Overview

Incoloy represents a family of nickel-iron-chromium superalloys developed by Special Metals Corporation, offering a cost-effective balance of high-temperature strength and corrosion resistance. Unlike nickel-chromium alloys (Inconel) that prioritize extreme heat performance, or nickel-copper alloys (Monel) that excel in marine environments, Incoloy alloys are engineered with higher iron content (typically >22%) to provide an economical solution for moderate-to-high temperature applications while maintaining excellent resistance to oxidation, carburization, and stress corrosion cracking .

These austenitic superalloys maintain structural stability during prolonged high-temperature exposure, making them the preferred choice for heat exchangers, process piping, and chemical processing equipment where both corrosion resistance and fabrication economics matter . Available in plate, sheet, strip, and other forms, Incoloy alloys bridge the performance gap between stainless steels and more expensive nickel-based superalloys.

Key Features

• Balanced Composition for Versatility: With nickel content ranging from 30-46% and chromium from 19-23%, Incoloy alloys combine the best attributes of stainless steel affordability with nickel alloy performance. The high iron content (22% minimum in grades like 825) reduces material costs while maintaining corrosion resistance .

• Superior High-Temperature Stability: Incoloy alloys maintain a stable austenitic microstructure during prolonged exposure to elevated temperatures. Grades like 800HT offer excellent resistance to oxidation and carburization up to 980°C, with minimal sigma phase embrittlement .

• Exceptional Resistance to Aqueous Corrosion: Specifically formulated to resist stress corrosion cracking (SCC) in chloride-containing environments. The addition of molybdenum and copper in grades like 825 provides outstanding protection against reducing acids including sulfuric and phosphoric acid .

• Excellent Fabricability: Higher iron content translates to better formability and weldability compared to high-nickel alternatives. Incoloy plates can be readily welded using conventional methods with matching filler metals, and require less complex post-weld heat treatment procedures .

• Cost-Effective Performance: Positioned as the most economical option among nickel-based superalloys, Incoloy delivers reliable performance in applications that don't require the extreme temperature capabilities of Inconel or the acid resistance of Hastelloy .

Specifications with Explanation

Incoloy Alloy Plate Chemical Composition Comparison (Typical values, wt%)

Mechanical Property Guarantees (Typical Room Temperature Minimums)

Physical Properties

Applications

Incoloy alloys serve critical functions across multiple industries where moderate-to-high temperatures combine with corrosive environments:

Chemical Processing Industry

• Heat Exchangers and Condensers: Ideal for sulfuric and phosphoric acid service where stainless steels fail but Hastelloy would be over-specified

• Reactor Vessels and Piping Systems: For processing aggressive chemicals at temperatures up to 540°C, particularly in nitric acid and organic acid environments

• Pickling Equipment: Tanks and components for steel pickling operations using sulfuric and hydrochloric acids

Power Generation and Nuclear

• Steam Generators: Nuclear power plant steam generator tubing, where resistance to stress corrosion cracking and high-purity water corrosion is essential

• Superheater and Reheater Tubing: Fossil fuel power plant components operating in high-temperature combustion environments

• Flue Gas Desulfurization (FGD) Systems: Scrubbers and ductwork requiring resistance to sulfuric acid condensate

Petroleum and Oil & Gas

• Sour Gas Service: Incoloy 925 and 945X are specifically engineered for OCTG (Oil Country Tubular Goods), subsurface safety valves, and completion equipment in hydrogen sulfide environments, meeting NACE MR0175/ISO-15156 requirements

• High-Strength Piping Systems: Components requiring both corrosion resistance and mechanical strength in downhole applications

• Wellhead Components: Valves, hangers, and packers for extreme pressure environments

Industrial Heating and Heat Treating

• Furnace Components: Muffles, retorts, radiant tubes, and conveyor belts operating up to 1148°C

• Heat Treating Baskets and Fixtures: Excellent resistance to thermal shock and carburizing atmospheres

• Annealing Covers and Inner Covers: For batch annealing operations in steel mills

Marine and Desalination

• Seawater Heat Exchangers: Resistance to chloride pitting and crevice corrosion

• Desalination Plant Components: Evaporators and heat recovery systems handling brine solutions

Comparison: Grade Selection Guide

Buying Guide

Selecting the right Incoloy alloy plate requires careful evaluation of operating conditions and economic factors:

1. Define Operating Temperature Range:

   • For continuous service above 540°C, select 800H/HT over 825 (825's properties optimize below 540°C)

   • For cyclic thermal applications, Incoloy 330 offers superior thermal shock resistance

2. Identify Corrosive Media:

   • Reducing acids (H₂SO₄, H₃PO₄) : Incoloy 825 with molybdenum and copper additions

   • Oxidizing environments: Standard 800 series with high chromium content

   • Chloride-containing solutions: All Incoloy grades offer good SCC resistance, with 825 providing the best pitting resistance

