Abstract
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.
