Alloy 825, 2.4858, UNS N08825, Incoloy 825 - Nickel alloy

Alloy 825, 2.4858, UNS N08825, Incoloy 825 according to ASTM and DIN 17744

Alloy 825, 2.4858, UNS N08825, Incoloy 825 – description

Alloy 825 (N08825) is an alloy from The Ni-Cr-Fe-Mo family and was developed in the 1950s. It contains a nominal 42% Ni, 32% Fe, 22% Cr, 2.5% Mo, and 2% Cu, and is stabilized with 0.8% Ti, which gives it excellent resistance to sulfuric and phosphoric acids.

The alloy resists wide range of corrosive environments and intergranular sensitization. Resistant to oxidizing and reducing acids, SCC, pitting, and intergranular corrosion, it is used in chemical and petrochemical processing, oil and gas extraction, pollution control, waste processing, and pickling applications

Applications

Alloy 825 is used for phosphoric acid evaporators, pickling equipment, chemical processing vessels and piping, equipment for recovery of spent nuclear fuel, propeller shafts, tank trucks

N08825 - physical and mechanical properties

Physical properties at room temperature:

• Density: 8.14 g/cm³
• Linear expansion coefficient: 14.0 *10^-6m/(m*K)
• Thermal conductivity: 11.1 W/(m*K)
• Specific heat capacity: 440 J/(kg*K)
• Young's modulus: 195 GPa
• Electrical resistivity: 1127 μΩ*m
• Magnetic permeability: 1.005
• Curie temperature: -196 °C
• Melting temperature: 1370-1400 °C

Mechanical properties of annealed Incoloy 825 bars:

• Yield strength: 324 MPa
• Tensile strength Rm: 690 MPa
• Elongation: 45 %
• Hardness: 90 HRB

Impact energy KV of annealed Alloy 825 plates, as a function of temperature:

• Impact energy KV 20°C: 107-113 J
• Impact energy KV -79°C: 106 J
• Impact energy KV -196°C: 91-97 J
• Impact energy KV -253°C: 92 J

Tensile strength and temperature:

• In ambient temperature: 693 MPa
• 93°C: 655 MPa
• 204°C: 637 MPa
• 316°C: 632 MPa
• 371°C: 621 MPa
• 427°C: 610 MPa
• 482°C: 608 MPa
• 538°C: 592 MPa
• 593°C: 541 MPa
• 649°C: 465 MPa
• 760°C: 274 MPa
• 871°C: 135 MPa
• 982°C: 75 MPa
• 1093°C: 42 MPa

Yield strength and temperature:

• In ambient temperature: 301 MPa
• 93°C: 279 MPa
• 204°C: 245 MPa
• 316°C: 232 MPa
• 371°C: 234 MPa
• 427°C: 228 MPa
• 482°C: 221 MPa
• 538°C: 229 MPa
• 593°C: 222 MPa
• 649°C: 213 MPa
• 760°C: 183 MPa
• 871°C: 117 MPa
• 982°C: 47 MPa
• 1093°C: 23 MPa

Elongation and temperature:

• In ambient temperature: 43 %
• 538°C: 43 %
• 593°C: 38 %
• 649°C: 62 %
• 760°C: 87 %
• 871°C: 102 %

Coefficient of thermal expansion and temperature (linear):

• 24-93°C: 14.0 μm/(m*K)
• 24-205°C: 14.9 μm/(m*K)
• 24-315°C: 15.3 μm/(m*K)
• 24-425°C: 15.7 μm/(m*K)
• 24-540°C: 15.8 μm/(m*K)
• 24-650°C: 16.4 μm/(m*K)
• 24-760°C: 17.1 μm/(m*K)
• 24-870°C: 17.5 μm/(m*K)

Thermal conductivity and temperature:

• In ambient temperature: 11.1 W/(m*K)
• 93°C: 12.3 W/(m*K)
• 205°C: 14.1 W/(m*K)
• 315°C: 15.8 W/(m*K)
• 425°C: 17.3 W/(m*K)
• 540°C: 18.9 W/(m*K)
• 650°C: 20.2 W/(m*K)
• 760°C: 22.3 W/(m*K)
• 870°C: 24.8 W/(m*K)
• 980°C: 27.7 W/(m*K)

Electrical resistivity and temperature:

• In ambient temperature: 1127 μΩ*m
• 93°C: 1142 μΩ*m
• 205°C: 1180 μΩ*m
• 315°C: 1210 μΩ*m
• 425°C: 1248 μΩ*m
• 540°C: 1265 μΩ*m
• 650°C: 1267 μΩ*m
• 760°C: 1272 μΩ*m
• 870°C: 1288 μΩ*m
• 980°C: 1300 μΩ*m

Corrosion behaviour

Alloy 825 excels in seawater, as well as sulfuric and phosphoric acid applications. Because it is stabilized with Ti against sensitization, Incoloy 825 resists intergranular corrosion. High nickel content makes it resistant to chloride stress-corrosion cracking. Its molybdenum content provides resistance to pitting. Its chromium content provides resistance to oxidizing media, such as nitric acid, nitrates, and oxidizing salts. Its high iron content makes it less resistant than higher-nickel-containing alloys to alkalis and halogens.

