Creep life prediction method and creep life prediction device

Abstract

This creep life prediction method comprises: a first nondestructive damage degree identifying step in which nondestructive analysis is used to identify, as a first nondestructive creep damage degree, a creep damage degree of a target steel material at a first time, the target steel material being subjected to remaining life prediction; a first rupture time identifying step for identifying, as a first Larson-Miller rupture time, a creep rupture time of the target steel material at the first time by applying, to a regression equation prescribed by the Larson-Miller method, a first stress imparted to the target steel material until the first time and a first temperature of the target steel material until the first time; and a degree-of-divergence identifying step for identifying a degree of divergence, which is a correction value for the first Larson-Miller rupture time, on the basis of the first Larson-Miller rupture time and a first nondestructive rupture time which is a creep rupture time at the first time calculated from the first nondestructive creep damage degree.

Description

Creep life prediction method and creep life prediction device

[0001] The present disclosure relates to a creep life prediction method and a creep life prediction device for predicting the remaining life of a steel material. This application claims priority to Japanese Patent Application No. 2024-005752, filed with the Japan Patent Office on January 18, 2024, the contents of which are incorporated herein by reference.

[0002] Conventionally, creep life prediction methods for predicting the creep life of steel materials have been known. For example, the creep life prediction method disclosed in Patent Document 1 calculates the fracture time of a welded portion of chromium steel based on test results performed on a base metal sample of the chromium steel. More specifically, the creep life prediction method disclosed in Patent Document 1 includes a precipitate reflection coefficient calculation step, a long-term behavior reflection coefficient calculation step, a base metal characteristic coefficient determination step, a weld characteristic coefficient determination step, and a fracture time calculation step.

[0003] In the precipitate reflection coefficient calculation step, a precipitate reflection coefficient corresponding to the number density of vanadium-based precipitates in a sample taken from the base metal of the chromium steel is calculated from the number density of vanadium-based precipitates and the results of a standard creep test. In the long-term behavior reflection coefficient calculation step, a long-term behavior reflection coefficient corresponding to the results of the small punch creep test of a test piece taken from the base metal of the chromium steel is calculated from the results of the small punch creep test and the standard creep test. In the base metal characteristic coefficient identification step, a base metal characteristic coefficient is identified from the precipitate reflection coefficient and the long-term behavior reflection coefficient. In the weld characteristic coefficient identification step, a weld characteristic coefficient corresponding to the value of the base metal characteristic coefficient is identified from the results of the standard creep test of the base metal and the standard creep test of the weld. In the rupture time calculation step, the rupture time of the weld of the chromium steel is calculated from the weld characteristic coefficient.

[0004] Patent No. 6976894

[0005] The above creep life prediction method only deals with modified 9Cr-1Mo steel, and a life prediction method that can accurately evaluate the remaining life of other types of steel is needed. Furthermore, the life prediction method disclosed in Patent Document 1 requires small punch creep tests, which require considerable cost and time. Furthermore, the steel (or the actual equipment incorporating the steel) is damaged to a considerable extent when the test specimens are collected. Therefore, a simpler life prediction method is needed.

[0006] An object of the present disclosure is to provide a creep life prediction method and creep life prediction device that can easily and accurately predict the remaining life of a target steel material regardless of the material properties of the target steel material.

[0007] The creep life prediction method according to at least one embodiment of the present disclosure includes a first non-destructive damage determination step of determining a creep damage level of a target steel material at a first time point for which a remaining life prediction is to be performed as a first non-destructive creep damage level using a non-destructive evaluation method; a first rupture time determination step of determining a creep rupture time (total life) of the target steel material at the first stress and the first temperature as a first Larson-Miller rupture time by applying a first stress of the target steel material up to the first time point and a first temperature of the target steel material up to the first time point to a regression equation defined by the Larson-Miller method; and a deviation determination step of determining a deviation level as a correction value of the first Larson-Miller rupture time based on a first non-destructive rupture time, which is the creep rupture time (total life) at the first time point calculated from the first non-destructive creep damage level, and the first Larson-Miller rupture time. and a remaining life prediction step of predicting the remaining life of the target steel material at the second time by applying a second stress of the target steel material at a second time after the first time and a second temperature of the target steel material at the second time to a corrected regression equation that reflects the deviation in the regression equation.

[0008] The creep life prediction device according to at least one embodiment of the present disclosure includes a first non-destructive damage determination unit that determines a creep damage level of a target steel material for which a remaining life prediction is to be performed at a first time as a first non-destructive creep damage level using a non-destructive evaluation method; a first rupture time determination unit that determines a creep rupture time (total life) of the target steel material at the first stress and the first temperature as a first Larson-Miller rupture time by applying a first stress of the target steel material up to the first time and a first temperature of the target steel material up to the first time to a regression equation defined by the Larson-Miller method; and a deviation determination unit that determines a deviation level that is a correction value of the first Larson-Miller rupture time based on a first non-destructive rupture time that is the creep rupture time (total life) at the first time calculated from the first non-destructive creep damage level and the first Larson-Miller rupture time. and a remaining life prediction unit that predicts the remaining life of the target steel material at the second time by applying a second stress of the target steel material at a second time after the first time and a second temperature of the target steel material at the second time to a corrected regression equation that reflects the deviation in the regression equation.

[0009] According to the present disclosure, it is possible to provide a creep life prediction method and a creep life prediction device that can easily and accurately predict the remaining life of a target steel material regardless of the material properties of the target steel material.

[0010] FIG. 1 is a schematic diagram of a heat exchanger in which a target steel material is used according to one embodiment; FIG. 2 is a schematic diagram showing a creep rupture curve according to one embodiment; FIG. 3 is a schematic diagram showing an overview of remaining life prediction according to one embodiment; FIG. 4 is a flowchart showing a method for predicting remaining life of a target steel material according to one embodiment; FIG. 5 is a schematic diagram of stress time series data according to one embodiment; FIG. 6 is a schematic diagram of temperature time series data according to one embodiment; FIG. 7 is a flowchart showing a first rupture time specifying step according to one embodiment; FIG. 8 is a flowchart showing an updated remaining life prediction method for a target steel material according to one embodiment; FIG. 9 is a schematic diagram showing the inspection timing of a heat exchanger according to one embodiment; FIG. 10 is a flowchart showing the inspection flow of a heat exchanger according to one embodiment; FIG. 11 is a schematic diagram of a creep life prediction device according to one embodiment;

[0011] Several embodiments of the present disclosure will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure and are merely illustrative examples. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is achieved. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is achieved. On the other hand, the expressions "comprise," "include," or "have" one component are not exclusive expressions that exclude the existence of other components. Note that similar components may be assigned the same reference numerals and descriptions thereof may be omitted.

