JPH0699886A - Electrolytic corrosion protector for marine vessel - Google Patents

Abstract

PURPOSE:To provide an electrolytic corrosion protector constituted in such a way as to suppress the electrochemical corrosion of the whole corrosion protected body including a rudder plate effectively by dissolving potential difference between the rudder plate and a hull. CONSTITUTION:In addition to a first positive electrode 34, a first d.c. power unit 32, a reference electrode 35 and a control circuit 33 existing to prevent the electrolytic corrosion of the whole corrosion protected body 20 of a marine vessel, a second positive electrode 40 electrically insulated from a rudder plate 24a is provided at least at the front side end part of the rudder plate 24a. An electrolytic corrosion protector thus constituted is further provided with a potential difference detecting circuit 52 for detecting potential difference between the rudder plate 24a and a hull 21, and a variable output second d. c. power unit 54 for relatively imparting positive potential to a second positive electrode 40 and negative potential to the rudder plate 24a so that the potential difference approaches to zero in response to a signal from the potential difference detecting unit 52.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an external power supply type anticorrosion device for preventing electrolytic corrosion (electrochemical corrosion) of a body to be protected including a hull of a ship, a propeller, a propeller shaft and a rudder.

[0002]

2. Description of the Related Art A galvanic anode (sacrificial anode) system is one of the means for cathodic protection against ships.

This is forcibly imparting a predetermined negative potential by attaching a galvanic anode made of a metal such as zinc, aluminum, or magnesium to an anticorrosive body such as a hull, a propeller, a propeller shaft, and a rudder. To do.

In this case, the potential of the body to be protected against seawater has an ideal range, and the potential is the corrosion potential of the body to be protected (this is the potential at which corrosion protection works, for example -785 mV for iron). ) When it is higher (that is, on the positive side), electrolytic corrosion occurs, and conversely, when it is significantly lower (that is, on the negative side), it is over-corrosion and causes problems such as peeling of the coating film of the hull due to alkali.

However, the potential of the body to be protected against seawater greatly changes due to changes in the corrosive environment such as the navigation speed of the ship, but the galvanic anode has energy determined by the material and size of the galvanic anode and corrodes the anticorrosion current. Since it cannot be changed according to changes in the environment, even if the potential of the body to be protected while the ship is stopped is ideal, the potential becomes higher than that during navigation and the anticorrosion effect is lost. On the contrary, if the galvanic anode is increased so that the potential during navigation becomes ideal, the weight increases and the potential of the corrosion-prevented body becomes too low while the ship is stopped, resulting in over-corrosion. .

As a solution to such a problem of the galvanic anode method, there is an external power source method which employs automatic control.

A conventional example of this type of cathodic protection device will be described with reference to FIG. 5. This cathodic protection device comprises a DC power supply device 32 of variable output, a control circuit 33 for controlling the same.
An anode 34 and a reference electrode 35 that are electrically insulated from the hull 21 and are attached to the seawater 10 outside the bottom of the hull 21 are provided, and a positive potential is relatively applied from the DC power supply device 32 to the anode 34. In this example of the hull 21, propeller shaft 2
2. A relative negative potential is applied to the body 20 to be protected, including the propeller 23 and the rudder 24, so that an anticorrosion current i is supplied from the anode 34 to the body 20 to be protected through the seawater 10.
36 is a brush.

Moreover, the reference electrode 35 detects the potential of the body 20 to be protected against seawater (more specifically, the hull 21 occupying most of it), and the detected potential is a predetermined set potential E (for example, -900 mV). The control circuit 33 automatically controls the anticorrosion current output from the DC power supply device 32 so as to approach.

According to such an anticorrosion device, the potential of the body 20 to be protected can be brought close to a constant value even if the corrosive environment changes, so that the body 20 to be protected is more effective than the galvanic anode. Electrolytic corrosion can be prevented.

