CN108802182A - The generator guard ring detection method of inner surface wave is encouraged based on graze - Google Patents

Abstract

The invention relates to a method for detecting a generator guard ring based on glancing excitation internal surface waves. The method includes the following steps: using the probe of a phased array ultrasonic flaw detector to excite a surface wave on the inner wall of the grommet to be tested by means of grazing incidence of sound waves, and making the surface wave propagate in the circumferential direction of the inner wall of the grommet, when the surface wave encounters a defect When a reflected wave is generated, the reflected wave is received by the transducer and converted into an electronic signal for recording or real-time display, and the defect on the guard ring to be tested is determined according to the recording result or the image displayed in real time. This method not only records and detects defects with high accuracy, but also only needs to select some points on the circumference of the retaining ring for axial scanning to realize 100% scanning of the inner wall of the retaining ring during detection, and the detection efficiency is greatly improved.

Description

Detection method of generator guard ring based on glancing excitation internal surface waves

technical field

The invention relates to a method for detecting a generator guard ring based on glancing excitation internal surface waves.

Background technique

The generator guard ring fixes the rotor end winding and is an important part of the generator rotor. During the operation of the generator retaining ring, it bears the effects of centrifugal stress, bending stress and tight fit stress. Due to stress corrosion and fatigue, etc., it is easy to produce microcracks on the inner wall. As the operation time increases, the microcracks produced will Gradually expand, if the existence of cracks cannot be detected in time, when the expansion reaches a certain critical value, the expansion speed will suddenly increase, and eventually lead to major accidents. Therefore, the detection of cracks on the inner wall of the retaining ring is of great significance.

At present, conventional A-type pulsed ultrasonic testing equipment is usually used for the inspection of the inner wall of the generator retaining ring. During the inspection, the transverse wave or longitudinal wave emitted by the equipment probe is mainly directed to the inner wall of the retaining ring. When the direct wave encounters defects such as cracks, reflected waves will be generated. The wave is received by the probe and converted into a pulse signal, thereby being recognized; this kind of detection defect is insufficient in discrimination and recording, and the probe needs to cover 100% of the outer wall of the guard ring to ensure that all the inner wall is scanned. Inspection less efficient.

Contents of the invention

The purpose of the present invention is to provide a detection method of generator guard ring based on glancing excitation internal surface wave with high accuracy and high detection efficiency.

A generator grommet detection method based on grazing excitation internal surface waves, which is particularly characterized in that it includes the following steps: using a probe of a phased array ultrasonic flaw detector to excite waves on the inner wall of the grommet to be tested by means of grazing incidence of sound waves Surface wave, and make the surface wave propagate in the circumferential direction of the inner wall of the guard ring, when the surface wave encounters a defect, a reflected wave is generated, the reflected wave is received by the transducer and converted into an electronic signal for recording or real-time display, according to Recorded results or real-time displayed images identify defects on the grommet under test.

The present invention adopts a new detection process method, that is, surface waves are excited on the inner wall of the retaining ring by means of grazing incidence of sound waves, and surface waves encounter defects when propagating in the circumferential direction of the inner wall of the retaining ring to generate reflected waves (as shown in Figure 1 ), the reflected wave is received by the transducer and converted into an electronic signal to realize the detection and recording of defects. This method not only performs image recording and detection of defects, but also has high accuracy. Axial scanning can realize 100% scanning of the inner wall of the retaining ring, and the detection efficiency is greatly improved.

Description of drawings

Accompanying drawing 1 is schematic diagram of principle of the present invention;

Accompanying drawing 2 is the schematic diagram of the detection result of embodiment 1 of the present invention, and the abscissa of the right part in the figure is the percentage of A-scan amplitude height, and the ordinate is the horizontal distance of A-scan.

Detailed ways

The invention provides a method for detecting a generator guard ring based on grazing excitation internal surface waves, which includes the following steps: using a probe of a phased array ultrasonic flaw detector to excite surface waves on the inner wall of the guard ring to be tested by means of grazing incidence of sound waves When the surface wave propagates in the circumferential direction of the inner wall of the protective ring, it encounters a defect to generate a reflected wave. The reflected wave is received by the transducer and converted into an electronic signal for recording or real-time display. According to the recorded result or the real-time displayed image, the protective ring is determined. ring flaws. Fig. 1 is a schematic diagram of the principle of the present invention. Fig. 1 includes an ultrasonic phased array probe 1, a shear wave fan scan 2, a shear wave sound ray grazing the inner wall 3, an inner wall surface wave 4, and an inner wall crack 5.

Example 1:

1. Instrument configuration:

The selection of phased array probe frequency, wedge, and host should take both attenuation and resolution into consideration. The phased array equipment should have the display function of sector scan and A scan on the same screen, the minimum repetition frequency of the equipment should not exceed 1000Hz, the maximum display sound path range should not be less than 450mm, the frequency of the phased array probe should not exceed 5MHz, and the effective area of the probe should not be less than 70mm2. The element length is not less than 8mm. The present invention uses a 128-channel ultrasonic phased array analysis system to emit narrow pulses to excite a phased array probe with an effective aperture of 64 array elements. The center frequency of the probe is about 5 MHz, and the equipment repetition frequency is 1000 Hz.

