sample for the reflected wave intensity to reach the signal level threshold value th from the ^{reflected wave intensity H *} is set. Ask.
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. 24, the entire life of the test piece 12 (penetration time in FIG. 16) _{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 formulas (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. 21, 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 S42 H ^* to reach the signal level threshold, in one embodiment, as shown in FIG. 21, 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.
As described above, in some embodiments, when there is no portion in the flaw detection region of the evaluation target where the flaw detection signal is equal to or higher than the signal level threshold value th (threshold for crack discrimination), the flaw detection signal has a known change characteristic with time. Based on this, the threshold arrival life estimation step S435 for predicting the ^{time Δt *} required for the flaw detection signal to reach the crack discrimination threshold from the signal level of the flaw detection signal is provided.
As a result, even if there is no part in the flaw detection region of the evaluation target where the flaw detection signal exceeds the crack discrimination threshold, the evaluation target has a pseudo-crack state based on the known tendency of the temporal change of the flaw detection signal. It is possible to accurately determine when the cracks occur.
In FIG. 21, t ^* indicates the time when the intensity of the reflected wave of the welded portion 4a to be evaluated ^{becomes H *} , and t5 indicates the time when the crack occurs.

(About other embodiments of the crack evaluation standard formulation process S100)
Hereinafter, other embodiments of the crack evaluation standard formulation step S100 will be described. In the crack evaluation standard formulation step S100 according to another embodiment, the conditions are significantly different between the crack generation site targeted for evaluation when the signal level threshold value is set and the crack generation site in the evaluation target, and have already been set. If it is not appropriate to use the signal level threshold th, the signal level threshold th is reset.
For example, it is necessary to obtain the size and position of the crack based on the signal level threshold th stored in the threshold database because the state of stress acting on the evaluation target portion, the temperature history, etc. are different from others. If it is not preferable in terms of life evaluation, the crack evaluation standard formulation step S100 is carried out to obtain a signal level threshold value th suitable for the evaluation target portion. The method for determining the signal level threshold th suitable for the evaluation target portion is the same as the procedure in the crack evaluation standard formulation step S100 described above, but the heating in the creep deformation step S111 of the evaluation standard formulation data acquisition step S110 is performed. And load conditions are changed as appropriate.
As a result, a crack discrimination threshold suitable for determining the crack size and position at the crack occurrence site in the evaluation object can be obtained, so that the crack size and position at the crack generation site can be accurately determined. The accuracy of the remaining life of the evaluation object is improved.

(Regarding still other embodiments of the crack evaluation standard formulation process S100)
Hereinafter, still another embodiment of the crack evaluation standard formulation step S100 will be described.
For example, when the signal level threshold value th for a certain flaw detection method (hereinafter referred to as the first flaw detection method) is not obtained, but the signal level threshold value th for the second flaw detection method different from the first flaw detection method is obtained. Can be considered. In such a case, in still another embodiment of the crack evaluation standard establishment step S100, the signal level threshold value for the second flaw detection method is based on the correlation between the flaw detection signal of the first flaw detection method and the flaw detection signal of the second flaw detection method. The signal level threshold th for the first flaw detection method is obtained from th.

For example, a test piece is prepared so that a flaw detection signal having a signal level threshold of about th for the second flaw detection method can be obtained by the second flaw detection method, and the test piece is detected by the first flaw detection method and the second flaw detection method, respectively. Get the flaw detection signal. Then, the strength of the flaw detection signal obtained by the first flaw detection method and the strength of the flaw detection signal by the second flaw detection method are compared, and the comparison result and the signal level threshold value th of the second flaw detection method are used to determine the first flaw detection method. The signal level threshold th of is estimated.

As described above, according to still another embodiment of the crack evaluation standard formulation step S100, the signal level threshold value th set in advance for the second flaw detection method different from the first flaw detection method used for obtaining the flaw detection signal. , The signal level threshold value th for the first flaw detection method can be obtained based on the correlation with the flaw detection signal of the first flaw detection method and the flaw detection signal of the second flaw detection method.
This makes it possible to simplify the preparation in advance for acquiring the signal level threshold value th.

(About other embodiments of the sensitivity setting / confirmation step S41)
If the flaw detector used in the flaw detection step S42 and the flaw detector used when calculating the signal level threshold value are different, in the sensitivity setting / confirmation step S41, the measurement of the flaw detector used in the present flaw detection step S42 is performed as follows. You may set the sensitivity.

