JPH04319660A - Method for detecting damaged pipe by ultrasonic inspection - Google Patents

Abstract

PURPOSE:To certainly detect a damaged pipe by evaluating the same by certainly grasping the propagation echo of a coated pipe even when the distance between test heads is changed in the title method detecting the damage of a pipe using ultrasonic waves. CONSTITUTION:An ultrasonic transmitting element and an ultrasonic detection element both of which are controlled in position by a driving control apparatus are arranged on both sides of a pipe to be inspected and the ultrasonic waves transmitted from the transmission element and propagated through the pipe to be inspected are detected by the detection element and the detection signal thereof is evaluated to detect the damage of the pipe to be inspected. The signal received by the detection element is selected by a multi-gate 11 composed of a plurality of gates of predetermined time width and the magnitude and propagation time of the detection signal selected by each gate and the data of an ultrasonic transmitting position obtained by the driving control apparatus are stored. The propagation wave of a pipe is selected from the propagation time difference and transmission position of the detection signal from the memory data and the damage of a pipe to be inspected is detected from the magnitude of the pipe propagation wave.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting broken tubes by ultrasonic inspection, which uses ultrasonic waves to detect breaks in tube bodies such as fuel rods of fuel assemblies for nuclear reactors.

0002

2. Description of the Related Art Conventionally, as a method for detecting damaged fuel rods in a fuel assembly for a nuclear reactor, a method using ultrasonic inspection has generally been used. That is, the fuel assembly is housed in an inspection pit filled with water for radiation shielding, and damaged fuel rods are detected based on the propagation state of ultrasonic signals. In this case, it is assumed that in the reactor fuel assembly, fuel rods (cladding tubes) 1 of the same diameter are regularly arranged in a grid pattern in a horizontal cross section as shown in FIG. 4(a). A fuel rod 1 is positioned between a transmitting test head 2 and a receiving test head 3, which are ultrasonic transmitters, and the ultrasonic signal transmitted by the transmitting test head 2 is received by the receiving test head 3, and its cladding propagation echo is detected. Damage to the fuel rod 1 is detected by evaluating. In addition, in FIG. 4(a), 4 is a transmitting side probe, 5 is a receiving side probe, and 6 is a guide tube.

In this case, the expected range (gate range) for each fuel rod 1 to be tested is determined in advance, and the cladding propagation echo is determined from the signal (direct echo) that reaches directly from the transmitting test head 2 to the receiving test head 3. By separating these, only the cladding propagation echoes can be evaluated with high accuracy.

This method determines in advance the starting point of the expected time range for each fuel rod 1 to be tested;
For the purpose of determining before the transmitting test head 2 and the receiving test head 3 are located between the transmitting test head 2 and the receiving test head 3, the transmitting test head 2 The transit time of the ultrasonic signal between the receiver test head 3 and the receiver test head 3 is measured, and from this value a constant value is selected so that the ultrasonic waves (orthogonal echoes) received during transit time measurement do not fall within the expected range. It is characterized by subtracting the value. That is, as shown in FIG. 4(a), before testing each fuel rod 1, the distance between the test heads, that is, the time TL between the transmitted pulse SI and the direct echo DE in FIG. 4(b) is determined.
After measuring , by setting the expected range 7 (B) starting from the point obtained by subtracting a certain value C from this time TL, the reception test head is set earlier than the direct echo DE as shown in Fig. 5. Only cladding propagation echoes UE reaching 3 will be obtained. With this method, even if the distance between the test heads changes for each test of each fuel rod 1, the expected range 7 can be followed for each cladding tube.

[0005]

[Problems to be Solved by the Invention] However, the above conventional method is a method in which the expected range 7 is followed for each fuel rod 1, and after setting the expected range 7 as shown in FIG. If this changes, the direct echo DE may fall within the expected range 7, or the cladding propagation echo UE may deviate from the expected range 7. That is,
The cladding tubes (fuel rods) are arranged in a grid pattern as described above, but some of them are replaced by control rod guide tubes 6 with larger diameters, so cladding tube propagation echoes UE from within the expected range 7 Sometimes it comes off. In such a case, it becomes impossible to separate the cladding propagation echo UE and the direct echo DE, and therefore there is a possibility that a damaged cladding tube (fuel rod) cannot be detected.

The present invention has been made in view of the above circumstances, and is an ultrasonic test that can reliably capture and evaluate cladding tube propagation echoes even when the distance between test heads changes, and can reliably detect damaged tubes. The purpose of the present invention is to provide a method for detecting broken pipes by using the following method.

[0007]

[Means for Solving the Problems] The present invention arranges an ultrasonic transmitting element and a receiving element whose positions are controlled by a drive control device on both sides of a tube to be inspected, and transmits an ultrasonic wave from the transmitting element to the tube to be inspected. In a method for detecting damaged pipes by ultrasonic inspection, in which a receiving element receives ultrasonic waves propagating inside the tube, and the received signal is evaluated to detect damage to the pipe to be inspected, the signal received by the receiving element is The received signal size and propagation time selected by each gate and the ultrasonic transmission position data obtained from the drive control device are stored in the stored data. The present invention is characterized in that a pipe propagating wave is selected from the propagation time difference of the received signal and the transmission position, and damage to the pipe to be inspected is detected based on the magnitude of the selected pipe propagating wave.

