JP7778658B2 - Steam turbine creep deformation evaluation device, method, and program - Google Patents

Description

An embodiment of the present invention relates to a technology for evaluating creep deformation of nozzle diaphragms in steam turbines operated in power generation plans involving large output fluctuations.

Until now, thermal power plants have mainly operated as baseload plants, generating electricity continuously at rated power, which is highly energy efficient. However, in recent years, there has been a growing demand for thermal power plants to adjust to output fluctuations from renewable energy sources such as solar and wind power. As a result, thermal power plants have increasingly been operating at partial loads, which is less energy efficient, and the number of starts and stops has also increased.

It is known that damage and deterioration occur and accumulate in various parts of thermal power plants, such as steam turbines, control valves, and boilers, during operation, resulting in a decline in power generation performance and an increased risk of damage. One example of this damage is creep deformation of various parts and the resulting cracking. Creep deformation is a phenomenon in which, when metallic materials are used in a temperature environment at approximately half their melting point, they gradually undergo permanent deformation over time, even at low stress levels below the material's yield strength, eventually causing cracks and the metal to fracture.

With regard to creep deformation, one component that is considered important in the maintenance and management of steam turbines is the nozzle diaphragm, which is exposed to steam at temperatures of over 500°C. This is because the gaps between the nozzle diaphragm and the adjacent moving blades and rotor are designed to be as narrow as possible to prevent steam leakage.

If the creep deformation of the nozzle diaphragm reaches a certain level, it will come into contact with adjacent rotor blades and the rotor that holds them, causing damage and scattering of parts, resulting in an unplanned shutdown of the thermal power plant.

To prevent contact between the nozzle diaphragm and the rotating body, maintenance management has traditionally been carried out by predicting the amount of creep deformation of the nozzle diaphragm from databases and operating data, and measuring the amount of deformation during regular inspections.

Japanese Patent Application Laid-Open No. 2003-303014

As mentioned above, modern thermal power plants undergo repeated start-stops and partial load operation to adjust for output fluctuations. This makes it more difficult to assess the risk of damage associated with creep deformation of the nozzle diaphragm. Conventional maintenance management of nozzle diaphragm creep deformation has been based on simulations assuming baseload operation.

In baseload operation, plants are often operated near their rated output, where plant efficiency is at its maximum. In such cases, the temperatures, pressures, etc. to which each nozzle diaphragm is exposed (hereinafter referred to as "operating state variables") are meticulously evaluated and optimized during turbine design. Furthermore, because fluctuations in turbine output during operation are small, there is no need to consider fluctuations in operating state variables. For this reason, the amount of nozzle diaphragm deformation during baseload operation could be easily simulated using design information and operating history.

On the other hand, as partial load operation and start-stops increase, operation outside the design point also increases. Furthermore, there are also more situations where the nozzle diaphragm is exposed to temperatures and pressures not anticipated during design for long periods of time, and where operating state variables fluctuate. For this reason, conventional databases and simulations regarding nozzle diaphragm creep deformation could not be applied directly to modern thermal power plants, where start-stops are repeated multiple times a day and partial load operation is widely practiced.

The most common method for managing creep deformation of nozzle diaphragms is to disassemble the steam turbine when the plant is shut down, remove the nozzle diaphragm, and directly measure its strain (deformation). However, there are multiple nozzle diaphragms located inside the steam turbine, and removing them all requires disassembling the turbine. Furthermore, not only is it time-consuming to disassemble the individual nozzle diaphragms located between the rotor blades, but it also requires the rotor to be lifted out of the turbine in order to remove the lower half of the nozzle diaphragm.

For this reason, this method is highly reliable as it can measure deformation with the greatest precision, but it also requires time (LT) and costs to perform measurements, and has the drawback of lengthening the period for regular inspections and increasing power generation costs. Additionally, methods have been considered for measuring the gap between the nozzle diaphragm and rotor while the turbine is operating, but it is difficult to set up such measuring equipment and to maintain high reliability over long periods of time in special environments.

