JP2001153756A - Method for predicting crack developing of turbine rotor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for predicting crack developing of a turbine rotor capable of predicting the developing amount of the crack in a future drive from the hardness, the vibration stress or the like of the rotor, and suitably measuring against a repair or the like of the rotor in view of the effective prediction of the crack development. SOLUTION: The method for predicting the crack developing of the turbine rotor comprises the steps of obtaining a vibration stress operated at a steam turbine modeled based on data of drive recording, obtaining a crack developing lower limit value from the hardness of the rotor, deciding a load band for developing the crack from a stress intensity factor range calculated based on the stress and a crack developing minimum stress corresponding to the rack developing lower limit value, obtaining crack developing characteristics of the load band, calculating a life consumption rate from the obtained characteristics, calculating a time up to a predetermined allowed crack length from the calculated consumption rate and the real crack length, and checking the presence or absence of the maintenance of the predicted crack length to next periodical inspection with respect to the predetermined allowed crack length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting crack growth of a turbine rotor, and more particularly to a life of a turbine rotor blade implanted in the turbine rotor based on a crack generated in a contact portion between the implanted portion and the turbine rotor. The present invention relates to a method for predicting the crack growth of a turbine rotor for predicting crack growth.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 20, in a steam turbine, a turbine rotor 5 supported by bearings 4 is accommodated in a turbine casing 3 divided into an outer casing 1 and an inner casing 2, and an inner casing is provided. A turbine stage 8 is formed by combining the turbine nozzle 6 engaged with the turbine nozzle 2 and the turbine blade 7 implanted in the turbine rotor 5, and the turbine stage 8 is arranged in multiple stages along the axial direction. .

[0003] Further, as shown in FIG. 21, a turbine blade 7 is formed by inserting an implanted portion 9 into an implanted groove 10 of a turbine rotor 5.
And is planted in an annular row along the circumferential direction.

Further, as shown in FIGS. 21 and 22, the turbine nozzles 6 are arranged in an annular row along the circumferential direction of the turbine rotor 5 so as to correspond to the turbine rotor blades 7, and a nozzle box is provided at the inlet side thereof. And a steam inlet 13 communicating with the nozzle box 12,
Four steam control valves (not shown) are provided.

As shown in FIG. 24, the steam control valve opens the first and second valves almost simultaneously as the turbine output increases, and further opens the third and fourth valves sequentially and sequentially. A so-called three-admission system, or a so-called two-admission system in which the first valve, the second valve, and the third valve are opened simultaneously, and the remaining fourth valve is opened next, although not shown. Alternatively, any one of so-called one-admission operation modes in which all of the first to fourth valves are simultaneously opened is adopted.

For example, when the steam control valve adopts the operation mode of the three admission system at the time of the start-up operation, the turbine rotor blade 7 rotates while the turbine rotor 5 makes one rotation (360 °) as shown in FIG. Receives the steam guided from the turbine nozzle 6 twice. For this reason, the turbine blade 7
Has a steam pressure fluctuating force based on whether steam is received or not. In addition, the turbine blade 7
In FIG. 23, there is a pressure difference between the ventral side and the dorsal side, and the steam flow based on this pressure difference fluctuates. As shown in FIG. 5, a strong excitation force F is received in the same direction as the rotation direction of the turbine rotor 5.

When such a vibration force F is repeatedly received,
As shown in FIG. 25, in the turbine rotor 5, a crack C was sometimes generated in the hook portion 11 of the implantation groove 10 to be engaged with the implantation portion 9 of the turbine blade 7. Since the generation of cracks in the turbine rotor 5 inevitably impairs the stable operation of the steam turbine, many inventions for predicting the progress of cracks have recently been proposed.

[0008] However, the prediction of crack growth depends on steam conditions,
For example, since many factors such as operating conditions such as pressure, temperature, steam flow rate and the number of startups are included, it is difficult to solve the problem, and it is currently in the stage of exploring.

[0009]

Conventionally, turbine blades 7
Uses a 12Cr alloy steel excellent in high-temperature strength, whereas the turbine rotor 5 uses a Cr-Mo-V alloy steel having a relatively low high-temperature strength as compared with the turbine blade material. I'm using The reason why the turbine rotor 5 is made of a Cr-Mo-V alloy steel whose high-temperature strength is lower than that of the turbine rotor blade material is to reduce the seizure of the bearing 4, but the high-temperature strength is low. Therefore, as a result of use for many years under the influence of the above-described excitation force F, a crack C may be generated in the hook portion 11 of the implantation groove 10 of the turbine rotor 5 as shown in FIG. This crack C
As a result of many years of use of the turbine rotor material, if the metallographic structure has changed compared to the beginning, even small excitation forces will develop further. Such fatigue failure is called fretting fatigue.