FIG. 25 is a table illustrating another embodiment of the sensitivity setting / confirmation step S41.
Step S411 is a step of setting the measurement sensitivity of the flaw detector used when calculating the signal level threshold value th to the reference condition, that is, the reference sensitivity by the above-mentioned reference sensitivity setting process.
Step S412 measures the maximum echo of a test piece having a quasi-cracked crack (sometimes simply referred to as a quasi-crack) by the flaw detector used when calculating the signal level threshold th.
In step S413, the maximum echo of the test piece having a pseudo-crack is measured by the flaw detection device used in the flaw detection step S42.

The reflected echo from the standard hole in the comparison test piece described in JIS Z 3060: 2015 "Ultrasonic flaw detection test method for steel welds" is clear, and the difference due to the flaw detector is unlikely to occur. However, the reflected echo from the pseudo-crack becomes a low-level signal, and differences are likely to occur due to differences in the flaw detector and subtle flaw detection conditions. Therefore, it is important to verify the validity of the flaw detection condition from the flaw detection result of the pseudo-crack instead of the above standard hole.

Regarding the flaw detection conditions, in step S412, the sensitivity is amplified from the reference sensitivity set in step S411 as described above to improve the quasi-reck discrimination performance. In step S413, the conditions are the same as the flaw detection conditions used in step S412 (that is, the difference between step S412 and step S413 is only the flaw detection device).
Here, the flaw detection conditions to be matched to the same include not only the sensitivity but also the wave type (transverse wave, longitudinal wave), frequency, transmitter voltage, and beam diameter (more specifically, the size and element of the probe). (The arrangement of the above may also be included). The wave type and frequency define the resolution, and the transmitter voltage and beam diameter define the power. The beam diameter is effective only when it has convergence, and may not be used in the high-frequency UT method or the aperture synthesis method.

In step S414, the maximum echoes from the pseudo-cracks obtained in step S412 and step S413 are compared. If the error is within a predetermined range (for example, within 5 to 30%), it is determined that the calibration of the flaw detector used in the flaw detection step S42 is completed, and it is determined that the flaw detector can be used in the flaw detection step S42. If the error is out of the predetermined range, the flaw detector and conditions are changed, and the process is repeated from step S411 or step S412.

In the above example, the flaw detection conditions are the same as those in step S412 in step S413, but the flaw detection conditions may be partially changed in step S413 to grasp the influence of the pseudo-crack on the maximum echo. For example, the frequency may be changed in step S413 to measure the maximum echo of the pseudo-crack, and the maximum echo of the pseudo-crack in step S412 and the frequency domain within a predetermined range of error may be grasped. If it is in the grasped frequency range, it is determined that it can be set (changed) at the time of carrying out the main flaw detection step S42.

As described above, in the above example, when the flaw detector used when the reference condition is set and the flaw detector used for flaw detection of the evaluation target are different, the measurement sensitivity is 10 dB to 30 dB higher than the reference state (reference condition). After setting the amplification conditions, the flaw detection results of the cracks in the pseudo-crack state by both flaw detectors are compared.

As a result, even if the flaw detector used when the reference condition is set and the flaw detector used for flaw detection of the evaluation target are different, the remaining life of the evaluation target can be accurately evaluated.

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 remaining life evaluation method and the maintenance management method according to the present invention are not limited to a part of the above, and can be applied to various welded parts exposed to high temperature and high pressure and parts other than the welded parts.

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 (20)

