CN113514553A - Piezoelectric guided wave detection method for steel pipe of water wall of boiler - Google Patents
Piezoelectric guided wave detection method for steel pipe of water wall of boiler Download PDFInfo
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- CN113514553A CN113514553A CN202110787386.5A CN202110787386A CN113514553A CN 113514553 A CN113514553 A CN 113514553A CN 202110787386 A CN202110787386 A CN 202110787386A CN 113514553 A CN113514553 A CN 113514553A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
- G01N29/0654—Imaging
- G01N29/069—Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/225—Supports, positioning or alignment in moving situation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/227—Details, e.g. general constructional or apparatus details related to high pressure, tension or stress conditions
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/24—Probes
- G01N29/2437—Piezoelectric probes
- G01N29/245—Ceramic probes, e.g. lead zirconate titanate [PZT] probes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/26—Arrangements for orientation or scanning by relative movement of the head and the sensor
- G01N29/265—Arrangements for orientation or scanning by relative movement of the head and the sensor by moving the sensor relative to a stationary material
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/28—Details, e.g. general constructional or apparatus details providing acoustic coupling, e.g. water
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
- G01N29/4409—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison
- G01N29/4427—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison with stored values, e.g. threshold values
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
- G01N29/48—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by amplitude comparison
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/023—Solids
- G01N2291/0234—Metals, e.g. steel
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/028—Material parameters
- G01N2291/0289—Internal structure, e.g. defects, grain size, texture
Abstract
The invention relates to a piezoelectric guided wave detection method for a boiler water wall steel pipe, which adopts the technical scheme that a piezoelectric guided wave detection technology is applied to the transverse crack detection of the boiler water wall steel pipe in a thermal power plant, an operation method for detecting the transverse crack of the boiler water wall steel pipe is provided, a special piezoelectric guided wave transducer for the water wall steel pipe is designed, and in the detection process, the scanning is gradually carried out in sections, and a sound beam of the transducer is obliquely incident into the steel pipe along the surface of the water wall steel pipe to carry out longitudinal detection, so that the detection sensitivity of transverse defects is improved, the operation intensity is reduced, and the in-service detection efficiency is greatly improved. Through the contrast steel pipe of preparation and boiler water wall steel pipe that awaits measuring with the material with, with diameter, with the wall thickness to set up artificial defect on the contrast steel pipe, confirm the back wave amplitude threshold value after scanning, carry out direct contrast with threshold value and back wave amplitude during the detection and can obtain unqualified defect position, its detection efficiency improves greatly, and the degree of accuracy is high.
Description
Technical Field
The invention belongs to the technical field of nondestructive testing, and particularly relates to a piezoelectric guided wave detection method for a boiler water wall steel pipe, which is suitable for detecting transverse crack defects of a boiler water wall of a thermal power generating unit.
Background
The water-cooled wall of thermal power plant is the main heated part of boiler, it is made up of several rows of steel pipes, distribute around the boiler furnace, its inside is flowing water or steam, absorb the radiation heat in the stove, heat water into saturated steam, the outside accepts the heat of the flame of the boiler furnace. The water wall of the boiler runs under the high-temperature and high-pressure environment for a long time, the running state of the water wall of the boiler directly influences the running efficiency of the boiler, the running load of the boiler is gradually increased, and the water wall of the boiler is interfered by various factors, so that the integrity of the water wall structure of the boiler is influenced to a certain extent, and the water wall pipe is easy to corrode, wear, crack and the like after the water wall of the boiler runs for a long time, so that the water wall pipe fails. Once the water wall steel pipe is damaged, the safety and the reliability of the operation of the boiler can be directly threatened.
