Box cooler anti-fouling system for tugs
An anode with a perforated cathode plate.
Warm coastal areas can cause all sorts of problems with the efficient running of water cooled engines, but box coolers can create another layer of problems.
So, when European company Cathelco was called on to design special box cooler anti-fouling systems for two tugs which are used by Rio Tinto to berth iron ore carrying vessels in the port of Dampier, Australia, it had to deal with not just the heat transfer, but biofouling on seachests. These also had to be protected from stray electrical currents while keeping the copper ions flowing through the system in order to keep the organisms at bay.
The problem, said Steve Ellis of Cathelco, was that the first set of box coolers were painted, and in the warm inshore waters this impeded heat transfer enough to make a difference. So, another company came up with deliberately unpainted coolers which had to be kept electrically isolated to prevent corrosion of the steel seachests. Since they were of cupro-nickel, it was thought that they would keep biofouling at bay without the need for antifoul. However, bio-organisms, starting with lowly bacterial slime, can grow on cupro-nickel surfaces over a period of a few months. This is aided by the sea water temperature which then allows larger organisms to gain a foothold.
Down went the box coolers’ efficiency, causing overheating to the engines on the Pilbara Vulcan and Pilbara Neptune.
So antifouling was needed, and copper anodes, fed with an electric current from a control panel, were mounted horizontally beneath the box coolers to create an even distribution of ions when the system is in operation. The ions create an environment where barnacles and mussel larvae do not settle or breed and are discharged harmlessly.
However, Rio Tinto needed to be sure that the anti-fouling system would not cause corrosion problems in the future, said Mr Ellis.
Stray currents from the anodes, which could have a corrosive effect if they were attracted to the tubes of the box cooler and then discharged back into the seawater while looking for a path to ground, were eliminated by, in effect, a ‘Faraday cage’.
“This covers the anode and provides an effective earth return, said Mr Ellis, “while still allowing the copper ions to flow around the system and stop the bio-fouling build up. In essence copper ions can flow through it but current can not."
In addition, Cathelco designed a corrosion monitoring system, essentially a multipoint Voltmeter, to measure the difference in voltage between the box coolers and the seachests to check that there is electrical isolation and to measure for any stray current effects. In the event of a failure in the isolation an alarm is registered on the control panel, which is also remotely monitored by a real time software program running on a vessel computer.
The system is being put in place by Marine Plant Systems, Cathelco’s well established Australian agent.
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