JP4394415B2 - Plate thickness relative comparison method and plate thickness relative comparison apparatus using electromagnetic pulses - Google Patents

Description

  The present invention relates to a plate thickness relative comparison method and a plate thickness relative comparison apparatus using electromagnetic wave pulses capable of detecting corrosion of, for example, a steel pipe covered with a heat insulating material. More specifically, at a plurality of measurement points, the electromagnetic wave pulse is transmitted from the transmitter to a steel material located at a position separated from the transmitter and receiver of the electromagnetic wave pulse and received by the receiver, and the received pulse at each measurement point. The present invention relates to a plate thickness relative comparison method using an electromagnetic wave pulse for relatively comparing plate thicknesses of the steel materials.

As a plate thickness relative comparison method using an electromagnetic wave pulse as described above, for example, an invention as described in Patent Document 1 is known. In the invention, as shown in FIG. 4 of the same specification, an infinitely thick conductor wall produces a straight response in the relationship between the decay time and the amplitude. It is known to attenuate at a large rate.
JP-A-1-202654

  Therefore, it is expected that the plate thicknesses are relatively compared by obtaining the inflection point of the attenuation waveform, but the specific technique is not disclosed in the above publication. In addition, this inflection point does not appear clearly in the received waveform, and it is very difficult to identify the inflection point itself. In fact, the received waveform has a lot of noise, and it has been extremely difficult to stably estimate the inflection point by approximation.

  An object of the present invention is to provide a plate thickness relative comparison method and a plate thickness relative comparison apparatus using electromagnetic wave pulses capable of relatively comparing plate thicknesses even under noisy environments.

  In order to solve the above-described problem, the feature of the relative thickness comparison method using electromagnetic pulses according to the present invention is that a plurality of measurement points are formed from the transmitter to a steel material existing at positions separated from the transmitter and receiver of the electromagnetic pulse. A method for comparing relative thicknesses of electromagnetic waves by transmitting electromagnetic waves and receiving them by the receiver and relatively comparing the thicknesses of the steel materials using the received pulses at each measurement location. Each axis is displayed on a logarithmic scale, and the received pulse is approximated by a linear approximation and a quadratic curve, and the gradient reference value in the quadratic curve is set to a value lower than the gradient of the straight line, and the gradient in the quadratic curve approximation portion Is obtained for each of the measurement points, and the steel material is determined based on the value of the time axis or the plate thickness equivalent value based on the value of the time axis. It is to relative comparison thickness.

  According to the same feature, the inflection point is obtained in the vicinity of the boundary between the straight line approximation portion and the curve approximation portion. In order to accurately perform curve approximation of the obtained data, it is ideal to perform approximation using a curve that can include higher-order parameters with a higher degree of freedom. However, according to experiments by the inventors, it has been found that high-dimensional curve approximation is easily affected by noise, and the position evaluation of the inflection point is inaccurate while performing high-precision curve approximation. Although such a tendency was also observed in the cubic curve approximation, it has been found that the position evaluation of the inflection point is performed remarkably accurately by using the quadratic curve approximation. In other words, when a quadratic curve is used, the curve approximation near the inflection point is not greatly influenced by noise due to the effect of noise as in the cubic curve approximation, and the quadratic curve approximation as a whole is skillfully performed. Using it, we succeeded in substantially canceling out the influence of noise near the inflection point. As a result, the value of the time axis at the point where the gradient in the quadratic curve approximation portion matches the reference value of the gradient can be obtained stably. Note that the lower limit amplitude of the received pulse can be substantially limited by the lower limit input unit. In the embodiment of the present invention, the amplitude lower limit value of the received pulse can be limited by the Y-axis lower limit field S2a, and an error in curve approximation due to noise or the like can be reduced. Further, when the degree of attenuation can be estimated, the amplitude lower limit value of the received pulse may be substantially limited by the X-axis field S1b which is a time axis.

The plate thickness equivalent value may be obtained by L = C · (10 ^T ) ^1/2 (where L is a plate thickness equivalent value, C is a plate thickness conversion coefficient, and T is a time axis value. is there.). Even if the steel material is covered with, for example, a heat insulating material and an exterior material, the relative thickness can be compared.

