SWRO stands for seawater reverse osmosis. It is a filtration process, applied at large scale, to produce freshwater from seawater for industrial processes, irrigation and drinking water.
How reverse osmosis works
Osmosis is the phenomenon whereby water flows from a solution of low concentration to one of high concentration, in order to balance the two solutions' concentrations. In plants, for example, nutrients are held in greater concentration at the roots, so water tends to flow to the roots from the surrounding soil.
Reverse osmosis does the opposite: water flows from a higher-concentration solution to a lower-concentration one. This requires a very high pressure difference to overcome the natural osmotic pressure that drives regular osmosis. In SWRO, seawater is pumped at high pressure towards a membrane. The membrane holds back the dissolved salts and inorganic molecules but lets the water molecules through. This process is typically greater than 95% efficient, though two passes may be required to produce fresh water suitable for drinking.
Why SWRO is the default for desalination
Desalination - removing salt from seawater - can be undertaken by a variety of processes. SWRO has developed into the most energy-efficient, making it the technology of choice at industrial scale in an increasing number of locations. As well as the largest projects supplying clean water to inhabitants of large conurbations in regions such as the Middle East, USA, North Africa, Spain and Australia, it can be packaged into smaller units aboard ships, or within factories, hotels and sports grounds, to provide a consistent supply of freshwater where access is otherwise limited.
Material selection
On the outlet side of the membrane, corrosion risk is much reduced, as you are effectively handling clean water. On the inlet side, you are handling seawater or a more concentrated brine, and when combined with high pressures this is why stainless steel piping and fittings are widely specified. Super duplex stainless steel has become the default specification for many operators, given its cost-effective combination of high strength and superior corrosion resistance. With a pitting resistance equivalent number (PREN) greater than 40, these alloys can be safely specified for long-term use thanks to their strong resistance to pitting and crevice corrosion.
We can provide a complete package of stainless steel pipes, flanges and fittings. In addition, the combination of our bar stock and machining capability can produce bespoke fittings, alongside our plate stock to support fabrication.