JPS639022B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cathodic protection of objects to be protected, such as facilities and equipment made of steel.

Cathodic protection methods for steel materials include galvanic anode methods and external power supply methods, which are selected depending on the scale and structure of the object to be protected, or the environment, and are widely applied as corrosion protection methods in water or in the soil.

The galvanic anode method uses a sacrificial anode made of Zn, Al, Mg, etc., and uses the natural potential difference between these anode materials and the object to be protected to selectively elute the anode material into water or soil. It protects the body from corrosion, and is an expensive method that requires a large amount of refining energy.
There is a possibility that using Al, Mg, or Zn, which has limited resources, as a consumable anode may become undesirable from the viewpoint of future resource and energy conservation. Also, the external power supply method uses an insoluble anode and is usually 5 to 60V.
Since the anti-corrosion current is constantly adjusted manually or automatically by applying a certain amount of voltage, it has disadvantages such as requiring relatively frequent voltage management or requiring a complicated automatic control circuit.

The object of the present invention is to provide a method for cathodic protection of steel materials that combines the advantages of the galvanic anode method and the external power supply method.

The feature of the present invention is that an iron anode is provided near the steel material as the object to be protected, and a weak voltage of 0.3 to 0.8V is applied between the iron anode and the object to be protected, similar to the external power supply system. Despite using iron anodes,
It is a cathodic protection method similar to the galvanic anode method using Zn, Al, Mg, etc.

In the present invention, a consumable iron anode is used and a weak DC voltage of 0.3 to 0.8V is applied between the iron anode and the object to be protected.By limiting the voltage to within this range, the DC voltage It is possible to automatically control the corrosion protection current almost ideally without making any adjustments. The technical principle will be explained below.

For example, if we consider the case where a corrosion protection current is applied to the cathode surface (steel material) in seawater, as shown in Figure 1, at the beginning of the current application, the relationship is as shown by line A, and when the current is 0, the cathode polarization is 0 and the cathode is at its natural potential, but as the current density increases, cathode polarization gradually occurs and the cathode potential drops. Then, at a current density of about 100 mA/m ² , the corrosion protection potential is reached and the corrosion protection state is reached. When the anticorrosion current continues to be supplied and the anticorrosion potential is maintained for a long period of time, an electrocoating is generated on the cathode surface, the anticorrosion effect is enhanced, and a polarization tendency as shown by line B is exhibited. Therefore, for example, at a current density of 50 mA/ ^m2 , the cathode potential is -920 mV. Note that the current density from wire B is 25 mA/m ²
It can be seen that the anti-corrosion potential is reached at , but if this state continues for a long time, the generated electrocoating will be consumed and the trend will return to line A, so the cathode potential should be kept within the range of -850 to -950 mV. This will keep the current density to a minimum.

On the other hand, the cathode polarization that occurs on the cathode surface occurs in a direction that cancels out the applied voltage, and from Ohm's law, the current is I=E-△E/R where I: energizing current value E: applied voltage △E: cathode polarization R: Indicates resistance between anode and cathode. Therefore, the rate at which the anticorrosion current is controlled by cathode polarization depends on the applied voltage, and becomes larger as the applied voltage is smaller. That is, I/Io=E-△E/E where I/Io: current reduction rate When cathodic polarization occurs, it becomes possible to reduce the anticorrosion current density, and there is a tendency that the value of the current flowing also decreases. If these two relationships are effectively combined, it is possible to automatically control the anticorrosion current without manually controlling it. For this purpose, the current reduction rate must be in a large range, that is, the applied voltage must be in a small range. Normally, cathodic polarization of 0.2V or more is generally required to make steel materials corrosion-proof.

Figure 2 shows the relationship between applied voltage, cathodic polarization, and applied current, and Figure 3 is a superimposition of Figure 2 and Figure 1. A case in which automatic current adjustment is performed will be explained. In this case, the reference point is 100m in seawater.
Assuming polarization of 0.18V at a current density of A/m ² , an applied voltage-current line passing through this point can be drawn. From FIG. 3, it is possible to know the range of applied voltage in which proper current control can be expected. For example, when the applied voltage is 0.4V, if the anode resistance (2.2Ω・^m2 ) can supply a current of 100mA/ ^m2 at a voltage of 0.22V minus polarization of 0.18V, the initial voltage of 100mA/ ^m2 is - 780
A potential of mV is obtained, and as time passes, the cathode potential becomes -900 mV at the intersection with line B at 48 mA/m ² . Therefore, when the applied voltage is 0.4 V, the current is automatically reduced by the electrocoating generated on the cathode surface, and can be maintained within the ideal potential range without any artificial control.

When the applied voltage is 0.3V, the intersection with line B shifts to the left compared to when the applied voltage is 0.4V, and the current density is 40mA/
^m2 , but the resistance of the anode is polarized by applying a voltage of 0.3V.
Subtracting 0.18V, in order to conduct a current of 100mA/ ^m2 at 0.12V, the resistance value needs to be as small as 1.2Ω・^m2 , which can be said to be the lower limit.

When the applied voltage is 0.8V, the intersection with line B is 62mA/
m ² has a potential of -1020 mV, which is effective, but the reduction rate of the anticorrosion current density is as small as 38%, which is at the limit of the effective range from the viewpoint of current control.

