This study was conducted to determine optimal coupon size and shape of the coupons with minimal edge effect in terms of cathodic current distribution. Specifically, experiments and corrosion modeling were conducted to develop an approach to evaluate optimal cathodic protection (CP) coupon size and shape for monitoring CP in field. Experiments were conducted with 10, 50, and 100 cm2 coupons in circular, triangular, and cylindrical shapes. The experiments included linear polarization resistance, potentiodynamic cathodic polarization, and potentiostatic polarization measurements. The experimental cells used in the experiments were modeled for the current distribution at the coupons surfaces. The pH of the sand directly next to the coupons surface was measured, which was found to be more basic than the bulk sand pH, indicating that cathodic currents resulted in generation of alkalinity which was absorbed by the sand. The experimental data were input in a pipeline CP model that included a 10 cm2 holiday and a coupon with varying sizes and shapes. The coupon sizes and shapes included a factorial combination of 10, 50, and 100 cm2 surface areas and circular and cylindrical shapes. The simulation data indicated that edge effects are minimal for a 10 cm2 cylindrical coupon and 100 cm2 circular coupon under various cathodic polarization conditions.
Key words: Cathodic protection, coupon, size, geometry