[0010] The fretting fatigue, as shown in FIG. 26, is believed to occur by the vibration stress sigma _a. That is, when the members Y and Z are in contact with the base portion X at a distance δ, when the excitation force F is repeatedly applied to the base portion X from the outside, the vibration stress ( Stress amplitude) σ _a is given. The vibration stress sigma _a is member Y,
Since the pressure is applied in the direction intersecting the surface pressure applied to the base portion X from the end of Z, the strength is reduced and a crack C is considered to be generated. This tendency is particularly strong when the members Y and Z are installed within a certain distance δ with respect to the base X. By the way, when the base part X and the members Y and Z are installed adjacent to each other, the vibration stress σ _a becomes as shown in FIG. 27 when the members Y and Z are not installed (no fretting). It has been confirmed by experiments that it is significantly lower than that.

The occurrence of the crack C due to fretting fatigue in the hook portion 11 of the implantation groove 10 of the turbine rotor 5 is considered to be due to the fact that the turbine blade 7 is implanted adjacent to the annular row. ing. In addition, the implantation part 9 of the turbine rotor blade 7 has high strength of its material,
No fretting fatigue was observed.

The crack C generated in the hook portion 11 of the implantation groove 10 of the turbine rotor 5 cannot be observed from the outside for a few minutes, and is only during a periodic inspection. If the crack C develops during the operation of the steam turbine, safe and stable operation is impaired. Therefore, an accurate technique for predicting the crack growth is required.

The present invention has been made in view of such circumstances, and the hardness of a hook portion of an implanted groove in a turbine rotor engaged with an implanted portion of a turbine rotor blade is determined by vibration stress or hardness generated during operation. Therefore, to provide a method for predicting the crack growth of a turbine rotor that predicts the amount of crack growth for future operation, and enables appropriate replacement or repair of the turbine rotor under accurate crack growth prediction. With the goal.

[0014]

SUMMARY OF THE INVENTION A method for predicting crack growth in a turbine rotor according to the present invention has the following objects.
As described in claim 1, a first step of recording operation results, a second step of obtaining a vibration stress from the modeled steam turbine by a finite element method, a third step of obtaining a hardness of a surface portion of the turbine rotor, A fourth step of multiplying the turbine rotor hardness, crack length, and stress ratio to obtain a crack growth lower limit value; a stress intensity factor range calculated by the influence function method based on the vibration stress obtained in the second step; The fifth step of determining the load zone in which the crack grows when the stress intensity factor range exceeds the lower limit of the crack growth by comparing the lower limit of the crack growth obtained in the fourth step with the lower limit value of the crack growth, which was determined in the fifth step A sixth step of obtaining crack growth characteristics in the crack growth load zone, a seventh step of calculating a life consumption rate from the crack growth characteristics in the crack growth load zone obtained in the sixth step, Eighth step for calculating the time required to reach a predetermined allowable crack length from the life consumption rate and the actual crack length calculated in the seven steps, and the next periodic inspection for the time required to reach the allowable crack length calculated in the eighth step If it cannot be maintained, a ninth step of considering repair and replacement of the turbine rotor is provided.

In order to achieve the above object, the method for predicting crack growth of a turbine rotor according to the present invention records the hardness of the surface layer portion of the turbine rotor in the third step as an operation record. The temperature and the operating time are determined using a stress-hardness diagram created in advance.

According to a third aspect of the present invention, there is provided a method for predicting crack growth of a turbine rotor, wherein the hardness of the surface layer portion of the turbine rotor in the third step is determined from the crack depth. It is determined using a previously created turbine rotor surface layer hardness change curve.

According to a fourth aspect of the present invention, there is provided a method for predicting crack growth of a turbine rotor, wherein the crack depth is determined by a replica of a potential difference detecting method for detecting a potential difference at a corresponding portion. Select one of the detection method, a crack depth-crack length diagram prepared in a database in advance, an equal stress distribution diagram prepared in a database in advance, and a crack depth-crack opening amount diagram prepared in a database in advance. It is what I sought.

In order to achieve the above object, the method for predicting crack growth of a turbine rotor according to the present invention is characterized in that the replica is made of one of a video film and a plastic material which is cured by ultraviolet rays. To choose.

According to a sixth aspect of the present invention, in order to achieve the above object, the hardness of the surface portion of the turbine rotor in the third step is such that a pulse is applied to the corresponding portion. , And Barkhausen noise is calculated from the generated magnetic change, and the Barkhausen noise method is used to determine the hardness of the surface layer from the calculated signal.