[0010]

However, even if the above-described cathodic protection device is provided, a part of the rudder plate 24a forming the rudder 24, more specifically, the front half B of the rudder plate 24a is electrolytically corroded. There was a problem of being lost by.

In pursuit of the cause, the hull 21, the propeller shaft 22, and the propeller shaft 22, when the ship is stopped or its navigation speed is low, even when the above-mentioned cathodic protection device is operated.
Although the propeller 23 and the rudder 24 are all set to a set potential E (for example, -900 mV as described above) to effectively prevent the corrosion, when the navigation speed of the ship is increased, the potential of the hull 21 is almost set. Although it is a set potential and the potentials of the propeller shaft 22 and the propeller 23 are slightly higher (for example, 20 to 30 mV) than the hull potential, the potential of the rudder blade 24a of the rudder 24 is significantly higher than the hull potential (for example, the speed is 20%). It was found that it was about 450 mV at knots and about 650 mV at 25 knots.

This is because the rudder blade 24a is farthest from the anode 34 in the body 20 to be protected and the corrosion protection current i from the anode 34 is difficult to be supplied to it, and the strong water flow from the propeller 23 is received. The rudder blade 24a (especially the front part)
It is considered that this is because the ionization tendency is more likely to be activated (that is, easier to be activated) than that of the other corrosion-prevented body 20.

When the electric potential of the rudder blade 24a becomes high as described above, a current flows from the rudder blade 24a through the seawater 10 toward the lower electric potential, more specifically, to the nearby propeller 23 or hull 21 and Means that the rudder blade 24a acts as if it were the aforementioned galvanic anode (sacrificial anode), which causes the rudder blade 24a to undergo electrochemical corrosion and become defective.

The potential difference between the rudder plate 24a and the hull 21 as described above tends to increase as the navigation speed of the ship increases, but in recent years, the speed of the ship tends to become higher and higher. The electrolytic corrosion of 24a has become a very big problem in high-speed ship design.

Therefore, according to the present invention, by eliminating the potential difference between the rudder blade and the hull as described above, it is possible to effectively suppress the electrochemical corrosion of the entire corrosion-protected body including the rudder blade. The main object of the present invention is to provide a cathodic protection device.

[0016]

In order to achieve the above object, the cathodic protection device of the present invention has, in addition to the structure of the conventional cathodic protection device described above, at least a front side of a rudder plate constituting the rudder. A second anode provided at the end electrically insulated from the rudder blade, a potential difference detection circuit for detecting the potential difference between the rudder blade and the hull, and a signal from the potential difference detection circuit And a variable output second DC power supply device that applies a positive potential relatively to the second anode and a negative potential relatively to the steering plate so that the potential difference approaches zero. Is further provided.

[0017]

According to the above construction, when a potential difference occurs between the rudder blade and the hull, this is detected by the potential difference detection circuit,
In response to the signal from the potential difference detection circuit, the second DC power supply device gives a positive potential relatively to the second anode so that the potential difference approaches zero and relatively to the rudder blade. Apply a negative potential to. As a result, the potential difference between the rudder blade and the hull approaches zero. Therefore, it is possible to prevent a corrosion current from flowing from the rudder blade toward the propeller or the hull due to this potential difference. As a result, it becomes possible to effectively suppress the electrochemical corrosion of the entire corrosion-protected body including the rudder blade.

[0018]

FIG. 1 is a schematic view showing a cathodic protection device according to an embodiment of the present invention. The same or corresponding portions as those of the conventional example shown in FIG. 5 are designated by the same reference numerals, and the differences from the conventional example will be mainly described below.

The cathodic protection device of this embodiment includes, in addition to the above-mentioned anode (first anode) 34, DC power supply device (first DC power supply device) 32, reference electrode 35 and control circuit 33, The second anode 40, the potential difference detection circuit 52, and the second DC power supply device 54 are further provided.

The second anode 40 is provided at least at an end of the rudder plate 24a constituting the rudder 24 on the front side (that is, the propeller 23 side) so as to be electrically insulated from the rudder plate 24a. .

