Marine Growth Prevention System (MGPS)

Seawater is used to cool machinery and plant on board all types of marine vessels. It is also used in petro-chemical plants, power stations and other land-based industries, where there is access to the ocean. Although this benefits supplying a free cooling agent, it also causes corrosion and blockage to the cooling water pipeline system.

Marine Growth Prevention System (MGPS) 

The larvae forms of primary marine life such as barnacles and mussels enter seawater intakes, settle on internal surfaces and develop causing bio-fouling.

Where bio-fouling exists corrosion is accelerated even on highly resistant surfaces. The reduced water flow resulting from blocked pipework can cause excessive wear, overheating and inefficiency throughout the system.

The growth of marine organisms in sea water systems can result in the blockage of pipework and restrict or completely prevent the use of the systems which incurs significant repair costs to the ship owners. Traditionally, chlorination treatment has been used to remove marine growth by the adding of chloride/ hypochlorite or by electro-chlorination.

However these methods have not been satisfactory solutions due to the accelerated corrosion on the structure and unacceptable environment pollution by environmental agencies.

The anode in the MGPS system generates ions that spread in the seawater system, producing an antifouling and anti-corrosive layer over the internal sides of sea pipes, heat exchanger (i.e. coolers and condensers), valves in seawater system, refrigeration systems, AC units etc.

Working Principle of Ler-Flow MGPS System

The system consists of a controlled power unit, anti-fouling anodes and anti-corrosion anodes. The controller power unit is installed in the ship’s engine room where it can be accessed easily.

One copper anode and one aluminum anode are installed in each sea chest or injection strainer or an intermediate suitable reaction tank. Anode sizes and dimensions vary accordingly to the construction of the sea chest or injection strainer, flow rate and time between dry docking.

Sea life is deterred from settling in environments where the natural level of copper is increased. The electrolytic Ler-Flow system releases a controlled amount of copper ions into the sea water to deter such settlement on pipes and cooler surfaces. The actual concentration of copper ions is extremely small and measured in micro grams per liter of sea water.

Ler-Flow has a fully automated control system supplying D.C current to alloyed anodes installed in the seawater intake or sea chest. It is a dual system, tackling both bio-fouling and corrosion:

a) Copper ions released from the copper alloyed anodes prevent the survival of microscopic marine life which would otherwise foul the cooling system.
b) Ferrous or aluminum ions released from the second ferrous or aluminum alloyed anodes rebuild and repair areas where protective oxides have worn away or are being damaged.

Power Supply Unit

Copper and Aluminum Anodes

Our copper and aluminum anodes come in different standard sizes and lengths. The most commonly used sizes are Ø75mm, Ø82.50mm, Ø102mm and Ø120mm.

Diameter (mm)	Length (mm)
Ø75.00	250	300	350	400	450	500	550	600
Ø82.50	250	300	350	400	450	500	550	600
Ø102.00	250	300	350	400	450	500	550	600
Ø120.00	250	300	350	400	450	500	550	600

Beside the above sizes, we can also customize to the owner’s/ buyer’s requirement upon request.

The three types of alloys used for anodes are:

Copper Alloyed Anodes: This is the most used type to prevent marine fouling in piping, strainers, heat exchangers, pumps etc.

Aluminium Alloyed Anodes: This type is used in conjunction with copper alloy anodes to prevent corrosion throughout the ferrous piping system.

Ferrous Alloyed Anodes: They are used in conjunction with copper alloy anodes to prevent corrosion throughout Cu/Ni pipework.

An MGPS system can be installed on the ship in following ways:

Anodes Mounted on Sea Chest: They are commonly installed in new buildings and have a working life such that they can run till the next drydocking.

Anodes Mounted in strainers in the seawater pipeline: They have an advantage of replacing the anodes without affecting the seawater supply to ship’s system.

Treatment tank setup with a spray nozzle in sea chest: In this system, a separate electrolysis tank with anodes is installed which sprays the ion through the nozzle in the sea chest. This system is installed on ships where sea chest or strainer mounting is not possible.