In order to achieve the above object, in the method for predicting crack growth of a turbine rotor according to the present invention, the load zone where cracks grow in the fifth step is obtained in the second step. It is calculated from the intersection of the vibration stress and the minimum crack growth stress value corresponding to the crack growth lower limit value obtained in the fourth step.

In order to achieve the above object, the method for predicting crack growth of a turbine rotor according to the present invention, as described in claim 8, includes:
The crack growth rate is obtained as a function of the stress intensity factor range, stress ratio, and crack growth lower limit.

In order to achieve the above object, the method for predicting crack growth of a turbine rotor according to the present invention includes, among the crack growth characteristics in the sixth step,
The crack growth life up to the allowable crack length is obtained by integrating a function of the stress intensity factor range, the stress ratio, and the reciprocal of the crack growth lower limit value.

In order to achieve the above object, the method for predicting the crack growth of a turbine rotor according to the present invention is characterized in that the life consumption rate in the seventh step is the sixth.
The crack growth life up to the permissible crack length obtained in the step is converted into a unit time.

In order to achieve the above object, the method for predicting crack growth of a turbine rotor according to the present invention, when repairing the turbine rotor in the ninth step, sets the repair width region to one of the turbines. This is to be deleted across the hook portion of the moving blade and the hook portion of the adjacent turbine moving blade.

In order to achieve the above object, the method for predicting the crack growth of a turbine rotor according to the present invention is characterized in that the repair of the turbine rotor in the ninth step is performed based on the operating temperature and the operating time. And the hardness is plotted on a stress-hardness diagram prepared in advance, and starts when the hardness falls below an allowable hardness limit value.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for predicting crack growth of a turbine rotor according to the present invention will be described below with reference to the drawings and reference numerals attached to the drawings.

FIG. 1 is a block diagram showing a procedure in an embodiment of a turbine rotor crack growth prediction method according to the present invention.

The method for predicting crack growth of a turbine rotor according to the present embodiment includes a first step (ST1) of recording operation results such as a load and an operation time, and a second step of obtaining a vibration stress in each load zone during operation. Step (ST2), a third step (ST) for determining the hardness of the surface portion of the turbine rotor
3), a fourth step (ST4) of obtaining a lower limit of crack growth from the hardness of the turbine rotor, and a stress intensity factor range calculated by the influence function method based on the vibration stress obtained in the second step, and a fourth step. Zone where cracks propagate from the lower limit of crack growth (load range from minimum load to maximum load)
In the crack growth load zone determined in the fifth step, specifically, the crack growth rate, the crack growth life up to the allowable crack length, and the like (ST6). ), A seventh step (ST7) of calculating the life consumption rate from the crack growth characteristics in the crack growth load zone obtained in the sixth step, and an allowable tolerance predetermined from the life consumption rate calculated in the seventh step and the actual crack length. Eighth step (S) to calculate the time to reach the crack length
T8) If the time required to reach the allowable crack length determined in the eighth step cannot be maintained until the next periodic inspection, the procedure goes through a ninth step (ST9) for examining measures to repair or replace the turbine rotor. .

The hardness of the turbine rotor obtained in the third step (ST3) can be obtained from a stress-hardness diagram prepared in advance, as shown in FIG. This stress-hardness diagram shows the hardness of the surface layer of the turbine rotor on the vertical axis and the temperature and operation time of the turbine rotor on the horizontal axis. The hardness of the surface layer according to the stress 2 is larger than the stress 1) is plotted. In the present embodiment, the hardness of the surface layer of the turbine rotor is obtained from the stress-hardness diagram, but is not limited to this. For example, as shown in FIG. You may.

This turbine rotor surface layer hardness change curve H
( _Ax ) is

(Equation 1) Given as

Here, a _x is the crack depth from the turbine rotor surface layer, H ₁ is the turbine rotor surface layer hardness, H
₀ is, for example, 200 to 3 depths from the surface of the turbine rotor.
Hardness at 00 μm and C represent constants, respectively.

The above equation (1) indicates that the hardness H ₁ and the crack depth a _{x of} the surface layer of the turbine rotor, for example, 200 to 30 from the surface layer
It is a master curve created by actually measuring with a test material over a range between two points with a hardness H ₀ at a depth of 0 μm.
This master curve is applied when the surface layer portion of the turbine rotor is a tissue layer in which a soft layer and a hard layer are mixed, and it is necessary to obtain hardness from a certain depth.

It should be noted, the crack depth a _x can be obtained by using a non-destructive test method described below.

