Incoloy 825 (UNS N08825) – Nickel-Iron-Chromium Alloy with Titanium Stabilization for Acid and Sour Service

Short Description:

Incoloy 825 (UNS N08825 / W.Nr. 2.4858 / NS142) is a nickel-iron-chromium alloy with titanium stabilization, specifically designed for exceptional resistance to reducing and oxidizing acids. Womic Steel supplies Incoloy 825 in multiple product forms including seamless pipe, welded pipe, steel bar, steel plate, steel coil, strip, flanges, fittings, forgings, wire, springs, and valves for chemical processing, oil and gas, nuclear power generation, and marine applications.

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Product Overview

The alloy is also known by trade names Incoloy 825®, Nickelvac® 825, Nicrofer 4241®, and domestic equivalent NS142. Incoloy 825 was developed to provide superior resistance to sulfuric, phosphoric, and nitric acid environments while maintaining good mechanical properties from cryogenic temperatures up to 538°C (1000°F). The titanium addition (0.6-1.2%) provides stabilization against intergranular corrosion, making it suitable for welded construction without sensitization concerns.

Key characteristics include:

Excellent resistance to sulfuric, phosphoric, and nitric acids
Outstanding resistance to pitting and crevice corrosion (PREN ~36)
Resistance to chloride-induced stress corrosion cracking
Titanium stabilization prevents intergranular corrosion
Good mechanical properties from cryogenic to 538°C
Sour service compliant (NACE MR0175 / ISO 15156)
Excellent weldability using standard processes

Chemical Composition

Element	Content (%)	Role
Nickel (Ni)	38.0 – 46.0	Base element, provides SCC resistance
Chromium (Cr)	19.5 – 23.5	Oxidation resistance, corrosion resistance
Iron (Fe)	Balance (≥22.0)	Cost-effective base element
Molybdenum (Mo)	2.5 – 3.5	Pitting and crevice corrosion resistance
Titanium (Ti)	0.6 – 1.2	Stabilization against intergranular corrosion
Copper (Cu)	1.5 – 3.0	Resistance to sulfuric and phosphoric acids
Aluminum (Al)	≤ 0.20	Deoxidizer, minor strengthening
Carbon (C)	≤ 0.05	Controlled to avoid sensitization
Manganese (Mn)	≤ 1.00	Deoxidizer
Silicon (Si)	≤ 0.50	Deoxidizer
Sulfur (S)	≤ 0.030	Controlled for hot workability

Mechanical Properties

Room Temperature Properties (Annealed)

Property	ASTM Requirement	Typical Achieved
Tensile Strength	≥ 586 MPa (85 ksi)	586 – 724 MPa
Yield Strength (0.2% Offset)	≥ 338 MPa (49 ksi)	338 – 380 MPa
Elongation	≥ 45%	45 – 55%
Hardness	135 – 165 HRB	140 – 160 HRB
Density	8.14 g/cm³
Melting Range	1350 – 1400°C
Thermal Conductivity at 20°C	11.1 W/m·K
Coefficient of Thermal Expansion (20-100°C)	13.9 × 10⁻⁶/°C
Elastic Modulus	196 GPa
Magnetic Permeability	1.005 (non-magnetic)

Spring Temper Properties

Property	Value
Tensile Strength	≥ 1,035 MPa (150 ksi)
Operating Temperature	Up to 260°C (500°F)

Key Advantages of Incoloy 825

Superior Acid Resistance – Incoloy 825 provides outstanding resistance to sulfuric, phosphoric, and nitric acids across a wide concentration and temperature range. The combination of nickel, chromium, molybdenum, and copper creates a material that resists both reducing and oxidizing acid environments. In sulfuric acid up to 40% concentration at 100°C, the corrosion rate is less than 0.5 mm/year.

Pitting and Crevice Corrosion Resistance – The molybdenum content (2.5-3.5%) provides excellent resistance to pitting and crevice corrosion in chloride-containing environments. The PREN value of approximately 36 ensures reliable performance in seawater and chloride-rich process streams where 316L stainless steel would fail.

Stress Corrosion Cracking Resistance – The high nickel content (38-46%) provides exceptional resistance to chloride-induced stress corrosion cracking. Incoloy 825 is virtually immune to SCC in seawater, salt spray, and chloride-containing environments where 304/316 stainless steels frequently fail.

