Iveco Marine Diesel Engines, Installation Handbook, Page: 122 / 132

Other factors favouring corrosion are:
■
Important relation difference between the cathode surface and the anodic one.
■
High saline concentration in sea water.
■
High water speed on surfaces
■
Temperature and sea water ventilation rise.
Since eddy or galvanic currents are reduced in intensity, they may leak to the important vessel compo-
nents risking corrosions on the engine elements or on the keel. To avoid this phenomenon, an appro-
priate protection system must be provided, which consists of:
■
Electric equipotential connexions or electric ground connexion;
■
Availability of disposable metallic elements or sacrificial anodes in the involved parts.
Some useful indications to avoid the appearance of corrosion phenomena are:
■
Periodical control of the ground connexion electric continuity.
■
Visual examination to detect wear and tear at the anodes and other hull parts
■
Measurement of eddy current and of the potential differences among the hull components
■
Controls of ground connexion conditions at zinc anodes, engine and ground connexion rod.
■
Periodical control of to clear the contact points from rust and dirt.
■
Cathode protection with supplementary outboard anodes.
■
Tin-based painting of the involved parts.
13.2 GROUND CONNEXION
All the vessel metallic components must be connected to one another to minimise or annul the dif-
ferences in potential among the several components, thus eliminating the cause of the eddy currents
(see figure 2).
The equipotential ground circuit may also eliminate such currents avoiding their circulation on elements
and the consequent hazardous corrosion.
The ground connexions indicated resistance values must be lower than 0.01
Ω , whereas the circulating
stray current value in the ground connexion and the zinc anodes connexions must be lower than 100
mA.
Measurement must be carried out during normal operation conditions, using a proper multimeter to
measure limited intensity currents, paying special attention to the reference scale rate.The parts should
be disconnected to apply the measuring devices.
Control of anodes proper connexion could be carried out in the previously described conditions; the
anodes must be connected in a regular manner while measuring the existing voltage between the com-
ponent and the ground connexion rod or the storage battery negative pole.The expected value must
be some mV.
13.3 DISPOSABLE ANODES PROTECTION
Due to the usual phenomena that take place in marine manufactures and since the vessel is completely
soaked in seawater, the components placed in the hull and at exposed areas must be made of active
metal. Due to their intrinsic nature, these materials will act as anodes in the case of the eddy current
phenomenon, and they will wear down in place of the vessel parts.
MARCH 2004 GALVANIC CORROSION PROTECTION
13.122
MARINE ENGINES INSTALLATION