JPS6271855A - Defect detecting method for turbine rotor - Google Patents

Abstract

PURPOSE:To detect a harmful defect in a stationary state safely with high precision by cooling the center part of a rotor, heating the outer peripheral part and generating a tensile stress distribution at the center part of the rotor, and detecting an AE signal from the defect part. CONSTITUTION:Cooling pipes 4a and 4b transport cooling oil for cooling the center hole 1b of the turbine rotor 1. A high frequency coil 7 for heating is wound around the rotor 1 and plural temperature detectors 9 composed of a thermocouple, etc., are fitted on the surface of the hole 1b and the outer periphery of the rotor 1. Plural resonance type AE sensors 11 and wide-band AE sensors 12 for position evaluation are arranged nearby both ends of the rotor 1 and connected to an AE signal analyzing device 13. The sensors 11 and 12 detect and send AE signals to the device 13 for a specific period from the start of heating. The device 13 reads the difference in the rise starting time of the signal from the sensor 11 to evaluate a signal generation position and analyzes the frequency and energy of the signal from the sensor 12 to evaluate the position and degree of the harmful defect.

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention relates to a method for detecting defects in a turbine rotor of a steam turbine, a gas turbine, etc., and in particular, a method for detecting defects in a turbine rotor that can accurately detect defects under stress load conditions. Regarding the method.

[Technical background of the invention and its problems]

Since turbine rotors such as steam turbines and gas turbines are used at high speeds, large tensile stress due to centrifugal force acts on the center of the rotor.

In addition, inclusions such as MnS, which are generated during the manufacture of rotor materials, tend to concentrate around the center hole of the turbine rotor, and peeling of these inclusions from the base material can cause cracks. J may occur.

Once a crack occurs in a turbine rotor, this crack will rapidly propagate within a short period of time, and there is a danger that it will eventually lead to a major accident such as the rotor flying off.

In order to prevent such serious accidents, various non-destructive tests such as ultrasonic flaw detection, 4A powder flaw detection, and penetrant flaw detection are carried out during the manufacturing process of turbine rotors and during periodic inspections during service. However, although these non-destructive inspections are effective in detecting the presence or absence of defects that cause injuries to a certain extent and the extent δ thereof, they have the disadvantage that they cannot accurately detect the shape and properties of defects. Furthermore, since the inspection is performed in a static state without any stress being applied, it is insufficient to evaluate whether or not the defect causes harmful effects during operation.

Therefore, from the viewpoint of preventive maintenance, the behavior of defects is monitored during the operation of the turbine rotor or during rotational tests during regular inspections during service, where stress is applied, that is, in dynamic conditions, and the harmfulness of the defects is evaluated. It was hoped that the evaluation method would be published in January.

As a method for evaluating defects in the second dynamic state, a method for monitoring defects or evaluating harmful defects has been proposed that applies the AE method to detect acoustic emissions from defects (hereinafter referred to as 8E) using an E sensor. (For example, Japanese Patent Application Laid-Open No. 59-19332
9).

In this method, as shown in FIG.
Multiple E sensors 2 are installed to detect low AE signals when the turbine 0-1 is rotated at rated speed or overspeed during a dynamic balance test during periodic inspections, and this is calculated by the signal processing circuit 3. (By doing so, it is possible to monitor the occurrence of cracks due to harmful defects and to evaluate the integrity of the turbine rotor material.)

However, this method has the following drawbacks. First, since low AE signals are detected while the turbine rotor is rotating at high speed, if a crack develops from a harmful defect, it will progress to Q speed and there is a risk that the zero rotor will fly off. . Of course, in the dynamic balance test, in order to prevent brittle fracture of the turbine rotor material, measures such as heating the test turbine rotor to a temperature above the ductile-brittle transition '/Q degree of the rotor material and increasing the rotation speed are taken. However, in turbine rotors that have been used for a long period of time, the transition temperature may have increased due to embrittlement over time, and in such situations, the normal heating temperature falls within the temperature range that causes brittle fracture. Also,
Even if the temperature is in a temperature range where heating force 1 above the transition temperature causes ductile fracture without brittle fracture, cracks generated from harmful defects can rapidly grow due to ductile instability 1tl [LP current ↑]. Even if the rotor does not fly off, there is a risk that the rotor will be in a state where it cannot be repaired.

