Creep life prediction method, and creep life prediction device

Abstract

To provide a creep life prediction method and a creep life prediction device that can simply and accurately predict the remaining life of a target steel material regardless of the properties of the target steel material.SOLUTION: A creep life prediction method includes: a first nondestructive damage degree identifying step of using a nondestructive evaluation method to identify, as a first nondestructive creep damage degree, a creep damage degree of a target steel material subjected to remaining life prediction at a first time; 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.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a creep life prediction method for predicting the remaining life of steel materials and a creep life prediction device.

Background Art

[0002] Conventionally, a creep life prediction method for predicting the creep life of steel materials has been known. For example, the creep life prediction method disclosed in Patent Document 1 calculates the fracture time of the welded portion of chromium steel based on the test results obtained for a sample of the base material portion of 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 material portion characteristic coefficient identification step, a welded portion characteristic coefficient identification step, and a fracture time calculation step.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The steel materials handled by the above creep life prediction method are only modified 9Cr-1Mo steel, and a life prediction method that can accurately evaluate the remaining life of other types of steel materials is required. In addition, in the life prediction method disclosed in Patent Document 1, it is necessary to conduct a small punch creep test or the like, which requires a significant amount of cost and time. In addition, the steel material (or the actual machine incorporating the steel material) is damaged to some extent when collecting the test piece. Therefore, a simpler life prediction method is required.

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

Means for Solving the Problems

[0007] The creep life prediction method according to at least one embodiment of the present disclosure includes: a first non-destructive damage degree specifying step of specifying a creep damage degree at a first time of a target steel material for which remaining life prediction is to be made as a first non-destructive creep damage degree by using a non-destructive evaluation method; a first fracture time specifying step of specifying a creep rupture time (total life) of the target steel material at the first stress and the first temperature 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 as a first Larson-Miller fracture time; a deviation degree specifying step of specifying 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 rupture time (total life) at the first time obtained from the first non-destructive creep damage degree, and the first Larson-Miller fracture time; In a corrected regression equation reflecting the degree of deviation in the regression equation, by applying the second stress of the target steel material at a second time after the first time and the second temperature of the target steel material at the second time, a remaining life prediction step of predicting the remaining life of the target steel material at the second time is provided.

[0008] A creep life prediction device according to at least one embodiment of the present disclosure 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 for which remaining life prediction is to be made, using a non-destructive evaluation method; a first fracture time specifying unit that specifies, as a first Larson-Miller fracture time, the creep rupture time (total life) of the target steel material at the first stress and the first temperature 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 that is the creep rupture time (total life) of the target steel material at the first time obtained from the first non-destructive creep damage degree and the first Larson-Miller fracture time; a remaining life prediction unit that predicts the remaining life of the target steel material at a second time by applying the second stress of the target steel material at a 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 is provided.

Advantages of the Invention

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

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

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Figure 4

Figure 5

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Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0011] Hereinafter, some embodiments of the present disclosure 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 disclosure, but are merely illustrative examples. For example, expressions indicating relative or absolute arrangements such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric", or "coaxial" not only strictly represent such arrangements, but also represent states of relative displacement with tolerances or angles and distances that can obtain the same function. For example, expressions indicating that things such as "identical", "equal", and "homogeneous" are in an equal state shall represent not only a strictly equal state, but also a state in which there are tolerances or differences to the extent that the same function can be obtained. For example, expressions representing shapes such as a square shape or a cylindrical shape shall represent not only shapes such as a square shape or a cylindrical shape in a geometrically strict sense, but also shapes including concavo-convex portions, chamfered portions, etc. within the range where the same effect can be obtained. On the other hand, the expressions "comprising", "including", or "having" a certain component are not exclusive expressions excluding the existence of other components. Note that the same reference numerals may be given to similar configurations and the description may be omitted.

[0012] <Overview of the target steel material 8> FIG. 1 is a schematic view 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, improved 9Cr-1Mo steel, or austenitic stainless steel may be employed.

[0013] The target steel material 8 constitutes at least a part of the heat exchanger 5. The heat exchanger 5 illustrated in FIG. 1 is a superheater used in a boiler, and more specifically, it is a superheater or a reheater. The heat exchanger 5 includes two tube sheets 6 and heat transfer tubes 7 connected to each tube sheet 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 arranged along the extending direction of the tube sheet 6. Each of these heat transfer tubes 7 may be composed of a plurality of pipe groups. The steel material constituting the pipe group is the above-mentioned target steel material 8.