[0012] 1 is a schematic diagram of a heat exchanger 5 in which a target steel material 8 according to an embodiment of the present disclosure is used. There are no particular restrictions on the material of the target steel material 8, and for example, modified 9Cr-1Mo steel, austenitic stainless steel, or the like may be used.

[0013] The target steel material 8 constitutes at least a part of a heat exchanger 5. The heat exchanger 5 illustrated in FIG. 1 is a superheater used in a boiler, more specifically, a superheater or a reheater. The heat exchanger 5 includes two headers 6 and heat transfer tubes 7 connected to each header 6. The heat transfer tubes 7 include a first heat transfer tube 1, a second heat transfer tube 2, a third heat transfer tube 3, and a fourth heat transfer tube 4 that are aligned along the extension direction of the header 6. Each of these heat transfer tubes 7 may be made up of multiple pipe groups. The steel material that constitutes the pipe groups is the target steel material 8.

[0014] High-temperature combustion gas generated in the boiler furnace flows outside the first heat transfer tube 1, the second heat transfer tube 2, the third heat transfer tube 3, and the fourth heat transfer tube 4. The combustion gas heats the water or steam flowing inside each heat transfer tube 7, and the heat exchanger 5 generates superheated steam.

[0015] Each heat transfer tube 7 is used in a high-temperature, high-pressure environment. Therefore, as the cumulative operating time of the heat exchanger 5 (i.e., the cumulative usage time of the target steel material 8) increases, creep damage progresses inside the target steel material 8. Therefore, in order to safely manage the target steel material 8, it is preferable to accurately predict the remaining life of the target steel material 8.

[0016] <Conventional Remaining Life Prediction of Target Steel Material 8> Conventionally, the creep damage degree has been estimated when predicting the remaining life of the target steel material 8. The creep damage degree is also called the creep life consumption rate, and is a value obtained by dividing the cumulative usage time of the target steel material 8 by the creep rupture time (total life) of the target steel material 8. The creep rupture time is the time from the start of use of the target steel material 8 until creep rupture occurs.

[0017] The Larson-Miller method is a well-known method used to estimate creep damage. The Larson-Miller method is a method for predicting the creep rupture time of a target steel material 8 based on creep rupture data obtained by performing creep tests on test specimens made of the same material as the target steel material 8. The creep rupture data is data obtained from creep tests performed under various test conditions, and the test conditions include the stress and temperature of the test specimen as control factors.

[0018] In the Larson-Miller method, the creep rupture time of the target steel material 8, t ｒ is defined as the following equation (1): T(C+logt ｒ ) = A ０ +A １ ×logσ+A ２ × (log σ) ２ ...Formula (1) A ０ , A １ , A ２is a regression coefficient determined from creep rupture data, σ is the stress acting on the target steel material 8, T is the temperature (absolute temperature) at which the target steel material 8 is used, and C is a material constant (material eigenvalue) determined by the type of material of the target steel material 8. The left side of equation (1) is the so-called Larson-Miller parameter.

[0019] By transforming equation (1), equation (2) is obtained. ｒ = {A ０ +A １ ×logσ+A ２ × (log σ) ２} / T-C ...Equation (2) The right-hand side of equation (2) is a regression equation defined by the Larson-Miller method. Hereinafter, the regression equation shown on the right-hand side of equation (2) will be simply referred to as the "regression equation" and may be expressed as a mathematical formula as f(σ, T). Figure 2 is a schematic diagram showing a creep rupture curve created assuming that the environmental temperature is approximately constant. The regression equation is shown by a solid line in Figure 2. Note that the horizontal axis of the graph in Figure 2 is expressed on a logarithmic scale (logarithmic graduations).

[0020] The conventionally known regression equation (2) does not take into account the scatter of values ​​indicated by creep rupture data. ０ ) is calculated by the regression equation as the predicted value of creep rupture time t ０ Even if it is calculated as ｋ is ０ It may be sooner than that.

[0021] Therefore, in order to improve the accuracy of prediction of the creep rupture time, the inventors of the present application have devised a corrected regression equation (the right side of the following equation (3)) that reflects the deviation (x) in the regression equation. ｒ = f (σ, T) + x ... Equation (3) If the temperature (T) is assumed to be constant, the correction regression equation corresponds to the two-dot chain line in Figure 2, and if the stress (σ ０ The corrected predicted creep rupture time corresponding to t' ０The deviation (x) is a corrected value of the creep rupture time of the target steel material 8 derived from the regression equation. Note that the deviation (x) is different from the correction value that has been conventionally proposed and is obtained by multiplying the reliability coefficient of creep rupture data (e.g., 2.33) by the standard deviation of the data.

[0022] <Deviation and Corrected Regression Equation> The basic concept of the deviation (x) devised by the present inventors will be explained. The higher the reliability of the deviation (x), the higher the reliability of the creep damage obtained using Equation (3) (corrected Larson-Miller creep damage). On the other hand, the reliability of creep damage obtained based on a nondestructive evaluation method other than the Larson-Miller method (nondestructive creep damage) is also high. This is because the nondestructive creep damage is determined through direct evaluation of the target steel material 8. If the reliability of the deviation is high, the corrected Larson-Miller creep damage at the first time is substantially the same as the nondestructive creep damage at the first time. In other words, the present inventors have concluded that a highly reliable deviation can be determined by back-calculating from an equation indicating that the two creep damages are equal. In this way, at the second time point after the first time point, the corrected regression equation including the deviation degree can be applied to the Larson-Miller method to accurately determine the remaining life of the target steel material 8. The process of deriving the deviation degree will be described below.

