Duplex stainless steel is known for its high strength and excellent corrosion resistance, making it a preferred choice in industries that demand performance and durability. Among its many forms, high strength duplex square tube products stand out for their structural efficiency, reliability, and versatility in harsh environments.
This blog offers an easy-to-understand overview of the common sizes and standards associated with duplex square tubing to help buyers and engineers select the most suitable options for their applications.
What is Duplex Square Tubing?
Duplex square tubing is a hollow structural section made from duplex stainless steel. Duplex steel has a dual-phase microstructure consisting of approximately 50% austenite and 50% ferrite, offering a unique combination of strength and corrosion resistance.
These square tubes are used across various industries, including offshore oil and gas, marine, structural, and chemical processing plants. A high strength duplex square tube delivers greater mechanical strength than conventional austenitic stainless steel tubes, while also reducing weight and material costs.
Key Features of High Strength Duplex Square Tubes
Superior corrosion resistance in acidic, marine, and chloride-rich environments
High yield strength, often twice that of austenitic grades
Excellent weldability and formability
Good fatigue and impact resistance
Cost-effective due to thinner wall requirements with comparable strength
Common Sizes of Duplex Square Tubes
High strength duplex square tubes are available in a wide range of standard sizes, typically defined by their outside dimension (OD) and wall thickness (WT). Sizes can be customized based on the requirement, but some of the most common dimensions include:
| OD (mm) | Wall Thickness (mm) |
|---|---|
| 20 x 20 | 1.5 to 3.0 |
| 25 x 25 | 1.5 to 4.0 |
| 30 x 30 | 2.0 to 4.5 |
| 40 x 40 | 2.0 to 5.0 |
| 50 x 50 | 2.0 to 6.0 |
| 60 x 60 | 2.5 to 6.0 |
| 75 x 75 | 3.0 to 8.0 |
| 100 x 100 | 4.0 to 10.0 |
Larger sizes are also available based on project needs, especially in structural or offshore applications.
Industry Standards for Duplex Square Tubing
Manufacturers produce duplex square tubes in accordance with several international standards to ensure consistency, reliability, and performance.
1. ASTM Standards
ASTM A790 – Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Pipe
ASTM A928 – Standard Specification for Ferritic/Austenitic (Duplex) Stainless Steel Electric Fusion Welded Pipe
ASTM A554 – For mechanical tubing applications, particularly for decorative or light structural uses
2. ASME Standards
ASME standards mirror ASTM in many cases and are used for pressure vessel and piping applications.
3. EN Standards (European Norms)
EN 10210 / EN 10219 – For cold or hot-finished structural hollow sections
4. ISO Standards
ISO 1127 – Stainless steel tubes dimensions and tolerances
Each standard specifies tolerances, mechanical properties, testing methods, and acceptable manufacturing processes, helping ensure the high strength duplex square tube meets its intended purpose.
Material Grades Commonly Used
Some of the most commonly used duplex stainless steel grades for square tubing include:
UNS S31803 / S32205 – Known as Duplex 2205; offers excellent strength and corrosion resistance
UNS S32750 / S32760 – Super Duplex grades with higher strength and resistance, often used in aggressive environments
UNS S32101 (Lean Duplex) – More cost-effective option with decent strength and corrosion performance
Applications of Duplex Square Tubes
Thanks to their superior mechanical and corrosion-resisting properties, high strength duplex square tube products are widely used in:
Oil and gas platforms
Marine structures and shipbuilding
Desalination and water treatment plants
Architectural and structural projects
Heat exchangers and pressure vessels
Chemical and petrochemical industries
Their shape makes them ideal for applications where uniform load-bearing is important, such as frames, railings, and support structures.
Conclusion
When selecting a high strength duplex square tube, understanding the available sizes and applicable standards is crucial for ensuring safety, performance, and cost-efficiency. Whether used in offshore rigs or architectural frameworks, these tubes provide exceptional value due to their strength, durability, and resistance to harsh environments.
If you’re looking for long-lasting and reliable tubular solutions, duplex square tubes offer a smart and sustainable choice.
