JP2617914B2 - Method for measuring liner thickness of double pipe and biaxial follower for ultrasonic probe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring a liner thickness of a double pipe and a two-axis tracking device for an ultrasonic probe.

(Prior art) For applications such as nuclear fuel cladding tubes and oil well tubes, zircaloy (Zr alloy) tubes with pure zirconium lining on the inner surface or carbon steel tubes with stainless steel lining on the inner or outer surface are used. ing. Pipes in which different kinds of metals (liners) having different functions such as corrosion resistance are bonded to the inner and outer surfaces of these base metal pipes are generally called double pipes or liner pipes. Measuring the thickness of the relatively thin liner described above has become important in quality control.

For example, a zircaloy liner tube for a cladding tube used in a light water cooled reactor has a liner of a pure zirconium layer adhered to the inner surface of the tube. A technique for measuring the thickness of the liner from the stage of the raw tube before being made into a product tube is indispensable.

Therefore, conventionally, a method has been adopted in which both ends of the pipe are cut and sampled, and the liner thickness is measured in a gold phase.

(Problems to be Solved by the Invention) However, in the conventional method of measuring by cutting both ends of the pipe, although the liner thickness at that portion can be measured, there is a drawback that the liner thickness cannot be guaranteed over the entire surface and the entire length of the pipe. Was.

In addition, since both ends of the pipe are sampled, there is a problem that the material yield is reduced due to the destruction sample.

Furthermore, for example, in the case of the Dicaloy liner tube,
The liner is relatively thin, about 1.6 mm, for the thickness of the base material pipe of 10 mm, and although there was an attempt to continuously measure such a thin liner thickness by a non-contact measurement method, There were problems such as bending due to the raw tube, and it was not enough to guarantee the thickness of the liner over the entire surface and the entire length of the tube.

The present invention has been made in view of such conventional problems, and provides a double pipe liner measuring method capable of accurately measuring the thickness of the double pipe liner over the entire pipe length using ultrasonic waves, and its method. It is an object of the present invention to provide a two-axis ultrasonic probe follow-up apparatus which can surely follow the bending of a double tube during measurement.

(Means for Solving the Problems) The method for measuring the liner thickness of a double pipe according to the present invention comprises immersing a double pipe 2 having a liner thickness of about 1.6 mm, such as a Zircaloy liner base pipe, in water, While moving the tube in the axial direction while rotating the tube around the axis, the ultrasonic probe 5 makes the ultrasonic wave incident on the ultrasonic wave from the surface of the double tube and receives the reflected echo. When measuring the liner thickness of at least one of the inner surface and outer surface of the tube by performing time measurement, the frequency of the ultrasonic probe is set to 10 MHz or more so that the sensitivity of the boundary echo I of the double tube 2 is increased. The ultrasonic probe 5 is any one within the range of 15 MHz and has a wide band, and uses lead niobate as the ultrasonic probe 5.

The ultrasonic probe according to the present invention has a two-axis
A holding table 26 is disposed above the heavy pipe 2 and supported by a following roller 31 that rolls on the double pipe 2 so as to be able to follow and move vertically and horizontally. Horizontal axis 27
Are disposed on the left and right sides of the double pipe 2 with a gap between the pair of left and right support bases 24 supported through the double pipe 2 and are attached to each support 24 so as to be vertically adjustable. A pair of left and right ultrasonic probes 5, an adjusting screw 28 provided between the holding table 26 and each support 24 and adjusting a gap between the double pipe 2 and each ultrasonic probe 5; And a pair of left and right bearing bodies 33 which are provided on the frame 35 so as to be vertically movable and support both ends of the horizontal shaft 27.

(Example) Hereinafter, the flaw detection method of the present invention will be described with reference to the illustrated example.

FIG. 1 shows an outline of a measuring device for carrying out the flaw detection method of the present invention, 1 is a water tank, 2 is a zircaloy liner tube as a test material, and is immersed in water 3 of a water tank 1. It is transported in the axial direction while rotating around the axis by the tube rotation drive roll feeder 4. An ultrasonic probe 5 transmits an ultrasonic beam from the surface to the liner tube 2 and receives a reflected echo. The ultrasonic probe 5 is perpendicular to the axis of the liner tube 2 by a two-axis follower 22. The ultrasonic probe 5 is a broadband type in order to prevent the influence of crystal grains of the tube material.