The boiler water wall of the thermal power plant is arranged in the hearth, the radiation heat of high-temperature flame or smoke in the hearth is absorbed for a long time, and the water wall pipe is easy to generate corrosion fatigue cracking on the pipe wall of the fire side of the water wall pipe under the combined action of thermal fatigue stress of wall temperature fluctuation and corrosive atmosphere, so that densely distributed transverse cracks are formed and finally the water wall pipe is leaked. Because the water-cooled wall can form a continuous oxidation film on the outer wall of the fire facing side in the high-temperature operation process, because the oxidation film and the metal matrix have the difference of thermal expansion coefficient and temperature gradient, when the furnace is started or stopped or the load of the unit is changed, the oxide film and the metal matrix can bear thermal fatigue stress, the strength and the plasticity of the oxide film are not as good as those of the metal matrix, so that a transverse crack groove is generated on the oxide film to release the stress, in corrosive atmosphere, the corrosive medium can locally contact with the metal matrix at the crack groove and cause selective corrosion, and due to stress concentration at the crack groove, the cracks can be further expanded under the action of thermal fatigue stress, corrosion and fatigue interaction are carried out in the process, the expansion process of the cracks is greatly accelerated, the cracks penetrate through the inner wall to cause leakage, the unplanned shutdown maintenance of a unit is caused, and serious economic loss is brought to a power generation enterprise. Therefore, when the transverse cracks appear in the water wall pipe, the large-range nondestructive testing of other pipe bundles is enhanced, the pipe sections are reasonably replaced according to the detection result, the water wall failure accident caused by crack propagation is prevented, and the method has great significance for the safe operation of the unit.
The transverse cracks of the water cooling wall are typical corrosive thermal fatigue damage, the axial thermal stress of the fire facing side of the wall of the water cooling wall is high due to frequent and large amplitude fluctuation of the local wall temperature of the water cooling wall during operation, and the transverse cracks are generated on the fire facing side of the water cooling wall under the action of alternating thermal stress. In order to prevent the failure accident caused by the crack defect expansion of the boiler water wall pipe, the in-service detection of the crack defect of the boiler water wall pipe is carried out by adopting an effective nondestructive detection method, and the pipe section is replaced reasonably according to the detection result, so that the method is an effective means for ensuring the safe operation of the boiler water wall.
The common boiler water wall nondestructive testing methods at the present stage include eddy current testing, ray testing, ultrasonic testing, magnetic powder and penetration testing and the like, and the testing capability is shown in table 1:
TABLE 1 comparison of the detection Capacity of common nondestructive testing methods
As shown in Table 1, the conventional nondestructive testing method has certain defects in the detection of transverse defects of the water-cooled wall of the in-service boiler, and the problems of low crack detection sensitivity, high large-range detection working strength and the like can occur, so that the in-service detection efficiency is low and the defects are missed. Therefore, a detection method with high detection sensitivity and low requirement on the surface smoothness of the detected workpiece is needed, so that the field operation efficiency is improved.
Disclosure of Invention
In view of the above situation, in order to overcome the defects of the prior art, the present invention aims to provide a method for detecting piezoelectric guided waves of a steel pipe of a water wall of a boiler, which can effectively solve the problem of efficient detection of the piezoelectric guided waves of the steel pipe of the water wall of the boiler.