More specifically, as shown in FIGS. 2 and 3, in this example, a groove 24c is formed in the front end face of the rudder blade 24a.
And a titanium rod 40a is embedded so that the front side thereof is exposed with an insulator 42 interposed therebetween. The exposed portion of the titanium rod 40a is clad with chemically stable platinum 40b. The titanium rod 40a and the platinum 40b constitute the second anode 40.

The provision of the anode 40 at least at the front end of the rudder blade 24a is because the water pressure of the seawater is the highest at that portion, and bubbles are unlikely to occur, so that the current from the anode 40 is sufficiently and stable in seawater. And flow through the steering plate 24a, which will be described later.
This is because the potential control can be effectively and stably performed. For the same reason, the anode 34 is provided at least at the front end of the support portion 25a of the overhang bearing 25 as in the example of FIG. 4 described later.

In this example, a connection conductor 44 penetrating the rudder shaft 24b of the rudder 24 is connected to the anode 40, and the connection conductor 44 is connected via a connection lead wire 47 to the DC power supply unit 5.
4 is connected to the anode terminal. This connecting conductor 44 is
The insulator 46 is electrically insulated from the rudder shaft 24b and the like. This connecting conductor 44 is also made of titanium, for example.

The insulator 42 not only insulates the anode 40 from the rudder blade 24a, but also is provided so as to cover at least the surface of the rudder blade 24a around the anode 40, as shown in FIGS. Is preferred. This is preferable because the current (corrosion protection current) flowing from the anode 40 through the seawater 10 to the rudder blade 24a is widely dispersed to uniformly control the electric potential of the entire rudder blade 24a.

The extent to which the rudder blade 24a should be covered with the insulator 42 cannot be generally stated, but for example, the width W of the insulator 42 from the tip of the rudder blade 24a and the tip of the anode 40 can be considered. The length L from 10 to 20
The effect of about cm is sufficient.

The insulator 42 is a reinforced plastic such as glass polyester. The insulator that covers the surface of the rudder blade 24a may be integrated with the insulator that insulates the anode 40 or may be separate.

Referring again to FIG. 1, the potential difference detection circuit 52
Is for detecting a potential difference ΔV between the rudder blade 24a and the hull 21. Since the rudder blade 24a and the rudder shaft 24b are connected with almost no electric resistance, in this example, the potential difference ΔV between the rudder blade 24a and the hull 21 is detected via the rudder shaft 24b. Therefore, in this example, one of the input parts of the potential difference detection circuit 52 is connected to the rudder shaft 24b via the connecting conductor 48, and the other is connected to the hull 21 via the connecting conductor 50.

The second DC power supply device 54 has a variable output, and responds to a signal from the potential difference detection circuit 52 by
A positive potential is relatively applied to the anode 40 and a negative potential is relatively applied to the steering plate 24a so that the potential difference ΔV approaches zero. In this example, the negative potential is also applied to the rudder blade 24a via the rudder shaft 24b. Therefore, in this example, the anode terminal of the DC power supply device 54 is connected to the anode 40 via the connecting conductor 47 and the connecting conductor 44 as described above, and the cathode terminal is connected to the rudder shaft 24b via the connecting conductor 49. Has been done.

It is to be noted that the connection conductor 49 is connected to the same rudder shaft 24b, but the connection conductor 48 on the potential difference detection circuit side and the connection conductor 49 on the negative potential applying side are separated from each other on the connection conductor 49 side. This is because a relatively large current flows from the DC power supply 54 to cause a voltage drop, and this voltage drop does not cause an error in potential difference detection. The connecting wire on the cathode side of the first DC power supply device 32 and the control circuit 3 described above.
The reason why the connecting conductor on one side of 3 is separate is also for the same reason.

