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UNS N08028 (Sanicro 28)

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

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Introduction

UNS N08028 (Sanicro 28) is a highly corrosion-resistant, iron-nickel-chromium-molybdenum alloy with an ultra-low carbon content, originally developed in Sweden during the 1960s. It offers excellent resistance to a wide range of aggressive environments, particularly those containing hydrogen sulfide (H₂S), chlorides, phosphoric acid, and sulfuric acid.

Available Products and Specifications

Equivalent Grade

Standard Grade
ISO 4563-080-28-I
EN Number 1.4563
EN Name X1NiCrMoCu 31-27-4
W. Nr. 1.4563
DIN X1NiCrMoCuN 31 27 4
SS 2584
AFNOR Z1NCDU31-27-03

Related Product Standards

Standard Grade
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 applications:

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

Applications

Thanks to its exceptional corrosion resistance, Sanicro 28 is a versatile alloy suited for extremely demanding environments. Below are key application areas where Sanicro 28 has demonstrated outstanding performance:

1. Phosphoric Acid Production

Sanicro 28 is the most widely used metallic material for evaporator tubes in the wet-process phosphoric acid industry. With over a decade of proven service in many units, it has replaced graphite heat exchangers, which were prone to frequent tube failures and production downtime.

2. Sulfuric Acid Service

Sanicro 28 is highly suitable for piping and heat exchangers in sulfuric acid concentrations ranging from 40–70% (deaerated) and above 85%. Its corrosion resistance in 98% H₂SO₄ is comparable to that of Alloy C, making it a cost-effective and reliable alternative in acid environments.

3. Oil and Gas Industry

Sanicro 28 is widely used in sour gas wells for:

  • Production tubing, casing, and liners.
  • Corrosive oil wells, particularly in cold-rolled, high-strength form.
  • Solution annealed piping in surface treatment facilities.
  • Wirelines for deep well tool deployment and instrument control.

Its resistance to H₂S and chlorides makes it ideal for high-pressure, high-temperature (HPHT) environments.

4. Fluoride-Bearing Media

In the phosphate fertilizer industry, Sanicro 28 performs excellently in handling fluoride-bearing off-gases and gypsum recovery systems. It surpasses even higher-alloyed CrNiMo grades in terms of long-term stability and resistance in these aggressive media.

5. Nuclear Power Plants

Due to its superior resistance to stress corrosion cracking (SCC), pitting, and crevice corrosion, Sanicro 28 is chosen for heat exchangers and critical piping systems in nuclear power facilities.

6. Seawater and Chloride-Containing Cooling Systems

Sanicro 28’s high pitting and crevice corrosion resistance makes it ideal for:

  • Seawater piping systems
  • Seawater-cooled heat exchangers
  • Chloride-bearing industrial cooling circuits

It has successfully replaced nickel alloys, Cu-Ni, bimetallic tubes, and coated carbon steel, which failed due to corrosion. The alloy also withstands shutdown periods up to one month without the need for system drainage or flushing, as long as the water temperature stays below 30°C (85°F).
Note: For even higher resistance in seawater, SAF™ 2507 duplex stainless steel may be more suitable.

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:

Property Value
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:

Element Content Range
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.
PREN Number: PREN=%Cr + 3.3 x %Mo + 16 x %N=38.55 ~ 46.85

Mechanical Properties

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

Property Value
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.

Hastelloy C22 vs C276: Key Factors You Need to Know

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Introduction

In industries such as oil and gas, chemical processing, marine engineering, and aerospace, selecting the suitable material for highly corrosive environments is critical to ensuring the longevity and safety of equipment. Hastelloy C22 and Hastelloy C276 are two widely used nickel-chromium-molybdenum alloys that resist corrosion and withstand harsh conditions. This blog will explore the Hastelloy C22 vs C276 in properties, applications, and factors to consider when choosing for your specific requirements.

Overview: Hastelloy C22 vs C276

Hastelloy C22

Engineers developed Hastelloy C22 (UNS N06022), an advanced nickel-based superalloy combining nickel, chromium, molybdenum, and tungsten. They designed it to improve corrosion resistance, especially in environments with aggressive oxidizing and reducing acids.

Hastelloy C276

Hastelloy C276 (UNS N10276) is a versatile nickel-molybdenum-chromium alloy containing tungsten, designed to resist various corrosive environments. C276 is particularly effective in extreme conditions where pitting, stress corrosion cracking (SCC), and crevice corrosion are concerns. It has been widely used for decades in industries exposed to harsh chemical conditions.

Chemical Composition: Hastelloy C22 vs C276

Element Hastelloy C22 (%) Hastelloy C276 (%)
Nickel (Ni) 55 min 57 min
Chromium (Cr) 20.0–22.5 14.5–16.5
Molybdenum (Mo) 12.5–14.5 15.0–17.0
Tungsten (W) 2.5–3.5 3.0–4.5
Iron (Fe) 2.0–6.0 4.0–7.0
Cobalt (Co) 2.5 max 2.5 max

Both alloys contain high levels of nickel, which provides resistance to chloride-induced stress corrosion cracking. C22 has higher chromium content, enhancing its resistance to oxidizing agents, while C276 has higher molybdenum and tungsten levels, improving its resistance to localized corrosion such as pitting and crevice corrosion.

