JPH0679015B2 - Non-destructive measuring device and measuring method for graphitized corrosion depth of cast iron pipe - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nondestructive measuring device for nondestructively measuring the depth of corrosion of a graphite pipe that occurs in a cast iron pipe buried in the ground or in water for a long time. It is a thing.

(Prior Art) It is known that in a cast iron pipe buried in the ground or in water, a phenomenon called so-called graphitization corrosion occurs in which iron is selectively lost from the surface and only a graphite layer remains.

This graphitization corrosion not only causes leakage of fluid passing through the cast iron pipe, but also causes breakage etc. due to insufficient strength against external loads, so the depth of graphitization corrosion during pipe digging, etc. Need to investigate.

Therefore, the most commonly used method for measuring the depth of graphitization corrosion is a method of hitting and removing the graphitization corrosion part with a hammer and measuring with a depth gauge. There are drawbacks such that it requires labor and time, there are large individual differences in measurement results, and there is a risk of breaking the cast iron pipe. There is also a method of using ultrasonic waves as another method, but there is a problem that it takes time to prepare the measurement because the cast iron pipe is cut and the measurement is performed from the inner surface in water, which is not practical.

(Object and Structure of the Invention) The present invention has been made in view of the above points, in which cast iron has a larger magnetic field penetration depth than steel and the graphitized corrosion portion loses conductivity. The purpose is to measure the depth of graphitization corrosion of cast iron pipes from the outer surface in a non-destructive and short-time manner. Used as
The corrosion depth of the cast iron pipe is measured by referring to the prepared corrosion depth table for the detection output obtained by detecting the signal output from the oscillation circuit when the sensor is applied to the cast iron pipe.

(Example) The present invention will be described below with reference to the drawings.

FIG. 4 shows the principle of nondestructive measurement of graphitized corrosion depth according to the present invention.

When the coil L of the LC oscillating circuit 1 composed of the capacitors C ₁ and C ₂ , the coil L and the amplifier circuit 1a is brought close to the conductor M as the sensor S, an eddy current is generated on the surface of the conductor and LC oscillation occurs. Since the oscillation intensity of circuit 1, that is, the amplitude, decreases,
The AC output signal from the oscillation circuit 1 is detected by the detection circuit 2 and extracted as DC voltage from the output terminals a and b. Since the DC voltage output from the terminals a and b changes according to the distance d between the sensor S and the conductor M, the depth of the graphitized corrosion portion can be measured by the DC voltage value. That is, as shown in FIG. 5, when the distance d between the sensor S and the conductor M is (a) very large, that is, when the depth of the graphitized corrosion portion is large, the DC voltage V ₁ becomes large, and ) When the voltage is medium, the DC voltage V ₂ becomes medium, and (c) the DC voltage V ₃ becomes extremely small when the graphitized corrosion part is sound and sound.
In the figure, the graphitized corrosion part is shown by the diagonal lines. In this case, the eddy current generated in the cast iron pipe is affected to a large extent by the age and manufacturing method of the cast iron and the carbon content. Fig. 2 shows the detection output obtained by applying this principle to two typical types of cast iron graphitized corrosion parts, where the vertical axis is the output of the detection circuit and the horizontal axis is the depth of the graphitized corrosion part. Show.

FIG. 1 is a block diagram of an embodiment of a nondestructive measuring device according to the present invention, and 10 is a coil 10 used as a sensor.
An oscillation circuit having a constant oscillation frequency determined by a, other resistors, and a capacitor 10b, 20 is a detection circuit for detecting and smoothing an amplitude change of the oscillation circuit 10 as a DC voltage, and 30 is an output of the detection circuit 20 A / D converter for D conversion, 40 is the third
According to the flow chart as shown in the figure, the material of the cast iron pipe is judged from the detection circuit output of the sound part at the initial setting, and is stored in the internal memory during the measurement as shown in FIG. CPU that calculates the graphitized corrosion depth using, 50 is an indicator that displays the graphitized corrosion depth, 6
Reference numeral 0 is a power source for the above components.

Next, the depth measurement of the graphitized corrosion portion will be described based on the flow chart shown in FIG. In this example, it is assumed that the detection output table for each material is stored in the memory of the CPU for the two types of cast iron pipe materials A and B.