As shown in FIG. 4, the first method for measuring the crack depth a _x is to set the electrodes 14a, 1
This is a method in which measurement is performed using a potential difference at a site separated from the crack by a certain distance via the wire 4b. Electrodes 14a, 14
when the constant potential difference _{V 0} (reference electrode) between the b, the potential difference V between the measuring electrodes, the function V = _{V (a} x, _{V 0)} is given as. Therefore, if the potential difference V is measured, the crack depth a _x can be obtained.

The second method for measuring the crack depth a _x is as follows:
As shown in FIG. 5, a bioden film (plastic film) may be attached to the crack. The video film can be softened by methyl acetate and cured with the vaporization of the methyl acetate to replicate the shape of the crack. Further, a plastic material which is cured by ultraviolet rays may be used instead of the bioden film.

Further, when obtaining the other crack depth a _x, for example, as shown in FIG. 6, pre-database and crack depth - crack length diagram, as shown in FIG. 7, a database in advance of the like As shown in the stress distribution diagram or FIG.
A crack depth-crack opening amount (opening width) diagram prepared in advance in a database may be used.

In the present embodiment, the hardness is not limited to the above-described stress-hardness diagram. For example, as shown in FIGS. 9 and 10, the hardness may be obtained by the Barkhausen noise method.

In the embodiment based on the Barkhausen noise method, as shown in FIG.
The pulse from 6 is supplied via an amplifier 17 and a sensor 18, a magnetic change generated in the subject 15 is detected by the sensor 18, and the detected signal is calculated by a frequency analyzer 21 via an amplifier 19 and a filter 20. As shown in FIG. 10, the hardness of the turbine rotor surface layer can be obtained from the Barkhausen noise output based on the operation signal.

According to the Barkhausen noise method, a change in magnetic noise generated when a magnetic domain wall is discontinuously generated and moved in a process of magnetizing a ferromagnetic material corresponds to a change in hardness of a material. It focuses on that. Therefore, the Barkhausen noise method is effective for determining the hardness of the surface layer of a ferromagnetic material.

FIG. 11 shows that, in the second step (ST2), prior to obtaining the vibration stress of each load zone, the relationship between the load output of the steam turbine and the operation modes 1 and 2 through the turbine rotor blade is determined. Turbine load output to calculate the exciting force applied to the hook of the turbine rotor
It is an excitation force diagram.

The exciting force of the steam fluctuates remarkably in different operation modes even when the load output of the steam turbine is constant.
In particular, the driving mode 1, specifically the three admission system, has a higher excitation force than the operation mode 2, specifically the two admission system. In addition, the 3 admission method
When the load output of the steam turbine reaches a load output in a predetermined region, the excitation force becomes high, and the steam turbine enters a danger region where cracks are generated in the turbine rotor.

As described above, while the exciting force fluctuates in the operation modes 1 and 2, in the second step (ST2), the vibrating stress (stress amplitude) σ is obtained (average) in consideration of the fluctuating exciting force. Stress).

Vibration stress (stress amplitude) σ of turbine rotor
As shown in FIG. 12, the blade cover 22 and the tenon 2
3, turbine blade 7, implanted part 9, turbine rotor 5,
The actual steam turbine constituted by the hook portion 11 is modeled, and the model is obtained by the finite element method using the model.

The vibration stress σ obtained by the finite element method is plotted corresponding to the steam turbine load as shown in FIG. 13, and a vibration stress diagram is created as a master curve.

On the other hand, when determining the crack growth load zone in the fifth step (ST5), since the stress intensity factor range [Delta] K and crack propagation lower limit value [Delta] K _th is concerned, first of all, the stress intensity factor range [Delta] K and crack propagation lower limit value [Delta] K _th, since the starting point for crack propagation of the turbine rotor, be kept clearly defined is important, will be described with reference to FIG. 15.

[0046] Figure 15, crack depth showing the size relationship between the lower crack propagation limit value [Delta] K _th and the stress intensity factor range [Delta] K - is an illustration of the stress intensity factor range diagram. In this figure, a crack depth region 1 is defined based on a predetermined crack depth a.
And a crack depth region 2.

[0047] Now, the crack depth region 1, a steam turbine, for example mode 1, and in particular with running at 3 Admission system, stress intensity factor range [Delta] K is the crack propagation lower limit value [Delta] K _th Because it exceeded, it is in the danger zone. Therefore, in order to avoid the danger zone, the steam turbine is required to change its operation mode from the 3 admission mode to the 2 admission mode, or to avoid the high excitation force area shown in FIG. Increase rapidly,
The steam turbine output load corresponding to the high excitation force area is quickly passed.

