A Full Guide to Super Duplex Stainless Steel (SDSS) in the Oil and Gas Industry
What is Super Duplex Stainless Steel (SDSS)?
Super Duplex Stainless Steel (SDSS) is a high-performance material that combines the best properties of austenitic and ferritic stainless steels. Its unique microstructure consists of approximately 50% ferrite and 50% austenite, which gives it exceptional strength and corrosion resistance.
The development of duplex stainless steel began in Sweden in the 1930s for use in the sulfite paper industry, where chloride-induced corrosion was a significant problem. These early duplex alloys were a breakthrough but had limitations in terms of corrosion resistance and mechanical properties. In the 1960s, Langley Alloys introduced Ferralium 255, the first Super Duplex Stainless Steel (SDSS) alloy, which offered improved performance.
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The term "super" refers to its enhanced pitting resistance, particularly in highly corrosive environments or under extreme stress. Super Duplex Stainless Steel (SDSS) was developed in the 1980s to meet the demands of industries requiring materials with a pitting resistance equivalent (PRE) of 38 to 45. Since then, advancements such as Super Duplex F61 have further enhanced the material's properties, making it a cornerstone in industries like oil and gas, chemical processing, and marine engineering.
This makes Super Duplex Stainless Steel ideal for applications in the oil and gas industry, where materials must withstand harsh conditions such as seawater exposure, high pressures, and aggressive chemicals.
Chemical Composition of Super Duplex Stainless Steel (SDSS)
The chemical composition of Super Duplex Stainless Steel (SDSS) is carefully balanced to optimize its mechanical and corrosion-resistant properties. Key elements include:
- Chromium (Cr): 24-28% - Provides excellent corrosion resistance and stability.
- Nickel (Ni): 6-8% - Enhances toughness and resistance to stress corrosion cracking.
- Molybdenum (Mo): 3-4% - Improves resistance to pitting and crevice corrosion.
- Nitrogen (N): 0.24-0.32% - Increases strength and corrosion resistance.
- Carbon (C): Less than 0.03% - Minimizes the risk of carbide precipitation during welding.
- Other elements: Iron (Fe), Manganese (Mn), Silicon (Si), and traces of Copper (Cu) - Contribute to overall performance and workability.
This unique composition ensures that Super Duplex Stainless Steel (SDSS) offers superior resistance to pitting, crevice corrosion, and stress corrosion cracking (SCC), making it a preferred choice for demanding environments.
Chemicals composition of Duplex stainless steel grades from EN 10088-1 (2014) Standard are given in the table below. Composition by weight (%)
| ISO Steel Designation | EN Number | UNS Equiv | C, Max. | Si | Mn | P, Max. | S, Max. | N | Cr | Cu | Mo | Ni | Other |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| X2CrNiNi22-2 | 1.4062 | S32202 | 0.03 | ≤1.00 | ≤2.00 | 0.04 | 0.010 | 0.16 to 0.28 | 21.5 to 24.0 | - | ≤0.45 | 1.00 to 2.90 | - |
| X2CrCuNiN23-2-2 | 1.4669 | - | 0.045 | ≤1.00 | 1.00 to 3.00 | 0.04 | 0.030 | 0.12 to 0.20 | 21.5 to 24.0 | 1.60 to 3.00 | ≤0.50 | 1.00 to 3.00 | - |
