CN113514553B - Piezoelectric guided wave detection method for steel pipe of water-cooled wall of boiler - Google Patents
Piezoelectric guided wave detection method for steel pipe of water-cooled wall of boiler Download PDFInfo
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- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/24—Probes
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- G01N29/245—Ceramic probes, e.g. lead zirconate titanate [PZT] probes
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- 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
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- G01N29/48—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by amplitude comparison
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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 transverse crack detection of the boiler water wall steel pipe of a thermal power plant, a transverse crack detection operation method for the boiler water wall steel pipe is provided, a piezoelectric guided wave transducer special for the water wall steel pipe is designed, and in the detection process, a transducer sound beam is scanned step by step in a sectional manner and obliquely enters the steel pipe along the surface of the water wall steel pipe for 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. The method has the advantages that the comparison steel pipe which is the same in material, diameter and wall thickness with the boiler water wall steel pipe to be detected is manufactured, the artificial defect is arranged on the comparison steel pipe, the reflected wave amplitude threshold value is determined after scanning, the threshold value and the reflected wave amplitude are directly compared during detection, the unqualified defect position can be obtained, the detection efficiency is greatly improved, and the 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 steel pipe of a boiler water wall, which is suitable for transverse crack defect detection of the boiler water wall of a thermal power generating unit.
Background
The water cooling wall of the thermal power plant is a main heated part of the boiler and consists of a plurality of rows of steel pipes which are distributed around the boiler hearth, the inside of the water cooling wall is flowing water or steam, radiant heat in the boiler is absorbed, the water is heated into saturated steam, and the outside receives heat of flame of the boiler hearth. The boiler water wall operates in a high-temperature and high-pressure environment for a long time, the operation state of the boiler water wall directly influences the operation efficiency of the boiler, the operation load of the boiler is gradually increased, the boiler water wall is interfered by various factors, the integrity of the boiler water wall structure can be influenced to a certain extent, and the defects of corrosion, abrasion, cracking and the like are easily generated during long-time operation, so that the water wall pipe is invalid. Once the water-cooled wall steel pipe is damaged, the safety and the reliability of the operation of the boiler are directly threatened.
The boiler water-cooling wall of the thermal power plant is arranged inside a hearth and absorbs radiation heat of high-temperature flame or smoke in the hearth for a long time, so that corrosion fatigue cracking occurs on the wall of the water-cooling wall pipe towards the fire side pipe wall under the combined action of thermal fatigue stress and corrosion atmosphere of wall temperature fluctuation, and densely distributed transverse cracks are formed, so that the water-cooling wall pipe is finally leaked. Because the water cooling wall can form a continuous oxide film on the outer wall of the fire side in the high-temperature operation process, the oxide film and the metal matrix can bear thermal fatigue stress when the furnace is started and stopped or the load of a unit is changed due to the difference of thermal expansion coefficients and temperature gradients, the strength and plasticity of the oxide film are lower than those of the metal matrix, so that transverse crack grooves can be formed on the oxide film to release stress, under the corrosive atmosphere, a corrosive medium can be in local contact with the metal matrix at the crack grooves and cause selective corrosion, cracks can be further expanded under the action of thermal fatigue stress due to the stress concentration at the crack grooves, the corrosion and fatigue interaction in the process greatly accelerates the expansion process of the cracks, the leakage is caused by the fact that the cracks penetrate through the inner wall, the unit is subjected to unplanned shutdown maintenance, and serious economic loss is caused for power generation enterprises. Therefore, when transverse cracks appear in the water wall pipe, the large-scale nondestructive detection of other pipe bundles is enhanced, the pipe sections are replaced reasonably according to the detection result, the failure accident of the water wall caused by crack expansion is prevented, and the method has great significance for the safe operation of the unit.
