Hastelloy X flanges (UNS N06002) are precision-forged nickel-chromium-iron-molybdenum superalloy flanges engineered specifically for extreme high-temperature service up to 1200°C (2200°F). Unlike conventional corrosion-resistant nickel alloys, Hastelloy X — also designated Alloy X — derives its value from an outstanding combination of oxidation resistance, high-temperature structural strength, and excellent fabricability across the full range of service conditions encountered in gas turbines, aerospace components, petrochemical furnaces, and industrial heating systems.
Tesco Steel & Engineering manufactures Hastelloy X flanges per ASTM B564 (UNS N06002) in all standard ASME flange types. Our flanges are supplied with full EN 10204 3.1 mill traceability, dimensional inspection certificates, and third-party inspection by Bureau Veritas, SGS, or Intertek on request. We export to 65+ countries with quotes delivered within 24 hours.
Hastelloy X is a nickel-chromium-iron-molybdenum (Ni-Cr-Fe-Mo) superalloy originally developed by Haynes International for applications requiring exceptional performance at temperatures where most other alloys lose structural integrity. With a nominal composition of ~47% Ni, 21.5% Cr, 18.5% Fe, and 9% Mo, the alloy is uniquely positioned as both a high-temperature structural material and a material with good resistance to oxidizing, reducing, and neutral high-temperature atmospheres.
A critical distinction that engineers and procurement teams must understand: Hastelloy X is a high-temperature alloy — not primarily a wet corrosion alloy. Where Hastelloy C276 excels in resisting HCl, H₂SO₄, and chloride-induced corrosion at near-ambient temperatures, Hastelloy X is the material of choice when the application involves sustained temperatures above 800°C combined with oxidizing or combustion atmospheres. This makes it indispensable in gas turbine combustors, afterburners, industrial furnace hardware, and aerospace transition ducts.
| Element | Composition (wt %) | Role in Alloy |
|---|---|---|
| Nickel (Ni) | Balance (~47%) | Austenitic matrix; high-temp ductility & oxidation resistance |
| Chromium (Cr) | 20.5 – 23.0 | Forms protective Cr₂O₃ scale; primary oxidation resistance element |
| Iron (Fe) | 17.0 – 20.0 | Cost control; aids fabricability & weldability |
| Molybdenum (Mo) | 8.0 – 10.0 | Solid-solution strengthening; enhances high-temp strength |
| Cobalt (Co) | 0.5 – 2.5 | Improves high-temp strength & microstructural stability |
| Tungsten (W) | 0.2 – 1.0 | Additional solid-solution strengthening at elevated temperature |
| Carbon (C) | 0.05 – 0.15 | Carbide formation contributes to creep resistance at high temp |
| Manganese (Mn) | ≤ 1.0 | Deoxidation during melting; minor strengthening |
| Silicon (Si) | ≤ 1.0 | Oxidation resistance enhancement at very high temperatures |
| Boron (B) | ≤ 0.010 | Grain boundary strengthening; creep resistance improvement |
| Sulfur (S) | ≤ 0.030 | Controlled as impurity; minimised to preserve ductility |
| Phosphorus (P) | ≤ 0.040 | Controlled as impurity; low levels required for weldability |
| Property | Value | Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 785 MPa (114 ksi) | ASTM B564 |
| Yield Strength (0.2% offset) | ≥ 310 MPa (45 ksi) | ASTM B564 |
| Elongation | ≥ 35% | ASTM B564 |
| Hardness | ≤ 241 HBW | ASTM B564 |
| Density | 8.22 g/cm³ | — |
| Modulus of Elasticity | 205 GPa (29.8 × 10⁶ psi) | — |
| Max. Service Temperature (continuous) | 1200°C (2200°F) | — |
| Max. Service Temperature (short-term) | 1230°C (2250°F) | — |
Procurement engineers frequently ask whether to specify Hastelloy X, C276, or Inconel 625. The answer depends entirely on the service environment — these are fundamentally different alloys designed for different failure modes:
