System and method for protecting metals

Abstract

This invention pertains to the protection of metals from corrosion and/or fouling from exposure to environments such as, for example, seawater. The protection in accordance with this invention is achieved through the use of conductive zinc-containing coatings in combination with applied current cathodic protection.

1 . A method for protecting a metal structure from corrosion and/or fouling, said metal structure comprising a metal which has a higher electrochemical potential than zinc, and an exposure surface exposed to an environment conducive to corroding and/or fouling said metal, said exposure surface being at least partially coated with a conductive zinc-containing coating in conductive contact with said metal and in direct contact with said environment, said method comprising the step of applying a direct current through said conductive zinc-containing coating via a resistive circuit in which said metal functions as a cathode.  
     
     
         2 . The method of  claim 1 , wherein the exposure surface is substantially covered with said conductive zinc-containing coating.  
     
     
         3 . The method of  claim 1 , wherein said conductive zinc-containing coating is a zinc-rich coating having a zinc loading in excess of 80% by weight based upon solids.  
     
     
         4 . The method of  claim 1 , wherein said direct current is such that the cathodic current density is between about 1 mA/sq.ft to about 100 mA/sq.ft.  
     
     
         5 . The method of  claim 1 , wherein said metal is iron or an iron-based alloy.  
     
     
         6 . The method of  claim 1 , wherein said structure is a ship hull.  
     
     
         7 . The method of  claim 1 , wherein said structure is a bridge.  
     
     
         8 . The method of  claim 1 , wherein said structure is a storage tank.  
     
     
         9 . The method of  claim 1 , wherein said exposure surface is substantially covered with said conductive zinc-containing coating; said conductive zinc-containing coating is a zinc-rich coating having a zinc loading in excess of 80% by weight based upon solids; said direct current is such that the cathodic current density is between about 1 mA/sq.ft to about 100 mA/sq.ft; and said metal is iron or an iron-based alloy.  
     
     
         10 . A system for protecting a metal structure from corrosion and/or fouling, said metal structure comprising a metal which has a higher electrochemical potential than zinc, and an exposure surface exposed to an environment conducive to corroding and/or fouling said metal, said system comprising: 
 (1) a conductive zinc-containing coating on at least a part of said exposure surface, said conductive zinc-containing coating being in conductive contact with said metal and in direct contact with said environment;    (2) a direct current supply having a positive terminal and a negative terminal; and    (3) a resistive circuit connecting said positive and negative terminals, said resistive circuit comprising said metal as a cathode and an anode resistively connected thereto, and wherein said resistive circuit is structured so that a direct current will flow through said conductive zinc-containing coating.    
     
     
         11 . The system of  claim 10 , wherein said exposure surface is substantially covered with said conductive zinc-containing coating.  
     
     
         12 . The system of  claim 10 , wherein said conductive zinc-containing coating is a zinc-rich coating having a zinc loading in excess of 80% by weight based upon solids.  
     
     
         13 . The system of  claim 10 , wherein said direct current is such that the cathodic current density is between about 1 mA/sq.ft to about 100 mA/sq.ft.  
     
     
         14 . The system of  claim 10 , wherein said metal is iron or an iron-based alloy.  
     
     
         15 . The system of  claim 10 , wherein said structure is a ship hull.  
     
     
         16 . The system of  claim 10 , wherein said structure is a bridge.  
     
     
         17 . The system of  claim 10 , wherein said structure is a storage tank.  
     
     
         18 . The system of  claim 10 , wherein said exposure surface is substantially covered with said conductive zinc-containing coating; said conductive zinc-containing coating is a zinc-rich coating having a zinc loading in excess of 80% by weight based upon solids; said direct current is such that the cathodic current density is between about 1 mA/sq.ft to about 100 mA/sq.ft; and said metal is iron or an iron-based alloy.