JPH01244307A - Thickness measuring method of double-layered body - Google Patents

Abstract

PURPOSE:To measure the thickness of a double-layered body positively even when the difference of acoustic impedances between the layers is small, by calculating each thickness of said two layers based upon the receiving result of echoes of both waves from the reverse surface of said body. CONSTITUTION:The ultrasonic probes 3, 4 are provided on a double-layered body 1a, 1b which are transferred by a pair of pinch rollers 2, 2. The probe 3 projects transversal ultrasonic waves, while the probe 4 projects longitudinal ultrasonic waves, respectively in a vertical direction to the body. These ultrasonic waves are reflected respectively by the reverse surface of the body and received by the probes 3, 4. An operating unit 6 measures the time since each of the transversal and longitudinal ultrasonic waves is sent out until it is received. The operating unit calculates the thickness of each layer of the body 1 based on the measured result, and the total thickness of the body 1 from the sum total of the thicknesses of the two layers.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides an ultrasonic method to measure the thickness of each layer and the total thickness of a two-layer body such as a clad steel material made by laminating two layers of a base material and a laminate material. Concerning how to measure using.

[Prior art]

Crund steel materials, which are made by laminating high alloy steel with excellent corrosion resistance and low carbon steel or low alloy steel with high strength and bonding them metallurgically, are used, for example, in sour gas transport pipes or It has a wide range of use as a material for clad steel pipes, which are used in situations where the inside or outside is exposed to corrosive environments and economical efficiency is required, such as pipelines laid on the seabed. For clad steel materials used in such applications, it is important to accurately know not only the total thickness but also the thickness of each of the two layers.

Conventionally, as a method for measuring the thickness of such a two-layer body,
There are two methods: one using ultrasonic waves and the other using magnetic lines of force. In the former method, ultrasonic waves are incident from the surface of the two-layer body in a direction perpendicular to the two-layer body, and the echoes generated when the ultrasonic waves are reflected from the boundary surface and the back surface of the two layers are received, and the echoes from the boundary surface are This method calculates the thickness of the layer on the front side based on the time until the echo is received, and the total thickness based on the time until the echo from the back side is received. In a two-layer body where one is a magnetic material and the other is a non-magnetic material, a magnet with two magnetic poles is placed facing the surface of the non-magnetic material layer, and the amount of magnetic flux passing through the magnet is equal to that of the non-magnetic material. This is a method of measuring the thickness of a non-magnetic layer by utilizing the fact that it increases or decreases in accordance with the thickness of the layer.

[Problem to be solved by the invention]

However, in the former method, if there is no large difference between the acoustic impedances (a value obtained by multiplying the speed of sound in an object by the density of the object, and indicates the difficulty of sound waves passing through the object) in the two layers, the boundary There is a problem that the echo from the surface is small and difficult to detect, and depending on the combination of two layers, it may become difficult or impossible to measure the thickness of each layer.

For example, the acoustic impedance of two layers is Z.

In the case of Z2, the sound pressure reflectance r at the boundary surface is expressed by the following well-known formula.

2++22 Therefore, the ratio of the echo ■ from the boundary surface obtained in this case to the echo B from the back surface is as follows.Applying this formula to a general raft steel material made of carbon steel and stainless steel (JISSUS 304), Acoustic impedance Z of carbon steel, =46.3X10'kg/tm"s
and the acoustic impedance of SOS 304 Zz = 45
．． By substituting OX10hkg/m”s, I
/B is approximately 0.01, that is, the echo from the boundary surface is about one layer of the echo from the back surface, and it is clear that it is difficult to detect the echo from the boundary surface. In many clad steels, there is no large difference in acoustic impedance between the two layers, and the above-mentioned method cannot be applied to the thickness measurement of clad steel.

Furthermore, as mentioned above, the latter method is applicable only to two-layer bodies in which one layer is magnetic and the other is non-magnetic, and the range of application is limited. For example, if the object to be measured is a tube having a magnetic layer on the outside, the measurement must be carried out from the inside, making the measurement work difficult. Furthermore, only the thickness of the non-magnetic layer is measured by this method; if both thicknesses are required, the thickness of the magnetic layer can be measured by other methods, such as using ultrasound. There was the trouble of having to measure the total thickness using the method and then subtracting the thickness of the nonmagnetic layer from this measured value.

The present invention has been made in view of such circumstances, and is based on 2N
It is an object of the present invention to provide a thickness measuring method that can reliably and simultaneously measure the thickness of each layer of a body, or even the total thickness, regardless of the material of each layer.

