What Are Duplex Fasteners and Why Are They So Popular?

Fasteners are a vital component of industrial use, which joins components together and maintain the strength of structures. They are used in a vast array of industries ranging from automotive and construction to aerospace and marine. As industries grow and operate in more hostile environments, the demand for sophisticated materials resistant to hostile conditions, such as corrosive chemicals, high pressure and high temperatures, has increased.

Duplex fasteners which are manufactured using a stainless steel alloy called Duplex stainless steel have become extremely popular because of their outstanding mechanical and corrosion-resistant properties. With more industries looking for dependable, cost-efficient solutions for demanding environments, Duplex fasteners have become the first choice.

What Are Duplex Fasteners?

Duplex fasteners, are manufactured using Duplex stainless steel, a blend of two microstructures that are austenitic and ferritic. Duplex stainless steel normally consists of approximately equal proportions of 50% austenitic and 50% ferritic phases. This unique composition gives Duplex fasteners their distinctive properties—excellent strength and good  resistance to corrosion.

As compared to other stainless steel types, which are mainly austenitic or ferritic, Duplex fasteners are the best.The austenitic component gives them superior toughness and formability while the ferritic component provides them with greater strength and corrosion resistance. This makes Duplex fasteners suitable for use in corrosive environments and severe industrial applications.

Chemical Composition of Duplex Stainless Steel

Duplex stainless steel has several major elements that improve its performance:

• Chromium (Cr):Offers corrosion resistance, especially to rust and oxidation.
• Nickel (Ni): Increases the resistance of steel to corrosion and increases its toughness.
• Molybdenum (Mo): Enhances pitting and crevice corrosion resistance especially in chloride bearing environments.
• Nitrogen (N): Improves strength and resistance to stress corrosion cracking (SCC).

These components combine to form a robust material that can resist some of the most harsh surrounding.

Key Features of Duplex Fasteners

Duplex fasteners have several distinguishing characteristics that differentiate them from regular fasteners:

• High tensile and yield strength: Duplex fasteners are stronger than most other stainless steel types, so they are well-suited for high-pressure applications.
• Good resistance to pitting and crevice corrosion: This makes them a good choice for use in high-chloride environments, such as seawater or chemical processing.
• Resistant to SCC: Duplex fasteners are very resistant to stress cracking even in harsh environments.
• High fatigue strength: It is particularly beneficial in applications where parts experience frequent loading and unloading.
• Excellent weldability and formability: Duplex fasteners are easily welded and shaped, hence widely used in many different applications.
• Extended life in harsh conditions: Due to their high resistance to corrosion, Duplex bolts have an extended service life with minimal need for replacements.

Types of Duplex Fastener Grades

There are many grades of duplex stainless steel each offering certain advantages for certain application:

• Duplex 2205: The most widely used grade offering fairly good corrosion resistance, strength and toughness.It is suitable for use in general purpose applications.
• Super Duplex 2507: Known for its remarkable strength and superior corrosion resistance, especially in chloride-rich environments. Super Duplex is frequently used in offshore platforms and chemical processing.
• Zeron 100: Provides exceptional resistance to corrosion in highly aggressive environments, such as desalination plants and seawater applications.

Comparison of Grades:

6. Advantages Over Standard Stainless Steel Fasteners

Duplex fasteners offer several significant advantages over traditional stainless steel fasteners:

• 2x the strength of 300-series stainless steel: Duplex fasteners are much stronger than their austenitic counterparts (like 304 and 316), making them more suitable for high-stress applications.
• Reduced weight for the same strength: Due to their higher strength, Duplex fasteners can be used with a smaller size and weight, offering significant weight savings in large-scale projects.
• Lower cost than exotic alloys: Duplex fasteners are generally more affordable than high-end alloys like Inconel or Titanium, providing a cost-effective alternative for critical applications.
• No need for additional coatings: Duplex fasteners often do not require additional coatings, saving on maintenance and coating costs.

Common Applications

Duplex fasteners are widely used in various industries due to their remarkable properties:

• Offshore platforms and oil rigs: The corrosion resistance of Duplex fasteners is ideal for the harsh, saltwater-rich environments of offshore structures.
• Marine environments and shipbuilding: Their resistance to pitting and crevice corrosion makes them perfect for ship hulls and other marine structures.
• Chemical processing plants: Duplex fasteners can withstand aggressive chemicals, making them crucial for chemical reactors, pumps, and other equipment.
• Desalination and water treatment facilities: The material’s excellent resistance to chlorides makes it ideal for water treatment applications.
• Heat exchangers, tanks, and pressure vessels: Duplex fasteners ensure the integrity of pressure vessels in demanding thermal environments.
• Structural components in bridges and buildings: Their strength and durability make Duplex fasteners a reliable choice for construction in aggressive environments.

Why Are Duplex Fasteners So Popular?

Duplex fasteners have quickly gained popularity for several reasons:

• Ideal balance of strength, corrosion resistance, and cost: They provide an optimal combination of performance and affordability, making them a popular choice in industries that require both durability and cost-efficiency.
• Performance under high-pressure and high-temperature conditions: Duplex fasteners can withstand the rigors of high-stress environments, making them essential in fields like offshore oil and gas extraction.
• Lower maintenance and replacement costs: Due to their long service life and high resistance to corrosion, Duplex fasteners reduce the need for frequent replacements and maintenance.
• Compliance with global industry standards: Duplex fasteners meet international standards like ASTM, ASME, and NORSOK, ensuring that they are trusted in various industrial sectors.
• Availability in a wide range of sizes and specifications: Duplex fasteners come in numerous sizes and specifications, making them versatile for a variety of applications.

Conclusion

Duplex fasteners are unique due to their combination of high strength, excellent corrosion resistance, and cost-effectiveness. As industries increasingly demand materials that can perform in challenging environments, Duplex fasteners offer a reliable and durable solution. Their versatility, combined with their resistance to corrosion and stress, has led to widespread adoption across industries like offshore drilling, chemical processing, and construction.

For businesses and industries seeking long-lasting, robust fasteners, Duplex stainless steel offers an outstanding solution that balances performance, cost, and reliability. Choosing Duplex fasteners for your applications can significantly enhance operational efficiency while reducing maintenance costs in the long term.