According to this electrocorrosion protection device, the basic corrosion protection of the entire body 20 to be protected including the hull 21, the propeller shaft 22, the propeller 23 and the rudder 24 is the same as in the conventional example.
First anode 34, first DC power supply 32, reference electrode 3
5 and the control circuit 33. Therefore, duplicate description of the operation will be omitted.

In addition to this, in this cathodic protection device, when a potential difference ΔV is generated between the rudder blade 24a and the hull 21 due to navigation of the vessel, this is detected by the potential difference detection circuit 52 and the second DC power source is detected. In response to the signal from the potential difference detection circuit 52, the device 54 gives a positive potential relatively to the second anode 40 so that the potential difference ΔV approaches zero, and relatively to the rudder blade. Apply a negative potential to. As a result, the potential difference ΔV between the rudder blade 24a and the hull 21 approaches zero. Therefore, it is possible to prevent the corrosion current from flowing from the rudder blade 24a toward the propeller 23 and the hull 21 due to the potential difference ΔV. As a result, it becomes possible to effectively suppress the electrochemical corrosion of the entire body 20 to be protected including the rudder blade 24a.

Moreover, such an effect can be obtained not only when the ship is stopped, but also when the navigation speed of the ship is low or high. Therefore, the problem of electrochemical corrosion of the rudder blade 24a and the like in the high-speed ship design is also solved.

Further, if only the control circuit 33 and the first DC power supply device 32 side are used, the rudder blade 24 during navigation of the ship is assumed.
If the potential of the entire body 20 to be protected is lowered so that the potential of a becomes appropriate, the potential of the hull 21 drops too much and over-corrosion occurs, causing problems such as peeling of the coating film of the hull 21. According to this cathodic protection device, the control circuit 33 and the DC power supply device 32 side may be arranged such that the potential of the hull 21 occupying most of the object 20 to be protected becomes appropriate. In addition to preventing excessive corrosion protection, it is possible to save the power because it is not necessary to supply an excessive corrosion protection current from the DC power supply device 32.

The potential difference detection circuit 52 may be capable of correcting the detection voltage by the set potential E ₀ (for example, a variable including 0), and by doing so, the potential of the rudder blade 24a can be adjusted. Since the control method can be slightly shifted, it is possible to prevent the electric potential of the rudder blade 24a from lowering than the electric potential of the propeller 23, and it is possible to perform more detailed control according to the situation of each individual ship.

Further, as shown in FIG. 4, the first anode 34 is not provided on the bottom of the hull 21 as shown in FIG. 1, but as shown in FIG. It may be attached to the supporting portion 25a while being electrically insulated from the supporting portion 25a. More specifically, in the example of FIG. 4, the support portion 25a of the overhang bearing 25 is covered with an insulator 56 such as glass polyester (the dotted area in FIG. 4 is the area), and the surface thereof is Therefore, the triangular anode 34 is attached to the portion from the front end portion of the support portion 25a to the left and right side portions by, for example, an epoxy adhesive.

When the anode 34 is thus provided on the support portion 25a of the overhang bearing 25, a sufficient anticorrosion current can be supplied from the anode 34 in the immediate vicinity to the steering plate 24a and the propeller 23, which is apt to be activated next, through the seawater 10. Therefore, the functions of the control circuit 33 and the DC power supply device 32 side can more effectively suppress the electrochemical corrosion of the rudder blade 24a and the propeller 23.

In addition, when the anode 34 is provided on the bottom of the ship, a hole through which a bolt for fixing the anode 34 is inserted must be formed, and the anode 34 protruding outside the bottom of the ship has floating objects such as driftwood. While there is a risk that the bolt will be cut off and water will enter when the bolt is hit, the anode 34 is extended and the bearing 2
When it is provided in the support portion 25a of No. 5, it is not necessary to make a hole for attaching the support portion 25a in the bottom of the vessel, so that there is no danger of extra flooding. Further, even if the floating object rises from the bottom as shown by arrow C in FIG. 4, the propeller shaft 22 guards, so that the floating object is less likely to be damaged and the anode 34 The life can be extended. Up to now, the anode 34 has been provided in a place unrelated to the propeller shaft 22, so that the above-described guard effect by the propeller shaft 22 cannot be expected.