Titanium Stabilization – The titanium addition (0.6-1.2%) stabilizes the alloy against intergranular corrosion. By forming stable TiC and TiN precipitates, titanium prevents the formation of chromium carbides at grain boundaries during welding, ensuring corrosion resistance in the heat-affected zone.

Excellent Weldability – Incoloy 825 can be welded using TIG, MIG, resistance welding, and other standard processes. Matching filler metal ERNiFeCr-1 (AWS A5.14) is recommended for applications requiring identical chemistry. No preheating is generally required, and post-weld heat treatment is not necessary for most applications.

Good Mechanical Properties – The alloy maintains good mechanical properties from cryogenic temperatures down to -184°C up to 538°C (1000°F). Cold working significantly increases strength (up to 1,035 MPa tensile) while maintaining adequate ductility.

NACE MR0175 / ISO 15156 Compliance – Incoloy 825 is qualified for sour service applications in the oil and gas industry, resisting sulfide stress cracking (SSC) and hydrogen induced cracking (HIC) in H₂S-containing environments.

Available Product Forms from Womic Steel

Seamless Pipe & Seamless Tube

Outside Diameter: 6mm – 300mm
Wall Thickness: 1mm – 30mm
Length: Up to 12m
Standards: ASTM B423, ASTM B829, ASME SB-423
Applications: Heat exchanger tubes, process piping, acid handling systems
Keywords: Incoloy 825 seamless pipe, UNS N08825 tube, 2.4858 pipe, alloy 825 seamless tube

Welded Pipe

Outside Diameter: 50mm – 1200mm
Wall Thickness: 1.0mm – 25mm
Standards: ASTM B704, ASTM B705, ASME SB-704
Applications: Large-diameter process piping, heat exchanger shells
Keywords: Incoloy 825 welded pipe, alloy 825 ERW pipe

Steel Bar (Round, Square, Flat, Hex)

Diameter: 6mm – 300mm
Surface: Hot rolled, Bright (cold drawn), Ground, Turned
Standards: ASTM B425, ASME SB-425
Applications: Valve stems, fasteners, shafts, pumps, machining stock
Keywords: Incoloy 825 round bar, UNS N08825 bar stock, nickel alloy bar

Steel Plate & Sheet

Thickness: 1mm – 80mm
Width: Up to 2500mm
Standards: ASTM B424, ASME SB-424
Applications: Vessel shells, heat exchanger plates, structural components, flange blanks
Keywords: Incoloy 825 plate, alloy 825 sheet, N08825 plate

Steel Coil & Strip

Thickness: 0.5mm – 6.0mm
Width: 10mm – 1500mm
Standards: ASTM B424
Applications: Formed components, bellows, expansion joints, stampings
Keywords: Incoloy 825 coil, nickel alloy strip

Flanges & Pipe Fittings

Types: Weld Neck, Slip-On, Blind, Socket Weld, Threaded, Lap Joint
Sizes: 1/2" – 48"
Pressure Rating: Class 150 – Class 2500
Standards: ASTM B366, ASME SB-366, ASME B16.5, ASME B16.47
Fittings: Elbows, Tees, Reducers, Caps, Stub Ends, Couplings
Keywords: Incoloy 825 flanges, alloy 825 pipe fittings, UNS N08825 weld neck flange

Forgings

Types: Rings, disks, shafts, valve bodies, pump parts, custom geometries
Weight: Up to 3,000kg per piece
Standards: ASTM B564, ASME SB-564
Keywords: Incoloy 825 forging, alloy 825 ring, forged block

Incoloy 825 Valves

Types: Ball valves, Gate valves, Globe valves, Check valves, Plug valves
Sizes: 1/2" – 24"
Pressure Rating: Class 150 – Class 2500
Temperature Range: -184°C to +538°C
Design Standards: API 608, API 6D, BS 6364, ASME B16.34
Seating: Stellite hardfaced, PCTFE (cryogenic), RPTFE, PEEK
Actuation: Manual, Pneumatic, Electric
Applications: Sulfuric acid service, chemical plants, oil and gas sour service
Keywords: Incoloy 825 ball valve, alloy 825 gate valve, nickel alloy valve

Wire & Springs

Wire Diameter: 0.5mm – 12mm
Springs: Custom spring manufacturing
Standards: ASTM B425
Keywords: Incoloy 825 wire, alloy 825 springs, nickel alloy wire

Applications of Incoloy 825

Chemical Processing – Incoloy 825 is widely used in sulfuric acid, phosphoric acid, and nitric acid plants. Applications include heat exchangers, extraction columns, mixing tanks, piping systems, pumps, and valves handling corrosive acid streams. The alloy's copper content provides exceptional resistance to sulfuric acid across a wide concentration range.

