Marine-Corrosion-Data-Sheet-8-1.pdf - DATA SHEET Marine Corrosion Corrosion Revision 1 When two dissimilar metals are connected in an electrolyte such

Marine-Corrosion-Data-Sheet-8-1.pdf - DATA SHEET Marine...

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C O R R O S I O N C O N T R O L E N G I N E E R I N G DATA SHEET Page 1 of 7 NSW +61 2 9763 5611 VIC +61 3 9338 4900 QLD +61 7 3393 3200 WA +61 8 9248 9133 Auckland +64 9 415 2440 New Plymouth +64 6 751 4537 All written data and statements herein are provided in good faith and believed to be reliable and appropriate at the time of drafting this document. However it is given without implied or express guarantee. Potential users are urged to trial and/or conduct conformity test of the product to deem its suitable in application for a particular end use prior to purchase. Marine Corrosion Revision 1 DATA SHEET Corrosion When two dissimilar metals are connected in an electrolyte such as sea-water, a corrosion cell is formed in which one metal becomes an anode and suffers corrosion while the other metal becomes the cathode and is preserved. Anodic and cathodic areas exist on the surface of all steel structures due to slight variations in materials composition, local stresses, differences in coating condition and availability of oxygen. On a bare steel plate in sea-water, these areas form on what is apparently a uniform surface. Since corrosion will result in metal loss, roughening and wastage will occur on an uncoated plate. Where an imperfect coating exists, corrosion will take the form of accelerated pitting at the location of the bare spots and eventual breakdown of the coating. Whatever the circumstances, in the absence of cathodic protection, corrosion will eventually occur. Cathodic Protection The principal of cathodic protection involves the introduction into the electrical circuit of a metal that is more electro-negative than the existing anodic and cathodic areas. This additional metal becomes the anode and will corrode while providing current to the metal it is protecting, thereby overcoming the local anodic areas and making them cathodic. A cathodic protection solution to a galvanic corrosion problem is to introduce an anode in a suitable alloy of magnesium, aluminium or zinc which will suffer corrosion and so be ‘sacrificed’ in protecting the cathode. This approach is used in Sacrificial Systems. As an alternative solution, the protective current needed to make the structure fully cathodic may be obtained by applying low voltage DC derived from normal AC mains supply. This is achieved by transformer/rectifiers which supply DC to specially designed ‘inert’ anodes which will dissipate large currents without themselves suffering significant wastage. This
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C O R R O S I O N C O N T R O L E N G I N E E R I N G DATA SHEET Page 2 of 7 NSW +61 2 9763 5611 VIC +61 3 9338 4900 QLD +61 7 3393 3200 WA +61 8 9248 9133 Auckland +64 9 415 2440 New Plymouth +64 6 751 4537 All written data and statements herein are provided in good faith and believed to be reliable and appropriate at the time of drafting this document. However it is given without implied or express guarantee. Potential users are urged to trial and/or conduct conformity test of the product to deem its suitable in application for a particular end use prior to purchase.
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  • Spring '18
  • Aluminium, Anode, Cathodic protection

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