Duplex Steel UNS S32750 and UNS S32760 pipes are two high-performance duplex stainless steels with good corrosion resistance, high strength and good weldability. These two materials are widely used in highly corrosive industries such as oil and gas, chemical, offshore, paper, power and other industries due to their reliable performance in harsh environments.
Duplex stainless steel because of its unique austenitic – ferritic duplex organization, both austenitic stainless steel excellent corrosion resistance and ferritic stainless steel high strength. UNS S32750 and UNS S32760, is based on ordinary duplex stainless steel, by increasing the content of chromium (Cr), molybdenum (Mo) and nitrogen (N) and other elements, to further improve its corrosion resistance and mechanical properties, so as to make it suitable for more demanding environments.
ASTM A790 S32750 / UNS S32760 Pipes Specification
| Processing Method | Seamless and Welded |
| Size Range | 1/8” – 30” / DN6 – 750 |
| Thickness Schedule | SCH10 SCH20 STD SCH40 SCH60 SCH80 SCHXS SCH100 SCH120 SCH140 SCH160 SCHXXS |
| Length | 6m or 12 m or Random |
| Standard | ASME B36.19,ASTM A789, ASTM A790, ASTM A928, ASME SA789, |
| Surface Treatment | Polish , Mirror , Epoxy Powder FBE, 2PE, 3PE Coating |
| Material Grade | ASTM A790 S32205, S31803, 32750, 32760, S32550 |
| Pipes Ends | Plain Ends / Beveled Ends |
ASTM A790 Standard
The ASTM A790/A790M specification specifies the fabrication, dimensions, tolerances, test conditions for duplex welded and seamless steel pipe.
This specification covers seamless and straight-seam welded ferritic/austenitic steel pipe for general corrosive applications, with particular emphasis on resistance to stress corrosion cracking. The pipe shall be manufactured by seamless welding or automatic welding processes, and no filler metal shall be added during welding. Thermal analysis shall be performed to determine the percentage of the specified elements. Tensile tests, hardening tests, flattening tests, hydrostatic tests, and nondestructive electrical tests shall meet the specified requirements.
ASTM A790 UNS S32750 / S32760 Pipes Chemical Composition
| CHEMICAL | LIMITS | C | Mn | P | S | Si | Ni | Cr | Mo | N | Cu | w |
| ASTM A790 UNS S32750 | MIN | 6.00 | 24.00 | 3.00 | 0.24 | |||||||
| MAX | 0.030 | 1.20 | 0.035 | 0.020 | 0.80 | 8.00 | 26.00 | 5.00 | 0.32 | 0.5 | ||
| ASTM A790 S32760 | MIN | 6.00 | 24.00 | 3.00 | 0.20 | 0.50 | 0.50 | |||||
| MAX | 0.03 | 1.00 | 0.03 | 0.01 | 1.00 | 8.00 | 26.00 | 4.00 | 0.30 | 1.00 | 1.00 |
Effect of the addition of copper and tungsten on S32760:
The addition of copper (Cu) significantly improves the corrosion resistance of S32760 in reducing acids such as sulfuric acid and phosphoric acid, especially in the medium concentration of sulfuric acid environment.
The addition of tungsten (W) further enhances the strength and pitting resistance of S32760.
UNS S32750 / S32760 Pipes Mechanical Property
| MATERIAL | T.S (MPA) | Y.S (MPA) | EL % | HARDNESS |
| ASTM A790 S32750 | 800min | 550min | 15min | 300max |
| ASTM A790 S32760 | 750min | 550min | 25min | 310max |
Duplex Steel Pipes Dimension
| Nominal Size | OD | Sch5s | Sch10s | Sch40s | Sch80s | |||||
| DN | NPS | 0 | T | kg/m | T | kg/m | T | kg/m | T | kg/m |
| 6 | 1/8 | 10.3 | 1.24 | 0.28 | 1.73 | 0.37 | 2.41 | 0.47 | ||
| 8 | 1/4 | 13.7 | 1.65 | 0.49 | 2.24 | 0.63 | 3.02 | 0.8 | ||
| 10 | 3/8 | 17.1 | 1.65 | 0.63 | 2.31 | 0.84 | 3.2 | 1.1 | ||
| 15 | 1/2 | 21.3 | 1.65 | 0.82 | 2.11 | 1 | 2.77 | 1.27 | 3.73 | 1.62 |
| 20 | 3/4 | 26.7 | 1.65 | 1.04 | 2.11 | 1.28 | 2.87 | 1.69 | 3.91 | 2.2 |
| 25 | 1 | 33.4 | 1.65 | 1.33 | 2.77 | 2.09 | 3.38 | 2.5 | 4.55 | 3.24 |
| 32 | 1 1/4 | 42.2 | 1.65 | 1.68 | 2.77 | 2.7 | 3.56 | 3.39 | 4.85 | 4.47 |
| 40 | 1 1/2 | 48.3 | 1.65 | 1.95 | 2.77 | 3.11 | 3.68 | 4.05 | 5.08 | 5.41 |
| 50 | 2 | 60.3 | 1.65 | 2.44 | 2.77 | 3.93 | 3.91 | 5.44 | 5.54 | 7.48 |
| 65 | 2 1/2 | 73.0 | 2.11 | 3.77 | 3.05 | 5.26 | 5.16 | 8.63 | 7.01 | 11.41 |
| 80 | 3 | 88.9 | 2.11 | 4.6 | 3.05 | 6.45 | 5.49 | 11.29 | 7.62 | 15.27 |
| 90 | 31/2 | 101.6 | 2.11 | 5.29 | 3.05 | 7.4 | 5.74 | 13.57 | 8.08 | 18.63 |
| 100 | 4 | 114.3 | 2.11 | 5.96 | 3.05 | 8.36 | 6.02 | 16.07 | 8.56 | 22.32 |
| 125 | 5 | 141.3 | 2.77 | 9.67 | 3.4 | 11.57 | 6.55 | 21.77 | 9.53 | 30.97 |
| 150 | 6 | 168.3 | 2.77 | 11.55 | 3.4 | 13.48 | 7.11 | 28.26 | 10.97 | 42.56 |
| 200 | 8 | 219.1 | 2.77 | 15.09 | 3.76 | 19.96 | 8.18 | 42.55 | 12.7 | 64.64 |
