
The key features of Nickel Alloy 625 include:
• Outstanding resistance to chloride pitting and crevice corrosion cracking
• Immune to chloride ion stress corrosion cracking
• Resistant to caustics
• Resistant to seawater, in both flowing and stagnant • conditions, and under fouling
Typical Applications for the Nickel Alloy 625 include:
• Chemical process equipment handling mixed acids both oxidizing and reducing
• Flue gas desulfurization scrubbers
• Evaporators for wet-process phosphoric acid containing H2SO4, HF and ferric salts
• Weld Overlay
The composition range for Nickel Alloy 625 is provided in table 1.
Table 1. Composition of nickel alloy 625.
Chemistry, % | AMS 4967 | |
Min | Max | |
Chromium | 20.00 | 23.0 |
Nickel | 58.00 | Balance |
Molybdenum | 8.00 | 10.00 |
Cobalt | - | 1.00 |
Columbium + Tantalum | 3.15 | 4.15 |
Aluminum | - | 0.40 |
Titanium | - | 0.40 |
Carbon | - | 0.10 |
Iron | - | 5.00 |
Manganese | - | 0.50 |
Silicon | - | 0.50 |
Phosphorus | - | 0.015 |
Sulfur | - | 0.015 |
The various forms of nickel alloy 625 are covered by the following standards:
• UNS/W. Nr N06625/2.4856
• Rod and bar ASTM B 446 and ASME SB-446 Gr 1
Density: | 0.305 lb/inch3 |
Melting Range: | 2350-2460°F |
The thermal properties of Nickel Alloy 625 are summarised in table 2.
Table 2. Thermal properties of Nickel Alloy 625.
Temp | Coefficient of Thermal Exp. | Thermal Conductivity | Modulus of Elasticity Dynamic |
°F | in/in °F x 10-6 | Btu. ft/ft2.hr°F | psi x 106 |
70 | - | 5.7 | 29.8 |
400 | 7.3 | 7.2 | 28.4 |
600 | 7.4 | 8.2 | 27.5 |
800 | 7.6 | 9.1 | 26.6 |
1000 | 7.8 | 10.1 | 25.6 |
1200 | 8.2 | 11.0 | 24.4 |
1400 | 8.5 | 12.0 | 23.1 |
1600 | 8.8 | 13.2 | - |
The thermal properties of Nickel Alloy 625 are summarised in table 2.
Table 2. Thermal properties of Nickel Alloy 625.
Temp | Coefficient of Thermal Exp. | Thermal Conductivity | Modulus of Elasticity Dynamic |
°F | in/in °F x 10-6 | Btu. ft/ft2.hr°F | psi x 106 |
70 | - | 5.7 | 29.8 |
400 | 7.3 | 7.2 | 28.4 |
600 | 7.4 | 8.2 | 27.5 |
800 | 7.6 | 9.1 | 26.6 |
1000 | 7.8 | 10.1 | 25.6 |
1200 | 8.2 | 11.0 | 24.4 |
1400 | 8.5 | 12.0 | 23.1 |
1600 | 8.8 | 13.2 | - |
The minimum mechanical properties of nickel alloy 625 are provided in table 3.
Table 3. Minimum Specified Tensile Properties, Room Temperature ASTM B 446 Bar, Grade 1
Property | Value |
Ultimate Tensile Strength | 120 ksi |
0.2% Yield | 60 ksi |
Elongation (2”) | 30% |
Table 4. Corrosion by quiet & flowing seawater, Wrightsbille Beach, NC.
Alloy | Quiet | Flowing, 2 ft/sec | ||||
Weight Loss, g | Range of Pit Depth, mils | Weight Loss, g | Range of Pit Depth, mils | |||
Panel | Crevice Area | Panel | Crevice Area | |||
625 | Nil | Nil | Nil | 0.25 | Nil | Nil |
C-276 | Nil | Nil | Nil | 0.10 | Nil | Nil |
René 41 | 0.80 | Nil | Nil | 0.30 | Nil | Nil |
X | 0.10 | Nil | Nil | 0.60 | Nil | Nil |
825 | 0.25 | 0-1 | 0-9 | 0.20 | 3-6 | 1-26 |
718 | 2.70 | Nil | 37-165P | 5.15 | Nil | 40-165P |
Test duration two years. P=perforated by local attack
Table 5. Crevice corrosion temperature (CCT).
Alloy | UNS No. | Molybdenum Content | °C | °F | Pitting Resistance Equivalent, (PRE)N |
316L | S31603 | 2.1 | -3 | 27 | 23 |
825 | N08825 | 2.7 | -3 | 27 | 30 |
2205 | S31803 | 3.1 | 20 | 68 | 38 |
317L | S31703 | 3.2 | 2 | 35 | 29 |
AL-6XN® | N08367 | 6.2 | 43 | 110 | 48 |
625 | N06625 | 9.0 | 45 | 113 | 51 |
C-276 | N10276 | 15.4 | 55 | 130 | 66 |
10% FeCl3.6H2O, per ASTM G 48 Practice B
(PRE) N=Cr + 3.3Mo + 16N
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