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API 20F Corrosion Resistant Bolting
QS Fastener: API 20F Corrosion Resistant Bolting
Name: API 20F Corrosion Resistant Bolting
Dimension: M36
Length: 360mm
Type: Full Thread Stud
Standard: API 20F
Material: UNS N07718
Technical: Maximum Hardness Limits Shall Be in Accordance with ANSI/NACE MR0175
Dimension: M36
Length: 360mm
Type: Full Thread Stud
Standard: API 20F
Material: UNS N07718
Technical: Maximum Hardness Limits Shall Be in Accordance with ANSI/NACE MR0175
Quantity
API 20F Corrosion Resistant Bolting refers to fully threaded studs certified to API 20F standard, manufactured from high-performance UNS N07718 nickel-based alloy. This material delivers exceptional mechanical strength combined with superior corrosion resistance, making it ideal for petroleum, natural gas, offshore platforms and other applications involving acidic (H₂S) environments under high pressure and temperature. Its hardness strictly complies with ANSI/NACE MR0175 standards, ensuring long-term stability in hydrogen sulfide corrosive conditions.
The high strength of UNS N07718 primarily stems from the γ'' (Ni₃Nb) strengthening phase precipitated during age-hardening treatment, a characteristic that establishes it as the preferred material for API 20F Corrosion Resistant Bolting. This phase exhibits a body-centered tetragonal (D022) structure with excellent coherency to the matrix, effectively impeding dislocation movement. Compared to A286 (Fe-Ni-Cr based, with γ'-Ni₃Ti as primary strengthening phase), N07718's γ'' phase offers distinct advantages:
- Enhanced thermal stability: The γ'' phase shows negligible coarsening below 650°C, while A286's γ' phase rapidly agglomerates above 600°C - the fundamental reason API 20F Corrosion Resistant Bolting favors N07718 in high-temperature service.
- Enhanced thermal stability: The γ'' phase shows negligible coarsening below 650°C, while A286's γ' phase rapidly agglomerates above 600°C - the fundamental reason API 20F Corrosion Resistant Bolting favors N07718 in high-temperature service.
- Higher volume fraction: Aged N07718 contains 15%-20% γ'' phase versus only 8%-12% γ' phase in A286.
Mechanical properties comparison (aged condition):
| Alloy | Yield Strength (MPa) | Tensile Strength (MPa) | Yield Strength Retention at 700°C |
| N07718 | 1030 | 1240 | 75% (~775 MPa) |
| A286 | 850 | 1000 | 50% (~425 MPa) |
For API 20F Corrosion Resistant Bolting applications, N07718's temperature resistance manifests in two aspects:
1. High-temperature strength retention mechanism
- Niobium (Nb) solid solution strengthening: Nb atoms form short-range ordered structures in the nickel matrix, critical for meeting API 20F's anti-relaxation requirements at elevated temperatures.
1. High-temperature strength retention mechanism
- Niobium (Nb) solid solution strengthening: Nb atoms form short-range ordered structures in the nickel matrix, critical for meeting API 20F's anti-relaxation requirements at elevated temperatures.
- Molybdenum grain boundary strengthening: Mo segregation at grain boundaries inhibits high-temperature grain boundary sliding (N07718 exhibits 40% higher grain boundary strength than A286 at 650°C).
Experimental data (ASTM E139):
- After 1000 hours at 650°C:
- N07718's yield strength decreases merely 8% (vs. 25% for A286), ensuring outstanding long-term performance for API 20F Corrosion Resistant Bolting.
- After 1000 hours at 650°C:
- N07718's yield strength decreases merely 8% (vs. 25% for A286), ensuring outstanding long-term performance for API 20F Corrosion Resistant Bolting.
2. Creep resistance
N07718 demonstrates one order of magnitude lower creep rate than A286 at 600-700°C, crucial for high-pressure sealing applications of API 20F Corrosion Resistant Bolting:
- Slow γ'' phase coarsening: Activation energy for coarsening reaches 280 kJ/mol (vs. 180 kJ/mol for A286's γ' phase).
N07718 demonstrates one order of magnitude lower creep rate than A286 at 600-700°C, crucial for high-pressure sealing applications of API 20F Corrosion Resistant Bolting:
- Slow γ'' phase coarsening: Activation energy for coarsening reaches 280 kJ/mol (vs. 180 kJ/mol for A286's γ' phase).
- Carbide pinning: Dispersed MC-type carbides (e.g., NbC) at grain boundaries suppress boundary migration.
Typical application comparison:
- Aircraft engine bolts: CFM56 high-pressure turbine bolts employing API 20F Corrosion Resistant Bolting standard achieve 5,000 cycles at 700°C peak conditions with N07718.
- Aircraft engine bolts: CFM56 high-pressure turbine bolts employing API 20F Corrosion Resistant Bolting standard achieve 5,000 cycles at 700°C peak conditions with N07718.
- Oil drilling equipment: API 20F-compliant N07718 bolts in H₂S-containing wellhead environments at 600°C show 3× longer stress corrosion cracking life than A286.
Through γ'' phase strengthening and Nb/Mo synergistic effects, UNS N07718 has become the optimal choice for API 20F Corrosion Resistant Bolting in service above 650°C. Although prolonged use at 700°C gradually transforms γ'' to δ phase, its performance under short-term (≤100 hours) high-temperature/high-pressure conditions remains unmatched by conventional A286 material - a critical advantage.
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