3. Determine Mechanical Requirements:

   • For standard pressure vessel applications, solution-annealed 800/825 (220-310 MPa yield)

   • For high-strength components requiring 140 ksi+ yield, age-hardenable 925 or 945X

4. Verify Specifications and Standards:

   • ASTM/ASME Standards:

     • Incoloy 800/800H/800HT: ASTM B409 / ASME SB-409 (plate)

     • Incoloy 825: ASTM B424 / ASME SB-424

     • Incoloy 330: ASTM B536 / ASME SB-536

   • NACE Compliance: For sour service, verify MR0175/ISO-15156 certification

5. Consider Fabrication Requirements:

   • Incoloy alloys generally offer better machinability and formability than Inconel or Hastelloy

   • Specify solution-annealed condition for optimal forming and corrosion resistance

   • For welded construction, request ERNiCrMo-3 or matching filler metal recommendations

FAQ

Q1: What is the difference between Incoloy and Inconel?
A: The primary difference lies in nickel and iron content. Incoloy contains 30-46% nickel with high iron (22%+), while Inconel contains 58%+ nickel with lower iron. This makes Incoloy more cost-effective and easier to fabricate, but with lower high-temperature strength limits. Inconel excels above 980°C, while Incoloy is optimal for applications up to 980°C (800 series) or 540°C (825) .

Q2: Can Incoloy 825 replace stainless steel in acid service?
A: Yes, and it's often the logical upgrade path. Where 316L stainless steel fails in sulfuric or phosphoric acid environments due to general corrosion or pitting, Incoloy 825 typically provides 5-10x longer service life. It's particularly effective in the 10-40% sulfuric acid concentration range at moderate temperatures .

Q3: Does Incoloy require special welding procedures?
A: Incoloy alloys are considered more weldable than high-nickel alloys. Standard techniques like GTAW (TIG), GMAW (MIG), and SMAW work well with proper procedures. Use low heat input, clean surfaces thoroughly, and select matching filler metals (ERNiCrMo-3 for 825, ERNiCr-3 for 800 series). Post-weld heat treatment is typically not required for corrosion service, though stress relief may be beneficial for complex geometries .

Q4: What is the maximum service temperature for Incoloy 825?
A: Incoloy 825 is generally rated for continuous service up to 540°C (1004°F). Above this temperature, mechanical properties may degrade, and the alloy's optimized corrosion resistance for acidic environments is less relevant. For higher temperatures, consider Incoloy 800H/HT which performs well up to 980°C .

Q5: Is Incoloy magnetic?
A: In the solution-annealed condition, Incoloy alloys are essentially non-magnetic due to their austenitic structure. However, significant cold working may induce some magnetic response. This makes them suitable for applications requiring non-magnetic properties, such as instrument components .

Q6: How does Incoloy 925 achieve its high strength?
A: Unlike other Incoloy grades that are solid-solution strengthened, Incoloy 925 is precipitation-hardenable. Additions of aluminum, titanium, and niobium form strengthening precipitates (γ' and γ") during controlled aging heat treatment (typically 1350°F/732°C for 6-8 hours). This achieves yield strengths up to 160 ksi while maintaining corrosion resistance .

Delivery, Certification & Service

Quality Certification

• Material Traceability: Full heat traceability from melt to finished plate, with unique identification markings on each plate

• Mill Test Certificates (MTC) : EN 10204 3.1/3.2 compliant certificates provided with every shipment, including:

  • Heat number and chemical composition analysis

  • Full mechanical property test results (tensile, yield, elongation)

  • Grain size determination (for 800H/HT)

  • Corrosion test results where specified

• Third-Party Inspection: Available through Lloyds, DNV, Bureau Veritas, or customer-nominated agencies

Available Product Forms and Dimensions

Surface Finishes Available

• Hot-rolled and pickled (HRAP)

• Hot-rolled annealed and pickled

• Cold-rolled bright annealed

• Ground and polished (various grits)

• Plasma-cut or sheared edges

Packaging and Protection

• Interleaving: Paper or plastic interleaving between plates to prevent surface scratching

• Bundling: Steel-strapped bundles with edge protectors for smaller plates

• Crating: Export-grade wooden crates for high-value or precision-cut plates

• Waterproofing: Waterproof paper and vapor-phase corrosion inhibitors for marine shipment

After-Sales Technical Support

• Fabrication Assistance: Technical guidance on forming parameters, welding procedures, and heat treatment cycles

• Failure Analysis: Support for investigating in-service material performance issues

• Material Selection Consulting: Assistance with grade selection for new applications or environments

• Inventory Management: Consignment stocking and just-in-time delivery programs available

Delivery Commitment

• Stock Items: 1-2 weeks for standard sizes

• Mill Orders: 8-12 weeks for non-standard dimensions or special certifications

• Express Service: Rush processing available for emergency requirements