JP2518721B2 - Cathodic protection equipment for ships - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an external power supply type anticorrosion device for preventing electrolytic corrosion (electrochemical corrosion) of corrosion-protected objects such as a hull of a ship, a propeller, and a propeller shaft. .

[Conventional technology]

One of the means of cathodic protection for ships is a galvanic anode (sacrificial anode) system.

This is to forcibly apply a predetermined negative potential to a corrosion resistant body such as a hull, a propeller, a propeller shaft, and a rudder by attaching a galvanic anode made of a metal such as zinc, aluminum, or magnesium. is there.

In this case, there is an ideal range for the potential of the corrosion-prevented body against seawater, and that potential is the corrosion-prevention potential of the corrosion-prevented body (this is the potential at which corrosion protection works, for example -785 m in the case of iron).
If it is higher than V (that is, on the plus side), electrolytic corrosion occurs, and conversely, if it is significantly lower (that is, on the minus side), it causes over-corrosion and alkali causes the coating film of the hull to peel off.

However, the potential of the body to be protected against seawater changes greatly due to changes in the corrosive environment such as the traveling speed of the ship, but the galvanic anode has energy determined by the material and size of the galvanic anode, and the anticorrosion current changes the corrosive environment Therefore, even if the potential of the corrosion-prevented body while the ship is stopped is ideal, the potential becomes higher than that during traveling and the anticorrosion effect is lost. On the other hand, if the galvanic anode is increased so that the electric potential during traveling becomes ideal, the weight increases and the electric potential of the corrosion-prevented body becomes too low while the ship is stopped, resulting in over-corrosion.

An external power supply system with automatic control is a solution to such problems of the galvanic anode system.

A conventional example of this type of cathodic protection device will be described with reference to FIG. 5. This cathodic protection device comprises a variable-power DC power supply device 32, a control circuit 33 for controlling the same, and a hull 21 outside the bottom of the ship. The anode 34 and the reference electrode 35, which are electrically insulated from the hull 21 and are mounted in the seawater 10 of the above, are provided with a positive potential relative to the anode 34 from the DC power supply device 32, and the hull 2 of the ship.
1, a relative negative potential is applied to the corrosion-prevented body such as the propeller shaft 22, the propeller 23, and the rudder 24, and the corrosion-prevention current i is supplied from the anode 34 to the corrosion-protected body through the seawater 10. 36
Is a brush that is in sliding contact with the propeller shaft 22.

Moreover, the reference electrode 35 detects the potential of the body to be protected against seawater 10 (more specifically, the hull 21 which occupies most of the body), and the detected potential is a predetermined set potential E (for example, -900 m).
Control circuit 33 so that the DC power supply 3
The corrosion protection current output from 2 is automatically controlled.

According to such an anticorrosion device, the potential of the object to be protected can be brought close to a constant value even if the corrosive environment changes, so that electrolytic corrosion of the object to be protected is prevented more effectively than in the case of the galvanic anode. be able to.

[Problems to be Solved by the Invention]

However, even if the above-described cathodic protection device is provided, conventionally, the propeller 23, particularly the blade root portion thereof, suffers from the phenomenon of erosion corrosion.

Conventionally, this is due to cavitation other than electrolytic corrosion, and it has been considered that this cannot be suppressed by the electrolytic protection device.

In order to prevent this, conventionally, for example, a hole (cavitation hole) 23a is provided in the propeller 23 and the blade root portion, and through this, seawater is supplied from the side of the propeller 23 that pushes out water to the back side where water separation phenomenon easily occurs. In some cases, the propeller 23 needs to be drilled for that purpose, which increases the man-hours.When the cavitation hole 23a is opened, the strength of the propeller 2 decreases.
It is necessary to increase the thickness of the blade root of No. 3 and the propeller efficiency deteriorates, which causes other problems.

Therefore, the main object of the present invention is to improve the above-mentioned cathodic protection device, and thereby to make it possible to suppress the above-mentioned erosion and corrosion of the propeller that has been considered impossible in the past. To do.