The technical scheme of the invention is as follows:
the method for detecting the piezoelectric guided wave of the steel pipe of the water wall of the boiler is characterized by comprising the following steps of:
step one, selecting instrument and equipment
Selecting an ultrasonic guided wave detector with the function of selecting a frequency dispersion curve in an ultrasonic guided wave mode and a detection device adaptive to a water wall steel pipe of a boiler to be detected;
the detection device comprises a fixed support, the fixed support is a groove-shaped integrated structure formed by a top plate and side plates vertically and downwards connected to two sides of the top plate, a transducer which vertically slides up and down along the height direction of the fixed support is arranged between the two side plates, the transducer comprises a shell, a backing material body is arranged at the top of the shell, the lower surface of the cross section of the backing material body is in an upwards-concave arc shape, a detection surface layer is fixed on the lower surface of the backing material body, the detection surface layer is in an arc shape formed by protective films at two ends of the arc shape of the lower surface of the backing material body and a piezoelectric wafer arranged between the two protective films, the radian of the lower surface of the detection surface layer is matched with the radian of the surface of a water wall steel pipe of a boiler to be detected, a spring for tightly pressing and coupling the piezoelectric wafer on the surface of the water wall steel pipe of the boiler to be detected is arranged between the top of the fixed support and the lower surface of the top plate, and a magnetic block which is used for being adsorbed on the fins of the water wall steel pipe is fixed at the bottom end of the side plate, the energy converter is scanned by firmly adsorbing the magnetic block at the bottom of the side plate on the fin, when the detection surface layer of the energy converter is contacted with the surface of the steel pipe of the water wall of the boiler to be detected, the magnetic block is adsorbed on the fin, the surface of the water wall steel pipe of the boiler to be measured pushes the energy converter to move upwards, the spring contracts and applies a constant downward pressure to the energy converter when the energy converter moves, so that the piezoelectric chip of the transducer is tightly attached to the wall of the steel pipe of the water-cooled wall of the boiler to be measured and tightly coupled with the steel pipe of the water-cooled wall, the detection range of the transducer adopting the piezoelectric chip reaches more than 3 meters, the transducer is not required to be moved in a group of detection processes, the transducer is firmly adsorbed on the detected workpiece through the detection device, therefore, huge physical consumption caused by manual operation is solved, sufficient time is provided for analysis and storage of detection data, and the in-service detection capacity and detection efficiency of the boiler water wall are greatly improved;
step two, determining the wave amplitude threshold of the reflected wave
The preparation and the boiler water wall steel pipe that awaits measuring with the material with, with the diameter, with the contrast steel pipe of wall thickness, one end at the contrast steel pipe sets up transducer fixed position, the contrast steel pipe internal surface or the surface that in proper order apart from transducer fixed position increment equidistance position arrange the artifical defect that the multichannel was arranged along the circumferencial direction, fix detection device's transducer on transducer fixed position, and link to each other with supersound guided wave detector through the lead wire, adopt the piezoelectricity guided wave method to detect above-mentioned artifical defect respectively, obtain the reflected wave amplitude, wherein reflected wave amplitude minimum LminThe threshold value of the amplitude of the reflected wave is obtained;
step three, detecting the water-cooled wall steel pipe of the boiler to be detected
Determining a transducer detection position every 3000mm from the starting end of the water wall steel pipe of the boiler to be detected, fixing the transducers on the determined transducer detection positions in sequence after connecting equipment, and detecting by adopting a piezoelectric guided wave method, wherein when the amplitude of the collected radiation wave is greater than the threshold L of the amplitude of the reflected waveminNamely, judging that unqualified defects exist in the section of steel pipe, replacing the section of steel pipe with a new section of steel pipe, and when the wave amplitude of the collected radiation wave is smaller than the wave amplitude threshold L of the reflected waveminNamely, the steel pipe section is judged to have no unqualified defect, does not need to be replaced, and is allowed to be continuously used.
Preferably, the distance between the simulated defect farthest from the transducer fixing position in the second step and the transducer fixing position is less than or equal to 3m so as to adapt to the transducer detection range of the piezoelectric wafer.
The method is simple, the piezoelectric guided wave detection technology is applied to the transverse crack detection of the boiler water wall steel pipe in a thermal power plant, the operation method for detecting the transverse crack of the boiler water wall steel pipe is provided, the piezoelectric guided wave transducer special for the water wall steel pipe is designed, the transducer is attached to the detected pipe in an arc shape and covers the semi-circumference of the water wall steel pipe, the transducer is embedded into the fixed support, the fixed support is attached to the pipe wall through the magnetic block, the transducer is connected with the fixed support through the spring and applies constant pressure through the spring, the transducer is stably distributed on the semi-circumference of the water wall, in the detection process, the scanning is gradually carried out in sections, the sound beam of the transducer is obliquely incident into the steel pipe along the surface of the water wall steel pipe to carry out the longitudinal detection, so that the detection sensitivity of the transverse defect is improved, the transducer does not need to be manually moved or pressed, and because the guided wave is attenuated very little along the propagation path, therefore, the device can be spread for a long distance along the pipe wall, the effective range of one-time scanning can reach 3 meters, the polishing operation is not needed in the detection range, the operation intensity is reduced, and the in-service detection efficiency is greatly improved. By manufacturing a comparison steel pipe which has the same material, diameter and wall thickness as the water wall steel pipe of the boiler to be measured, setting artificial defects on the comparison steel pipe, determining the threshold of the wave amplitude of the reflected wave after scanning, directly comparing the threshold with the wave amplitude of the reflected wave during detection to obtain the unqualified defect position, the detection efficiency is greatly improved, the accuracy is high, the accuracy reaches more than 99 percent through practical application, in addition, the detection system of the ultrasonic guided wave detector optimizes the scanning data imaging function, can provide multi-channel data display, improves the defect positioning and quantitative analysis capability, thereby leading the detection result to be more intuitive and easier to understand, ensuring the true and reliable detection data, reasonably replacing the pipe section according to the detection result, preventing the water wall from generating failure accidents caused by crack propagation, the method has great significance for the safe operation of the unit and also has great social and economic benefits.
