Inconel 690 Flanges (UNS N06690 / Alloy 690 / ISO NW6690) are precision-manufactured pipe flanges made from one of the most corrosion-resistant nickel alloys available. With a nominal composition of approximately 58% Nickel, 29% Chromium, and 9% Iron, Alloy 690 carries the highest chromium content of the commercially important Inconel grades — and it is that chromium that delivers its hallmark properties: outstanding resistance to oxidising acids, negligible susceptibility to stress corrosion cracking in high-temperature water, and excellent oxidation resistance at elevated temperatures.
These properties have made UNS N06690 flanges the material of choice for pressurised water reactor (PWR) nuclear steam generators, nitric acid production trains, spent nuclear fuel reprocessing plants, and high-temperature chemical processing systems worldwide. Tesco Steel & Engineering manufactures Inconel 690 flanges in all standard types and pressure classes, supplying project requirements from individual spares to large mill-order quantities for engineering, procurement & construction (EPC) contractors across six continents.
| Element | Minimum % | Maximum % | Significance |
|---|---|---|---|
| Nickel (Ni) | 58.0 | Balance | Primary matrix; provides ductility, toughness & corrosion resistance |
| Chromium (Cr) | 27.0 | 31.0 | Key element — highest of any Inconel grade; drives oxidation & acid resistance |
| Iron (Fe) | 7.0 | 11.0 | Strengthening element; improves oxidation resistance at elevated temperature |
| Carbon (C) | — | 0.05 | Low carbon limits sensitisation & grain-boundary carbide precipitation |
| Manganese (Mn) | — | 0.50 | Deoxidiser during melting |
| Silicon (Si) | — | 0.50 | Minor deoxidiser |
| Sulfur (S) | — | 0.015 | Controlled low to prevent hot cracking during welding |
| Copper (Cu) | — | 0.50 | Minor presence; does not significantly affect corrosion behaviour |
Note: For nuclear-grade Alloy 690 (RCC-M / ASME III applications), additional restrictions on trace elements and thermal treatment requirements apply per the applicable procurement specification.
| Property | Annealed (Typical) | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 586 MPa (85 ksi) | ASTM B564 / ASME SB-564 |
| 0.2% Proof Stress (YS) | ≥ 241 MPa (35 ksi) | ASTM B564 |
| Elongation | ≥ 30% | ASTM B564 |
| Hardness (Brinell) | ≤ 220 HB | ASTM E10 |
| Density | 8.19 g/cm³ | — |
| Melting Range | 1343–1377 °C (2449–2511 °F) | — |
| Modulus of Elasticity | 211 GPa (30.6 × 10⁶ psi) | — |
| Thermal Expansion Coefficient | 13.3 μm/m·°C (20–100 °C) | — |
| Thermal Conductivity | 12.8 W/m·K (at 100 °C) | — |
| Full Specification Range — Inconel 690 (UNS N06690) Flanges | |
|---|---|
| Material Standard | ASTM B564 / ASME SB-564 (Forgings) · UNS N06690 · ISO NW6690 · DIN 2.4642 |
| Dimensional Standards | ASME B16.5 · ASME B16.47 Series A (MSS SP-44) & Series B (API 605) · DIN EN 1092-1 · BS 4504 · JIS B 2220 |
| Size Range | ½″ NB to 60″ NB (DN 15 to DN 1500) |
| 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 / Wall Thickness | SCH 10, 20, 40, STD, 80, XS, 100, 120, 140, 160, XXS |
| Face Types | Raised Face (RF) · Flat Face (FF) · Ring Type Joint (RTJ) · Tongue & Groove (T&G) · Male & Female (M&F) |
| Manufacturing Process | Open-die forging · Rolled ring forging · Machined from bar (small sizes) |
| Heat Treatment | Solution annealed (1066–1093 °C, rapid quench) · Thermally treated (TT) for nuclear-grade |
| Surface Finish | Mill finish · Pickled & passivated · Electropolished · Custom per spec |
| Testing & Inspection | Chemical analysis · Mechanical testing · Hardness · IGC (ASTM A262 Practice C) · PMI (XRF) · UT/RT · Hydrostatic test |
| Certifications Available | EN 10204 3.1 / 3.2 MTR · ASME Section III N-Cert · RCC-M · NACE MR0175 · PED 2014/68/EU · AD2000 |
| Flange Type | UNS N06690 Designation | Common Applications |
|---|---|---|
| Weld Neck Flange (WNRF) | Inconel 690 WNRF / RFWN Flange | Nuclear steam generator nozzles, high-pressure chemical reactors, high-temperature piping critical joints |
| Slip-On Flange (SORF) | Inconel 690 Slip-On Flange | Moderate-pressure process lines, instrumentation, utility connections in corrosive environments |
| Blind Flange (BL) | Inconel 690 Blind Flange | Pressure testing end closures, vessel manways, inspection ports in nuclear and acid service |
| Socket Weld Flange (SW) | Inconel 690 Socket Weld Flange | Small-bore (≤ NPS 2) high-pressure nuclear and chemical instrumentation lines |
| Threaded Flange | Inconel 690 Screwed Flange | Low-pressure utility and sampling connections where welding is not permitted |
| Lap Joint Flange | Inconel 690 Lap Joint Flange | Systems requiring frequent dismantling for inspection, with stub ends in corrosion-resistant alloy |
| Long Weld Neck Flange (LWN) | Inconel 690 Long Weld Neck | Pressure vessel nozzle connections, reactor head penetrations in nuclear plant |
| Ring Type Joint (RTJ) Flange | Inconel 690 RTJ Weld Neck | Very high-pressure chemical reactors, wellheads, and subsea applications |
| Orifice Flange | Inconel 690 Orifice Flange Pair | Flow measurement in nitric acid, radioactive liquid streams, and critical process lines |
The exceptional corrosion resistance of Alloy 690 / UNS N06690 stems directly from its 27–31% chromium content — the highest of any commercially produced Inconel grade. This chromium level forms a tenacious, self-repairing Cr₂O₃ oxide film that protects the underlying alloy under oxidising conditions where lower-chromium nickel alloys are attacked.