On the other hand, studies are also being conducted to sequentially estimate the deformation amount of the nozzle diaphragm using operating state variables obtained from detection data from various sensors during turbine operation. Generally, calculating the appropriate operating state variables requires heat balance calculations at the turbine inlet, outlet, and inside. However, because the operating state variables obtained in heat balance calculations have many variable terms, it is difficult to determine them uniquely, and search calculations are required, resulting in a huge computational load. For this reason, performing sequential calculations while obtaining detection data during operation poses the problem of long calculation cycles and reduced ability to track fluctuating operating state variables.

Embodiments of the present invention have been made in consideration of these circumstances, and aim to provide technology that sequentially evaluates, with excellent tracking capability, the creep deformation behavior of nozzle diaphragms in steam turbines operated in power generation plans involving large output fluctuations.

The steam turbine creep deformation evaluation device according to the embodiment includes an acquisition unit that acquires detection data from each of a plurality of sensors installed on the steam turbine or its periphery; a first calculation unit that calculates an optimal solution for an operating state variable of a nozzle diaphragm in the steam turbine based on the detection data; a second calculation unit that calculates an approximate solution for the operating state variable based on the detection data at a shorter period than the optimal solution; an update unit that updates an approximation formula that calculates the approximate solution based on the optimal solution; a calculation unit that calculates the creep deformation rate of the nozzle diaphragm based on the approximate solution; and an estimation unit that estimates the deformation amount of the nozzle diaphragm from the creep deformation rate based on an operation plan for the steam turbine.

An embodiment of the present invention provides a technology that sequentially evaluates, with excellent tracking capability, the creep deformation behavior of nozzle diaphragms in steam turbines operated under power generation plans involving large output fluctuations.

1 is a block diagram of a steam turbine creep deformation evaluation device according to a first embodiment of the present invention; FIG. 10 is a block diagram of a steam turbine creep deformation evaluation device according to a second embodiment. 4 is a graph showing the relationship between the equivalent stress acting on the nozzle diaphragm and the creep deformation rate. 10 is an evaluation graph showing a future prediction of the amount of creep deformation of the nozzle diaphragm. 2 is a flowchart showing steps of a method for evaluating creep deformation of a steam turbine according to an embodiment and an algorithm of a program for evaluating creep deformation of a steam turbine.

(First embodiment)
1 is a block diagram of a steam turbine creep deformation evaluation device 10A (10) (hereinafter simply referred to as "evaluation device 10A") according to a first embodiment of the present invention.

As described above, the evaluation device 10A includes an acquisition unit 15 that acquires detection data x ( _x1 , _x2 , ... _xn ) from each of a plurality of sensors 21 ( ₂₁₁ , ₂₁₂ , ... _21n ) installed on the steam turbine 20 or its periphery, a first calculation unit 11 that calculates an optimal solution _φ1 of the operating state quantity of the nozzle diaphragm in the steam turbine 20 based on the detection data x, a second calculation unit 12 that calculates an approximate solution _φ2 of the operating state quantity based on the detection data x at a shorter period than the optimal solution _φ1 , an update unit 16 that updates an approximate equation f(x) that calculates the approximate solution _φ2 based on the optimal solution _φ1 , a calculation unit 17 that calculates the creep deformation rate V of the nozzle diaphragm based on the approximate solution _φ2 , and an estimation unit 18 that estimates the deformation amount D of the nozzle diaphragm from the creep deformation rate V based on an operation plan 28 of the steam turbine 20.

A nozzle diaphragm (not shown) is a component installed between each stage of the multiple rows of rotor blades arranged in the steam turbine 20. The nozzle diaphragm has multiple nozzle plates (stationary blade plates) arranged circumferentially so as to face the rotor blades arranged on the rotor surface.

Furthermore, the inner and outer peripheries of these nozzle plates are held in place by ring-shaped structures called inner and outer rings. The nozzle plates and inner and outer rings are fixed together by welding or other methods, and have a structure that allows them to be separated at 0-degree and 180-degree positions. The nozzle diaphragm has this type of separate structure, and is installed so that it sandwiches the rotor from above and below, allowing it to be installed between each stage of moving blades embedded in the rotor.

