For manufacturers of subsea studs, mandrels, and high-voltage connectors, lead times for heavy-duty forgings are a major pain point. Standard rolling mills typically require 12-16 weeks to produce forgings larger than 3 inches in diameter, severely hindering critical offshore oilfield development projects.
Furthermore, "commercial-grade" large-diameter bars often exhibit centerline porosity-internal voids-that only become apparent after costly machining, resulting in 100% material waste.
At Gnee Alloy, we eliminate these supply chain risks. As a dedicated Tier-1 manufacturer, we maintain a large wholesale inventory of AMS 5666 (equivalent to Inconel 625) forged bars, readily available for global shipment.
Click to get an Inconel 625 product quote
Recommended Bar Diameters for AMS 5666 Subsea Stud Bolts
Recommended Bar Diameters for AMS 5666 Subsea Stud Bolts
For submersible studs conforming to AMS 5666 (Inconel 625) standards, the recommended diameter for the round bar is typically 1/2 inch to 4 inches (12.7 mm to 101.6 mm). These diameters are chosen because the specification guarantees the highest minimum yield strength (60 ksi) when the material size reaches 4 inches.
What are the material specifications for AMS 5666?
Ni-based alloy AMS 5666 (Alloy 625) bars and forgings
Alloy 625 is a nickel-chromium-based alloy with a nickel content of at least 58%. This alloy is enhanced in stiffness by the addition of molybdenum and niobium, thus eliminating the need for aging treatment.
1. Chemical composition (by weight) of Inconel 625 submarine stud rods
| Element | AMS 5666 (UNS N06625) | Subsea Supplement (Typical Tighter Limits) | Key Difference |
|---|---|---|---|
| Nickel (Ni) | ≥ 58.0 (Balance) | Same | Same |
| Chromium (Cr) | 20.0 – 23.0 | Same | Same |
| Molybdenum (Mo) | 8.0 – 10.0 | Same | Same |
| Niobium (Nb) | 3.15 – 4.15 | Same | Same |
| Iron (Fe) | ≤ 5.0 | Same | Same |
| Titanium (Ti) | ≤ 0.40 | Same | Same |
| Aluminum (Al) | ≤ 0.40 | Same | Same |
| Carbon (C) | ≤ 0.10 (0.05 typical) | ≤ 0.05 (preferred for weldability) | Same |
| Manganese (Mn) | ≤ 0.50 | Same | Same |
| Silicon (Si) | ≤ 0.50 | Same | Same |
| Phosphorus (P) | ≤ 0.015% | ≤ 0.010% | Stricter (subsea supplement) |
| Sulfur (S) | ≤ 0.015% | ≤ 0.005% | Stricter (subsea supplement) |
| Cobalt (Co) | ≤ 1.0 | Same | Same |
| Copper (Cu) | ≤ 0.07 | ≤ 0.05 | Stricter (subsea supplement) |
2. Inconel 625 bar melting and manufacturing requirements
| Parameter | AMS 5666 (Bar Stock) | Subsea Stud Bolt Supplement |
|---|---|---|
| Melting Process | VIM + VAR (double melt – mandatory) | VIM + VAR (mandatory – no exception) |
| Alternative Melting | Not allowed | Not allowed |
| Bar Manufacturing | Hot rolled / forged – concentricity controlled | Same, with controlled reduction ratio (≥ 3:1) to ensure grain refinement |
| Heat Treatment (Bar) | Solution Annealed (Condition A) at 1065–1095°C, rapid cool | Solution Annealed – mandatory |
| Grain Size (Bar) | ASTM 6 or finer (mandatory) | ASTM 6 or finer – mandatory for subsea fatigue resistance |
| Micro-cleanliness | ≤ 1.0 (ASTM E45 – Method A) | ≤ 1.0 – mandatory |
| Macro-etch / Flow Lines | Not typical | Required – no laps, seams, or pipe |
| Bar Straightness | 0.5 mm/m (typical) | ≤ 0.3 mm/m (for long stud machining) |
| Decarburization | Not applicable (alloy) | Not applicable |
3. Room temperature mechanical properties of Inconel 625 bars (annealed)
| Property | AMS 5666 (Condition A) | Subsea Supplement Requirement | Difference |
|---|---|---|---|
| Tensile Strength, Ultimate | ≥ 827 MPa (120 ksi) | ≥ 827 MPa (120 ksi) | Same |
| Tensile Strength, Yield (0.2% Offset) | ≥ 414 MPa (60 ksi) | ≥ 414 MPa (60 ksi) | Same |
| Elongation at Break (4D) | ≥ 30% | ≥ 30% | Same |
| Reduction of Area | ≥ 30% (typical) | ≥ 35% (often specified for bolting) | Stricter for subsea |
| Hardness (Bar Stock) | ≤ 96 HRB (≈ 20 HRC) | ≤ 35 HRC (NACE limit) – annealed bar typically 15–22 HRC | Same base; NACE cap applies |
