API 6A CRA Alloy 718 Forging Rings Inconel 718 Customized Forgings
for Critical Oil & Gas Applications
API 6A CRA Alloy 718 forging rings—crafted from Inconel 718 (UNS
N07718), a nickel-chromium superalloy—represent the pinnacle of
engineered components for harsh oil and gas environments. Designed
to meet the stringent requirements of API Specification 6A (which
governs wellhead and Christmas tree equipment), these
corrosion-resistant alloy (CRA) forgings deliver unmatched
strength, durability, and resistance to extreme conditions. Below
is a detailed breakdown of their specifications, customization
capabilities, and performance attributes.
API 6A sets rigorous standards for equipment used in oil and gas
wellheads, including pressure ratings, material integrity, and
corrosion resistance. As a CRA (Corrosion-Resistant Alloy), Inconel 718 is specifically selected for API 6A applications due
to its ability to withstand corrosive downhole
environments—including exposure to H₂S (sour gas), CO₂, and
brines—where carbon steels or lower-grade alloys would fail.
These forging rings are manufactured to meet API 6A’s material
traceability requirements, with full documentation of heat
treatment, chemical composition, and mechanical testing to ensure
compliance with pressure ratings (up to 15,000 psi) and temperature
ranges (-29°C to 121°C, or as specified for extreme service).
Inconel 718’s exceptional performance stems from its unique
chemical composition and microstructure, optimized for high
strength and corrosion resistance:
- Chemical Composition: Dominated by nickel (50-55%), chromium (17-21%), and iron
(balance), with key alloying elements including niobium
(4.75-5.5%), molybdenum (2.8-3.3%), titanium (0.65-1.15%), and
aluminum (0.2-0.8%). These elements form strengthening
intermetallic phases (γ’ and γ”) during heat treatment, enabling
the alloy to retain strength at temperatures up to 650°C (1200°F).
- Mechanical Strength: Tensile strength exceeding 1300 MPa (188,500 psi) and yield
strength over 1000 MPa (145,000 psi) when heat-treated, making it
ideal for high-pressure API 6A components.
- Corrosion Resistance: Resistant to pitting, crevice corrosion, and stress corrosion
cracking in aggressive media, including sour environments (NACE
MR0175/ISO 15156 compliance for H₂S service).
- Fabricability: Despite its high strength, Inconel 718 can be hot-forged into
complex shapes (like rings) with precise dimensional control,
followed by solution annealing and aging to achieve optimal
properties.
API 6A CRA Alloy 718 forging rings are tailored to customer
specifications, with customization options including:
- Dimensions: Outer diameter (OD) ranging from small-scale (e.g., 100mm) to
large, heavy-wall rings (OD up to 2000mm+), with wall thicknesses
and inner diameters (ID) precision-machined to meet drawing
requirements.
- Forging Process: Hot die forging or open-die forging, depending on size and
complexity, to refine grain structure, eliminate porosity, and
enhance mechanical properties. The forging process ensures
directional strength, critical for withstanding cyclic loads in
wellhead operations.
- Heat Treatment: Customized cycles (solution annealing at 980-1065°C, followed by
aging at 700-730°C) to achieve the required hardness (typically
32-44 HRC) and toughness, balancing strength with ductility for API
6A’s impact resistance demands.
- Surface Finish: Options include as-forged, machined (Ra 1.6μm or better), or
coated (e.g., anti-galling treatments) to prevent seizing in mating
components like valves or flanges.
To ensure reliability in critical applications, API 6A Alloy 718
forging rings undergo rigorous quality control:
- Non-Destructive Testing (NDT): Mandatory ultrasonic testing (UT) per ASTM A388 or API 6A
requirements to detect subsurface defects; magnetic particle
inspection (MPI) for surface cracks; and liquid penetrant testing
(LPT) for tight tolerance areas.
- Mechanical Testing: Tensile, impact (Charpy V-notch), and hardness tests on each heat
lot to verify strength and toughness.
- Chemical Analysis: Spectroscopic analysis to confirm compliance with Inconel 718
composition standards (ASTM B637, AMS 5663).
- Traceability: Full documentation, including heat numbers, test reports, and
material certificates (EN 10204 Type 3.1 or 3.2), to meet API 6A’s
audit requirements.
These customized forgings are integral to API 6A wellhead systems,
including:
- Valve bodies and bonnets
- Flanges and connectors
- Choke and kill manifold components
- Wellhead adapters and spools
Their ability to perform in high-pressure, high-temperature (HPHT)
and corrosive environments makes them indispensable for safe and
efficient oil and gas production.
Chemical Composition of Alloy 718 (%)
| Grade | UNS | Density | Tensile Strength (MPa min) | Yield Strength (MPa min) | Reduction of Area min (%) | Elongation min (%) | Hardness (HRC) |
| INCONEL 718 | N07718 | 8.19 | 1275MPa min | 1034MPa min | 15% | 12% min | HRC 35-40 |
| Ni | Cr | Fe | C | Mn | S | Si |
| 50.0-55.0 | 17.0-21.0 | Remainder | 0.08max | 0.35max | 0.015max | 0.35max |
| B | P | Mo | Ti | Al | Cu | Co |
| 0.006max | 0.015max | 2.8-3.3 | 0.65-1.15 | 0.2-0.8 | 0.3max | 1.0max
|
| Material | DIN Grade | ASTM Grade | Werkstoff number |
| MONEL 400 | NiCu30Fe | N04400 | 2.436 |
| INCONEL 600 | NiCr15Fe | N06600 | 2.4816 |
| INCONEL 625 | NiCr22Mo9Nb | N06625 | 2.4856 |
| INCONEL 718 | / | N07718 | / |
| INCOLOY 800 | X5NiCrAlTi31-20 | N08800 | 1.4958 |
| INCOLOY 825 | NiCr21Mo | N08825 | 2.4858 |
| INCOLOY 028 | X1NiCrMoCuN 31 27 4 | N08028 | 1.4563 |
| HASTELLOY C276 | NiMo16Cr15W | N10276 | 2.4819 |
| F44 | X1CrNiMoCuN20-18-7 | S31254 | 1.4547 |