| Property | Hastelloy X (N06002) | Hastelloy C276 (N10276) | Inconel 625 (N06625) |
|---|---|---|---|
| UNS Number | N06002 | N10276 | N06625 |
| Ni Content | ~47% (balance) | ~57% (balance) | ≥58% (balance) |
| Cr Content | 20.5–23% | 14.5–16.5% | 20–23% |
| Mo Content | 8–10% | 15–17% | 8–10% |
| Fe Content | 17–20% | 4–7% | ≤5% |
| Max. Service Temp. | 1200°C — Excellent | ~500°C — Limited | ~980°C — Good |
| Oxidation Resistance | Outstanding | Moderate | Good |
| HCl / Wet Cl₂ Resistance | Moderate | Outstanding | Good |
| H₂SO₄ Resistance | Moderate | Outstanding | Good |
| Seawater / Pitting Resistance | Moderate | Excellent | Outstanding (PREN >45) |
| High-Temp Structural Strength | Outstanding | Limited | Good |
| Primary Application | Gas turbines, furnaces, aerospace | Chemical process, FGD, offshore | Offshore, subsea, chemical |
| ASTM Standard (Forgings) | B564 (N06002) | B564 (N10276) | B564 (N06625) |
| Cost Index | High | Very High | Very High |
All standard ASME flange types are available in Hastelloy X (UNS N06002), forged per ASTM B564 and dimensioned per ASME B16.5 (Class 150–2500) or ASME B16.47 (large diameter NPS 26″–60″):
| Flange Type | Standard | Typical Application |
|---|---|---|
| Weld Neck (WNRF / WNFF / RJWN) | ASME B16.5 | High-temp furnace nozzles, gas turbine fuel lines, pressure vessels |
| Slip-On (SORF / SOFF) | ASME B16.5 | Moderate-temp process piping, economical installations |
| Blind | ASME B16.5 | End-of-line closures on high-temp process systems |
| Socket Weld | ASME B16.5 | Small-bore high-pressure instrumentation at elevated temp |
| Threaded | ASME B16.5 | Low-pressure fittings where welding is not feasible |
| Long Weld Neck | ASME B16.5 | Pressure vessel nozzles, columns, heat exchanger heads |
| Lapped Joint | ASME B16.5 | Systems requiring frequent dismantling or alignment adjustment |
| Spectacle Blind (Figure-8) | ASME B16.48 | Line isolation on high-temp process headers |
| Standard Specifications — Hastelloy X (UNS N06002) Flanges | |
|---|---|
| Material Standard | ASTM B564 — UNS N06002 (forgings) |
| Equivalent Designations | Alloy X · Haynes Alloy X · DIN 2.4665 · W.Nr. 2.4665 |
| Size Range | NPS ½″ to 24″ (ASME B16.5) | NPS 26″ to 60″ (ASME B16.47) |
| Pressure Classes (ASME) | Class 150, 300, 400, 600, 900, 1500, 2500 |
| Pressure Ratings (DIN/EN) | PN 6, PN 10, PN 16, PN 25, PN 40, PN 64, PN 100, PN 160, PN 250, PN 320, PN 400 |
| Schedule / Bore | Sch 10S, 40S, 80S, STD, XS, XXS · Custom bore on request |
| Flange Standards | ASME B16.5 · ASME B16.47 Series A & B · ASME B16.48 · MSS SP-44 · EN 1092-1 |
| Face Types | Raised Face (RF) · Flat Face (FF) · Ring Type Joint (RTJ) · Tongue & Groove (T&G) · Large Male/Female |
| Testing Standards | ASTM B564 · EN 10204 3.1 MTC · PMI · Hydrostatic · Hardness · TPI on request |
| ASME B16.5 Hastelloy X Flange Dimensions — NPS ½″ to 24″, Class 150 to 2500 |
| ASME B16.47 Hastelloy X Flange Dimensions — NPS 26″ to 60″, Series A & B |
Outstanding Oxidation Resistance to 1200°C
At temperatures above 800°C, most stainless steels and conventional nickel alloys suffer rapid oxidation, scale spalling, and structural degradation. Hastelloy X maintains a dense, adherent chromium oxide (Cr₂O₃) scale at temperatures up to 1200°C continuous service. This protective scale re-forms rapidly if damaged, giving the alloy self-healing oxidation protection unmatched by lower-alloyed grades. In cyclic high-temperature service — such as gas turbine combustion chambers that heat up and cool down repeatedly — this scale stability is critical.