[0023] The corrected Larson-Miller creep damage index (first corrected Larson-Miller creep damage index) at the first time obtained by the Larson-Miller method using the corrected regression equation is defined by Equation (4). Ｌ１ = t １ / t ｒ１ ...Formula (4) D Ｌ１ is the first corrected Larson-Miller creep damage index, and t １ is the cumulative usage time of the target steel material 8 at the first time point. ｒ１ is the creep rupture time (first Larson-Miller rupture time) calculated at the first time by the Larson-Miller method using equation (3), and is expressed by equation (3A).

[0024] In formula (3A), σ １is the stress (first stress) of the target steel material 8 up to the first time, and T １ is the temperature (first temperature) of the target steel material 8 up to the first time. １ , T １ ) is added to the regression equation on the right side of equation (2) by adding σ = σ １ , and T=T １ This is the value obtained by applying f(σ １ , T １ ) is the creep rupture time at the first time (first Larson-Miller rupture time) calculated by the conventional Larson-Miller method.

[0025] The first stress may be a stress acting on the target steel material 8 at the first time, or may be an average value of stress acting from a time before the first time to the first time. Similarly, the first temperature may be a temperature of the target steel material 8 at the first time, or may be an average value of temperatures from a time before the first time to the first time.

[0026] Non-destructive creep damage degree at the first time (first non-destructive creep damage degree: D Ｎ１ ) is the first corrected Larson-Miller creep damage factor (D Ｌ１ ), the following equation (5) holds. Equation (5) defines a highly reliable deviation (x). x = log(t １ / D Ｎ１ ) -f(σ １ , T １ )...Equation (5) log(t １ / D Ｎ１ ) is the first non-destructive creep damage (D Ｎ１ ) is the logarithm of the creep rupture time (first non-destructive rupture time) at the first time. １ , T １ ) is the logarithm of the first Larson-Miller break time.

[0027] By applying equation (5) to equation (3), equation (3B) is obtained. The right side of equation (3B) defines the correction regression equation as a general formula. logt ｒ =f(σ,T)+log(t １ / D Ｎ１ ) -f(σ１ , T １ )...Formula (3B)

[0028] The creep rupture time (t ｒ２ To calculate logt, a correction regression equation is used. Specifically, the following equation (3C) is used, in which the stress at the second time (second stress) and the temperature at the second time (second temperature) are applied to σ and T in equation (3B). ｒ２ = f(σ ２ , T ２ ) + log(t １ / D Ｎ１ ) -f(σ １ , T １ ) = f(σ ２ , T ２ )+x...Formula (3C) σ ２ is the second stress, and T ２ is the second temperature. Using equation (3C), the remaining life (R) of the target steel material 8 at the second time is expressed as in equation (6). t ２ is the cumulative usage time of the target steel material 8 at the second time.

[0029] The remaining life prediction of the target steel material 8 explained above will be outlined with reference to FIG. 3. First, １ ), a first non-destructive creep damage degree and a first non-destructive rupture time are calculated. Furthermore, a first Larson-Miller rupture time is calculated based on the first stress and the first temperature. This allows the deviation (x) and the correction regression equation to be calculated. Then, at a second time (M ２ ), the remaining life of the target steel material 8 is calculated based on the second stress, the second temperature, and the correction regression equation, and the predicted fracture time (C １ ) can be obtained.

[0030] <Method for predicting remaining life of target steel material 8> Fig. 4 is a flowchart showing a method for predicting remaining life of target steel material 8 according to an embodiment of the present disclosure. In the following description, steps may be abbreviated as "S".

[0031] First, the creep damage degree of the target steel material 8 at the first time is calculated as a first non-destructive creep damage degree (DＮ１ A first non-destructive damage level determination step (S1) is executed to determine the first non-destructive damage level as a creep damage level. The non-destructive evaluation method is executed at a first time (a specific example of the non-destructive evaluation method will be described later). In S1, the rupture time (first non-destructive rupture time) of the target steel material 8 is also determined based on the first non-destructive creep damage level.

[0032] Next, a first rupture time determination step (S3) is executed in which the creep rupture time of the target steel material 8 at the first time point of the target steel material 8 is determined as a first Larson-Miller rupture time using the Larson-Miller method. The first Larson-Miller rupture time is determined by applying a first stress (σ １ ) and the first temperature (T １ ) can be found by applying

[0033] Next, a deviation determination step (S5) is executed to determine a deviation (x) based on the first non-destructive fracture time and the first Larson-Miller fracture time. The deviation is calculated by equation (5).

[0034] Next, at a second time, a remaining life prediction step (S7) is executed to evaluate the remaining life (R) of the target steel material 8. The remaining life is calculated using equation (6). After that, this flowchart ends. Note that steps S1 to S7 may be executed by an operator, or may be executed by a computing device such as a creep life prediction device 30 (see FIG. 11) described later.

[0035] According to the above configuration, the deviation reflected in the correction regression equation is determined based on the results of the nondestructive evaluation method in the first nondestructive damage determination step (S1). Therefore, the actual creep damage level of the target steel material 8 can be more accurately reflected in the correction regression equation used in the remaining life prediction step (S7), thereby enabling a more accurate prediction of the remaining life of the target steel material 8. Furthermore, because both the nondestructive evaluation method and the Larson-Miller method are standardized techniques, there are no restrictions on the material of the target steel material 8 for which the remaining life prediction is performed, and the time and cost required for the prediction can be reduced. Furthermore, because the nondestructive evaluation method is employed in this embodiment, there is no damage to the target steel material 8 or the heat exchanger 5 in which the target steel material 8 is incorporated. As described above, a creep life prediction method is realized that can easily and accurately predict the remaining life of the target steel material 8 regardless of the material of the target steel material 8.

[0036] <Non-destructive evaluation method> Examples of the non-destructive evaluation method used in the first non-destructive damage level determination step (S1) include a hardness measurement method, a precipitate grain distance method, a structure comparison method, a void number density method, or a combination of these.

