CN102944610A - Method for detecting weld defect of stainless steel runner blade of water turbine - Google Patents

Abstract

The invention discloses a method for detecting weld seam defects of stainless steel runner blades of water turbines, which is carried out according to the following steps: Step 1, selecting an instrument; Step 2, calibrating the instrument; Step 3, drawing a waste judgment line for detection: 1) Making a reference test 2) Use the probe of the instrument to test the detection surface of the reference test block through the wedge, record the current gain of the instrument and the reflection amplitude height values of the through holes at different heights on the reference test block, and compare the reflection amplitude height values in two Points are drawn on the three-dimensional coordinate system, and connected with a smooth curve to draw a waste judgment line; Step 4, detect the blade weld; Compared with the waste line, corresponding marks are made on the surface of the blade. According to the marks on the surface of the blade, it is finally possible to detect whether there is a defect in the blade. Reliable, convenient and rapid detection of weld defects of stainless steel runner blades is realized.

Description

A detection method for weld defects of stainless steel runner blades of hydraulic turbines

technical field

The invention belongs to a non-destructive testing method, in particular to a detection method for weld seam defects of stainless steel runner blades of water turbines, which is suitable for detecting the upper crown and lower ring weld seams of stainless steel runner blades of large and medium-sized Francis turbine units.

Background technique

In recent years, the large and medium-sized Francis turbines for new power generation generally use low-carbon martensitic stainless steel ZG0Cr13Ni4-6Mo for the turbine blades. Penetrating cracks often appear, and some units even have extreme cases where the same position of the runner blade is repeatedly repaired and cracked repeatedly, which seriously affects the safe and stable operation of the hydroelectric generating unit.

The more practical way to completely solve the cracks of stainless steel runners is to use the opportunity of overhaul to remove the cracks and repair them, but the key lies in the early and effective detection of cracks or other internal defects. At present, the internal quality inspection method of the blade is mainly the conventional ultrasonic technology, which uses the probe of the ultrasonic instrument and the wedge matched with the probe to detect the blade. When testing the weld seam of the stainless steel runner, its limitations are: 1) water turbine The coarse grain of the blade material leads to large attenuation coefficient and noise signal of the ultrasonic wave, and the detection sensitivity is reduced; 2) The blade shape of the three-dimensional curved surface makes it difficult to predict the propagation of the ultrasonic sound beam inside the workpiece, making it difficult to interpret the detected defect signal and perform defect detection. Positioning and quantification; 3) The in-service inspection of turbine runners is limited by space, and the probe can only be used to scan on the blades, resulting in limited coverage of the welded joints to be inspected, and it is difficult to align the direction of the sound beam and the effective detection of dangerous defects . Therefore, new detection methods must be studied to ensure that all defects can be effectively detected and the safe and reliable operation of the hydroelectric generator set can be ensured.

Contents of the invention

The technical problem to be solved by the present invention is to propose a detection method for weld defects of stainless steel runner blades of hydraulic turbines, using ultrasonic phased array Acoustic beam deflection and focusing performance, reliable, convenient and rapid detection of weld defects of stainless steel runner blades, so as to detect and deal with defects in time, and avoid runner failure accidents caused by weld defects.

Technical solution of the present invention is:

The detection method for the weld defect of the stainless steel runner blade of the water turbine is carried out according to the following steps:

Step 1. Select the instrument: the instrument is equipped with an ultrasonic phased array instrument equipped with a probe and a wedge and has a sector scanning function, and the minimum continuously adjustable gain is not less than 76db; the probe requires a frequency of 2.25MHz, no less than 64 chips, and a single chip size The maximum is 0.5×10mm, and the maximum wafer gap is 0.1mm; the wedge angle is 45°, and the size is not greater than 40×30mm;

Step 2. Calibrate the instrument: Set the scanning type of the instrument to sector scanning; The start angle is 30°; The end angle is 70°; The focus distance should be greater than the thickness of the blade to be detected by 5mm;

Step 3. Draw the waste judgment line for detection:

1) Make a reference test block: the reference test block is a rectangular strip with length×width×height. There are several through holes of different heights on the length×height surface of the reference test block. The two length×height of the reference test block are The wide surface is used as the detection surface;

2) Apply couplant on the detection surface of the reference test block, test the detection surface of the reference test block with the probe of the instrument through the wedge, and record the current gain of the instrument and the reflection of the through holes of different heights on the reference test block Amplitude height value, the reflection amplitude height value is plotted on the two-dimensional coordinate system, and connected with a smooth curve to draw a waste judgment line;