[Means to solve the problem]

The method for measuring the thickness of a two-layer body according to the present invention is a method for measuring the thickness of each layer or the total thickness of a 2N body having two layers laminated in the thickness direction. A sound wave is made incident on each side of the two-layer body in a direction perpendicular thereto, and the echoes of both waves are detected from the back side of the two-layer body, and the time taken to detect the two waves is equal to The present invention is characterized in that each wave is measured and the thickness of each layer is calculated based on the remeasurement results.

[Effect]

In the present invention, the thickness of the two layers is calculated based on the reception results of echoes from the back side of longitudinal wave ultrasound and transverse wave ultrasound, without using echoes from the boundary surface, and the thickness of the two layers is calculated as the sum of both. Calculate the total body thickness.

〔Example〕

The present invention will be described in detail below based on drawings showing embodiments thereof. FIG. 1 is a schematic block diagram showing an embodiment of the method for measuring the thickness of a two-layer body according to the present invention (hereinafter referred to as the method of the present invention).

In the figure, 1 is a two-layer body formed by laminating an upper layer 1a and a lower layer 1b in the thickness direction, and the two-layer body 1 includes a pair of pinch rolls 2.
It is held between them and transported in a predetermined direction (to the right in the figure). In the figure, 3 is an ultrasonic probe that transmits and receives transverse ultrasound waves, and 4 is an ultrasound probe that transmits and receives longitudinal ultrasound waves. a predetermined distance apart from the surface of the two-layer body 10 (the upper
The ultrasonic waves emitted by each layer are transmitted to the inside of the two-layer body 1.
The beam is arranged so as to be incident in a direction perpendicular to the surface, that is, in the thickness direction.

As the ultrasonic probe 4 that vertically injects longitudinal ultrasonic waves,
Generally known probes may be used, and as the ultrasonic probe 3 that vertically injects transverse ultrasonic waves, for example, an electromagnetic ultrasonic method may be used to direct transverse ultrasonic waves into the interior of the object to be inspected. (see "Steel Manufacturing Research" No. 310, p. 374), or a device that converts longitudinal ultrasonic waves emitted by a vibrator into transverse ultrasonic waves by passing them through two types of wedges having a predetermined angle. etc. can be used.

Oscillation of ultrasonic waves from the ultrasonic probes 3.4 is performed according to an oscillation command signal from the common oscillation unit 5, and the ultrasonic waves from the ultrasonic probes 3.
The reception result of the reflected echo at 4 is sent to each separate receiving section 30.
．． 40 is input. The oscillator 5 includes
For example, each time the pinch rolls 2, 2 rotate by a predetermined amount, that is, each time the two-layer body 1 is conveyed by a predetermined distance, a pulse signal generated by a pulse generator 21 attached to the drive motor 2o is applied. The oscillating section 5 is configured to emit the oscillation command signal in accordance with this pulse signal.

FIG. 2 is an explanatory diagram of the progress state of the ultrasonic waves inside the two carcasses I, and FIG. 3 is a graph showing input signals in the receiving section 30, 40. As shown in FIG.
A part of it is reflected at the boundary surface of Both echoes travel in the opposite direction inside the two-layer body 1 and are received by the ultrasound probe 3 or 4.

Therefore, as shown in FIG.
A peak I accompanying the reception of the boundary surface echo and an echo B accompanying the reception of the back surface echo appear. Note that T in the figure is a peak associated with ultrasonic oscillation. As mentioned above, the conventional 2
In the method for measuring the thickness of a layered body, the time from the point of ultrasonic oscillation to the appearance of peaks 1 and 1, respectively, is 1.
and t2, respectively, and the thickness sI of the upper layer 1a is determined from the former.
and the total thickness S of the 2N body 1 from the latter. are calculated respectively, and the lower layer 1
The thickness s2 of b is 3. It is calculated by subtracting . Therefore, the thicknesses s and s2 of both layers could be measured only when the peak (2) had a sufficient height.

In the method of the present invention, only the time until the appearance of peak B, which occurs with the reception of the bottom echo, is used, without using the peak I that accompanies the reception of the boundary echo. That is, the receiving sections 30 and 40 monitor each input signal, detect the time until a peak exceeding a preset value appears, and output respective signals corresponding to the detection results. The predetermined value is set to be smaller than the expected level of the peak B and larger than the expected level of the peak I. Therefore, the output signal of the receiving unit 30 corresponds to the time it takes for the backside echo to be received by the transverse ultrasonic waves emitted by the ultrasonic probe 3, that is, the time it takes for the transverse ultrasonic waves to reciprocate between the front and back surfaces of the two carcasses 10 in the thickness direction. The output signal of the receiver 4o corresponds to the time required for the longitudinal ultrasound emitted by the ultrasound probe 4 to travel back and forth between the front and back surfaces of the two-layer body 1 in the thickness direction. handle.