The transverse crack of the water wall is typical corrosion thermal fatigue damage, and the local wall temperature of the water wall frequently fluctuates during operation and has large amplitude, so that the axial thermal stress of the fire side of the pipe wall of the water wall is high, and the transverse crack is generated on the fire side of the pipe wall of the water wall under the action of alternating thermal stress. In order to prevent failure accidents caused by crack growth of the boiler water wall pipe, an effective nondestructive detection method is adopted to detect the crack defect of the boiler water wall pipe in service, and pipe sections are reasonably replaced according to detection results, so that the method is an effective means for ensuring safe operation of the boiler water wall.
The conventional nondestructive detection method for the water-cooled wall of the boiler at the present stage comprises vortex detection, ray detection, ultrasonic detection, magnetic powder and penetration detection and the like, and the detection capacity is shown in table 1:
table 1 comparison of detection capabilities of common non-destructive detection methods
Table 1 shows that the traditional nondestructive testing method has certain defects on the transverse defect detection of the water-cooled wall of the in-service boiler, and the problems of low crack detection sensitivity, high large-scale 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 requirements for detecting the surface finish of the workpiece is needed, so that the field operation efficiency is improved.
Disclosure of Invention
Aiming at the situation, the invention aims to overcome the defects of the prior art and provide a piezoelectric guided wave detection method for a boiler water wall steel pipe, which can effectively solve the problem of high-efficiency detection of the piezoelectric guided wave of the boiler water wall steel pipe.
The technical scheme of the invention is as follows:
the piezoelectric guided wave detection method for the steel pipe of the water-cooled wall of the boiler is characterized by comprising the following steps of:
step one, instrument selection
Selecting an ultrasonic guided wave detector with the function of selecting a dispersion curve in an ultrasonic guided wave mode and a detection device which is adaptive to a steel pipe of a water-cooled wall of a boiler to be detected;
the detection device comprises a fixed support, the fixed support is of a groove-shaped integrated structure formed by a top plate and side plates which are vertically and downwards connected to two sides of the top plate, a spring for tightly coupling the piezoelectric wafers to the surface of a water-cooled wall steel pipe of a boiler to be detected 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 section of the backing material body is in an upward concave circular arc shape, a detection surface layer is fixed on the lower surface of the backing material body, the detection surface layer is in a circular arc shape formed by protective films at two ends of the circular arc shape of the lower surface of the backing material body and piezoelectric wafers 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 the water-cooled wall steel pipe of the boiler to be detected, a magnetic block used for adsorbing the piezoelectric wafers to be detected on the surface of the water-cooled wall steel pipe of the boiler to be detected is arranged between the top of the transducer and the lower surface of the top plate, the magnetic blocks are fixedly adsorbed on the bottom of the side plates, the magnetic blocks at the bottom of the side plates are firmly adsorbed on the fins for scanning, when the detection surface layers of the transducer are in contact with the surface of the water-cooled wall steel pipe, the magnetic blocks at the bottom of the transducer is adsorbed on the fins, the surfaces of the water-cooled wall, the magnetic blocks are pushed by the transducer, the transducer to move upwards, the transducer, and the spring is contracted, and the wafer is constantly attached to the water-cooled surface of the water-cooled wall steel pipe to the boiler to be detected, and the wafer is tightly tested tightly, the storage provides sufficient time, and the in-service detection capability and the detection efficiency of the boiler water wall are greatly improved;
step two, determining the reflected wave amplitude threshold value
Manufacturing a comparison steel pipe which is made of the same material, has the same diameter and has the same wall thickness as a steel pipe of a boiler water-cooled wall to be tested, arranging a transducer fixing position at one end of the comparison steel pipe, arranging a plurality of artificial defects which are arranged along the circumferential direction on the inner surface or the outer surface of the comparison steel pipe at positions which are gradually increased from the transducer fixing position by equal distances, fixing the transducer of a detection device at the transducer fixing position, connecting the transducer with an ultrasonic guided wave detector through a lead wire, respectively detecting the artificial defects by adopting a piezoelectric guided wave method to obtain a reflected wave amplitude, wherein the minimum value L of the reflected wave amplitude min Namely, the reflected wave amplitude threshold value;
step three, detecting the steel tube of the water-cooled wall of the boiler to be detected
Determining a transducer detection position from the starting end of a water-cooled wall steel pipe of a boiler to be detected at intervals of 3000mm, connecting equipment, sequentially fixing the transducers on the determined transducer detection position, detecting by adopting a piezoelectric guided wave method, and when the acquired radiation wave amplitude is larger than a reflected wave amplitude threshold L min Namely judging that the defect of disqualification exists in the section of the steel pipe, and replacing a new section of the steel pipe, when the amplitude of the collected radiation wave is smaller than Yu Fanshe wave amplitude threshold value L min And judging that no unqualified defect exists in the section of steel pipe, and allowing the steel pipe to be used continuously without replacement.