Nozzle diaphragms are designed to allow steam that has passed through the upstream rotor blades to pass between the nozzle plates, and have the function of directing the steam to the downstream rotor blades at an appropriate flow rate. Due to this function, a pressure difference occurs in the steam between the upstream and downstream sides of the nozzle diaphragm. Furthermore, because nozzle diaphragms are used in high-temperature regions, the pressure difference with the outer ring side held in the turbine casing makes them prone to creep deformation, in which the inner ring side tilts toward the downstream steam side.

Sensors 21 are installed in multiple locations on or around the steam turbine 20, and output detection data x such as the temperature and pressure on the steam inlet and steam outlet sides of the steam turbine 20, and the temperature and pressure of extracted steam. In addition to this, sensors 21 also output detection data x such as the temperature and pressure before and after the steam valve, and detection data x of the turbine casing and steam valve casing to which they are attached. Sensors 21 also include those installed on equipment (not shown) other than the steam turbine 20 within the power plant, such as generator output, and output detection data x for these pieces of equipment.

The acquisition unit 15 sequentially acquires, at an appropriate sampling frequency, the detection data x that is continuously output from each of the multiple sensors 21. When the steam turbine 20 is started from a stopped state, it passes through a transient state and then transitions to a steady state in which the power generation output becomes constant. Furthermore, in response to a request for output adjustment, the steam turbine 20 may transition from one steady state to another steady state or be stopped. In such cases, it also passes through a transient state. Furthermore, the steady state after the transition can be broadly classified into rated operation, which is highly energy efficient, and partial load operation, which is less energy efficient.

As the operating state of the steam turbine 20 fluctuates frequently in this way, the creep deformation rate experienced by the nozzle diaphragm also fluctuates. For this reason, the detection data x acquired by the acquisition unit 15 can be said to be information that directly reflects the behavior of creep deformation in the nozzle diaphragm. Furthermore, this detection data x is subjected to corrections such as averaging and noise removal in the acquisition unit 15 so that it can be appropriately processed in subsequent processes.

The first calculation unit 11 calculates the heat balance of the steam turbine 20 based on this detection data x. Here, the heat balance indicates the distribution of thermal energy in each of the components of the steam turbine 20 (including the nozzle diaphragm).

That is, the first calculation unit 11 calculates and outputs the optimal solution φ ₁ of the operation state quantity based on the detected data x such as temperature, pressure, enthalpy, flow rate, etc., which are related to at least the nozzle diaphragm among these components. Note that the calculation method for the optimal solution φ ₁ of the operation state quantity of the nozzle diaphragm is not limited to being based on the heat balance of the steam turbine 20, and may be based on other calculation methods.

Specifically, the first calculation unit 11 calculates the heat balance at each stage of the steam turbine 20 by heat balance calculation based on the detected data x output by temperature sensors 21 and the like installed on the inlet and outlet sides of the steam turbine 20. However, since the operating state variables calculated by these heat balance calculations have many variable terms, it is difficult to uniquely calculate them. Therefore, search calculations are required, but performing search calculations each time on the detected data constantly acquired during operation would result in an enormous computational load. Therefore, the calculation cycle for the optimal solution _φ1 is long, and tracking performance deteriorates when the operating state variables fluctuate.

The second calculation unit 12 calculates an approximate solution φ2 of the operating state quantity at a shorter period than the optimal solution _φ1 using an approximate equation f(x) expressed as a polynomial with detected data x ( _x1 , _x2 ..., _xn ) as a variable, as in the following equation ( ₁ ). Note that the approximate equation f(x) applied by the second calculation unit 12 is not particularly limited to equation (1).

φ ₂ =f(x)=f(x ₁ ,x ₂ …,x _n )
=A ₀ +A ₁・x ₁ +A ₂・x ₂ +...+A _n・x _n ...(1)
A _i : constant, x _i : detected data (i = 1 to n)

Incidentally, some of the detected data x that form the calculation basis for the optimal solution _φ1 are difficult to detect sequentially, and so there are cases where limited detected data x are selected to calculate the approximate solution _φ2 of the operating state quantity. By reading this approximate formula f(x), the second calculation unit 12 calculates the approximate solution _φ2 of the operating state quantity in a shorter period than the optimal solution _φ1 without imposing a calculation load.