[0037] The hardness measurement method is a known technique for predicting the creep damage degree of the target steel material 8 based on the hardness of the target steel material 8. More specifically, the hardness of the target steel material 8 of the heat exchanger 5 is measured using, for example, an ultrasonic hardness tester. The hardness obtained by the measurement is compared with master data showing the relationship between hardness and remaining life obtained in advance, thereby determining the creep damage degree of the target steel material 8.

[0038] The precipitate intergranular distance method is a well-known technique for predicting the creep damage level of a target steel material 8 based on the interparticle distance of precipitates appearing on the outer surface of the target steel material 8. More specifically, the creep rate of the target steel material 8 is calculated based on the interparticle distance determined by measurement, the stress of the target steel material 8, and the temperature of the target steel material 8. Then, the time required to reach the allowable strain is calculated based on a creep curve estimated from the creep rate. This allows the creep damage level to be calculated.

[0039] The structure comparison method is a known technique for predicting the degree of creep damage of a target steel material 8 based on a comparison of an image of the metal structure of the target steel material 8 with an image of the structure of a reference steel material.

[0040] The void number density method is a known technique for predicting the creep damage level of a target steel material 8 based on the void number density in the target steel material 8 of a heat exchanger 5. More specifically, the void number density of the target steel material 8 is measured by, for example, observing under a microscope a metal structure sampled by a replica method (Sump method), and the creep damage level of the target steel material 8 is predicted based on the void number density determined by the measurement.

[0041] The nondestructive evaluation methods used in the present disclosure are not limited to the above four. For example, the void area fraction method, the A parameter method, the electrical resistance method, or the grain deformation method may also be used. These methods are well known, so detailed explanations will be omitted.

[0042] In some embodiments, in the first nondestructive damage level determination step (S1), multiple nondestructive evaluation methods may be performed on the target steel material 8. In this case, multiple nondestructive creep damage levels are obtained as a result of the multiple nondestructive evaluation methods. A representative first nondestructive creep damage level may be determined by applying statistical processing to these multiple nondestructive creep damage levels. The statistical processing may be an averaging process or a process of extracting a maximum or minimum value. According to the above configuration, the reliability of the first nondestructive creep damage level can be improved, and the remaining life prediction accuracy of the target steel material 8 can be improved.

[0043] When applying multiple nondestructive evaluation methods, it is necessary to perform evaluation on multiple portions of the target steel material 8. In this case, if the first heat transfer tube 1, the second heat transfer tube 2, the third heat transfer tube 3, and the fourth heat transfer tube 4 are made from the same manufacturing lot of material, different nondestructive evaluation methods may be applied to different portions of the multiple different heat transfer tubes 7.

[0044] <First Stress, First Temperature> The first stress and the first temperature used in the first rupture time specifying step (S3) will be described with reference to FIGS.

[0045] As shown in FIG. 5, the first stress (σ １) may be obtained based on the stress time series data D1. The stress time series data D1 is １ ) before the specified time (M ｓ ) to the first time point. The data may be obtained from the measurement results of the pressure (internal pressure) caused by steam flowing inside the target steel material 8, for example.

[0046] As shown in FIG. 6, the first temperature (T １ ) may be obtained based on the temperature time series data D2. The temperature time series data D2 may be obtained based on the specified time (M ｓ ) to the first time (M １ ) The data may be obtained from the measurement results of the outer surface temperature of the target steel material 8.

[0047] 7 is a flowchart showing the details of the first rupture time specifying step (S3 in FIG. 4) for specifying the first Larson-Miller rupture time. First, a first stress (σ １ In S11, the stress indicated by the stress time-series data D1 is averaged to obtain a first stress. Next, the first temperature (T １ In S13, the temperatures indicated by the temperature time-series data D2 are averaged to obtain a first temperature.

[0048] According to the above configuration, it is possible to specify the first stress and the first temperature that more accurately reflect the actual usage environment of the target steel material 8, which changes over time. This allows the actual creep damage level of the target steel material 8 to be more accurately reflected in the correction regression equation used in the remaining life prediction step (S7). Therefore, it is possible to improve the prediction accuracy of the remaining life of the target steel material 8.

[0049] Furthermore, in the temperature identification step (S13), an optical fiber temperature sensor 9 may be used to measure the temperature of the target steel material 8. FIG. 1 is a schematic diagram showing an optical fiber temperature sensor 9 according to an embodiment of the present disclosure. The optical fiber temperature sensor 9 is configured to measure the temperature of the outer surface of the target steel material 8 constituting the heat transfer tube 7. The optical fiber temperature sensor 9 is connected to a creep life prediction device 30 (details of which will be described later) as a computing device. The optical fiber temperature sensor 9 continuously acquires the temperature of the target steel material 8, allowing the creep life prediction device 30 to acquire temperature time series data D2. The optical fiber temperature sensor 9 can measure temperatures at a large number of evaluation points on the outer surface of the target steel material 8. Therefore, temperature time series data D2 may be generated for each evaluation point.

[0050] Even when measuring the temperature at each evaluation point to predict the creep damage degree at multiple evaluation points on the target steel material 8, the cost of the equipment for measuring the temperature can be reduced. More specifically, the cost of the equipment can be reduced compared to when thermocouples are placed at a large number of evaluation points (for example, 100 or more).

[0051] <Additional Components of Creep Life Prediction Method> Returning to FIG. 3 , the predicted fracture time (C １ Even if the true creep rupture time (t ｋ ) may occur earlier than that. This is because the creep strength of the target steel material 8 may weaken as the cumulative usage time of the target steel material 8 increases. Here, creep strength refers to the stress in the target steel material 8 that causes a specified creep rate. If the creep strength weakens, the rate at which creep deformation of the target steel material 8 progresses increases.

[0052] In some embodiments of the present disclosure, the predicted break time (C １ ) may be revised. This is performed by updating the deviation (x) and the correction regression equation. This update is performed at a third time (M ３More specifically, at the third time, a new deviation (updated deviation) and a new correction regression equation (updated correction regression equation) may be calculated in accordance with the same procedure as that performed at the first time. The details are as follows.

[0053] At the third time, the creep damage of the target steel material 8 is determined by the non-destructive evaluation method to be a second non-destructive creep damage (D Ｎ２ The nondestructive evaluation method used at the third time point may be the same as or different from the nondestructive evaluation method used at the first time point. Once the second nondestructive creep damage level is determined, the creep rupture time (second nondestructive rupture time) of the target steel material 8 at the third time point can be determined.