[Means for solving problems]

In order to achieve the above object, the first cathodic protection device according to the present invention is an anode mounted on a support portion of an overhanging bearing that rotatably supports a propeller shaft of a ship from the hull, electrically insulated from the support portion. And a first direct-current power supply device of variable output for supplying an anticorrosion current from the anode to the hull of the ship through the seawater, and the seawater of the hull electrically attached to the seawater outside the hull of the ship and electrically insulated from the hull. Attached to the propeller shaft, a reference electrode for detecting an electric potential with respect to the control electrode, a control circuit for controlling an anticorrosion current output from the first DC power supply so that the electric potential of the hull detected by the reference electrode approaches a set electric potential. A potential difference detection circuit for detecting the potential difference between the propeller and the overhang bearing via the propeller shaft, and in response to a signal from the potential difference detection circuit,
And a variable output second DC power supply device that applies a relatively negative potential to the propeller via a propeller shaft and a relatively positive potential to the anode so that the potential difference approaches zero. And

A second cathodic protection device according to the present invention is an anode attached to a support portion of an overhanging bearing that rotatably supports a propeller shaft of a ship from the hull and electrically insulated from the support portion. A first direct-current power supply device with variable output for supplying anticorrosion current to a propeller shaft of a ship and a shaft system including a propeller attached thereto through seawater, and electrically isolated from the hull in seawater outside the hull of the ship Control electrode for detecting the potential of the shaft system with respect to seawater, and control for controlling the anticorrosion current output from the first DC power supply device so that the potential of the shaft system detected by the reference electrode approaches a set potential. A circuit, a potential difference detection circuit for detecting a potential difference between the overhang bearing and the propeller through a propeller shaft, and the potential in response to a signal from the potential difference detection circuit. There characterized in that it comprises a second DC power supply to impart a relatively positive potential to the anode to approach zero output variable of relatively negative potential applied to the projecting bearing and hull.

[Action]

As a result of repeated experiments, by mounting the anode of the cathodic protection device in the above-mentioned place, and further by providing a potential difference detection circuit and a second DC power supply device for canceling the potential difference between the propeller and the overhang bearing, the propeller is provided. It was also possible to effectively suppress the erosion and corrosion of. The reason is as follows.

That is, in a ship, the relative water velocity with respect to the propeller is extremely large compared to other parts, and since the oxide film on the surface of the propeller is peeled off by cavitation or dust in the water to become a bare metal, the propeller is different from other parts. The ionization tendency is easier to activate (that is, easier to activate) than the part. Therefore, even if the conventional external power supply type cathodic protection device is provided, the potential of the propeller is the highest with respect to the potential of the hull (for example, about -900 mV) (for example, about -750 mV to -350 mV). Then, a phenomenon occurs in which a current flows from the propeller to a lower potential through the seawater, for example, to an overhang bearing or a hull that rotatably supports the propeller shaft. This is because the propeller acts as if it were the galvanic anode (sacrificial anode) described above, which causes the propeller to undergo electrochemical corrosion.

Erosion corrosion of propellers was conventionally thought to be mostly due to cavitation water hammer, but the inventor
As a result of various experiments, it was found that the erosion corrosion of the propeller is a combination of the above-described electrochemical corrosion and erosion due to water hammer, and moreover, the electrochemical corrosion is larger.

In order to suppress the electrochemical corrosion of the propeller, it is sufficient to supply an anticorrosion current to this easily propelled propeller from the anode through seawater. It was not reflected in the position. For example, in the case of the conventional anode 34, the propeller shaft 22 is located in the hull 21 as shown in FIG.
About the position in the ship width direction, it was installed at an appropriate place on the left and right of the bottom of the ship, as shown in Fig. 6 (the propeller shaft 22 and the propeller 23 are two in the example shown). Although a two-axis ship is shown, the position of the anode 34 is almost the same in the case of one axis as well.).

In such a place, the anticorrosion current i mainly flows into the hull 21 near the anode 34, and the propeller 23, which is easily activated, is the anode.
Since it is far from 34, it is not in a situation where it can sufficiently supply the anticorrosion current i. Therefore, conventionally, even if the anticorrosion device was provided, the electrochemical corrosion of the propeller 23 could not be suppressed so much.

On the other hand, in the present invention, since the anode is provided in the support portion of the overhanging bearing that rotatably supports the propeller shaft, the position of the anode is very close to the propeller that is easily activated, and as a result, the seawater passes from this anode. Sufficient anticorrosive current can be supplied to the propeller. As a result, the electrochemical corrosion of the propeller can be effectively suppressed.