Drawings
FIG. 1 is a cross-sectional view of a test device of the present invention.
Fig. 2 is a cross-sectional view of a transducer of the present invention.
FIG. 3 is a side view of a transducer of the present invention.
FIG. 4 is a schematic diagram illustrating an arrangement of artificial defects of a steel pipe according to an embodiment of the present invention.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
As shown in FIGS. 1 to 4, the method for detecting the piezoelectric guided wave of the steel pipe on the water wall of the boiler comprises the following steps:
step one, selecting instrument and equipment
Selecting an ultrasonic guided wave detector with the function of selecting a frequency dispersion curve in an ultrasonic guided wave mode and a detection device adaptive to a water wall steel pipe of a boiler to be detected;
the ultrasonic guided wave detector has the functions of digital filtering, wavelet noise reduction and digital averaging of 64-order echo signals, and can realize the automatic calibration of guided wave sound velocity and the capability of reproducing waveforms and detection results; the ultrasonic guided wave detector is the prior art (a commercial product), for example, the model number of the ultrasonic guided wave detector is HS900GW model sold by Wuhan Zhongke Innovation technology GmbH, and the main parameters are shown in the following table 2:
TABLE 2 parameters of HS900GW ultrasonic guided wave detector
| Item | Attenuator accuracy | Operating frequency range | Gain stepping | Emission voltage | Width of transmitted pulse |
| Data of | ＜1dB/20dB | 50KHz～2MHz | 110dB/0.1、2.0、6.0 | 800V | 50ns～2000ns |
| Item | Vertical linearity error | Horizontal linearity error | Range of sound velocity | Sampling frequency | Position sensor accuracy: |
| data of | ≤3％ | ≤0.1％ | 1000～20000mm/s | 150M/12bit | ≤0.18mm |
The detection device comprises a fixed support 5, the fixed support 5 is a groove-shaped integrated structure formed by a top plate 51 and side plates 52 vertically and downwards connected to two sides of the top plate, a transducer 4 which vertically slides along the height direction of the fixed support is arranged between the two side plates, the transducer 4 comprises a shell 45, a backing material body 41 is arranged at the top of the shell 45, the lower surface of the cross section of the backing material body 41 is in an upwards-concave arc shape, a detection surface layer is fixed on the lower surface of the backing material body 41, the detection surface layer is in an arc shape formed by protective films 44 at two ends of the arc-shaped lower surface of the backing material body and a piezoelectric wafer 43 arranged between the two protective films, the arc-shaped lower surface of the detection surface layer is matched with the arc-shaped surface of a steel pipe 8 of the water wall of the boiler to be detected, a spring 2 for tightly pressing and coupling the piezoelectric wafer 43 on the surface of the steel pipe of the water wall of the boiler to be detected is arranged between the top of the top plate 4 and the lower surface of the top plate 51, the bottom end of the side plate 52 is fixed with a magnetic block 6 which is used for being adsorbed on a water wall steel pipe fin 7, as shown in figure 1, the water wall steel pipe of the boiler to be tested is welded and molded by adopting a rolling molded fin between two semicircular components, namely, the adjacent water wall steel pipes are in a sealed state, the transducer is scanned by firmly adsorbing the magnetic block at the bottom of the side plate on the fin, when the detection surface layer of the transducer is contacted with the surface of the water wall steel pipe of the boiler to be tested, the magnetic block is adsorbed on the fin, the surface of the water wall steel pipe of the boiler to be tested pushes the transducer to move upwards, the spring can contract and apply a constant downward pressure to the transducer when moving, so that a piezoelectric wafer of the transducer is tightly attached to the wall of the water wall steel pipe of the boiler to be tested and is tightly coupled with the water wall steel pipe, the detection range of the transducer adopting the piezoelectric wafer reaches more than 3 meters, the transducer does not need to be moved in a group of detection processes, and is firmly adsorbed on a detected workpiece through the detection device, so that huge physical consumption caused by manual operation is solved, sufficient time is provided for analysis and storage of detection data, and the in-service detection capacity and detection efficiency of the boiler water wall are greatly improved;
