Marine growth in sea chests, box coolers and seawater piping systems is a potential threat for the performance and condition of your ship or installation. Blockages caused by barnacles (hầu) and mussels (trai) are expensive and time consuming to remove and can have serious consequences.
Engines will run at abnormally high temperatures, resulting in unnecessary increased fuel consumption and lower performance. To combat this risk the Marine Growth Prevention System (MGPS) was developed. Once installed it provides low maintenance and continuous protection against most hard and soft foulings as well as corrosion.
The Marine Growth Prevention System utilizes an impressed current (see the MARINE COROSSION AND PROTECTION (Part 2) ), usually consists of pairs of copper and aluminium anodes which are mounted in seachests or strainers and wired to a control panel. In the case of copper-nickel pipework, a ferrous anode is used instead of the aluminium anode. In operation, the copper anode produces ions which are carried by the flow of seawater, creating an environment in which barnacles and mussels will not settle or multiply.
Copper Anode: These are used in the majority of installations to protect steel pipework against bio-fouling through the creation of copper ions into the system to create an environment in which primary forms of marine life do not grow. Standard sizes range from 60mm to 120mm in diameter and 100mm to over 1,000mm in length. The photograph shows the anode fitted with a flange mounting arrangement.
Aluminium anodes: Impressed current applied to the aluminum anodes releases a ‘floc’, a precipitate of aluminum hydroxide. The aluminum hydroxide products reduce corrosion rates on ferrous components in the seawater system by modifying the ferrous oxides and formed a copper-aluminium film which acts as an anti-corrosive layer on the internal surfaces of pipes. The anode is shown with a weld-in mounting sleeve.
Ferrous anodes: These are used to protect copper-nickel pipework which is
commonly found on naval vessels. By producing ferrous ions, the ‘soft iron’ anode helps to maintain a protective oxide layer on the internal surfaces of pipes to suppress corrosion. The anode is shown with a cofferdam arrangement.
In some cases, when using standard anodes, it may be beneficial to have a dedicated cathode to avoid any problems resulting from stray current corrosion. This particularly applies where strainer bodies are internally lined and the strainer basket is isolated – OPEN CIRCUIT.
It is also advisable in situations where seachests are well painted and do not contain sacrificial anodes or where there is the need to avoid any interference with impressed current cathodic protection systems (ICCP). The cathode can be either isolated (dedicated) or connected to the ship’s earth ( both connect to Filter casing and Hull ).