[0014] 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, high-temperature combustion gas generated in the furnace of the boiler flows. By heating the water or steam flowing inside each heat transfer tube 7 with the combustion gas, the heat exchanger 5 generates superheated steam.

[0015] Each heat transfer tube 7 is used in a high-temperature and 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 that the remaining life of the target steel material 8 be accurately predicted.

[0016] <Prediction of the remaining life of the conventional target steel material 8> Conventionally, when predicting the remaining life of the target steel material 8, the degree of creep damage has been estimated. The degree of creep damage, also called the creep life consumption rate, is a numerical 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] As a known method used for estimating the degree of creep damage, the Larson-Miller method can be mentioned. The Larson-Miller method is a method for predicting the creep rupture time of the target steel material 8 based on creep rupture data obtained by performing a creep test on a test piece of the same type of material as the target steel material 8. The creep rupture data is data obtained from creep tests performed by changing various test conditions, and these test conditions include the stress in the test piece and the temperature of the test piece as control factors.

[0018] In the Larson-Miller method, t r which is the creep rupture time of the target steel material 8, is defined as in the following formula (1). T(C + logt r ) = A0 + A1×logσ + A2×(logσ) 2 ··· Formula (1) A0, A1, and A2 are regression coefficients obtained from the 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 (an eigenvalue of the material) determined by the type of material of the target steel material 8. The left side of formula (1) is the so-called Larson-Miller parameter.

[0019] When formula (1) is transformed, formula (2) is obtained. logt r ={A0 + A1×logσ + A2×(logσ) 2} / T - C ··· Equation (2) The right side of Equation (2) is a regression equation defined by the Larson - Miller method. Hereinafter, the regression equation shown on the right side of Equation (2) may be simply referred to as the "regression equation" and may be denoted as f(σ, T) as a mathematical formula. Figure 2 is a schematic diagram showing a creep rupture curve created assuming that the environmental temperature is substantially constant. The regression equation is shown by the solid line in Figure 2. Note that the horizontal axis of the graph in Figure 2 is represented by a logarithmic scale (logarithmic scale).

[0020] The conventionally known regression equation of Equation (2) does not consider the variation in the values shown by the creep rupture data. Therefore, in Figure 2, even if the creep rupture time as the predicted value corresponding to the stress (σ0) is obtained as t0 by the regression equation, the true creep rupture time t k may be earlier than t0.

[0021] Therefore, in order to improve the prediction accuracy of the creep rupture time, the inventor of the present application devised a corrected regression equation (the right side of the following Equation (3)) that reflects the degree of deviation (x) in the regression equation. logt r = f(σ, T)+x ··· Equation (3) If the temperature (T) is assumed to be constant, the corrected regression equation corresponds to the two - dotted line in Figure 2, and the creep rupture time as the corrected predicted value corresponding to the stress (σ0) is obtained as t'0. The degree of 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 degree of deviation (x) is different from the corrected value obtained by multiplying the reliability coefficient of the creep rupture data (for example, 2.33), which has been conventionally proposed, by the standard deviation of the data.

[0022] <Degree of deviation and corrected regression equation> The basic concept of the deviation degree (x) devised by the inventor of the present application will be described. As the reliability of the deviation degree (x) increases, the reliability of the creep damage degree (corrected Larson-Miller creep damage degree) obtained using Equation (3) also increases. On the other hand, the reliability of the creep damage degree (non-destructive creep damage degree) obtained based on a non-destructive evaluation method different from the Larson-Miller method is also similarly high. This is because the non-destructive creep damage degree is obtained through a direct evaluation of the target steel material 8. If the reliability of the deviation degree is high, the corrected Larson-Miller creep damage degree at the first time is substantially the same as the non-destructive creep damage degree at the first time. That is, the inventor of the present application has come to the conclusion that a highly reliable deviation degree can be obtained by inverse calculation from the equation indicating that both creep damage degrees are equal. Then, at the second time after the first time, by applying the corrected regression equation including the deviation degree to the Larson-Miller method, the remaining life of the target steel material 8 with high accuracy can be specified. Hereinafter, the derivation process of the deviation degree will be described.

[0023] The corrected Larson-Miller creep damage degree (first corrected Larson-Miller creep damage degree) at the first time obtained by the Larson-Miller method using the corrected regression equation is defined by Equation (4). D L1 =t1 / t r1 ···Equation (4) D L1 is the first corrected Larson-Miller creep damage degree, and t1 is the cumulative usage time of the target steel material 8 at the first time. t r1 is the creep rupture time (first Larson-Miller rupture time) obtained at the first time by the Larson-Miller method using Equation (3), and is represented by Equation (3A).

