JPH0224915B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a wear detection device for anti-corrosion electrodes in an iron water storage tank that is always filled with water, such as a hot water storage tank for an electric water heater.

Prior Art Iron water storage tanks are equipped with anti-corrosion electrodes mainly made of magnesium to form a battery between the iron forming the tank, and the battery is used as a power source to flow an anti-corrosion current through the tank. This is to prevent tank corrosion caused by local batteries formed on the inner wall surface of the tank.

This technology is especially effective among cathodic protection technologies.
It is called Galvanic Protection, and its feature is that it does not require an external power source to supply the anti-corrosion current.

With Galvanic Protection, the corrosion protection potential of the tank required to completely prevent the progression of corrosion on a steel tank is -0.44V, which is the natural corrosion potential of iron, plus a margin of (-0.2 to -0.3)V. Look at -0.77V
It is said that it is sufficient if the voltage is below, and if the entire surface of the tank can be maintained at -0.77V or below using the anti-corrosion electrode, the purpose of anti-corrosion can be achieved.

Therefore, the anticorrosion electrode in Galvanic Protection wears out over time and its weight decreases, so it has a certain lifespan, and the degree of wear of the anticorrosion electrode must be periodically checked. This inspection work is important because if the wear of the corrosion protection electrode is overlooked, corrosion of the tank may rapidly progress and cause fatal damage to the tank, but in the past, only the corrosion protection electrode There is no established method for easily and reliably inspecting the tank from outside the tank, which is only a visual inspection.

Japanese Utility Model Application Publication No. 51-54848 discloses that, as a method for achieving this purpose, the tank and anticorrosion electrode are installed insulated, and the two are electrically connected via an indicator. Therefore, although a technique has been disclosed in which the degree of wear of the anti-corrosion electrode is monitored by the index of the indicator, this technique does not require the indicator to be connected in series with the battery formed by the tank and the anti-corrosion electrode. Since the indicator is inserted in The purpose is to measure the anti-corrosion current flowing through the battery, so it is possible to measure the specific resistance of the water in the tank, the condition of the inner wall of the tank, the presence or absence of pinholes in the lining material, and external factors such as scale adhesion. This method has disadvantages such as the fact that it is strongly influenced by the conventional method, and as a result, detection tends to be inaccurate.

Purpose of the Invention In view of the actual situation and shortcomings of the prior art, an object of the present invention is to directly detect the anti-corrosion potential of the tank so that the meter can be connected in series with the battery formed by the tank and the anti-corrosion electrode. Since it is not inserted into the
Furthermore, it is an object of the present invention to provide a novel wear-out detection device for a corrosion-protective electrode in a water storage tank, which is less likely to reduce detection accuracy since it does not measure a corrosion-protection current.

Structure of the Invention The structure of the present invention to achieve the above object is that a detection electrode made of a metal having a smaller ionization tendency than iron is provided on the inner wall of an iron water storage tank equipped with an anti-corrosion electrode, insulated from the water storage tank. , by inserting and connecting a high impedance potentiometer between the water storage tank and the detection electrode,
The potentiometer measures the difference between the corrosion protection potential of the tank due to the battery formed by the tank and the corrosion protection electrode and the natural corrosion potential of the detection electrode.
The gist is that by treating the latter as a known constant, the former can be directly monitored.

Example Examples will be described below with reference to the drawings.

The anti-corrosion electrode wear detection device in the water storage tank uses a detection electrode 21 attached to the water storage tank 11.
and a potentiometer 22 inserted and connected between the water storage tank 11 and the detection electrode 21 (FIG. 1).

The water storage tank 11 is an iron tank, and has a water supply pipe 11a at the bottom and a drain pipe 11b at the top, and the inside is always filled with water W.

On the upper and lower walls of the water storage tank 11, anti-corrosion electrodes 12 made mainly of a metal having a higher ionization tendency than iron, such as magnesium, are attached, and most of the electrodes 12 are immersed in water W.

A detection electrode 2 is provided on the lower wall of the water storage tank 11.
1 is provided through it. The detection electrode 21 is
The metal electrode is formed entirely of a metal having a lower ionization tendency than iron, such as nickel, or at least has its surface plated so as not to be consumed. It is attached in a state where it is electrically insulated from the water storage tank 11 via.

The potentiometer 22 is a DC potentiometer with high internal impedance, such as a Wheatstone bridge, a high input impedance type voltmeter with a DC amplifier in front of it, or an analog comparator with a high gain amplifier. The comparison result between the potential difference V and its monitoring level may be directly obtained.

Now, the electrical equivalent circuit inside the water storage tank 11 is as shown in FIG. In other words, when the anticorrosion electrode 12 is made of magnesium, the natural corrosion potential VMg of magnesium becomes the power source.
As the anti-corrosion current I flows through the resistance Ro of the water W, the potential of the water storage tank 11 becomes the anti-corrosion potential -
Held in VFe. That is, if VFe=VMg-Ro·I≧0.77 (V), the anti-corrosion electrode 12 is healthy and the anti-corrosion effect is maintained.