The characteristic of the plate thickness relative comparison device using electromagnetic pulses that can be used in the above-described method for comparing plate thickness using electromagnetic pulses is characterized by having an electromagnetic pulse transmitter and receiver, and these transmitters at a plurality of measurement locations. And electromagnetic wave pulses are transmitted to and received from a steel material located at a position separated from the receiver, the time and amplitude axes are substantially displayed on a logarithmic scale, and the received pulses are approximated by a linear approximation and a quadratic curve. The reference value of the gradient in the quadratic curve is set to a value lower than the gradient of the straight line, and the value of the time axis at the point where the gradient in the quadratic curve approximation portion coincides with the reference value of the gradient is determined for each measurement point, The thickness of the steel material is relatively compared based on the value of the time axis or the value corresponding to the thickness based on the value of the time axis.

  As described above, according to the present invention, using the quadratic curve approximation, the value of the time axis at the point where the gradient in the quadratic curve approximation portion matches the reference value of the gradient can be obtained stably. It was. As a result, it is possible to provide a plate thickness relative comparison method and a plate thickness relative comparison device using electromagnetic pulses that can be compared in a noise environment.

  Other objects, configurations, and effects of the present invention will become apparent in the best mode for carrying out the invention shown below.

  Next, an embodiment of the present invention will be described with reference to FIGS. A plate thickness relative comparison device 1 shown in FIG. 1 includes a transmitter 2 for transmitting an electromagnetic wave pulse, and a receiver 3 for receiving an electromagnetic wave signal from a steel plate 101 excited by the electromagnetic wave pulse transmitted from the transmitter 2. , A controller 4 for controlling the transmitter 2 and the receiver 3, and a personal computer 5 for analyzing the received waveform. The test body N covers the steel plate 101 on which the defective portion 101 a is formed with a heat insulating material 102, and further covers the surface with an exterior material 103. Usually, the steel plate 101 is a steel pipe or the like, and the defective portion 101a is formed on the surface of the steel plate 101 by corrosion or the like.

  FIG. 3 is a graph showing a received waveform after a pulse is transmitted, in which the horizontal axis represents the time axis, the vertical axis represents the received intensity, and both are displayed on a logarithmic scale. In addition, although only one measurement condition is displayed as a representative, there is a problem in that the reference point cannot be stably specified by cubic curve approximation even though the six conditions described later are close enough to appear to be almost overlapped on the same scale. is doing. The flat part in the first half means a pulse signal, and the part that attenuates becomes the object of analysis. In the personal computer 5, as shown in FIG. 4, the received waveform is approximated by the approximate straight line FL at the portion before the boundary point P1, and the second half from the boundary point P1 is approximated by the approximate curve FR. In the vicinity of the boundary point P1 in the approximate curve FR in the latter half of the boundary point P1, a reference point P2, which is the point at which the gradient of the approximate curve FR matches the reference value of the gradient, is obtained, and the plate thicknesses are relatively compared based on this value. To do.

The parameter input items for analysis in the personal computer 5 will be described with reference to FIG. The X-axis range S1 has an input part for an X-axis lower limit field S1a and an X-axis upper limit field S1b, and the Y-axis range S2 has an input part for a Y-axis lower limit field S2a and a Y-axis upper limit field S2b. The gradient field S3 is a portion for inputting a gradient reference value B, and the plate thickness coefficient field S4 is an input column for a plate thickness conversion coefficient C. In the log time field S5, the time T of the reference point P2, which is the point where the slope of the approximate curve FR coincides with the reference value B, is displayed by automatic calculation, and the value T of the log time field S5 is set to 10 ^T in the linear time field S6. The value obtained by the automatic calculation is displayed, and the plate thickness field S7 is obtained by multiplying the square root of the linear time field S6 by the plate thickness coefficient field S4.

  Further, with reference to FIGS. 2 and 4, a processing procedure performed for deriving a plate thickness equivalent value in the personal computer 5 will be described. First, a data range is designated for the X-axis range S1 and the Y-axis range S2 (ST1). The Y-axis lower limit field S2a has a meaning of cutting a low S / N portion so that a region having a small S / N ratio is taken in and noise does not adversely affect the fitting. First, linear approximation is performed on the original attenuation line F in FIG. 3 (ST2), and a boundary point P1 that is an end point of the approximate line FL is determined (ST3).

  Next, fitting by a quadratic curve is performed on the latter half of the boundary point P1 of the original attenuation line F based on the least square method (ST4), and the approximate curve FR is determined. Next, a reference point P2, which is a point that coincides with the reference value B of the previous gradient in the approximate curve FR in the vicinity of the boundary point P1, is obtained (ST5). And the plate | board thickness equivalent value L is estimated by following Formula (ST6).