Preferably, the distance between the simulation defect furthest from the fixed position of the transducer and the fixed position of the transducer in the second step 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-cooled wall steel pipe of the thermal power plant, the transverse crack detection operation method of the boiler water-cooled wall steel pipe is provided, the piezoelectric guided wave transducer special for the water-cooled wall steel pipe is designed, the transducer is in arc fit with the detected pipe and covers the half circumference of the water-cooled wall pipe, the transducer is embedded into the fixed support, the fixed support is adhered to the pipe wall through the magnetic block, the transducer is connected with the fixed support through the spring, constant pressure is applied through the spring, the transducer is stably distributed on the half circumference of the water-cooled wall, in the detection process, the transducer sound beam is obliquely incident into the steel pipe along the surface of the water-cooled wall steel pipe for longitudinal detection, so that the detection sensitivity of the transverse defect is improved, the transducer is not required to be manually moved or pressed, the attenuation of the guided wave along the propagation path is very small, the distance can be propagated along the pipe wall, the effective range of one scanning can reach 3 meters, the operation of polishing is not required in the detection range, the operation intensity is reduced, and the in-service detection efficiency is greatly improved. The method has the advantages that the comparison steel pipe which is the same in material, diameter and wall thickness with the steel pipe of the boiler water-cooled wall to be detected is manufactured, the artificial defect is arranged on the comparison steel pipe, the reflected wave amplitude threshold value is determined after scanning, the threshold value and the reflected wave amplitude are directly compared during detection, the unqualified defect position can be obtained, the detection efficiency is greatly improved, the accuracy is high, the accuracy reaches more than 99% through practical application, in addition, the ultrasonic guided wave detector detection system optimizes the scanning data imaging function, the multichannel data display can be provided, the defect positioning quantitative analysis capability is improved, the detection result is more visual and understandable, the detection data is ensured to be real and reliable, the pipe section is reasonably replaced according to the detection result, the failure accident of the water-cooled wall caused by crack expansion is prevented, and the method has great significance to the safe operation of a unit, and simultaneously has great social benefit and economic benefit.
Drawings
FIG. 1 is a cross-sectional view of a test device according to 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 showing the artificial defect arrangement of a comparative steel pipe according to an embodiment of the present invention.
Detailed Description
The following describes the embodiments of the present invention in further detail with reference to the drawings.
