Method for protecting surfaces against biological macro-fouling

Abstract

The present invention relates to a method for protecting surfaces (S) which are in contact or come into contact with a water-containing medium (M) against biological macro-fouling, wherein 1) S is electrically conducting and 2) such a potential (P) fluctuating over time is applied to S that it inhibits the growth of organisms that live in M and/or propagate therein and which have the tendency to form deposits on S, characterised in that P does not assume values that are higher than the corrosion potential of S in M and the average value of P is lower than the said corrosion potential. The method according to the invention is particularly suitable for the protection of surfaces S where S comprises: a) internal walls of systems through which (M) is fed, such as cooling system tubes, heat exchangers or fluid transport tubes and associated parts which come into contact with (M); b) internal walls and parts of installations, equipment or storage facilities in which (M) is subjected to specific treatments, such as filter installations, purification installations or reaction vessels; c) external walls of vessels and constructions that are in contact with (M).

1 . Method for protecting surfaces (S) which are in contact or come into contact with a water-obtaining medium (M) against biological macro-fouling, wherein 
 1) S is electrically conducting and    2) such a potential (P) fluctuating over time is applied to S that it inhibits the growth of organisms that live in M and/or propagate therein and which have the tendency to form deposits on S, characterised in that P does not assume values that are higher than the corrosion potential of S in M and the average value of P is lower than the said corrosion potential.    
     
     
         2 . Method according to  claim 1 , characterised in that the maximum value of P is at least 50 mV lower than the corrosion potential of S in M.  
     
     
         3 . Method according to  claim 1  or  2 , characterised in that fluctuations of P with respect to SCE are within the range from −300 to −3000 mV.  
     
     
         4 . Method according to one or more of the preceding claims, characterised in that the amplitude of the potential fluctuations is at least 50 mV and the frequency is at least once per 24 hours.  
     
     
         5 . Method according to  claim 4 , characterised in that P is applied to S at intervals (T) or is varied over time in some way or other and the periods for which P is applied to S have a duration of 0.01-600 seconds and T is 0.1 second-48 hours.  
     
     
         6 . Method according to one or more of the preceding claims, characterised in that the electrical conductivity of S is at least such that a reduction in the potential on S of at least 300 mV can be achieved within one minute.  
     
     
         7 . Method according to one or more of the preceding claims, characterised in that S comprises: 
 a) internal walls of systems through which (M) is fed, such as cooling system tubes, heat exchangers or fluid transport tubes and associated parts which come into contact with (M);    b) internal walls and parts of installations, equipment or storage facilities in which (M) is subjected to specific treatments, such as filter installations, purification installations or reaction vessels;    c) external walls of vessels and constructions that are in contact with (M).    
     
     
         8 . Method according to one or more of the preceding claims, characterised in that S consists of or contains: 
 a) iron, copper, nickel, titanium, aluminium or an alloy based on these metals,    b) electrically conducting or semiconducting coating or top layer, such as a metallic coating, ceramic coating, intrinsically conducting polymer or paint system to which electrically conducting components have been added,    c) non-metallic, non-conducting structural material or coating to which a conducting component, for example in the form of a filer or fibres, has been added,    d) non-metallic, conducting or semiconducting structural material.    
     
     
         9 . Use of a negative potential (P) that fluctuates over time for the protection of electrically conducting surfaces (S) which are in contact or come into contact with a water-containing medium (M), characterised in that P both 
 a) impedes the growth of organisms that live and/or propagate in M and have the tendency to form deposits on S, and    b) counteracts corrosion of S by means of cathodic protection.    
     
     
         10 . Device for the protection of external walls of vessels and/or other constructions that usually come into long-term contact with water, as well as of internal walls of systems through which water is fed, against biological macro-fouling, which device comprises: 
 a) an electrically conducting internal or external wall,    b) a voltage source that is connected to the internal or external wall and that is able to achieve a reduction in potential of at least 300 mV on the wall within one minute, characterised in that the voltage source is capable of producing a negative polarisation that varies over time on the surface to be protected against macro-fouling.