With the MGPS functioning efficiently, the systems using seawater will have following benefits:

• Marine organisation growth on the surface of pipe or valve will decrease the flow. MGPS helps in maintaining a good seawater circulation
• Eliminating corrosion in the pipelines
• Increasing the cleaning duration of the seawater system which will be very frequent in the absence of MGPS
• Maintain the efficiency of the system and machinery supplied with seawater
• MGPS adds to the energy savings of the ship.

Tips to ensure Marine Growth Prevention System (MGPS) always provide the top-notch performance to get the benefits stated above:

1. Ensure there is no aluminium pipes or parts attached to the seawater system in which MGPS copper anodes are connected. In a copper-based anode or MGPS systems, the aluminium will have a chemical reaction and act as an anode in the vicinity of copper, leading to severe corrosion of aluminium parts

2. The current settings for the MGPS should always be maintained as prescribed by the maker. A high current value setting will lead to a shorter anode life, and a lower current setting will increase the anode life

3.The typical current value on which the majority of MGPS anodes work comes in the range of 0 to 2 amps per anode. This value can be manually adjusted in a range of 0.2 amp steps

4. When the MGPS is installed on a non-ferrous metal surface (e.g. pipe upstand), the installation flanges of the anodes must be provided with an isolation material to ensure there is no electrical contact between the anode and non-ferrous surface, i.e. between two dissimilar metals

5. When the MGPS anode assembly is installed on the strainer (the anodes usually are installed on the strainer lid), it is essential to correctly place the anode inside the strainer basket in such a way that the anode surface does not touch any metallic components

6. Whenever the strainer is opened up for inspection or cleaning by lifting the lid, ensure to disconnect the supply of these anodes and not to damage them when removing the strainer basket lifting bar

7. When the MGPS anodes are installed in a sea chest, ensure they are not placed in the “dead zones”, i.e. where the water flow is minimal. They should be mounted in the central passage of the seawater flow from the inlet grids to the seawater suction

8. Ensure not to use oversize cables for the MGPS anodes as they are likely to cause mechanical overload on the terminal blocks.

9. Under daily watchkeeping duties, check the digital display ammeters are working properly. When an anode has nearly consumed, the corresponding display will show a low value.

10. If the anode current value is dropped to a low level, turn off the current knob to zero, i.e. no supply to the anode and renew the anode at the first chance. After renewing the anode, reset the current to the previously given current settings

11. For treatment tank type MGPS, open the air vent on a daily basis to prevent air pockets inside the tank

12. When replacing or renewing the anodes, ensure to carefully unscrew the mounting nuts to prevent the anodes falling down the sea chest, which may damage the chest or the anode itself

While drydocking of ships, the MGPS anodes are normally opened up for overhauling and checks as no water is present in the sea chest.

Following points to be considered when working on MGPS system in drydock:

13. While opening the anode, never lift or support the anode from its cable or apply any mechanical load to anode cable.

14. The new spare anode which is of held-in type or flange sleeves type is supplied unpainted with a rust prevention coating. Ensure to remove this coating before the installation. Never use a wire brush or mechanical instrument to remove this layer. White spirits or turpentine can be used for the removal of this coating. 

15. If anodes are installed in a space where blast cleaning or painting is not finished, they must be suitably protected. Before flooding the spaces, check to ensure that the protection has been removed. Also, remove any paint, tape adhesive residue or grease from the anode surfaces.

16. Ensure the renewed anodes are mounted in the vertical position unless otherwise stated by the makers or manufacturer.

17. During dry docking for retrofit systems, before the vessel is launched or refloated, check the isolation of each anode from the hull, as well as continuity of the positive feed circuit to the anode

The MGPS installed on a ship must be effective against a large variety of organisms due to the multiple numbers and complex nature of fouling communities present in waters of different parts of the world the ship ply to.

Any antifouling agent used within the MGPS must comply with the local and international regulations and requirements, particularly about biocidal discharges.

 

Next Read: Preferential Trips Construction and working.