A step of determining the size and position of a crack in the evaluation object by comparing the flaw detection signal obtained by the flaw detection of the evaluation object with the threshold for crack discrimination, and
A step of inputting the size and the position of the crack into the remaining life evaluation model and obtaining the remaining life of the evaluation object is provided.
The crack discrimination threshold is set so that at least a crack in a pseudo-crack state in which the local creep life consumption rate is X% or more and 90% or less (provided that 50 <X <90 is satisfied) can be discriminated .
The crack discrimination threshold is
Creep deform the test piece to the third time point,
The flaw detection was performed on the test piece at the fourth time point prior to the third time point, and the flaw detection signal at the fourth time point was acquired.
Of the estimated size of the crack at the fourth time point obtained by tracing the crack growth process from the third time point to the fourth time point, the time is later than the time corresponding to the detection lower limit of the flaw detector. The estimated size of the crack at the fourth time point corresponding to the time closest to is compared with the flaw detection signal at the fourth time point.
This is a method for evaluating the remaining life, which is characterized by being preset. The crack discrimination threshold is
The time of the crack size predicted by inputting the size and position of the crack in the pseudo-crack state obtained from the flaw detection result of the sample material at the first time point using the threshold for crack discrimination into the remaining life evaluation model. in variation curve, the prediction time t _2CAL said localized creep life consumption rate corresponds to the crack size Z ₂ after having reached 100%, the crack of the crack size Z ₂ is actually measured in the sample material The remaining life evaluation method according to claim 1, wherein the ratio of time to the second time point t _{2ACT (t 2ACT} / t _2CAL ) is a threshold value verified to satisfy a predetermined range. The remaining life evaluation method according to claim 2, wherein the predetermined range is 0.5 or more and 2.0 or less. Prior to the step of determining the size and position of the crack in the evaluation object, it is verified or the verification result is confirmed that the _{threshold for crack discrimination satisfies 0.5 × t 2CAL} ≦ t _2ACT ≦ 2.0 × t _2CAL. The remaining life evaluation method according to claim 3, wherein the step is provided. Prior to the step of determining the size and position of the crack in the evaluation object, the measurement sensitivity of the flaw detector used for the flaw detection is 10 dB compared to the reference condition of the flaw detector for detecting a visually observable crack. The remaining life evaluation method according to any one of claims 1 to 4, further comprising a step of setting an amplification condition increased by about 30 dB. When the flaw detector used when the reference condition is set and the flaw detector used for flaw detection of the evaluation object are different, the measurement sensitivity is set to the amplification condition, and then the crack in the pseudo-crack state by both flaw detectors. The remaining life evaluation method according to claim 5, further comprising a step of comparing the flaw detection results of the above. The invention according to any one of claims 1 to 6, wherein the local creep life consumption rate is specified to be 100% at the time when a locally visually observable crack occurs. Remaining life evaluation method. The remaining life evaluation method according to any one of claims 1 to 7, wherein the crack in the pseudo-crack state is a set of creep voids. The remaining life evaluation method according to any one of claims 1 to 8, wherein the flaw detection is an internal flaw detection capable of detecting at least a crack in a pseudo-crack state generated inside the evaluation object. When there is no portion in the flaw detection region of the evaluation target where the flaw detection signal is equal to or higher than the crack discrimination threshold value, the flaw detection signal is obtained from the signal level of the flaw detection signal based on the known temporal change characteristics of the flaw detection signal. The remaining life evaluation method according to any one of claims 1 to 9, further comprising a step of predicting the ^{time Δt *} required for reaching the crack discrimination threshold. The remaining life according to any one of claims 1 to 10, wherein the crack discrimination threshold is a threshold individually set for a combination of the flaw detection method and the remaining life evaluation model. Evaluation method. The flaw detection method used to obtain the flaw detection signal from the threshold database in which a plurality of the crack discrimination thresholds corresponding to the combination of the flaw detection method and the plurality of types of the residual life evaluation model are stored, and the residual life. The remaining life evaluation according to any one of claims 1 to 11, further comprising a step of acquiring the crack discrimination threshold value corresponding to the combination of the remaining life evaluation model adopted in the step of obtaining. Method. It is characterized by including a step of resetting the crack discrimination threshold value when the conditions are different between the crack generation site targeted for evaluation at the time of setting the crack discrimination threshold value and the crack generation site in the evaluation target object. The remaining life evaluation method according to any one of claims 1 to 12. The crack discrimination threshold is a threshold set in advance for a second flaw detection method different from the first flaw detection method used to obtain the flaw detection signal, and the flaw detection signal of the first flaw detection method and the second flaw detection method. The remaining life evaluation method according to any one of claims 1 to 13, which is obtained based on the correlation of the flaw detection signal. 13. Remaining life evaluation method. The remaining life evaluation according to any one of claims 1 to 15 , wherein the flaw detection includes at least one flaw detection of a phased array method, an aperture synthesis method, a high frequency UT method, or an ultrasonic noise method. Method. In the step of determining the size and position of the crack,
One of claims 1 to 16 , wherein, among the evaluation objects, a region in which the signal level of the flaw detection signal acquired for the evaluation object is equal to or higher than the crack discrimination threshold value is specified as the crack. Remaining life evaluation method described in the section. The remaining life evaluation method according to any one of claims 1 to 17 , wherein the evaluation target is a high-strength ferritic steel including a welded portion. A step of evaluating the remaining life of the evaluation object by the method according to any one of claims 1 to 18.
Based on the evaluation result of the remaining life 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 19 , wherein the maintenance management includes at least one of replacement, repair, or life extension measures of the evaluation object.

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