[0038]

As described above, according to the present invention, basically, the first anode, the first DC power supply device, the reference electrode, and the control circuit prevent electrochemical corrosion of the entire body to be protected, With this alone, the phenomenon that the potential of the rudder plate rises above the potential of the hull accompanying the navigation of the ship can be suppressed by the second anode, the potential difference detection circuit, and the second DC power supply device. Regardless of the above, it is possible to effectively suppress the electrochemical corrosion of the entire corrosion-protected body including the rudder blade.

Moreover, if it is attempted to lower the potential of the entire body to be protected by the control circuit and the first DC power supply side so that the potential of the rudder blade during navigation of the ship becomes appropriate, the potential of the hull will be reduced. However, according to the present invention, the control device and the first DC power supply device side have a hull that occupies most of the body to be protected against corrosion. Since it is only necessary to make the electric potential appropriate, it is possible to prevent the above-mentioned over-corrosion protection of the hull, and it is not necessary to supply an excessive protection current from the first DC power supply unit, so that power The effect of being able to save is also obtained.

When the first anode is attached to the support portion of the overhanging bearing that rotatably supports the propeller shaft of the ship from the hull, electrically insulated from the support portion, the control circuit and the first anode are provided. The function of the DC power supply device makes it possible to more effectively suppress the electrochemical corrosion of the rudder blade and the propeller. Moreover, since it is not necessary to open the hole for attaching the first anode in the bottom of the ship, the risk of flooding can be reduced. Further, since the propeller shaft protects the first anode from the floating material, the floating material is less likely to be damaged by the floating material, and the life of the anode can be extended.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cathodic protection device according to an embodiment of the present invention.

2 is an enlarged view of the rudder portion of FIG. 1. FIG.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is an enlarged view showing the periphery of a bulge bearing.

FIG. 5 is a schematic view showing an example of a conventional cathodic protection device.

[Explanation of symbols]

 20 Corrosion Protection Body 21 Ship Body 22 Propeller Shaft 23 Propeller 24 Rudder 24a Rudder Plate 24b Rudder Shaft 25 Overhang Bearing 32 First DC Power Supply Device 33 Control Circuit 34 First Anode 35 Reference Electrode 40 Second Anode 42 Insulator 52 Potential Difference Detection circuit 54 Second DC power supply device

Claims (3)

[Claims] 1. A first anode attached to a structure in the seawater of a ship, electrically insulated from the structure, and a hull of the ship, a propeller, through seawater from the first anode.
A first direct-current power supply device with variable output for supplying anticorrosion current to an anticorrosion body including a propeller shaft and a rudder, and a structure that is electrically insulated from the structure in the seawater of a ship. A reference electrode for detecting the potential of the anticorrosion body with respect to seawater, and a control circuit for controlling the anticorrosion current output from the first DC power supply device so that the potential of the anticorrosion body detected by the reference electrode approaches a set potential. In a cathodic protection device for a ship, comprising: a second anode, which is electrically insulated from the rudder plate at least at a front end of a rudder plate that constitutes the rudder, and between the rudder plate and the hull. A potential difference detection circuit for detecting a potential difference, and in response to a signal from this potential difference detection circuit, a positive potential is relatively applied to the second anode so that the potential difference approaches zero, and the rudder blade is provided. Relatively negative potential Cathodic protection system of vessels Azukasuru the second DC power supply output variable, characterized in that the further provided. 2. The cathodic protection device for a ship according to claim 1, wherein the surface of at least a portion of the rudder plate around the second anode is covered with an insulator. 3. The first anode is attached to a support portion of an overhanging bearing that rotatably supports the propeller shaft of the ship from the hull, while being electrically insulated from the support portion.
Or the ship's cathodic protection device according to 2.