Closed-Loop Chiller Inhibitor

Even a sealed loop corrodes when oxygen enters through make-up water, leaks or open expansion tanks, when the inhibitor residual falls, or when mixed metals and deposits set up galvanic and under-deposit attack. Water that is not monitored drifts out of its protective range unnoticed.

It is a corrosion inhibitor based on sodium nitrite that forms a thin protective film on steel surfaces in closed chilled-water circuits. Its protection depends on keeping the nitrite residual within the range stated for the product, which is why regular testing of the loop water is part of the programme.

A closed loop is never perfectly closed: make-up water, small leaks and maintenance openings let in oxygen, minerals and microorganisms. Untreated, the loop corrodes, sheds iron that fouls heat exchangers and may support microbial growth, all of which reduce cooling efficiency and shorten equipment life.

Test the loop water for the inhibitor residual, nitrite in the case of a nitrite product, together with pH, conductivity and iron, and compare corrosion coupon results over time. A falling residual or rising iron signals a leak, make-up dilution or active corrosion that needs a response.

Every addition of make-up water dilutes the inhibitor and brings in fresh oxygen, hardness and chlorides. Frequent or unexplained make-up is therefore a warning of leakage, and the inhibitor residual should be re-tested and restored after any significant top-up or draining.