JPH0365608A - Method and apparatus for measuring thickness of scale in piping - Google Patents

Abstract

PURPOSE:To enable accurate measurement of the thickness of a scale even when the thickness is small, by conducting an operation by a prescribed formula on the basis of a frequency interval and a velocity of sound transmitted through the metal material of a piping. CONSTITUTION:An ultrasonic contactor 3 is brought into contact with the outer periphery 1' of a piping 1 and an ultrasonic wave 11 is transmitted in the direction intersecting the axial line l of the piping 1 perpendicularly. Then, a boundary part ultrasonic echo 13 and an inner-peripheral part ultrasonic echo 15 generated by reflection on the boundary 12 between the piping 1 and a scale 2 and on an inner periphery 14 respectively are sent to a frequency analyzer 7 through a gate circuit 5. In the analyzer 7, a frequency interval DELTAf between energy peak parts 20 generated by the interference of the boundary part ultrasonic echo 13 with the inner-peripheral part ultrasonic echo 15 is determined. Next, the frequency interval DELTAf is inputted to an arithmetic unit 8, and the thickness of the scale 2 can be determined exactly from a preset velocity C of sound transmitted through a metal material and the frequency interval DELTAf between the energy peak parts 20 by a formula C/2DELTAf.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for measuring scale thickness in piping.

[Background Art] In a boiler, scale adheres to the inside of tubes such as a furnace wall tube and a superheating tube due to aging deterioration. For this reason, heat transfer from the outside of the tube to the inside of the tube is inhibited, and the tube temperature increases due to insufficient heat formation for the fluid inside the tube, which may lead to damage to the tube.

Therefore, conventionally, during periodic inspections, a part of the pipe was cut out and the tendency of scale adhesion was examined using a microscope. If the scale exceeded the allowable amount, the inside of the pipe was washed with acid to remove the scale. .

However, as mentioned above, when a part of the pipe was cut out to examine the scale adhesion, it was necessary to repair that part.

Therefore, as a non-destructive method to measure the scale thickness without cutting the pipe, as shown in Figs. The ultrasonic wave 11 transmitted from the sonic transmitter/receiver is transmitted from the ultrasonic probe 3 in a direction intersecting the axis l of the pipe 1, and the scale attached to the inner circumference 12° of the pipe i and the inner circumference 12° are transmitted. Boundary ultrasonic echo 13 reflected back from the boundary 12 with 2
and the time difference A when the inner circumference ultrasonic echo 15 reflected and returned from the inner circumference 14 of the scale 2 is received by the ultrasonic transceiver, and the image sound wave echo 13.15 is received by the transceiver.
t, and based on this time difference At, scale thickness dS
It is conceivable to obtain d, -Jt-C/2 (1). However, C is the speed of sound transmitted through the metal pipe.

[Problems to be Solved by the Invention] However, in the above measurement method, the scale 2 is thick and there is a time difference At, and as shown in FIG. If the boundary ultrasound echo 13 and the inner circumferential ultrasound echo 15 can be clearly distinguished, measurement is possible, but if the scale 2 is thin and the time difference At is small, the boundary ultrasound echo 13 and the inner circumference ultrasound echo 15 can be clearly distinguished. 13 and the inner circumferential ultrasonic echo 15 overlap to form a superimposed waveform, making it impossible to distinguish between the two and making measurement impossible.

That is, in the above measurement method, the thickness of scale 2 is 500 mm.
If it is more than μ, it can be measured, but if it is less than that, it cannot be measured. Note that t in FIG. 6 is the time from when the ultrasonic transmission wave 21 is emitted from the ultrasonic transceiver until it is returned and received by the ultrasonic transceiver as the boundary ultrasonic echo 13.

On the other hand, in large boilers, the steam flowing through the piping is at high temperature and high pressure, so strict management of scale thickness is required, and there is no point in measuring the thickness of about 100g1.Therefore, the above measurement method is meaningless. It is difficult to apply this method to large boilers, and even if it were applied, it would not be possible to accurately determine the scale thickness.

In view of the above-mentioned circumstances, the present invention has been made with the object of making it possible to accurately measure the thickness of the scale even when the thickness is thin.

[Principle of the present invention] First, the principle of the present invention will be explained with reference to FIGS. 2 and 13.

That is, the sound waves 18 and 19 emitted from the sound source A collide with the reflector 17 and are reflected, but the reflected ultrasound scattered waves t
g' and t9° spread as waves and interfere with each other. Now, if the wavelength of the sound wave is λ, the inclination of the reflector 17 is θ, and the interval between BC is d, then from the law of sound waves, 2d@sinθ-nλ...■ λ-C/f...(towards) holds true. Here, n is an integer, f is the frequency, and C is the speed of sound that travels through the metal pipe.

