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UNS N08028 (Sanicro 28)

UNS N08028 (Sanicro 28): A High-Performance Alloy for Extreme Applications

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Introduction and Overview

UNS N08028, commonly known by its trade name Sanicro 28, is an advanced nickel-chromium alloy designed to deliver outstanding resistance to a wide range of corrosive environments. This alloy is primarily used in industries that require high performance in chemically aggressive applications. Its exceptional resistance to oxidation, stress corrosion cracking, and pitting, combined with its high strength and formability, makes it an excellent material choice for various critical applications.

Sanicro 28 is especially effective in environments that contain acids, chlorides, and sulfur compounds. These properties make it ideal for industries such as oil and gas, chemical processing, marine, and power generation, where durability and resistance to corrosion are paramount.

Available Products and Specifications

Equivalent Grades

  • Common Name: Sanicro 28
  • UNS No.: N08028
  • DIN: 2.4603
  • EN: 2.4603
  • ISO: 9723
  • JIS: No direct equivalent
  • W.Nr.: 2.4603

Related Product Standards

  • ISO: ISO 9723
  • JIS: JIS G 4305, JIS G 4303
  • EN: EN 10088-3
  • ASTM: ASTM B575, ASTM B622, ASTM B829
  • ASME: ASME SB 575, ASME SB 622

Available Product Forms

UNS N08028 (Sanicro 28) is available in multiple forms suitable for a wide variety of applications:

  • Pipe & Tube: Ideal for handling aggressive chemicals and high-temperature processes.
  • Plate & Sheet: Used in structural and mechanical applications where corrosion resistance is needed.
  • Bar & Rod: Used for machining into custom components or structural parts.
  • Wire & Strip: Ideal for fabrication, electrical, and mechanical uses.
  • Forging Stock: Forged into complex shapes for heavy-duty applications.

Applications

UNS N08028 (Sanicro 28) is widely utilized in environments where conventional stainless steels and other alloys may not provide adequate protection. Its key applications include:

  • Oil and Gas: Used in piping, heat exchangers, and offshore structures exposed to chloride-rich environments and elevated temperatures.
  • Chemical Processing: Handling aggressive acids, such as phosphoric acid, sulfuric acid, and other highly corrosive substances.
  • Marine and Offshore: Piping systems, desalination plants, and other applications exposed to seawater and other corrosive marine environments.
  • Power Generation: Heat exchangers, cooling systems, and condensers, where high strength and corrosion resistance at elevated temperatures are required.
  • Food Processing and Pharmaceuticals: Used in equipment that must resist corrosion from chemicals used in cleaning and manufacturing processes.

Corrosion Resistance Properties

UNS N08028 (Sanicro 28) offers superb corrosion resistance, making it an ideal choice for applications in harsh environments. Its key corrosion-resistant properties include:

  • Pitting and Crevice Corrosion Resistance: Excellent resistance to pitting and crevice corrosion in chloride-rich environments, which is common in seawater and acidic solutions.
  • Stress Corrosion Cracking: High resistance to stress corrosion cracking (SCC), particularly in environments with chlorides and high temperatures.
  • Oxidation Resistance: Outstanding oxidation resistance, especially in high-temperature applications, where oxidation can significantly degrade other materials.

Physical and Thermal Properties

UNS N08028 (Sanicro 28) exhibits impressive physical and thermal properties, making it suitable for high-temperature and high-stress applications:

  • Density: 8.0 g/cm³
  • Melting Point: 1350–1410°C
  • Thermal Conductivity: 14.5 W/m·K
  • Specific Heat: 420 J/kg·K at 25°C
  • Modulus of Elasticity: 200 GPa

Chemical Composition

The chemical composition of UNS N08028 (Sanicro 28) is carefully controlled to provide its exceptional properties. It typically contains:

  • Nickel (Ni): 31–35%
  • Chromium (Cr): 27–32%
  • Molybdenum (Mo): 3.5–4.5%
  • Iron (Fe): Balance
  • Copper (Cu): 0.5–1.5%
  • Silicon (Si): 0.5–1.0%
  • Manganese (Mn): 1.5–2.0%
  • Carbon (C): Max 0.02%
  • Sulfur (S): Max 0.01%

This precise composition ensures exceptional resistance to corrosion, high mechanical strength, and excellent performance in various aggressive environments.

Mechanical Properties

UNS N08028 (Sanicro 28) provides outstanding mechanical properties, making it ideal for structural applications and pressure-containing components:

  • Tensile Strength: 620 MPa (min)
  • Yield Strength: 290 MPa (min)
  • Elongation: 40% (min)
  • Hardness: 240 HB (max)

These mechanical properties ensure that the alloy can perform well under both static and dynamic loading conditions.

Heat Treatment

UNS N08028 (Sanicro 28) is typically delivered in the annealed condition. The recommended heat treatment for this alloy involves heating to 1040–1100°C followed by rapid cooling, which helps to relieve any residual stresses and optimize its corrosion resistance and mechanical properties.

Forming

UNS N08028 (Sanicro 28) can be easily formed using conventional forming techniques. It exhibits good ductility and can be cold worked, bent, or drawn into various shapes. Hot working is performed at temperatures between 1100°C and 1150°C, followed by rapid cooling to maintain the desired microstructure.

Welding

Welding of UNS N08028 (Sanicro 28) is highly feasible using standard welding techniques such as TIG, MIG, and SMAW. It is essential to use a filler metal with a compatible composition to preserve the alloy’s properties and prevent defects such as cracking or reduced corrosion resistance in the weld zone.

Corrosion of Welds

While UNS N08028 (Sanicro 28) has excellent corrosion resistance, it is crucial to carefully control the welding process to avoid weld-related corrosion issues. Post-weld heat treatment or proper cleaning techniques are recommended to reduce the risk of corrosion in welded areas.

Descaling, Pickling, and Cleaning

After forming or welding, UNS N08028 (Sanicro 28) should undergo pickling or descaling to remove surface oxides and other impurities. A common method for pickling involves using a mixture of nitric acid and hydrofluoric acid, followed by thorough rinsing and neutralization. This process enhances the material’s corrosion resistance and restores its surface quality.

Surface Hardening

Surface hardening techniques, such as nitriding or shot peening, can be applied to UNS N08028 (Sanicro 28) to improve its mechanical properties. These processes enhance wear resistance and surface strength without compromising corrosion resistance, making the alloy suitable for applications with high wear and tear.

Conclusion

UNS N08028 (Sanicro 28) is a highly versatile and corrosion-resistant alloy ideal for use in demanding industries such as oil and gas, chemical processing, marine, and power generation. Its exceptional resistance to pitting, stress corrosion cracking, and oxidation, combined with high strength and excellent formability, makes it a go-to material for applications exposed to aggressive chemical environments and elevated temperatures.

By understanding the properties, applications, and processing techniques of UNS N08028 (Sanicro 28), engineers and professionals can confidently select this alloy for critical applications, ensuring long-lasting performance and reliability in some of the harshest conditions. Whether you’re working in high-corrosion environments, demanding manufacturing processes, or structural applications, UNS N08028 (Sanicro 28) provides the durability and performance needed to meet stringent requirements.