[0054] Furthermore, using the regression equation defined by the Larson-Miller method, the creep rupture time at the third time is identified as the second Larson-Miller rupture time. The second Larson-Miller rupture time is f(σ ３ , T ３ ) can be determined by taking the logarithm of

[0055] where σ ３ is the stress of the target steel material 8 up to the third time, and T ３ is the temperature of the target steel material 8 up to the third time. The third stress may be the average value of the stress from the first time to the third time. Similarly, the third temperature may be the average value of the temperature from the first time to the third time.

[0056] Furthermore, an updated deviation is determined based on the second non-destructive rupture time and the second Larson-Miller rupture time. The updated deviation (x') is an updated correction value of the second Larson-Miller rupture time and is defined by the following equation (5A): x'=log(t ３ / D Ｎ２ ) -f(σ ３ , T ３ )...Formula (5A) t ３ is the cumulative usage time of the target steel material 8 at the third time. The update correction regression equation as a general equation is defined by equation (3D) using equation (5)A. ｒ =f(σ,T)+log(t ３ / D Ｎ２ ) -f(σ３ , T ３ ) = f (σ, T) + x' ... Formula (3D)

[0057] Furthermore, at a fourth time after the third time, the updated remaining life (R') which is the remaining life of the target steel material 8 at the fourth time is predicted using equation (3D). In predicting the updated remaining life, the stress (fourth stress) of the target steel material 8 at the fourth time and the temperature (fourth temperature) of the target steel material 8 at the fourth time are used. Adding σ=σ to equation (3D) ４ , T=T ４ By applying the above formula, the renewal remaining life (R′) is calculated as shown in the following formula (6A). t ４ is the cumulative usage time of the target steel material 8 at the fourth time.

[0058] The above-described method for predicting the remaining life of the target steel material 8 before renewal will be described with reference to FIG. ３ ), the second non-destructive creep damage level and the second non-destructive rupture time are calculated. Furthermore, the second Larson-Miller rupture time is calculated based on the third stress and the third temperature. This allows the updated deviation (x) and the updated correction regression equation to be calculated. Then, at the fourth time (M ４ ) is calculated based on the fourth stress, the fourth temperature, and the correction regression equation, the renewal remaining life of the target steel material 8 is calculated, and the renewal predicted fracture time (C ２ ) is obtained. ２ ) is the predicted break time (C １ ), it is preferable to update the predicted fracture time to the updated predicted fracture time and manage the target steel material 8.

[0059] <Method for Predicting Remaining Renewal Life of Target Steel Material 8> FIG. 8 is a flowchart showing a method for predicting the remaining renewal life of a target steel material 8 according to an embodiment of the present disclosure.

[0060] First, the remaining life at the second time is predicted (S19). S19 includes S1 to S7 shown in Fig. 4. The details of S1 to S7 are as described above.

[0061] Next, the creep damage degree at the third time is calculated by a non-destructive evaluation method as a second non-destructive creep damage degree (DＮ２ A second non-destructive damage level determination step (S21) is executed to determine the second non-destructive creep damage level. The non-destructive evaluation method is executed at a third time. In S21, the fracture time (second non-destructive fracture time) of the target steel material 8 is also determined based on the second non-destructive creep damage level.

[0062] Next, a second rupture time specifying step (S23) is executed to specify the creep rupture time of the target steel material 8 at the third time as a second Larson-Miller rupture time. The second Larson-Miller rupture time is determined by adding a third stress (σ ３ ) and the third temperature (T ３ ) can be found by applying

[0063] Next, an updated deviation determination step (S25) is executed to determine an updated deviation (x') based on the second non-destructive rupture time and the second Larson-Miller rupture time. The updated deviation is calculated by Equation (5A).

[0064] Next, at the fourth time, a renewal remaining life prediction step (S27) is executed to evaluate the renewal remaining life (R') of the target steel material 8. The renewal remaining life is calculated using the formula (6A). Next, the renewal predicted fracture time (C ２ ) is the predicted fracture time (C １ ), a remaining life update step (S29) is executed to update the predicted fracture time to the updated predicted fracture time. Then, this flowchart ends.

[0065] According to the above configuration, the updated remaining life of the target steel material 8 at the fourth time is calculated based on the updated deviation (x') identified at a timing later than the second time. This makes it possible to improve the prediction accuracy of the remaining life of the target steel material 8.

[0066] Furthermore, according to the configuration in which the remaining life updating step (S29) is executed, the creep rupture time of the target steel material 8 can be predicted more accurately.

[0067] <Periodic Inspection of Heat Exchanger 5> Fig. 9 is a schematic diagram showing the inspection timing of the heat exchanger 5 according to an embodiment of the present disclosure. For example, in accordance with the laws and regulations of the country in which the heat exchanger 5 is installed, the heat exchanger 5 is inspected periodically. Ｎ－１ , B Ｎ , B Ｎ＋１ , B Ｎ＋２ indicates the timing of inspection (where N is a natural number greater than or equal to 2, and B Ｎ indicates the Nth inspection). The heat exchanger 5 is stopped while the inspection is being carried out. The inspection is carried out every time a predetermined number of years has passed. Although it is merely an example, the predetermined number of years is one year or more and five years or less, more specifically, one year or more and three years or less. The predetermined number of years is determined by the predetermined time (M ｓ ) to the first time (M １ ) may be the same as the period up to the end of the period.

[0068] In this example, B Ｎ－１ During the inspection indicated by B, the first non-destructive creep damage level, the first non-destructive rupture time, and the first Larson-Miller rupture time are identified. Ｎ－１ is M shown in FIG. １ And B Ｎ－１ From B Ｎ The remaining life is evaluated within the period (operation period of the heat exchanger 5) up to (M ２ ). That is, M ２ At the timing indicated by , the predicted fracture time (C １ At this time, the predicted break time (C １ ) is B Ｎ＋１ From B Ｎ＋２ It is assumed that the period is within the section (the specified operating period of the heat exchanger 5).