Second, since the AE low signal is detected during rotation, if there is a large amount of noise caused by the cooling of the sensing part, it is difficult to isolate the weak signal caused by cracks from defects. can be,
Therefore, there is a drawback that the detection accuracy of harmful defects is significantly reduced.

Thirdly, since the AF sensor is attached to a rotating body, it is necessary to guide the signal processing by a wireless transmission method using an AE low signal FM telemeter or the like. Conventionally, FM telemeters have been widely used and have a proven track record in transmitting signals in the relatively low frequency range of 82 or less, such as vibration stress on turbine blades.
Those that carry high frequency signals of several 100KH2 to several MH7, such as E-low signals, are very 9s, and the S/N ratio,
Since various properties such as frequency characteristics are significantly degraded, there is a drawback that IS reliability of signal detection is degraded.

[Purpose of the invention]

The present invention has been made to eliminate the above-mentioned drawbacks in the background art, and is a method for detecting defects in a turbine rotor that can safely and accurately detect harmful defects while the turbine rotor is stationary. The purpose is to provide

[Summary of the invention]

In order to achieve the above-mentioned object, the method for detecting a defect in a turbine rotor according to the present invention cools the inner core of the turbine rotor.
jl L,, by heating the outer periphery, a tensile stress distribution is generated in the center of the rotor.
Et? It is characterized by detecting the presence of a harmful defect and determining its location by performing signal processing. At this time, the stress distribution at the center of the rotor is controlled to the same magnitude as in the actual operating state by controlling the temperature difference between the inner and outer surfaces of the rotor detected by a temperature detector.

As described above, the present invention monitors the behavior of defective parts in the turbine rotor in a state simulating the operating state of an actual machine, and evaluates harmful defects and detects harmful defects.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail with reference to the drawings.

In FIG. 1, cooling vibes 4a, 4b are installed at both ends of a center hole 1b provided through the center of the rotor of the turbine rotor 1.
are connected. These cooling vibes 4a, 4b are used to carry cooling oil for cooling the center hole 1b of the bottle rotor 1, and these II! ! The cap side is connected via the oil pump 5 and the σ heat exchanger C, forming a closed loop.

Cooling water vibros a and 6b are connected to the heat exchanger 6, and secondary cold 7Jl water is flowing therethrough to exchange heat with cold IJ1 oil flowing on the primary side of the heat exchanger 6.

A high frequency coil 7 is wound on the outside of the turbine rotor 1 in sections, and both ends of each coil are connected to a high frequency power source 8. Further, a plurality of temperature detectors 9 each made of a thermal lightning pair are attached to the surface of the center hole 1b of the turbine rotor and the outer periphery of the turbine rotor. These temperature detector 9 and high frequency power source 8 are connected to a temperature controller 10.

Near both ends of the turbine rotor 1 are AE for AE signal detection.
J-11 and J-12 are installed.

There are two types of AE sensors: one is a resonant AE sensor for position estimation, and the other is a broadband 1a AE sensor 12. A plurality of these AE sensors are installed, and the lead wires from the sensors 11 and 12 of each are connected to the AE signal analyzer 13.

In the turbine rotor defect detection device J3 configured as described above, the cooling oil sent out from the oil pump 5 flows from the cooling vibe 4a through the center hole 1b in the direction of arrow 14, and passes through the center of the rotor through the cold moon 1. After cooling, the heat exchanger IIJ! passes through the cooling via 4b! Return to vessel 6. In the heat exchanger 6, the cooling oil is cooled to about 20° C. by the cooling water supplied from the cooling water vibro a, pressurized by the oil pump 5, and sent into the center hole 1b of the rotor again. By circulating the cooling oil in this manner, the center of the rotor is maintained at about 20°C.