| 250 | 10 | 273.1 | 3.4 | 23.08 | 4.19 | 27.78 | 9.27 | 60.31 | 12.7 | 96.01 |
| 300 | 12 | 323.9 | 3.96 | 31.89 | 4.57 | 36 | 9.53 | 73.88 | 12.7 | 132.08 |
| 350 | 14 | 355.6 | 3.96 | 35.06 | 4.78 | 41.3 | ||||
| 400 | 16 | 406.4 | 4.19 | 42.41 | 4.78 | 47.29 | ||||
| 450 | 18 | 457.2 | 4.19 | 47.77 | 4.78 | 53.26 | ||||
What is the difference between UNS S32750 and S32760?
UNS S32750 (2507) and UNS S32760 are both super duplex stainless steels with excellent performance. They are very similar in chromium, nickel, molybdenum and nitrogen content, but the key difference is that S32760 has additional copper (Cu) and tungsten (W).
S32750 (2507): It is a general-purpose super duplex steel that performs well in most chloride environments.
S32760 : Due to the addition of copper and tungsten, it has stronger corrosion resistance in reducing acids (especially sulfuric acid) and has a slight advantage in certain specific high corrosion/erosion combined environments. The selection should be based on the specific media and working conditions. If the environment contains sulfuric acid or requires extreme corrosion resistance, S32760 is often a better choice.
Duplex Steel Pipes Corrosion Resistance
Chloride Stress Corrosion Cracking (SCC) Resistance: This is one of the major weaknesses of austenitic stainless steels in chloride-containing environments, to which super duplex steels are extremely resistant.
Resistance to pitting and crevice corrosion: The high chromium, molybdenum and nitrogen content gives it an excellent pitting equivalent (PREN) value and excellent resistance to environments containing chloride ions, such as seawater.
Resistance to uniform corrosion: It also shows good corrosion resistance in a variety of acidic and alkaline environments.
Manufacturing Standards
ASTM A790/A790M: Standard Specification for Seamless and Welded Duplex Stainless Steel Pipe.
ASTM A928/A928M: Standard Specification for Electric Resistance-Welded and Fusion-Welded Duplex Stainless Steel Pipe for High-Pressure Service.
ASTM A999/A999M: General Requirements for Stainless Steel Pipe.
ASME B36.19M: Dimensional Standard for Stainless Steel Pipe.
EN 10216-5: European Standard for Stainless Steel Pipe.
NORSOK MDS (M-630): Norwegian petroleum industry standard with very stringent requirements for materials for offshore applications, often specifying super duplex stainless steels.
Benefits
✅ Extremely high strength (more than twice that of 316L)
✅ Excellent resistance to chlorine ions
✅ Excellent resistance to fatigue, impact and stress corrosion
✅ Stability in extreme environments
✅ Long service life, low maintenance and overall cost-effective performance.
Challenges and Considerations
Higher price: Due to the high content of alloying elements, the cost of duplex steel UNS S32750 and UNS S32760 pipes are generally higher than that of austenitic stainless steel and ordinary duplex stainless steel.
Processing difficulty: High strength and hardness make it more difficult to process (such as cutting and drilling) than austenitic stainless steel.
Welding process control: Heat input and cooling rate need to be strictly controlled during welding to maintain the ideal austenite-ferrite phase balance and avoid the precipitation of harmful phases (such as sigma phase), otherwise it will seriously damage the toughness and corrosion resistance of the material.
Common Applications
Offshore engineering equipment
Oil and gas industry
Pulp and paper equipment
Chemical processing systems
Reverse osmosis desalination units
Conclusion
Duplex steel UNS S32750 and S32760 pipes are characterized by their unique chemical composition, which gives them excellent performance in terms of strength, corrosion resistance and weldability. They are used in a wide range of important applications in the oil and gas, chemical, and offshore industries, where their performance is critical to the stable operation and development of each industry. In actual application, engineers need to consider and reasonably select UNS S32750 or S32760 tubing according to specific working conditions, such as the type of media, temperature, pressure, corrosive environment, etc., in order to give full play to their advantages, ensure the safe and efficient operation of piping systems, and at the same time realize the best economic and social benefits.
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