2. Test block:

The test block is made of a full-circle retaining ring material cut from a real retaining ring produced by a domestic professional manufacturer of retaining rings. The wall thickness is 75mm, and the material is 18Mn18Cr. Both the size and material are consistent with the real generator retaining ring, which ensures the reliability of the test results. At the same time, due to the high strength, non-magnetic and excellent stress corrosion resistance of 18Mn18Cr material, at present, most of the in-service and newly-built steam turbine generator units above 300MW in China are made of this material, so it has a strong advantage in using it as a test material. representative. The retaining ring test block is engraved with a 10×10 keyway and a 0.5mm deep and 10mm long defect groove to simulate crack defects, which are used to verify the feasibility of the detection method.

3. Detection method verification:

In order to verify the feasibility of this method, a 10mm long and 1mm deep defect groove was processed on the generator retaining ring test block to simulate a crack defect. If the defect can be successfully detected, it proves that this method can detect small defects. capacity and effectiveness.

During the test, connect the probe, scanner, and encoder to the host, then set the focal law of the host of the phased array equipment, and apply coupling agent on the surface of the retaining ring test block, so that the probe is well coupled in the circumferential direction of the retaining ring. Prevent the air gap between the probe and the outer wall of the guard ring, ensure the transmittance of the sound wave, so that the sound wave emitted by the phased array can be well incident into the inside of the guard ring and reach the inner wall of the guard ring; place the probe at a distance of about The position of the sound path distance of 500mm, that is, the position of the maximum sound path range of the equipment, ensures that the detection process still has the ability to find 1mm groove defects at the position of the maximum sound path distance from the probe.

Move the phased array probe back and forth along the circumferential direction at the maximum sound path position, and adjust the gain value of the equipment at the same time. When adjusting, it is necessary to consider that the sound waves emitted by the phased array equipment have sufficient energy and have a suitable signal-to-noise ratio; the final test equipment A 1mm groove defect was successfully found at a position with a sound path distance of about 500mm.

4. Scanning method:

In the actual scanning, after setting and adjusting the main engine and the probe according to the above method, move the probe along the axial direction of the guard ring in the circumferential direction of the guard ring, and scan from one end of the guard ring to At the other end, scan the circumferential defects on the inner wall of the retaining ring; then turn the direction of the probe and scan in the opposite direction along the same path to ensure that crack defects in different directions can be accurately detected; The surface wave detection distance of 0.9 times (considering the scanning overlap rate of 10%) is placed at the second scanning point, and the above scanning steps are repeated until the inner wall of the guard ring is completely scanned. Pay attention to observe the screen of the equipment during the scanning process. When the surface wave encounters a defect, the echo reflected by the defect will be received by the phased array probe, and converted into an electronic signal and displayed on the display screen. At the same time, the length of the defect will be recorded , the situation within the entire scanning range will be recorded and stored by the host computer for later reference and analysis.

5 Conclusion:

1) It is feasible to detect internal cracks in the retaining ring by means of shear wave grazing incidence to excite internal surface waves. At present, there is no introduction of this method in China, and this technology has certain research value.

2) Although the material of the grommet is austenitic stainless steel, the grains are coarse and the thickness is large, which will cause the attenuation of the incident sound wave inside the grommet, but the use of phased array equipment overcomes these adverse effects and successfully excites surface waves, and The attenuation of the surface wave is small when propagating inside the guard ring, which can realize long-distance detection;

3) The phased array ultrasonic testing technology with controllable beam angle is a more reliable technical means to realize grazing incidence on the inner wall of the retaining ring and excite surface waves;

4) Compared with conventional ultrasonic detection, when using this experimental detection method, the probe does not need to cover the entire outer surface of the retaining ring to achieve 100% detection of its inner surface, and the detection efficiency is greatly improved;

5) The inner and outer surfaces of the retaining ring are relatively smooth and regular. For parts with complex shapes such as forged tees, the outer surface is hexagonal, etc., but the inner surface is smooth and regular cylindrical. Conventional ultrasonic testing is very difficult. It is difficult to detect inner surface cracks, but related detection can be completed by using the method of the invention, which has obvious technical advantages in this respect.

Claims (1)

1. a kind of generator guard ring detection method encouraging inner surface wave based on graze, which is characterized in that include the following steps：With The probe of phased-array ultrasonic defectoscope motivates surface wave by way of sound wave glancing incidence in retaining ring inner wall to be measured, and makes The surface wave, to propagation, generates back wave, by the back wave by changing in retaining ring inner wall circumference when the surface wave encounters defect Can device receive and be converted into electronic signal and carry out record either real-time display comes out according to record result or real-time display Image determines the defect on the retaining ring to be measured.