Equation

[0024] In Equation (3A), σ1 is the stress (first stress) of the target steel material 8 up to the first time, and T1 is the temperature (first temperature) of the target steel material 8 up to the first time. f(σ1, T1) in Equation (3A) is a value obtained by applying σ = σ1 and T = T1 to the regression equation that is the right side of Equation (2). The f(σ1, T1) power of 10 is the creep rupture time (first Larson-Miller rupture time) at the first time obtained by the conventional Larson-Miller method.

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

[0026] The non-destructive creep damage degree (first non-destructive creep damage degree: D N1 ) at the first time is assumed to be equal to the first corrected Larson-Miller creep damage degree (D L1 ), then the following Equation (5) holds. Equation (5) defines the divergence degree (x) with high reliability. x = log(t1 / D N1 ) - f(σ1, T1) ··· Equation (5) log(t1 / D N1 ) is the logarithmic value of the creep rupture time (first non-destructive rupture time) at the first time obtained from the first non-destructive creep damage degree (D N1 ). Also, f(σ1, T1) is the logarithmic value of the first Larson-Miller rupture time.

[0027] By applying Equation (5) to Equation (3), Equation (3B) is obtained. The right side of Equation (3B) defines the corrected regression equation as a general formula. logt r = f(σ, T) + log(t1 / D N1 ) - f(σ1, T1) ··· Equation (3B)

[0028] The creep rupture time (t of the target steel material 8 at the second time after the first timer2 ) When obtaining, a correction regression equation is used. Specifically, the following equation (3C) 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) is used. logt r2 =f(σ2,T2)+log(t1 / D N1 )-f(σ1,T1) =f(σ2,T2)+x ··· Equation (3C) σ2 is the second stress, and T2 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).

Equation

[0029] The outline of the remaining life prediction of the target steel material 8 described above will be described with reference to FIG. 3. First, at the first time (M1), the first non-destructive creep damage degree and the first non-destructive rupture time are obtained. Further, based on the first stress and the first temperature, the first Larson-Miller rupture time is obtained. Thereby, the deviation degree (x) and the correction regression equation are obtained. Then, at the second time (M2), based on the second stress, the second temperature, and the correction regression equation, the remaining life of the target steel material 8 is obtained, and the predicted rupture point (C1) of the target steel material 8 is obtained.

[0030] <Method for predicting remaining life of target steel material 8> FIG. 4 is a flowchart showing a method for predicting the remaining life of the 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 obtained as the first non-destructive creep damage degree (D using a non-destructive evaluation method N1A first non-destructive damage degree specifying step (S1) for specifying as [the first non-destructive damage degree] is executed. The non-destructive evaluation method is executed at the first time (a specific example of the non-destructive evaluation method will be described later). In S1, based on the first non-destructive creep damage degree, the fracture time (the first non-destructive fracture time) of the target steel material 8 is obtained accordingly.

[0032] Next, a first fracture time specifying step (S3) for specifying the creep fracture time of the target steel material 8 at the first time as the first Larson-Miller fracture time by using the Larson-Miller method is executed. The first Larson-Miller fracture time is obtained by applying the first stress (σ1) and the first temperature (T1) to the regression equation (that is, f(σ, T)).

[0033] Next, a deviation degree specifying step (S5) for specifying the deviation degree (x) based on the first non-destructive fracture time and the first Larson-Miller fracture time is executed. The deviation degree is obtained by Equation (5).

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

[0035] According to the above configuration, the degree of deviation reflected in the correction regression equation is specified based on the result of the non-destructive evaluation method in the first non-destructive damage degree specification step (S1). Therefore, the actual creep damage degree of the target steel material 8 can be more accurately reflected in the correction regression equation used in the remaining life prediction step (S7), and the remaining life of the target steel material 8 can be predicted more accurately. Also, since both the non-destructive evaluation method and the Larson-Miller method are standardized methods, the material of the target steel material 8 for which the remaining life is predicted is not restricted, and the time and cost required for the prediction can be reduced. Furthermore, in this embodiment, since the non-destructive evaluation method is adopted, the target steel material 8 and the heat exchanger 5 in which the target steel material 8 is incorporated are not damaged. From the above, a creep life prediction method that can simply and accurately predict the remaining life of the target steel material 8 regardless of the material of the target steel material 8 is realized.

[0036] <Non-destructive evaluation method> Examples of the non-destructive evaluation method used in the first non-destructive damage degree specification step (S1) include a hardness measurement method, a precipitate interparticle distance method, a microstructure comparison method, a void number density method, or a combination thereof.

