The main difference between duplex and super duplex is in the higher alloying content (Chromium, Molybdenum, and Nitrogen) of Super Duplex. Super duplex is based on approximately 25% chromium compared to 22% in standard duplex. This makes it stronger and gives it a PREN value above 41, compared to typically 30–38 for standard duplex. This makes it significantly more resistant to pitting and crevice corrosion.
Super Duplex Steel Pipe Manufacturer
We are Zhejiang Xintongda Special Steel (XTD), one of the leading China-based manufacturers and global suppliers of super duplex stainless steel pipe. Super duplex steel pipe is a dual-phase stainless pipe with roughly equal parts of ferrite and austenite in the microstructure. Compared with standard duplex, it uses higher levels of chromium (about 25%), molybdenum (about 4%), and nitrogen (about 0.28%). The top super duplex grades include S32750 and S32760. They carry a PREN above 40, which is the industry line between standard duplex and super duplex. That translates to near-nickel-alloy chloride pitting resistance and about three times the minimum yield strength of 316L stainless steel. We manufacture seamless super duplex pipe to ASTM A790 (equivalent ASME SA-790) in the grades UNS S32750 (SAF 2507), UNS S32760 (Zeron 100), and UNS S32550 (Ferralium 255). Typical service is offshore oil and gas, chemical and petrochemical, marine, and seawater desalination, wherever 304, 316L, or standard duplex would pit or fail from chloride stress corrosion cracking. We hold multiple international certifications, listed on our Certificate page, and we run an annual supply capacity of 25,000 tons.
Our ASTM A790 super duplex steel pipe meets these specifications:
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OD Range
6-720mm
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Thickness
1-65 mm
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Length
≤ 18 m
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What is a Super Duplex Pipe?
Super duplex pipe is made from austenitic-ferritic stainless steel, a dual-phase alloy classified as a high-alloy grade. Its chemical composition primarily includes chromium (24–26%), nickel (~7%), molybdenum (3–5%), nitrogen (0.24–0.32%), and the balance being iron. This unique combination provides the pipe with high strength from the ferritic phase and good toughness from the austenitic phase. Chromium, molybdenum, and nitrogen work across both phases to deliver its superior corrosion resistance. Each element enhances the performance of this pipe and provides it with the exceptional ability to resist stress corrosion cracking as well.
Features and Benefits of Super Duplex Steel Pipe
The features and benefits of super duplex stainless steel pipe include high alloying content, cost-effectiveness, fatigue resistance, high strength, stress corrosion cracking resistance and toughness. These are explained below in detail:
- High Alloying Content: The high amounts of chromium, molybdenum, and nitrogen make it less likely to suffer pitting and crevice corrosion. This puts super duplex pipe in the high-alloy grade category. It also enhances its overall performance and strength.
- Cost-Effectiveness: Compared to austenitic stainless steels like 304 and 316, super duplex steel pipe's high strength allows for thinner walls and less material usage. This helps offset its higher material cost and reduces the total cost of the project. The better corrosion resistance also means that the product will last longer and cost less to maintain and replace.
- Fatigue Resistance: The pipe's dual-phase microstructure gives it a higher fatigue limit and better resistance to cyclic loading than regular austenitic grades. This makes it perfect for applications that involve pressure cycling or vibrating equipment. This ensures that it will work reliably for a long time.
- High Strength: SDSS pipe has a high yield strength, which leads to greater design flexibility. This enables the construction of lighter and stronger pressure vessels and piping systems.
- Stress Corrosion Cracking Resistance: The pipe offers excellent resistance to stress corrosion cracking (SCC) caused by chloride. It is very reliable for marine and chemical processing due to its high chromium, nitrogen and molybdenum content, and a ferritic phase.
- Toughness: The pipe stays tough even when it's as cold as -50°C (-58°F). This property makes sure that the pipe can absorb energy and not break when it is hit, especially when it is used in cold weather.
Super Duplex Pipe Specification
The specifications for Super Duplex Stainless Steel Pipe define the thickness, dimensions and manufacturing standards. This ensures that the pipes provide optimal performance.
Standard
ASTM A790
Outside Diameters
6 - 720 mm
Length
≤ 18 m
Thickness Range
1 - 65 mm
Grades
S32750, S32760 and S32550
Form
Round (per ASTM A790 and ASME B36.19M)
End
Plain End, Beveled End, Threaded
Testing
PMI, Radiography, Mechanical, Chemical
Types & Shapes Of Super Duplex Steel Pipe
Following are the types and shapes of super duplex steel pipes. However, we, at XTD, specialise only in producing seamless pipes.
Super Duplex Steel Seamless Pipe
Super Duplex Steel Round Pipe
Super Duplex Steel Square Pipe
Super Duplex Rectangular Pipe
Super Duplex Steel Pipe Grades
The grades of super duplex stainless steel that are used in pipe systems include UNS S32750 (2507, 1.4410), UNS S32760 (Zeron 100), and UNS S32550.