step two, determining the wave amplitude threshold of the reflected wave
Manufacturing a comparison steel pipe 10 which is made of the same material as a steel pipe of a water wall of a boiler to be detected, has the same diameter and the same wall thickness, wherein the material specification of the comparison steel pipe is phi 60mm multiplied by 4mm multiplied by 3600mm/20G, the comparison steel pipe is the same as the steel pipe of the water wall of the boiler to be detected, the comparison steel pipe is formed by welding two semicircular components through a fin formed by rolling, a transducer fixing position 10a is arranged at one end of the comparison steel pipe 10, as shown in figure 4, five artificial defects which are arranged along the circumferential direction are sequentially arranged at a distance of 1000mm, 1500mm, 2000mm, 2500mm and 3000mm from the transducer fixing position, the length of the artificial defect is 10mm, and the depth is 0.5 mm;
the first artificial defect which is 1000mm away from the fixed position of the transducer is positioned on the outer surface of the contrast steel pipe, and the central point of the first artificial defect is offset leftwards by 10mm from the central line b of the transducer shaft;
a second artificial defect 1500mm away from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the central point of the second artificial defect is positioned on the axial central line b of the transducer;
a third artificial defect 2000mm away from the fixed position of the transducer is positioned on the outer surface of the contrast steel pipe, and the central point of the third artificial defect is offset to the right by 10mm from the central line b of the transducer shaft;
a fourth artificial defect 2500mm away from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the central point of the fourth artificial defect is positioned on the axial central line b of the transducer;
and a fifth artificial defect 3000mm away from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the central point of the fifth artificial defect is positioned on the central line b of the transducer shaft.
Fixing the transducer of the detection device on the transducer fixing position 10a, connecting with the ultrasonic guided wave detector through a lead wire, respectively detecting the artificial defects by adopting a piezoelectric guided wave method to obtain the amplitude of the reflected wave, wherein the detection data are shown in the following table 3:
TABLE 3 piezoelectric guided wave test data
Wherein, the minimum value of the wave amplitude of the reflected wave is 25 percent of the wave amplitude threshold value of the reflected wave; smearing a couplant at a fixed position of the transducer before detection, wherein the couplant is a CG-98 type couplant, and the smearing range of the couplant is more than or equal to the contact surface area of the transducer;
when the transducer is fixed, the detection device is adsorbed on the fins of the water-cooled wall of the comparison steel pipe by means of the magnetic force of the magnetic block, and the detection surface of the transducer is tightly coupled with the detected workpiece under the action of the elastic force of the spring;
step three, detecting the water-cooled wall steel pipe of the boiler to be detected
The method comprises the steps of determining a transducer detection position every 3000mm from the starting end of a boiler water wall steel pipe to be detected, fixing the transducers on the determined transducer detection position in sequence after connecting equipment, detecting by adopting a piezoelectric guided wave method, judging that an unqualified defect exists in the section of the steel pipe when the amplitude of the collected radiation wave is greater than 25%, replacing a new pipe section, judging that an unqualified defect does not exist in the section of the steel pipe when the amplitude of the collected radiation wave is less than 25%, and allowing the steel pipe to be used continuously without replacement.