First, the sensor is applied to the sound part of the cast iron pipe, and the oscillation amplitude V _O of the sound part is input at the time of initial setting (F-1). Next, it is determined whether or not the oscillation output V _O is equal to the initial oscillation output V _AO from the sound part of the cast iron pipe of the material A that has been measured in advance (F-2), and if V _O = V _AO , the measurement target CPU4 that the material of a certain cast iron pipe is A
It is stored in the internal memory of 0 (F-3). However, V _O = V _AO
If not, then it is judged whether or not this oscillation output V _O is equal to the initial oscillation output V _BO from the sound part of the cast iron pipe of another material B which has been measured in advance (F-4), and V _O = V If it is _BO , the fact that the material of the cast iron pipe to be measured is B is also stored in the internal memory of the CPU 40 (F-5). The material of the cast iron pipe is A or B
If not, it cannot be measured.

Next, the sensor is moved from the sound section to the inspection section and the oscillation output V from the sensor is output (F-6). Here, it is confirmed whether the material of the cast iron is A or B from the data of the internal memory (F-7). If the material is A, the graphitization corrosion of the material A stored in the internal memory of the CPU 40 is confirmed. Obtain the corrosion depth based on the sensor output from the depth table (F-
8). If the material is B, the corrosion depth is similarly obtained from the graphitization corrosion depth table for material B (F-9).

In any case, the corrosion depth thus obtained is displayed on the display unit 50.

After that, the sensor is moved to another place and the depth measurement described above is performed a desired number of times (F-11).

Although the depth measurement of the graphitized corrosion portion of two types of cast iron pipes having different materials has been described in the above-mentioned examples, since the properties of cast iron pipes with respect to eddy currents are remarkably different depending on the manufacturing age and the manufacturing method, it is possible to determine the depth of the different materials A plurality of graphitized corrosion depth tables may be prepared so as to be compatible with cast iron pipes.

(Effects of the Invention) As described above, in the present invention, a coil that constitutes an LC oscillation circuit is used as a sensor, and a detection output obtained by detecting a signal output from the oscillation circuit when the sensor is applied to a cast iron pipe is obtained. Since it is configured to measure the corrosion depth of the cast iron pipe by referring to the corrosion depth table prepared in advance, it is possible to measure the corrosion depth of the cast iron pipe in a non-destructive and short time. Soon, a measuring device with excellent practicability will be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the apparatus for measuring the depth of graphitized corrosion of cast iron pipe according to the present invention, and FIG. 2 is a diagram showing the relationship between the depth of graphitized corrosion and the detection output for each material of the cast iron pipe. FIG. 3 is a flow chart showing the graphitization corrosion depth measuring operation according to the present invention, FIG. 4 is a circuit diagram for explaining the non-destructive measurement principle of the graphitization corrosion depth according to the present invention, and FIG. 5 is shown in FIG. It is a detection output waveform diagram of the circuit. 10 ... Oscillation circuit, 10a ... Coil, 20 ... Detection circuit, 40
...... CPU, 50 …… Display unit

Claims (2)

[Claims] 1. An LC having a coil used as a sensor
An oscillation circuit, a detection circuit that detects and smoothes the output of the oscillation circuit, and a memory that stores data indicating the relationship between the output of the detection circuit and the depth of the graphitized corrosion portion for each type of cast iron pipe to be measured. A CPU for calculating the depth of the graphitized corrosion portion based on the data stored in the memory and the measured output of the detection circuit, and a display for displaying the calculated depth of the graphitized corrosion portion. Provided, first, in order to determine the type of the cast iron pipe to be measured, the transmission output to the sound part of the cast iron pipe and the data stored in the memory are compared in the comparison part of the CPU, and subsequently stored in the memory. It is characterized in that the depth of the graphitized corrosion portion of the cast iron pipe can be quickly obtained by reading the data corresponding to the determined cast iron pipe based on the measured output by the calculation unit of the CPU. Cast iron pipe graphitized rot Non-destructive measurement device of depth. 2. A cast iron pipe measured by comparing an initial transmission output measured by applying an LC oscillating circuit serving as a sensor to a sound part of the cast iron pipe to be measured with a plurality of types of data stored in a memory read by a CPU. To determine the type of, and to actually measure the transmission output of the detection unit by applying the sensor to the detection unit of the measurement cast iron pipe, the actual output and the data about the measurement cast iron pipe read from the memory Based on
Cast iron characterized by comprising the steps of obtaining the graphitized corrosion depth of the inspection portion of the measured cast iron pipe by placing it in the arithmetic section of the CPU and displaying the measurement result thus obtained on the display. Nondestructive measurement method for graphitized corrosion depth of pipe.