Effect of Barnacles on the Corrosion Behavior of 304 Stainless Steel

Abstract

Wire-beam, potentiodynamic polarization, electrochemical impedance spectroscopy and surface corrosion morphology analysis techniques were used to investigate the corrosion characteristics of 304 stainless steel (304SS) specimens subjected to different degrees of fouling; these analyses were conducted to clarify the corrosive effects of biofilms and barnacles. The experimental results indicated that the gradual thickening of the biofilm reduces the corrosion rate of 304SS (Icorr = 0.0677 μA/cm2). Mature biofilm acts as a barrier and significantly increases the protection of the substrate (Z = 905,000 Ω·cm2). The corrosion mechanisms of 304SS fouled with barnacles at various stages of growth are distinct: the corrosion rates of the microelectrodes fouled by living and recently dead barnacles are low because the overall structure is still intact. This structure creates a closed environment between the barnacles and the metal, limiting the transfer of corrosive factors from the outside to the inside. Despite the influences of corrosive bacterial decomposition, the Ecorr values of recently dead barnacles dramatically decrease to −668.8 mV. The microelectrode covered by the empty-shell barnacles corrodes heavily. Bacteria decompose the barnacle body and calcite shell, and glue damages their originally closed structures. Direct contact between the metal and reactive ions occurs, resulting in the continuous ingress of Cl− into the cracks, which intensifies crevice corrosion.