Reference numeral 6 denotes a measuring device, which includes a power supply circuit 7, a synchronization circuit 8, a transmission circuit 9, a reception circuit 10, a time axis sweep circuit 11, a cathode ray tube 12, and the like. The synchronizing circuit 8 repeatedly generates a synchronizing signal of the frequency selected by the frequency changeover switch, and triggers the time axis sweeping circuit 11 and the transmitting circuit 9 with the synchronizing signal. The time axis sweep circuit 11 generates a horizontal sweep voltage for the time axis sweep of the cathode ray tube 12 when triggered by the synchronization signal, and is triggered before the transmission circuit 9 is triggered due to a delay in synchronization so as to start the sweep. Has become. The transmission circuit 9 generates a high-frequency pulse when triggered by the synchronization signal and adds it to the probe 5.
For transmitting ultrasonic waves from Receiving circuit 10
Is for amplifying and detecting a high-frequency pulse when the probe 5 receives the reflected echo of the ultrasonic wave reflected from the liner tube 2 side, converts it into a video signal, and sends the video signal to the cathode ray tube 12. The sensitivity can be adjusted.

Reference numeral 14 denotes a thickness measuring module circuit, which measures the time between reflected echoes by a predetermined measuring method using a video waveform and a synchronization signal obtained from the measuring device 6, and uses the sound velocity set value and the internal electronic circuit to determine the thickness of the liner base tube 2. The value is converted to an analog voltage proportional to the value. Reference numeral 16 denotes a data processing circuit, which inputs thickness data, and when the value exceeds a preset value, processes the data to calculate the thickness.
It is incorporated in the thickness measurement module circuit 14. Numeral 18 denotes a special attenuation DAC circuit for attenuating and removing a reflected echo reflected from the inner surface of the liner tube 2 and delayed after the first bottom echo.

15 is a thickness display and upper and lower limit alarm module circuit, 17 is an alarm output signal processing circuit, and 20 is a sensor amplifier. The thickness display and upper and lower limit alarm module circuit 15 displays the measured liner thickness, and the optical sensor 19 controls the liner tube 2.
Is detected, a warning is issued if the thickness exceeds the upper and lower limits. 21 is a switch circuit.

The two-axis follow-up device 22 is configured as shown in FIG. 2 and FIG. That is, the probes 5 are arranged in a pair on the left and right with the liner tube 2 interposed therebetween.
It is attached to the lower end of. The vertical shaft 23 is vertically and rotatably inserted into the support 24, and the axis of the probe 5 is perpendicular to the axis of the liner tube 2 by the fixing screw 25 screwed into the support 24. The thickness of the liner is fixed so as to be adjustable vertically and rotationally so as to be vertical, that is, by applying an ultrasonic longitudinal wave to the surface of the material to be inspected perpendicularly. The support 24 is vertically attached to a holding table 26 disposed on the liner tube 2.
It is slidably supported in the left-right direction by the horizontal shaft 27 of the book. Each support 24 is slidably adjustable along a horizontal axis 27 by turning a screw adjustment screw 28 supported only on a holding table 26 so as to be rotatable only with an adjustment handle 29.
In addition, each support 24 is positioned at a position where the probe 5 and the liner tube 2 are at a predetermined gap water distance, and is fixed to the upper and lower horizontal shafts 27 by fixing screws 30 screwed into the support 24. Is fixed. The lower end of the holding base 26 has a bifurcated shape, and at each end thereof, four follow-up rollers 31 on the front and rear and left and right that roll on the liner tube 2 are freely rotatably supported by a support shaft 32. I have. The left and right ends of the upper and lower two horizontal shafts 27 are slidably supported by bearings 33, and each bearing 33 has a vertical axis 34,
Numerals 34 are inserted into a bearing cylinder 36 fixed on a frame 35 so as to be slidable up and down, and are connected to each other by a connecting plate 37 at the upper end. One end of the frame 35 is pivotally supported on a bracket 38 on the water tank 1 by a support shaft 39 so as to be vertically rotatable, and the other end is detachably attached to the bracket 40 by a fixing screw 41. Reference numeral 42 denotes a vertical adjustment knob for vertically adjusting the vertical shaft 23, and reference numeral 43 denotes a rotation adjustment lever for rotating and adjusting the vertical shaft 23, which is attached to an arm 44 fixed to the vertical shaft 23. 45
Is a fixed knob for stopping the rotation of the vertical shaft 23 via the arm 44. The photo sensor 19 for detecting the liner tube 2 is
It is attached to both sides of the holding base 26.