The output signals of the receiving units 30 and 40 are input to the calculation unit 6, and the calculation unit 6 processes the output signals from the upper layer 1 in a procedure as described below.
The thickness of a, S, and the thickness s2 of the lower layer 1b are calculated, and the calculation results are output to the display section 7 and displayed on the display section 7. The output signal of the receiving section 40 attached to the ultrasonic probe 4 on the downstream side in the conveyance direction of the two-layer body 1 is directly given to the calculation section 6, but is not transmitted to the ultrasonic probe 3 on the upstream side in the conveyance direction. The output signal of the accompanying receiving section 3o is first stored in a storage section 31, and then provided from the storage section 31. This is to simultaneously input the respective outputs corresponding to the same point on the two-layer body 1 to the calculation section 6. To achieve this, the distance between the ultrasonic probes 3 and 4 is is set to an integer multiple of the transport distance of the two-layer body 1 between the ultrasound oscillation points, and for example, the separation distance between the ultrasonic probes 3 and 4 is one time the transport distance. In this case, the storage section 31 outputs the stored contents at the same time as the next input signal is given from the reception section 30, and further stores the output signal anew.

The calculation unit 6 is given the round trip time of the transverse wave ultrasound and the round trip time of the longitudinal ultrasound as described above.
The propagation velocities of the transverse wave ultrasound and the longitudinal ultrasound in the lower layer 1b are input in advance, and the calculation unit 6 calculates the thicknesses s and s2 from these respective values.

That is, the round trip time of the transverse ultrasonic wave is 2·t, and the upper layer 1a
and the propagation velocity of the transverse ultrasonic wave in the lower layer 1b are respectively V,
and ■2, the following equation holds true.

V, 　　　V.

On the other hand, the round trip time of the longitudinal ultrasound is 2·t4, and the upper layer 1a
and the propagation velocity of the longitudinal ultrasound in the lower layer 1b are respectively v1
and v2, the following equation holds true as well.

■I ■2 Equations (3) and (4) are simultaneous equations in which S and S2 are unknowns, and by solving them, the following equations giving s and S2, respectively, are obtained.

The calculation unit 6 calculates the above j from the output signal of the reception unit 30.40.
ff+t4, respectively, and substitute them into the above equations (5) and (6) to calculate the thickness Sl of the upper layer 1a and the thickness S2 of the lower layer 1b, respectively, and further calculate 2 if necessary.
The total thickness S0 of the layered body 1 is calculated as the sum of the above S1 and 32.

As is clear from equations (5) and (6), the ratio between the propagation velocity of the transverse ultrasonic wave in the upper layer N1a, ■, and the propagation velocity of the transverse ultrasonic wave in the lower layer, 1b, is As long as the ratio between the propagation velocity v1 of the sound wave and the propagation velocity Vg of the longitudinal ultrasound in the lower layer 1b is different, in other words, as long as the denominators of equations (5) and (6) are not O, the calculation unit 6 Although the calculation is possible.

The denominator of both equations is O when the Poisson's ratio of the upper layer 1a and that of the lower layer 1b match, and in the combination of materials commonly used for clad steel materials, the Poisson's ratio of both materials is different. is known, so as long as the material of the upper layer 1a and the material of the lower layer 1b are different, it is possible to calculate the thickness of both layers using equations (5) and (6) regardless of the materials of both layers. be.

〔effect〕

As described in detail above, the method of the present invention involves injecting longitudinal ultrasound waves and transverse ultrasound waves from the surface of a two-layer body, and
Since the thickness of the two layers is calculated based on the echo reception results of both waves from the back side of the f-body, regardless of the materials of both layers,
For example, even if there is only a very small difference in acoustic impedance between the two layers, as long as the materials of the two layers are different, it is possible to reliably measure the thickness of the two-layer structure, and other excellent effects can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a schematic block diagram showing the implementation state of the method of the present invention, Fig. 2 is an explanatory diagram showing the propagation state of ultrasound inside the two-layer body, and Fig. 3 is an example of the output signal of the ultrasound probe. This is a graph showing. 1...2-layer body 1a...Upper Jl ib...
Lower layer 3.4...Ultrasonic probe 6...Calculation section frame
Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney
Noboru Kono, HusbandFigure 2Figure 3

Claims (1)

[Claims] 1. A method for measuring the thickness of each layer or even the total thickness of a two-layer body having two layers laminated in the thickness direction, comprising: From the surface of the two-layer body,
The echoes of both waves are detected from the back surface of the two-layered body, and the time until this detection is made is measured for each of the two waves, and the results of both measurements are A method for measuring the thickness of a two-layer body, characterized in that each thickness is calculated based on the above.