High-Temperature Structural Strength and Creep Resistance
The addition of molybdenum (8–10%), cobalt (up to 2.5%), and tungsten (up to 1%) provides Hastelloy X with solid-solution strengthening that is retained at temperatures where precipitation-hardened alloys may over-age and lose strength. The alloy's creep rupture life significantly exceeds that of Type 310 stainless steel and most Inconel grades at temperatures above 900°C — making it the preferred material for flanges on furnace headers, radiant tube supports, and catalyst inlet manifolds.
Resistance to Both Oxidizing and Reducing Atmospheres
Many high-temperature alloys perform well in either oxidizing or reducing atmospheres, but not both. Hastelloy X offers good performance in oxidizing, reducing, and neutral atmospheres — a unique versatility that makes it suitable for reformer furnaces and other process environments where the atmosphere can shift between oxidizing and reducing conditions during operation.
Excellent Fabricability and Weldability
Despite its complex composition, Hastelloy X has excellent weldability. It is readily joined by GTAW (TIG), GMAW (MIG), and SMAW (stick) processes. The recommended filler metal is ERNiCrMo-2 (AWS/SFA 5.14). Post-weld heat treatment (PWHT) is not required for most applications, which simplifies field installation of Hastelloy X flanged assemblies. Interpass temperature should be kept below 177°C (350°F) to minimise heat input and prevent sensitisation of the heat-affected zone.
| Industry | Application | Why Hastelloy X |
|---|---|---|
| Aerospace | Gas turbine combustion chambers, afterburners, transition ducts, tail pipes | Retains structural integrity at 1100–1200°C under cyclic thermal fatigue |
| Industrial Gas Turbines | Combustor liners, transition pieces, burner nozzle flanges | Outstanding oxidation resistance under continuous high-temp combustion |
| Petrochemical | Furnace tube flanges, reformer headers, pyrolysis furnace nozzles | Withstands 900–1100°C in steam reforming and cracking service |
| Power Generation | Boiler superheat headers, heat recovery steam generator (HRSG) nozzles | High-temp strength and oxidation resistance in superheated steam service |
| Industrial Furnaces | Radiant tube flanges, retort flanges, furnace atmosphere headers | Long service life in cycling oxidizing/reducing furnace atmospheres |
| Nuclear | Fuel reprocessing equipment, high-temp process connections | Stability in high-temp oxidizing environments with low activation potential |
| Chemical Processing | High-temperature reactor flanges, calciner nozzles, oxidiser inlets | Combined resistance to high temp and mildly corrosive process streams |
All Hastelloy X (UNS N06002) flanges from Tesco Steel & Engineering are manufactured and tested in full compliance with ASTM B564 requirements. Our ISO 9001:2015 certified quality system governs every stage:
| Test / Document | Standard / Method |
|---|---|
| Mill Test Certificate | EN 10204 3.1 — heat & lot traceable |
| Chemical Composition | Optical Emission Spectrometry (OES) per ASTM B564 |
| Tensile & Yield Strength | ASTM E8 — per ASTM B564 requirements |
| Hardness Testing | Brinell (HBW) — ≤241 HBW per ASTM B564 |
| Dimensional Inspection | 100% per ASME B16.5 / B16.47 tolerances |
| PMI (Positive Material Identification) | XRF or OES — on request or per project spec |
| Hydrostatic Pressure Test | ASME B16.5 test pressure — available on request |
| Third-Party Inspection | Bureau Veritas · SGS · Intertek · Lloyd's Register |
Hastelloy X is marketed and referenced under several equivalent designations across different standards and manufacturers:
| Designation Type | Name / Number |
|---|---|
| UNS Number | N06002 |
| Trade Name | Hastelloy X · Alloy X · Haynes Alloy X |
| DIN / W.Nr. | 2.4665 |
| ASME SB564 | UNS N06002 |
| AMS | AMS 5536 (sheet/plate), AMS 5754 (bar), AMS 5798 (filler wire) |
| AWS Filler (GTAW) | ERNiCrMo-2 (AWS/SFA 5.14) |
What is Hastelloy X (UNS N06002)?
