Pretreatment of cooling water systems

Effective corrosion control programs are essential in reducing unit downtimes. To be effective, the program must address not only specific corrosion problems, but anticipate and prevent them as well. Consequently, effective pretreatment in addition to other corrosion control measures is important. 

Corrosion control of metal surfaces depends on the formation and maintenance of a protective corrosion inhibitor film on the exposed metal surface. This protective film may be established during normal application of a corrosion inhibitor program however, there will be some lag time before the film is completely built up. Metal surfaces that are exposed to the cooling water before the film is completed may become candidates for accelerated corrosion during the initial system operation. Normally, localized corrosion or pitting is common during these early stages of operation. 

Allowing a unit to undergo no treatment for periods of time before being placed into operation can result in severe damage to exposed metal surfaces. In addition to the loss of the metal and shortened equipment life, voluminous and porous corrosion by-products may form and actually act as a barrier to the formation of the protective inhibitor film. 

In dealing with metal water cooling systems, today s trend is toward the use of nonchromate-based treatment chemicals. Nonchromate applications rely on less tenacious films for corrosion protection, rather than conventional chromate systems. As such, it is extremely important that the corrosion protection film be established very early in the operation. 

We can define pretreatment as the initial conditioning period whereby a corrosion inhibitor is applied to the metal surfaces of the cooling system. Pretreatment conditions must be conducive to the rapid formation of the protective barrier. The conditioning procedure should involve (1) the cleaning and preparation of metal surfaces, and (2) the actual application of higher than normal inhibitor concentrations. 

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