The update unit 16 compares the optimal solution _φ1 and the approximate solution _φ2 of the driving state quantity calculated from the detection data x acquired at the same timing, and updates the approximate formula f(x) so that the two match. In the approximate formula f(x) expressed as a polynomial such as the above formula (1), the coefficient _Ai is updated. Furthermore, a threshold value may be used to determine whether the compared optimal solution _φ1 and approximate solution _φ2 match, and if a "match" is determined at the timing when the optimal solution _φ1 is calculated, the approximate formula f(x) may not be updated.

The calculation unit 17 calculates the creep deformation rate V based on the design information K of the nozzle diaphragm and the approximate solution _φ2 of its operating state quantity. Alternatively, a data set of the operating state quantity φ of the nozzle diaphragm and the creep deformation rate V may be constructed, and the calculation unit 17 may output the corresponding creep deformation rate V for any input approximate solution _φ2 of the operating state quantity. Note that the creep deformation rate V calculated here may only be a component in the direction along the rotation axis of the steam turbine 20.

The estimation unit 18 can estimate the deformation amount D of the nozzle diaphragm at the current time by integrating the creep deformation rate V output from the calculation unit 17 in real time. Furthermore, the future deformation amount D of the nozzle diaphragm can also be estimated from the operating time and creep deformation rate V estimated from the operation plan 28 of the steam turbine 20. The operation plan 28 here refers to, for example, the equipment availability rate, average output, start-up and shutdown frequency, etc.

The display unit 19 (see Figure 4) displays the creep deformation amount D of the nozzle diaphragm versus the operating time t of the steam turbine 20. Here, the creep deformation amount D at the current time is displayed as "calculated results" based on the creep deformation rate V calculated in real time. Furthermore, the creep deformation amount D in the future is displayed as "future prediction (before correction)" based on the operation plan 28.

In this way, based on the creep deformation amount D in the current "calculated results" and "future predictions," it is possible to present effective maintenance recommendations for nozzle diaphragms designed with a small margin of clearance.

Second Embodiment
Next, a second embodiment of the present invention will be described with reference to Fig. 2. Fig. 2 is a block diagram of a steam turbine creep deformation evaluation device 10B (10) (hereinafter simply referred to as "evaluation device 10B") according to the second embodiment. In Fig. 2, parts having the same configuration or function as those in Fig. 1 are designated by the same reference numerals, and duplicated explanations will be omitted.

The evaluation device 10B of the second embodiment, like the evaluation device 10A of the first embodiment, includes an acquisition unit 15 for detection data x, a first calculation unit 11 for an optimal solution φ ₁ of the operating state quantity, a second calculation unit 12 for an approximate solution φ ₂ thereof, an update unit 16 for the approximate equation f(x), a calculation unit 17 for the creep deformation rate V, and an estimation unit 18 for the deformation amount D of the nozzle diaphragm.

In the evaluation device 10B of the second embodiment, the creep deformation rate V is calculated in the calculation unit 17 based on the equivalent stress σ of the nozzle diaphragm derived from the approximate solution _φ2 of the operating state quantity. Furthermore, the evaluation device 10B includes a correction unit 29 that corrects the calculation formula G for the creep deformation rate V based on the actual measurement value 27 of the nozzle diaphragm and the creep deformation amount D estimated by the estimation unit 18.

Figure 3 is a graph showing the relationship between the equivalent stress σ acting on the nozzle diaphragm and the creep deformation rate V. This graph was created so that it can be universally applied to structures made of common materials, not just the nozzle diaphragm being evaluated.

The calculation unit 17 calculates the creep deformation rate V based on the equivalent stress σ of the nozzle diaphragm derived from the approximate solution _φ2 of the operating state quantity. That is, the calculation unit 17 inputs the approximate solution _φ2 of the operating state quantity of the nozzle diaphragm and design information K into the function formula g(φ, K) shown in the following equation (2), and calculates the equivalent stress σ generated in the nozzle diaphragm.

Furthermore, this equivalent stress σ is determined using the theory of elasticity or elastic creep theory as a stress representative of the amount of creep deformation based on the creep deformation behavior of the nozzle diaphragm, and the calculation formula G(φ, K, σ) shown in equation (3) below is determined. If it is difficult to determine the calculation formula G(φ, K, σ) for the equivalent stress σ using these theoretical formulas, it can also be determined in advance using the finite element method, etc.

