JP4148373B2 - Cathodic protection method and apparatus for metal structures - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cathodic protection method and apparatus for preventing metal structures exposed to the atmosphere, such as building outer walls, roofs, and bridges, from being oxidatively corroded by an electrical system.
[0002]
[Prior art]
Even if the metal surface is exposed to the atmosphere, the metal structure exposed to the atmosphere, over time, the electrolyte moisture formed on the surface due to rainwater, moisture in the air and pollutants in the atmosphere, etc. Oxidation corrosion is caused by dissolved oxygen in the moisture.
[0003]
As a protective anode and cathode protection system that protects the painted surface of such metal structures, there is a device developed and marketed by CEL Systems, Inc. (US) 3-306342).
[0004]
Although this cathodic protection device is effective in preventing corrosion of a metal structure that is exposed to the atmosphere and whose surface is protected by painting, the following two problems are unavoidable. That is,
(1) The current control means, which is a constituent element, has a function of flowing a current having a value directly proportional to the environmental humidity detected by the humidity sensitive element. However, in practice, even if the thickness of the water film is the same at the same humidity, depending on the degree to which sea salt particles and air pollutants are dissolved in the water film, it is clear that the electricity per unit length of the water film itself Resistance varies greatly. For this reason, the amount of current required for anticorrosion varies depending on the water quality of the water film, and even if the same amount of current is applied, the reach of the anticorrosive current varies depending on the environmental water quality at that time.
[0005]
In addition, the coating film for the surface coating of a metal structure is partially deteriorated due to dust and other environmental influence factors, and a part thereof is defective. When this defect site is enlarged, the amount of current required for corrosion protection of a wide surface of the metal structure including the defect site is greatly increased even if the environmental humidity is the same. For example, when a large amount of sea salt particles are dissolved in the water film and a coating film defect occurs around the protective anode of the device, the humidity is 60 to 70% and the current is small. If only the current is supplied, the supplied current flows into the above-described defective portion, so that it is consumed in a narrow range around the protective anode, and the range where the anticorrosion current reaches becomes narrow.
[0006]
(2) In order to prevent over-corrosion of the metal structure near the protective anode, the output voltage of the anode is set to 12 V at the maximum. However, as described above, when the area of the defective portion of the coating film increases, in order to achieve the desired range of corrosion protection, it is necessary to further increase the voltage and pass a large amount of current. This need cannot be met by applying current with an output voltage of 12 V at maximum.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned conventional circumstances, and its problem is to maximize the range that can be prevented by one anode in the corrosion protection of a metal structure without causing overcorrosion. It is an object of the present invention to provide a cathodic protection method and apparatus for a metal structure that can be expanded to a maximum.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have conducted the following experimental study and have come to make the present invention.
[0009]
In the experiment, various systems were constructed, and trial and error were repeated to determine whether or not the desired function could be performed, and the system shown in FIG.
[0010]
In the figure, 1 is a terminal of an AC 100 to 200V power source, 2 is a fuse, and 3 is a surge current absorbing varistor. Reference numeral 4 denotes a transformer that drops the output to 18 to 20V. Reference numeral 5 denotes a rectifier circuit that converts alternating current into direct current. Reference numerals 6 and 7 denote capacitors. A regulator 8 controls the voltage applied to the main anode 15. 9 and 10 are capacitors, and 21 is also a capacitor. A regulator 22 controls the voltage applied to the pilot anode 20 to a constant value. Reference numerals 23 and 24 denote capacitors.
[0011]
The power supply terminal 1 to the capacitor 10, the capacitor 21, the regulator 22, and the capacitors 23 and 24 are housed in the controller 30.
[0012]
The transistor 11, resistors 12, 14, and zener diode 13 constitute first current limiting means 100 that prevents the current supplied to the main anode 15 from flowing beyond a certain value. The capacitor 25, the operational amplifier 26, and the resistors 27, 28, and 29 constitute the second current limiting means 101, and the current that flows from the pilot anode 20 into the coated steel plate (metal structure) 16 that is a corrosion protection target. And the output voltage of the regulator 8 is controlled via the ground of the regulator 8 in accordance with the detected current value, thereby causing the desired optimum current to flow from the main anode 15 to the coated steel plate 16. A special medium 70 having electrical resistance is interposed between the main anode 15 and the coated steel plate 16.