1-4, the piezoelectric guided wave detection method of the boiler water wall steel pipe comprises the following steps:
step one, instrument selection
Selecting an ultrasonic guided wave detector with the function of selecting a dispersion curve in an ultrasonic guided wave mode and a detection device which is adaptive to a steel pipe of a water-cooled wall of a boiler to be detected;
the ultrasonic guided wave detector has the functions of 64-order digital filtering, wavelet noise reduction and digital average of 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 in the prior art (commercial product), for example, the model is an HS900GW ultrasonic guided wave detector sold by the Innovative technology Co., ltd in the Wuhan China, and the main parameters are shown in the following table 2:
table 2 parameters of HS900GW type ultrasonic guided wave detector
| Project | Attenuator accuracy | Operating frequency range | Gain stepping | Emission voltage | Pulse width of emission |
| Data | ＜1dB/20dB | 50KHz～2MHz | 110dB/0.1、2.0、6.0 | 800V | 50ns～2000ns |
| Project | Vertical linearity error | Horizontal linearity error | Range of sound velocity | Sampling frequency | Position sensor accuracy: |
| data | ≤3％ | ≤0.1％ | 1000～20000mm/s | 150M/12bit | ≤0.18mm |
The detection device comprises a fixed bracket 5, the fixed bracket 5 is of a groove-shaped integrated structure formed by a top plate 51 and side plates 52 which are vertically and downwardly connected at two sides of the top plate, a transducer 4 which slides up and down along the height direction of the transducer 4 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 section of the backing material body 41 is in an upward 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 shape of the lower surface of the backing material body and piezoelectric wafers 43 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 steel pipe 8 of a water-cooled wall of a boiler to be detected, a spring 2 for tightly coupling the piezoelectric wafers 43 to the surface of the steel pipe of the water-cooled wall of the boiler to be detected is arranged between the top of the transducer 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 for adsorbing on the water-cooled wall steel pipe fins 7, as shown in figure 1, the water-cooled wall steel pipe of the boiler to be tested is formed by welding two semicircular components by adopting rolling forming fins, namely, adjacent water-cooled wall steel pipes are in a sealing state, the transducer scans by firmly adsorbing the magnetic block at the bottom of the side plate on the fins, when a detection surface layer of the transducer contacts with the surface of the water-cooled wall steel pipe of the boiler to be tested, the magnetic block is adsorbed on the fins, the surface of the water-cooled wall steel pipe of the boiler to be tested pushes the transducer to move upwards, and a spring contracts and applies a constant downward pressure to the transducer at the same time of moving, so that a piezoelectric wafer of the transducer is tightly attached to the steel pipe wall of the water-cooled wall steel pipe of the boiler to be tested and tightly coupled with the water-cooled wall steel pipe, the transducer detection range of the piezoelectric wafer reaches more than 3 meters, the transducer is firmly adsorbed on a detected workpiece through a detection device without moving the transducer in the detection process, 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 capability and detection efficiency of the boiler water wall are greatly improved;
step two, determining the reflected wave amplitude threshold value
Manufacturing a comparison steel pipe 10 which is made of the same material, has the same diameter and has the same wall thickness as the steel pipe of the water-cooled wall of the boiler to be detected, wherein the specification of the material 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-cooled wall of the boiler to be detected, and is formed by welding two semicircular assemblies through adopting rolling forming fins, one end of the comparison steel pipe 10 is provided with a transducer fixing position 10a, and five artificial defects which are arranged along the circumferential direction are sequentially arranged at the positions 1000mm, 1500mm, 2000mm, 2500mm and 3000mm from the transducer fixing position, wherein the length of the artificial defect is 10mm, and the depth is 0.5mm;
the first artificial defect which is 1000mm away from the fixed position of the transducer is positioned on the outer surface of the comparison steel pipe, and the center point of the first artificial defect is offset to the left by 10mm away from the center line b of the transducer shaft;
the second artificial defect with a distance of 1500mm from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the center point of the second artificial defect is positioned on the center line b of the transducer shaft;
the third artificial defect which is 2000mm away from the fixed position of the transducer is positioned on the outer surface of the comparison steel pipe, and the center point of the third artificial defect is offset to the right by 10mm from the center line b of the transducer shaft;
the fourth artificial defect with the distance of 2500mm from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the center point of the fourth artificial defect is positioned on the center line b of the transducer shaft;
the fifth artificial defect with a distance of 3000mm from the fixed position of the transducer is positioned on the inner surface of the comparison steel tube, and the center point of the fifth artificial defect is positioned on the central line b of the transducer shaft.
