Seawater desalination represents one of the most aggressive corrosive environments for metallic materials. The combination of high chloride concentration (approximately 19,000 ppm in seawater), elevated temperatures, high pressure, and dissolved oxygen creates multiple corrosion pathways that can compromise equipment integrity within months if improper materials are selected.
Primary Corrosion Mechanisms in Seawater Systems:
Pitting Corrosion occurs when chloride ions penetrate the passive chromium oxide layer on stainless steel surfaces, creating localized attack sites that propagate rapidly beneath the surface. This is particularly dangerous because pits can be difficult to detect visually until catastrophic failure occurs. The resistance to pitting is quantified by the PREN value.
Crevice Corrosion develops in confined spaces where oxygen depletion occurs—such as under gaskets, flange connections, and bolt heads. Even stainless steel grades with adequate pitting resistance can suffer crevice corrosion in seawater if design doesn't account for this mechanism. Recent 2026 research on super duplex stainless steel (SDSS) versus super austenitic stainless steel (SASS) reveals that SDSS demonstrates superior passive film stability, while SASS tends to develop deeper slit-like pits in coastal environments [3].
Stress Corrosion Cracking (SCC) is a particular concern for duplex and austenitic grades under tensile stress in chloride-containing environments. Temperature plays a critical role—SCC risk increases significantly above 60°C for standard austenitic grades.
Microbiologically Influenced Corrosion (MIC) is often overlooked but represents a significant threat in seawater systems. Sulfate-reducing bacteria (SRB) can establish biofilms on metal surfaces, creating localized acidic conditions that accelerate corrosion even on high-alloy grades. Rolled Alloys technical documentation indicates that 6% molybdenum super austenitic grades demonstrate superior MIC resistance compared to standard duplex grades [4].
