Closed recirculating systems corrosion inhibitors

Inhibitors The use of various substances or inhibitors as additives to corrosive environments to decrease corrosion of metals in the environment is an important means of combating corrosion. This is generally most attractive in closed or recirculating systems in which the annual cost of inhibitor is low. However, it has also proved to be economicaUv attrac tive for many once-through systems, such as those encountered in petroleum-processing operations. Inhibitors are effective as the result of their controlling influence on the cathode- or anode-area reactions. 

It is important not to leave the system empty of water for any long period, as rapid surface rusting will take place. As soon as the closed-loop system is declared free of contamination, sufficient corrosion inhibitor is added to provide long-term corrosion protection. The corrosion inhibitor is usually an anodic, passivating formulation, typically based on nitrite or tannin (and often in combination with phosphate, silicate, borate, or molybdate, etc.). Finally, after confirmation that the entire system is adequately treated (which usually requires the inhibited water in the system to be recirculated for a further 16 to 24 hours), the system is signed off and handed over. 

DEWT L. [Drew Ind. Div.] Chromate/ (xgaiic blend corrosion inhibitor for closed recirculating water systems. 

Inhibitors are very important for corrosion of irons and other metals. The corrosion of irons and other metals in aqueous solutions can frequently be minimized or inhibited by the addition of soluble chromates, molybdates, silicates, and amines or other chemicals, singly or in combination. Such materials are called inhibitors and are generally attractive for use in recirculating systems or closed systems. They are also used in neutral or very slightly acid solutions. The concentration of an inhibitor for maximum control depends on the solution, composition, temperature, velocity, metal system, and the presence of dissimilar metals in contact in the solution. Care should be taken in the selection and application of inhibitors, since in some instances they can increase localized attack. 

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