Cathelco MGPS systems technology description

The system 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 cupro-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.

By introducing copper ions in very small concentrations, around 2 parts per billion, the Cathelco system interrupts the settlement sequence of mussel and barnacle larvae.
Instead of adhering to the surface of seachests, strainers and pipework, the larvae pass harmlessly through the cooling water system to the point of discharge.

Without anti-fouling protection, pipes become encrusted with organisms leading to partial or total blockages which reduce the efficiency of the seawater cooling system.

Bio-fouling in pipe flange

A dual action system

The action of the copper ions is assisted by aluminium hydroxide created by the aluminium anodes which flocculates the released copper from the copper anodes.

This highly gelatinous copper-aluminium hydroxide floc is carried throughout the system and tends to spread out into the slow moving areas closer to the pipe surfaces where marine larvae are most likely to settle.

As a result, marine growth larvae do not settle, instead passing direct to discharge. At the same time, a cupro-aluminium film is built up on the internal surfaces of pipes to suppress corrosion. In this way, the system has a dual action protecting seawater pipework against bio-fouling and corrosion.

Seachest or strainer mounted anodes

When systems are installed at newbuilding, anodes are generally fitted in the seachests using special sleeves or flange mountings.

Alternatively, if systems need to be installed prior to scheduled drydocking, the anodes can be mounted in the seawater strainers. This also simplifies replacement when anode renewal becomes necessary.

In special cases, where the Cathelco system supersedes existing chemical based anti-fouling equipment, the anodes can be mounted in treatment (electrolysis) tanks in order to economise on the installation costs by utilising existing pipework.

  • Steel pipework – protected by copper and aluminium anodes.
  • Cupro-nickel pipework – protected by copper and ferrous anodes.
  • Seachest mounted anodes – generally installed at newbuilding and are replaced at drydocking.
  • Strainer mounted anodes – can be replaced at any time when the vessel is alongside.
  • Electrolysis tanks – can be used to replace chemical systems or in specialised applications where seachest or strainer mounting is not possible.
  • Environmentally friendly – does not use chemicals. Generally operates with copper concentrations of just 2 parts per billion.

SeaChest diagram

Image above: Seachest anode installations

 

Strainer diagram

Image above: Strainer mounted anodes

Cathelco MGPS dual purpose (copper and aluminium anode)

Biofouling and corrosion

Corrosion can be accelerated in two ways. The presence of biofouling on a metal surface results in a decreased oxygen concentration below the fouling layer. This area becomes anodic with respect to areas of the metal surface exposed to oxygenated seawater. The result is pitting corrosion under the fouling. An additional problem is the corrosion caused by the action of bacteria. Sulphate reducing and iron bacteria are well known examples of organisms whose biological activity or metabolic by-products cause corrosion. Such bacteria live in areas of low oxygen concentrations, for instance under a layer of aerobic fouling organisms, or in de-aerated water such as that found in oil storage tanks and well flood water. Efficient fouling control results in reduced pitting and crevice corrosion.

Most Cathelco systems have dual action, eliminating bio-fouling and suppressing corrosion. In the case of steel pipework the corrosion suppression anodes are made from aluminium, whereas cupro-nickel pipework is protected against corrosion with ferrous anodes. When these are fitted, corrosion rates are significantly reduced resulting in a longer working for the pipework and any other equipment which is connected to the seawater system.