Rate of zinc consumption during sacrificial cathodic protection of pipelines carrying saline water

Rates of zinc consumption during cathodic protection of a copper pipeline carrying saline water were measured by the loss in weight technique. Variables studied were solution flow rate, temperature and NaCl concentration. It was found that within the present range of conditions the rate of zinc consumption increases with increasing solution flow rate, temperature and NaCl concentration. Results were explained on the basis that cathodic protection in saline water is controlled by the rate of diffusion of dissolved oxygen towards the walls of the copper tube. Implication of the present results for protecting heat exchangers used in the desalination industry and coolers employing seawater as a coolant was highlighted. Under the present range of conditions the rate of Zn dissolution during cathodic protection of copper ranged from 9.96×10–3 to 20.9×10–3 g/cm2.s.

The study of the cathodic protection of short copper tubes, such as those used in heat exchangers by using Zn wire or zinc strip extended axially in the pipe, revealed that under the present range of conditions the rate of Zn consumption ranged from 9.96×10–3 to 20.9×10–3 g/cm2.s depending on salinity of water and its temperature.