Also, strictly speaking, even if the above is done, there is still a potential difference between the propeller and the closest overhanging bearing due to the difference in the degree of activation, and this causes the propeller, especially the overhanging bearing from the blade root of the propeller. It is undeniable that a corrosion current may flow toward the wing and remain as a cause of erosion corrosion of the blade root of the propeller. However, in the present invention, a potential difference detection circuit and a second DC power supply device are further provided, and the propeller and the Since the potential difference between the overhanging bearing and the overhanging bearing approaches zero, it is possible to prevent the corrosion current from flowing.

As a result, it has become possible to effectively suppress the erosion corrosion of the propeller, which has been considered impossible in the past, especially the blade root portion thereof, by the electrolytic protection device.

The first cathodic protection device uses the control circuit and the first DC power supply device so that the potential of the hull approaches the set potential. Therefore, rather, the hull is the main component of the cathodic protection. It can be said that the second cathodic protection device uses the control circuit and the first DC power supply device so that the potential of the shaft system approaches the set potential. However, in any case, since the potential difference between the propeller and the overhang bearing is canceled out, erosion corrosion of the propeller, especially the root portion of the propeller is effectively suppressed. be able to.

〔Example〕

FIG. 1 is a schematic diagram showing a cathodic protection device according to an embodiment of the present invention. The same parts 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 propeller shaft 22 is normally rotatably supported by the hull 21 by an overhang bearing 25 provided in the immediate vicinity of the propeller 23 as shown in the figure.

Therefore, in this embodiment, as an alternative to the anode 34 attached to the ship bottom of the conventional example, the anode 34a is attached to the support portion 25a of the overhang bearing 25 in an electrically insulated manner from the anode 34a. DC power supply (first
DC power supply device 32) is used to relatively apply a positive potential. Further, in this example, a negative potential is relatively applied from the DC power supply 32 to the hull 21 and the overhanging bearing 25 attached thereto.

Furthermore, the potential difference ΔV between the overhang bearing 25 and the propeller 23
And a potential difference detection circuit 38 for detecting via the propeller shaft 22,
In response to the signal from the potential difference detection circuit 38, the propeller shaft 22 is attached to the propeller 23 so that the potential difference ΔV approaches zero.
And a second DC power supply device 39 for relatively negative potential and relatively positive potential to the anode 34a. Further, in this example, the rudder 24 is also relatively negatively applied from the DC power supply device 39.

Specifically, the input portion of the potential difference detection circuit 38 is a point P which is the base of the overhang bearing 25 and is covered with an insulator 50 described later.
And a brush 37 that is in sliding contact with the propeller shaft 22.

Most of the overhang bearing 25 is made of metal, and the hull 21 and the hull 21 are electrically connected to each other through the structural material of the support portion 25a, but the overhang bearing portion of the overhang bearing 25 with the propeller shaft 22 is in contact. Since the lubricating oil cannot be used because it is in seawater, a resin type is usually used instead of a metal.Therefore, the overhang bearing 25 and the propeller shaft 22 are electrically connected directly. It has not been. However, an electric current flows through the seawater 10 in a liquid junction.

More specifically, the structure around the supporting portion 25a will be described. As shown in FIG. 2 and FIG.
25a is covered with an insulating material 50 such as epoxy glass (the area is marked with dots in FIG. 2), and its surface is the front side of the supporting portion 25a (that is, in this embodiment). A triangular anode 34a is attached to a portion from the end portion (on the traveling direction side) to the left and right lateral portions by, for example, an epoxy adhesive.

The anode 34a is, for example, a titanium surface plated with platinum. Incidentally, the above-mentioned reference electrode 35 is, for example, a silver chloride electrode.

The support portion 25a is attached to the thickened portion 26 of the bottom of the hull 21 by a plurality of attachment bolts 64 (see FIG. 3) at the attachment seat 25b.

Then, the power feeding conductor 52 connected to the anode 34a is pulled out from the root of the supporting portion 25a through the inside of the front side of the insulator 50, which electrically insulates the mounting seat 25b and the thickened portion 26 in this embodiment. Connect to the head of the bolt 56 that penetrated,
A putty 54 covers the connection.

