JPH085598A - Corrosion rate meter - Google Patents

Abstract

PURPOSE:To realize easy and inexpensive measurement of corrosion rate by feeding high and low frequency driving signals, while time sharing, between a sample electrode and a pair electrode and then operating a pure polarization resistance based on the difference of measured resistance. CONSTITUTION:When a low frequency driving signal of 0.1-0.01Hz is applied between a sample electrode 1 and a pair electrode 2 from a driving signal source 3, effect of an interface capacitor C is negligible and only the sample electrode 1 and resistances RD+RW (RD represents the polarization resistance and RW represents the solution resistance) exist apparently. When a high frequency driving signal of 10Hz-10kHz is applied between the electrodes 1 and 2, the resistance RD is bypassed by the capacitor C and only the resistance RW exists apparently between the electrodes 1, 2. When low and high frequency driving signals are applied alternately, while sharing the time, and the resistance RW is subtracted from the obtained resistance RD+RW through an operating unit 4, only the pure polarization resistance RD can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion rate meter for measuring the corrosion rate of iron pipes and the like.

[0002]

2. Description of the Related Art In a cooling system of a building or a plant, an iron pipe is often used as a pipe for circulating cooling water, and water stains such as calcium, generation of algae, secretion of microorganisms and mud are clogged. This lowers the cooling effect and causes corrosion due to these factors. Since the life of the iron pipe due to corrosion greatly affects the life of the building or plant itself, it is important to know the progress of corrosion of the iron pipe.

As a method for measuring the corrosion rate, the following three methods are specified in JIS K0100.

DC constant current method: This is a DC constant voltage device between a sample electrode and a counter electrode which is arranged at a constant interval with respect to this sample electrode and which is paired with this and is used for polarization resistance measurement. As a result, a minute DC constant current as shown in FIG. 10 (a) is passed, the change in the indicated value of the voltmeter as shown in FIG. 10 (b) is tracked, and when the voltage becomes almost steady, the This is done by reading the voltage and turning off the current. Then, the polarization resistance is obtained by dividing the difference between the voltage immediately before energization and the voltage immediately before the current disconnection by the current value.

AC constant current method: In this method, a small constant current of low frequency AC as shown in FIG. 11 (a) is made to flow from an AC constant current device between a sample electrode and a counter electrode, and shown in FIG. 11 (b). Track changes in voltmeter and ammeter readings. Then, the polarization resistance is obtained by dividing the voltage peak-peak value by the current peak-peak value.

AC constant voltage method: This is a method in which a low frequency AC minute voltage as shown in FIGS. 12 (a) and 12 (b) is applied between a sample electrode and a counter electrode by an AC constant voltage device, and a voltmeter and an electric current are applied. Keep track of total readings. Then, the polarization resistance is obtained by dividing the peak value of the voltage by the final peak value of the current. Incidentally, in the case of alternating current, it is possible to avoid the disadvantage that corrosion resistance cannot be gradually measured due to electrolysis in the vicinity of the electrodes when direct current is used.

Then, as shown in FIG. 13, for example, as shown in FIG. 13, the measured values measured by the above-described methods include the polarization resistances R _D1 and R _D2 between the two electrodes 12 and 13 connected to the AC power supply 11. In addition, the solution resistance R _W between the electrodes 12 and 13 is included, and the pure polarization resistance R _D (R _D1 + R _D2 ) itself is not obtained.

Therefore, as a method for eliminating the influence of the solution resistance, (a) a method of correcting the solution resistance by subtracting the solution resistance with a conductivity meter, or (b) in the two-electrode system, the interval between the sample electrode and the counter electrode is narrowed. In the three-electrode type, JIS describes a method of narrowing the distance between the sample electrode and the reference electrode.

[0009]

However, in the above method (a), it is necessary to prepare a conductivity meter separately, which inevitably leads to an increase in cost. Further, the measurement result of the conductivity meter and corrosion are unavoidable. The measurement work is complicated and inefficient, such as matching the measurement results by speed and correcting,
When each measurement result is read into a computer through an inter-measuring device network interface such as GPIB and correction calculation is performed, the measurement system becomes bulky, which causes a problem of cost increase.

