Closed loop cooling circuits operate with good quality, low dissolved solids, make up water. Treatment
packages are used to control corrosion and bacteria within the medium. Problems with this type of
system can arise from a number of causes such as excessive make-up medium, lack of treatment
chemical, bacterial degradation of treatment chemical, excessive ingress of oxygen, and poor water
quality.
The work presented was initiated to investigate a nitrite / molybdate corrosion inhibitor due to ongoing
integrity concerns in the closed loop system. There is not clear published guidance on application of
this type of inhibitor package and testing was conducted to evaluate sensitivities around its application
to close loop systems.
A thorough technical review of design and previous corrosion issues was conducted to identify likely
causes and key contributing factors. A laboratory test programme was conducted to determine the
magnitude to which the identified parameters influence corrosion.
The work highlighted in the background review and the laboratory test programme provides clear
conclusions as to appropriate dose rate of inhibitor and factors associated with corrosion risks. The
laboratory data highlights that of the factors investigated, the salinity of the make-up water had a
significant effect on the inhibitor performance and corrosion risk. Such work provides a basis for
generating operating key performance indicators (KPI) to monitor and ensure efficient operation of
closed loop systems and limit failures in the future.