| X2CrNiMoSi18-5-3 | 1.4424 | S31500 | 0.03 | 1.40 to 2.00 | 1.20 to 2.00 | 0.035 | 0.015 | 0.05 to 0.10 | 18.0 to 19.0 | - | 2.50 to 3.00 | 3.50 to 5.20 | |
| X2CrNiN23-4 | 1.4362 | S32304 | 0.03 | ≤1.00 | ≤2.00 | 0.035 | 0.015 | 0.05 to 0.20 | 22.0 to 24.5 | 0.10 to 0.60 | ≤0.50 | 3.50 to 5.50 | |
| X2CrMnNiN21-5-1 | 1.4162 | S32101 | 0.04 | ≤1.00 | 4.00 to 6.00 | 0.040 | 0.015 | 0.20 to 0.25 | 21.0 to 22.0 | 0.10 to 0.80 | 0.10 to 0.80 | 1.35 to 1.90 | |
| X2CrMnNiN21-5-3 | 1.4482 | - | 0.03 | ≤1.00 | 4.00 to 6.00 | 0.035 | 0.030 | 0.05 to 0.20 | 19.5 to 21.5 | ≤1.00 | 0.10 to 0.60 | 1.50 to 3.50 | |
| X2CrNiMoN22-5-3 | 1.4462 | S31803, S32205 | 0.03 | ≤1.00 | ≤2.00 | 0.035 | 0.015 | 0.10 to 0.22 | 21.0 to 23.0 | 0.10 to 0.80 | 1.00 to 3.50 | 3.0 to 6.5 | |
| X2CrNiMnMoCuN24-4-3-2 | 1.4662 | S31803, S32205 | 0.03 | ≤0.70 | 2.5 to 4.0 | 0.035 | 0.005 | 0.20 to 0.30 | 23.0 to 25.0 | 1.00 to 2.50 | 3.0 to 4.5 | 6.0 | |
| X2CrNiMoCuN25-6-3 | 1.4507 | S32520 | 0.03 | ≤0.70 | ≤2.00 | 0.035 | 0.015 | 0.20 to 0.30 | 24.0 to 26.0 | 1.00 to 2.50 | 3.0 to 4.0 | 6.0 | |
| X3CrNiMoN27-5-2 | 1.4460 | S31200 | 0.05 | ≤1.00 | ≤2.00 | 0.035 | 0.015 | 0.05 to 0.20 | 25.0 to 28.0 | - | 1.30 to 2.00 | 4.5 to 6.5 | |
| X2CrNiMoN25-7-4 | 1.4410 | S32750 | 0.03 | ≤1.00 | ≤1.00 | 0.035 | 0.015 | 0.24 to 0.35 | 24.0 to 26.0 | 0.50 to 1.00 | 3.0 to 4.0 | 6.0 to 8.0 | |
| X2CrNiMoCuWN25-7-4 | 1.4501 | S32760 | 0.03 | ≤1.00 | ≤1.00 | 0.035 | 0.015 | 0.20 to 0.30 | 24.0 to 26.0 | 0.50 to 1.00 | 3.0 to 4.0 | 6.0 to 8.0 | |
| X2CrNiMoN29-7-2 | 1.4477 | S32906 | 0.03 | ≤0.50 | ≤2.00 | 0.035 | 0.015 | 0.30 to 0.40 | 28.0 to 30.0 | 1.50 to 2.60 | 5.8 to 7.5 | - | |
| X2CrNiMoCoN28-8-5-1 | 1.4658 | S32707 | 0.03 | ≤0.50 | ≤1.50 | 0.035 | 0.010 | 0.30 to 0.50 | 26.0 to 29.0 | ≤1.00 | 4.0 to 5.0 | 5.5 to 9.5 | Co 0.50 to 2.00 |
| X2CrNiCuN23-4 | 1.4655 | S32304 | 0.03 | ≤1.00 | ≤2.00 | 0.035 | 0.015 | 0.05 to 0.20 | 22.0 to 24.0 | 1.00 to 3.00 | 0.10 to 0.60 | 3.5 to 5.5 | - |
Properties of Super Duplex Stainless Steel
Corrosion Resistance
Super Duplex Stainless Steel is renowned for its exceptional resistance to uniform corrosion, particularly in chloride-rich environments such as seawater. This makes Super Duplex Stainless Steel a preferred material for offshore platforms, subsea pipelines, and marine applications. Its high resistance to pitting and crevice corrosion is especially valuable in the oil and gas industry, where exposure to aggressive chemicals and saline environments is common. The material's ability to withstand these conditions ensures long-term reliability and reduces maintenance costs.
Mechanical Properities of Super Duplex Stainless Steel (SDSS)
One of the standout features of Super Duplex Stainless Steel (SDSS) is its mechanical strength. It boasts twice the yield strength of standard austenitic stainless steels like 304 and 316. This high strength allows for the design of thinner-walled components, reducing weight and material costs without compromising performance. Additionally, its high tensile strength makes it suitable for high-pressure applications, ensuring structural integrity under extreme conditions.