Further, in the above method (b), the gap between the electrodes is narrowed, so that dust adheres between them, and the gap is further narrowed or a measurement error occurs. Therefore, there is a problem that it is necessary to frequently perform maintenance around each electrode.

The present invention has been made by paying attention to the above-mentioned conventional problems. The corrosion rate can be measured easily and at low cost without separately preparing a measuring instrument such as a conductivity meter. It is an object of the present invention to obtain a corrosion velocity meter that can suppress the influence of solution resistance even if the distance between the electrodes is widened, and thus can prevent adhesion of dust between the electrodes and deterioration of measurement accuracy due to the dust.

[0012]

The corrosion velocity meter according to the invention of claim 1 is obtained by time-divisionally supplying a driving signal of a low frequency and a driving signal of a high frequency to a computing device between a sample electrode and a counter electrode. The polarization resistance is calculated from the difference between the measured resistances.

In the corrosion velocity meter according to the second aspect of the present invention, the ratio of the average value of the response voltage immediately before and immediately after the polarity of the drive current supplied between the sample electrode and the counter electrode to the arithmetic unit is reversed to the drive current. Therefore, the polarization resistance is calculated.

In the corrosion velocity meter according to the third aspect of the present invention, the arithmetic unit is provided with a section where the drive signal is opened at an intermediate point where the polarity of the drive signal supplied between the sample electrode and the counter electrode is inverted. The polarization resistance is calculated from the ratio of the voltage value immediately after the section and the current value immediately before the opening.

[0015]

In the corrosion velocity meter according to the present invention, the driving signal group of low frequency for measuring the polarization resistance including the solution resistance and the driving signal group of high frequency for measuring the solution resistance are alternately arranged in a time division manner. And a pure polarization resistance is obtained as a difference between the resistance values obtained from the measured values in each section.

In the corrosion rate meter according to the second aspect of the present invention, in the AC constant current method, the response voltage value immediately before and after the driving current is inverted is measured, and the polarization resistance is calculated from the ratio of the average voltage value and the driving current. Ask.

In the corrosion rate meter according to the third aspect of the invention, in the AC constant current method and the AC constant voltage method, the drive signal is open at an intermediate point at which the polarity of the drive signal is inverted from positive to negative and from negative to positive. Is provided, the voltage value immediately after this section is measured, and the polarization resistance is obtained from the ratio of this voltage value and the current value immediately before the drive signal is opened.

[0018]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. Figure 1 shows the equivalent circuit of a two-electrode corrosion rate meter,
Reference numeral 1 is a sample electrode such as an iron pipe, 2 is a counter electrode (corresponding to a reference electrode in a three-electrode type corrosion rate meter), and R _D is a polarization resistance.
In this case, the resistance is the sum of R _D1 and R _D2 . R _W is a solution resistance between the sample electrode 1 and the counter electrode 2, and C is a large-capacity interface capacitor between the electric double layers generated at the interface between the electrodes 1 and 2.

An alternating voltage or current as a drive signal is supplied from the drive signal source 3 between the sample electrode 1 and the counter electrode 2, and the polarization resistance R _D and the solution resistance R are also supplied.
Based on the measured value of _W , the arithmetic unit 4 functions to calculate a pure polarization resistance.

Next, the operation will be described. Generally, when measuring the polarization resistance R _D , the frequency of the drive signal is 0.
It is selected as low as about 1 to 0.01 Hz. By driving at such a low frequency, the influence of the interfacial capacitor C can be ignored, and it is apparently the same as having only the sample electrode 1 and the resistance R _D + R _W.

On the other hand, 10 to 10 KH is placed between each of these electrodes.
When a high frequency of about z is applied, the polarization resistance R _D is bypassed by the interface capacitor C, and therefore, apparently,
This is the same as having only the solution resistance R _W between the electrodes 1 and 2.

Therefore, as shown in FIG. 2, sections T ₁ for applying a low-frequency drive signal and sections T ₂ for applying a high-frequency drive signal are provided alternately. And the arithmetic unit 4
The voltage of the period T _1, a resistor R _D + R _W that was determined as a ratio of the current value, the voltage at the T ₂ period, by subtracting the R _W that was determined as a ratio of the current value, i.e. (R _D + R _W)
Only the pure polarization resistance R _D can be determined from −R _W = R _D.

