Effect of seawater level on corrosion behavior of different alloys

Seawater is inherently chemically aggressive, and therefore, constructional materials used in seawater handling and processing systems including desalination plants are subjected to varying degree of corrosion depending upon the nature of the material(s) and operational conditions. Broadly speaking, for applications in seawater, the materials are usually exposed to three zones, namely, fully immersed, partially immersed or seawater surrounding environment. Interestingly, from corrosion point of view, the seawater behaves differently under the aforementioned conditions. A study was undertaken to investigate the effect of seawater level on a number of alloys having wide applications as structural materials in seawater processing plants. The laboratory immersion test technique has been applied to evaluate the effect of seawater level on the corrosion behavior of different alloys. In three sets of experiments, carbon steels (G1010 and 1020), austenitic stainless steels (304 SS and 316L SS), cupro-nickel (90/10 Cu/Ni and 70/30 Cu/Ni), Ni-based alloys (Incoloy 825 and Inconel 625) were utilized. The specimens were fixed at three locations namely, above seawater surface, semi submerged in seawater and fully submerged in seawater. The experiments were carried out at room temperature with very slow seawater movement (12 L/h). The exposure time was varied between 1–2 years. In this study the corrosion behavior of different alloys has been evaluated based on exposure location. Besides corrosion rate calculations, the localized attack has also been discussed on the basis of the magnitude of pit depths.