Nitric Acid (HNO₃): Alloy 690 is among the most resistant nickel alloys to nitric acid across a wide range of concentrations and temperatures. Corrosion rates are extremely low even in boiling concentrated HNO₃, making it the preferred alloy for nitric acid coolers, heat exchangers, and associated piping flanges in fertiliser and explosives manufacturing.
Nitric-Hydrofluoric Acid Mixtures: In stainless steel pickling operations and nuclear fuel reprocessing (PUREX process), mixed HNO₃/HF solutions are highly aggressive. Inconel 690 flanges exhibit far superior resistance compared to 304/316 stainless steels or even Inconel 600 in these environments.
Stress Corrosion Cracking (SCC) in High-Purity Water: At 300–340 °C, Inconel 600 (N06600) is susceptible to primary water stress corrosion cracking (PWSCC) — the principal degradation mechanism in PWR nuclear steam generators. Inconel 690 was developed specifically to solve this problem. Its higher Cr content, lower carbon level, and controlled thermal treatment (TT) microstructure make it essentially immune to PWSCC under normal PWR operating conditions. This is why all modern PWR steam generators worldwide use Alloy 690 tubing and associated Alloy 690 flanges and fittings.
Intergranular Corrosion (IGC): The low carbon content (≤ 0.05%) limits carbide precipitation at grain boundaries during welding, preventing sensitisation. Alloy 690 passes the ASTM A262 Practice C (Huey Test) for intergranular corrosion resistance after standard solution annealing.
Oxidation at High Temperatures: In air and combustion atmospheres up to ~1000 °C, the thick, adherent Cr₂O₃ scale formed on Alloy 690 provides excellent protection against oxidation and carburisation — performance that surpasses most stainless steels and other nickel alloys.
| Property | Inconel 690 (N06690) | Inconel 600 (N06600) | Inconel 625 (N06625) | Inconel 825 (N08825) |
|---|---|---|---|---|
| Chromium % | 27–31% | 14–17% | 20–23% | 19.5–23.5% |
| Nickel % | ≥ 58% | ≥ 72% | 58–69% | 38–46% |
| Molybdenum % | None | None | 8–10% | 2.5–3.5% |
| Nitric Acid Resistance | Excellent | Poor | Good | Moderate |
| PWSCC Resistance (Nuclear) | Excellent | Poor (susceptible) | Good | Not typically specified |
| Seawater / Pitting Resistance | Moderate | Moderate | Excellent | Good |
| Reducing Acid Resistance | Moderate | Good | Excellent (with Mo) | Good |
| Primary Applications | Nuclear, HNO₃, high-Cr service | High-temp reducing, dry heat | Seawater, mixed acids, offshore | Phosphoric acid, sulphuric acid, sour oil & gas |
Nuclear Power Generation
This is the defining application of Alloy 690. Inconel 690 flanges and fittings are specified for PWR steam generator nozzles, head penetrations (CRDM nozzles), reactor coolant pump flanges, pressuriser heater sleeves, and emergency core cooling system (ECCS) piping. The alloy's immunity to PWSCC eliminates the weld repair cycles that plagued earlier Inconel 600 installations, dramatically improving plant availability and safety.
Nitric Acid (HNO₃) Production & Handling
Inconel 690 flanges are used in nitric acid cooler-condensers, absorption columns, and associated piping where 304/316 stainless steel corrodes unacceptably at high HNO₃ concentrations. The alloy's low corrosion rate translates to extended component life and reduced maintenance downtime in fertiliser and specialty chemical plants.