In the AC constant current method, the drive signal is current and the response signal is voltage. In the AC constant voltage method, the drive signal is voltage and the response signal is current. The above method can be applied to any of the methods.

Example 2. Next, another embodiment of the present invention will be shown. The equivalent circuit of the corrosion rate meter used in this embodiment is shown in FIG.
The same description is omitted here and the duplicated description is omitted here.

Next, the operation will be described. The relationship between the drive current and the response voltage in the AC constant current method is as shown in FIG. 3, and the response voltage waveform has a certain voltage value V ₂ (or −V ₂ ) immediately after the polarity of the drive current waveform is inverted at t ₂ . To a certain constant voltage value -V ₁ '(or V
₁ ) reach.

Generally, the equivalent circuit between the measuring electrodes is the same as that of the first embodiment.
The drive current frequency is 0.1 to 10.
It is selected to be about 0.01 Hz. Therefore, the response voltage value measured at t ₁ is V ₁ = I · (R _D + R _w ).

At this time, the interface capacitor C is charged to V
The voltage is _c = I · R _D. Immediately after the drive current is inverted (t ₂ , t ₄ ), the electric charge stored in this interface capacitor does not change suddenly. The abruptly changing voltage component is only the component resulting from the solution resistance R _w .

[0028] Thus, the response voltage value V ₂ at t ₂ is, V ₂
= Is as _{I · R D -I · R W} . Where I ・ R _D
Is the voltage stored in the interface capacitor C. The average value V of the _two voltage values V ₁ and V ₂ measured at t ₁ and t ₂ is V = (1/2) (V ₁ + V ₂ ) = (1 /
2) a _{I (R D + R W +} R D -R W) = I · R D.
Therefore, the polarization resistance is calculated as R _D = V / I.

Normally, both the voltage value and the current value are measured in both positive and negative directions, and the peak value and the peak value are calculated. This is because the polarization resistance is slightly different depending on the direction of the current flowing through the sample electrode. Therefore, the polarization resistances in both positive and negative directions are averaged. For example, R _D = (V ₁ + V ₁ '+ V
₂ + V ₂ ') / 2I.

Example 3. FIG. 4 shows still another embodiment of the present invention. In this embodiment, a switch 5 for releasing a drive signal is connected to an equivalent circuit similar to that shown in FIG.

In this embodiment, in the AC constant current method or the AC constant voltage method, the polarity of the drive signal (current signal in the AC constant current method, voltage signal in the AC constant voltage method) is positive, negative, or negative. A section in which the drive signal is opened is provided at the midpoint of positive inversion.

As a result, the drive signal appears between the sample electrode and the counter electrode (between the sample electrode and the reference electrode in the three-electrode system) in the intervals (t _{3 to} t ₄ ) and (t _{6 to} t ₇ ). The voltage waveforms are as shown in FIGS. FIG. 5 is a voltage waveform in the case of the AC constant current method, and FIG. 6 is a voltage waveform in the case of the AC constant voltage method.

Now, assuming that a driving signal having a frequency low enough to ignore the influence of the interface capacitor C is input,
Immediately before the drive signal is inverted (t ₂ , t ₅ , t ₈ ), the interface capacitor C is charged to a constant value of V _c = I · R _D.

Therefore, immediately after the drive signal is released (t
_{At 3} , t ₆ and t ₉ ), the voltage of the counter electrode 2 is V _C itself. Therefore, V ₁ = V _c = I · R _D , and the polarization resistance is obtained with R _D = V ₁ / I.

Since the value of the polarization resistance R _D actually differs slightly depending on the direction of the current, it is necessary to take the average value of the polarization resistance measured in both the positive and negative directions. R _D = (V ₁ + V
_An accurate polarization resistance value can be obtained as ₁ ') / 2I.

In the above embodiment, the magnitude of the drive signal is always constant even if the drive signal changes to positive or negative as shown in FIG.
It can also be applied to the differential step method as shown in, and the influence of solution resistance can be removed by the same method as above.

Further, in FIGS. 7 and 8, as the drive signal and the response signal, those which are positive and negative symmetrical with respect to 0 potential are described. This is because if the same electrode material is used for the sample electrode, the counter electrode, the reference electrode, etc., the corrosion potentials generated at the electrode interfaces cancel each other out, and it is not necessary to consider the corrosion potential.

