In recent years, the detection of many MIC failure events affecting copper alloys in heat exchange plant drove the setting-up of experimental monitoring systems regarding these phenomena.
The formation of protective oxide layers growing on CuNi 70/30, commonly employed in seawater, and the positive role of chlorination treatments were particularly addressed.
For this purpose measurements were carried out in plants and pilot circuits, with different characterized environments.
Innovative electrochemical sensors integrated with traditional probes and data acquisition system have been used to monitor on-line the biofilm growth and the corrosion rate affecting the CuNi 70/30 specimens and some physical-chemical parameters of the water (flow, temperature, turbidity).
Weight loss determination, chemical and metallographic analyses have been completed the characterisation of coupons exposed to sea water before and after the tests.
The results confirm that short-time chlorination treatments, daily and discontinuously imposed, in the range of 0.4 – 1 mg/l of free oxidant for 0.5 – 1 hour, few time a day, promoted the formation of a protective layer on the Cu based alloy.
This layer was able to avoid the onset of localized corrosion phenomena even when seawater becomes of particular aggressiveness, as it happens in presence of flux interruption or slime.
(*) Work financed by the Italian Ministry of Economic Development with the Research Fund for the Italian Electrical System under the Contract Agreement established with the Ministry Decree of march 23, 2006.