[0037] The hardness measurement method is a known method 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 meter. The creep damage degree of the target steel material 8 is obtained by comparing the hardness obtained by the measurement with master data showing the relationship between the hardness and the remaining life obtained in advance.

[0038] The precipitate interparticle distance method is a known method for predicting the creep damage degree of the target steel material 8 based on the interparticle distance of precipitates appearing on the outer surface of the target steel material 8. More specifically, based on the interparticle distance obtained by the measurement, the stress of the target steel material 8, and the temperature of the target steel material 8, the creep rate of the target steel material 8 is obtained. Then, based on the creep curve estimated from the creep rate, the time required until the allowable strain is reached is obtained. Thereby, the creep damage degree is obtained.

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

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

[0041] The non-destructive evaluation method used in the present disclosure is not limited to the above four. For example, the void area ratio method, the A parameter method, the electrical resistance method, or the crystal grain deformation method, etc. may be used. Since these methods are known methods, detailed description is omitted.

[0042] In some embodiments, in the first non-destructive damage degree specifying step (S1), a plurality of non-destructive evaluation methods may be executed on the target steel material 8. In this case, as a result of the plurality of non-destructive evaluation methods, a plurality of non-destructive creep damage degrees are obtained. By applying statistical processing to these plurality of non-destructive creep damage degrees, the first non-destructive creep damage degree as a representative value may be specified. The statistical processing may be an averaging process, or a process of extracting the maximum value or the minimum value. According to the above configuration, the reliability of the first non-destructive creep damage degree can be improved, and the prediction accuracy of the remaining life of the target steel material 8 can be improved.

[0043] In addition, when applying a plurality of non-destructive evaluation methods, it is necessary to evaluate a plurality of parts of the target steel material 8. In this case, if the production lots of the materials are the same among 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, different non-destructive evaluation methods may be applied to each part of the plurality of different heat transfer tubes 7.

[0044] <First stress, first temperature> Referring to FIGS. 5 to 7, the first stress and the first temperature used in the first rupture time specifying step (S3) will be described.

[0045] As shown in FIG. 5, the first stress (σ1), which is the stress of the target steel material 8 up to the first time, may be obtained based on the stress time series data D1. The stress time series data D1 shows the change over time of the stress related to the target steel material 8 from a specified time (M s ) before the first time (M1) to the first time. The data may be obtained, for example, from the measurement results of the pressure (internal pressure) of the steam flowing inside the target steel material 8.

[0046] Also, as shown in FIG. 6, the first temperature (T1), which is the temperature of the target steel material 8 up to the first time, may be obtained based on the temperature time series data D2. The temperature time series data D2 shows the change over time of the temperature related to the target steel material 8 from a specified time (M s ) to the first time (M1). The data may be obtained, for example, from the measurement results of the outer surface temperature of the target steel material 8.

[0047] FIG. 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 stress specifying step (S11) for obtaining the first stress (σ1) based on the stress time series data D1 is executed. In S11, the first stress is obtained by averaging the stress indicated by the stress time series data D1. Next, a temperature specifying step (S13) for obtaining the first temperature (T1) based on the temperature time series data D2 is executed. In S13, the first temperature is obtained by averaging the temperature indicated by the temperature time series data D2.

[0048] According to the above configuration, the first stress and the first temperature that more accurately reflect the actual usage environment of the target steel material 8 that changes over time can be specified. As a result, the correction regression formula used in the remaining life prediction step (S7) can more accurately reflect the actual creep damage degree of the target steel material 8. Therefore, the prediction accuracy of the remaining life of the target steel material 8 can be improved.

[0049] Furthermore, in the temperature determination step (S13), an optical fiber temperature sensor 9 for measuring the temperature of the target steel material 8 may be used. FIG. 1 is a schematic diagram showing the 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 that constitutes the heat transfer tube 7. The optical fiber temperature sensor 9 is connected to a creep life prediction device 30 (details will be described later) as an arithmetic device. By continuously acquiring the temperature of the target steel material 8 by the optical fiber temperature sensor 9, the creep life prediction device 30 can acquire temperature time series data D2. The optical fiber temperature sensor 9 can measure the temperature at the evaluation points on the outer surfaces of a large number of target steel materials 8. Therefore, the 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 a plurality of evaluation points of the target steel material 8, it is possible to reduce the cost of the equipment for measuring the temperature. More specifically, compared with the case of arranging thermocouples at a large number (for example, 100 points or more) of evaluation points, it is possible to reduce the cost of the equipment.