The transducer of the detection device is fixed on the transducer fixing position 10a and is connected with an ultrasonic guided wave detector through a lead wire, the above-mentioned artificial defects are detected by adopting a piezoelectric guided wave method respectively, reflected wave amplitude is obtained, and detection data are shown in the following table 3:
table 3 piezoelectric guided wave test data
Wherein the minimum value of the reflected wave amplitude is 25 percent, namely the reflected wave amplitude threshold value; smearing a couplant at a fixed position of the transducer before detection, wherein the couplant adopts a type CG-98 type couplant, and the smearing range of the couplant is more than or equal to the area of a contact surface 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 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 steel tube of the water-cooled wall of the boiler to be detected
From the beginning end of the boiler water wall steel pipe to be tested, determining a transducer detection position every 3000mm, connecting equipment, sequentially fixing the transducers on the determined transducer detection position, detecting by adopting a piezoelectric guided wave method, judging that unqualified defects exist in the section of steel pipe when the amplitude of the acquired radiation wave is more than 25%, replacing a new pipe section, judging that unqualified defects do not exist in the section of steel pipe when the amplitude of the acquired radiation wave is less than 25%, and allowing continuous use without replacement.
Smearing a couplant on the detection position of the transducer before detection, wherein the couplant adopts a type CG-98 type couplant (the couplant with the same specification is needed for determining and detecting the threshold value), 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 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 use effect, the inner walls of the two side plates of the fixed support 5 are provided with rails 3 arranged along the height direction, the two side walls of the shell of the transducer 4 are provided with sliding blocks 42 matched with the rails 3, and the sliding blocks 42 are arranged in the rails 3 and slide up and down along the length direction thereof to form a sliding guide structure of the transducer along the height direction of the fixed support.
The axis a of the circular arc shape of the lower surface of the detection surface layer along the length direction is mutually perpendicular to the sliding direction of the transducer.
The piezoelectric chip 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-wafer probe structure, a beam of guided wave is generated by a single wafer, the coverage area of detection is an acoustic beam line, the coverage of the area is realized by moving the single-wafer probe, and the scanning image with a certain area cannot be observed at the same time. In order to improve the piezoelectric guided wave detection efficiency of the steel pipe of the water-cooled wall of the boiler of the thermal power plant, the piezoelectric crystal plate of the transducer adopts an arc shape, can be tightly coupled with the water-cooled wall pipe, can adopt a multi-crystal matrix combination, is positioned between the protective films at the two sides of the bottom of the backing material body, can be formed by a plurality of spliced, for example, a plurality of strip-shaped transversely telescopic vibration crystal plates are spliced to form an arc shape, each crystal plate is connected with a corresponding channel of equipment through a lead wire, and the crystal plates are made of piezoelectric ceramic materials with high sensitivity and no magnetic field scattering and overflowing and are arranged in a matrix along the arc direction at the bottom of the backing material body of the transducer; because all wafers of the matrix piezoelectric guided wave transducer can be excited simultaneously to generate a plurality of guided waves, detection is carried out within a certain area range, 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 wall are greatly improved.
The backing material body is made of tungsten powder, and has larger attenuation capability and acoustic impedance close to that of piezoelectric ceramics;
the protective film 4 is made of copper sheets with the thickness of 120 mu m, and can protect the piezoelectric ceramic wafer of the transducer from being damaged when in use; 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 operation of holding is convenient.
The invention has good technical effects through practical application, and the application is as follows:
in 2021, during 3 months, a leakage event occurs in a water wall pipe of a boiler of a certain factory, and the boiler of the factory is a one-time intermediate reheating reverse double-tangent circular combustion mode and million high-efficiency ultra-supercritical pressure variable-pressure operation boiler produced by Harbin boiler factory Limited liability company, the boiler model is HG-2913/29.3-YM2, and the material specification of the water wall is 12Cr1 MoVG/phi 60mm multiplied by 7.5mm. The leakage of the water wall is caused by the transverse crack expansion caused by typical corrosive thermal fatigue damage, the unit is forced to stop and overhaul, and is entrusted by power generation enterprises, and the applicant adopts a piezoelectric guided wave detection method to carry out spot check on the water wall pipe of the plant, wherein the detection conditions are as follows:
and (3) cutting a standby pipe to process a comparative steel pipe on site, processing and manually simulating crack defects at positions 1000mm (outer surface), 1500mm (inner surface), 2000mm (outer surface), 2500mm (outer surface) and 3000mm (inner surface) from the transducer, wherein the defect specification is 10mm multiplied by 4mm multiplied by 1mm, and the defect amplitude at the position of 3000mm is adjusted to 25% through test calibration. The defect data are shown in Table 4 by in-service inspection to find that 10 defects exist in the inspected pipe.