Hydrochloric acid HCl - Alloy 825 is reasonably resistant to hydrochloric acid, but is subject to pitting and crevice corrosion, particularly in stagnant, enaerated solutions. Corrosion rates as a function of temperature:

• Acid concentration 5%; 20°C: 0.12 mm/year
• Acid concentration 10%; 20°C: 0.18 mm/year
• Acid concentration 15%; 20°C: 0.18 mm/year
• Acid concentration 5%; 40°C: 0.45 mm/year
• Acid concentration 10%; 40°C: 0.47 mm/year
• Acid concentration 20%; 40°C: 0.44 mm/year
• Acid concentration 5%; 66°C: 2.00 mm/year
• Acid concentration 10%; 66°C: 2.60 mm/year
• Acid concentration 20%; 66°C: 1.52 mm/year

Organic acids corrosion rates:

• In vapors of 85% acetic acid, 10% acetic anhydride, 5% water, plus some acetone, acetonitrile, in vapor line just before condenser; 120°C: 0.008 mm/year
• In 99.9% acetic acid, less than 0.1% water in still; 105°C: 0.006 mm/year
• In mixture of 94% acetic acid, 1% formic acid, 5% high boiling esters; 125°C: 0.02 mm/year
• In mixture of 96.5–98% acetic acid, 1.5% formic acid, 1–1.5% water; 125°C: 0.15 mm/year
• In mixture of 91.5% acetic acid, 2.5% formic acid, 6.0% water; 120°C: 0.079 mm/year
• In mixture of 95% acetic acid, 1.5–3.0% formic acid, 0.5% potassium permanganate, balance water; 130°C: 0.038 mm/year
• In mixture of 40% acetic acid, 6% propionic acid, 20% butane, 5% pentane, 8% ethyl acetate, 5% methyl ethyl ketone, plus other esters and ketones; 175°C: 0.051 mm/year
• In liquid phthalic anhydride containing phthalic acid, some water, and small amounts of maleic acid, maleic anhydride, benzoic acid, and napthaquinones. On re- flux plate of crude phthalic anhydride still; 165-260°C; 0.2 mm/year

Nitric acids mixtures corrosion rates:

• In evaporator during concentration of nitric acid solution saturated with potassium nitrate and containing chlorides:
  - liquid 40–70% HNO3 + 0.2–0.02% Cl; 110°C: 0.1 mm/year
  - vapor, 10–50% HNO3, 0.05–1.5% Cl: 0.279 mm/year
• In evaporator during concentration of nitric acid solution from 35–45% nitric acid, saturated with zirconyl nitrate and containing 10–35% ZrO(NO3)2 crystals 120°C:
  - liquid: 0.533 mm/year
  - vapor: 0.66 mm/year
• Liquid solution of 53% nitric acid containing 1% hydrofluoric acid, 80°C:
  - liquid 5.08 mm/year
  - vapor: 2.18 mm/year
• In evaporator during concentration of raffinate solution containing 30–40% nitric liquid acid and variable chlorides up to 2000 ppm Cl, 80°C:
  - liquid 0.02 mm/year
  - vapor: 0.028 mm/year

Phosphoric acid H₃PO₄ - Alloy 825 excels in phosphoric acid applications. Plant tests corrosion rates for various phosphoric acid solutions are following:

• Recycle liquor from evaporator fume scrubber containing 15% phosphoric acid, 20% hexafluorosilicic acid and 1% sulphuric acid, 80°C: 0.025 mm/year
• Slurry in digester tank. Mixture contains 20% H3PO4, 2% H2SO4, 1% HF, 40% H2O, plus CaSO4, 85°C: 0.02 mm/year
• Slurry containing 37% H3PO4 (27% P2O5) in acid transfer tank. Velocity 1 m/s, temperature 75°C: 0.02 mm/year
• Evaporator heated with hot gases in acid containing 53% H3PO4, 1–2% H2SO4, 1.5% HF plus Na2SiF6, 120°C: 0.15 mm/year
• In wet separator on top of concentrating drum in vapors from concentration of crude acid to 50–55% H3PO4 containing HF, 125°C: 0.79 mm/year

Atmospheric corrosion - Alloy 825 shows great resistance to atmospheric corrosion. Results of a 20 year exposure to atmosphere near the ocean at Kure Beach show that average weight loss is 8.7 mg/dm² and the average pit was less than 0.025 mm deep.

Sulphure Stress Cracking SSC - Alloy 825 is a bit more resistant to SSC in caustic environment than Alloy C-276.

Stress-corrosion cracking - Alloy 825, when tested in boiling 42% Magnesium Chloride solution for 192h, was etched and pitted, but showed no cracks.

Weldability

Weldability - the alloy belongs to 45th weldability group according to ISO 15608. For brazing, p-number is equal 111, according to ASME/AWS.

Selection of welding consumables for Alloy C-276

• Coated electrodes: ENiCrMo3
• Filler metals: ERNiCrMo-3

If forged pieces are supposed to be welded and operate in an environment that could cause intergranural corrosion, the pieces should be given a stabilizing anneal to prevent sensitization of the heat-affected zone.

Heat treatment and working

Recommended working and heat treatment parameters for C-276 alloy:

• Forging: 870-1175 °C
• Stabilizing anneal: 940 °C; 1h

Some reduction must be accomplished between 870 and 980 °C during final forging in order to ensure maximum corrosion resistance.

The alloy should be cooled at a rate equal to or faster than air cooling. Stabilizing anneal of 1h restores corrosion resistance.

We deliver this steel alloy as:

• Plates
• Pipes
• Bars
• Sheets

Replacements, equivalents and other designations:

Alloy 825, NS142, 02Ch21N42M3, Ni8065, NiFe30Cr21Mo3, CrNiMo21-42-3, NiCr21Mo, 2.4858, Na16, Sy825, AN2, NCF825, Sanicro 41, AL 825, Incoloy 825, DMV 825, Nickelvac 825