[0051] <Additional components of the creep life prediction method> Returning to FIG. 3, even if the predicted fracture time (C1) is obtained based on the remaining life of the target steel material 8 at the second time, the true creep fracture time (t k ) may be earlier than that. This is because as the cumulative use time of the target steel material 8 increases, the creep strength of the target steel material 8 may decrease. Here, the creep strength refers to the stress in the target steel material 8 that causes a specified creep rate. If the creep strength decreases, the progress rate of the creep deformation of the target steel material 8 increases.

[0052] In some embodiments of the present disclosure, a review of the predicted fracture time point (C1) may be performed. This is executed by updating each of the degree of deviation (x) and the corrected regression equation. This update may be performed at a third time (M3) after the second time. More specifically, at the third time, a new degree of deviation (updated degree of deviation) and a new corrected regression equation (updated corrected regression equation) may be obtained according to the same procedure as the procedure performed at the first time. The details are as follows.

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

[0054] Furthermore, using the regression equation defined by the Larson-Miller method, the creep rupture time at the third time is specified as the second Larson-Miller rupture time. The second Larson-Miller rupture time can be specified by obtaining the logarithmic value of f(σ3, T3).

[0055] Here, σ3 is the stress of the target steel material 8 up to the third time, and T3 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, based on the second non-destructive rupture time and the second Larson-Miller rupture time, the updated degree of deviation is specified. The updated degree of deviation (x') is the updated correction value of the second Larson-Miller rupture time and is defined by the following equation (5A). x’=log(t3 / D N2 )-f(σ3,T3)···Equation (5A) t3 is the cumulative usage time of the target steel material 8 at the third time. By Equation (5)A, the updated corrected regression equation as a general formula is defined by Equation (3D). logt r = f(σ, T) + log(t3 / D N2 ) - f(σ3, T3) = f(σ, T) + x’ ··· Equation (3D)

[0057] Furthermore, at the fourth time after the third time, using Equation (3D), the updated remaining life (R’) of the target steel material 8 at the fourth time is predicted. When predicting the updated remaining life, the stress (the fourth stress) of the target steel material 8 at the fourth time and the temperature (the fourth temperature) of the target steel material 8 at the fourth time are used. By applying σ = σ4 and T = T4 to Equation (3D), the updated remaining life (R’) is obtained as shown in the following Equation (6A). [Number] t4 is the cumulative usage time of the target steel material 8 at the fourth time.

[0058] The method for predicting the updated remaining life of the target steel material 8 described above will be described with reference to FIG. 3. At the third time (M3), the second non-destructive creep damage degree and the second non-destructive rupture time are obtained. Furthermore, based on the third stress and the third temperature, the second Larson-Miller rupture time is obtained. Thereby, the updated deviation degree (x) and the updated correction regression equation are obtained. Then, at the fourth time (M4), based on the fourth stress, the fourth temperature, and the correction regression equation, the updated remaining life of the target steel material 8 is obtained, and the updated predicted rupture point (C2) of the target steel material 8 is obtained. When the updated predicted rupture point (C2) is earlier than the predicted rupture point (C1), it is preferable to update the predicted rupture point to the updated predicted rupture point and manage the target steel material 8.

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

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

[0061] Next, a second non-destructive damage degree specifying step (S21) for specifying the creep damage degree at the third time as a second non-destructive creep damage degree (D N2 ) by a non-destructive evaluation method is executed. The non-destructive evaluation method is executed at the third time. In S21, based on the second non-destructive creep damage degree, the fracture time (second non-destructive fracture time) of the target steel material 8 is obtained accordingly.

[0062] Next, a second fracture time specifying step (S23) for specifying the creep fracture time of the target steel material 8 at the third time as a second Larson-Miller fracture time is executed. The second Larson-Miller fracture time is obtained by applying the third stress (σ3) and the third temperature (T3) to a regression equation (that is, f(σ,T)).

[0063] Next, an updated deviation degree specifying step (S25) for specifying an updated deviation degree (x’) based on the second non-destructive fracture time and the second Larson-Miller fracture time is executed. The updated deviation degree is obtained by Equation (5A).

[0064] Next, at the fourth time, an updated remaining life prediction step (S27) for evaluating the updated remaining life (R’) of the target steel material 8 is executed. The updated remaining life is obtained by using Equation (6A). Next, when the updated predicted fracture point (C2) obtained from the updated remaining life is earlier than the predicted fracture point (C1) obtained from the remaining life specified in S7, a remaining life update step (S29) for updating the predicted fracture point to the updated predicted fracture point is executed. Then, this flowchart ends.