When the applied voltage is 1.6V, the intersection with line B is 82mA/
The potential is -1130mV at ^m2 , and the current reduction rate is 18%.
Not only is the potential low (-1130 mV), but it is inappropriate as it is a bit excessive.

From the above, it can be said that in the present invention, the appropriate voltage range is 0.3 to 0.8V, and the most effective range is around 0.4V.

The iron anode used in the present invention can be considered in the same way as an anode using a normal galvanic anode method, and has an amount of electricity (weight) depending on the generated current value and lifespan, and has an amount of electricity (weight) depending on the applied voltage (potential difference) and the generated current value. It is only necessary to install a suitable number of them in a distributed manner according to the object to be protected, with shapes and dimensions having suitable ground resistance values. In general, iron has excellent galvanic anode properties as it is, so there is no need to make it into an alloy to improve anode performance, and in addition to ordinary steel, cast iron and scrap iron can also be used. Note that stainless steel, which is strong, has good workability, and is economical, can be used as the core metal of the iron anode of the present invention. It is possible to economically prevent a decrease in the mounting strength due to this and a decrease in usage efficiency due to falling off.

FIG. 4 shows an outline of an example of a cathodic protection device in which the present invention is actually applied.

In Fig. 4, the power receiving transformer 1 inputs commercial power and outputs 60V AC, and in addition to an isolation transformer, it only needs to have a molded case circuit breaker and a pilot lamp on the input side, an output voltage switch, You don't need an ammeter, voltmeter, etc. The input power consumption is extremely low even if the object to be protected is large in size.
Single phase 100V is sufficient except in special cases. As for the installation location, since the equipment is small and lightweight and can be installed even if it is far from the object to be protected, it can be installed in a corner of an electrical room or office, etc., without having to install it outdoors. There is no need to control energization at all, and if you adjust the output voltage at the beginning, you can easily check the circuit during inspection.
Other than turning it off, it is sufficient to check the pilot lamp indicating that power is being received.

Fixed rectifier 2 receives AC 60V and has a voltage of 0.3
It outputs ~0.8V DC current of 2~5A, and is composed of an isolation transformer and a rectifying element.A molded circuit breaker, output voltage switch, ammeter, and voltmeter are not included except for incorporating a smoothing circuit as necessary. Not necessary. Basically, one fixed rectifier 2 is provided for each iron anode, but from the standpoint of anti-corrosion design, one fixed rectifier may supply anti-corrosion current to a plurality of iron anodes. Since the DC side output of the fixed rectifier 2 is usually about 2W, which is extremely small, the dimensions are inevitably ultra-small and lightweight, and the amount of heat loss is also small. Therefore, sealing treatment such as hardening with a curable resin becomes easy, and not only insulation but also complete waterproofing can be achieved, and the installation location can be underwater or in a splash zone. Furthermore, it is also possible to install the device by using a wiring device, for example, by plugging it into an outlet. In addition, this fixed rectifier 2
does not require any artificial control of the output current, so it does not require any control function such as a switch.

In Fig. 4, 3 is an iron anode, 4 is an object to be protected from corrosion,
5 is a primary side wiring, 6 is a secondary side wiring, 7 is an anode lead wire, and 8 is a drain line. In such a device, the iron anode 3 is connected to the positive terminal of the fixed rectifier 2, and the object 4 to be protected from corrosion is connected to the negative terminal of the fixed rectifier 2, and a corrosion protection current is supplied from the iron anode 3 to the object 4 to be protected.

In the present invention, by applying a weak voltage in the range of 0.3 to 0.8 V between the iron anode 3 and the object to be protected 4, the current is stabilized at the equilibrium point between the current and the cathode polarization as described above, and the water flow and water temperature are Even if depolarization occurs due to other changes, as the effective current increases, the anticorrosive current also increases, and an equilibrium state is always maintained and stabilized within an appropriate range in response to environmental changes.

As is clear from the above description, the present invention has only the advantages of the galvanic anode method and the external power supply method, and by applying an extremely fine voltage, corrosion protection is always stably achieved without voltage adjustment. Because it can protect the body from corrosion and uses inexpensive iron as the anode material, it meets the requirements for resource and energy conservation, and is extremely useful in industry as a method for cathodic protection of steel materials. is big.

[Brief explanation of the drawing]

Figure 1 is a diagram of the relationship between current density and cathode polarization (cathode potential), Figure 2 is a diagram of the relationship between applied current and cathode polarization when the applied voltage is changed, and Figure 3 is a diagram of the relationship between current density and cathode polarization (cathode potential). FIG. 4 is a schematic diagram showing an example of an apparatus in which the present invention is actually applied. 1...Power receiving transformer, 2...Fixed rectifier, 3...
Iron anode, 4... Corrosion protected object, 5... Primary side wiring, 6
...Secondary side wiring, 7...Anode lead wire, 8...Drain wire.

Claims (1)

[Scope of Claims] 1. When electrolytically protecting a steel material as a target object, an iron anode is provided near the target object, and a voltage of 0.3 to 0.8 V is applied between the iron anode and the target object. A cathodic protection method for steel materials characterized by: 2. The electrolytic corrosion protection method for steel materials according to claim 1, which uses an iron anode whose core metal is made of stainless steel.