Copper corrosion & clogging in APS deionized water cooling system

An extensive amount of work has been performed on copper corrosion in last century due to its abundant use in domestic and industrial water systems. However, work on copper corrosion in deionized water is very limited. The water cooling system of Advanced Photon Source (APS) at Argonne National Laboratory uses deionized water containing very low dissolved oxygen (less than 10 ppb). Therefore, It is expected that copper corrosion would be less in this system. On the contrary, APS suffers significant clogging in its water cooling circuit resulting from the deposition of corrosion product and carries out frequent expensive maintenance to retain the required flow rate. The location of pH and corrosion potential of APS water cooling system is very close to the boundary condition of the two oxides (CuO and Cu 2O) of the Pourbaix diagram of copper. While a single phase presence of either of these two oxides is stable as a protective layer, a mixture of the two oxides is unstable. An unstable protective layer results in spalling of the oxide layer. A fluctuation in water chemistry (which is common in an industrial facility) triggers a phase transformation between these two oxides due to its near boundary values. It was observed that the location of pH and corrosion potential was away from the boundaries in high dissolved oxygen condition (more than 2000 ppm). Hence, the possibility of phase transformation becomes lesser in high dissolved oxygen condition than in low dissolved oxygen condition. A test station, that was a replica of the APS water cooling system, was used to perform experiments in both high and low oxygen condition. It was demonstrated that high oxygen condition results in less clogging than in low oxygen condition. Microstructural characterization was performed on the coupons from test station and on some components from APS to evaluate oxide surface and determine phases. Mechanism of the phase transformation was suggested.