What Is the Difference Between INCOLOY 825 and SS316

When it comes to corrosion-resistant metals, INCOLOY 825 and SS316 stainless steel are two of the most discussed and widely used alloys in industrial applications. Both materials perform exceptionally well in aggressive environments, but they are designed for different levels of corrosion, temperature, and mechanical stress.

In this comprehensive guide, SASAALLOY explains in detail the difference between INCOLOY 825 and SS316, including their composition, mechanical properties, corrosion resistance, and key applications. Understanding these differences helps engineers and buyers make informed decisions for critical projects where material performance is essential.

1. Introduction

Selecting the right alloy is crucial for the long-term success of any engineering or industrial project. While SS316 is one of the most popular stainless steels, known for its balance of corrosion resistance and cost-effectiveness, INCOLOY 825 is a high-performance nickel-iron-chromium alloy designed for extremely corrosive environments.

At first glance, both may appear similar, but their chemical makeup and metallurgical behavior set them apart. Let us explore what makes each unique and how to choose the right one for your specific needs.

2. Overview of SS316 Stainless Steel

SS316, also known as AISI 316 or UNS S31600, is an austenitic stainless steel belonging to the 300-series family. It contains 16 to 18 percent chromium, 10 to 14 percent nickel, and 2 to 3 percent molybdenum. The molybdenum addition provides better resistance to pitting and crevice corrosion, especially in chloride environments such as seawater.

Key Features of SS316

• Excellent corrosion resistance in marine and mildly acidic environments

• Good mechanical strength and toughness

• Non-magnetic in the annealed condition

• Easily weldable and formable

• Performs well at temperatures up to 870°C

Common Variants

• SS316L (Low Carbon): Better weldability and resistance to sensitization

• SS316Ti: Stabilized with titanium for high-temperature applications

SS316 is considered the standard material for food, pharmaceutical, chemical, and marine industries because of its balance between cost and performance.

3. Overview of INCOLOY 825

INCOLOY 825 (UNS N08825) is a nickel-iron-chromium alloy with significant additions of molybdenum, copper, and titanium. It was developed specifically for use in highly corrosive environments, particularly those involving sulfuric, phosphoric, and nitric acids.

It belongs to the INCOLOY family of alloys, designed by Special Metals Corporation, known for their exceptional resistance to both oxidizing and reducing conditions.

Key Features of INCOLOY 825

• Excellent resistance to general and localized corrosion

• Outstanding resistance to sulfuric and phosphoric acids

• Exceptional performance in oxidizing and reducing environments

• Maintains strength and ductility at elevated temperatures

• Resistant to stress corrosion cracking in chloride-rich conditions

INCOLOY 825 is typically used in chemical process plants, offshore pipelines, marine equipment, and pollution control systems, where long-term corrosion resistance is critical.

4. Chemical Composition

The main difference between INCOLOY 825 and SS316 begins with their chemical composition.

• INCOLOY 825 Composition (Weight Percent):

  • Nickel (Ni): 38–46

  • Iron (Fe): 22–30

  • Chromium (Cr): 19.5–23.5

  • Molybdenum (Mo): 2.5–3.5

  • Copper (Cu): 1.5–3.0

  • Titanium (Ti): 0.6–1.2

  • Carbon (C): ≤ 0.05

  • Manganese (Mn): ≤ 1.0

  • Silicon (Si): ≤ 0.5

• SS316 Composition (Weight Percent):

  • Chromium (Cr): 16–18

  • Nickel (Ni): 10–14

  • Molybdenum (Mo): 2–3

  • Carbon (C): ≤ 0.08

  • Manganese (Mn): ≤ 2

  • Silicon (Si): ≤ 1

Key Takeaway

INCOLOY 825 has a much higher nickel content, making it more stable and corrosion-resistant in acidic and chloride conditions. The addition of copper and titanium further enhances its resistance to sulfuric acid and intergranular corrosion, while SS316 remains a cost-effective alternative for less severe conditions.

5. Mechanical Properties

Both alloys offer good mechanical performance, but INCOLOY 825 maintains its strength across a wider temperature range.