The surface of the portion of the bolt 56 that penetrates the mounting seat 25b and the thickened portion 26 is covered with an insulator (not shown) such as glass epoxy. Further, an insulator 60 such as glass epoxy is sandwiched between the nut 58 for fixing the bolt 56 and the thickened portion 26. The bolt 56 is connected to the anode terminal of the DC power supply device 32 by the power feeding conductor 62.

Further, the detection conductor 72 is passed through the rear inside of the insulator 50, and one end thereof is structurally and electrically connected to the overhang bearing 25 at a point P which is the root of the overhang bearing 25 and is covered with the insulator 50. Is connected to the member connected to. Detection conductor 72
Is connected at such a point P when the detection conductor 72 is connected to the overhanging bearing 25 at the point where it is exposed to seawater, the dissimilar metals are connected at a place where they come into contact with seawater. This is to avoid this because a potential difference is generated and causes a disturbance.

Then, the other end of the detection conductor 72 is pulled out from the root of the supporting portion 25a, and this is connected to the head of the bolt 76 that electrically penetrates the mounting seat 25b and the thickened portion 26, and the connecting portion. Is covered with putty 74. The insulating structure of the bolt 76 is the same as that of the bolt 56 described above, and therefore detailed description thereof will be omitted. 78 is a nut and 80 is an insulator. Then, this bolt 76 is connected to the potential difference detection circuit by the detection conductor 82.
I am trying to connect to the input part of 38.

When the anode 34a is provided on the support portion 25a of the overhang bearing 25 in this way, as described above, it is possible to sufficiently supply the anticorrosion current i through the seawater to the propeller 23, which is easily activated, from the immediate vicinity thereof. Electrochemical corrosion can be effectively suppressed. Even if the anode 34a is provided on the support portion 25a of the overhang bearing 25, the anticorrosion current i is also supplied to parts other than the propeller 23, for example, the hull 21, the propeller shaft 22, the rudder 24, etc. Of course, it can be prevented at least to the same extent as in the conventional example.

In addition, the potential difference ΔV between the propeller 23 and the overhang bearing 25 is
Is detected by the potential difference detection circuit 38, and the DC power supply device 39 responds to the signal from the potential difference detection circuit 38 to cause the propeller shaft to move to the propeller shaft so that the potential difference ΔV approaches zero. Negative potential is forcibly applied via 22. As a result, it is possible to prevent a corrosion current from flowing from the propeller 23, particularly from the blade root portion thereof to the overhang bearing 25 due to the potential difference ΔV between the propeller 23 and the overhang bearing 25.

As a result, propellers that were previously considered impossible
Erosion corrosion of the blade roots of 23, especially its blade root can be effectively suppressed by the cathodic protection device.

As a result, cavitation holes 23a
Even if the propeller 23 is not provided, the life of the propeller 23 can be significantly extended. Moreover, when the cavitation hole 23a is not provided, the machining of the propeller 23 is facilitated and the wall thickness of the propeller 23 can be reduced, so that the propeller efficiency does not decrease.

The potential difference detection circuit 38 may be configured to be able to correct the detection voltage only by the set potential E ₀ (for example, variable including 0), which makes it possible to slightly shift the control method. Therefore, finer control according to the situation of each ship is possible (the same applies to the case of the cathodic protection device in FIG. 4).

By the way, in the above-mentioned cathodic protection device, the control circuit 33 and the DC power supply device 32 are used so that the electric potential of the hull 21 approaches the set electric potential E. Can be said to be

On the other hand, the cathodic protection device of FIG.
Also, the DC power supply device 32 is used to bring the electric potential of the shaft system including the propeller shaft 22 and the propeller 23 close to the set potential E. If anything, it is said that the shaft system is mainly used for electrolytic protection. I can say.

The difference between the cathodic protection device of FIG. 4 and the cathodic protection device of FIG. 1 will be mainly described. In this cathodic protection device, the DC power supply device 32 described above is relatively positive with respect to the anode 34a. A potential is applied so that a negative potential is applied relatively to the shaft system including the propeller shaft 22 and the propeller 23 attached to the propeller shaft 22. Then, the reference electrode 35 detects the potential of the shaft system with respect to the seawater 10, and the control circuit 33 automatically controls the anticorrosion current output from the DC power supply device 32 so that it approaches the predetermined set potential E. I have to.