[0069] Furthermore, B Ｎ During the inspection indicated by B, the second non-destructive creep damage level, the second non-destructive rupture time, and the second Larson-Miller rupture time are determined. Ｎ is M shown in FIG. ３ And B Ｎ ~B Ｎ＋１ The remaining life for renewal is evaluated within the period (operation period of the heat exchanger 5) between ４ ). That is, M４ At the timing shown by , the updated predicted fracture time point (C ２ At this time, the updated predicted break time (C ２ ) but B Ｎ＋１ From B Ｎ＋２ Predicted break time within the interval (C １ ) was earlier than

[0070] In this case, even if the predicted fracture time is updated to the updated predicted fracture time, B Ｎ＋１ During the inspection indicated by , measures can be taken to the target steel material 8 to prepare for creep fracture.

[0071] 10 is a flowchart showing a creep prediction method according to an embodiment of the present disclosure. First, an N-1th inspection step (S31) for inspecting the heat exchanger 5 is executed. Ｎ－１ The inspection is performed to identify the first non-destructive creep damage level, the first non-destructive rupture time, and the first Larson-Miller rupture time. At this time, in S31, S1, S3, and S5 in FIG. 4 are performed. After S31 is performed, the heat exchanger 5 is restarted.

[0072] Thereafter, the time when the target steel material 8 will break is predicted (S33). ２ 4 is executed. As a result, the predicted fracture time (C １ ) is predicted.

[0073] Next, it is determined whether the next inspection timing has arrived (S35). The step waits until the inspection timing arrives (S35: NO). Then, when the next inspection timing arrives (S35: YES), the step returns to S31.

[0074] In the next step S31, the Nth inspection is carried out. This timing is B shown in FIG. Ｎ (M ３) and the second non-destructive creep damage level, the second non-destructive rupture time, and the second Larson-Miller rupture time are identified. In S31 at this time, steps S21, S23, and S25 in FIG. 8 are executed. Then, the rupture time is predicted again (S33). The timing of S33 at this time is determined by M ４ 8 are executed. As a result, the fracture time of the target steel material 8 is determined as the predicted fracture time (C １ ) to the updated predicted break time (C ２ ) After that, S35, S31, and S33 are repeated.

[0075] <Creep life prediction device 30> Fig. 11 is a schematic diagram of a creep life prediction device 30 according to an embodiment of the present disclosure. The creep life prediction device 30 is a computing device configured to predict the remaining life of the target steel material 8. Hereinafter, the processor of the computing device may be simply referred to as the "processor".

[0076] The creep life prediction device 30 includes a first non-destructive damage level identification unit 31, a first rupture time identification unit 32, a deviation level identification unit 33, a remaining life prediction unit 34, a second non-destructive damage level identification unit 35, a second rupture time identification unit 36, an updated deviation level identification unit 37, an updated remaining life prediction unit 38, and a life update unit 39.

[0077] The first non-destructive damage level identifying unit 31 is configured to identify a first non-destructive creep damage level. The first non-destructive damage level identifying unit 31 may be configured to accept the first non-destructive creep damage level input by an operator. For example, the processor executing S1 is an example of the first non-destructive damage level identifying unit 31.

[0078] The first rupture time specifying unit 32 is configured to specify the first Larson-Miller rupture time. The first rupture time specifying unit 32 specifies the first Larson-Miller rupture time by acquiring the first stress, the first temperature, and the regression equation. Note that the first rupture time specifying unit 32 may acquire the first stress and the first temperature based on the stress time series data D1 and the temperature time series data D2. For example, a processor executing S3 is an example of the first rupture time specifying unit 32.

[0079] The deviation degree determining unit 33 is configured to determine the deviation degree based on the first non-destructive rupture time calculated from the first non-destructive creep damage degree and the first Larson-Miller rupture time. For example, the processor executing S5 is an example of the deviation degree determining unit 33.

[0080] The remaining life prediction unit 34 is configured to predict the remaining life of the target steel material 8 at the second time by applying the second stress and the second temperature to a corrected regression equation that reflects the degree of deviation in the regression equation. The second stress and the second temperature may be measurement results from a measuring device or may be values ​​input by an operator. For example, a processor that executes S7 is an example of the remaining life prediction unit 34.

[0081] The second non-destructive damage level identifying unit 35 is configured to identify a second non-destructive creep damage level. For example, a processor that executes S21 is an example of the second non-destructive damage level identifying unit 35. The second rupture time identifying unit 36 ​​is configured to identify a second Larson-Miller rupture time. For example, a processor that executes S23 is an example of the second rupture time identifying unit 36.

[0082] The updated deviation determination unit 37 is configured to determine the updated deviation based on the second non-destructive fracture time calculated from the second non-destructive creep damage level and the second Larson-Miller fracture time. For example, a processor executing S25 is an example of the updated deviation determination unit 37. The updated remaining life prediction unit 38 is configured to predict the updated remaining life of the target steel material 8 by applying the fourth stress and the fourth temperature to an updated corrected regression equation that reflects the updated deviation in the regression equation. For example, a processor executing S27 is an example of the updated deviation determination unit 37. The life update unit 39 is configured to update the predicted fracture time to the updated predicted fracture time if the updated predicted fracture time is earlier than the predicted fracture time. For example, a processor executing S29 is an example of the life update unit 39.

[0083] <Others> The creep life prediction device 30 described above is an arithmetic device configured by a computer, and includes a processor, a memory (storage medium), and an external communication interface. The processor may be a CPU, a GPU, an MPU, a DSP, or a combination thereof. The processor according to other embodiments may be realized by an integrated circuit such as a PLD, an ASIC, an FPGA, or an MCU. The memory is configured to temporarily or non-temporarily store various data, and may be realized by at least one of a RAM, a ROM, or a flash memory, for example. The processor executes various control processes according to instructions of a program loaded into the memory.

[0084] <Summary> The contents described in the above-described embodiments can be understood, for example, as follows.

