Corrosion behavior of AISI 316 stainless steel coated with modified fluoropolymer in marine condition

In the maritime industry, stainless steel corrosion resistance requires further surface improvement and further enhanced protection using surface coatings. In this study, an engineered copolymer of polyvinylidene fluoride (PVDF) with polymethylmethacrylate (PMMA)-blended coating was found to provide outstanding corrosion resistance for metal surfaces affording protection against severely corrosive marine environments. Electrochemical measurements indicate that corrosion protection of 316 stainless steel was drastically increased when utilizing the KP blend (a combination of PVDF + PMMA), producing a new set of corrosion properties and morphological characteristics. The corrosion protection of the KP coating proved to be very effective in reducing the passive region current density from 2.19 × 10⁻⁵ A/cm² (for bare stainless steel) to 2.63 × 10⁻¹⁰ A/cm² and the breakdown passive region potential at 0.25 V. This was followed by a significant decrease in corrosion rate, when compared to pure PMMA and PVDF films, during exposure to artificial marine seawater. With the KP film, impedance measurements surpassed those of other films, with a noticeable nonpeak straight line in the phase angle diagram. Optical observation showed that corrosion pits and delamination areas existed under the coatings.