Further, by applying a positive potential relative to the anode 34a from the DC power supply device 39 described above, the hull 21, rudder 24 and overhang bearing
A negative potential is relatively applied to 25, and the potential difference ΔV between the propeller 23 and the overhang bearing 25 is detected by the potential difference detection circuit 38 in the same manner as described above.
The output from the DC power supply device 39 is controlled so that V approaches zero.

Also in the case of the cathodic protection device shown in FIG. 4, since the potential difference ΔV between the propeller 23 and the overhang bearing 25 is canceled out, the propeller 23 as in the case of the cathodic protection device shown in FIG.
In particular, it is possible to effectively suppress erosion and corrosion of the blade root portion.

Further, in the case of the electrocorrosion protection apparatus of both FIG. 1 and FIG. 4, the anode 34a is not the bottom of the ship as in the conventional example, but the overhang bearing 2
By providing it on the support portion 25a of 5, the effect of being able to reduce the risk of flooding can be obtained.

That is, in the conventional mounting structure of the anode 34, as shown in FIG. 7, the anode 34 is mounted on the tip of the dish-shaped insulator 40, and the head of the bolt 42 having a hole is embedded in the insulator 40. Insert the bolt 42 through the hole in the bottom of the hull 21 and the nut 44
It is something to fix with. Then, the power supply behavior 46 connected to the DC power supply device 32, which is insulated, is connected to the anode 34 through the hole of the bolt 42.

However, there is a risk that floating materials such as driftwood may hit the anode 34 and the insulator 40 protruding outside the bottom of the ship, and if they hit, there is a risk that the bolt 42 will be cut and water will enter. In order to reduce the risk of this water infiltration, the bolts 42 may be covered with a box 48 called a dam on the inside of the ship as shown in the illustrated example, but even then, the outer shell of the ship is not very strong. Therefore, it is not perfect and the structure is complicated.

On the other hand, as described above, the anode 34a is overhanging the bearing 25
If it is attached to the support portion 25a, it is not necessary to make an attachment hole in the bottom of the ship as in the conventional example, and the risk of extra water immersion is eliminated. Attach the power supply bolt 56 to the mounting seat 25b and the thickened portion 2.
Even if the portion of 6 is penetrated, the head can be embedded in the mounting seat 25b as in this embodiment, so that the bolt 56
There is no danger of floating objects hitting the and flooding. The same applies to the bolt 76 on the detection side.

Further, as described above, the support portion 2 of the overhanging bearing 25 is provided with the anode 34a.
When mounted on 5a, the propeller shaft 22 guards the floating object even if the floating object rises from the bottom as shown by arrow A in FIG. 2, so that the floating material is less likely to damage the anode 34a. Also, an effect that the life of the anode 34a can be extended can be obtained. Since the anode 34 of the conventional example is provided in a place unrelated to the propeller shaft 22, the above-mentioned guard effect by the propeller shaft 22 cannot be expected.

Further, instead of providing the power supply bolts 56 as in the above-described embodiment, one of the plurality of mounting bolts 64 for mounting the mounting seat 25b of the overhang bearing 25 to the hull 21 is used, for example, in FIG. The mounting bolt 64a shown in FIG. 6 may be electrically insulated from the others (the insulating structure is the same as that of the bolt 56, for example), and this mounting bolt 64a may also be used for supplying power to the anode 34a. Since it is not necessary to make another hole in the hull 21 for power supply to 34a,
The risk of flooding can be further reduced. The same applies to the detection-side bolt 76, and instead of providing it, the mounting bolt 64b shown in FIG.

Further, the anode 34a is closer to the propeller 23 when it is provided at the rear portion of the support portion 25a of the overhang bearing 25, but when the speed of the ship is high, water bubbles are formed at the rear portion of the support portion 25a and the electric resistance of the seawater 10 is increased. Is increased and it becomes difficult for the anticorrosion current i to flow,
As in this embodiment, it is preferable to provide the support portion 25a at least from the front end portion to the left and right side portions, and by doing so, the anticorrosion current i can be stably supplied. Further, the anode 34a may be provided so as to surround the support portion 25a in a strip shape.