The detection electrode 21 made of nickel or nickel metal has a natural corrosion potential of nickel -VNi.
appears, the detection electrode 21 and water storage tank 11
The potential difference V measured by the potentiometer 22 connected between is V=VFe-VNi. where VNi is a known constant (0.25V)
Therefore, the corrosion protection potential VFe of the water storage tank 11 can be determined as VFe=V+VNi, and depending on whether this is greater than 0.77V, that is, V≧0.77−0.25=0.52(V ) The wear of the anticorrosive electrode 12 can be detected depending on whether the corrosion protection electrode 12 is successful or not.

As water storage tank 11, inner diameter 550mm, height 1750mm
An iron hot water storage tank of an electric water heater with a capacity of 380 liters and a length of 1210 mm was used as the anti-corrosion electrode 12.
When a magnesium electrode with a diameter of 21 mm is used and a nickel-plated copper rod is used as the detection electrode 21, the change in the potential difference V detected by the potentiometer 22 due to wear of the anti-corrosion electrode 12 is as shown in Figure 3. It was hot. However, in the figure, curves a and b indicate the maximum and minimum values of the detected potential difference V, respectively,
The detected potential difference V can vary between curves a and b depending on the quality and temperature of the water W in the water storage tank 11. Therefore, as the minimum allowable value of the detected potential difference V,
By taking 0.75, it was possible to reliably detect the wear limit of the anti-corrosion electrode 12 (dotted chain line in the figure).

Other Examples When the water storage tank 11 is a hot water storage tank for an electric water heater, the heater 31 is used, so
This can also be used as the detection electrode 21 (FIG. 4). However, the heater 31 is installed electrically insulated from the water storage tank 11 via an insulating bushing 31a, and at least its surface is made of a metal that has a lower ionization tendency than iron, such as copper or nickel. It is assumed that it is formed by Furthermore, it goes without saying that the heater 31 may be not only an electric heater but also a heat exchanger that passes steam or hot water.

Furthermore, the present invention can be similarly applied when the heater 31 has a discharge resistance R (FIG. 5). That is, when the current flowing through the drain resistance R is △I, the anticorrosion potential −V′Fe of the water storage tank 11 near where the drain resistance R is connected is V′Fe=VFe−Ro・△ Compared to when I<VFe and no drainage resistance R is used,
The corrosion protection potential decreases only by Ro・△I. However, in general, this effect does not affect the entire water storage tank 11, but only near the connection point of the drain resistance R, and Ro・△I is usually sufficiently small compared to VFe. It is. Now, assuming that the anticorrosion potential of the heater 31 is -VH, the potential difference V detected by the potentiometer 22 is V=V'Fe-VH, as in the previous example. Since anti-corrosion current △I flows through the heater 31, VH>VNi and V'Fe<VFe
Therefore, by monitoring the value of V+VNi, wear of the anticorrosion electrode 12 can be detected more safely.

Note that this device has a water storage tank 11 that is powered by a battery formed by the anticorrosion electrode 12 and the water storage tank 11.
Since the anticorrosive potential -VFe is monitored, when the water W inside the water storage tank 11 is insufficient and the battery cannot be formed, it is natural that the anticorrosive potential -VFe is monitored.
VFe also no longer appears, and the detected potential difference V of the potentiometer 22 shows zero. Therefore, this invention
It can also be used as a water level monitoring device for the water storage tank 11, or as an empty heating prevention device for an electric water heater.
It is applicable.

Effects of the Invention As explained above, according to the present invention, a detection electrode made of a metal having a smaller ionization tendency than iron is provided on the inner wall surface of an iron water storage tank equipped with an anti-corrosion electrode, and the detection electrode is insulated from the water storage tank. At the same time, by connecting a high impedance potentiometer between the two, the potentiometer can measure the difference between the corrosion protection potential of the water storage tank due to the corrosion protection electrode and the natural corrosion potential of the detection electrode. Therefore, by treating the latter with known constants, the former can be directly monitored. Therefore, a meter is inserted in series with the battery formed by the anti-corrosion electrode and the tank to measure the anti-corrosion current. This is an advantage in that it can effectively eliminate the possibility that the voltage drop caused by the meter will reduce the corrosion protection performance, or that the detection accuracy will decrease due to the influence of external factors such as water quality or the condition of the inner wall surface of the tank. It has a positive effect.

[Brief explanation of drawings]

Figures 1 to 3 show examples, with Figure 1 being an explanatory diagram of the overall configuration, Figure 2 being an electrical equivalent circuit diagram, and Figure 3 being an electrical equivalent circuit diagram.
The figure is a performance curve diagram. FIG. 4 is a diagram corresponding to FIG. 1 showing another embodiment, and FIG. 5 is an explanatory diagram of the main part configuration showing still another embodiment. DESCRIPTION OF SYMBOLS 11... Water storage tank, 12... Corrosion protection electrode, 21... Detection electrode, 22... Potentiometer, 31... Heater.

Claims (1)

[Scope of Claims] 1. An iron water storage tank equipped with an anti-corrosion electrode made of a metal with a higher ionization tendency than iron, at least the surface of which is made of a metal with a lower ionization tendency than iron; A wear detection device for a corrosion protection electrode in a water storage tank, comprising: a detection electrode insulated from the water storage tank; and a potentiometer connected between the water storage tank and the detection electrode. 2. The wear detection device for a corrosion protection electrode in a water storage tank according to claim 1, wherein the detection electrode also serves as a heater or a heat exchanger for raising the temperature of water in the water storage tank. .