[0013]
The first current control means 100 is integrated with the main anode 15, and the second current control means 101 is integrated with the pilot anode 20. In the figure, reference numeral 17 denotes a coating film applied to the coated steel plate 16 that is the object of corrosion protection. Reference numeral 18 denotes a defective portion of the coating film 17, and 19 denotes a water film formed on the surface of the coated steel plate 16.
[0014]
In the apparatus having the above-described configuration, when the output voltage of the regulator 22 is controlled to a certain value of 8V to 12V and the current increases due to the increase in the electric conductivity of the water film 19 and the enlargement of the defect portion 18, the regulator The output voltage of 8 is increased from 10V to 15V, for example, and the desired optimum anticorrosion current is supplied to the coated steel plate 16.
[0015]
FIG. 2 shows an outline of a test facility for confirming the anticorrosion function of the cathodic protection device having the configuration shown in FIG. The main anode 15 and the pilot anode 20 were affixed to the coated steel plate 16 via an insulating double-sided joined body. The anode wires 30 a and 30 a from the controller 30 were connected to the corresponding main anode 15 and pilot anode 20, and the cathode wire 30 b was connected to the base material 32 of the coated steel plate 17.
[0016]
A part of the coating film at a position away from the anode mounting position of the coated steel plate 16 was peeled off to form an artificial coating film defect portion 18 having a diameter of 10 mm. An Ag / AgCl microelectrode (φ = 0.1 mm) 31 coated with agar containing saturated KCl was placed on the coating film defect portion 18. The potential of the steel plate base material 17 with respect to the electrode 31 was output to a computer through a buffer, and data was collected.
[0017]
An AC 100V power source was connected to the controller 30 and after confirming that the voltage of the pilot anode 20 was constant at a set value of 10V, the coated steel plate 16 was subjected to an exposure test for about 30 days. As a result, when the humidity was less than 60%, the voltage applied to the main anode 15 showed a minimum value of 10V. The higher the humidity, the higher the potential and reached around 13V during rainfall.
[0018]
Further, in addition to the above-mentioned position, a coating film defect portion is also formed between each of the anodes of the main anode 15 and the pilot anode 20 and the coating film defect portion 18 at the above position, so that the main anode 15 at the time of raining is formed. The applied voltage reached 15 V, the maximum.
[0019]
Even in this state, the potential of the coating film defect portion 18 showed a value of around −850 mV, and it was found that corrosion protection was sufficiently achieved.
[0020]
Furthermore, no sign of overcorrosion is observed in the coating film 17 near the main anode 15 and the current flowing from the main anode 15 to the defective portion 18 of the coating film 17 is sufficiently large. It can be inferred that the voltage drop in the water film on the surface of the body (special medium) 70 is lower than the voltage that causes over-corrosion protection in the coating film near the main anode 15.
[0021]
That is, when the other coating film defect part is increased between the coating film defect part 18 and the main anode 15 at a position 2.5 to 3.0 m away from the main anode 15 and the required anticorrosion current is increased, In the above technique, the voltage of the main anode 12V becomes a limit, and the potential of the coating film defect portion 18 does not decrease to the anticorrosion potential. On the other hand, in the method and apparatus of the present invention, In the test, the maximum value was 15V), but the voltage increased. Therefore, even if the coating film defect part increased considerably, the potential of the farthest defect part 18 was sufficiently lowered to reach the anticorrosion potential. confirmed. Therefore, according to the present invention, a new technology having an anticorrosive ability superior to that of the conventional technology could be established.
[0022]
The most economical method of corrosion protection of metal structures by the combination of coating film forming coating and cathodic protection is to apply a general-purpose insulating coating to the lower layer and a conductive coating with low electrical resistance to the uppermost layer. The applied metal structure (coated steel plate) was subjected to the test shown in FIG. 2 using the cathodic protection method equipment according to the present invention.
[0023]
An uppermost coating material having an electrical resistance value of 0.2 Ωcm is used, an artificial defect portion of the coating film is provided at a position 5 m away from the main anode 15, the controller 30 is energized, and the surface of the coated steel plate 16 is applied. Water was sprayed and the potential of the coating film defect portion 18 was measured.
[0024]
The potential showed a value of −850 to −950 mV, which was in the inactive region, and it was revealed that the anticorrosion was sufficiently achieved.
[0025]
In the color steel plate using normal insulating paint, the artificial defect part reaches the anticorrosion potential only up to about 2.5 to 3.5m from the main anode, but by the optimal combination of paint and cathodic protection, the anticorrosion range We were able to establish a technology that can greatly expand
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.