[0008]

[Operation] If the correspondence between the position of the tube to be inspected and the position of the test head (transmitting element and receiving element) is clear, select signals for each state of the test head from the recorded test head position signals. In addition, a plurality of signal propagation time signals and echo height data corresponding to the position signal can be obtained by multi-gate. The maximum echo height data in this data is a direct echo, that is, a direct echo in which the ultrasonic wave transmitted from the transmitting element directly reaches the receiving element without passing through the tube to be inspected. Therefore, based on the direct echo signal propagation time data at this time, by arranging the signal propagation times before and after this point in chronological order, we can calculate the direct echo signal propagation time and the echo height data corresponding to that data. It becomes possible to select. Then, damage to the tube to be inspected can be detected based on the propagation echo of the selected tube to be inspected.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show an example of detecting a damaged fuel rod in a nuclear reactor fuel assembly, in which the signals of the cladding propagation echo UE and the direct echo DE with respect to the test head position of the flaw detector are shown. Propagation time and echo height are shown. As the flaw detector, one with a multi-gate function, the details of which will be described later, is used.

FIG. 1(a) shows a transmission test head 2 and a reception test head 3 connected to a drive control device (Fig. (not shown) shows the state when inserted/extracted. As the cladding tube of the fuel rod 1, a metal such as a zirconium-based alloy is used, for example. The transmission test head 2 is connected to an evaluation device (not shown) via a transmission probe 4, and the reception test head 3 is connected to an evaluation device (not shown) via a reception probe 5.
connected to. In FIG. 1(a) above, state A is a case where the fuel rod 1 is not interposed between the test heads 2 and 3, and the ultrasonic waves from the transmitting test head 2 directly reach the receiving test head 3, and the direct echo DE Only exists. State B is a case where the fuel rod 1 is interposed between the test heads 2 and 3, and the ultrasonic wave from the transmitting test head 2 passes through the tube wall of the fuel rod 1 and reaches the receiving test head 3, and the cladding tube propagation Only echo UEs exist. Condition C is a case where the fuel rod 1 is interposed in a part between the test heads 2 and 3, and the direct echo DE and the cladding propagation echo UE coexist.

FIG. 1(b) corresponds to the state of the test heads 2 and 3 and the arrangement of the fuel rods 1 in FIG. 1(a),
The signal propagation time of the cladding propagation echo UE (solid line) and the direct echo DE (dashed line) obtained at each position of the test heads 2 and 3 is shown. In the figure, the section shown by a solid line is the section where the cladding propagation echo UE is obtained, and the section shown by the broken line is the section where the direct echo DE is obtained. The above cladding propagation echo UE is transmitted by the transmission test head 2.
The direct echo DE is a signal in which the ultrasonic waves output from the transmitting test head 2 do not pass through the tube wall of the fuel rod 1 and propagate underwater. It is a signal that propagates as is. The height of the echo changes due to attenuation. The direct echo DE passing through the water is not attenuated much despite its low propagation speed, so its level is relatively high. Further, since the cladding tube of the fuel rod 1 is usually made of metal as described above, the propagation speed of the cladding tube propagation echo UE is high, but the level is low.

FIG. 1(c) corresponds to the state of the test heads 2 and 3 and the arrangement of the fuel rods 1 shown in FIG. 1(a),
The echo heights of the cladding tube propagation echo UE (solid line) and the direct echo DE (broken line) obtained at each position of the test heads 2 and 3 are shown.

FIGS. 2(a) to 2(c) show the signals of the cladding propagation echo UE and the direct echo DE with respect to the test head position and the distance between the test heads when the distance between the test heads 2 and 3 changes. Propagation time and echo height are shown. Even in the case shown in FIG. 2, if the test heads 2 and 3 are located at the end positions of the fuel rods 1 as in the case of FIG.
E is mixed, but not in other positions. In addition, when cladding propagation echoes UE and direct echoes DE coexist,
The propagation time difference between each echo is approximately constant. Therefore,
By arranging the echo propagation time and echo height data of each test head position signal in chronological order, it is possible to separate the cladding propagation echo UE and the direct echo DE.

Therefore, in the present invention, using a flaw detector having a multi-gate function, the data of the echo propagation time and echo height of each test head position signal is arranged in chronological order and directly communicated with the cladding propagation echo UE. The echo DE is separated from the echo DE, and time-series data processing will be described below.

FIGS. 3(a) to 3(c) show the relationship between the echo signal propagation time and the echo height obtained in states A, B, and C of the test heads 2 and 3 shown in FIG. 1(a). ing. Note that FIG. 3 shows a case where five gates (a, b, c, d, e) are provided as the multi-gate 11 in the evaluation device. In other words, the multi-gate function is
When the ultrasonic wave emitted from the transmitting test head 2 is received by the receiving test head 3, the multi-gate 11 is activated according to the signal propagation time to select and extract the signal having the preset propagation time. This is what I did.