[0048] Also, in the crack depth region 1, a steam turbine, for example the mode 2, and in particular with running at 2 admission scheme, the stress intensity factor range [Delta] K is the crack propagation lower limit value [Delta] K _th Since it has not exceeded, the operation of the steam turbine is continued as it is.

However, when the operation of the steam turbine reaches the crack depth region 2, the steam turbine enters a risk zone where a crack is developed. For this reason, measures are taken to repair the cracked portion of the steam turbine or replace it with a new turbine rotor.

[0050] Thus, in the relationship between the crack propagation lower limit value [Delta] K _th stress intensity factor range [Delta] K, since the crack growth initiation point of the turbine rotor, under crack propagation limit value K _th and the stress intensity factor range [Delta] K together It needs to be clearly defined.

The stress intensity factor range ΔK is given by ΔK = K _s −K
It can be represented as _c . Here, K _s is the maximum stress intensity factor, Kc is the minimum stress intensity factor.
This stress intensity factor range ΔK is determined in the second step (ST2).
In it is calculated by the influence function method based on the vibration stress and crack depth a _x at excitation force load and exciting force unloading in the vibration stress diagram created.

The lower limit value for the crack growth ΔK _th is determined by the crack depth a _x and the stress ratio R because the evaluation of the crack growth characteristics obtained in the sixth step (ST6) becomes inaccurate. Step 4 (ST4) by using
Determined.

The lower limit of crack growth △ _Kth determined in the fourth step (ST4) is the lower limit of stress ratio dependency shown in FIG. 14A in the diagram for determining the lower limit of crack growth shown in FIG. Crack growth lower limit value K _th1 obtained from the value diagram, FIG.
The crack growth lower limit K _th2 obtained from the crack length dependence lower limit diagram of (b) and the crack growth lower limit obtained from the hardness dependence lower limit diagram of FIG. 14 (c). Value K _th3
Is calculated, and the calculated values are multiplied to _obtain △ K _th = K _th1
It is calculated as × K _th2 × K _th3 .

Thus, the crack growth lower limit value ΔK _th
In the fifth step (ST5), as shown in FIG. 13, a crack growth minimum stress value σ _min corresponding to the crack growth lower limit value ΔK _th is plotted on a vibration stress line, and The intersection X is defined as a minimum crack growth load _Lmin ,
The intersection Y is defined as a maximum crack growth maximum load _Lmax . The range from the minimum crack growth load _Lmin to the maximum crack growth load _Lmax is defined as a crack growth region CR. Note that the region before and after the crack growth region CR is a range where the growth of the crack has stopped.

When the crack propagation load zone (L _{min to} L _max ) is determined in the fifth step (ST5), the steam turbine performs the stress intensity factor range ΔK obtained by the above-described influence function method as shown in FIG. And the crack growth lower limit value △ K _th obtained in the fourth step (ST4), and 合 わ せ K _th > △
In the case of K, it is determined that the actual load L (x) has not yet entered the crack propagation region CR, and the actual load L (x) is added to the increase load ΔL.
And continue driving.

[0056] Also, the steam turbine, butt and the stress intensity factor range △ K and crack propagation lower limit value △ K _th, △ K
_{When th} <△ K, the actual load L (x) is equal to the crack propagation region CR.
Finding that has entered the sixth crack propagation characterization at step (ST6), specifically, crack growth rate dl / dN, calculated crack growth life N _f until acceptable crack length, further allowable crack Step 7 The life consumption rate φL up to the length is obtained, respectively.

Firstly, the crack growth rate dl / _{d N} is the stress intensity factor range △ K, crack length l, stress ratio R (Kc / K
s), which is obtained by the following equation in consideration of the dependence of the crack growth lower limit value △ _Kth .

[0058]

(Equation 2)

Next, the crack propagation life N up to the allowable crack length
_f is from actual crack length l ₀ to acceptable crack length l ₁ with a predetermined given by the following equation.

[0060]

(Equation 3)

The predetermined allowable crack length l
₁ is determined based on empirical rules such as the maximum crack length that can be operated within a range that does not hinder operation.

[0062] In a seventh step (ST7), the unit of crack growth life _{N f} until acceptable crack length above time _{n 0}
The life consumption rate φL per unit is calculated by the following equation.

[0063]

ΦL = n ₀ / N _f (4) Next, the life consumption rate φL and the crack growth load zone (L _{min to} L
_max ), the total crack growth life T is calculated by the following equation from the operation time tL.