The present invention is not limited to a two-shaft ship having two propeller shafts 22 and two propellers 23 and the like, and can of course be applied to a single-shaft ship having one of them.

〔The invention's effect〕

Since the present invention is configured as described above, it has the following effects.

That is, the anode of the cathodic protection device is attached to the supporting portion of the overhanging bearing that rotatably supports the propeller shaft of the ship from the hull, electrically insulated from the supporting portion, and the potential difference between the propeller and the overhanging bearing is canceled. By providing the potential difference detection circuit and the second DC power supply device, the electrochemical corrosion of the propeller can be effectively suppressed, and by this, the propeller, which has been considered to be impossible in the past, especially the blade root portion thereof is broken. Corrosion can be effectively suppressed by the cathodic protection device.

As a result, the life of the propeller can be significantly extended without providing a cavitation hole as in the conventional case. And if you don't have a cavitation hole,
Propeller processing becomes easier and the propeller wall thickness can be reduced, so there is no concern that propeller efficiency will drop.

Moreover, according to the above configuration, it is not necessary to form a hole for attaching the anode in the ship bottom unlike the conventional example, so that there is an effect that the risk of flooding can be reduced.

Furthermore, since the propeller shaft protects the anode against 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 diagram showing a cathodic protection device according to an embodiment of the present invention. FIG. 2 is an enlarged view showing the periphery of the overhang bearing of FIG. FIG. 3 is a view of the supporting portion and the mounting seat portion of the overhang bearing of FIG. 2 as seen from below. FIG. 4 is a schematic view showing a cathodic protection device according to another embodiment of the present invention. FIG. 5 is a schematic view showing an example of a conventional cathodic protection device. FIG. 6 is a view of the ship of FIG. 5 viewed from the rear side. FIG. 7 is an enlarged sectional view showing the periphery of the anode of FIG. 10 …… Seawater, 21 …… Hull, 22 …… Propeller shaft, 23 …… Propeller, 25 …… Overhang bearing, 25a …… Supporting part, 32 …… First DC power supply unit, 33 …… Control circuit, 34a ...... Anode, 35
...... Checking electrode, 38 ... Potential difference detection circuit, 39 ... Second DC power supply device, 50 ... Insulator

Claims (2)

(57) [Claims] Claim: What is claimed is: 1. An anode attached to a support portion of an overhanging bearing that rotatably supports a propeller shaft of the vessel from the hull and electrically insulated from the support portion, and an anticorrosion current is applied from the anode to seawater through the hull of the vessel. A first direct-current power supply device with a variable output to be supplied, a reference electrode that is electrically insulated from the hull in seawater outside the hull of the ship, and detects a potential of the hull with respect to seawater, and detection by the reference electrode The control circuit that controls the anticorrosion current output from the first DC power supply so that the potential of the hull approaches the set potential, and the potential difference between the propeller attached to the propeller shaft and the overhang bearing is determined by the propeller shaft. In response to a signal from the potential difference detection circuit and the potential difference detection circuit,
And a variable output second DC power supply device that applies a relatively negative potential to the propeller via a propeller shaft and a relatively positive potential to the anode so that the potential difference approaches zero. Cathodic protection device for ships. 2. An anode attached to a support portion of an overhanging bearing that rotatably supports the propeller shaft of the vessel from the hull, electrically insulated from the support portion, and a propeller shaft of the vessel and seawater which are attached to the propeller shaft of the vessel through seawater. A variable output first DC power supply device for supplying an anticorrosion current to the shaft system including the propeller, and electrically attached to the seawater outside the hull of the ship, electrically isolated from the hull. A verification electrode for detecting a potential, and a control circuit for controlling an anticorrosion current output from the first DC power supply so that the potential of the shaft system detected by the verification electrode approaches a set potential.
A potential difference detection circuit that detects a potential difference between the overhang bearing and the propeller via a propeller shaft, and in response to a signal from the potential difference detection circuit, relatively to the anode so that the potential difference approaches zero. A second variable output for applying a positive potential and relatively negative potential to the overhang bearing and the hull
And a DC power supply device.