TABLE 4 boiler water wall defect detection data for certain power plant
The method comprises the steps that a power generation enterprise cuts a pipe at a position where the piezoelectric guided wave detects the defect on the inner surface, the pipe is polished with the pipe section where the defect on the outer surface exists after the pipe is cut, the penetration detection is adopted for rechecking after the pipe is processed, the verification result is consistent with the detection result of the piezoelectric guided wave, the reflection amplitude is 15% and 22% of defects, the verification result is superficial corrosion and mechanical scratch defects, the defects of cracks and the defects with the expansion property are not seen, the defects with the reflection amplitude being greater than or equal to 25% are defects such as transverse cracks and deep pits, the power generation enterprise respectively adopts corresponding processing measures, and the abnormal condition of the water wall pipe is not seen after the power generation enterprise is put into operation. The field test shows that the circular arc piezoelectric guided wave detection technology can effectively solve the problem of large-area defect scanning of the water wall pipe of the in-service boiler of the thermal power plant, and is suitable for transverse crack defect detection of the water wall pipe.
Claims (6)
1. The piezoelectric guided wave detection method for the steel pipe of the water-cooled wall of the boiler is characterized by comprising the following steps of:
step one, instrument selection
Selecting an ultrasonic guided wave detector with the function of selecting a dispersion curve in an ultrasonic guided wave mode and a detection device which is adaptive to a steel pipe of a water-cooled wall of a boiler to be detected;
the detection device comprises a fixed bracket (5), the fixed bracket (5) is of a groove-shaped integrated structure formed by a top plate (51) and side plates (52) which are vertically and downwards connected to two sides of the top plate, a transducer (4) which slides up and down along the height direction of the transducer 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 section of the backing material body (41) is in an upward concave circular arc shape, a detection surface layer is fixed on the lower surface of the backing material body (41), the detection surface layer is in a circular arc shape formed by protective films (44) at two circular arc ends of the lower surface of the backing material body and piezoelectric wafers (43) 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 boiler water-cooling wall steel pipe (8) to be detected, a spring (2) for tightly coupling the piezoelectric wafers (43) to the surface of the boiler water-cooling wall steel pipe to be detected is arranged between the top of the transducer (4), a magnetic block (6) which is adsorbed on the bottom end of the side plate (52), a magnetic block (7) of the boiler is adsorbed on the water-cooling wall steel pipe, the transducer is firmly contacted with the upper surface of the transducer to be detected water-cooling wall by the magnetic block, and the magnetic block is firmly adsorbed on the upper surface of the transducer to the water-cooling wall steel pipe to be detected surface, the piezoelectric wafer of the transducer is tightly attached to the steel wall of the water-cooled wall of the boiler to be detected and tightly coupled with the steel pipe of the water-cooled wall, the detection range of the transducer adopting the piezoelectric wafer reaches more than 3 meters, the transducer is not required to be moved in the detection process of one group, and is firmly adsorbed on a detected workpiece through a detection device, so that the huge physical consumption caused by manual operation is solved, and meanwhile, sufficient time is provided for analysis and storage of detection data, and the in-service detection capability and detection efficiency of the water-cooled wall of the boiler are greatly improved;
step two, determining the reflected wave amplitude threshold value
Manufacturing a comparison steel pipe (10) which is made of the same material, has the same diameter and has the same wall thickness as a steel pipe of a boiler water-cooled wall to be tested, arranging a transducer fixing position (10 a) at one end of the comparison steel pipe (10), arranging a plurality of artificial defects which are arranged along the circumferential direction on the inner surface or the outer surface of the comparison steel pipe at positions which are gradually increased from the transducer fixing position by equal distances, fixing the transducer of a detection device on the transducer fixing position (10 a), connecting the transducer with an ultrasonic guided wave detector, detecting the artificial defects by adopting a piezoelectric guided wave method respectively to obtain a reflected wave amplitude, wherein the reflected wave amplitude has a minimum value L min Namely, the reflected wave amplitude threshold value;
step three, detecting the steel tube of the water-cooled wall of the boiler to be detected
Determining a transducer detection position from the starting end of a water-cooled wall steel pipe of a boiler to be detected at intervals of 3000mm, connecting equipment, sequentially fixing the transducers on the determined transducer detection position, detecting by adopting a piezoelectric guided wave method, and when the acquired radiation wave amplitude is larger than a reflected wave amplitude threshold L min Namely judging that the defect of disqualification exists in the section of the steel pipe, and replacing a new section of the steel pipe, when the amplitude of the collected radiation wave is smaller than Yu Fanshe wave amplitude threshold value L min And judging that no unqualified defect exists in the section of steel pipe, and allowing the steel pipe to be used continuously without replacement.