[0064]

(Equation 5)

When the total crack growth life T is calculated by the equation (5), in the eighth step (ST8), the crack growth time up to the allowable crack length is evaluated. In the evaluation of the crack growth time, if the remaining operation time can be maintained until the next periodic inspection, the operation is continued in the ninth step (ST9).

If the remaining operation time cannot be maintained until the next periodic inspection, a ninth step (ST9) is performed. Repair of the turbine rotor, driving to avoid exchange or crack growth load zone (L m _{in ~L max)} (e.g., rapidly passing the steam turbine output load corresponding to a high vibrating force sharply increases the amount of steam) One of them is selected as an emergency measure.

When repair such as removal of a material deteriorated layer or a crack generation portion of the turbine rotor is selected, as shown in FIG. 16, the repair width region shown by hatching is a hook portion A of one turbine blade as shown in FIG. And hook part B of the next turbine blade
And delete it. The removal of the repair width region across the hook portion B of the turbine blade, which is the hook portion A of one turbine blade, is because the distance between the contact ends of the turbine blade is larger than before the removal. This is because the proximity effect between the contact ends is reduced and the fatigue strength is improved, and the increase in both pressures is suppressed by the gap between the turbine blades.

When the turbine rotor blades are implanted after the repair of the turbine rotor, the turbine rotor blades are displaced on the circumference or the implantation positions are changed so that the crack generation portion does not become a contact portion again. The turbine rotor may be returned to the original position, and the removed portion of the turbine rotor may be a hook contact portion. In both cases, fretting fatigue strength can be improved.

As described above, in the method for predicting the crack growth of the turbine rotor according to the present embodiment, the vibration stress is calculated by the finite element method based on the load and the operation time obtained from the first step (ST1). while setting the crack growth load zone by the crack propagation lower limit value △ K _th calculated from the stress intensity factor range △ K and crack hardness, which is calculated using the influence function method from the vibration stress or the like, the steam turbine crack propagation When operating in the load zone, the crack growth rate, the crack growth life, etc. are determined as the crack growth characteristics evaluation, then the crack life consumption rate and the total crack growth life are calculated, and the allowable crack length is calculated from the calculated total crack growth life. If the remaining operation time cannot be maintained until the next periodic inspection, appropriate measures shall be taken for the turbine rotor, Stable operation can be performed.

FIG. 17 shows that, when the turbine rotor material was changed, the crack growth rate dl / dN
FIG. 4 is a crack growth velocity diagram applied to the method for predicting crack growth of a turbine rotor according to the present invention when calculating the crack growth velocity.

[0071] Recent steam turbine, the turbine driving steam is research underway to ultra high pressure and ultra high temperature, a C _{r M} o _V material that has been conventionally used as a turbine rotor material changes to 12C _r material Considerations are being made.

In this embodiment, the turbine rotor material is 12C
_{Even if the} material is changed to the _r material, the crack growth rate dl / dN for the stress intensity factor range ΔK of the _12Cr material can be easily calculated.

[0073] Thus, this embodiment, a turbine rotor material 12C also been changed to _r material crack growth rate dl /
Since dN can be easily calculated, the crack growth of the turbine rotor can be easily predicted.

[0074] In addition, C r _M o from _V material Upon predicting the crack growth of the turbine rotor was changed to 12C _r material, in the present embodiment, as shown in FIG. 18, the stress created in advance as a master curve - Hardness Using the diagram, determine the hardness of the surface layer of the turbine rotor with respect to the operating temperature and operating time, and if the determined hardness is lower than the predetermined allowable hardness limit, repair such as removal of the softened layer of the turbine rotor It may be used as a start condition. This is effective when examining whether or not the turbine rotor needs to be repaired.

FIG. 19 is a turbine rotor blade excitation force diagram applied to the method for predicting the crack growth of a turbine rotor according to the present invention when calculating the excitation force on the turbine rotor blade.

Conventionally, turbine driving steam often contains foreign particles such as oxide scale. For this reason, the turbine nozzle located on the upstream side of the turbine blade is eroded as a result of long-term use due to the impact of oxide scale or the like.

Further, in the steam turbine, when the turbine drive steam performs expansion work, heat may be lost to generate water droplets (drain), and the water droplets erode the turbine nozzle. For this reason, the excitation force applied to the turbine blade varies depending on the degree of erosion of the turbine nozzle.

In this embodiment, the exciting force applied to the turbine blade is modified according to the degree of erosion of the turbine nozzle, and the crack propagation load zone can be obtained from the modified exciting force. It is.

In this embodiment, when the turbine nozzle is eroded, it is possible to determine whether or not a crack has occurred in the turbine rotor by using a turbine rotor blade excitation force diagram. In the case of progress, repair measures can be taken promptly.