[0085] 1) A creep prediction method according to at least one embodiment of the present disclosure includes: a first non-destructive damage determination step (S1) of determining a creep damage level at a first time of a target steel material (8) for which a remaining life prediction is to be performed as a first non-destructive creep damage level using a non-destructive evaluation method; a first rupture time determination step (S3) of determining a creep rupture time of the target steel material at the first time as a first Larson-Miller rupture time by applying a first stress of the target steel material up to the first time and a first temperature of the target steel material up to the first time to a regression equation defined by the Larson-Miller method; and a deviation determination step (S5) of determining a deviation level, which is a correction value of the first Larson-Miller rupture time, based on a first non-destructive rupture time, which is the creep rupture time at the first time calculated from the first non-destructive creep damage level, and the first Larson-Miller rupture time. The method further includes a remaining life prediction step (S7) for predicting the remaining life of the target steel material at the second time by applying a second stress of the target steel material at a second time after the first time and a second temperature of the target steel material at the second time to a corrected regression equation that reflects the deviation in the regression equation.

[0086] According to the configuration 1), the deviation reflected in the correction regression equation is determined based on the results of the nondestructive evaluation method in the first nondestructive damage determination step. Therefore, the actual creep damage level of the target steel can be more strongly reflected in the correction regression equation used in the remaining life prediction step, resulting in a more accurate prediction of the target steel's remaining life. Furthermore, because both the nondestructive evaluation method and the Larson-Miller method are standardized techniques, the material of the target steel for which the remaining life prediction is performed is not restricted, and the time and cost required for the prediction can be reduced. Furthermore, because the above configuration employs a nondestructive evaluation method, there is no damage to the target steel or to the actual equipment, such as a heat exchanger, in which the target steel is incorporated. As a result, a creep life prediction method is realized that can easily and accurately predict the remaining life of a target steel regardless of the steel's material.

[0087] 2) In some embodiments, in the creep life prediction method described in 1) above, the first rupture time identification step includes: a stress identification step (S11) of identifying the first stress based on stress time series data (D1) regarding the target steel material from a specified time before the first time to the first time; and a temperature identification step (S13) of identifying the first temperature based on temperature time series data (D2) regarding the target steel material from the specified time to the first time.

[0088] According to the above configuration 2), it is possible to specify the first stress and the first temperature that more accurately reflect the actual usage environment of the target steel material, which changes over time. This allows the actual creep damage level of the target steel material to be more strongly reflected in the correction regression equation used in the remaining life prediction step. Therefore, it is possible to improve the prediction accuracy of the remaining life of the target steel material.

[0089] 3) In some embodiments, in the creep life prediction method described in 1) or 2) above, the first non-destructive damage level identification step identifies the first non-destructive creep damage level by applying statistical processing to the results obtained from each of the multiple non-destructive evaluation methods performed on the target steel material.

[0090] According to the above configuration 3), the reliability of the first non-destructive creep damage degree can be improved, and the accuracy of predicting the remaining life of the target steel material can be improved.

[0091] 4) In some embodiments, in the creep life prediction method described in any one of 1) to 3) above, in the first fracture time determination step, the temperature of the target steel material obtained based on the measurement results of an optical fiber temperature sensor (9) for measuring the temperature of the target steel material is applied to the regression equation to determine the first Larson-Miller fracture time.

[0092] According to the above configuration 4), even when measuring the temperature at each evaluation point to predict the creep damage degree at multiple evaluation points on the target steel material, the cost of the equipment for measuring the temperature can be reduced. More specifically, the cost of the equipment can be reduced compared to when a thermocouple is placed at each evaluation point.

[0093] 5) In some embodiments, the creep life prediction method according to any one of 1) to 4) above includes: a second non-destructive damage determination step (S21) of determining the creep damage of the target steel material at a third time later than the second time as a second non-destructive creep damage using a non-destructive evaluation method; a second rupture time determination step (S23) of determining the creep rupture time at the third time as a second Larson-Miller rupture time by applying a third stress of the target steel material up to the third time and a third temperature of the target steel material up to the third time to the regression equation defined in the Larson-Miller method; and an updated deviation determination step (S25) of determining an updated deviation as an updated correction value of the second Larson-Miller rupture time based on the second non-destructive creep damage, which is the creep rupture time at the third time calculated from the second non-destructive creep damage, and the second Larson-Miller rupture time. The method further includes an update remaining life prediction step (S27) for evaluating the remaining life of the target steel material at the fourth time by applying a fourth stress of the target steel material at a fourth time after the third time and a fourth temperature of the target steel material at the fourth time to an update corrected regression equation that reflects the update deviation in the regression equation.

[0094] According to the inventor's findings, creep strength, which is the stress that causes a specified creep rate, may weaken as the cumulative usage time of the target steel material increases. Therefore, there is a risk that the true remaining life of the target steel material at the second time point predicted in the remaining life prediction step may be shorter. In this regard, according to the configuration of 5) above, the updated remaining life of the target steel material at the fourth time point is calculated based on the updated deviation determined at a timing after the second time point. This improves the accuracy of the prediction of the remaining life of the target steel material.

[0095] 6) In some embodiments, the creep life prediction method described in 5) above further comprises a remaining life update step (S29) of updating the predicted fracture time of the target steel material determined from the renewed remaining life predicted in the renewed remaining life prediction step to the renewed predicted fracture time if the predicted fracture time of the target steel material determined from the remaining life evaluated in the remaining life prediction step is earlier than the predicted fracture time of the target steel material determined from the remaining life evaluated in the remaining life prediction step.

[0096] According to the above feature 6), the creep rupture time of the target steel material can be predicted more accurately.

[0097] 7) In some embodiments, the creep life prediction method described in 6) above further comprises an inspection step (S31) of periodically inspecting a heat exchanger incorporating the target steel material, wherein the remaining life update step is performed between the Nth inspection step and the N+1th inspection step, where N is defined as a natural number, and wherein the remaining life update step updates the predicted fracture time within the specified operating period of the heat exchanger from the N+1th inspection step to the N+2th inspection step to the updated predicted fracture time within the specified operating period.

[0098] According to the configuration of 7) above, even if the predicted fracture time of the target steel material is brought forward to the updated predicted fracture time, measures to prepare for creep fracture can be taken on the target steel material in the N+1th inspection work step, which occurs before the updated predicted fracture time.

