Seawater Desalination Guide: How to Choose Anti-Corrosion Valves

Seawater desalination has become an increasingly important solution in regions facing fresh-water shortages. In recent years, large-scale desalination projects have been built across the Middle East, North Africa and coastal parts of Asia in order to secure a stable supply of potable water. From a technical point of view, one of the most critical topics in these projects is valve selection — especially when it comes to anti-corrosion performance.

Once seawater enters the pretreatment stage, most piping components come into prolonged contact with highly saline, corrosive media. Compared with fresh water, seawater contains higher concentrations of chloride ions, which cause serious pitting and crevice corrosion. Choosing the wrong valve can lead to leaks, sudden failure or constant replacement costs. This is why engineers must evaluate not only flow control performance, but also corrosion resistance, durability and long-term O\&M considerations.

So how do we select the right anti-corrosion valve for a seawater desalination plant? The answer depends on four key aspects: the type of desalination process, the media conditions, the valve body material, and the coating/lining technology. Below you’ll find a practical guide on how to evaluate these factors.

Identify the Desalination Stage and Operating Conditions

In a typical seawater desalination plant, there are three major stages: pretreatment, reverse osmosis (RO) and post-treatment. The valve requirements of each stage are different:

1.Pretreatment stage

This stage involves coarse filtration, fine filtration and chemical conditioning. Valves are exposed to raw seawater, which has a high chloride ion concentration and often contains biological contaminants and suspended solids. Components must therefore resist abrasion and biological fouling in addition to regular corrosion.

2.Reverse osmosis stage

 In RO modules, the operating pressure can reach 60–80 bar. The brine becomes even more concentrated, and valves need to endure high pressure and high salinity at the same time. Any failure in this section can cause severe downtime.

3.Post-treatment stage  

Treated water often needs chemical re-mineralization or disinfection with chlorine. Although the salinity is reduced, chemical resistance becomes more relevant, especially when dosing systems are involved.

At the very beginning of valve selection, you should define the actual medium (seawater, brine or chemical solution), the pressure range, and the fluid temperature. Without this information, you can hardly select the correct material or valve type.

Choose the Right Valve Body Material

Valve corrosion resistance is largely determined by the base material. The following are commonly used in desalination projects:

You don’t always need the most expensive material. For example, duplex stainless steel often provides a very balanced combination of price and performance. Titanium or nickel alloys are usually reserved for the most corrosive conditions where normal stainless steel might fail rapidly.

Pay Attention to Internal Coating and Lining

In many desalination applications, the media does not only attack the outer body, but also the internal surfaces, especially near sealing areas. That’s why internal coating is vital. Common lining/coating options include:

• Fusion-bonded epoxy (FBE)– a cost-effective protection for internal surfaces in pre-treatment systems.

• PTFE lining – excellent chemical resistance; suitable for dosing sections after RO.

• Rubber lining– useful for abrasion resistance when dealing with suspended solids.

• Glass flake coatings– provide barrier protection when combined with stainless steel.

A frequently overlooked detail is the bond strength between the coating and the metal surface. Poor surface preparation or low-quality coatings can cause blistering and local corrosion underneath the lining.

Tip: If the coating breaks or peels, even a high-grade stainless steel valve can corrode quickly. Always check the coating specification and application procedure.

Select the Appropriate Valve Type

Different valve types offer different advantages in seawater service. Here’s a short summary:

In RO systems, high-pressure ball valves with super-duplex construction are commonly selected because they maintain tight shut-off at high pressures and have low torque.

Evaluate Long-Term Maintenance and Total Cost of Ownership

Many project owners focus purely on initial purchase price, but the total cost of ownership can be much higher if a valve fails prematurely. These costs include:

• Valve replacement
• Plant downtime
• Labor for disassembly and re-assembly
• Water loss / production interruption
• Recoating or relining costs

That’s why it’s important to analyze maintenance intervals, the availability of spare parts, and the life expectancy of the selected material.

For example, a super duplex valve might cost 30–40% more than a standard duplex valve, but if it doubles the service life in the RO section, it usually results in a lower total life-cycle cost.

Confirm Compliance with Industry Standards

Make sure the selected valves comply with standards that apply to seawater desalination: