JPH062171A - Electrode system for ground embedding type corrosion protection - Google Patents

Abstract

PURPOSE:To provide a system, in which lowering of pH at the surface part of an electrode is restrained and also contact of the generated gas with the electrode is restrained by diffusing the gas into the ground so as to extend the service life of the electrode, by positively supplying liquid to the near part of the electrode. CONSTITUTION:A liquid supplying pipe 9 is arranged near the electrode 3 for corrosion protection and the liquid is supplied to the near part of the electrode 3 from a liquid supplying device 10 through the liquid supplying pipe 9. By supplying this liquid, the lowering of the pH at the near part of the electrode is relaxed and further, the gas generated from the electrode 3 for corrosion resistance is diffused to the surroundings of this electrode 3 by the supplying pressure of this liquid to prevent the contact of the gas with the electrode 3. By this method, the deterioration of the electrode 3 is restrained and the cathode corrosion protection of a metal to prevent the corrosion is attained without executing the exchange or the repair of the electrode 3 for corrosion protection for a long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underground buried electrode system used for a cathodic protection method using an external power supply system.

[0002]

[Prior art and its problems] In order to prevent the corrosion of a metal structure buried in the soil, an insulating member such as anti-corrosion coating, coating or lining is applied to the surface of the metal structure to protect it from the environment. Although the method has been adopted, if a defective portion occurs in the coating due to deterioration of the coating material over time, external damage, etc., the metal surface is exposed and corrosion occurs, so that complete corrosion protection cannot be performed for a long period of time. In recent years, a cathodic protection method has been adopted alone or in combination with the above coating in order to perform the corrosion protection completely. The cathodic protection method is a method of electrochemically stabilizing by causing a direct current to flow into a body to be protected such as a steel structure to polarize it, and as long as this state continues, the corrosion protection action continues, and It is a very important anticorrosion means because the anticorrosion state can be confirmed by monitoring the potential of the anticorrosion body.

The cathodic protection method is roughly classified into two types, a galvanic anode method and an external power supply method, depending on the method of supplying a direct current flowing into the body to be protected. The former galvanic anode method is a method in which a Mg alloy or the like having a base potential lower than that of the corrosion-preventing body is embedded in the vicinity of the corrosion-preventing body and electrically connected to the corrosion-preventing body. When the anode is selectively ionized and consumed, a weak DC current flows into the body to be protected. In the latter external power supply method, a durable electrode is buried in the soil, and a direct current power supply is connected to the body to be corroded to energize the body to allow a direct current to flow into the body to be protected. The external power supply system has an advantage that the output current can be arbitrarily adjusted according to the potential condition of the corrosion-preventing object, and that the potential of the corrosion-preventing object can be automatically adjusted so as to be kept at a constant value. However, it is widely adopted despite the large scale of equipment.

When the external power source method is applied to the underground steel structure, graphite, magnetic iron oxide,
Although refractory materials such as ferrite, high-silicon cast iron, and platinum-plated titanium are used, in recent years, titanium or titanium alloy substrates, which are more durable, are coated with platinum group metal oxides. To occupy. In the external power supply method, it is desirable to ground the electrode deep in the soil for the purpose of reducing interference with other buried metal bodies,
Usually, a diameter of Φ100 mm to Φ400 mm is bored for several tens of meters to hundreds of tens of meters underground, the durable electrode is installed in the borehole, and the periphery of the electrode is further reduced in order to reduce the installation resistance of the electrode. Is filled with powder or granular graphite called backfill.

When a direct current is applied from the durable electrode thus installed, the groundwater existing in the voids between the backfill particles is electrolyzed to generate oxygen gas and chlorine gas from the surface of the electrode. At the same time, the pH of groundwater in the vicinity of the electrode becomes strongly acidic because H ⁺ becomes excessive with the discharge of OH ⁻ ions. When the gas is generated and convection occurs on the surface of the electrode, the current density locally rises, the wear rate of the electrode increases, and the generation of strong acid on the surface of the electrode accelerates the deterioration of the electrode. , Not only the life of the electrode is significantly reduced, but when the convection of the gas progresses, the ground resistance of the electrode rises and it becomes impossible to pass a predetermined current, so that the current can be stably fed for a long time. It was difficult.

[0006]

It is an object of the present invention to effectively prevent deterioration of the above-mentioned conventional anticorrosion system, that is, a system for performing anticorrosion of a metal to be protected by supplying a direct current from the anticorrosion electrode buried in the soil. It is an object of the present invention to provide an anticorrosion system that suppresses corrosion of the metal to be protected for a long period of time.

[0007]

DISCLOSURE OF THE INVENTION The present invention relates to an underground corrosion protection system in which an anticorrosion metal buried in soil is energized to conduct corrosion protection of the corrosion protection metal, and one end of which is used for the corrosion protection. The liquid supply pipe is installed so as to reach the vicinity of the electrode, and the gas generated from the electrode is dispersed in the surroundings by positively supplying the liquid from the other end of the liquid supply pipe. It is a soil corrosion protection system characterized by alleviating a decrease in pH on the surface of an electrode.

The present invention will be described in detail below. The anticorrosion system of the present invention is a method in which oxygen and chlorine gas generated from an anticorrosion electrode buried in soil is dissolved in the liquid by supplying the liquid around the anticorrosion anode, or the above-mentioned anticorrosion is performed by the water pressure of the liquid. While suppressing the contact between the gas and the anticorrosion electrode by diffusing to the periphery of the anticorrosion electrode, the strong acid generated on the surface portion of the anticorrosion electrode is diluted to alleviate the pH decrease, thereby deteriorating the deterioration of the anticorrosion electrode. It is characterized by suppressing. As a result, it is possible to minimize the labor-intensive and cost-consuming work of replacing or re-installing the anticorrosion electrode buried in the soil.

The anticorrosion electrode that can be used in the present invention is not particularly limited, and various conventionally used sparingly soluble electrodes such as high silicon iron electrodes and platinum group metal oxide coated titanium electrodes can be used as they are. The shape is also not particularly limited, and the other end is connected to the cable connected to the corrosion-protected body via the DC power supply device and embedded in the soil. The body to be protected against corrosion by the anticorrosion electrode is not particularly limited, and various metals requiring corrosion protection such as pipelines, foundation piles, and reinforcing bars in concrete are targeted. The liquid supply pipe is embedded so that one end thereof is located in the vicinity of the anticorrosion electrode. The liquid supply pipe and the power supply cable for the anticorrosion electrode do not have to be located close to each other, but they should be embedded in the soil as an integral unit with an adhesive tape or the like to reduce the time and labor required when they are buried deep in the soil. Is preferred. The other end of the liquid supply pipe is located on the ground, and is connected to, for example, a tap of a water supply or a well via a liquid supply device having an electric pump built therein. The type of liquid supplied to the vicinity of the anticorrosion electrode by the liquid supply pipe is not limited, and tap water,
Well water, rainwater and the like can be used without limitation, and may be supplied after being made basic with sodium hydroxide and the like.

Since the liquid supply pipe is buried in the soil and is often subjected to high pressure, it is preferable to mold the liquid supply pipe with a material having relatively high strength such as hard PVC or ABS. It is desirable to apply a fluorine resin coating or the like to improve acid resistance and oxidation resistance. The liquid supply to the anticorrosion electrode by the liquid supply pipe may be performed continuously or intermittently, and the liquid supply may be automatically controlled according to the pH in the vicinity of the electrode or the electrode ground resistance. Good. The liquid supplied in the vicinity of the anticorrosion electrode is usually water, and since the solubility of the generated gas such as oxygen gas is not so high, most of the generated gas is dispersed around the anticorrosion electrode due to the pressure of the liquid, and The strong acid generated in the vicinity of the anticorrosion electrode is diluted at the same time as it does not come into contact with the anticorrosion electrode, and therefore deterioration of the anticorrosion electrode is suppressed.

Next, an example of the anticorrosion electrode system of the present invention will be described in more detail with reference to the accompanying drawings, but the anticorrosion electrode system of the present invention is not limited thereto. Figure 1
FIG. 3 is a schematic cross-sectional view showing an example of the anticorrosion electrode system of the present invention. 1 is a boring hole, 2 is a cylindrical resin casing installed in the boring hole, and the lower side surface thereof has a large number of holes. An anticorrosion electrode 3 made of a platinum group metal oxide coated titanium material or the like is installed in the perforated portion of the casing 2, and graphite is provided inside the casing 2 and outside the perforated portion of the casing 2. Is filled with a granular backfill 4, and the upper part outside the perforated portion of the casing 2 is filled with gravel 5. The electrode 3
Is connected to one end of an electric wire 8 connected to the corrosion-protected body 7 buried in the soil through the DC power supply device 6. 9
Is a liquid supply pipe whose lower end is located in the vicinity of the anticorrosion electrode 3 and whose upper end reaches the ground, and the liquid supply device 10 having a built-in water supply pump is connected to the ground-side end of the liquid supply pipe 9. The tap water or the like is pressure-fed from the liquid supply device to supply the liquid to the vicinity of the electrode 3. When anticorrosion is performed by energizing between the electrode 3 and the corrosion-prevented body 7, oxygen gas is generated from the anticorrosion electrode 3 as in normal water electrolysis, and chloride ions are contained in groundwater. In this case, chlorine gas is also generated, and at the same time, the pH in the vicinity of the electrode 3 drops. The oxygen gas and the chlorine gas are diffused from the electrode 3 to the surroundings by the pressure of the liquid supplied from the lower end side surface of the liquid supply pipe 9 so as not to contact with the electrode 3, and at the same time, the pH in the vicinity of the electrode 3 is lowered.
The decrease is also alleviated and the deterioration of the electrode 3 is suppressed.

[0012]

[Examples] A hard vinyl chloride pipe having an inner diameter of 20 mm, an outer diameter of 26 mm, and a length of 4 m was closed by attaching a cap to the end, and a PVDF heat-shrinkable tube was coated on a portion 1 m from the end, and a liquid of φ1 mm was used. A liquid supply pipe having 600 discharge holes at 10 mm intervals was manufactured. Boring with a diameter of 270 mm and a depth of 16 m was performed. Inside the boring hole, there were 852 φ32 mm current passage holes all around the side surface 7 m from the lower end.
An ABS resin casing having an inner diameter of 159 mm and an inner diameter of 146 mm was inserted from the bottom of the hole to the ground. A rod-shaped anticorrosion electrode made of platinum-plated titanium having a diameter of 10 mm and an exposed length of 500 mm, which was connected to one end of an 8 mm ² PVDF-coated cable, was fixed to the liquid supply hole of the liquid supply pipe with a vinyl tape, and then hard-chlorided. PVD while connecting vinyl pipe with coupling
With the F-coated cable, the ABS resin casing is effectively fixed up to a position 3 m from the lower end, and then the backfill is filled inside and outside the casing from the bottom of the hole to a position 9 m, and then outside the casing to the ground. Was filled. The other end of the PVDF cable was connected via a DC power supply device to a steel pipe (corrosion-protected body) embedded at a point 50 m away from the boring hole. Connect the other end of the liquid supply pipe to a water pump, and use a timer twice a day for 2 times each.
An electrode system for corrosion protection was constructed in which the pump was operated for a period of time to supply tap water to the vicinity of the electrode at a pressure of 10 kg / cm ² .