| Modulus of Elasticity | ~207 GPa | ~207 GPa | Same |
| Impact Toughness (Charpy V-Notch) | Not specified | ≥ 80 J @ -46°C (typical subsea requirement) | Additional – critical for low-temperature subsea |
Click to download the Inconel 625 alloy PDF file now
4. Inconel 625 bar non-destructive testing (NDT) requirements
| Parameter | AMS 5666 (Bar Stock) | Subsea Stud Supplement |
|---|---|---|
| Ultrasonic Testing (UT) | 100% mandatory (per AMS 2154 / AMS 2630) | 100% mandatory – with stricter acceptance criteria (e.g., < 1.2 mm FBH equivalent) |
| Liquid Penetrant Testing (PT) | As specified | 100% mandatory on bar surface after final machining (to detect surface cracks) |
| Eddy Current Testing (ET) | Not typical (for bar) | As specified – for near-surface defect detection |
| Hardness Testing (Bar) | Per heat / per lot | Per heat + per bar – documented in MTR |
| Visual Inspection | 100% | 100% – with 10× magnification on critical areas |
| Grain Size Verification | Per heat / per lot | Mandatory – per ASTM E112 |
5. Gnee Alloy's commonly used Inconel 625 bar stock for submarine fasteners comes in various sizes.
We stock sizes optimized for the fastener industry, ensuring optimal throughput and minimal processing time. All materials are finished using VIM + VAR processes to guarantee absolute structural integrity.
| Diameter (Inches) | Diameter (mm) | Supply Condition | Tolerance | Ideal Application |
| 1.00" - 2.50" | 25.4 - 63.5 mm | Bright Ground / BA | h9 / h10 | Precision Stud Bolts & Pins. |
| 2.75" - 4.00" | 69.8 - 101.6 mm | Peeled / Smooth | h11 / k12 | Subsea Connectors & Bolts. |
| 4.25" - 6.50" | 107.9 - 165.1 mm | Hot Forged / Rough | +2mm / -0 | Heavy-Duty Mandrels. |
| 7.00" - 12.0" | Up to 300 mm | Rough Machined | Custom | Wellhead Components. |
Click to view Gnee Alloy Inconel 625 inventory list
6. Why source Inconel 625 bars from Gnee Alloy's wholesale inventory?
✅️Direct Factory Price: Eliminate the 15-25% markup from international trading agents and secure original manufacturer rates.
✅️Cut-to-Length Service: We utilize high-precision bandsaws to provide Ready-to-Machine Blanks, saving you up to 10% on material waste and logistics costs.
✅️Fast Global Shipping: Optimized logistics to major global hubs (Houston, Aberdeen, Singapore, Dubai) within 5-7 business days for stock items.
✅️MTC 3.1 Traceability: Full heat-analysis and mechanical property verification documented with every meter of bar.
Gnee Alloy Inconel 625 certificate
Gnee Alloy Product Packaging
All stainless steel products are:
✅️Packed in wooden pallets or crates
✅️Covered with moisture-proof wrapping
✅️Labeled with heat number, standard, and size
✅️Shipped worldwide via sea, air, or express
Gnee Alloy 625 Alloy Packaging
Gnee Alloy Production Equipment and Product Testing
Contact us now to get the latest export price for Inconel 625 in 2026
FAQ
Q1: Is your GH3625 (Inconel 625) interchangeable with AMS 5666?
A: Yes. GH3625 is the technische designation within the Chinese national standard for the exact same metallurgical system as UNS N06625. Our material meets and exceeds the technical threshold of AMS 5666 and ASTM B446, ensuring total interchangeability.
Q2: Do you offer centerless grinding for precision studs?
A: Absolutely. We offer Precision Ground bright rods with h9 and h10 tolerances on diameters up to 100mm, ensuring a Smooth Finish that is ideal for high-speed automated thread rolling.
Q3: Can you provide material with restricted hardness for NACE compliance?
A: Yes. We follow specific thermal protocols to guarantee that our Inconel 625 bars maintain a hardness below 35 HRC, meeting the requirements for Sulfide Stress Cracking (SSC) resistance in sour gas environments.
Q4: Do you support small batch trial orders for R&D?
A: Yes. As a Reliable Supplier, we support Innovation. We offer Flexible MOQs on our in-stock wholesale inventory to support your prototype testing.
