Process for inhibiting scale on metal surfaces
This invention relates to a process for inhibiting scale on metal surfaces exposed to an aqueous system, particularly a circulating aqueous system. The process comprises adding ethylenediamine-N,N-disuccinic acid, or salts thereof, to the aqueous system. Ethylenediamine-N,N-disuccinic acid, or salts thereof, act as a chelating agent and are biodegradable. The process is useful for inhibiting the formation of scale on metal surfaces of steam generating and cooling systems.
1 . A process for inhibiting scale formation and fouling on a metal surface exposed to an aqueous system, which comprises
adding an effective scale inhibiting amount of ethylenediamine-N,N-disuccinic acid, or salts thereof, to said aqueous system.
2 . The process in claim 1 wherein a salt of ethylenediamine-N,N-disuccinic acid is used and the salt is the tetrasodium salt.
3 . The process of claim 1 wherein the aqueous system contains calcium cations and the metal surface is subjected to pressures ≦450 psi.
4 . The process of claim 3 wherein metal surface is the metal surface of a boiler.
5 . The process of claim 4 wherein the metal surface of the boiler is steel.
6 . The process of claim 5 wherein the boiler operates at a temperature of at least 120° C.
7 . The process of claim 1 , 2 , 3 , 4 , 5 , or 6 wherein the concentration of ethylenediamine-N,N-disuccinic acid, or salt thereof, is from 1 ppm to 500 ppm.
8 . The process of claim 7 wherein the concentration of ethylenediamine-N,N-disuccinic acid, or salt thereof, is from 10 ppm to 50 ppm.