[ Duplex / Desalination ]
[ Duplex / Desalination ]
coatings / AB excellent choices for intake systems, with FRP / PVDF for posttreatment. Finally, high silt and erosion along the Atlantic coast makes super duplex with erosion-resistant linings and sacrificial sleeves the preferred choice.
Recommended valve types in desalination plants Valve selection should also consider operational frequency, actuation method( manual, pneumatic, or electric), and valve pressure rating( typically Class 600 – 900). Automated control valves help maintain pressure stability across the reverse osmosis system and extend membrane life by minimizing flow fluctuations. Different valve designs are suited for specific roles within a desalination plant, as shown in table 3:
The economic argument Choosing materials based solely on the upfront price( initial investment) is often an expensive mistake over the long run. To make smart, sustainable decisions, we must use the Total Cost of Ownership( TCO) analysis. This calculation factors in all costs including future maintenance, downtime, and replacement over the entire life of the equipment. By way of example, we have compared the costs of a full AB valve against a full super duplex steel valve. This was based on the following assumptions: critical DN200 manual butterfly valve in high-pressure reverse osmosis system; twenty-year operational life; a realistic 7 % discount rate to reflect the 2024 – 2025 financial climate; 3 % annual inflation.
Table 4: Economic comparison, showing the total cost of ownership of AB and |
super duplex DN200 manual butterfly valves |
Factor |
Aluminum bronze( AB) |
Super duplex( 2507) |
Initial purchase( CAPEX) |
USD 950 |
USD 1700 |
Estimated lifespan |
7 years |
20 + years |
Replacement cost( at years 7 & 14) |
USD 1293 |
0( No replacement expected) |
Net present value( NPV) of maintenance( 20 years)
Table 2: Pitting resistance equivalent number comparison
As Table 4 clearly shows, over a twenty-year lifespan the super duplex valve has a higher initial purchase price but delivers a significantly lower TCO, representing a saving of USD 618. These findings clearly demonstrate that optimizing for longterm operational sustainability( TCO) provides better value than focusing on the initial purchase price( CAPEX), especially for critical components exposed to highly corrosive environments.
Conclusion Valve selection in SWRO plants is a strategic design decision, not a routine purchase. Matching material performance( PREN), pressure class, and sealing design to local seawater conditions significantly reduces lifecycle costs, improves uptime, and safeguards plant integrity. This study confirms that super duplex steels( PREN ≥ 40) offer the best longterm value for high-pressure reverse osmosis and brine lines, while AB or lined valves remain suitable for intake
USD 120 USD 45 Annual maintenance cost USD 8 USD 3
Material PREN value Seawater suitability
316L stainless steel ~ 25 Poor – unsuitable for seawater
Total cost of ownership( TCO) USD 2363 USD 1745
Duplex steel ~ 35 Marginal – limited long-term use
Daily Operational Cost USD 0.324 USD 0.239
Super duplex steel ~ 42 Excellent – high corrosion resistance 904L / Alloy 625 35 – 40 Good – specialized applications
Table 3: Recommended valve types in desalination plants |
Valve type |
Typical applications |
Butterfly |
Commonly used in large-diameter intake and pre-treatment lines. Super duplex variants provide excellent resistance to both corrosion and erosion |
Control |
Used in RO stages for flow and pressure regulation; pneumatically-actuated super duplex control valves are the industry standard |
Ball Gate
For chemical dosing where precise shut-off is required. PVDF or FRP-lined options are preferred Used selectively for isolation duties and low-pressure zones. Given that SWRO systems operate 20 – 40 bar above osmotic pressure, pressure rating and mechanical strength must meet or exceed API / ANSI class margins, verified through site salinity data. Regional conditions also guide material choice— Red Sea( high salinity), Indian Ocean( biofouling), and Atlantic coasts( erosion). In summary, valve selection should follow a clear sequence:( 1) determine osmotic pressure,( 2) compare materials via PREN,( 3) choose optimal sealing,( 4) consider regional factors, and( 5) complete a Total Cost of Ownership( TCO) analysis. This integrated approach ensures sustainable, reliable, and economically sound SWRO operations across diverse coastal environments.
Sources available on request.
About the authors
Ömer Yıldız is a mechanical engineer with over 25 years of professional experience in the industrial valve and actuator industry. He is the founder and general manager of Starvalve Process Valves and Actuator Technology Inc. His expertise focuses on process automation, valve design, and energy-efficient flow control solutions.
Mechatronics engineer Abdellah El Khobzi provides engineeringdriven valve and actuator solutions for desalination, water treatment, and industrial fluid control applications across the MENA, Africa, and APAC regions. His work at Starvalve combines technical analysis, material selection, and performance optimization with data-based market intelligence. He is currently pursuing a master’ s degree in industrial engineering, focusing on optimization, simulation, data analysis, and artificial intelligence.
48 Stainless Steel World April 2026 www. stainless-steel-world. net