ASTM A789 S32750 Super Duplex Stainless Steel U-Bent Tubes contain approximately 25% chromium, 7% nickel, 4% molybdenum, and 0.3% nitrogen. They are specially designed for heat exchangers, condensers, seawater desalination systems, and high-pressure corrosive chemical processing applications.
The 2507 duplex stainless steel U-bent tubes supplied by GNEE are manufactured using a solution annealing process. After bending, the tubes undergo heat treatment at 1050–1100°C to eliminate internal stress caused by the bending process. For long-term service, the operating temperature is recommended to remain below 300°C (600°F) to prevent material embrittlement and reduction in corrosion resistance.
S32750 U-bent tubes offer outstanding resistance to chloride-induced pitting corrosion, crevice corrosion, and stress corrosion cracking. The Critical Pitting Temperature (CPT) reaches ≥50°C, while the material can withstand temperatures up to 315°C. In seawater, brine, and acidic media, the service life is more than 8 times longer than conventional austenitic stainless steel tubes.
UNS S32750 stainless steel straight tubes are available with outside diameters ranging from 6.35 mm to 219 mm and wall thicknesses from 1.0 mm to 25 mm. Bending radii can be customized according to standard or non-standard requirements. The outside diameter tolerance is controlled within ±0.13 to ±0.76 mm, while wall thickness tolerance is maintained within ±10%. The bent section is free from flattening and wrinkling, and ovality is strictly controlled within ≤1.5%, meeting the precision assembly requirements of heat exchangers.
Each tube undergoes eddy current testing, ultrasonic non-destructive testing, and 100% hydrostatic pressure testing to ensure reliable pressure resistance and sealing performance. The finished product qualification rate reaches as high as 99.8%, and all products are supplied with EN 10204 3.2 material certificates and third-party inspection reports.
Click to obtain EN 10204 3.2 material certificates
S32750 Stainless Steel U Bend Tube Specifications
| Item | Specification |
|---|---|
| Standard | ASTM A789 / ASME SA789 |
| Grade | S32750 (SAF 2507 / Super Duplex) |
| Tube Type | Seamless or Welded (Seamless is most common for U-bends) |
| Form | U-Bent Heat Exchanger Tubes |
| Main Applications | Oil & Gas, Desalination, Chemical Processing, Marine Heat Exchangers |
| Outside Diameter (OD) Tolerance | ±0.1 mm – ±0.2 mm (according to ASTM A1016/A789) |
| Wall Thickness (WT) | Average Wall or Minimum Wall (Tolerance ±10%) |
| Bending Radius (R) | Minimum: 1.5 × OD; Maximum: 1250 mm |
| Bending Radius Tolerance | ±1.5 mm for R ≤ 1000 mm; ±2.0 mm for R > 1000 mm |
| Leg Length | Up to 12,000 mm per leg; Tolerance +5 mm / -0 mm |
| Ovality (Flattening) | Maximum 5% of the original tube diameter |
| Leg Parallelism | ≤ 1.5 mm at the end of the legs |
Chemical Composition
| C max | Mnmax | Simax | Smax | Pmax | Cr | Ni |
Mo |
Cumax |
N |
| 0.03 | 1.2 | 0.8 | 0.02 | 0.035 | 24-26 | 6-8 | 3-5 | 0.5 | 0.24/0.32 |
Mechanical Properties
| Heat treatment | Tensile strength Mpa min | Yeild strenth Mpa min | A % min | Hardness HB | Hardness HR |
| 1025-1125 water quench | 800 | 550 | 15 | 310 | 32 |
UNS S32750 Heat Treatment and Surface Condition
Solution Annealing: Heat to 1025°C – 1125°C (1880°F – 2060°F), followed by rapid quenching in water or air.
U-Bend Stress Relief: For Super Duplex Steel S32750, it is typically required to perform solution annealing on the bent region-along with at least 150 mm of the adjacent straight pipe sections on both sides-in order to restore phase equilibrium (ferrite-austenite) and relieve bending stresses.
Surface Finish: Pickled and Annealed (AP), Bright Annealed (BA), or Polished.
Applications
Widely used in heat exchange systems with extremely demanding material performance requirements, including:
Oil & Gas: Subsea pipelines, wellhead equipment, offshore platforms.
Chemical & Petrochemical: Reactors, high-pressure heat exchangers.
Marine Industry: Ship propellers, pumps, and valves.
Pollution Control: Wet scrubbers.
Seawater Desalination Plants.
Why choose S32750 over S31803/S32205 for heat exchangers?
S32750 (Super Duplex Stainless Steel) contains higher levels of chromium, molybdenum, and nitrogen. Its PREN (Pitting Resistance Equivalent Number) exceeds 41, whereas that of S32205 is only 34–35. This endows S32750 with exceptional resistance to pitting corrosion, crevice corrosion, and stress corrosion cracking (SCC) in harsh environments containing high concentrations of chloride ions-such as seawater, strong acids, and bleaching agents.
How are U-bend tubes pressure tested?
Hydrostatic Test: Upon the completion of bending and annealing, each tube undergoes a hydrostatic test, with the test pressure calculated according to the formula P = 2St/D.
Air Under Water Test: The U-bend tube is submerged in water and pressurized with high-pressure air; it is then inspected for the presence of bubbles to detect minute leaks.
Packaging for S32750 U-Tubes
To prevent deformation and chloride ion contamination during transit, the following methods are typically employed:
Wooden Crates: Robust packaging designed to prevent mechanical damage.
Separators: Plastic or wooden comb-style separators are placed between layers and individual tubes to prevent collision.
End Caps: Used to seal the tube ends, preventing the ingress of debris and moisture.