If we put the equation 0 into the equation Oi) and rearrange it, we get the ultrasound scattered wave 18
', the frequency fn at which an energy peak occurs due to interference at 19° is expressed by fyl - nC/2 d * sin θ - fhe,
The frequency interval Jf between is ΔfMfn−fn−.

-C/2d-sinθ-(V) becomes.

When measuring the thickness of the scale 2, since it is θ-90'', the equation (V) becomes d-C/2Δf...0D. However, it is assumed that Δf≠0.

Therefore, the thickness d of the scale can be measured by finding the frequency interval Δf of the energy beak portion 20 caused by the interference of sound waves using the same concept as in the case of interference fringes.

[Means for Solving the Problems] The method of the present invention transmits ultrasonic waves from an ultrasonic probe brought into contact with the outer periphery of a pipe in a direction perpendicular to the axis of the pipe, and Calculate the frequency interval between the energy peak parts from the frequency of the energy peak part caused by interference between the boundary ultrasound echo reflected at the boundary with the scale attached to the scale and the inner periphery ultrasound echo reflected at the inner periphery of the scale. , the thickness of the scale is determined by C/2At from the frequency interval and the sound speed transmitted through the pipe metal material (where Δf is the frequency interval and C is the sound speed transmitted through the pipe metal material), and the present invention The device includes an ultrasonic probe that emits ultrasonic waves in a direction perpendicular to the axis of the pipe, and a probe that transmits the ultrasonic waves to the ultrasonic probe and detects the inner circumference of the pipe and the scale attached to the inner circumference. an ultrasonic transmitter/receiver that receives boundary ultrasonic echoes reflected at the boundary and inner circumferential ultrasonic echoes reflected at the inner periphery of the scale, and frequency-analyzes both ultrasonic echoes input from the ultrasonic transceiver; A frequency analyzer that calculates the frequency interval between the energy peak parts caused by the interference of both ultrasonic echoes, and the scale thickness from the frequency interval of the energy peak parts obtained by the frequency analyzer and the speed of sound that travels through the pipe metal. It is equipped with a computing unit that calculates .

[Function] The ultrasonic waves emitted from the ultrasonic probe are reflected at the boundary between the inner circumference of the pipe and the scale, and are also reflected at the inner circumference of the scale. The frequency of the ultrasonic echo is analyzed, and the frequency interval of the energy peak is determined from the frequency of the energy peak caused by interference between the two ultrasonic echoes.The thickness of the scale is determined from the frequency interval and the speed of sound traveling through the pipe metal. is required. The thickness of the scale is calculated by C/2Δf, where Δf is the frequency interval and C is the speed of sound transmitted through the pipe metal material.

[Example] Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention. In the figure, 1 is a pipe such as a boiler pipe with scale 2 attached on the inner circumference 12°, 3 is a pipe 1 in contact with the outer periphery 1°, and an ultrasonic wave 11 is applied to the pipe 1. axis line! An ultrasonic probe 4 transmits ultrasonic waves to the ultrasonic probe 3 in a direction crossing the inner circumference 12' of the pipe l and the scale 2 attached to the inner circumference 12'. boundary with 12
An ultrasonic transceiver 5 receives the boundary ultrasonic echo 13 reflected from and returned from the scale 2 and the inner circumferential ultrasonic echo 15 reflected from the inner periphery 14 of the scale 2; 6 is an A/D converter that converts both ultrasonic echoes 13.15 given as analog signals from the gate circuit 5 into digital signals; 7 analyzes the frequency of both ultrasonic echoes 13.15 converted into digital signals from the A/D converter 6, and calculates the energy peak portion 20 (see Figure 1 @ 3) caused by interference between both ultrasonic echoes 13.15. A frequency analyzer for determining the frequency interval Δf; 8 is an energy peak portion 20 obtained by analysis by the frequency analyzer 7;
A calculator that calculates the thickness d of the scale 2 according to the 9D formula from the frequency interval Δf and the sound speed C transmitted through the pipe metal, which has been input in advance, and 9 is a display on a cathode ray tube or the like that displays the calculated thickness d of the scale 2. Apparatus, lO is measured scale 2
This is a recording device that records the thickness d of .

When measuring the thickness d of the scale 2 attached to the inner circumference 12゛ of the pipe l, the ultrasonic probe 3 is brought into contact with the outer circumference l° of the pipe l, and the The sound waves 11 are directed and emitted in a direction perpendicular to the axis I of the pipe 1.

A portion of the emitted ultrasonic wave 11 is reflected at the boundary 12 between the pipe 1 and the scale 2, and the other part is reflected at the inner circumference 14 of the scale 2, and the ultrasonic wave echo I3 at the boundary and the inner circumference generated by the reflection is The ultrasonic echo 15 is returned from the ultrasonic probe 3 to the ultrasonic transceiver 4 as an ultrasonic echo having a separated waveform or a superimposed waveform, and is input from the ultrasonic transceiver 4 to the gate circuit 5, and then input to the gate circuit 5. The ultrasonic echoes 13 and 15 thus obtained are outputted from the gate circuit 5 and sent to the frequency analyzer 7.