[0065] According to the above configuration, based on the updated deviation degree (x’) specified at a timing after the second time, the updated remaining life of the target steel material 8 at the fourth time is obtained. Thereby, the prediction accuracy of the remaining life of the target steel material 8 can be improved.

[0066] Also, according to the configuration in which the remaining life update step (S29) is executed, the creep fracture point 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 where the heat exchanger 5 is installed, a periodic inspection is performed on the heat exchanger 5. B N-1 ,B N ,B N+1 ,B N+2 respectively indicate the timing of inspection (where N is a natural number of 2 or more, and B N indicates the Nth inspection.). During the inspection, the heat exchanger 5 is stopped. The inspection is performed every time a predetermined number of years has elapsed. Although this is merely an example, the predetermined number of years is 1 year or more and 5 years or less, and more specifically, 1 year or more and 3 years or less. The predetermined number of years may be the same as the period from the specified time (M s ) to the first time (M1) shown in FIGS. 5 and 6.

[0068] In this example, B N-1 At the time of inspection indicated by, the first non-destructive creep damage degree, the first non-destructive rupture time, and the first Larson-Miller rupture time are specified. That is, B N-1 coincides with M1 shown in FIG. 3. And B N-1 to B N During the interval (operating period of the heat exchanger 5), the remaining life is evaluated (M2). That is, at the timing indicated by M2, the predicted rupture time (C1) of the target steel material 8 is specified. At this time, it is assumed that the predicted rupture time (C1) is within the interval (specified operating period of the heat exchanger 5) from B N+1 to B N+2 .

[0069] Furthermore, B N At the time of inspection indicated by, the second non-destructive creep damage degree, the second non-destructive rupture time, and the second Larson-Miller rupture time are specified. That is, B N coincides with M3 shown in FIG. 3. And B N ~B N+1During the period between (the operating period of the heat exchanger 5), the updated remaining life is evaluated (M4). That is, at the timing indicated by M4, the updated predicted fracture time point (C2) of the target steel material 8 is specified. At this time, if the updated predicted fracture time point (C2) is earlier than the predicted fracture time point (C1) within the period from B N+1 to B N+2 Let's assume it is at a faster timing.

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

[0071] FIG. 10 is a flowchart showing a creep prediction method according to an embodiment of the present disclosure. First, the N-1th inspection step (S31) of inspecting the heat exchanger 5 is executed. That is, the inspection at B N-1 is executed, and the first non-destructive creep damage degree, the first non-destructive fracture time, and the first Larson-Miller fracture time are specified. At S31 at this time, S1, S3, and S5 in FIG. 4 are executed. After the execution of S31, the heat exchanger 5 restarts operating.

[0072] Thereafter, the prediction of the fracture time point of the target steel material 8 is executed (S33). The timing of S33 at this time is M2, and S7 in FIG. 4 is executed. As a result, the predicted fracture time point (C1) of the target steel material 8 based on the remaining life evaluation is predicted.

[0073] Next, it is determined whether the next inspection timing has arrived (S35). Until the inspection timing arrives (S35: NO), the steps wait. And when the next inspection timing arrives (S35: YES), the steps return to S31.

[0074] In the next S31, the Nth inspection is executed. This timing is B shown in FIG. 9 NIt is (M3), and the second non-destructive creep damage degree, the second non-destructive rupture time, and the second Larson-Miller rupture time are specified. At S31 at this time, FIGS. S21, S23, and S25 in FIG. 8 are executed. Thereafter, the prediction of the rupture time is executed again (S33). The timing of S33 at this time is (M4), and S27 and S29 in FIG. 8 are executed. As a result, the rupture time of the target steel material 8 is updated from the predicted rupture time (C1) to the updated predicted rupture time (C2). Thereafter, 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 an arithmetic device configured to predict the remaining life of the target steel material 8. Hereinafter, the processor of the arithmetic device may be simply referred to as the "processor".

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

[0077] The first non-destructive damage degree specifying unit 31 is configured to specify the first non-destructive creep damage degree. The first non-destructive damage degree specifying unit 31 may be configured to receive the first non-destructive creep damage degree input by an operator. For example, the processor that executes S1 is an example of the first non-destructive damage degree specifying 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 formula. 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, the processor that executes S3 is an example of the first rupture time specifying unit 32.