[0080]

As described above, the method for predicting the crack growth of a turbine rotor according to the present invention uses the hardness, the exciting force, and the vibration stress to predict the presence or absence of cracks and the amount of crack growth in the turbine rotor. Based on the calculated stress intensity factor range and the lower limit value for crack growth, the crack growth load zone is determined from the calculated stress intensity factor range and the lower limit value for crack growth, and the amount of crack growth in the crack growth load zone is predicted,
Since the presence or absence of repair of the turbine rotor is determined from the difference between the predicted crack growth amount and the allowable crack amount, the steam turbine can be operated safely and stably.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a procedure of an embodiment of a turbine rotor crack growth prediction method according to the present invention.

FIG. 2 is a graph showing stress-hardness used in the method for predicting crack growth of a turbine rotor according to the present invention.

FIG. 3 is a graph showing a hardness change curve of a surface layer portion of a turbine rotor used in the method for predicting crack growth of a turbine rotor according to the present invention.

FIG. 4 is a conceptual diagram used to explain electrically measuring a crack depth.

FIG. 5 is a conceptual diagram used for explaining that the crack depth is measured by a replica method.

FIG. 6 is a graph used to explain that a crack depth is determined from a crack depth-crack length diagram prepared in a database in advance when measuring the crack depth.

FIG. 7 is a graph used to explain that a crack depth is determined from an iso-stress distribution diagram prepared in a database in advance when measuring the crack depth.

FIG. 8 is a graph used to explain that the crack depth is determined from a crack opening amount (opening width) diagram prepared in a database in advance when measuring the crack depth.

FIG. 9 is a block diagram showing an embodiment in which the hardness of the surface layer is obtained by the Barkhausen noise method.

FIG. 10 is a graph used to explain obtaining the hardness of the surface layer portion from the Barkhausen noise output obtained by the configuration shown in FIG. 9;

FIG. 11 is a graph used to explain that when a crack occurs in the turbine rotor, the crack is removed and emergency treatment is performed.

FIG. 12 is a partially cutaway perspective view showing an assembled state before modeling the steam turbine.

FIG. 13 is a graph used to explain each step of the method for predicting crack growth of a turbine rotor according to the present invention in detail.

FIG. 14 is a diagram for obtaining a crack growth lower limit value used in the method for predicting crack growth of a turbine rotor according to the present invention, and (a).
FIG. 3B is a lower limit diagram of stress ratio dependency, FIG. 4B is a lower limit diagram of crack length dependency, and FIG. 3C is a lower limit diagram of hardness dependency.

FIG. 15 is a diagram showing a range of crack depth-stress intensity factor used in the method for predicting crack growth of a turbine rotor according to the present invention.

FIG. 16 is a view used to explain a repair state of the turbine rotor when the turbine rotor needs to be repaired in the method for predicting crack growth of the turbine rotor according to the present invention.

FIG. 17 is used for explaining a method of predicting crack growth of a turbine rotor according to the present invention, in which a crack growth rate is obtained from each of a stress intensity factor range ΔK of CrMoV steel and a stress intensity factor range ΔK of 12Cr steel. Graph.

FIG. 18 is a graph showing stress / hardness of CrMoV steel and stress / hardness of 12Cr steel in the method for predicting crack growth of a turbine rotor according to the present invention.

FIG. 19 is a diagram illustrating a method for predicting crack growth of a turbine rotor according to the present invention, in which a turbine nozzle arranged upstream of a turbine blade is subjected to vibration applied to the turbine blade when the turbine nozzle is eroded. 4 is a graph showing a crack growth load zone based on force and a crack growth load zone based on an exciting force applied to a turbine rotor blade when the turbine nozzle is not eroded.

FIG. 20 is a partially cutaway sectional view showing a conventional steam turbine.

FIG. 21 is a schematic diagram showing a positional relationship between a turbine rotor blade and a turbine nozzle.

FIG. 22 is a sectional view taken in the direction of arrows AA in FIG. 21;

FIG. 23 is a view used to explain that an exciting force is applied to the turbine blade by steam flowing from the turbine nozzle to the turbine blade.

FIG. 24 is a view used to explain a valve opening order of the steam control valve.

FIG. 25 is a view used to explain that a crack has occurred in a hook portion of the turbine rotor.

FIG. 26 is a view used to explain that a crack is generated by an exciting force when a member is installed adjacent to a base.

