Seawater Reverse Osmosis Desalination And Equipment Material Protection

Water scarcity has become a global challenge, particularly in the Middle East, North Africa, and coastal regions of China where limited freshwater supply restricts economic and social development. As the most widely adopted seawater desalination technology, Seawater Reverse Osmosis (SWRO) is rapidly expanding due to its advantages of low energy consumption, flexible system design, and strong scalability. However, ensuring long-term operational stability-especially corrosion protection of high-pressure piping systems-has become a critical issue for the industry

The core principle of SWRO is to apply high pressure to force seawater through semi-permeable membranes. With a pore size of approximately 0.0001 microns, these membranes allow only water molecules to pass while rejecting over 99% of salts, microorganisms, and organic matter.
The overall process includes pretreatment, reverse osmosis modules, and energy recovery devices. Pretreatment involves coagulation, filtration, and ultrafiltration to remove suspended solids and organic matter, extending membrane lifespan. High-pressure pumps and pressure vessels overcome osmotic pressure, while energy recovery systems significantly reduce operating costs.

Despite the maturity of SWRO technology, equipment materials still face severe corrosion risks under harsh seawater environments:

1.Pitting and Crevice Corrosion
Austenitic stainless steels (such as 316L and 904L) are vulnerable to localized corrosion in high-salinity or chlorine-residual environments. In regions such as the Middle East and the Mediterranean, high seawater temperatures further accelerate these issues.

2.Influence of Temperature and Salinity
Elevated seawater temperatures promote chloride ion adsorption, reducing the Critical Pitting Temperature (CPT). For example, the CPT of 316L stainless steel in 3.5% NaCl solution is only about 10°C-much lower than actual seawater temperatures in tropical zones.

3.Processing and Microstructural Factors
The corrosion resistance of duplex stainless steel depends not only on alloy composition but also on processing and heat treatment quality. Improper annealing can lead to sigma-phase precipitation, reducing corrosion resistance and accelerating failure.

To address these challenges, the industry has developed various material and protection solutions:

1.Duplex and Super Stainless Steels
Grades such as 2205 and 2507 duplex stainless steels, combining both austenitic and ferritic phases, provide stronger corrosion resistance than conventional stainless steels and are widely used in SWRO high-pressure pipelines.

2.Titanium and Titanium Alloys
Titanium materials are virtually immune to chloride-induced corrosion, effectively preventing pitting and crevice corrosion. Proven in projects across the South China Sea, the Middle East, and North Africa, titanium piping has become the best choice in extreme environments.

3.Cathodic Protection and Corrosion Inhibitors
Sacrificial anode cathodic protection can delay localized corrosion, while new eco-friendly corrosion inhibitors offer potential for dual-scale and corrosion control in future projects.

4.Coatings and Surface Modification
In low-pressure systems, non-metallic materials such as FRP, PVC, and rubber linings are widely applied. Although not yet mature for high-pressure systems, advanced coating technologies are under study and may be introduced in the future.

Looking ahead, the development of SWRO desalination will focus on:

• Material Innovation: Wider adoption of titanium alloys and super duplex steels to extend equipment life in high-salinity and high-temperature environments.
• Green and Energy-Efficient Solutions: Integration with renewable energy sources such as solar and wind, moving toward "zero-carbon" desalination plants.
• Smart Operations and Maintenance: Use of big data and AI for fouling prediction, corrosion monitoring, and intelligent maintenance.
• Scalable and Modular Applications: From large coastal cities to islands, vessels, and remote arid areas, modular SWRO systems will meet diverse freshwater demands.

As a vital technology to address global freshwater scarcity, SWRO desalination not only ensures stable water supply but also drives sustainable, low-carbon development. While corrosion and material degradation remain technical challenges, they also provide opportunities for innovation in alloys, coatings, and intelligent monitoring. With continuous advancements, SWRO systems will operate safely, reliably, and durably in harsher environments-contributing significantly to global water security.