Seawater cooling is one of the most aggressive duties in the process industry. Chloride content above 19,000 mg/L, dissolved oxygen, biological activity, and operating temperatures of 30–60°C combine to attack conventional stainless steels from every direction. This is why super duplex S32750 heat exchanger tubes have replaced 316L and even standard 2205 duplex in a growing number of offshore, desalination, and coastal power projects.

Type 316L relies on a molybdenum addition to resist pitting, and it performs well in many chloride environments. In seawater, however, two mechanisms defeat it:

• Chloride pitting and crevice corrosion — 316L has a pitting resistance equivalent number (PREN) of roughly 25, which is below the threshold for reliable seawater service, particularly in crevices at tube-to-tubesheet joints.
• Chloride stress corrosion cracking — austenitic stainless steels crack under the combined action of tensile stress and chlorides above about 60°C, which is well within the range of condenser outlet temperatures.

UNS S32750 is a super duplex stainless steel with a balanced austenite-ferrite microstructure of roughly 50/50. That structure delivers the properties that matter in seawater cooling:

Note: CPT values are test-medium dependent. The figures above refer to the standard ASTM G48 6% ferric chloride test; measured values are higher in less aggressive chloride media. Always confirm against the actual chloride concentration, temperature, and oxygen level of the seawater system rather than against a single headline number.

Because the yield strength is more than twice that of 316L, S32750 also allows thinner walls for the same design pressure, which improves heat transfer and reduces weight — a decisive advantage on offshore platforms where every kilogram counts.

• Shell and tube condensers and coolers using raw seawater as the cooling medium
• Multi-stage flash and multi-effect desalination plants
• Offshore platform and FPSO utility cooling systems
• Coastal power station condensers and auxiliary coolers
• Chemical plants handling chlorinated brines and hypochlorite streams

S32750 tube is normally supplied as seamless tube to ASTM A789, with welded tube to ASTM A790, using the UNS S32750 / W.Nr. 1.4410 designation. Two points deserve attention when writing the purchase order:

1. Ferrite content and intermetallic phases — the tube must be solution annealed and water quenched, with the ferrite fraction verified, otherwise sigma phase can form and destroy toughness.
2. Corrosion testing — ASTM G48 practice A or B testing is the standard acceptance evidence for super duplex, and it should be stated explicitly rather than left to mill discretion.

Yuhong supplies S32750 seamless tube with eddy current examination, hydrostatic testing, and full material certification, along with matching duplex and super duplex U-bend tubes, tubesheets, and return bends for complete bundle fabrication.

Super duplex costs more per kilogram than 316L, but the comparison that matters is cost per year of service. A 316L bundle that pits through in 18 months carries the shutdown, gaskets, crane time, and lost production on top of the tube cost. On seawater duty, S32750 is usually the lower-cost option over the life of the exchanger.

Provide the chloride concentration, maximum tube metal temperature, flow velocity, and design pressure, and our engineering team will confirm whether S32750, 2205, or a 6Mo grade is the correct choice for your seawater cooler.

Approximately 65°C in the standard ASTM G48 ferric chloride test, compared with roughly 35°C for 2205 duplex. In less aggressive chloride media the measured value is higher, so CPT should be confirmed against the real seawater chemistry rather than treated as a fixed threshold.

Both standards cover duplex and super duplex tube. In practice, seamless tube is normally supplied to ASTM A789 and welded tube to ASTM A790. Confirm the product form and supplementary requirements against the purchase specification.

S32750 is commonly selected for seawater cooling in the 30–60°C range where 316L and 2205 become marginal, but suitability still depends on flow velocity, oxygen level, and crevice conditions. Provide the chloride concentration, maximum metal temperature, and design velocity, and the grade can be confirmed against the actual duty rather than a single temperature figure.