On the other hand, the high frequency coil 7 is supplied with a high frequency current from the high frequency electric current Δ≦18, and heats the turbine rotor 1 by induction heating. The temperature of the center hole 1b and the outer circumference of the turbine rotor is detected by the Get temperature sensor 9, and its output voltage is guided to the temperature controller '10. Temperature control! - The roller 10 controls the current of the high frequency source 8 so that the temperature difference between the center and the outer circumference of the rotor becomes 1, which will be described in detail below.

FIG. 2 shows the change in temperature of the inner surface A of the turbine rotor 1 over time after the start of heating, so 15 shows the temperature change in the center of the rotor, and 16 shows the temperature change in the outer peripheral part. While the temperature at the center of the rotor is almost constant, the temperature at the outer periphery starts from the upper back immediately after heating starts, and the temperature difference is set at T
Back up to 1. Outside lp section Atsura set bllJ T 1
Once the temperature is reached, the heating is reduced to medium 1, and the temperature at the outer periphery gradually decreases to 4 degrees.

Setting (il'l T 1 is a temperature difference of 115 that is equal to the entrance stress of the turbine rotor center hole 1b due to the centrifugal force of the overspeed guard, which makes the thermal stress on the surface of the center hole 1b 120%, and is as follows. It is determined by

Generally, the thermal stress distribution at the rotor center depends on the temperature difference between the rotor center and the outer circumference, and the larger the temperature difference, the greater the thermal stress.

Curve 17 in FIG. 3 is F for the turbine rotor of the example.
The relationship between the tangential thermal stress σ on the surface of the turbine rotor center hole 1b obtained as a result of EM analysis and the temperature difference between the rotor center and the outer circumference is shown below. The tangential thermal stress on the surface σ,) is increasing. σ1 in the figure is the maximum value of the tensile stress in the rotor circumferential direction due to centrifugal force when the turbine rotor of this example is rotating at 120% overspeed. A set value T1 for the outer surface is determined.

Figure 1 shows the tangential response 711 in the rotor cross section at this time.
>) Shows the cloth, 18 shows the thermal stress distribution, 19 shows the stress distribution due to centrifugal force, 10 shows the stress distribution due to centrifugal force 1
9 has the maximum value σ1 on the surface of the center hole 1b! 5. Although it gradually decreases toward the outer periphery, the odor on the outer periphery surface is also in a tensile state. On the other hand, the stress distribution 18 has a maximum value σ1 of 1.1 on the surface of the center hole 1b, and it gradually decreases near the center hole 1b, similar to the stress caused by centrifugal force, but near the outer periphery The stress gradually decreases and becomes 1f compressive stress near the outer periphery of the turbine rotor.

FIG. 5 shows the nitridation of the tangential thermal stress σ on the surface of the center hole 1b over time after the heating of the outer circumference of the turbine rotor is started, which is derived from the results shown in FIGS. 2 and 3. The stress σ increases after the start of heating, reaches the maximum stress σ1 at time t1, and then gradually decreases. The AE sensor 11.12 installed at the turbine [1-t1] detects the AU signal 2 from the start of heating to tl and sends it to the Δ11 signal analyzer 13.

l\[In the code analysis equipment 13, after amplifying the AE low signal,
Perform the following analysis for each sensor. First, resonance type Δ[L? Regarding the signal from +)-11, the position of the signal is evaluated by reading the difference in the start time of the rising and falling signals from the sensors 11 installed on the left and right sides of the test rotor. Further, the signal from the wideband AE sensor 12 is subjected to frequency analysis and No. 15 energy analysis, and from the results, the number n of harmful defects and their degree of harmfulness are evaluated.