However, when different electrode materials are used, the difference between the corrosion potentials generated between the electrodes 1 and 2 is added to the signal voltage as the bias potential _Vb as shown in FIG. Also in this case, the difference between the corrosion potentials appearing between the electrodes 1 and 2 at the time of starting the measurement is measured, and if this bias voltage is used as the apparent reference potential, the same method as that performed for each of the above-described examples is used. Thus, the influence of the solution resistance R _W can be eliminated.

[0039]

As described above, according to the first aspect of the present invention, the low-frequency driving signal and the high-frequency driving signal are supplied to the arithmetic unit in a time-divisional manner between the sample electrode and the counter electrode. Since the polarization resistance is calculated from the difference in the measured resistance, the corrosion rate can be measured easily and at low cost without separately preparing a measuring instrument such as a conductivity meter, and even if the interval between the electrodes is widened. There is an effect that it is possible to suppress the influence of the solution resistance component, and thus to prevent the adhesion of dust between the electrodes and the deterioration of the measurement accuracy due to this.

According to the second aspect of the present invention, the arithmetic unit is calculated based on the ratio of the average value of the response voltage immediately before and after the polarity of the drive current supplied between the sample electrode and the counter electrode is inverted to the drive current. Since the polarization resistance is calculated, there is an effect that the polarization resistance can be easily calculated from the average value of the response voltage with respect to the drive current near the peak and immediately after the inversion.

Further, according to the third aspect of the invention, the arithmetic unit is provided with a section where the drive signal is opened at an intermediate point where the polarity of the drive signal supplied between the sample electrode and the counter electrode is inverted. Since the polarization resistance is calculated from the ratio of the voltage value immediately after and the current value immediately before the opening, the polarization resistance can be easily obtained by reading the voltage remaining at both ends of the interface capacitor immediately after the switch is opened. There is an effect that can be obtained.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram showing a corrosion rate meter according to an embodiment of the present invention.

FIG. 2 is a timing chart of drive signals input to the circuit of FIG.

FIG. 3 is a timing chart showing current and voltage waveforms for explaining the operation of another embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram showing a corrosion rate meter according to another embodiment of the present invention.

5 is a timing chart showing voltage waveforms in the AC constant current method of the embodiment of FIG.

6 is a timing chart showing a voltage waveform in the AC constant voltage method of the embodiment of FIG.

FIG. 7 is a timing chart showing a drive signal waveform of the present invention.

FIG. 8 is a timing chart showing another example of drive signal waveforms.

FIG. 9 is a timing chart showing still another example of the drive signal waveform.

FIG. 10 is a timing chart showing currents and voltages obtained by performing a conventional DC constant current method.

FIG. 11 is a timing chart showing currents and voltages obtained by performing a conventional AC constant current method.

FIG. 12 is a timing chart showing currents and voltages obtained by performing a conventional AC constant voltage method.

FIG. 13 is an explanatory diagram showing a conventional interelectrode resistance.

[Explanation of symbols]

 1 sample pole 2 counter pole 3 drive signal source 4 arithmetic unit

Claims (3)

[Claims] 1. A sample electrode of a pipe through which a solution flows, a counter electrode or a reference electrode arranged in the sample electrode, and a low-frequency driving signal and a high-frequency driving signal are time-divisionally supplied between the sample electrode and the counter electrode. A corrosion rate meter equipped with an arithmetic unit for calculating the polarization resistance from the difference between the measured resistances obtained by the above. 2. A sample electrode of a pipe through which a solution flows, a counter electrode or a reference electrode arranged in the sample electrode, and a response voltage immediately before and after the polarity of a drive current supplied between the sample electrode and the counter electrode is reversed. From the ratio of the average value of and the above drive current,
A corrosion speedometer equipped with a calculation device for calculating polarization resistance by calculation. 3. The driving electrode is provided at a sample electrode of a pipe through which a solution flows, a counter electrode or a reference electrode disposed in the sample electrode, and an intermediate point at which the polarity of a drive signal supplied between the sample electrode and the counter electrode is reversed. A corrosion velocity meter comprising a section in which a signal is opened, and an arithmetic unit for calculating a polarization resistance by an operation from a ratio of a voltage value immediately after this section and a current value immediately before the opening.