ISO 20313:2018 pdf free

ISO 20313:2018 pdf free.Ships and marine technology一Cathodic protection of ships
The objective of a cathodic protection system is to deliver sufficient current to protect each part of the structure and fixtures and distribute this current so that the structure-to-electrolyte potential of each part of the structure is within the limits given by the protection criteria. Electrolytic anti-fouling systems cannot be assumed to provide cathodic protection to the sea chest and internal pipework. The impact of these systems on the overall cathodic protection design and control shall not be neglected. The designer shall consider the location of anti-fouling system anodes, current outputs, current attenuation,structure isolation (if any), local sacrificial anodes and current exchange across any hull grating in the overall cathodic protection design.
Potentials should be as uniform as possible over the whole submerged surface. This objective is best achieved by adequate distribution of the protective current over the structure during the vessel’s normal operating service conditions. This can be difficult to achieve in some areas of the structure (e.g. water intakes, thrusters, and sea chests) where specific provisions can be required.
Cathodic protection for a ship is generally combined with a protective coating system. Although some fixtures, (e.g propellers), are not usually coated.
The cathodic protection system should be designed to mitigate galvanic coupling. The minimum protection potentials (most positive potential) listed in Table 1 shall be achieved on all steel surfaces adjacent to more noble materials.
Cathodic protection within sea chests can adversely affect, by stray current interaction, box coolers in sea chests if the box coolers are electrically isolated from the sea chest. Box coolers are often manufactured from copper nickel alloy tubes. The possibility of interaction shall be considered when designing the cathodic protection requirements for the sea chest. These considerations should include methods of controlling corrosion on steel surfaces shielded by the cooler, whether the cooler is electrically isolated or not. The designer should also resolve the adequacy of any cooler manufacturer installed anodes. These may not last the intended service interval. The principles of concern for sea chest coolers shall be extended to copper-nickel keel coolers that are similarly installed.ISO 20313 pdf download.