The following is used as the probe 5.

Test frequency: 10MHz to 15MHz Frequency characteristics: Broadband type Lens dimensions and shape: Line focus Length Effective diameter 3 x 0.5mm (-3db) Material: Lead niobate Focal length: 10 to 15mm Liner using the measuring device with the above configuration The ultrasonic measurement of the thickness of the liner portion 2a of the pure zirconium layer adhered to the inner surface of the raw tube 2 by the water immersion method is performed as follows.

First, the liner blank 2 is passed through the water 3 in the water tank 1, placed on the feeder 4, and the probe 5 supported by the biaxial follower 22 is set as shown in FIG. In this case, the vertical shaft 23 is adjusted up and down so that the axis of the probe 5 is oriented in a direction perpendicular to the axis of the liner tube 2, and the rotation is adjusted around the axis. Then, the feeder 4 causes the liner tube 2
Is rotated at a predetermined feed rate in the axial direction while rotating about the axial center, and ultrasonic waves are incident from the tube surface by the probe 5,
The reflected echo is received.

That is, when a high-frequency pulse is applied to the probe 5 from the transmission circuit 9 of the measuring device 6, the probe 5 transmits an ultrasonic wave and makes the ultrasonic wave enter from the tube surface into the inside. Then, as shown in FIG. 4, the ultrasonic wave is reflected on the surface, the boundary surface and the bottom surface of the liner tube 2, respectively, so that the probe 5 sequentially receives the surface echo S, the boundary echo I and the bottom surface echo B. Then, the signal is converted into a high-frequency pulse and sent to the receiving circuit 10. Then, the receiving circuit 10 amplifies and detects the received signal, converts it to a video signal, and sends the video signal to the CRT 12 of the display circuit.
The reflected echo waveform appears above. This entire process is repeated at the frequency selected by the repetition frequency switch.

In the thickness measuring module circuit 14, the time between the boundary echo I and the bottom echo B is measured by a predetermined measuring method using the video waveform and the periodic signal obtained from the measuring device 6, and the liner pipe 2 is measured from the measured time and the sound velocity set value. An analog voltage that is proportional to the thickness of the liner is converted, and the data processing circuit 16
Calculate the thickness of 2a. Then, the thickness is displayed and recorded by the thickness display and upper / lower limit alarm module circuit 15. The thickness measurement in this case is started by switching the mode switch of the thickness measurement module circuit 14. Which echo is measured is set by the echo height determined by the measuring device 6 and the gate blocking level measured by the level control (determining at what percentage of the echo height the measurement gate is closed).

If the sensitivity of the receiving circuit 10 for detecting the boundary echo I at the boundary between the liner tube 2 and the liner section 2a is increased, the pulse width of the bottom echo B of the liner section 2a is increased.
Also, depending on the setting conditions of the search probe 5, etc., the bottom echo B
After that, other echo signals are generated, so it is necessary to eliminate the influence of these echoes and the like. Therefore, the attenuation DAC circuit 1
8 attenuates the reflected echo that is delayed later than the bottom echo B, and the subsequent reflected echo prevents the influence.

