IMPRESSED CURRENT THODIC PROTECTION UTOMATIC SYSTEMS Corrosion is a spontaneous electrochemical process in which a metal reacts with oxide or other compound, rusting of steel. This of a corrosion cell which solution (electrolyte). CORROSION CELL Corrosion always develops at the anode, where current leaves the metal and enters the electrolyte, whilst a protective effect occurs at the cathode Corrosion Cell Current Flow the whole metal surface is made sufficiently cathodic, corrosion will not occur. This is the basic principle of Cathodic Protection. In marine structures, such corrosion cells may result from the use of dissimilar metals. Usually, however, localised anodic and cathodic areas arise on the surface of the same metal through differences in the metal itself, variations in protective films or changes in the electrolyte, ie: aeration, temperature and salinity. Corrosion may be prevented by removing one or more of these corrosive elements and for marine structures, the most practicable method is to apply a protective coating, thus introducing an electrical resistance between the metal and the electrolyte. Paint in various forms normally provides the first level of protection. However, even the most efficient coatings are subject to defects during application or service, with inevitable corrosion of the exposed metal. It is therefore generally accepted that cathodic protection, in conjunction with a high performance paint system provides the most effective and economic safeguard against corrosion. MG Duff International Ltd. 1 Timberlaine Estate, Gravel Lane, Quarry Lane, Chichester, West Sussex. P019 8PP

CATHODIC PROTECTION A technique for preventing corrosion which is the most important of all methods used to control corrosion of marine structures, including ships' hulls. The essential factor in cathodic protection is to ensure that the unwanted anodic reactions are suppressed by the application of an opposing current. This opposing current can be achieved by either of two techniques: 1. Sacrificial Anodes - By corroding away a more reactive (base) metal. Anodes based on alloys of Zinc, Aluminium and occasionally Magnesium, are attached to the structure and corrode in preference to the protected...

AUTOMATIC POWER/CONTROL UNITS A comprehensive range of high specification units are available as wall mounted models or floor standing arrangements for large capacity systems. The whole range features rugged, sheet steel enclosures with double door protection as standard. Designed for ease of installation, these compact, functional units are fully rated for ambient/operating temperatures between 0-50 C and accept standard a.c. inputs; 380/440 volt; Single or three phase, Standard Features: 0 Input circuit breaker: Magnetic trip & Thermal overload 0 Fully automatic control with Manual override...

BONDING SYSTEMS M G Duff Shaft Earthing Systems meet the requirements of BS Code of Practice CP. 1021 as well as major engine manufacturers recommendations. High efficiency silver tracked Sliprings and silver graphite brushes effectively extend cathodic protection to exposed propeller and shaft surfaces whist at the same time reducing spark erosion damage to shaft bearings. (A more economic, but less efficient copper based version is The effectiveness of the shaft bonding may be monitored by an optional Shaft Condition Monitor. Rudder and stabiliser bonding cables are provided as standard SYSTFM...