Equivalent stress σ = g (φ, K) ... (2)
Creep deformation speed V = G (φ, K, σ) = A・σ ^B ... (3)
Here, A and B are constants determined by φ and K. Assuming deformation of the nozzle diaphragm, similar to the function g for determining the equivalent stress σ described above, these may be determined from the theory of elasticity or elastic creep theory, or may be determined using the finite element method, etc. The correction unit 29 updates the coefficients A and B in the calculation formula G such as the above formula (3).

In this embodiment, the calculation formula G for the creep deformation rate V is calculated using the power law of the equivalent stress σ, but other calculation formulas are also applicable. Because the shape of the nozzle diaphragm differs for each plant and each turbine stage, a calculation formula appropriate for each nozzle can be applied. In all of these calculation formulas, the constants used in the formula are determined from φ and K. Furthermore, while the second embodiment has been described assuming that the configuration of the first embodiment is provided, it is also possible to adopt a configuration in which the update unit 16 is not provided and only one of the first calculation unit 11 and the second calculation unit 12 is provided.

Figure 4 is a creep deformation risk assessment graph showing future predictions of the creep deformation amount D of the nozzle diaphragm. The correction unit 29 corrects the calculation formula G so that the estimated value 26 of the creep deformation amount D matches the actual measured value 27 of the nozzle diaphragm, allowing for an accurate evaluation of the future predictions of creep deformation (after correction).

In other words, the accuracy of future predictions can be improved by reflecting information on actual measurement values 27, such as those obtained through visual inspections conducted when the steam turbine 20 is shut down. The deviation between the estimated value 26 of the creep deformation amount D output in advance from the estimation unit 18 and the actual measurement value 27 obtained through inspection can be quantified, and the future creep deformation prediction line can be corrected in accordance with this deviation, as shown by the arrow. Note that the actual measurement values 27 input to the correction unit 29 are not limited to values obtained through actual inspections, but can also include hypothetical values set.

Based on the flowchart in Figure 5 (and also referring to Figure 2 as appropriate), the steps of the steam turbine creep deformation evaluation method according to the embodiment and the algorithm of the steam turbine creep deformation evaluation program will be explained.

First, an approximate equation f(x) for finding an approximate solution _φ2 of the operational state quantity and an arithmetic equation G for calculating the creep deformation rate V are initialized (S11). Then, detection data x ( _x1 , x2, ... _xn ) are acquired from each of a plurality of sensors 21 ( ₂₁₁ , ₂₁₂ , ... _21n ) installed on the steam turbine ₂₀ or its periphery (S12).

Next, the approximate equation f(x) is called (S13), and an approximate solution _φ2 of the operational state quantity is calculated based on the detected data x (S14). In parallel with these steps (S13, S14), the heat balance of the steam turbine 20 is calculated based on the detected data x (S15), and an optimal solution _φ1 of the operational state quantity of the nozzle diaphragm is calculated (S16).

Then, based on the output optimal solution φ ₁ (S17, YES), the approximate formula f(x) is updated (S18). Note that since the calculation time for the optimal solution φ ₁ is longer than the calculation time for the approximate solution φ ₂ , the update frequency of (S18) is lower than the call frequency of (S13).

Next, the calculation formula G is called (S19), and the creep deformation rate V of the nozzle diaphragm is calculated based on the approximate solution _φ1 (S20). Furthermore, the deformation amount D of the nozzle diaphragm is estimated from this creep deformation rate V (S21). If a new actual measurement value 27 of the nozzle diaphragm (including a hypothetical value) has been acquired here (S22, YES), the calculation formula G is corrected (S23) so that the actual measurement value of the nozzle diaphragm and the estimated value match, and steps (S19) to (S21) are executed again.

If no new actual measurement values of the nozzle diaphragm have been acquired (S22, NO), the estimated nozzle diaphragm deformation amount D is output (S24). Then, steps (S12) to (S24) are repeated until turbine operation ends (S25, NO, YES, END).