The same anticorrosion electrode system was separately installed except that the liquid supply pipe and the water pump were not installed. A DC constant current power supply device was connected between the electrodes of both anticorrosion systems and the anticorrosion body, and each was energized at 3 A to monitor the power supply voltage. The power supply voltage for both systems was initially 21V,
In the system in which the liquid supply pipe was not installed, the power supply voltage gradually increased with the start of energization and reached 45 V after two years. On the other hand, in the system with the liquid supply pipe installed, the power supply voltage was maintained at about 22V even after two years had passed. After two years, tap water was pumped into the casing and circulated to overflow the backfill, and then the electrode was collected to determine the consumption rate of platinum plating from the weight reduction and the amount of electricity applied. The wear rate of the energized electrode was 105 mg / A · Yr in the system without the tube installed, but the wear rate of the electrode energized in the system with the liquid supply tube installed was 28 mg / A · Yr.
It was Yr.

[0014]

INDUSTRIAL APPLICABILITY According to the present invention, a DC power supply device is connected between an anticorrosion electrode buried in soil and a metal structure to be protected, and a DC power supply is supplied from the anticorrosion electrode to the metal structure to prevent corrosion. In the cathodic protection system for performing the above, a liquid supply pipe, one end of which reaches the vicinity of the anticorrosion electrode, is buried in the soil, and the liquid is supplied from the other end of the liquid supply pipe for underground corrosion protection. It is an electrode system. In the conventional anticorrosion system, oxygen gas or chlorine gas is generated from the anticorrosion electrode buried in the soil, and since these gases are difficult to diffuse in the soil, the current density increases by staying near the anticorrosion electrode, Also, due to energization,
Since H ⁻ ions are consumed and H ⁺ ions become excessive and the vicinity of the anticorrosion electrode becomes strongly acidic, deterioration of the anticorrosion electrode progresses and repair or replacement of the anticorrosion electrode is required at an early stage. Since the anticorrosion electrode is buried in the soil, a lot of labor and cost are required for its repair and replacement, and its economic burden is great.

According to the system of the present invention, oxygen gas or the like generated from the anticorrosion electrode diffuses to the surroundings from the anticorrosion electrode mainly due to the pressure of the liquid supplied from the liquid supply pipe to prevent contact with the anticorrosion electrode. Further, since the strong acid generated near the electrode is diluted, deterioration of the anticorrosion electrode can be surely reduced. Therefore, the service life of the anticorrosion electrode is increased, and it becomes possible to perform anticorrosion of the anticorrosion metal structure for a long period of time without performing repair and replacement, which requires labor and cost. When an electrode obtained by coating a platinum group metal on a titanium or titanium alloy substrate is used as the anticorrosion electrode, the durability of the electrode itself is increased, and when the system of the present invention is applied to this electrode, the life of the electrode can be further extended. In the anticorrosion electrode system of the present invention, the periphery of the anticorrosion electrode is not limited to the backfill, and similar effects can be obtained even with various aqueous solutions and soils.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of implementation of a deep-burying underground corrosion protection system according to the present invention.

[Explanation of symbols]

1 ・ ・ ・ Boring hole 2 ・ ・ ・ Resin casing 3 ・
..Corrosion-proof electrodes 4 ... Backfill 5 ... Gravel 6 ... DC power supply 7 ... Corrosion-preventing body 8 ... Wire 9 ... Liquid supply pipe 10 ... Liquid supply device

Front page continuation (72) Inventor Yoshiaki Kanda 1-6-4 Marunouchi, Chiyoda-ku, Tokyo Nihon Corrosion Industry Co., Ltd. (72) Inventor Mitsuo Akutsu 1-6-4 Marunouchi, Chiyoda-ku, Tokyo Nihon Corrosion Protection Industry Co., Ltd.

Claims (2)

[Claims] 1. A cathodic protection, in which a DC power supply device is connected between an anticorrosion electrode buried in soil and a metal structure to be protected, and a DC current is passed from the anticorrosion electrode to the metal structure for corrosion protection. In the system, a solution supply pipe is installed so that one end of the system reaches the vicinity of the anticorrosion electrode, and the solution is supplied from the other end of the solution supply pipe. 2. The anticorrosion system according to claim 1, wherein the anticorrosion electrode is a titanium or titanium alloy substrate coated with a platinum group metal.