What makes warm, salty seawater so aggressive
Enclosed and tropical seas such as the Arabian Gulf and the Red Sea run hotter and saltier than the open ocean, and they support far more marine fouling. In the Gulf, salinity often exceeds 40,000 ppm and water temperatures climb past 35 °C in summer. Higher temperatures accelerate pitting and crevice attack on stainless steels, while low flow allows sediment to build up and corrode the surface beneath it.
Materials engineers usually consider
- Titanium. At ordinary cooling-water temperatures it is effectively unaffected by seawater. The purchase price is higher, yet across the full service life it normally works out as the most economical choice.
- Copper-nickel (90/10, 70/30). Inherently discourages biofouling and has decades of proven service behind it. It suffers, however, under high flow velocities, sand-laden water or sulphide pollution.
- Super duplex (2507) and 6Mo (254 SMO). High strength at a sensible price for shells and pipework. Above about 30 to 40 °C, though, crevice corrosion becomes a real threat, so respect the alloy's temperature ceiling.
- Ordinary stainless steel (316L). Not a material we advise for this kind of seawater, because chloride pitting tends to appear early.
A straightforward guideline
On seawater-cooled shell and tube exchangers, titanium tubing paired with a tubesheet that is clad or coated delivers the most dependable result. Copper-nickel deserves a look where the water is clean, temperatures are moderate and flow speed is kept under control.
How we decide: when the exchanger is difficult to access, or a single leak would halt the plant, specify titanium.
Small details, long life
Service life also depends on gaskets, tubesheet design, velocity limits, dissimilar-metal (galvanic) contact and cathodic protection. Even the best alloy will fail prematurely in a badly engineered unit.
Share your process data with us and we will recommend the most cost-effective material for your site, with the reasoning behind it.