2. The piezoelectric guided wave detection method for the steel pipe of the water-cooled wall of the boiler according to claim 1, wherein rails (3) arranged along the height direction are arranged on the inner walls of two side plates of the fixed support (5), sliding blocks (42) matched with the rails (3) are arranged on the two side walls of the shell of the transducer (4), and the sliding blocks (42) are arranged in the rails (3) and slide up and down along the length direction of the sliding blocks to form a sliding guide structure of the transducer along the height direction of the fixed support.
3. The method for detecting the piezoelectric guided wave of the steel pipe of the water-cooled wall of the boiler according to claim 1, wherein the axis (a) of the circular arc shape of the lower surface of the detection surface layer along the length direction is mutually perpendicular to the sliding direction of the transducer.
4. The piezoelectric guided wave detection method for the boiler water wall steel pipe is characterized in that the top end of the top plate of the fixed support (5) is connected with a handle (1) and is convenient to hold.
5. The method for detecting the piezoelectric guided wave of the steel pipe of the water-cooled wall of the boiler according to claim 1, wherein the distance between the simulation defect furthest from the fixed position of the transducer and the fixed position of the transducer in the second step is less than or equal to 3m so as to adapt to the detection range of the transducer of the piezoelectric wafer.
6. The piezoelectric guided wave detection method for the boiler water wall steel pipe according to claim 1, wherein the steel pipe with the material specification of phi 60mm multiplied by 4mm multiplied by 3600mm/20G is compared with the steel pipe with the material specification of phi 60mm multiplied by 3600mm/20G, the compared steel pipe is the same as the boiler water wall steel pipe to be detected, and is also formed by welding two semicircular assemblies through adopting rolling formed fins, a transducer fixing position (10 a) is arranged at one end of the compared steel pipe (10), five artificial defects which are arranged along the circumferential direction are sequentially arranged at the distance of 1000mm, 1500mm, 2000mm, 2500mm and 3000mm from the transducer fixing position, and the length of the artificial defect is 10mm and the depth of the artificial defect is 0.5mm;
the first artificial defect which is 1000mm away from the fixed position of the transducer is positioned on the outer surface of the comparison steel pipe, and the center point of the first artificial defect is offset to the left by 10mm away from the center line b of the transducer shaft;
the second artificial defect with a distance of 1500mm from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the center point of the second artificial defect is positioned on the center line b of the transducer shaft;
the third artificial defect which is 2000mm away from the fixed position of the transducer is positioned on the outer surface of the comparison steel pipe, and the center point of the third artificial defect is offset to the right by 10mm from the center line b of the transducer shaft;
the fourth artificial defect with the distance of 2500mm from the fixed position of the transducer is positioned on the inner surface of the comparison steel pipe, and the center point of the fourth artificial defect is positioned on the center line b of the transducer shaft;
the fifth artificial defect with a distance of 3000mm from the fixed position of the transducer is positioned on the inner surface of the comparison steel tube, and the center point of the fifth artificial defect is positioned on the central line b of the transducer shaft.
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