FIG. 27 is a diagram comparing normal fatigue strength with fretting fatigue strength when a vibration force is repeatedly applied to a material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer casing 2 Inner casing 3 Turbine casing 4 Bearing 5 Turbine rotor 6 Turbine nozzle 7 Turbine rotor blade 8 Turbine paragraph 9 Implantation part 10 Implantation groove 11 Hook part 12 Nozzle box 13 Steam inlet 14a, 14b Electrode 15 Subject 16 Pulse generator 17 amplifier 18 sensor 19 amplifier 20 filter 21 frequency analyzer 22 bucket cover 23 tenon

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshihiro Matsuura 2-4, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Within Toshiba Keihin Works Co., Ltd. (72) Inventor Kazunari Fujiyama 2-chome, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa No. 4 F-term in Toshiba Keihin Works (reference) 2G024 AD05 BA12 CA11 CA23 3G071 BA26 CA00 FA00 FA09 GA02 HA00 JA02

Claims (12)

[Claims] 1. A first step for recording operation results, a second step for obtaining vibration stress from a modeled steam turbine by a finite element method, a third step for obtaining hardness of a surface portion of a turbine rotor, and a hardness of a turbine rotor. A fourth step of obtaining a lower limit value for crack growth by multiplying the crack length and the stress ratio, a stress intensity factor range calculated by the influence function method based on the vibration stress obtained in the second step, and the fourth step 5th step of determining the load zone in which the crack grows when the stress intensity factor range exceeds the crack growth lower limit value by comparing with the crack growth lower limit value obtained in In the sixth step of calculating the crack growth characteristic in the above, the seventh step of calculating the life consumption rate from the crack growth characteristic in the crack growth load zone obtained in the sixth step, and the seventh step Eighth step of calculating a time to reach a predetermined allowable crack length from the calculated life consumption rate and actual crack length, and a time to reach the allowable crack length obtained in the eighth step cannot be maintained until the next periodic inspection. And a ninth step of examining repair and replacement of the turbine rotor. 2. The hardness of the surface layer portion of the turbine rotor in the third step is obtained by using a stress-hardness diagram prepared in advance from a temperature and an operation time recorded in operation results. The crack growth prediction method of the turbine rotor described in the above. 3. The turbine rotor according to claim 1, wherein the hardness of the surface portion of the turbine rotor in the third step is obtained by using a hardness change curve of the surface portion of the turbine rotor prepared in advance from the crack depth. Crack growth prediction method. 4. A crack depth is determined by a potential difference detection method for detecting a potential difference of a corresponding portion, a method for detecting by a replica, a crack depth-crack length diagram prepared in a database in advance, and an equal stress distribution diagram prepared in a database in advance. 4. The method for predicting crack growth of a turbine rotor according to claim 3, wherein any one of a crack depth-crack opening amount diagram prepared in a database in advance is selected and obtained. 5. The method according to claim 4, wherein the replica selects any one of a video film and a plastic material which is cured by ultraviolet rays. 6. The hardness of the surface portion of the turbine rotor in the third step is determined by applying a pulse to a corresponding portion, calculating Barkhausen noise from a generated magnetic change, and calculating the hardness of the surface portion from the calculation signal. The method for predicting crack growth of a turbine rotor according to claim 1, wherein the Hausen noise method is used. 7. The load zone in which the crack propagates in the fifth step is calculated from the intersection of the vibration stress obtained in the second step and the minimum crack growth stress value corresponding to the lower limit of the crack growth obtained in the fourth step. The method for predicting crack growth of a turbine rotor according to claim 1, wherein: 8. The crack of the turbine rotor according to claim 1, wherein, among the crack growth characteristics in the sixth step, the crack growth rate is determined as a function of a stress intensity factor range, a stress ratio, and a crack growth lower limit. Progress prediction method. 9. The crack growth life up to an allowable crack length among the crack growth characteristics in the sixth step is obtained by integrating a function of a stress intensity factor range, a stress ratio, and a reciprocal of a crack growth lower limit, and integrating them. The method for predicting crack growth of a turbine rotor according to claim 1. 10. The life consumption rate in the seventh step is:
The method for predicting crack growth of a turbine rotor according to claim 1, wherein the crack growth life up to the allowable crack length obtained in the sixth step is converted into a unit time. 11. The repair of the turbine rotor in the ninth step, wherein a repair width region is deleted across a hook portion of one turbine rotor blade and a hook portion of an adjacent turbine rotor blade. 2. The method for predicting crack growth of a turbine rotor according to item 1. 12. In the repair of the turbine rotor in the ninth step, the hardness is determined from the operating temperature and the operating time, and the hardness is plotted on a stress-hardness diagram prepared in advance, and the hardness is determined as the allowable hardness. The method according to claim 1, wherein the method is started when the value falls below a limit value.