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The vast majority of Victorian owners of cooling towers systems would now have completed the first audit of their Risk Management Plan.  One aspect of a Risk Management Plan is to limit nutrient growth of legionella bacteria by preventing corrosion.  But corrosion should also be minimised to ensure the maximum effective life of your equipment. There is a conflicting demand to minimise corrosion and prevent legionella.

Corrosion monitoring is a predictive approach to minimising the consequences of corrosion and can be done at low cost with limited personnel.  Corrosion monitoring can be more complex than you think.  Your cooling tower system can be susceptible to a number of different types of corrosion and there is no single method that will detect all of these.

Nevertheless, the common approach to monitoring corrosion is using corrosion coupons exposed to your cooling tower water. This offers the advantage of:

• Minimal cost;

• Simple to implement and

• Provides information about most forms of corrosion mechanisms.

The disadvantages include:

• A measurement period of one to three months;

• Not a real-time measurement.  Usually an on-line exposure followed by an off-line analysis;

• Historical data is needed to establish trends.

With most cooling tower systems copper and mild steel coupons are used.  Copper coupons are exposed for periods between three and six months.  Mild steel coupons are exposed for one to three months.

To be of most help both the uniform corrosion rate and maximum pit rate must be measured. In many cases the former is reported only.  The uniform corrosion rate is based on the weight loss of the coupon during the exposure period.  The maximum pit rate involves measuring pits or localised spots of corrosion on the coupon.  Mild steel materials will tend to pit rather than corrode uniformly and so focussing upon a uniform corrosion rate can under-estimate the extent of corrosion in your system.

Choosing the acceptable tolerance for corrosion in your system is also essential, as is a policy of reducing the tolerance over time.

CETEC offers a variety of services that helps reduce your risk from the destructive threat of corrosion to your cooling tower system, including:

• Independent advice and auditing of your corrosion monitoring plan;

• Corrosion coupon testing and analysis and

• Investigative studies into corrosion failures.

Please contact us here to start or improve your corrosion monitoring and reduce your corrosion risk.