Before detection, a couplant is coated at the detection position of the transducer, the couplant is CG-98 type (the couplant with the same specification is required to be used for threshold determination and detection), and the coating range of the couplant is more than or equal to the contact surface area of the transducer;
when the transducer is fixed, the detection device is adsorbed on the fins of the water-cooled wall of the contrast steel pipe by means of the magnetic force of the magnetic block, and the detection surface of the transducer is tightly coupled with the detected workpiece under the action of the elastic force of the spring.
In order to ensure the using effect, the inner walls of the two side plates of the fixed support 5 are provided with rails 3 arranged along the height direction, two side walls of the shell of the transducer 4 are provided with sliders 42 matched with the rails 3, and the sliders 42 are arranged in the rails 3 and slide up and down along the length direction of the sliders to form a sliding guide structure of the transducer along the height direction of the fixed support.
And the axis a of the arc shape of the lower surface of the detection surface layer along the length direction is vertical to the sliding direction of the transducer.
The piezoelectric wafer 43 is led out through the lead 9 and then connected with an ultrasonic guided wave detector.
Because the traditional piezoelectric guided wave probe is of a single-chip probe structure, a beam of guided waves is generated by a single chip, the coverage range of detection is an acoustic beam line, the coverage of the area is realized by moving the single-chip probe, and the scanned image of a certain area cannot be observed simultaneously. In order to improve the piezoelectric guided wave detection efficiency of the steel pipe of the water wall of the boiler in the thermal power plant, the piezoelectric wafer of the transducer of the invention adopts an arc shape and can be tightly coupled with the water wall pipe, the piezoelectric wafer of the transducer can adopt a multi-wafer matrix combination, the piezoelectric wafer is positioned between the protective films at two sides of the bottom of the backing material body and can be formed by assembling a plurality of long-strip transverse telescopic vibration wafers, for example, the piezoelectric wafer is assembled into an arc shape by adopting a plurality of long-strip transverse telescopic vibration wafers, each wafer is connected with a corresponding channel of equipment by a lead wire, and the wafers are made of piezoelectric ceramic materials which have high sensitivity and no magnetic field scattering overflow and are arranged in a matrix way along the arc direction at the bottom of the backing material body of the transducer; because all the wafers of the matrix piezoelectric conductive transducer can be excited simultaneously to generate a plurality of guided waves to detect in a certain area range, the detection data can be presented on an instrument display screen simultaneously, and the in-service detection capability and the detection efficiency of the boiler water-cooling wall are greatly improved.
The backing material body is made of tungsten powder, and has high attenuation capacity and acoustic impedance close to that of piezoelectric ceramic;
the protective film 4 is made of a copper sheet with the thickness of 120 mu m, so that the piezoelectric ceramic wafer of the transducer can be protected from being damaged when the protective film is used; the shell is made of metal aluminum.
The top end of the top plate of the fixed support 5 is connected with a handle 1, so that the holding operation is convenient.
Through practical application, the invention obtains good technical effect, and the application is as follows:
in 3 months 2021, a leakage event occurs in a water wall tube of a boiler of a certain factory, and the boiler of the factory is a boiler which is produced by Harbin boiler factory Limited liability company and operates in a once intermediate reheating, reverse double tangential circle combustion mode and million-effect ultra-supercritical pressure variable pressure mode, wherein the model of the boiler is HG-2913/29.3-YM2, and the specification of the material of the water wall is 12Cr1 MoVG/phi 60mm multiplied by 7.5 mm. The leakage reason of the water wall is caused by the transverse crack propagation caused by typical corrosive thermal fatigue damage, the unit is forced to be shut down and overhauled and entrusted by power generation enterprises, the applicant adopts a piezoelectric guided wave detection method to carry out spot check on the water wall pipe of the plant, and the detection conditions are as follows:
the spare pipe is intercepted on site to process a comparison steel pipe, crack defects are artificially simulated at positions of 1000mm (outer surface), 1500mm (inner surface), 2000mm (outer surface), 2500mm (outer surface) and 3000mm (inner surface) away from the transducer, the defect specifications are 10mm multiplied by 4mm multiplied by 1mm, and the amplitude of the defect at the position of 3000mm is adjusted to be 25% through test calibration. The in-service detection shows that the detected pipes have 10 defects, and the defect data are shown in Table 4.
