The use of galvanized systems in the fabrication of cooling towers, varies from industry to industry. Galvanizing provides a zinc coating on the metal substrate. The zinc coating performs as a sacrificial anode, preventing corrosion of the metal substrate. However, control on the formation of white rust should be taken into consideration when using a galvanized system. White rust is characterized by the accumulation of white and fluffy non-protective zinc corrosion product. When kept untreated, white rust corrosion can seriously damage the galvanized zinc coating. Once the zinc layer has been consumed, corrosion of the metal substrate, like mild steel, progresses rapidly shortening the life of the cooling tower.
Phosphate passivation is a typical method utilized for protection of galvanized coatings. Passivation of galvanized coatings with phosphate is a complex, time consuming process that often leads to poor passivation. This paper details the use of non-phosphate and non-zinc corrosion inhibitors, able to rapidly passivate and protect galvanized coatings. This newly developed chemistry can also be applied after a utilized galvanized surface has been placed in service (i.e. online passivation), in conditions with heat load, low hardness, high chlorides, and high dissolved solids. Considering the costs of known passivation techniques’, time and impractical water chemistry required, as well as the prevalence of equipment deterioration from white rust, one can immediately appreciate the value of this new, rapid, online passivation chemistry program.
Key words: galvanized system, corrosion inhibitor, cooling tower, water treatment, passivation