API 6A718 stud bolt API 6ACRA Bolt and Nut ASTM B637 UNS N07718
API 6A 718 Stud Bolt | API 6ACRA Bolt & Nut
ASTM B637 UNS N07718 (Inconel 718)
High-Strength Nickel Alloy Fasteners Manufacturer
API 6A 718 stud bolts and API 6ACRA bolts & nuts manufactured from ASTM B637 UNS N07718 (Inconel 718) are premium nickel-based alloy fasteners designed for extreme pressure, high temperature, and corrosive oil & gas environments. These fasteners offer exceptional yield strength, corrosion resistance, and stress corrosion cracking resistance, making them ideal for subsea, wellhead, Christmas tree, and HPHT (High Pressure High Temperature) applications.n
What Is API 6ACRA?
API 6ACRA is the specification for corrosion-resistant alloy (CRA) bolting used in API 6A and API 17D equipment.
It defines additional requirements beyond ASTM standards, including:
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Controlled chemistry
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Heat treatment qualification
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Mechanical testing at temperature
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Enhanced traceability
API 6ACRA ensures fasteners are suitable for severe sour, chloride, and subsea environments.
Material Grade: UNS N07718 (Inconel 718)
UNS N07718 (Inconel 718) is a precipitation-hardened nickel-chromium alloy offering an exceptional combination of very high strength and outstanding corrosion resistance.
UNS N07718 Chemical Compsotion
| Element | N07718 |
| Ni | 50.0 to 55.0 |
| Cr | 17.0 to 21.0 |
| Fe a | Balance |
| Nb | — |
| Cb(Nb) + Ta | 4.87 to 5.20 |
| Mo | 2.80 to 3.30 |
| Ti | 0.80 to 1.15 |
| Al | 0.40 to 0.60 |
| C | 0.045 |
| Co | 1.00 |
| Mn | 0.35 |
| Si | 0.35 |
| P | 0.010 |
| S | 0.010 |
| B | 0.0060 |
| Cu | 0.23 |
| Pb | 0.0010 |
| Se | 0.0005 |
| Bi | 0.00005 |
| Ca b | 0.0030 |
| Mg b | 0.0060 |
| W | — |
N07718 Heat Treatment Procedures
| Heat Treatment Procedures | ||||
| UNS Number | Material Designation | Solution Annealing | Age Hardening | |
| Material Temperature | Time (hours) | Material Temperature and Time | ||
| N07718 | 120K | 1870 °F–1925 °F (1021 °C–1052 °C) | 1.0 to 2.5 | 1425 °F–1475 °F (774 °C–802 °C) for 6–8 hours |
| 140K | 1870 °F–1925 °F (1021 °C–1052 °C) | 1.0 to 2.5 | 1400 °F–1475 °F (760 °C–802 °C) for 6–8 hours | |
| 150K | 1870 °F–1925 °F (1021 °C–1052 °C) | 1.0 to 2.5 | 1292 °F–1382 °F (700 °C–750 °C) for 8 hours minimum, furnace cool to 1112 °F–1202 °F (600 °C–650 °C), and hold for 8 hours minimum | |
N07718 Tensile Requirements
| Table 6 — Tensile Requirements | |||||||
| UNS Number | Material Designation | QTC Cross-section Thickness in. (mm) | 0.2% Yield Strength Min. ksi (MPa) | 0.2% Yield Strength Max. ksi (MPa) | Tensile Strength Min. ksi (MPa) | Elongation in 4D Min. % | Reduction of Area Min. % |
| N07718 | 120K | ≤10 (254) | 120 (827) | 145 (1000) | 150 (1034) | 20 | 35 |
| >10 (254) | 120 (827) | 145 (1000) | 150 (1034) | 20 | 25 | ||
| N07718 | 140K | ≤10 (254) | 140 (965) | 150 (1034) | 165 (1138) | 20 | 35 |
| >10 (254) | 140 (965) | 150 (1034) | 165 (1138) | 20 | 25 | ||
| N07718 | 150K | ≤10 (254) | 150 (1034) | 175 (1207) | 175 (1207) | 20 | 35 |
| >10 (254) | 150 (1034) | 175 (1207) | 175 (1207) | 20 | 25 | ||
Impact Toughness Requirements
4.2.4.1 Test Location, Method, and Frequency Charpy V-notch impact testing shall be performed on all material in accordance with ASTM A370 or ASTM E23. All tests shall be performed at or below -75 °F (-60 °C) regardless of API 6A temperature classification. Rounding of test results to determine conformance to specification shall be in accordance with ASTM E29
| Table 7 — Charpy V-notch Impact Toughness Requirements (10 mm × 10 mm) | ||||||
| UNS Number | Material Designation | QTC Cross-section Thickness in. (mm) | Orientation | Minimum Average ft-lbs (J) | Minimum Single ft-lbs (J) | Minimum Lateral Expansion in. (mm) |
| N07718 | 120K | < 3 (76) | Longitudinal | 50 (68) | 45 (61) | 0.015 (0.38) |
| ≥ 3 (76) through 10 (254) | Transverse | 35 (47) | 30 (41) | 0.015 (0.38) | ||
| > 10 (254) | Transverse | 30 (41) | 27 (37) | 0.015 (0.38) | ||
| 140K | < 3 (76) | Longitudinal | 50 (68) | 45 (61) | 0.015 (0.38) | |
| ≥ 3 (76) through 10 (254) | Transverse | 35 (47) | 30 (41) | 0.015 (0.38) | ||
| > 10 (254) | Transverse | 30 (41) | 27 (37) | 0.015 (0.38) | ||
| 150K | < 3 (76) | Longitudinal | 50 (68) | 45 (61) | 0.015 (0.38) | |
| ≥ 3 (76) through 10 (254) | Transverse | 35 (47) | 30 (41) | 0.015 (0.38) | ||
| > 10 (254) | Transverse | 30 (41) | 27 (37) | 0.015 (0.38) | ||
Products Forms
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Stud Bolts (API 6A 718)
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Bolts & Nuts (API 6ACRA)
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Threads: UNC / UNF / 8UN
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Finish: Plain or coated (as specified)
Size Range
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Diameter: 1/4″ – 4″ (larger on request)
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Length: As per API 6A drawing or customer requirement
API 6A718 stud bolt API 6ACRA Bolt and Nut ASTM B637 UNS N07718
Testing & Inspection
API 6A 718 stud bolts and API 6ACRA bolts & nuts undergo rigorous testing, including:
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Chemical analysis
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Tensile and hardness testing
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Impact testing (when specified)
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NDT (PT / UT as required)
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Dimensional inspection
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Full traceability documentation
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Certification: API 6A / API 6ACRA + EN 10204 3.1 / 3.2
Typical Applications
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Subsea wellheads and Christmas trees
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Blowout preventers (BOPs)
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API 17D subsea equipment
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HPHT oil & gas wells
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Sour service (H₂S) environments
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Offshore and deepwater production systems
API 6A 718 vs ASTM A193 B7 Stud Bolts
| Item | API 6A 718 | A193 B7 |
|---|---|---|
| Material | Nickel alloy | Alloy steel |
| Strength | Very high | High |
| Corrosion Resistance | Excellent | Limited |
| Sour Service | Yes | No |
| Subsea Use | Yes | No |
API 6A 718 stud bolts and API 6ACRA bolts & nuts manufactured from ASTM B637 UNS N07718 (Inconel 718) deliver unmatched strength, corrosion resistance, and reliability for subsea, HPHT, and sour service oil & gas applications. Fully compliant with API 6A and API 6ACRA requirements, Inconel 718 fasteners are the industry-standard solution for the most demanding environments.
