Carbon-induced corrosion of MSF condenser tubes in Arabian Gulf water

The present investigation was undertaken to shed light on the failure of some 90/10 CuNi condenser tubes in a MSF distiller. The tubes showed numerous tiny pits of unusual features. Particles of C were discovered inside the tubes and were suspected of initiating micro-galvanic cells leading to pitting. The study involved the measurement of open circuit potentials (OCP) of C and 90/10 and 70/30 CuNi electrodes in stagnant-, stirred-, natural- and synthetic seawaters at various temperatures. The way these changed with time till constant values were recorded was followed over long exposure times. The EMF of the C/CuNi galvanic cells varied between 400 and 450 mV. Contact between C and the copper alloys resulted in dissolution of copper, and the development of galvanic corrosion potentials and galvanic corrosion currents. These were discussed in the light of Evans corrosion diagrams. The study was extended to include the C/316 stainless steel system under similar conditions. The OCP behaviour of the steel electrode depended upon whether measurements were carried out in stagnant-, stirred-, natural- or synthetic seawaters. Galvanic coupling with C resulted in intensified pitting attack of steel in stagnant, artificial seawater. Similar measurements were conducted on the C/Ti couple. The anode reaction led to the thickening of TiO, Insignificant corrosion was recorded with the Ti/316 stainless steel system.