Mechanical properties of duplex stainless steels from European Standard EN 10088-3 (2014)[9] (for product thickness below 160 mm) Mechanical properties at room temperature of solution-annealed austenitic–ferritic stainless steels
| ISO Designation | EN Number | 0.2% Proof Stress, Min. | Ultimate Tensile Strength | Elongation, Min. (%) |
|---|---|---|---|---|
| X2CrNiN23-4 | 1.4362 | 400 MPa (58 ksi) | 600 to 830 MPa (87 to 120 ksi) | 25 |
| X2CrNiMoN22-5-3 | 1.4462 | 450 MPa (65 ksi) | 650 to 880 MPa (94 to 128 ksi) | 25 |
| X3CrNiMoN27-5-2 | 1.4460 | 450 MPa (65 ksi) | 620 to 680 MPa (90 to 99 ksi) | 20 |
| X2CrNiN22-2 | 1.4062 | 380 MPa (55 ksi) | 650 to 900 MPa (94 to 131 ksi) | 30 |
| X2CrCuNiN23-2-2 | 1.4669 | 400 MPa (58 ksi) | 650 to 900 MPa (94 to 131 ksi) | 25 |
| X2CrNiMoSi18-5-3 | 1.4424 | 400 MPa (58 ksi) | 680 to 900 MPa (99 to 131 ksi) | 25 |
| X2CrMnNiN21-5-1 | 1.4162 | 400 MPa (58 ksi) | 650 to 900 MPa (94 to 131 ksi) | 25 |
| X2CrMnNiN21-5-3 | 1.4482 | 400 MPa (58 ksi) | 650 to 900 MPa (94 to 131 ksi) | 25 |
| X2CrNiMnMoCuN24-4-3-2 | 1.4662 | 450 MPa (65 ksi) | 650 to 900 MPa (94 to 131 ksi) | 25 |
| X2CrNiMoCuN25-6-3 | 1.4507 | 500 MPa (73 ksi) | 700 to 900 MPa (100 to 130 ksi) | 25 |
| X2CrNiMoCuWN25-7-4 | 1.4410 | 530 MPa (77 ksi) | 730 to 930 MPa (106 to 135 ksi) | 25 |
| X2CrNiMoN29-7-2 | 1.4477 | 550 MPa (80 ksi) | 750 to 1,000 MPa (109 to 145 ksi) | 25 |
| X2CrNiMoCoN28-8-5-1* | 1.4658 | 650 MPa (94 ksi) | 800 to 1,000 MPa (120 to 150 ksi) | 25 |
Stress Corrosion Cracking Resistance of Super Duplex Stainless Steel
Super Duplex Stainless Steel is highly resistant to stress corrosion cracking (SCC), a common failure mode in stainless steels exposed to tensile stress and corrosive environments. This resistance is crucial for long-term reliability in oil and gas operations, where components are often subjected to high stresses and harsh conditions.
Weldability of Super Duplex Stainless Steel (SDSS)
While Super Duplex Stainless Steel (SDSS) is more challenging to weld than austenitic stainless steels, it can still be welded using appropriate procedures. The key is to maintain a balanced microstructure and avoid excessive heat input, which could lead to the formation of brittle phases. Proper welding techniques, such as using low heat input and post-weld heat treatment, are essential to ensure the integrity of Super Duplex Stainless Steel welded joints.
Comparison Between Duplex and Super Duplex Stainless Steel (SDSS)
While both duplex and Super Duplex Stainless Steels share a dual-phase structure, Super Duplex (SDSS) offers enhanced performance due to its higher alloy content. Key differences include:
- Strength: Super Duplex (SDSS) provides greater yield and tensile strength, making it suitable for more demanding applications.
- Corrosion Resistance: Super Duplex (SDSS) grades have enhanced resistance to pitting and crevice corrosion, making them ideal for aggressive environments like offshore oil and gas extraction.
- Cost: Although Super Duplex Stainless Steel (SDSS) is more expensive initially, its long-term durability and reduced maintenance costs often justify the investment.
These advantages make Super Duplex Stainless Steel (SDSS) the material of choice for critical applications in the oil and gas industry.
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Key Alloys and Specifications of Super Duplex Stainless Steel (SDSS)
Super Duplex Stainless Steel (SDSS) is available in several key alloys, each with specific properties and applications:
- UNS S32205 (Duplex 2205): Offers a balance of strength and corrosion resistance, commonly used in oil and gas pipelines, pressure vessels, and marine structures.
- UNS S32750 (Super Duplex 2507): Provides higher corrosion resistance and strength, ideal for desalination plants, chemical processing, and offshore platforms.
- UNS S32760 (Super Duplex Zeron 100): Known for its exceptional resistance to corrosion and high mechanical strength, used in highly corrosive environments.