According to at least one embodiment of the steam turbine creep deformation evaluation device described above, by updating the approximate equation for the approximate solution of the operating state quantity with a short calculation cycle with an optimal solution with a long calculation cycle, it becomes possible to sequentially evaluate the creep deformation behavior of the nozzle diaphragm in a steam turbine operated under a power generation plan involving large output fluctuations with excellent tracking capability.

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

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

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

The steam turbine creep deformation evaluation program according to this embodiment may also be stored on a computer connected to a network such as the Internet and provided by downloading it via the network. The steam turbine creep deformation evaluation device may also be configured by combining separate modules that independently perform the functions of their components and interconnect them via a network or dedicated lines.

10 (10A, 10B)...Creep deformation evaluation device, 11...First calculation unit, 12...Second calculation unit, 15...Acquisition unit, 16...Update unit, 17...Calculation unit, 18...Estimation unit, 19...Display unit, 20...Steam turbine, 21 (21 ₁ , 21 ₂ ...21 _n )...Sensor, 26...Estimated value, 27...Actual measurement value, 28...Operation plan, 29...Correction unit, x (x ₁ , x ₂ ...x _n )...Detection data, f...Approximation formula, G...Calculation formula, φ ₁ ...Optimal solution of operating state quantity, φ ₂ ...Approximation solution of operating state quantity, σ...Equivalent stress, K...Design information, V...Creep deformation rate (deformation rate), D...Creep deformation amount (deformation amount).

Claims (7)

an acquisition unit that acquires detection data from each of a plurality of sensors installed in the steam turbine or its periphery;
a first calculation unit that calculates an optimal solution for an operating state quantity of a nozzle diaphragm in the steam turbine based on the detection data;
a second calculation unit that calculates an approximate solution of the operating state quantity at a shorter period than the optimal solution based on the detection data;
an update unit that updates an approximation formula for calculating the approximate solution based on the optimal solution;
a calculation unit that calculates a creep deformation rate of the nozzle diaphragm based on the approximate solution;
an estimation unit that estimates a deformation amount of the nozzle diaphragm from the creep deformation rate based on an operation plan of the steam turbine. 2. The steam turbine creep deformation evaluation device according to claim 1,
The sensor is installed on at least one of a steam inlet side, an outlet side, and an extraction pipe of the steam turbine,
The first calculation unit is a steam turbine creep deformation evaluation device that obtains the optimal solution from a calculation result of the heat balance of the steam turbine based on the detection data. 3. The steam turbine creep deformation evaluation device according to claim 1,
the approximation formula is expressed by a polynomial with the detection data as a variable,
The update unit updates the coefficients of the approximation equation. 3. The steam turbine creep deformation evaluation device according to claim 1,
The creep deformation evaluation device for a steam turbine, wherein the creep deformation rate is calculated based on an equivalent stress of the nozzle diaphragm derived from the approximate solution of the operational state quantity. 5. The steam turbine creep deformation evaluation device according to claim 4,
The creep deformation evaluation device for a steam turbine includes a correction unit that corrects the calculation formula for the creep deformation rate based on the actual measurement value of the nozzle diaphragm and the estimated deformation amount. acquiring detection data from each of a plurality of sensors installed on or around the steam turbine;
calculating an optimal solution for an operating state quantity of a nozzle diaphragm in the steam turbine based on the detection data;
calculating an approximate solution of the operational state quantity at a shorter period than the optimum solution based on the detection data;
updating an approximation formula for calculating the approximate solution based on the optimal solution;
calculating a creep deformation rate of the nozzle diaphragm based on the approximate solution;
and estimating a deformation amount of the nozzle diaphragm from the creep deformation rate based on an operation plan of the steam turbine. On the computer,
acquiring detection data from each of a plurality of sensors installed on or around the steam turbine;
calculating an optimal solution for an operating state quantity of a nozzle diaphragm in the steam turbine based on the detection data;
calculating an approximate solution of the operational state quantity at a shorter period than the optimum solution based on the detection data;
updating an approximation formula for calculating the approximate solution based on the optimal solution;
calculating a creep deformation rate of the nozzle diaphragm based on the approximate solution;
a creep deformation evaluation program for a steam turbine that executes a step of estimating a deformation amount of the nozzle diaphragm from the creep deformation rate based on an operation plan of the steam turbine.