Influence of flow accelerated corrosion on corrosion protection of mild steel in 3.5% NaCl solution

Mild steel is a primary material used to construct ships and other maritime structures. Corrosion protection systems are sometimes ineffective in aqueous mediums subjected to movement, flow, waves, and even turbulence under unpredictable conditions. This study aims to ascertain the influence of flow velocity on mild steel corrosion in the aqueous medium. The mild steel samples are immersed in a 3.5% sodium chloride (NaCl) solution for five days. They were protected against corrosion using an impressed current cathodic protection (ICCP) system. The flow velocity is increased to 200-800 rpm, while the stationary flow is also examined as a control. Data on the metal's potential and current density were collected, and the surface morphology was analyzed using a stereomicroscope. Corrosion protection occurs exclusively in stationary flow, whereas corrosion occurs in solutions flowing at a most studied velocity. Metals show corrosion severity levels ranging from 200 to 600 rpm with increasing current consumption and metal potential. At 800 rpm, the metal surface appears to begin passivating, reducing the current consumption and potential. The flow velocity accelerates corrosion, yet at the high-speed stream, the corrosion is slowed because the steel surface becomes passive and assists the corrosion protection.