Cathodic Polarization Behavior of Steel with Different Marine Fouling Morphologies on Submerged Bridge Elements with Cathodic Protection

Severe localized corrosion of submerged steel bridge piles in Florida was associated with fouling and microbial-influenced-corrosion (MIC). The research in this study evaluated the efficacy of cathodic protection (CP) in those environments. Field tests were conducted in two natural rivers with different marine fouling morphologies. The test steel arrays were coupled to a zinc-sacrificial anode, and system potentials of approximately -923 mV with respect to the saturated-calomel electrode (SCE) developed. Global CP currents to the steel exceeded 3 mu A/cm2 and generally reduced the overall corrosion rate. The CP current was related to cathode surface availability under fouling, and portions of the array did not receive sufficient cathodic polarization. Laboratory tests were conducted using specimens with different surface crevice morphologies that were cathodically polarized at -850 and -950 mVSCE and immersed in solutions inoculated with sulfate-reducing bacteria. Tests confirmed that the presence of crevices reduce CP effectiveness. Fouling environments caused insufficient levels of CP and supported the growth of bacteria associated with MIC. CP alone may not be adequate to mitigate crevice corrosion and MIC under heavy fouling.