Step 4. Detect the blade welds: apply coupling agent near the upper crown and lower ring welds of the blade to be tested, and use the wedge on the instrument probe to stick to and perpendicular to the centerline of the weld of the blade to be tested, and perform zigzag scanning and detection , the range of the probe moving back and forth should be greater than 2 times the thickness of the blade;

Step 5. Defect record: Taking the waste judgment line as a reference, when the instrument shows that the height of the echo signal exceeds the waste judgment line during the detection process, it is determined that the reflector is a defect, and corresponding marks are made on the blade surface, and corresponding The height coordinate value records the defect burial depth; when the echo signal height is lower than the waste judgment line, it will not be recorded; according to the mark on the blade surface, it can finally detect whether there is a defect in the blade.

The length, width, and height of the reference test block are 320mm, 40mm, and 100mm respectively, and the inner diameter of the through hole is 3mm. Arranged vertically, the distance between the top and bottom of the through holes is 20mm, the initial height of one group of through holes is 10mm; the initial height of the other group of through holes is 20mm; the distance between the two groups of through holes and the side is 40mm.

The principle of the present invention is: if there is a defect in a steel workpiece, due to the existence of this defect, an interface between different media is formed between the defect and the steel material, and the acoustic impedance between the interfaces is different. When the emitted ultrasonic wave encounters this interface, it will be reflected, and the reflected energy will be received by the probe again, and a reflected wave waveform will be displayed at a certain position of the abscissa on the display screen, the position of the abscissa It is the depth of the defect in the tested material.

The beneficial effects of the present invention are: when using this method to detect, it overcomes difficulties such as coarse material grains, limited detection space, and changes in blade thickness, and has the characteristics of simplicity, safety, reliability, and high sensitivity, so the environmental requirements for detection are relaxed, and It is convenient and fast, especially for the internal defects of the weld, which can be effectively detected, thereby greatly improving the detection efficiency and detection sensitivity, so as to find and deal with the defects in time, and avoid the failure accident of the runner caused by the weld defects.

Description of drawings

Fig. 1 is a schematic diagram of a reference test block and an instrument scanning on the reference test block according to the present invention.

Fig. 2 is the waste judgment line drawn by the present invention.

Fig. 3 is a schematic diagram of the instrument scanning on the blade to be tested.

Fig. 4 is a display diagram of waste judgment line and echo signal drawn during blade detection.

Figure 5 is a flow chart of the detection process.

Detailed ways

The upper crown, lower ring and blades of unit 2 of a hydropower plant are all made of 0Crl3Ni5Mo martensitic stainless steel. After the blades are molded, they are welded with the upper crown and lower ring to form a runner. The maximum thickness of the blades is about 50mm. Since the unit was put into operation, the runner blades have cracks in different degrees on the upper crown and the lower ring outlet edge, and the cracks of individual blades are relatively serious. In November 2010, in the process of welding triangular ribs to water turbine blades during C-level maintenance, in order to ensure that the cracks in the weld seams of the blades were cleaned and the welding quality of the triangular ribs was removed, ultrasonic waves were carried out on the welding seams of the runner blades, the upper crown and the lower ring. Phased array detection. The specific method is as follows:

Step 1, select the instrument: the present invention adopts the Omniscan-MX type phased array instrument produced by RD-Tech Company, has sector scanning function, continuously adjustable gain 80db, instrument is equipped with probe and wedge, probe frequency 2.25MHz, 64 wafers , The single chip size is 0.5×10mm, the chip gap is 0.1mm; the wedge angle is 45°, and the size is 24×16mm.

Step 2. Calibrate the instrument: set the scanning type of the instrument to sector scanning; the start angle is 30°; the end angle is 70°; the focus distance: 57mm.