Oil and Gas – Incoloy 825 is specified for sour service equipment in oil and gas production, including downhole tubing, wellhead equipment, subsea trees, flowlines, and production manifolds. Its NACE MR0175 / ISO 15156 compliance ensures reliable performance in H₂S-containing environments. The alloy is also used for chemical injection lines and offshore platform equipment.

Nuclear Power Generation – Incoloy 825 is used in nuclear fuel reprocessing plants, spent fuel storage systems, and radioactive waste treatment facilities. Its resistance to nitric acid and radiation makes it suitable for these demanding applications.

Marine Engineering – The alloy is used in seawater piping, desalination equipment, and marine platform components. Its resistance to pitting and crevice corrosion in seawater makes it suitable for offshore applications where 316L stainless steel is inadequate.

Pollution Control – Incoloy 825 is used in flue gas desulfurization (FGD) systems, waste incineration plants, and toxic waste management facilities. Its resistance to acid gases and corrosive condensate ensures long service life.

Standards & Specifications

Product Form	ASTM Standard	ASME Standard
Seamless Pipe/Tube	ASTM B423, ASTM B829	ASME SB-423, SB-829
Welded Pipe	ASTM B704, ASTM B705	ASME SB-704, SB-705
Bar/Rod	ASTM B425	ASME SB-425
Plate/Sheet/Strip	ASTM B424	ASME SB-424
Forgings	ASTM B564	ASME SB-564
Fittings	ASTM B366	ASME SB-366
UNS Designation	N08825
Werkstoff Number	2.4858
DIN Designation	NiCr21Mo
Chinese Equivalent	NS142

Frequently Asked Questions

Q: Why is Incoloy 825 the preferred material for sulfuric acid service?

A: Incoloy 825's combination of nickel, chromium, molybdenum, and copper provides outstanding resistance to sulfuric acid across a wide concentration and temperature range. The copper addition (1.5-3.0%) is particularly effective in improving corrosion resistance in reducing acid environments.

Q: What is the difference between Incoloy 825 and Inconel 625?

A: Incoloy 825 contains copper (1.5-3.0%) for superior sulfuric acid resistance and is more economical. Inconel 625 contains higher molybdenum (8-10%) and niobium for superior pitting resistance in seawater. Choose 825 for acid service; choose 625 for marine and high-chloride environments.

Q: Is Incoloy 825 suitable for sour service?

A: Yes. Incoloy 825 is qualified to NACE MR0175 / ISO 15156 for sour service applications in the oil and gas industry, resisting sulfide stress cracking and hydrogen induced cracking in H₂S-containing environments.

Q: Is Incoloy 825 readily weldable?

A: Yes. Incoloy 825 can be welded using TIG, MIG, resistance welding, and other standard processes. Matching filler metal ERNiFeCr-1 (AWS A5.14) is recommended. No preheating is generally required, and post-weld heat treatment is not necessary for most applications.

Q: What is the maximum service temperature for Incoloy 825?

A: For corrosion resistance: continuous service up to 538°C (1000°F). For spring applications: up to 260°C (500°F). The alloy maintains good mechanical properties from cryogenic temperatures (-184°C) to 538°C.

Q: What is the Chinese equivalent of Incoloy 825?

A: The Chinese equivalent grade is NS142 (耐蚀合金). It is also commonly referenced by its UNS designation N08825 and Werkstoff number 2.4858.

Q: What product forms are available for Incoloy 825?

A: Womic Steel supplies Incoloy 825 in seamless pipe, welded pipe, steel bar, steel plate, steel coil, strip, flanges, pipe fittings, forgings, wire, springs, and valves. Complete product specifications and size ranges are listed in the product availability section.

Contact Womic Steel

Website: www.womicsteel.com

E-mail: sales@womicsteel.com

Tel / WhatsApp / WeChat:

Victor: +86 15575100681

Jack: +86 18390957568

Womic Steel – Your reliable partner for Incoloy 825 (UNS N08825) seamless pipe, welded pipe, steel bar, steel plate, steel coil, flanges, fittings, forgings, springs, and valves for chemical processing, oil and gas sour service, nuclear power, and marine applications worldwide. Full traceability, classification society certification, NACE MR0175 compliance, and EN 10204 Type 3.1/3.2 documentation available.