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UNS S32750 Pipe (2507, 1.4410)
UNS S32750 pipe is the most common and widely recognised Super Duplex grade. It is known for its blend of high strength and corrosion resistance. It is often utilised in chemical processes, oil and gas and marine environments due to its high PREN value (more than 41).
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UNS S32760 Pipe (Zeron 100, 1.4501)
The addition of tungsten and copper makes UNS S32760 pipe a little more resistant to corrosion than S32750. This means that its PREN is at least 41. This pipe is often used in highly demanding environments, such as handling seawater, desalination plants, and chemical processing units that are very aggressive.
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UNS S32550 Pipe (Ferralium 255, 1.4507 or SD50)
UNS S32550 pipe is often referred to as Ferralium 255 or SD50. It has a higher copper content (approximately 2%), which enhances its resistance to sulphuric acid, phosphoric acid, nitric acid, and other corrosive acids. The pipe provides very high strength and good ductility. This makes it a reliable choice for the pulp and paper industry and certain mineral processing applications.
Industrial Applications of Super Duplex SS Pipe
Super duplex SS pipes have 6 major industrial applications. These include:
Chemical Processing
Super duplex steel pipe is used in heat exchangers, scrubbers and reactors due to its resistance to stress corrosion cracking and aggressive chemicals. The uses also include highly corrosive environments like phosphoric acid, acetic acid, and various oxidising agents.
Petrochemical Equipment
Super duplex pipe is used in separator vessels, distillation columns, and flare systems for corrosive and high-pressure hydrocarbon service. In refineries, it is used for cooling water piping, heat exchangers, and process piping that carry chloride-bearing streams where 316L would pit.
Oil and Gas
In harsh offshore and deep-sea settings, this pipe is important for flowlines, risers and manifolds. In these situations high pressures and corrosion from seawater are major concerns. The uses also involve downhole equipment, process piping, and separators on fixed and floating platforms.
Pipelines and Mechanical Components
Super duplex stainless steel (SDSS) pipe is used in high-pressure piping systems, pumps, and valves that require both exceptional strength and resistance to internal erosion/corrosion. It is also employed in structural parts and shafts. In these applications, high yield strength allows for thinner, lighter designs.
Pulp and Chemical Containers
This pipe is used in storage tanks, digesters, and bleaching equipment because it doesn't corrode easily when exposed to chemicals like chlorine dioxide. The uses also include different types of mixers, washers and piping that handle dangerous substances in pulp and paper mills that are part of industrial piping systems.
Marine Engineering
It is used for seawater cooling systems, ballast water systems, and firefighting systems on ships and offshore structures. It is also used in shipbuilding components like propellers, pumps, and desalination units, where exposure to corrosive seawater is constant.
100% Certified Testing & Documentation
XTD ensures every pipe meets industry requirements through rigorous testing and complete material traceability. The following certifications and test reports are provided with each delivery:
- Raw Materials Certificate
- 100% Positive Material Identification (PMI)
- Heat Treatment Charts
- Third-Party Inspection Report
- Surface roughness and size measurement
- Manufacturer Test Certificate (Impact Testing, Flattening, Flare, Bend, Hardness, Intergranular Corrosion, Pitting Corrosion, Grain size, Eddy Current (ET), Ultrasonic Testing (UT), Hydrostatic Testing (HT), etc.)
- Laboratory Test Certificate from Government-Approved Lab
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Frequently Asked Questions
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What is the difference between duplex and super duplex stainless steel?
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Is Super Duplex Pipe better than 316 or 304 stainless steel?Yes, Super Duplex pipe is typically considered to be better because it is almost twice as strong and much better at resisting localised corrosion and stress corrosion cracking than 316L or 304 stainless steel.
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Can I weld a super duplex steel pipe?Yes. Super duplex is weldable, but the dual-phase microstructure requires disciplined welding to keep the ferrite-to-austenite ratio in balance. Use a matching filler, typically ER2594 (25Cr-9Ni-4Mo) per AWS A5.9 for S32750 and S32760, control heat input, and keep interpass temperature at or below 150 °C per NORSOK M-601 practice. Solution annealing is not usually required if the welding parameters are correct.
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Where to Buy Super Duplex SS Pipe?You can buy Super duplex SS pipe from us, at XTD. We are a trusted manufacturer of seamless pipes, based in Songyang, China. We offer super duplex pipes in different grades like UNS S32750, S32760, and S32550. We also have an annual supply capacity of 25,000 tons and a MOQ of 200 kg for stock items. We can supply these pipes in about 1 week for stock orders. It can take 15-60 days for production orders (domestic or international). Get in touch with us for the right specifications.