[0099] 8) A creep life prediction device (30) according to at least one embodiment of the present disclosure includes: a first non-destructive damage determination unit (31) that determines the creep damage level of a target steel material (8) for which a remaining life prediction is to be performed at a first time as a first non-destructive creep damage level using a non-destructive evaluation method; a first rupture time determination unit (32) that determines the creep rupture time of the target steel material at the first time as a first Larson-Miller rupture time by applying a first stress of the target steel material up to the first time and a first temperature of the target steel material up to the first time to a regression equation defined by the Larson-Miller method; and a deviation determination unit (33) that determines a deviation level that is a correction value of the first Larson-Miller rupture time based on a first non-destructive rupture time that is the creep rupture time at the first time calculated from the first non-destructive creep damage level and the first Larson-Miller rupture time. The apparatus is provided with a remaining life prediction unit (34) that predicts the remaining life of the target steel material at the second time by applying a second stress of the target steel material at a second time after the first time and a second temperature of the target steel material at the second time to a corrected regression equation that reflects the deviation in the regression equation.

[0100] The configuration 8) above provides the same technical advantages as the configuration 1).

[0101] 1: First heat transfer tube 2: Second heat transfer tube 3: Third heat transfer tube 4: Fourth heat transfer tube 5: Heat exchanger 7: Heat transfer tube 8: Target steel material 9: Optical fiber temperature sensor 30: Creep life prediction device 31: First non-destructive damage level determination unit 32: First fracture time determination unit 33: Deviation degree determination unit 34: Remaining life prediction unit 35: Second non-destructive damage level determination unit 36: Second fracture time determination unit 37: Updated deviation degree determination unit 38: Updated remaining life prediction unit 39: Life update unit D1: Stress time series data D2: Temperature time series data

Claims

1. A first non-destructive damage degree specifying step of specifying the creep damage degree of the target steel material at the first time to be predicted for remaining life as a first non-destructive creep damage degree by using a non-destructive evaluation method; a first rupture time specifying step of specifying the creep rupture time of the target steel material at the first time as a first Larson-Miller rupture time by applying the first stress of the target steel material up to the first time and the first temperature of the target steel material up to the first time to a regression equation defined by the Larson-Miller method; a deviation degree specifying step of specifying a deviation degree, which is a correction value of the first Larson-Miller rupture time, based on a first non-destructive rupture time, which is the creep rupture time at the first time obtained from the first non-destructive creep damage degree, and the first Larson-Miller rupture time; and a remaining life prediction step of predicting the remaining life of the target steel material at the second time by applying the second stress of the target steel material at the second time after the first time and the second temperature of the target steel material at the second time to a corrected regression equation reflecting the deviation degree in the regression equation. A creep life prediction method comprising the above steps.

2. The first rupture time specifying step includes a stress specifying step of specifying the first stress based on stress time series data regarding the target steel material from a specified time before the first time to the first time, and a temperature specifying step of specifying the first temperature based on temperature time series data regarding the target steel material from the specified time to the first time. The creep life prediction method according to claim 1.

3. The first non-destructive damage degree specifying step specifies the first non-destructive creep damage degree by applying statistical processing to the results obtained from each of the plurality of non-destructive evaluation methods executed on the target steel material. The creep life prediction method according to claim 1 or 2.

4. In the first rupture time specifying step, the first Larson-Miller rupture time is specified by applying the temperature of the target steel material obtained based on the measurement result of an optical fiber temperature sensor for measuring the temperature of the target steel material to the regression equation. The creep life prediction method according to claim 1 or 2.

5. A second non-destructive damage degree specifying step of specifying the creep damage degree of the target steel material at a third time after the second time as a second non-destructive creep damage degree by a non-destructive evaluation method; a second fracture time specifying step of specifying the creep rupture time at the third time as a second Larson-Miller rupture time by applying the third stress of the target steel material up to the third time and the third temperature of the target steel material up to the third time to the regression equation defined in the Larson-Miller method; an update deviation degree specifying step of specifying an update deviation degree, which is an update correction value of the second Larson-Miller rupture time, based on a second non-destructive rupture time, which is the creep rupture time at the third time obtained from the second non-destructive creep damage degree, and the second Larson-Miller rupture time; an update remaining life prediction step of evaluating an update remaining life, which is the remaining life of the target steel material at the fourth time, by applying the fourth stress of the target steel material at a fourth time after the third time and the fourth temperature of the target steel material at the fourth time to an update correction regression equation reflecting the update deviation degree in the regression equation. The creep life prediction method according to claim 1 or 2 includes these steps.

6. The creep life prediction method according to claim 5 further includes a remaining life update step of updating the predicted fracture time to the update predicted fracture time when the update predicted fracture time of the target steel material obtained from the update remaining life predicted in the update remaining life prediction step is earlier than the predicted fracture time of the target steel material obtained from the remaining life evaluated in the remaining life prediction step.

7. The creep life prediction method according to claim 6 further includes an inspection step of periodically inspecting a heat exchanger in which the target steel material is incorporated. The remaining life update step is executed between the Nth inspection step and the (N + 1)th inspection step, where N is defined as a natural number. In the remaining life update step, the predicted fracture time within the specified operation period of the heat exchanger from the (N + 1)th inspection step to the (N + 2)th inspection step is updated to the update predicted fracture time within the specified operation period.

8. A creep life prediction device comprising: a first non-destructive damage degree specifying unit that specifies, as a first non-destructive creep damage degree, the creep damage degree of a target steel material at a first time using a non-destructive evaluation method; a first fracture time specifying unit that specifies, as a first Larson-Miller fracture time, the creep fracture time of the target steel material at the first time by applying the first stress of the target steel material up to the first time and the first temperature of the target steel material up to the first time to a regression equation defined by the Larson-Miller method; a deviation degree specifying unit that specifies a deviation degree, which is a correction value of the first Larson-Miller fracture time, based on a first non-destructive fracture time, which is the creep fracture time at the first time obtained from the first non-destructive creep damage degree, and the first Larson-Miller fracture time; and a remaining life prediction unit that predicts the remaining life of the target steel material at a second time after the first time by applying the second stress of the target steel material at the second time and the second temperature of the target steel material at the second time to a corrected regression equation reflecting the deviation degree in the regression equation.

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