The frequency analyzer 7 divides the ultrasonic echo into fine frequency bands and determines the energy corresponding to each frequency band. From the results, it is determined that the boundary ultrasonic echo 13 and the inner circumferential ultrasonic echo 15 interfere. The frequency interval Δf between the energy peak portions 20 caused by this is determined (see FIG. 3).

The frequency interval At between the energy beak parts 20 is input to the calculator 8, and the calculator 8 scales the frequency interval Δf between the energy beak parts 20 and the preset sound speed C through the metal material using the 0D formula. The thickness d of 2 is determined, and the determined thickness d is displayed on the display device 9 or recorded on the recording device 10 as necessary.

The frequency interval Δf between the energy beak parts 20 can be determined regardless of the time difference between the image sound wave echoes 13 and 15 until the boundary ultrasonic echo 13 and the inner circumferential ultrasonic echo 15 return to the ultrasonic transceiver 4. Therefore, even if the thickness d of the scale 2 is small, it is possible to accurately measure the thickness d.

In addition, if the frequency interval/If between the energy peak parts 20 determined between the frequency bands is different from the frequency interval Δf determined between other frequency bands, the obtained frequency intervals Δ
The frequency band Δf is determined by taking the arithmetic mean of f.

In the embodiments of the present invention, a case has been described in which scale within boiler piping is measured, but the present invention is applicable not only to boiler piping but also to measurement of scale attached to various types of piping. Of course, various changes may be made within the scope.

[Effects of the Invention] According to the method and apparatus for measuring the scale thickness in piping of the present invention, even when the thickness of scale attached to the piping is thin,
The thickness can be determined accurately, and since there is no need to cut out the piping, various excellent effects can be achieved, such as shortening the inspection period and reducing inspection costs.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an embodiment of the method and apparatus for measuring scale thickness in piping according to the present invention, Fig. 2 is a conceptual diagram for explaining the present invention in detail, and Fig. 3 is a system diagram according to the principle of the present invention. A graph showing the frequency interval between the energy peaks of ultrasonic echoes; Fig. 4 is a front view for explaining a commonly considered method when measuring scale thickness without cutting the pipe; Fig. 5 The figure is a conceptual diagram to explain the reflection of ultrasonic waves in the same generally considered method, and Figure 6 shows the boundary between the inner circumference of the pipe and the scale and the scale of the ultrasonic waves emitted in the same commonly considered method. FIG. 4 is a diagram of an ultrasonic waveform showing a state when it is reflected at the inner circumference and returns. In the figure, 1 is the piping, 1゛ is the outer periphery, 2 is the scale, 3 is the ultrasonic probe, 4 is the ultrasonic transceiver, 7 is the frequency analyzer, 8 is the calculator, 11 is the ultrasonic wave, 12 is the boundary, 12゛ is the inner circumference, 1
3 is the boundary ultrasonic echo, 14 is the inner circumference, 15 is the inner circumference ultrasonic echo, 20 is the energy peak part, f is the frequency, Δ
f is the frequency interval between energy peak parts, C is the sound speed transmitted through the metal pipe, d is the thickness, and l is the axis line.

Claims (1)

[Claims] 1) Ultrasonic waves are emitted from an ultrasonic probe in contact with the outer periphery of the pipe in a direction perpendicular to the axis of the pipe to detect the inner periphery of the pipe and the scale attached to the inner periphery. Determine the frequency interval between the energy peak parts from the frequency of the energy peak part caused by interference between the boundary ultrasound echo reflected at the boundary and the inner periphery ultrasound echo reflected at the inner periphery of the scale, and calculate the frequency interval between the energy peak parts, and Measurement of scale thickness in piping, characterized by determining the thickness of the scale from the speed of sound traveling through the metal material of the piping by C/2Δf (where Δf is the frequency interval and C is the speed of sound traveling through the metal material of the piping) Method. 2) An ultrasonic probe that transmits ultrasonic waves in a direction perpendicular to the axis of the pipe, and a boundary between the inner circumference of the pipe and the scale attached to the inner circumference while transmitting ultrasonic waves to the ultrasonic probe. an ultrasonic transmitter/receiver that receives the boundary ultrasonic echoes reflected at the scale and the inner circumferential ultrasonic echoes reflected at the inner periphery of the scale; A frequency analyzer that determines the frequency interval between the energy peak parts caused by the interference of ultrasonic echoes, and a scale thickness that is calculated from the frequency interval of the energy peak parts obtained by the frequency analyzer and the speed of sound that travels through the pipe metal. A scale thickness measuring device in piping, characterized by being equipped with a calculation unit for calculating the thickness.