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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.

UNS N08904 904L PIPEGSM

UNS N08904 (904L): A Comprehensive Guide

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Introduction

UNS N08904, commonly referred to by its trade name 904L, is a high-performance stainless steel alloy known for its superior resistance to various corrosive environments. Unlike typical stainless steels, 904L contains higher levels of nickel, chromium, and molybdenum, which give it exceptional durability and resistance to corrosion. This makes it suitable for applications in industries such as oil and gas, chemical processing, marine environments, power generation, and pharmaceuticals.

904L is considered an austenitic stainless steel, which means it has a non-magnetic structure and excellent formability. Its high resistance to stress corrosion cracking, pitting, and crevice corrosion under extreme conditions makes it a versatile and reliable material choice for various demanding applications.

UNS N08904 (904L) Product Forms and Specifications

Equivalent Grades

Standard Grade
Common Name 904L
UNS Number N08904
DIN 1.4539
EN 1.4539
ISO 904L
JIS No direct equivalent
W. Nr. 1.4539

Related Product Standards

Standard Designation
ISO ISO 3506
JIS JIS G 4305
EN EN 10088-2
ASTM ASTM A240, ASTM A789, ASTM A790, ASTM B625, ASTM B677
ASME ASME SA240, ASME SA789, ASME SA790

Available Product Forms

UNS N08904 (904L) is available in multiple forms to cater to various industries and manufacturing processes:

  • Pipe and Tube: Suitable for high-pressure environments and chemical processing applications.
  • Plate and Sheet: Used for structural applications requiring corrosion resistance.
  • Bar and Rod: Machined into specific components for mechanical and structural purposes.
  • Wire and Strip: Often used for specialized applications such as spring manufacturing or as reinforcing materials.
  • Forging Stock: Ideal for custom shapes and complex geometries in demanding applications.
UNS N08904 (904L) Seamless Stainless Steel Pipe

UNS N08904 (904L) Seamless Stainless Steel Pipe

Applications

The superior properties of UNS N08904 (904L) make it an ideal material for several challenging applications:

  • Chemical Processing: Used in equipment such as reactors, heat exchangers, and tanks where resistance to aggressive chemicals like sulfuric acid, phosphoric acid, and acetic acid is required.
  • Oil and Gas Industry: Employed in pipelines, offshore platforms, and other equipment exposed to high levels of chloride and other corrosive substances.
  • Marine and Offshore: Excellent resistance to seawater and chloride stress corrosion makes it a go-to choice for marine piping systems, desalination plants, and offshore platforms.
  • Power Generation: Used in heat exchangers, cooling systems, and condensers where both corrosion and temperature resistance are crucial.
  • Pharmaceuticals and Food Processing: Because of its high purity and resistance to contamination, UNS N08904 (904L) is also used in pharmaceutical equipment, tanks, and pipelines in the food and beverage industries.

Corrosion Resistance Properties of UNS N08904 (904L)

One of the key advantages of UNS N08904 (904L) is its outstanding corrosion resistance. It offers the following corrosion-related benefits:

  • Pitting and Crevice Corrosion Resistance: 904L is highly resistant to pitting and crevice corrosion in chloride environments, including seawater and coastal areas.
  • Stress Corrosion Cracking (SCC): Unlike many other stainless steels, 904L excels in environments with chloride ions, preventing stress corrosion cracking in highly corrosive media.
  • Oxidation Resistance: Its high content of chromium and molybdenum provides excellent oxidation resistance at elevated temperatures, making it suitable for high-temperature applications where other stainless steels would degrade.

Physical and Thermal Properties of UNS N08904 (904L)

Understanding the physical and thermal properties of UNS N08904 (904L) is essential for determining its performance in various conditions:

Property Value
Density 8.0 g/cm³
Melting Point 1375–1400°C
Thermal Conductivity 14 W/m·K
Specific Heat (at 25°C) 500 J/kg·K
Modulus of Elasticity 200 GPa

These properties show that 904L can perform well under both thermal and mechanical stresses in harsh environments.

UNS N08904 (904L) Chemical Composition

The chemical composition of UNS N08904 (904L) is crucial in giving it its unique corrosion resistance and mechanical properties. Typical composition includes:

Element Content
Nickel (Ni) 23–28%
Chromium (Cr) 19–23%
Molybdenum (Mo) 4–5%
Iron (Fe) Balance
Copper (Cu) 1–2%
Carbon (C) Max 0.020%
Manganese (Mn) 2–2.5%
Silicon (Si) 1.00%
Sulfur (S) Max 0.005%

This alloy composition provides excellent resistance to various corrosive environments, including sulfuric acid, phosphoric acid, and chlorides.

UNS N08904 (904L) Mechanical Properties

The mechanical properties of UNS N08904 (904L) make it suitable for demanding applications where both strength and corrosion resistance are necessary:

Property Value
Tensile Strength ≥ 530 MPa
Yield Strength ≥ 240 MPa
Elongation ≥ 40%
Hardness (Brinell) ≤ 220 HB

These properties provide the necessary balance of strength and ductility, allowing the alloy to be used in both structural and pressure-containing applications.

Heat Treatment

UNS N08904 (904L) is typically used in an annealed condition, which ensures good formability and corrosion resistance. Annealing is performed by heating the material to a temperature range of 1050–1150°C and then cooling it rapidly. This treatment helps relieve internal stresses and improves the alloy’s ductility and corrosion resistance.

Forming

The alloy is easily formed using conventional techniques such as hot rolling, cold rolling, and forging. When hot working, 904L should be heated to temperatures between 1100°C and 1200°C, and rapid cooling should be applied afterward to ensure optimal performance.

Welding

Welding of UNS N08904 (904L) can be carried out using typical methods such as TIG, MIG, and SMAW. It is essential to use a compatible filler material to ensure that the welds retain the same level of corrosion resistance as the base material. Preheating is not required, but post-weld heat treatment may be recommended for thick sections to relieve stresses and enhance weld integrity.

Corrosion of Welds

While 904L exhibits excellent corrosion resistance, welding can sometimes lead to localized corrosion, such as weld decay. To mitigate this risk, proper post-weld treatment is essential. Descaling, pickling, or passivating the weld area can prevent the formation of chromium carbides and restore the material’s resistance to corrosion.

Descaling, Pickling, and Cleaning

To enhance the surface quality and corrosion resistance, UNS N08904 (904L) should undergo descaling or pickling processes. This removes oxide layers formed during manufacturing processes. Pickling typically involves using a mixture of nitric acid and hydrofluoric acid, followed by thorough rinsing and passivation to prevent future corrosion.

Surface Hardening

For specific applications requiring enhanced surface properties, surface hardening techniques such as nitriding or shot peening can be applied. These processes improve wear resistance without compromising the alloy’s corrosion resistance, making it suitable for parts exposed to high mechanical stress.

Conclusion

UNS N08904 (904L) is an ideal material for highly corrosive environments, offering exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking. Its high strength, combined with good formability, makes it suitable for a wide range of applications in industries such as chemical processing, marine, oil and gas, and pharmaceuticals.

By understanding the properties, fabrication processes, and maintenance practices associated with UNS N08904 (904L), engineers and professionals can confidently use this material in demanding environments, ensuring long-term performance and reliability in the most challenging conditions.