FIG. 3(a) shows the echo obtained in state A of FIG. 1(a), in which only a direct echo DE is generated at the receiving test head 3 in response to the transmitting pulse SI from the transmitting test head 2. is received, and the fourth
A state in which direct echo DE is taken out via gate d is shown.

FIG. 3B shows the echo obtained in state B of FIG. This shows a state in which only the UE is received and the cladding propagation echo UE is extracted via the second gate b in the multi-gate 11.

FIG. 3(c) shows an echo obtained in state C of FIG. 1(a), in which a cladding propagation echo is generated in the receiving test head 3 in response to the transmitting pulse SI from the transmitting test head 2. This shows a state in which the UE and the direct echo DE are received, the cladding propagation echo UE is extracted through the second gate b in the multi-gate 11, and the direct echo DE is extracted through the fourth gate d.

[0020] Thus, the position signals of each test head 2 and 3, that is, the position signals obtained from the head drive control device (not shown), and the propagation time and echo height of the echo obtained at each position are used as data. By recording and processing the data in time series, the cladding propagation echo UE and the direct echo DE are separated.

For example, the position of the fuel rod 1 and the test heads 2, 3
When the correspondence between the positions of A plurality of pieces of data (as many as the number of gates in the multi-gate 11) can be obtained. That is, in the example of FIG. 3, five signal propagation time signals and five echo heights are obtained. The maximum echo height data in this data is the direct echo DE. Therefore, based on the signal propagation time data of the direct echo DE at this time, the signal propagation times before and after this point are organized in chronological order. By selecting the echo DE, it becomes possible to select the signal propagation time of the direct echo DE and the echo height data corresponding to that data.

Next, regarding the cladding propagation echo UE, in state C, data with a certain time difference from the direct echo DE, that is, the echo already separated as described above (the second data of gate b)
By focusing on this and organizing the data in chronological order, it is possible to separate the cladding propagation echo UE. By performing the above processing for each fuel rod 1, the cladding propagation echo UE can be separated.

The evaluation is carried out by comparing and evaluating the echo heights of the cladding propagation echoes UE for each fuel rod 1 after the echo separation using an evaluation device. If the fuel rod 1 is damaged and liquid enters the cladding tube, the signal will be attenuated and the echo height will become low. By checking the echo height, the damaged fuel rod 1 can be detected accurately. can do.

In the above embodiment, the case of detecting a damaged fuel rod in a fuel assembly for a nuclear reactor has been described, but in addition,
It can be used to determine the presence of substances in pipes during maintenance and inspection of pipes in petroleum, chemical plants, etc.

[0025]

Effects of the Invention As detailed above, according to the present invention, even if the distance between the test heads changes, it is possible to separate and evaluate the cladding propagation echo and the direct echo. This allows for accurate detection of broken pipes.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the signal propagation time, echo height, and test head position of a cladding propagation echo and a direct echo in an embodiment of the present invention.

[Figure 2] Signal propagation time of cladding propagation echo and direct echo when the distance between test heads changes in the same example,
FIG. 3 is a diagram showing the relationship between echo height and test head position.

FIG. 3 is a diagram showing the relationship between echoes obtained in each state A, B, and C of the test head in FIG. 1 and a multigate.

FIG. 4 is a diagram showing a method for separating cladding tube propagation echoes and direct echoes in a conventional broken tube detection method using ultrasonic inspection.

FIG. 5 is a diagram showing a method for separating cladding tube propagation echoes and direct echoes in a conventional method for detecting a broken tube using ultrasonic inspection.

[Explanation of symbols]

1...Fuel rod, 2...Transmission test head, 3...Reception test head, 4...Sending side probe, 5...Receiving side probe, 6...Guide tube, 7...Expected range, 11...Multi-gate, DE...Direct echo, UE ...cladding tube propagation echo.

Claims (1)

[Claims] 1. An ultrasonic transmitting element and a receiving element whose positions are controlled by a drive control device are disposed on both sides of a tube to be inspected, and ultrasonic waves emitted from the transmitting element and propagating inside the tube to be inspected are In a method for detecting damaged pipes by ultrasonic inspection, in which a sound wave is received by a receiving element and the received signal is evaluated to detect damage to the pipe to be inspected, the signal received by the receiving element is detected by a plurality of gates with a predetermined time width. a selection means for selecting with a multi-gate, a storage means for storing data on the magnitude and propagation time of the received signal selected by each gate and the ultrasonic transmission position obtained from the drive control device, and data stored by this means. A method for detecting damage to a pipe to be inspected based on the magnitude of the selected pipe propagating wave by selecting a pipe propagating wave from among the received signals based on the propagation time difference and the transmission position. Method for detecting broken pipes using sonic testing.