• INCOLOY 825 (Annealed Condition):

  • Tensile Strength: 690 MPa

  • Yield Strength (0.2% offset): 275 MPa

  • Elongation: 30 percent

• SS316 (Annealed Condition):

  • Tensile Strength: 515 MPa

  • Yield Strength (0.2% offset): 205 MPa

  • Elongation: 40 percent

Mechanical Difference

INCOLOY 825 has higher tensile and yield strength, making it better suited for high-pressure and high-temperature applications. SS316, however, provides greater ductility and easier formability, making it ideal for fabrications and welded structures.

6. Corrosion Resistance

6.1 SS316

SS316 performs exceptionally well in marine environments, resisting saltwater corrosion and mild acids. However, it can suffer from pitting and crevice corrosion in concentrated chloride solutions or reducing acids such as hydrochloric acid.

6.2 INCOLOY 825

INCOLOY 825 excels in strong acids, alkalis, and chloride-rich environments. It is resistant to:

• Sulfuric, phosphoric, and nitric acids

• Stress corrosion cracking caused by chlorides

• Pitting and crevice corrosion under extreme conditions

• Oxidizing and reducing acid mixtures

It also remains stable in both aerated and deaerated conditions, making it suitable for harsh offshore and chemical plant operations where stainless steels like SS316 may fail prematurely.

Summary

If the application involves acidic solutions, hydrogen sulfide, or mixed environments, INCOLOY 825 is superior. For general corrosion in mildly saline conditions, SS316 remains sufficient and economical.

7. Temperature Resistance

Both materials perform well at elevated temperatures, but their limits differ.

• SS316: Suitable up to about 870°C (1600°F) in continuous service.

• INCOLOY 825: Retains mechanical strength and corrosion resistance up to about 1000°C (1830°F).

At higher temperatures, INCOLOY 825 maintains structural stability and oxidation resistance far better than SS316, making it ideal for heat exchangers, furnace parts, and chemical reactors.

8. Weldability and Fabrication

Both INCOLOY 825 and SS316 are readily weldable, but their welding techniques differ slightly due to composition.

SS316

• Weldable by all standard processes including TIG, MIG, and SMAW.

• Requires low heat input to prevent carbide precipitation.

• Often welded with 316L filler to improve corrosion resistance.

INCOLOY 825

• Can be welded by TIG or MIG using matching filler metal (ERNiCrMo-3).

• Post-weld annealing is not generally required.

• Heat input should be controlled to preserve corrosion resistance.

Fabrication

SS316 is easier to cut, form, and polish, while INCOLOY 825 is tougher and requires more powerful equipment due to its high nickel content.

9. Applications

Common Applications of SS316

• Food and beverage processing equipment

• Marine fittings and components

• Heat exchangers and piping systems

• Pharmaceutical and chemical plants

• Architectural and decorative structures

Common Applications of INCOLOY 825

• Offshore oil and gas production systems

• Chemical and petrochemical processing equipment

• Pollution control and flue gas treatment units

• Acid production plants

• Heat exchangers and evaporators in corrosive fluids

• Nuclear fuel reprocessing systems

Summary

SS316 is ideal for general corrosion and aesthetic uses, while INCOLOY 825 is the alloy of choice for highly corrosive industrial environments where equipment longevity is critical.

10. Cost Comparison

One of the most important factors in material selection is cost.

• SS316: Economical and widely available, offering good corrosion resistance at a moderate price.

• INCOLOY 825: More expensive due to its high nickel and alloying content but delivers longer service life and lower maintenance in aggressive conditions.

When total lifecycle cost is considered, INCOLOY 825 often proves more economical for critical chemical or marine projects where corrosion failure would be costly.

11. Standards and Certifications

Both alloys comply with international standards:

• INCOLOY 825:

  • ASTM B424 (Sheet and Plate)

  • ASTM B425 (Bars and Rods)

  • ASTM B163/B423 (Tubes and Pipes)

  • NACE MR0175 / ISO 15156 for sour service

• SS316:

  • ASTM A240 (Plate and Sheet)

  • ASTM A276 (Bars and Rods)

  • ASTM A312 (Pipes and Tubes)

  • ASME SA240 / SA312 for pressure vessels

All materials supplied by SASAALLOY are delivered with complete EN 10204 3.1 or 3.2 certificates, ensuring full traceability and compliance with industry requirements.

12. Summary of Key Differences