[0027]
FIG. 3 is a circuit diagram of an apparatus suitable for realizing the cathodic protection method for metal structures according to the present invention.
[0028]
In this method, the coating film 17 of the coated steel plate 16 that is the object to be protected has a defective portion 18, and an anode 150 made of aluminum or the like is bonded to the coated surface by an insulating double-sided bonded body 70. When the humidity is around 60%, the water film 19 covers the coated steel material 16 and air pollutants and sea salt particles are dissolved therein, so that the water constituting the water film 19 becomes an electrolyte aqueous solution, and the coating film defect portion 18 is rusted. The condition for generating is established. On the other hand, by supplying the optimum anticorrosive current from the controller and the anode 150 according to the present invention to the coating film defect portion 18 through the water film 19, rusting in the coating film defect portion 18 is prevented. .
[0029]
As shown in the figure, electricity is introduced from a terminal 33 of an AC 100 to 200 V power source, and the voltage is reduced to 18 to 20 V AC via a fuse 34, a surge current absorbing varistor 35, and a transformer 36. To do. The capacitor 38 absorbs the voltage fluctuation, and the regulator 39 supplies DC 17V electricity. Then, DC 17 V is stabilized by the capacitor 40.
[0030]
The voltage drop of the resistor 48 that changes depending on the magnitude of the current flowing from the defective part 18 of the coating film 17 through the water film 19 from the anode 150 to the coated steel plate 16 is detected by the operational amplifier 45, and the emitter of the transistor 44 is detected by the value. Control the voltage of the current flowing out of the. Resistors 41, 42, 46, 47, 49, 50 and capacitor 43 assist in the stable operation of the system. The transistor 51, the Zener diode 53, and the resistors 52 and 54 constitute current limiting means 102 that prevents the current flowing out from the anode 150 from exceeding a certain value.
[0031]
The power supply terminal 33, fuse 34, varistor 35, transformer 36, rectifier circuit 37, capacitor 38, regulator 39, and capacitor 40 are housed in a single controller 30. The resistors 41 and 42, the capacitor 43, the transistor 44, the operational amplifier 45, the resistors 46, 47, 48, 49, and 50, the transistor 51, the resistor 52, the Zener diode 53, and the resistor 54 are connected to the anode 150. Incorporated into the unit. One controller 30 supplies a constant voltage current to one or more anode systems.
[0032]
FIG. 4 shows an example of the anode 150.
[0033]
In the figure, 55 is a plate-like aluminum anode, and the current control means 102 including a transistor, an operational amplifier, a Zener diode, a resistor and the like is inserted into a recess 56 opened on the upper surface thereof, and the portion is hardened with a hard epoxy resin. It was.
[0034]
An external lead wire 58 is connected to the current control means 102. Reference numeral 59 denotes a crimp terminal for connecting the anode wiring from the controller 30. The anode 55 is attached to the coating film 17 of the coated steel plate 16 using the double-sided bonded body 70.
[0035]
【The invention's effect】
Innumerable pinholes that are invisible are often opened in the coating film of the surface coating of a metal structure. Also, the coating film becomes defective over time due to dust and other environmental factors in the atmosphere. Under such circumstances, when the humidity in the atmosphere exceeds 60%, a water film is formed on the surface of the coating film, and sea salt particles in the atmosphere are dissolved in the water film on the surface. The membrane water becomes electrolyte water. This electrolyte water comes into contact with the metal surface through the pinholes or coating film defects, and the conditions for rusting are established. At this time, it is a cathodic protection method that suppresses rusting by passing a corrosion protection current through the electrolyte water film. In this cathodic protection method, the method of the present invention, unlike the conventional method, increased the voltage applied to the anode in accordance with the increase in the required current amount, and was conventionally considered impossible for overcorrosion. The anticorrosion current can be passed to a region away from the anode. In the present invention, depending on the variation in characteristics of the special medium (electrolyte water film) having electrical resistance interposed between the coating film and the anode of the metal structure that is the object of corrosion prevention, and the size of the coating film defect portion Control the anticorrosion current, voltage optimally. By maintaining the maximum voltage at which the coating film in the vicinity of the anode does not cause over-corrosion even when the current is increased, the region where the cathodic protection is possible starting from the anode can be increased.