Also, the pulse width is narrowed so that the resolution and the S / N ratio at the time of measurement are increased, and the boundary echo I and the bottom echo B of the liner 2a can be reliably resolved even when the high sensitivity is set. That is, if the pulse width is large as shown in FIG. 4 (a), it becomes a disturbance factor when the amplification degree is increased. Therefore, if lead niobate is used as the transducer of the probe 5 and the pulse width of each echo is made as small as possible and the resolution and S / N ratio are made large as shown in FIG. The liner thickness can always be measured accurately without causing disturbance.

When measuring the thickness by ultrasonic waves, if there is a bend or the like in the liner tube 2, the follower roller 31 that contacts and rolls with the bend.
An external force in the up-down and left-right directions acts on the holding large 26 via the, and the holding base 26 and the support 24 integrally move left and right in the direction of the horizontal axis 27 and move up and down in the direction of the vertical axis 34. Therefore, the probe 5 follows the bend while maintaining a constant relationship with the liner tube 2 while maintaining the gap and the center thereof at ± 0.1 mm or less, without causing displacement. , It is possible to receive signals from the boundary surface under stable conditions.

Next, the results of an experiment performed by ultrasonic measurement using the ultrasonic probe 5 will be described. The following table shows the experimental results when the thickness of the liner portion 2a is measured ultrasonically by the water immersion method while changing the type of the ultrasonic probe 5.

The GAIN value in the above table means that the boundary echo I is 80
This is the GAIN value when it is set to%.

 From the above results, the following becomes clear.

When the frequency of the ultrasonic wave is 10 MHz, the sensitivity is the best. When the frequency is 10 MHz or less, the resolution is insufficient, and when the frequency is 15 MHz or more, the attenuation in the double tube 2 is large, and the measurement becomes impossible.

In addition, the line shape is considered to be the best as the focal point shape. In a flat, the sound pressure of the side lobe escapes and sensitivity decreases. In spot focus, the beam diameter is small.

In the embodiment, the case where the liner thickness on the inner surface of the tube is measured is exemplified. However, when the liner thickness on the outer surface is measured, the time between the surface echo S and the boundary echo I may be obtained. It is also possible to measure the liner thickness on both inner and outer surfaces.

(Effects of the Invention) According to the measuring method of the present invention, an ultrasonic wave is made incident from the surface of the double tube 2 by the ultrasonic probe 5 and the reflected echo is received, and the time of the reflected echo is obtained by the vertical method. When measuring the liner thickness of at least one of the inner surface and the outer surface of the pipe by performing the measurement, the frequency of the ultrasonic transducer is set to 10 MHz to 15 MHz so that the sensitivity of the boundary echo I of the double pipe 2 is increased. Since it is either within the range and the band is broadband and lead niobate is used as the ultrasonic transducer, the ultrasonic beam can be generated by a broadband probe experimentally determined from many prototype probes. By narrowing down to the line focus type, the measurement becomes possible, and the reflected echo can be received with good sensitivity without a lack of resolution or an increase in attenuation in the double tube 2. 2 liners The thickness, it is possible to directly measure using an ultrasonic vibrator 1 frequency, it requires without influence of attenuation by grain such Zry alloy layer, double pipe 2
Can be accurately measured.

The reason why the frequency of the ultrasonic vibrator is in the range of 10 MHz to 15 MHz and the band is wide, and lead niobate is used as the ultrasonic vibrator, is as follows. In general, when performing ultrasonic thickness measurement, it is said that the frequency f used for the measurement can be obtained by an equation represented by λ = C / f λ: wavelength C: sound velocity.

In this case, as in a double tube, a boundary in a multilayer structure,
To properly detect the thickness of the liner layer, the wavelength λ
Is required to have a wavelength of 1/2 or less of the thickness of the liner layer.
Japanese Patent Application Laid-Open No. Sho 60-12210 has been proposed based on such a principle of the basic ultrasonic thickness measurement.

On the other hand, it is known that the resolution of an ultrasonic thickness gauge decreases as the wavelength increases, and a high frequency is required to obtain a high resolution. When the size (thickness) to be measured increases, attenuation in a material using a high frequency decreases, and the sound pressure reflectance decreases. In other words, a reflected wave cannot be detected and measurement becomes impossible.