Next, the results of the examples will be described.

As shown in FIG. 4, the stresses near the center hole 1b of the turbine rotor are caused by centrifugal force and by thermal stress, which are almost equal. Therefore, the degree of harmfulness of defects existing in the vicinity of the surface of the center hole 1b, which may cause damage to the machine in the operating state, can be evaluated under conditions equivalent to those in the actual machine operating state. However, the thermal stress is compressive at the outer periphery of the turbine rotor, so even if a brittle fracture occurs due to a defect near the center hole 1b, the crack will stop growing at the compressive stress area. Therefore, the entire rotor is damaged.
It will never go to 0 and is safe. In addition, since stress is applied while keeping the center of the rotor at room temperature, the degree of damage caused by defects can be evaluated under harsher conditions than during the rotation test. Furthermore, since the E signal can be directly transmitted to the cracking device 13 without using radio, highly viscous signal processing and analysis becomes possible. 3 with the rotor stationary
It is possible to detect defects with high accuracy by detecting minute signals without any defects such as scratches caused by rotation.

In addition, as an example of Haku of wood origin, for example, the cold of the center hole! The same effect can be obtained even if a medium other than a tune is used as the Jl medium, and high temperature steam or the like is used as a method of heating the outer circumference of the turbine rotor.

Further, although frequency analysis is employed in the above embodiment as a method for evaluating the degree of harmfulness of defects, other methods suitable for the material, such as AE event 1-incidence rate, may be used.

[Effects of the Invention] According to the present invention, it is possible to realize the operating state of the actual machine and the state where the stress of the open base is applied in the stationary state, and to detect harmful defects with high precision and safely. I can do it.

[Brief explanation of drawings]

Is Figure 1 the one of the present invention? Fig. 2 is an explanatory diagram showing an embodiment of the turbine rotor. Fig. 2 is a graph showing the change in the temperature of the inner and outer surfaces of the turbine rotor. A graph showing the relationship with temperature difference, FIG. 4 is a graph that does not show the stress distribution in the rotor cross section, and FIG. 5 is a graph showing the change in internal stress of the center hole over time.
FIG. 6 is an explanatory diagram illustrating a conventional turbine rotor defect detection method. 1... Turbine rotor, 1b... Center hole, 2.11
゜12...Δ111 sensor, 4a, 4b...cold 2
JI river puff 1゛puff, 5... oil pump, 6...
Heat exchanger, l..., alpha frequency coil, 8... high frequency power supply, 9... A degree detector, 10... temperature controller 1 to roller, 13... AEIΔg analyzer. Applicant's representative Mr. Sato Figure 2 0 Temperature difference between the rotor center and outer circumference T 3 Figure 3

Claims (1)

[Claims] 1. A tensile stress is generated near the center of the rotor by cooling the center hole of the turbine rotor and heating the outer periphery of the turbine rotor, and in this state, an acoustic emission signal is emitted from the defective part. (AE signal) is detected by a plurality of AE sensors attached to the turbine rotor, and the obtained AE signal is analyzed by an AE signal analyzer to detect a defect in the turbine rotor. Detection method. 2 Detect the gain of the center hole and outer circumference of the turbine rotor,
A method for detecting defects in a turbine rotor according to claim 1, characterized in that a control signal is output from a temperature controller to a high frequency power source so that the temperature difference between these temperatures becomes a constant value. 3. A cooling pipe in which an oil pump and a heat exchanger are inserted is connected between both ends of the center hole of the turbine rotor, and a cooling medium is allowed to flow into the center hole. A method for detecting defects in turbine rotors. 4. A method for detecting defects in a turbine rotor according to claim 1, characterized in that a plurality of divided high-frequency coils are arranged on the outer periphery of the turbine rotor, and a high-frequency current is caused to flow through the divided high-frequency coils from a high-frequency power source.