[0079] The deviation degree specifying unit 33 is configured to specify the deviation degree based on the first non-destructive rupture time obtained from the first non-destructive creep damage degree and the first Larson-Miller rupture time. For example, a processor that executes S5 serves as an example of the deviation degree specifying 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 in which the deviation degree is reflected in the regression equation. The second stress and the second temperature may be measurement results of a measuring device or input values of an operator. For example, a processor that executes S7 serves as an example of the remaining life prediction unit 34.

[0081] The second non-destructive damage degree specifying unit 35 is configured to specify the second non-destructive creep damage degree. For example, a processor that executes S21 serves as an example of the second non-destructive damage degree specifying unit 35. The second rupture time specifying unit 36 is configured to specify the second Larson-Miller rupture time. For example, a processor that executes S23 serves as an example of the second rupture time specifying unit 36.

[0082] The updated deviation degree specifying unit 37 is configured to specify the updated deviation degree based on the second non-destructive rupture time obtained from the second non-destructive creep damage degree and the second Larson-Miller rupture time. For example, a processor that executes S25 serves as an example of the updated deviation degree specifying 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 in which the updated deviation degree is reflected in the regression equation. For example, a processor that executes S27 serves as an example of the updated deviation degree specifying unit 37. The life update unit 39 is configured to update the predicted rupture time to the updated predicted rupture time when the updated predicted rupture time is earlier than the predicted rupture time. For example, a processor that executes S29 serves as an example of the life update unit 39.

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

[0084] <Summary> The content described in several of the above embodiments is understood as follows, for example.

[0085] 1) The creep prediction method according to at least one embodiment of the present disclosure is a first non-destructive damage degree specifying step (S1) of specifying, as a first non-destructive creep damage degree, the creep damage degree of the target steel material (8) at a first time for which remaining life prediction is to be made, using a non-destructive evaluation method; a first breaking time specifying step (S3) of specifying, as a first Larson-Miller breaking time, the creep rupture 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 step (S5) of specifying a deviation degree, which is a correction value of the first Larson-Miller breaking time, based on a first non-destructive breaking 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 breaking time; a remaining life prediction step (S7) of predicting 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 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.

[0086] According to the configuration of 1) above, the degree of deviation reflected in the correction regression equation is specified based on the result of the non-destructive evaluation method in the first non-destructive damage degree specification step. Therefore, the actual creep damage degree of the target steel material can be more strongly reflected in the correction regression equation used in the remaining life prediction step, and the remaining life of the target steel material can be predicted more accurately. In addition, since both the non-destructive evaluation method and the Larson-Miller method are standardized methods, the material of the target steel material for which the remaining life is predicted is not restricted, and the time and cost spent on the prediction can be reduced. Furthermore, according to the above configuration, since the non-destructive evaluation method is adopted, the target steel material and the actual machine such as the heat exchanger in which the target steel material is incorporated are not damaged. From the above, a creep life prediction method that can simply and accurately predict the remaining life of the target steel material regardless of the material of the steel material is realized.

[0087] 2) In some embodiments, it is the creep life prediction method described in 1) above, The first rupture time specification step is Based on the stress time series data (D1) of the target steel material from a specified time before the first time to the first time, a stress specification step (S11) for specifying the first stress, Based on the temperature time series data (D2) of the target steel material from the specified time to the first time, a temperature specification step (S13) for specifying the first temperature, including.

[0088] According to the configuration of 2) above, the first stress and the first temperature that more accurately reflect the actual use environment of the target steel material that changes over time can be specified. Thereby, the actual creep damage degree of the target steel material can be more strongly reflected in the correction regression equation used in the remaining life prediction step. Therefore, the prediction accuracy of the remaining life of the target steel material can be improved.

[0089] 3) In some embodiments, it is the creep life prediction method described in 1) or 2) above, 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 performed on the target steel material.

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

[0091] 4) In some embodiments, there is a creep life prediction method according to any one of 1) to 3) above, In the first rupture time specifying step, the first Larson-Miller rupture time is specified by applying the temperature of the target steel material acquired based on the measurement result of the optical fiber temperature sensor (9) for measuring the temperature of the target steel material to the regression formula.

[0092] According to the configuration of 4) above, even when measuring the temperature at each of a plurality of evaluation points of the target steel material to predict the creep damage degree, it is possible to reduce the cost of the equipment for measuring the temperature. More specifically, compared with the case of arranging thermocouples at each evaluation point, the cost of the equipment can be reduced.

