This thesis is about the Impressed Current Cathodic Protection (ICCP) control and monitoring system, which brings protection against the corrosion of the ship's hull in the sea. The ship's hull is composed of iron which can be highly corroded, and therefore the corrosion brings about great physical and financial damages to the ship. Because of this, the protection against the corrosion of iron is a necessity. Since there is no one perfect way to protect against corrosion and rapid degradation, an anti-corrosive protection method, such as coating, has to run simultaneously with an electrical anti-corrosive device. The ICCP system which I will be discussing is one such method, and has several advantages. First, the life of the anode is long because the ICCP system uses an insoluble anode. Second, it can get enough protective current over a large area for protection.
Iron can be separated into three regions of corrosion, immunity and passivity. Without any external force, iron's corrosion potential under natural conditions is within a corrosion range, so such iron becomes corroded. On the other hand, protection of the vessel's hull can be made because iron's corrosion potential can be transferred to an immunity range when the ICCP system compels a protective current to be sent to the ship's hull. Iron's corrosion potential is -600mV with standard hydrogen electrode (SHE), and its protective potential is between -800mV and -900mV.
The ICCP system is composed of a power supply, anode, reference electrode and controller. AC sources from the ship's generator are converted to DC sources in terms of power supply, and a protective current is sent to ship's hull though anode. A Zinc electrode is used for a reference electrode. Zinc's potential is -1000mV with SHE. Differential potential is detected by a sensor between the ship's hull and the reference electrode, and its value must be controlled to maintain between +100mV and +200mV. Then ship's hull can always be protected. When the system is abnormal, it is designed to sound the alarm. The controller operates to increase the protective current at the anode if the value of the detected potential is lower than that of the setting potential, but it operates to decrease it if the former is higher than the latter. The controller fully senses whether or not the detected potential is within a range of protection and then it is automatically controlled to increase or decrease the amount of protective current to be sent to the anode.
The monitoring system with RS 232/485 communication is also studied in order to check the normal state of the system at a long distance, because an operator does not always watch over this system and thus the system cannot operate well because of his or her negligent management.
Since the ship always moves in the sea, an experiment of characteristics of the ICCP system is conducted by introducing various corrosional environmental factors such as velocity and pollution. First, the amount of the requisite protective current is not consistent enough to protect against corrosion of the ship's hull because the velocity is different at anchor and on the voyage. That is, the faster the velocity, the more the requisite protective current is increased. Second, the amount of the requisite protective current is also inconsistent because pollution levels are different when sailing along the coast compared to sailing out at sea. That is, the heavier the pollution, the more the requisite protective current is increased. These results must be referred to when the ICCP system is set up.
In short, the ICCP is a multi-system for use on ships and on land structures because it includes a safety device. Even over a long distance, the system's conditions can be watched through a monitoring system with communication. The system can be controlled to protect against corrosion of the ship's hull in different corrosional environments. I suggest that this system can accomodate a ship's automation and will be very useful.