L = C · (10 ^T ) ^1/2

T is displayed in the log time field S5, 10 ^T is displayed in the linear time field S6, and L is displayed in the plate thickness field S7.

  In actual relative comparison, the plate thickness is known in the healthy part N, and can be obtained by relative comparison with the healthy part N. If the reference value B and the plate thickness coefficient C of the previous gradient are adjusted so that the plate thickness equivalent value L in the sound portion N becomes the measured thickness L1, the presence of the defective portion 101a and the plate thickness equivalent of that portion It is possible to detect the value L2 and the value corresponding to the depth of the defect portion 101a.

  Next, Example 1 will be described with reference to FIGS. In FIG. 1, a defective portion 101a having a circular thinning was formed on a steel plate 101 having a thickness L1 = 10 mm. FIG. 3 shows data measured from above the exterior material 103 made of tin with the depth L3 = 4 mm and the diameter d = 50 mmφ, 100φ, and 150 mmφ of the defective portion 101a, the thickness L4 of the heat insulating material 102 = 100 mm.

In the present embodiment, data numbers 1 and 2 are data with a diameter of 50 mmφ, 3 and 4 are data with a diameter of 100 mmφ, and 5 and 6 are data with a diameter of 150 mmφ. The fitting was performed with the gradient reference value B = 1.8 and the plate thickness coefficient C = 1. For data numbers 1 to 6, fitting by a quadratic curve and fitting by a cubic curve were both performed. 4 is a quadratic curve fitting for data number 1, FIG. 5 is a cubic curve fitting for data number 1, FIG. 6 is a cubic curve fitting for data number 4, and FIG. The results of fitting a cubic curve to each are shown.

  As the fitting by the cubic equation is indicated by the standard deviation value, the fitting property with the data is superior to the quadratic equation. However, when the analysis is actually performed and the reference point P2, which is a change point corresponding to the thickness of the thinned portion, is obtained, it cannot be determined as an appropriate value by cubic fitting as in data 1 and 2, or the variation is large. There is a characteristic. In the tertiary data number 1 in FIG. 5, the slope is already lower than the value of the slope reference value B at the boundary point P1, and the reference point P2 cannot be determined. On the other hand, in the fitting by the quadratic equation, the reference point P2 can be determined stably, and the variation is smaller than in the case of the cubic equation. Thus, by performing the fitting analysis with a quadratic expression, a quantitative and stable relative thickness comparison can be performed.

Next, a second embodiment will be described with reference to FIGS. Although the received waveform of FIG. 8 is also displayed representatively of only one measurement condition, the reference point cannot be stably identified by cubic curve approximation even though the following eight conditions are close enough to appear to almost overlap on the same scale. The problem is the same as in the first embodiment. In the present embodiment, the data is obtained by repeatedly collecting measurements at the same place eight times for the on-site piping in operation in which the periphery of the steel pipe in the factory is covered with a heat insulating material and further covered with a zinc iron plate. The insulation thickness is 60 mm. After identifying the linear attenuation part for this data and determining the curved attenuation part, the curve part is analyzed for the fitting by the quadratic expression and the fitting by the cubic expression, and the change corresponding to the thickness of the thinned part The point time was determined.

  It is clear from Table 2 that the approximation using the cubic equation is superior to the quadratic equation in terms of the standard deviation.

  From the comparison of FIGS. 8 and 9 and Table 2, it can be seen that the reference point P2 can be stably estimated when the quadratic equation is used. On the other hand, when the cubic equation is used, the reference point P2 may be easily determined as data 2 in FIG. However, in the data 1 of FIG. 10 and the data 8 of FIG. 12, the boundary point P1 is already below the reference value B of the slope, and the position separated from the same point may be mistaken as the reference point P2. As can be seen, the reference point P2 is also excellent in stability in this case by approximation using a quadratic equation.

Finally, reference is made to the possibilities of other embodiments of the invention.
In the above embodiment, the logarithmic axis is used for the time axis and the signal intensity. However, it is also possible to use a normal decimal axis for both of these axes so that the logarithm is woven substantially as a function.

  Moreover, in the said embodiment, the flat thing was used as the test body N. FIG. However, the present invention is not limited to a flat plate shape but can be applied to various shapes such as a tube or a container having a bent surface.