[0093] 5) In some embodiments, there is a creep life prediction method according to any one of 1) to 4) above, a second non-destructive damage degree specifying step (S21) 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 rupture time specifying step (S23) 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 formula defined in the Larson-Miller method; An update deviation degree specifying step (S25) for specifying an update deviation degree, which is an updated 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 updated remaining life prediction step (S27) for evaluating an updated remaining life, which is 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 updated correction regression equation obtained by reflecting the update deviation degree in the regression equation.

[0094] According to the inventor's findings, the creep strength, which is the stress that causes a specified creep rate, may decrease as the cumulative usage time of the target steel material increases. Therefore, the true remaining life of the target steel material may be shorter than the remaining life of the target steel material at the second time predicted in the remaining life prediction step. In this regard, according to the configuration of 5) above, the updated remaining life of the target steel material at the fourth time is obtained based on the update deviation degree specified at a timing later than the second time. Thereby, the prediction accuracy of the remaining life of the target steel material can be improved.

[0095] 6) In some embodiments, there is provided the creep life prediction method according to 5) above, further comprising a remaining life update step (S29) of updating the predicted rupture time to the updated predicted rupture time when the updated predicted rupture time of the target steel material obtained from the updated remaining life predicted in the updated remaining life prediction step is earlier than the predicted rupture time of the target steel material obtained from the remaining life evaluated in the remaining life prediction step.

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

[0097] 7) In some embodiments, there is provided the creep life prediction method according to 6) above, further comprising an inspection step (S31) of periodically inspecting a heat exchanger in which the target steel material is incorporated. The remaining life update step is defined with N as a natural number and is executed between the Nth inspection step and the (N + 1)th inspection step, In the remaining life update step, the predicted fracture time within the specified operating period of the heat exchanger from the (N + 1)th inspection step to the (N + 2)th inspection step is updated 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 advances to the updated predicted fracture time, in the (N + 1)th inspection operation step that arrives before the updated predicted fracture time, measures for creep fracture can be applied to the target steel material.

[0099] 8) The creep life prediction device (30) according to at least one embodiment of the present disclosure a first non-destructive damage degree specifying unit (31) that specifies the creep damage degree at the first time of the target steel material (8) for which the remaining life is predicted as the first non-destructive creep damage degree using a non-destructive evaluation method; a first fracture time specifying unit (32) that specifies the creep fracture time of the target steel material at the first time as the first Larson-Miller fracture 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 the regression equation defined by the Larson-Miller method; a deviation degree specifying unit (33) that specifies the deviation degree, which is a correction value of the first Larson-Miller fracture time, based on the 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; a remaining life prediction unit (34) that predicts 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 the corrected regression equation that reflects the deviation degree in the regression equation.

[0100] According to the configuration of 8) above, the same technical advantages as in 1) above can be obtained.

Explanation of Signs

[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 degree specifying part 32: First fracture time specifying part 33: Deviation degree specifying part 34: Remaining life prediction part 35: Second non-destructive damage degree specifying part 36: Second fracture time specifying part 37: Updated deviation degree specifying part 38: Updated remaining life prediction part 39: Life update part 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 at a first time of a target steel material for which remaining life prediction is to be made as a first non-destructive creep damage degree by using a non-destructive evaluation method; A first fracture 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 that 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; 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 a second time after the first time and the second temperature of the target steel material at the second time to a corrected regression equation that reflects the deviation degree in the regression equation; A creep life prediction method comprising the above steps.

2. The first fracture 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; 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, including the above steps.

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 performed on the target steel material. The creep life prediction method according to Claim 1 or 2.

4. In the first fracture 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; ​ In the regression equation defined in the Larson-Miller method, 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, a second fracture time specifying step of specifying the creep rupture time at the third time as a second Larson-Miller fracture time; An update deviation degree specifying step of specifying an update deviation degree, which is an update correction value of the second Larson-Miller fracture time, based on a second non-destructive fracture 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 fracture 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; comprising The creep life prediction method according to claim 1 or 2.

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

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

8. A first non-destructive damage degree specifying unit that specifies, as a first non-destructive creep damage degree, the creep damage degree of the target steel material at the first time for which the remaining life is predicted, using a non-destructive evaluation method; 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 the regression equation defined by the Larson-Miller method, a first fracture time specifying unit that specifies the creep rupture time of the target steel material at the first time as the first Larson-Miller rupture time, A deviation degree specifying unit that specifies a deviation degree, which 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 of the target steel material at the first time obtained from the first non-destructive creep damage degree and the first Larson-Miller rupture time; A remaining life prediction unit that predicts the remaining life of the target steel material at the second time by applying the second stress of the target steel material at a 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 device comprising.

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