The resolution of the ultrasonic thickness gauge depends on the resolution of the ultrasonic transducer. In particular, when measuring the thickness of the liner tube, it is necessary to sharply separate the signals of the reflected waves from the boundary echo and the bottom surface echo. For this purpose, it is important to select a material that does not leave any after-waves as the vibrator. .

Therefore, from the viewpoint as described above, like a Zircaloy liner tube, the base material tube thickness is 10 mm and the liner thickness is 1.6 m
As a result of repeating various experiments including the material of the vibrator for measuring the liner thickness of the inner layer from the outside of the relatively thick tube having a relatively large thickness, the frequency was changed to a broadband type of 10 MHz to 15 MHz and its ultrasonic wave By using lead niobate as the vibrator, the liner thickness of the double pipe 2 can be measured with high accuracy.

According to the biaxial follower according to the present invention, the follower roller 31 disposed above the double pipe 2 and rolling on the double pipe 2
And a pair of left and right supports 24 supported on the left and right sides of the holding table 26 via a horizontal shaft 27, and a double pipe 2. Are disposed on both left and right sides of the double pipe 2 with a gap between
A pair of left and right ultrasonic probes 5 which are attached to the top 24 so as to be vertically adjustable;
An adjusting screw 28 for adjusting the gap between the heavy tube 2 and each ultrasonic probe 5;
27 is provided with a pair of left and right bearings 33 that support both ends of the dual tube 27. Therefore, even when the measurement is carried out while rotating the double tube 2 around the axis and moving in the axial direction, the double tube 2 The pair of left and right ultrasonic probes 5 can reliably follow the pair 2, and the liner thickness of the double tube 2 can be accurately measured over the entire surface and the entire length of the double tube 2 using ultrasonic waves.

[Brief description of the drawings]

1 shows an embodiment of the present invention, FIG. 1 is a block diagram of the entire measuring apparatus, FIG. 2 is a front view of a follow-up mechanism, FIG. 3 is a side view of the same main part, and FIG. It is. 1 ... water tank, 2 ... zircaloy liner tube, 2a ... liner part, 5 ... ultrasonic probe, 6 ... measuring instrument, 14 ...
Thickness measurement module circuit, 18 ... Special attenuation DAC circuit, 22
…… Two-axis follower, 24 …… Support, 26 …… Stand, 27…
... horizontal axis, 28 ... adjustment screw, 33 ... bearing body, 35 ... frame.

Claims (2)

(57) [Claims] A double pipe (2) having a liner thickness of about 1.6 mm, such as a Zircaloy liner pipe, is immersed in water.
While moving the heavy pipe (2) in the axial direction while rotating it around the axis, the ultrasonic probe (5) enters the ultrasonic wave from the surface of the double pipe (2) and receives the reflected echo thereof. When measuring the liner thickness of at least one of the inner surface and outer surface of the pipe by measuring the time of the reflected echo by the vertical method, the sensitivity of the boundary echo I of the double pipe (2) is increased. ,
The ultrasonic probe (5) has a frequency in the range of 10 MHz to 15 MHz, has a wide band, and uses lead niobate as the ultrasonic probe (5). Method for measuring liner thickness of heavy pipes. 2. A holding member which is disposed above the double pipe (2) and is movably supported in the vertical and horizontal directions via a following roller (31) which rolls on the double pipe (2). Stand (26)
And a double pipe (2) with a gap between a pair of left and right supports (24) supported on the left and right sides of the holding table (26) via a horizontal axis (27) and the double pipe (2). A pair of left and right ultrasonic probes (5) arranged on the right and left sides of the tube (2) and attached to each support (24) so as to be vertically adjustable, a holding table (26) and each support (24) An adjusting screw (28) provided between the ultrasonic probe and the ultrasonic probe (5) of the double tube (2) to adjust a gap between the ultrasonic probe (5) and
It is provided on the frame (35) so that it can move up and down, and the horizontal axis (27)
And a pair of left and right bearing bodies (33) for supporting both sides of the ultrasonic probe.