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Alloy 718 Double End Stud
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Name: Alloy 718 Double End Stud
Standard: ASME
Material: Inconel 718
Size: 3/4 inch
Lenght: 150 mm
Temperature: -250 to 700℃
Surface: Natural color
Standard: ASME
Material: Inconel 718
Size: 3/4 inch
Lenght: 150 mm
Temperature: -250 to 700℃
Surface: Natural color
Quantity
Alloy 718 Double End Stud is manufactured from nickel-based superalloy Inconel 718, complies with ASME standards, and is supplied as a 3/4-inch diameter × 150 mm double-ended stud. It retains full strength and toughness from –250 °C to 700 °C, is supplied in the plain, as-treated condition without coating, possesses clean grain boundaries, resists creep and fatigue, and is purpose-built for LNG, nuclear power, ultra-super-critical steam turbines and aerospace high-pressure reactors—install once, maintenance-free for life.
How do Inconel 718 fasteners differ from ordinary stainless fasteners such as 304 or 316?
The fundamental distinction is their “material DNA”: Inconel 718 is a nickel-base, precipitation-hardening superalloy, whereas 304/316 are iron-base austenitic stainless steels. This single difference drives a complete spectrum of contrasts, illustrated below with typical application examples for quick selection.
The fundamental distinction is their “material DNA”: Inconel 718 is a nickel-base, precipitation-hardening superalloy, whereas 304/316 are iron-base austenitic stainless steels. This single difference drives a complete spectrum of contrasts, illustrated below with typical application examples for quick selection.
1. Chemistry & microstructure
- Inconel 718: Ni 50–55 %, Cr 17–21 %, Nb 4.75–5.5 %, Mo 2.8–3.3 %, strengthened by γ″ (Ni₃Nb); after ageing Alloy 718 Double End Stud tensile strength ≥ 1 250 MPa.
- Inconel 718: Ni 50–55 %, Cr 17–21 %, Nb 4.75–5.5 %, Mo 2.8–3.3 %, strengthened by γ″ (Ni₃Nb); after ageing Alloy 718 Double End Stud tensile strength ≥ 1 250 MPa.
- 304/316: Fe ≈ 65 %, Cr ≈ 18 % (plus 2–3 % Mo in 316), single-phase austenite; cold-worked maximum ≈ 700 MPa, no precipitation hardening.
2. Temperature–mechanical window (same M12 diameter)
| Temperature | Alloy 718 Double End Stud | 316L | Notes |
| 25 °C | 1 250 MPa | 620 MPa | 2× strength |
| 650 °C | 1 000 MPa | 280 MPa | 316 already creeping |
| –196 °C | 1 550 MPa | 850 MPa | no embrittlement |
Example: LNG tank roof bolts at –162 °C. 316L would require three diameters larger; Alloy 718 Double End Stud allows direct M12 choice, saving 60 % weight and installation space.
3. Corrosion resistance
Pitting resistance equivalent PREN = %Cr + 3.3×%Mo + 16×%N: 316L ≈ 26, Alloy 718 ≈ 45. High Ni also raises chloride stress-corrosion-cracking (SCC) threshold by two orders of magnitude.
Pitting resistance equivalent PREN = %Cr + 3.3×%Mo + 16×%N: 316L ≈ 26, Alloy 718 ≈ 45. High Ni also raises chloride stress-corrosion-cracking (SCC) threshold by two orders of magnitude.
NACE MR0175 approves Alloy 718 Double End Stud for ≥ 3 bar H₂S partial pressure up to 200 °C; 316L is limited to < 0.1 bar at low temperature.
Example: sub-sea Christmas tree, 180 °C, 150 000 ppm Cl⁻, 2 bar H₂S. 316L showed SCC cracks within six months; Alloy 718 Double End Stud has operated for ten years without failure.
4. High-temperature creep & fatigue
At 650 °C and 500 MPa Alloy 718 Double End Stud residual elongation < 0.2 % after 10 000 h; 316 fractures in < 1 000 h.
Example: petrochemical reformer manway flange, 580 °C, 3 MPa, cyclic start-ups. 316 studs required hot re-torquing every six months; after upgrading to Alloy 718 Double End Stud the unit has run five years without shutdown, saving about 1.2 million ¥/year in maintenance.
At 650 °C and 500 MPa Alloy 718 Double End Stud residual elongation < 0.2 % after 10 000 h; 316 fractures in < 1 000 h.
Example: petrochemical reformer manway flange, 580 °C, 3 MPa, cyclic start-ups. 316 studs required hot re-torquing every six months; after upgrading to Alloy 718 Double End Stud the unit has run five years without shutdown, saving about 1.2 million ¥/year in maintenance.
5. Machinability & cost
Alloy 718 Double End Stud work-hardens three times faster than 316 and must be machined with carbide tools at low speed/high feed. Welding heat input must be ≤ 0.8 kJ/mm to avoid strain-age cracking. Material price is 5–6× that of 316, but life-cycle cost on critical plant is lower.
Alloy 718 Double End Stud work-hardens three times faster than 316 and must be machined with carbide tools at low speed/high feed. Welding heat input must be ≤ 0.8 kJ/mm to avoid strain-age cracking. Material price is 5–6× that of 316, but life-cycle cost on critical plant is lower.
6. Quick-selection table
| Application | Recommended alloy | Reason |
| Domestic water-heater flange | 304 | Ambient, low cost |
| Food/pharma fasteners | 316L | Steam, weak acids, GMP compliant |
| Aero-engine turbine case | Alloy 718 | 1 GPa at 700 °C |
| Liquid-H₂ rocket tank strut | Alloy 718 | No embrittlement at –253 °C, 10⁶-cycle fatigue |
| Offshore wind-tower bolt | 316L | Ambient humidity, cost-driven |
| Offshore wellhead | Alloy 718 Double End Stud | High Cl⁻ + H₂S, SCC risk |
Conclusion
Whenever two of the three factors “extreme temperature / high load / strong corrosion” are present, Alloy 718 Double End Stud should be the first choice; for mild duties and cost-sensitive projects, 304/316 is adequate.
Whenever two of the three factors “extreme temperature / high load / strong corrosion” are present, Alloy 718 Double End Stud should be the first choice; for mild duties and cost-sensitive projects, 304/316 is adequate.
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