  In addition, the code | symbol entered in the term of the claim is only for the convenience of contrast with drawing, and this invention is not limited to the structure of an accompanying drawing by this entry.

  The present invention transmits and receives an electromagnetic wave pulse to a steel material existing at positions separated from a transmitter and a receiver at a plurality of measurement locations, and compares the thickness of the steel material relative to each other using the received pulse. For example, it can be used for corrosion inspection of pipes and containers protected by a heat insulating material.

It is a block diagram of the board thickness relative comparison apparatus for enforcing the board thickness relative comparison method concerning the present invention. It is a flowchart which shows the analysis procedure in a plate | board thickness relative comparison apparatus. The received signal by a receiver is shown, a horizontal axis is a time axis, and a vertical axis | shaft is a graph which shows receiving intensity. It is an approximate graph by the straight line and quadratic curve of the graph of FIG. It is an approximate graph by the straight line and cubic curve of the graph of FIG. It is another approximate graph by the straight line and cubic curve of the graph of FIG. FIG. 6 is still another approximate graph by a straight line and a cubic curve of the graph of FIG. 3. The horizontal axis | shaft is a time axis | shaft and the vertical axis | shaft is a graph which shows a receiving strength. It is an approximate graph by the straight line and quadratic curve of the graph of FIG. It is an approximate graph by the straight line and cubic curve of the graph of FIG. It is another approximate graph by the straight line and the cubic curve of the graph of FIG. FIG. 9 is still another approximate graph using straight lines and cubic curves in the graph of FIG. 8.

Explanation of symbols

1: Thickness relative comparison device, 2: Transmitter, 3: Receiver, 4: Controller, 5: Personal computer, 101: Steel plate, 101a: Defect, 102: Insulating material, 103: Exterior material, S1: X Axis range, S1a: X axis lower limit field, S1b: X axis upper limit field, S2: Y axis range, S2a: Y axis lower limit field, S2b: Y axis upper limit field, S3: Gradient field, S4: Sheet thickness coefficient field, S5 : Log time field, S6: linear time field, S7: plate thickness field, F: original attenuation line, FL: approximate line, FR: approximate curve, P1: boundary point, P2: reference point, B: reference value of gradient, C: Plate thickness coefficient, d: Diameter, N: Specimen, T: Time of reference point P2

Claims (4)

In a plurality of measurement locations, an electromagnetic pulse is transmitted from the transmitter to the steel material present at a position separated from the transmitter and receiver of the electromagnetic pulse and received by the receiver, and the received pulse at each measurement location is used to A relative thickness comparison method using electromagnetic pulses for comparing relative thicknesses of steel materials,
The time and amplitude axes are substantially displayed in logarithmic scales, and the received pulse is approximated by linear approximation and a quadratic curve, and the reference value of the gradient in the quadratic curve is set to a value below the gradient of the straight line, The value of the time axis at the point where the gradient in the quadratic curve approximation portion matches the reference value of the gradient is determined for each measurement location, and the value of the time axis or the thickness equivalent value based on the value of the time axis A plate thickness relative comparison method using electromagnetic pulses to relatively compare the plate thicknesses of steel materials. 2. The plate thickness relative comparison method using electromagnetic pulses according to claim 1, wherein the plate thickness equivalent value is obtained by the following equation.
L = C · (10 ^T ) ^1/2
(However, L is a plate thickness equivalent value, C is a plate thickness conversion coefficient, and T is a time axis value.) The plate | board thickness relative comparison method by the electromagnetic wave pulse of Claim 1 or 2 with which the said steel materials are covered with the heat insulating material and the exterior material. A plate thickness relative comparison device using electromagnetic pulses that can be used in the plate thickness relative comparison method according to any one of claims 1 to 3,
It has a transmitter and a receiver for electromagnetic pulse, and at a plurality of measurement points, transmits and receives the electromagnetic pulse to a steel material located at a position separated from the transmitter and receiver, and substantially sets the time and amplitude axes respectively. The logarithmic scale is used to approximate the received pulse by linear approximation and a quadratic curve, and the gradient reference value in the quadratic curve is set to a value lower than the gradient of the straight line, and the gradient in the quadratic curve approximation portion is the gradient. An electromagnetic wave pulse that obtains a value of a time axis at a point that matches the reference value of each of the measurement points, and compares the thickness of the steel material relative to the value of the time axis or a thickness equivalent value based on the value of the time axis By plate thickness relative comparison device.

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