Cathodic Protection of a Ship. What is MGPS, ICCP, Shaft Earthing Device?

Cathodic protection of a ship is a method of preventing corrosion of the metal surfaces of a ship, especially the underwater part of the hull and submerged metal structures such as propellers and rudders.

There are two main types of cathodic protection: sacrificial protection and protection using an external current source.

The main elements of cathodic protection:

1. MGPS (Marine Growth Prevention System):

• This system is designed to prevent the fouling of the ship's hull, seachests, its underwater parts, as well as outboard fittings by marine organisms, such as seaweed, shells, etc.
• It works by applying a small electric current or using chemical methods to create an environment unfavorable for the growth of these organisms.
• One of the common technologies in MGPS is the use of copper and aluminum anodes, which emit ions that prevent the growth of fouling.

2. ICCP (Impressed Current Cathodic Protection):

• This system uses an external DC source that supplies electricity to anodes immersed in water.
• The anodes are connected to the positive pole of the current source, and the ship's hull is connected to the negative.
• Electric current passing through water creates a negative potential on the ship's hull, which prevents oxidation and, therefore, corrosion.
• The anodes used in ICCP do not deteriorate, as the electric current is maintained by an external source.

3. Shaft Earthing Device:

• This device is designed to prevent corrosion of the ship's engine shaft, main engine components and other associated metal parts.
• During the operation of the vessel, the shaft can accumulate electrical potentials that can cause electrochemical corrosion.
• The shaft grounding device creates a path for the safe discharge of these potentials into the water, thereby preventing corrosion processes.
• Most often, this is achieved using a sliding contact or a special brush mechanism that connects the shaft to the ship's hull and then to the ground.

Cathodic protection of a ship is a comprehensive system aimed at preventing corrosion and fouling of the underwater part of the ship. This includes the use of MGPS systems to prevent the growth of marine organisms, ICCP for cathodic protection using an external current source and shaft earthing devices to prevent corrosion of the engine shaft. All these systems work together to ensure the durability and reliability of the metal parts of the vessel submerged in water.

What is MGPS?

MGPS (Marine Growth Prevention System) on a ship is a system to prevent the formation of marine growth on the hull and underwater parts of the vessel. Such growth includes algae, barnacles, and other marine organisms that can attach to the hull and its systems, reducing efficiency and increasing operating costs.

MGPS operates on one tank through which sea water passes to the ship's systems

MGPS operates on both side and bottom seachests

MGPS typically includes the following components:

1. Electrochemical anodes and cathodes: These devices are installed on the hull and in the seawater systems. When an electric current is passed through them, a small amount of copper and chlorine is released, which prevents fouling.
2. Control system: Controls the anodes and cathodes, ensuring the correct amount of copper and chlorine ions in the water.
3. Chlorine supply system: Some systems use chlorine generation through the electrolysis of seawater to prevent fouling.

MGPS Anodes and Cathodes (50% wear)

The primary purpose of MGPS is to keep the vessel's underwater parts and cooling systems clean, which helps maintain its performance, reduce fuel consumption and improve overall operational efficiency.

Replacing anodes on MGPS CONHIRA HPGT-750NYP

Replacing anodes on MGPS CONHIRA HPGT-750NYP

Replacing anodes on MGPS CONHIRA HPGT-750NYP

Video of MGPS and ICCP in operation

What is ICCP?

ICCP (Impressed Current Cathodic Protection) is a system for protecting ships from corrosion by applying an external electric current to the ship's hull. Corrosion occurs due to electrochemical reactions that destroy the hull metal. The ICCP system prevents these reactions by creating and maintaining an electric field that neutralizes the corrosion processes.

ICCP Control Panel

ICCP Control Circuit

The main components of an ICCP system include:

• Anodes: Typically made of inert materials such as platinum-containing titanium or mixed metal oxides, which are mounted on the vessel's hull.
• Controller: An electronic device that regulates the strength and voltage of the current supplied to the anodes to provide optimum hull protection.
• Reference Electrodes: These electrodes measure the potential of the vessel's hull relative to the water and report this information to the controller, which regulates the current supplied to the anodes.
• Power Source: Typically the vessel's electrical system, which powers the ICCP system.

The ICCP system operates as follows:

• Electric current is supplied from the anodes through the water to the vessel's hull, creating a protective electric field.
• This field reduces the potential difference between the metal hull and the surrounding environment, preventing electrochemical reactions that cause corrosion.

Thus, ICCP provides long-term protection of the ship's metal structures, reducing the need for frequent repairs and painting, and increasing the service life of the vessel.

What is a Shaft Earthing Device?

A shaft earthing device is a device used on ships to prevent electrochemical corrosion of the propeller shaft and associated components.

It provides grounding for the rotating propeller shaft to prevent the build-up of electrical charges that can lead to corrosion of bearings and other metal parts.

Shaft Earthing Device Brush Apparatus

The main functions and components of a shaft earthing device include:

1. Grounding Contact: This is a conductive material that is installed to touch the surface of the shaft. It provides an electrical connection between the shaft and the vessel's hull.
2. Brush Assembly: These are usually carbon or graphite brushes that are pressed against the shaft by springs. The brushes conduct the electrical current from the shaft to the grounding conductor.
3. Grounding Conductor: A wire that connects the brush assembly to the vessel's hull, providing a path for the electrical current to the ground.

Shaft Earthing Device

Shaft earthing device performance indicators:

1. 5 - 50 mV: Excellent shaft grounding;
2. More than 50 mV: The ring and brushes need to be cleaned;
3. 0 - 5 mV: Additional testing is required. While the main engine shaft is rotating, lift the two brushes and separate them from the ring. If the millivoltmeter shows a voltage greater than 50 millivolts, the device is in good working order. If the readings do not change, it is faulty.

The main faults of the Shaft earthing device are usually related to poor contact between the shaft and the ship's hull. It is very important that the "Shaft - Ring - Brush apparatus - Cable to hull" circuit has a resistance of 0 Ohm. Otherwise, the millivoltmeter will show inflated readings. To achieve the minimum resistance between the shaft and the ship's hull, it is necessary to thoroughly clean all components of this circuit and check all connections. It is very easy to check the resistance of this circuit, it is enough to check the propeller shaft to the grounding contact of the vessel's hull.

Video of Shaft Earthing Device in operation

Video of cleaning the ring (best to use a rag and cleaner, do not use sandpaper)

The principle of operation of the shaft earthing device:

• During the operation of the vessel, the propeller shaft rotates and can accumulate electrical charges due to friction and other factors.
• Without grounding, these charges can cause electrochemical corrosion of the shaft and bearings, which can lead to damage and the need for expensive repairs.
• The grounding contact and brush assembly transfers the accumulated charges from the shaft to the vessel's hull, preventing their accumulation and, accordingly, corrosion.

It is recommended to use the original silver ring and Ag-C brushes, which contain silver.

Ag-C brushes are made of a composite material based on silver (Ag) and carbon (C). This material combines the high electrical conductivity of silver and the wear resistance of carbon, which makes them ideal for use in high current and high speed conditions.

Main properties of the material:

1. High electrical conductivity: thanks to silver.
2. Wear resistance: carbon base ensures durability in operation.
3. Low coefficient of friction: which reduces heating and reduces wear of both brushes and slip ring.
4. Corrosion resistance: silver resists oxidation well, which increases service life.

The shaft earthing device plays an important role in protecting the propeller shaft and bearings from damage, extending their service life and ensuring reliable operation of the vessel.