These alloys are covered under ASTM specifications for plate, sheet, and bar products, ensuring consistent quality and performance.
Applications of Duplex and Super Duplex Stainless Steel (SDSS)
Practical Uses of Super Duplex Stainless Steel (SDSS)
Super Duplex Stainless Steel (SDSS) is widely used in industries that demand high strength, durability, and corrosion resistance. Key applications include:
- Duplex and Super Duplex Stainless Steel (SDSS) in Oil and Gas: Used in subsea and offshore platforms, pipelines, pumps, and valves due to its resistance to seawater corrosion and high mechanical strength.
- Duplex and Super Duplex Stainless Steel (SDSS) in Water Treatment: Ideal for desalination plants and water transport systems, where resistance to chloride-induced corrosion is critical.
- Duplex and Super Duplex Stainless Steel (SDSS) in Food and Beverage Processing: Used in mixers, tanks, and piping due to its hygiene standards and ease of cleaning.
- Duplex and Super Duplex Stainless Steel (SDSS) in Power Generation: Employed in valves, turbine components, and cooling systems for its ability to withstand high temperatures and corrosive media.
- Duplex and Super Duplex Stainless Steel (SDSS) in Medical Equipment: Used in imaging components and other devices requiring high strength, biocompatibility, and resistance to stress corrosion.
Applications of Duplex and Super Duplex Stainless Steel (SDSS) in the Oil and Gas Industry
Duplex and Super Duplex Stainless Steel (SDSS) in Offshore and Subsea Pipelines
Super Duplex Stainless Steel is commonly used in offshore and subsea pipelines due to its excellent resistance to seawater corrosion and high mechanical strength. It ensures the integrity of pipelines transporting oil and gas from offshore platforms to onshore facilities.
Duplex and Super Duplex Stainless Steel (SDSS) in Heat Exchangers
In oil refineries and petrochemical plants, heat exchangers are exposed to high temperatures and aggressive chemicals. Super Duplex Stainless Steel (SDSS) provides the necessary corrosion resistance and mechanical strength to ensure long-term performance.
Duplex and Super Duplex Stainless Steel (SDSS) in Pressure Vessels
Pressure vessels used in the oil and gas industry must withstand high pressures and corrosive fluids. Super Duplex Stainless Steel’s high yield strength and resistance to SCC make it an ideal material for these critical components.
Duplex and Super Duplex Stainless Steel (SDSS) in Valves and Pumps
Super Duplex Stainless Steel (SDSS) is often used in the manufacture of valves and pumps that operate in corrosive environments. Its durability and resistance to corrosion ensure reliable operation and reduced maintenance costs.
Duplex and Super Duplex Stainless Steel (SDSS) in Desalination Plants
Super Duplex Stainless Steel (SDSS) is also employed in desalination plants, where seawater is processed to produce fresh water. The material’s resistance to pitting and crevice corrosion ensures long-lasting performance in these highly corrosive conditions.
Challenges and Considerations with Super Duplex Stainless Steel (SDSS)
Cost of Duplex and Super Duplex Stainless Steel (SDSS)
The cost of Super Duplex Stainless Steel (SDSS) is higher than standard stainless steels due to its alloying elements and complex manufacturing process. However, the material’s long-term performance and reduced maintenance costs often justify the initial investment.
Weldability of Duplex and Super Duplex Stainless Steel (SDSS)
Welding Super Duplex Stainless Steel (SDSS) requires careful control of heat input and post-weld heat treatment to avoid the formation of brittle phases. Proper welding techniques and qualified welders are essential to ensure the integrity of welded joints.
Availability of Duplex and Super Duplex Stainless Steel (SDSS)
Super Duplex Stainless Steel (SDSS) may not be as readily available as standard stainless steel, which could lead to longer lead times for projects. It’s essential to plan accordingly and work with reliable suppliers.
475°C Embrittlement
Super Duplex Stainless Steel (SDSS) is susceptible to 475°C embrittlement, a phenomenon caused by the formation of alpha prime (α′) phases at temperatures between 300°C and 475°C. This limits its maximum service temperature and reduces its range of applications.
Stress Corrosion Cracking (SCC) of Duplex and Super Duplex Stainless Steel
While Super Duplex Stainless Steel (SDSS) is highly resistant to SCC, certain conditions such as high tensile stress, corrosive environments, and elevated temperatures can still pose risks. Proper material selection and design are essential to mitigate these risks.