JPH0470396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an externally powered cathodic protection method for a structure near the stern in seawater.

``Prior art'' Structures near the stern, such as the stern shell plate, propulsion blades, and rudder, which are submerged in seawater, are exposed to dissolved substances in the seawater, differences in stress on the propulsion blade surface, impact force due to cavitation, and dissimilar materials. Influenced by the combination of metals, etc.
Since corrosion occurs, cathodic protection methods are employed to prevent this corrosion.

Conventionally, as cathodic protection methods for the structure near the stern, there are galvanic anode method and external power supply method.
Here, the cathodic protection means using the external power supply method will be explained with reference to FIG.

In Fig. 3, 1 is the hull outer plate, 2 is the propulsion wing,
Reference numeral 3 denotes a rotation axis of the propulsion blade 2, and numeral 4 denotes a rudder. The outer plate 1 of the stern part submerged in seawater, the propulsion blade 2, and the rudder 4 are collectively referred to as the stern vicinity structure.

An insoluble anode 5 is provided on the bottom outer plate 1 of the stern section, and the insoluble anode 5 is electrically connected to an output terminal of a rectifier 6 as an external power source provided inside the ship.

An electrode 7 for detecting the anti-corrosion potential of the hull is provided on the bottom shell plate 1 at the stern, which is located in front of the insoluble anode 5. This detection electrode 7 is connected to the control input terminal of the rectifier 6 and the connected.

Between the rotating shaft 3 of the propulsion blade 2 and the hull outer plate 1,
A rotating shaft grounding circuit 9 is provided via an arbitrary slip ring 8.

This rotary shaft grounding circuit 9 is designed to prevent stray wires from flowing into the rotary shaft 3 system when the rotary shaft 3 and the bearings become insulated due to an oil film of lubricating oil while the ship is sailing. The current is released to the hull outer plate 1,
This prevents corrosion of the rotating shaft 3 system due to stray current.

As a result, an anticorrosion current 11 flows from the insoluble anode 5 through the seawater 10 to the outer plate 1, propulsion blades 2, rudder 4, etc. of the stern, and these structures near the stern receive an electrolytic corrosion protection effect.

On the other hand, the corrosion protection potential to the structure near the stern is:
Detected by the detection electrode 7, this detection electrode 7
The rectifying device 6 is automatically controlled to change the output based on the detected potential from the insoluble anode 5 to the structure near the stern via the seawater 10.
We are trying to maintain this at an appropriate value.

"Problems to be Solved by the Invention" By the way, the detection of the anticorrosive potential of the structure near the stern by the detection electrode 7 is correlated to the distance between the insoluble anode 5 and the detection electrode 7, and the detection electrode 7 is In the past, when the propulsion blade 2 of the structure near the stern section was the main target for corrosion protection, the value of the anticorrosion current 11 for the propulsion blade 2 was different, and an appropriate corrosion protection potential could not be obtained in some cases.

In addition, due to insufficient control of the rotating shaft grounding circuit 9, stray current in the rotating shaft 3 system could not be reliably released to the hull shell 1, causing corrosion in the rotating shaft 3 system. .

"Means for Solving the Problems" The present invention is intended to solve the problems of the conventional art, and its configuration will be explained below based on FIG. 1.

As shown in FIG. 1, a bottom shell plate 1 at the stern section is located at a distance equal to or more than the distance between the propulsion blade 2 of the vessel and the insoluble anode 5 provided on the bottom shell plate 1 at the stern section. Anti-corrosion potential detection electrode 7 provided in
A grounding voltmeter 1 is installed in the rotating shaft grounding circuit 9 between the rotating shaft 3 of the propulsion blade 2 and the hull outer plate 1 to control the external power rectifier 6 for the insoluble anode 5.
2 and a magnetic-current conversion type grounding ammeter 13 to measure the grounding resistance of the rotating shaft grounding circuit 9.

"Function" As described above, by providing the anti-corrosion potential detection electrode 7 at a position in front of the insoluble anode 5 that is equal to or longer than the distance between the propulsion blade 2 and the insoluble anode 5, as shown in FIG. The anticorrosion potential from the insoluble anode 5 can be made approximately equal to the potential set by the anticorrosion potential detection electrode 7.

In addition, a grounding voltmeter 1 provided in the rotating shaft grounding circuit 9
2 and the magnetic-current conversion type grounding ammeter 13, the grounding resistance of the rotating shaft grounding circuit 9 can be measured and monitored.

"Effects of the Invention" According to the externally powered cathodic protection method for structures near the stern in seawater of the present invention described above, the corrosion protection potential from the insoluble anode to the propulsion blade is approximately equal to the set potential by the corrosion protection potential detection electrode. Since they can be made equal, an appropriate anticorrosion current can always be applied to structures near the stern including the propulsion wing, the stern outer plate, the rudder, and the like.

Moreover, since the grounding resistance of the rotary shaft grounding circuit can be constantly measured and monitored, corrosion of the propulsion blade rotary shaft system due to stray current due to poor grounding can be prevented.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an embodiment of the present invention of an externally powered cathodic protection method for a structure near the stern in seawater, and Fig. 2 shows the corrosion protection potential of an insoluble anode for a ship's propulsion blade and the setting by the corrosion protection potential detection electrode. FIG. 3 is a graph showing the relationship with electric potential, and is an explanatory diagram showing a conventional example of an externally powered cathodic protection method for a structure near the stern in seawater. DESCRIPTION OF SYMBOLS 1... Hull outer plate, 2... Propulsion blade, 3... Rotating shaft, 4... Rudder, 5... Insoluble anode, 6... External power supply rectifier, 7... Corrosion protection potential detection electrode, 8...
Slip ring, 9...Rotating shaft grounding circuit, 10...
...Seawater, 11...Anti-corrosion current, 12...Grounding voltmeter, 13...Magnetic-current conversion type grounding ammeter.

Claims (1)

[Claims] 1. An insoluble anode is detected by an anti-corrosion potential detection electrode provided on the bottom skin of the stern at a position equal to or more forward of the insoluble anode at a distance equal to or more than the distance between the propulsion blade of the vessel and the insoluble anode provided on the bottom skin of the stern. The rotary shaft is grounded by a grounding voltmeter and a magnetic current conversion type grounding ammeter installed in the rotary shaft grounding circuit between the rotary shaft of the propulsion blade and the hull outer plate. An externally powered cathodic protection method for a structure near the stern in seawater, which is characterized by measuring the earthing resistance of a circuit.