TABLE 4 Defect detection data for boiler water wall of certain power plant
The method comprises the steps that a power generation enterprise cuts a pipe at a position where a piezoelectric guided wave detection has an inner surface defect, the pipe is polished with a pipe section with an outer surface defect after being cut, the pipe section is subjected to rechecking by adopting penetration detection after being processed, the verification result is consistent with the piezoelectric guided wave detection result, the defects of 15% and 22% of reflection wave amplitude are verified, the verification result is defects of superficial corrosion and mechanical scratch, cracks are not seen, the defects have expansion properties, the defects of transverse cracks, deep pits and the like are detected by the defects of the reflection wave amplitude of more than or equal to 25%, the power generation enterprise respectively adopts corresponding processing measures, and the abnormal condition of the water cooling wall pipe is not seen after the unit is put into operation. The field inspection shows that the large-area defect scanning of the water wall tube of the in-service boiler of the thermal power plant can be effectively solved by adopting the arc-shaped piezoelectric guided wave detection technology, and the method is suitable for detecting the transverse crack defect of the water wall tube.
Claims (6)
1. The method for detecting the piezoelectric guided wave of the steel pipe of the water wall of the boiler is characterized by comprising the following steps of:
step one, selecting instrument and equipment
Selecting an ultrasonic guided wave detector with the function of selecting a frequency dispersion curve in an ultrasonic guided wave mode and a detection device adaptive to a water wall steel pipe of a boiler to be detected;
the detection device comprises a fixed support (5), the fixed support (5) is of a groove-shaped integrated structure consisting of a top plate (51) and side plates (52) vertically and downwardly connected to two sides of the top plate, a transducer (4) which vertically slides along the height direction of the transducer is arranged between the two side plates, the transducer (4) comprises a shell (45), a back lining material body (41) is arranged at the top of the shell (45), the lower surface of the cross section of the back lining material body (41) is in an upwards-concave arc shape, a detection surface layer is fixed on the lower surface of the back lining material body (41), the detection surface layer is in an arc shape formed by protective films (44) at two ends of the arc shape of the lower surface of the back lining material body and a piezoelectric wafer (43) arranged between the two protective films, the radian of the lower surface of the detection surface layer is matched with the surface radian of a water-cooling wall steel pipe (8) of a boiler to be detected, and a piezoelectric wafer (43) is arranged between the top of the transducer (4) and the lower surface of the top plate (51) and coupled to be detected by pressing in a water-cooling mode of the boiler to be detected water-cooling water The spring (2) on the surface of the wall steel pipe, the magnetic block (6) used for being adsorbed on the fins (7) of the water wall steel pipe is fixed at the bottom end of the side plate (52), the transducer is scanned by firmly adsorbing the magnetic block at the bottom of the side plate on the fins, when the detection surface layer of the transducer is contacted with the surface of the water wall steel pipe of the boiler to be detected, the magnetic block is adsorbed on the fins, the surface of the water wall steel pipe of the boiler to be detected pushes the transducer to move upwards, the spring can contract and apply a constant downward pressure to the transducer when the transducer moves, so that the piezoelectric wafer of the transducer is tightly attached to the wall of the water wall steel pipe of the boiler to be detected and is tightly coupled with the water wall steel pipe, the detection range of the transducer adopting the piezoelectric wafer reaches more than 3 meters, the transducer does not need to move in the group detection process, and the transducer is firmly adsorbed on the workpiece to be detected through the detection device, therefore, huge physical consumption caused by manual operation is solved, sufficient time is provided for analysis and storage of detection data, and the in-service detection capacity and detection efficiency of the boiler water wall are greatly improved;
step two, determining the wave amplitude threshold of the reflected wave
