Effect of Fluid Dynamics on the Corrosion of Copper-Base Alloys in Sea Water

A technique for testing materials in sea water under velocity conditions has been developed which utilizes fluid dynamics to evaluate the corrosion test results. The data obtained from this technique may then be applied to other hydrodynamic systems where the fluid dynamics equations are known. This allows high velocity corrosion data to be applied in a scientific and accurate manner. The copper-base alloys are shown to be susceptible to a critical surface shear stress in sea water where film breakdown begins and accelerated attack is initiated. When the critical shear stress is exceeded in a hydrodynamic system, the corrosion product film of a copper-base alloy degrades and is physically removed. At this point, the shear stress is greater than the binding force of the corrosion product film. This allows localized corrosion and/or accelerated general corrosion to occur. The critical surface shear stress value for a specific alloy includes in its determination the variables of sea water temperature, density, viscosity, flow pattern, etc., and therefore compensates for their important individual effects in the determination of velocity resistance. Critical surface shear stress data are obtained for 5 copper-base alloys, relating the effects of alloying to the adherence of the corrosion product in sea water. These data can be applied to other hydrodynamic systems to determine the critical sea water velocity for specific applications.