[0036]
In addition, after applying an undercoat of a general-purpose insulating paint, an electroconductive special paint is applied as a surface finish paint, and further, by applying the cathodic protection method according to the present invention, an electric source starting from the anode is used. It was possible to dramatically increase the anticorrosion area. Therefore, by optimizing the combination of the type of paint and the voltage and current values of the cathodic protection method according to the present invention, a highly economical corrosion prevention method for metal structures can be established.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an example of a cathodic protection device for a metal structure of the present invention.
2 is an explanatory diagram of a system for measuring the function of the apparatus shown in FIG. 1; FIG.
FIG. 3 is a circuit diagram of another example of the cathodic protection device for metal structures according to the present invention.
4 is a perspective view showing an example of a cathode of the apparatus shown in FIG. 3. FIG.
[Explanation of symbols]
1, 33 Power supply terminal 2, 34 Fuse 3, 35 Varistor 4, 36 Transformer 5, 37 Rectifier circuit 6, 7, 9, 10, 21, 23, 24, 25, 38, 40, 43 Capacitor 8, 22, 39 Regulator 11, 44, 51 Transistor 12, 14, 27, 28, 29 Resistor 13, 53 Zener diode 15 Main anode 16 Painted steel sheet (metal structure)
17 Coating film 18 Defect 19 of coating film Water film 20 formed on surface of coated steel plate Pilot anode 26, 45 Operational amplifier 30 Controller 30a Anode wire 30b from controller 31 Cathode wire 31 from controller Ag / AgCl minute Electrode (φ = 0.1mm)
32 Base material 41, 42, 46, 47, 48, 49, 50, 52, 54 of coated steel plate Resistor 55 Plate-like aluminum anode 56 Recess 58 Lead wire 59 Crimp terminal 70 Insulating double-sided bonded body (special with electric resistance) Medium)
100 First current limiting means 101 Second current limiting means 102 Current limiting means 150 Anode

Claims (7)

A cathodic protection method in which current is applied to a metal structure from an external power source to prevent corrosion of the metal structure,
A main anode and a pilot anode are attached on the coating film of the metal structure, a cathode is attached to a metal base material of the metal structure, and a predetermined voltage is applied from the pilot anode to the metal structure. The amount of corrosion prevention current required for the metal structure that is subject to corrosion prevention is read from the current value of the pilot anode that changes according to the change in the corrosion environment of the metal structure, and this current value The cathodic anticorrosion method for a metal structure is characterized in that the voltage applied to the main anode is increased or decreased in conjunction with this to thereby supply an optimum anticorrosion current corresponding to the corrosive environment of the metal structure. 2. The cathodic protection method according to claim 1, wherein the pilot anode and the main anode are in a one-to-one correspondence .   By attaching the pilot anode and the main anode to a metal structure that is an object to be protected through an insulating double-sided joined body, a water film is continuously formed from the surface of the metal structure to each of the anodes, When the corrosion condition of the metal structure is ready, an optimum current for corrosion prevention flows between the anode and the cathode connected to the metal base material of the metal structure. The cathodic protection method according to claim 1 or 2. A cathodic protection device for energizing a metal structure from an external power source to prevent corrosion of the metal structure,
Applying a predetermined voltage from the pilot anode to the metal structure, a main anode and a pilot anode attached on the coating film of the metal structure, a cathode connected to a metal base material of the metal structure, The magnitude of the required amount of anticorrosion current of the metal structure to be subjected to corrosion prevention is read from the current value of the pilot anode that changes according to the change in the corrosion environment of the metal structure, and the current value And a current control means for supplying and supplying an optimum anticorrosion current according to the corrosive environment of the metal structure by raising and lowering the voltage applied to the main anode in conjunction with the cathode of the metal structure. Anticorrosion equipment. The cathodic protection device according to claim 4, wherein the pilot anode and the main anode are in a one-to-one correspondence .   An insulating double-sided joined body for attaching the pilot anode and the main anode to the surface of the metal structure is further provided, and the respective anodes are attached to the metal structure that is an anticorrosion target via the insulating double-sided joined body. When a water film is continuously formed from the surface of the metal structure to each of the anodes and corrosion conditions of the metal structure are ready, the anode and the metal of the metal structure are attached. 6. The cathodic protection device according to claim 4, wherein an optimum current for corrosion prevention flows between the cathode connected to a base material. The coating of the metal structure which is the object of anticorrosion is performed by a combination of an insulating paint for the lower layer and a conductive paint for the uppermost layer. A method for cathodic protection of a metal structure, characterized by applying any cathodic protection.

Images