Corrosion Resistance: Hastelloy C22 vs C276

Hastelloy C22 Corrosion Resistance

Hastelloy C22 offers exceptional resistance to various chemical environments, including oxidizing and reducing acids. It provides superior resistance to oxidizing agents, such as nitric acid and ferric ions, making it particularly suitable for applications in environments with such agents. Its high chromium content ensures excellent protection against:

  • Aqueous corrosion
  • Pitting and crevice corrosion
  • Stress corrosion cracking (SCC)

Hastelloy C276 Corrosion Resistance

Hastelloy C276 has long been a benchmark for corrosion-resistant alloys in the industry. Its resistance to severe environments—including wet chlorine, hypochlorite, chlorine dioxide, hydrochloric acid, sulfuric acid, and phosphoric acid—is well documented. The molybdenum and tungsten in C276 enhance its ability to withstand pitting and crevice corrosion. It also excels in reducing environments where localized attacks can be a concern, such as in:

  • Sulfuric acid
  • Hydrochloric acid
  • Hydrogen chloride gas
  • Hot contaminated media

Mechanical Properties: Hastelloy C22 vs C276

Both Hastelloy C22 and C276 exhibit strong mechanical properties, especially at high temperatures, which make them suitable for demanding applications.

Property Hastelloy C22 Hastelloy C276
Tensile Strength (MPa) 690 655
Yield Strength (MPa) 310 283
Elongation (%) 50 40
Density (g/cm³) 8.69 8.89
Melting Point (°C) 1399–1421 1370–1400

Hastelloy C22 has slightly higher tensile and yield strengths, giving it an edge in some applications where mechanical strength is critical. However, both alloys offer excellent elongation, crucial for applications involving deformation and high-pressure environments.

Applications of Hastelloy C22 vs C276

Both industries exposed to aggressive environments widely use Hastelloy C22 and C276 due to their excellent corrosion resistance and mechanical properties. Below are specific applications based on each alloy’s strengths.

Typical Applications of Hastelloy C22:

  1. Oil and Gas Industry: Equipment exposed to highly corrosive fluids, such as sour gas processing with high concentrations of hydrogen sulfide (H₂S), benefits from C22’s high resistance to corrosion.
  2. Chemical Processing: C22 is ideal for reactors, heat exchangers, and piping systems handling mixed acids or chlorine-based chemicals because it is resistant to oxidizing environments.
  3. Marine Engineering: Hastelloy C22 is used in desalination systems and offshore platforms due to its superior protection against seawater corrosion.
  4. Aerospace: C22’s combination of corrosion resistance and mechanical strength makes it valuable for components exposed to harsh atmospheric and chemical conditions.

Typical Applications of Hastelloy C276:

  1. Chemical Processing Plants: We use Hastelloy C276 in equipment that handles reducing acids such as hydrochloric acid and sulfuric acid.
  2. Pharmaceutical Industry: Pharmaceutical manufacturers commonly use it because its purity and corrosion resistance are critical to preventing contamination.
  3. Pollution Control: For flue gas desulfurization (FGD) systems, engineers often choose C276 due to its robust resistance to acidic gases and sulfur compounds.
  4. Pulp and Paper Industry: C276 performs exceptionally well in environments where bleaching chemicals, such as chlorine dioxide and sulfurous acids, can severely corrode other materials.

Main Differences: Hastelloy C22 vs C276

  • Corrosion Resistance: For environments with oxidizing media, such as chlorine and nitric acid, choose Hastelloy C22 for its superior resistance to oxidizing agents. For reducing environments, such as sulfuric acid and hydrochloric acid applications, choose Hastelloy C276.
  • Temperature Resistance: C22 and C276 offer excellent high-temperature resistance, but C276 is known for slightly better performance in extreme heat, making it more suitable for high-temperature chemical processes.
  • Mechanical Strength: If your application demands higher tensile and yield strengths, Hastelloy C22 may be a better fit. C22 also offers slightly better resistance to stress corrosion cracking.
  • Cost: Due to its newer development and slightly enhanced properties, Hastelloy C22 tends to be more expensive than C276. However, if budget constraints are a concern and C276 offers adequate performance, it may be the more economical choice.

Conclusion: Selecting the Right Alloy for Your Application

In the end, the choice between Hastelloy C22 and C276 depends on your application’s specific needs. Both alloys are exceptional in their own right, offering industry-leading corrosion resistance and mechanical strength. However, when exposed to oxidizing conditions, Hastelloy C22 is often the superior option. Conversely, for reducing environments or applications requiring high resistance to localized attack, Hastelloy C276 is the better choice.

Understanding the operational environment, specific chemical exposures, mechanical demands, and cost constraints will allow for an informed decision that maximizes your equipment’s performance, longevity, and safety.

If you have any further questions about selecting Hastelloy alloys for your industry or need assistance with material specifications, feel free to email [email protected] for expert guidance.