Alloy 718
Introduction:
Nickel Alloy 718 is a precipitation hardenable nickel-chromium alloy. It combines high strength in the aged condition with good corrosion resistance and weldability.
718 NACE indicates material stocked in the heat treated condition to have high strength and meet the maximum hardness (40 Rockwell C) requirements of the NACE MR0175, MR0103, ISO 15156-3 specifications for use in oil tools used for sour service.
Features of Nickel Alloy 718
- Highly resistant to chloride and sulfide stress corrosion cracking
- High strength in the aged condition
- Good corrosion resistance
Applications of Nickel Alloy 718
- Valves
- Well head completion equipment
- Fasteners
- Blow out preventers (BOPs)
- Tubing hangers
- Mandrels
Chemical Composition of Nickel Alloy 718
| Chemistry, % | AMS 4967 | |
|---|---|---|
| Min | Max | |
| Nickel | 50.0 | 55.0 |
| Chromium | 17.00 | 21.00 |
| Molybdenum | 2.80 | 3.30 |
| Carbon | – | 0.045 |
| Columbian + Tantalum | 4.87 | 5.20 |
| Manganese | – | 0.35 |
| Silicon | – | 0.35 |
| Phosphorus | – | 0.010 |
| Sulfur | – | 0.010 |
| Copper | – | 0.230 |
| Cobalt | – | 1.00 |
| Lead | – | 10 ppm |
| Selenium | – | 5 ppm |
| Bismuth | – | 30 ppm |
| Magnesium | – | 60 ppm |
| Iron | – | remainder |
Specifications of Alloy 718
The various forms of nickel alloy 718 are covered by the following standards:
- API 6A
- API 6A718
- NACE MR0175, MR0103
- ISO 15156-3
- ASTM B 637
Heat Treatments
718 NACE is annealed between 1875-1925°F and water quenched. Subsequently it is aged in the range of 1425°-1475°F for 6-8 hours and air cooled or faster to room temperature.
Physical Properties of Nickel Alloy 718
|
Density: |
0.297 lb/inch3 |
|---|---|
|
Melting Range: |
2160 – 2449°F |
Thermal Properties of Nickel Alloy 718:-
| 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 | – | 6.4 | 29.0 |
| 200 | 7.3 | 7.2 | 28.4 |
| 400 | 7.5 | 8.2 | 27.6 |
| 600 | 7.7 | 9.3 | 26.7 |
| 1000 | 8.1 | 11.3 | 24.8 |
| 1200 | 8.4 | 12.3 | 23.7 |
Mechanical Properties of Nickel Alloy 718:-
| Property | Minimum | Maximum |
|---|---|---|
| Ultimate Tensile Strength | 150 ksi | – |
| 0.2% Yield | 125 ksi | 145 ksi |
| Elongation | 20% | – |
| Reduction of Area | 35% | – |
| Impact Strength*
Min Average/Min Single |
40/35 ft-lbs | – |
| Hardness | 32 RC | 40 RC |
Alloy 718 Avaliability
- Alloy 718 Seamless Pipe 1/4″ – 8″
- Alloy 718 Weld Pipe 1/2″ – 24″
- Alloy 718 Butt-Weld Fittings 1/2″ – 24″
- Alloy 718 Flanges 1/2″ – 24″
- Alloy 718 Pressure Fittings 1/4″ – 2″
- Alloy 718 150# Fittings 1/4″ – 2″
- Alloy 718 Tubing 1/4″ – 1″
- Alloy 718 Valves 1/2″ – 12″
- Alloy 718 Bar 1/8″ – 11″
- Alloy 718 Plate 1/8″ – 3″
Alloy 718 Specifications
ASTM B637, B 670, B 906
Alloy 718 Tensile Requirements
- Tensile Strength 135,000 psi
- Yield Strength 70,000 psi