Hastelloy X is a nickel-chromium-iron-molybdenum superalloy (UNS N06002) containing ~47% Ni, 21.5% Cr, 18.5% Fe, and 9% Mo. It is engineered for exceptional high-temperature oxidation resistance and structural strength at temperatures up to 1200°C. Crucially, it is a high-temperature alloy — not primarily a wet corrosion-resistant alloy like Hastelloy C276. Flanges in Hastelloy X are specified wherever sustained high-temperature service in oxidizing, reducing, or neutral atmospheres is required.
What is the maximum temperature Hastelloy X flanges can withstand?
Hastelloy X flanges maintain structural integrity and oxidation resistance at continuous service temperatures up to 1200°C (2200°F). Short-term excursions up to 1230°C are tolerated. This is among the highest service temperature limits of any commercially stocked nickel alloy flange. The alloy also performs exceptionally under cyclic thermal conditions — repeated heat-up and cool-down cycles — without spalling or cracking of its protective oxide scale.
How is Hastelloy X different from Hastelloy C276?
These two alloys serve fundamentally different purposes. Hastelloy X (N06002) is a high-temperature structural alloy — specified for gas turbines, aerospace, and furnace applications above 800°C. Hastelloy C276 (N10276) is a corrosion-resistant alloy — specified for wet chemical environments involving HCl, H₂SO₄, chlorides, and FGD scrubber service at near-ambient to moderate temperatures. Specifying C276 for high-temperature service, or Hastelloy X for aggressive acid service, would be a material selection error with serious operational consequences.
What standard covers Hastelloy X flanges?
Hastelloy X forgings and flanges are manufactured per ASTM B564 (UNS N06002). Flange dimensions and pressure-temperature ratings follow ASME B16.5 (NPS ½″–24″, Class 150–2500) and ASME B16.47 (NPS 26″–60″, Series A & B). EN 10204 3.1 Mill Test Certificates are provided as standard on all orders.
What industries use Hastelloy X flanges?
Primary industries include: Aerospace (combustion chambers, afterburners, transition ducts); industrial gas turbines (combustor liners, burner nozzle flanges); petrochemical furnaces (reformer tube flanges, pyrolysis furnace nozzles); power generation (HRSG headers, superheater nozzles); and industrial furnaces (radiant tube and retort flanges). The alloy is chosen wherever temperatures exceed 800°C in oxidizing or mixed atmospheres.
Is Hastelloy X the same as Inconel HX or Haynes 230?
No. Hastelloy X (N06002) is sometimes informally called "Inconel HX" but it is a Haynes International proprietary alloy, not an Inconel product. It is distinct from Haynes 230 (N06230), which contains more tungsten (14%) for superior long-term creep strength above 870°C, and from Inconel 625 (N06625), which is optimised for aqueous corrosion rather than high-temperature oxidation. Each alloy has a specific application niche and they are not interchangeable.
What welding filler is used for Hastelloy X flanges?
The standard filler metal for welding Hastelloy X (N06002) is ERNiCrMo-2 per AWS/SFA 5.14. GTAW (TIG) welding with argon back purge is preferred for root passes. No post-weld heat treatment (PWHT) is required for most applications. Interpass temperature must be controlled below 177°C (350°F). Do not use standard stainless steel fillers (e.g., ER316L) or carbon steel fillers — they will compromise the high-temperature properties of the weld joint.
What types of Hastelloy X flanges does Tesco Steel manufacture?
Tesco Steel & Engineering manufactures all standard ASME flange types in Hastelloy X (UNS N06002): Weld Neck (WNRF/WNFF/RJWN), Slip-On (SORF/SOFF), Blind, Socket Weld, Threaded, Long Weld Neck, Lapped Joint, and Spectacle Blind. Custom bore sizes, non-standard pressure classes, and special face finishes are available on request. All types supplied with full ASTM B564 material certification and EN 10204 3.1 MTC. Quotes within 24 hours.
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Hastelloy X — Key Facts
UNS: N06002
DIN / W.Nr.: 2.4665
Type: Ni-Cr-Fe-Mo Superalloy
Max. Temp: 1200°C (2200°F)
Forging Standard: ASTM B564
Flange Standard: ASME B16.5 / B16.47
Weld Filler: ERNiCrMo-2
PWHT Required: No