Step 3. Draw the waste judgment line for detection, see Figure 1:

1) Make a reference test block: the reference test block is a rectangular strip 1 with length L×width W×height H. There are several through holes 2 of different heights on the length×height surface of the reference test block. The reference test block The two length L×width W surfaces of the reference test block are used as the detection surface; the length L, width W, and height H of the reference test block are 320mm, 40mm, and 100mm respectively, and the inner diameter Φ of the through hole 2 is 3mm, and there are 8 through holes 2 in total, of which Every 4 through-holes 2 form a group, vertically arranged up and down in the height direction, the distance s2 between the upper and lower through-holes 2 is 20mm, and the initial height s1 of one group of through-holes 2 is 10mm; the other The initial height s4 of the set of through holes 2 is 20 mm; the distance s3 between the two sets of through holes 2 and the side is 40 mm;

2) Apply couplant on the detection surface of the reference test block, test the detection surface of the reference test block with the probe of the instrument through the wedge, and record the current gain of the instrument and the reflection of the through holes of different heights on the reference test block For the amplitude height value (percentage), the reflected amplitude height value is plotted on the two-dimensional coordinate system, and connected with a smooth curve to draw a waste line, as shown in Figure 2.

Table 1 shows the reflected wave height of the Φ3×40mm through hole 2 on the reference test block when the instrument gain is 38db.

Table 1 Test results of regular reflectors on reference test block

Step 4. Detect the blade welds, see Figure 3: Apply couplant near the upper crown weld 501 and the lower ring weld 502 of the blade 5 to be tested, and use the wedge 3 on the instrument probe to stick closely to and be perpendicular to the blade to be tested Weld center line, for zigzag scanning detection, the range of the probe moving back and forth should be greater than 100mm, that is, greater than 2 times the thickness of the blade;

Step 5. Defect record: Refer to Figure 4, take the reject line as a reference, during the detection process, the instrument shows that the heights of echo signals 1 and 3 are lower than the reject line, and will not be recorded; the height of echo signal 2 exceeds the reject line Height, if the reflector is judged to be a defect, it should be recorded on the blade, and the depth of the defect should be marked at about 33mm according to the depth coordinates. According to the mark on the surface of the blade, the defect and the defective part of the blade can be finally detected.

The flow chart of the above detection method is shown in FIG. 5 .

Claims (2)

1. a detection method for the weld defect of the stainless steel runner blade of a hydraulic turbine is characterized in that it is carried out according to the following steps: Step 1. Select the instrument: the instrument is equipped with an ultrasonic phased array instrument equipped with a probe and a wedge and has a sector scanning function, and the minimum continuously adjustable gain is not less than 76db; the probe requires a frequency of 2.25MHz, no less than 64 chips, and a single chip size The maximum is 0.5×10mm, and the maximum wafer gap is 0.1mm; the wedge angle is 45°, and the size is not greater than 40×30mm; Step 2. Calibrate the instrument: Set the scanning type of the instrument to sector scanning; The start angle is 30°; The end angle is 70°; The focus distance should be greater than the thickness of the blade to be detected by 5mm; Step 3. Draw the waste judgment line for detection: 1) Make a reference test block: the reference test block is a rectangular strip with length×width×height. There are several through holes of different heights on the length×height surface of the reference test block. The two length×height of the reference test block are The wide surface is used as the detection surface; 2) Apply couplant on the detection surface of the reference test block, test the detection surface of the reference test block with the probe of the instrument through the wedge, and record the current gain of the instrument and the reflection of the through holes of different heights on the reference test block Amplitude height value, the reflection amplitude height value is plotted on the two-dimensional coordinate system, and connected with a smooth curve to draw a waste judgment line; Step 4. Detect the blade welds: apply coupling agent near the upper crown and lower ring welds of the blade to be tested, and use the wedge on the instrument probe to stick to and perpendicular to the centerline of the weld of the blade to be tested, and perform zigzag scanning and detection , the range of the probe moving back and forth should be greater than 2 times the thickness of the blade; Step 5. Defect record: Taking the waste judgment line as a reference, when the instrument shows that the height of the echo signal exceeds the waste judgment line during the detection process, it is determined that the reflector is a defect, and corresponding marks are made on the blade surface, and corresponding The height coordinate value records the defect burial depth; when the echo signal height is lower than the waste judgment line, it will not be recorded; according to the mark on the blade surface, it can finally detect whether there is a defect in the blade. 2. the detection method of water turbine stainless steel runner blade weld defect according to claim 1, it is characterized in that the length, width and height of the reference test block are respectively 320mm, 40mm, 100mm, and the inner diameter of the through hole is 3mm, There are 8 through-holes in total, and every 4 through-holes form a group. They are vertically arranged up and down in the height direction. The distance between the upper and lower sides of the through-holes is 20mm. The starting height of one group of through-holes is 10mm. ; The initial height of the other group of through holes is 20mm; the distance between the two groups of through holes and the side is 40mm.

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