Preparation and boiler water wall steel pipe that awaits measuring are with the material, with the diameter, contrast steel pipe (10) with the wall thickness, one end at contrast steel pipe (10) sets up transducer fixed position (10a), it arranges the artifical defect that the multichannel was arranged along the circumferencial direction to keep gradually increasing gradually the contrast steel pipe internal surface or the surface of equidistance position apart from transducer fixed position in proper order, fix detection device's transducer on transducer fixed position (10a), and link to each other with supersound guided wave detector, adopt the piezoelectricity guided wave method to detect above-mentioned artifical defect respectively, obtain the reflected wave amplitude, wherein reflected wave amplitude minimum LminThe threshold value of the amplitude of the reflected wave is obtained;
step three, detecting the water-cooled wall steel pipe of the boiler to be detected
From the boiler under testDetermining a transducer detection position every 3000mm at the starting end of the water-cooled wall steel pipe, fixing the transducers on the determined transducer detection position in sequence after connecting equipment, and detecting by adopting a piezoelectric guided wave method when the amplitude of the collected radiation wave is larger than the threshold L of the amplitude of the reflected waveminNamely, judging that unqualified defects exist in the section of steel pipe, replacing the section of steel pipe with a new section of steel pipe, and when the wave amplitude of the collected radiation wave is smaller than the wave amplitude threshold L of the reflected waveminNamely, the steel pipe section is judged to have no unqualified defect, does not need to be replaced, and is allowed to be continuously used.
2. The boiler water wall steel pipe piezoelectric guided wave detection method according to claim 1, characterized in that rails (3) arranged along the height direction are arranged on the inner walls of two side plates of the fixed support (5), sliders (42) matched with the rails (3) are arranged on two side walls of the shell of the transducer (4), and the sliders (42) are arranged in the rails (3) and slide up and down along the length direction of the sliders to form a sliding guide structure of the transducer along the height direction of the fixed support.
3. The piezoelectric guided wave detection method for the steel pipe on the water wall of the boiler as claimed in claim 1, wherein the axis (a) of the arc shape of the lower surface of the detection surface layer along the length direction is perpendicular to the sliding direction of the transducer.
4. The boiler water wall steel pipe piezoelectric guided wave detection method according to claim 1, characterized in that a handle (1) is connected to the top of the top plate of the fixed support (5) to facilitate holding operation.
5. The method for detecting the piezoelectric guided waves of the steel pipe on the water wall of the boiler according to claim 1, wherein the distance between the simulation defect farthest from the fixed position of the transducer in the second step and the fixed position of the transducer is less than or equal to 3m so as to adapt to the detection range of the transducer of the piezoelectric wafer.
6. The boiler water wall steel pipe piezoelectric guided wave detection method according to claim 1, characterized in that the step of comparing steel pipes is a steel pipe with the specification of phi 60mm x 4mm x 3600mm/20G, the comparison steel pipe is the same as the boiler water wall steel pipe to be detected, and is also formed by welding two semicircular components through rolled fins, one end of the comparison steel pipe (10) is provided with a transducer fixing position (10a), five artificial defects arranged along the circumferential direction are sequentially arranged at a distance of 1000mm, 1500mm, 2000mm, 2500mm and 3000mm from the transducer fixing position, the length of the artificial defect is 10mm, and the depth is 0.5 mm;
the first artificial defect which is 1000mm away from the fixed position of the transducer is positioned on the outer surface of the contrast steel pipe, and the central point of the first artificial defect is offset leftwards by 10mm from the central line b of the transducer shaft;
a second artificial defect 1500mm away from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the central point of the second artificial defect is positioned on the axial central line b of the transducer;
a third artificial defect 2000mm away from the fixed position of the transducer is positioned on the outer surface of the contrast steel pipe, and the central point of the third artificial defect is offset to the right by 10mm from the central line b of the transducer shaft;
a fourth artificial defect 2500mm away from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the central point of the fourth artificial defect is positioned on the axial central line b of the transducer;
and a fifth artificial defect 3000mm away from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the central point of the fifth artificial defect is positioned on the central line b of the transducer shaft.
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