Nuclear Fuel Reprocessing
In PUREX (plutonium uranium reduction extraction) reprocessing facilities, mixed HNO₃/HF solutions dissolve spent fuel assemblies. Inconel 690 flanges for dissolvers, evaporators, and process lines outperform all other commercially available alloys in these extremely aggressive conditions.
High-Temperature Oxidising Environments
Gas turbine exhaust ducting, heat-treatment furnace components, reformer outlet manifolds, and other high-temperature systems where oxidising atmospheres are present benefit from Alloy 690's outstanding oxidation resistance up to 1000 °C.
Chemical Processing
Alloy 690 flanges are used in nitration reactors, anhydride production, specialty inorganic chemical manufacturing, and chlor-alkali anolyte circuits where high chromium content is essential for service life.
Pharmaceutical & High-Purity Systems
Where ultra-pure water systems require high-temperature sterilisation (SIP at 134 °C), Alloy 690's immunity to stress corrosion cracking makes it a premium material choice for critical flange connections in bioreactor and purified water distribution systems.
Inconel 690 (UNS N06690) is weldable by all conventional processes — GTAW (TIG), GMAW (MIG), SMAW (stick), SAW, and FCAW — following procedures qualified to ASME Section IX. Key fabrication guidelines:
Tesco Steel & Engineering implements a comprehensive quality management system for all Inconel 690 flange production:
Inconel 690 flanges are dimensioned to the same ASME B16.5 / B16.47 tables as other materials — only the material and pressure-temperature (P-T) rating group differs. For detailed dimension tables by pressure class, see:
Q: What does UNS N06690 mean?
UNS N06690 is the Unified Numbering System (UNS) designation for Inconel 690 — a nickel-chromium-iron alloy containing approximately 58% Ni, 29% Cr, and 9% Fe. It is also known by trade names Alloy 690, Nicrofer 6030, and Haynes 690. The ISO designation is NW6690 and the DIN material number is 2.4642.
Q: Is Inconel 690 the same as Incoloy 690?
The terms are sometimes confused, but Inconel 690 is the correct designation for UNS N06690. It belongs to the Inconel family (high-Ni, Cr-Fe base) rather than the Incoloy family (Ni-Fe-Cr base). Incoloy grades typically have a higher iron content (e.g., Incoloy 825 is 38–46% Ni, versus 690's ≥58% Ni).
Q: Why is Inconel 690 preferred over Inconel 600 in PWR nuclear plants?
Inconel 600 (N06600) steam generator tubes in early PWR plants experienced widespread stress corrosion cracking (PWSCC and IGA) in the primary coolant at ~325 °C, requiring costly replacements and forced outages. Alloy 690's higher chromium (29% vs. 16%) and lower carbon content, combined with optimised thermal treatment, makes it essentially immune to PWSCC under PWR primary water chemistry. All modern replacement steam generators worldwide use Alloy 690 tubing, and associated flanges specify N06690 accordingly.
Q: What welding consumable is used for Inconel 690 flanges?
The recommended filler metal is Alloy 52 (ERNiCrFe-7) or Alloy 52M (ERNiCrFe-7A) for TIG/MIG welding. For SMAW, Alloy 152 (ENiCrFe-7) electrodes are used. In nuclear applications involving dissimilar joints to low-alloy or carbon steel, Alloy 82/182 or the newer Alloy 52/152 filler metals are used depending on the applicable code (ASME Section III or RCC-M).
Q: Does Inconel 690 require post-weld heat treatment?
Standard pressure piping fabrication under ASME B31.3 does not require PWHT for Alloy 690 welds. However, nuclear-grade applications under ASME Section III or RCC-M may specify a controlled thermal treatment (TT) cycle after welding to optimise carbide distribution at grain boundaries and further reduce susceptibility to PWSCC — particularly for safety-critical components in nuclear primary coolant circuits.
Q: Can I use Inconel 690 flanges in seawater service?
Alloy 690 has moderate resistance to seawater and chloride-containing environments, but it is not the optimum choice for aggressive seawater service — Super Duplex (UNS S32750) or Inconel 625 (N06625) are generally preferred for seawater injection and offshore applications due to their higher molybdenum content. Alloy 690 may be suitable for seawater in low-velocity, low-temperature utility duties but should be evaluated against site-specific conditions before specification.
Q: What certifications can Tesco Steel provide with Inconel 690 flanges?
Tesco Steel & Engineering can supply Inconel 690 flanges with: EN 10204 Type 3.1 (manufacturer's) or 3.2 (third-party) MTRs; PED 2014/68/EU conformity; AD2000-W2 compliance; ASME Section III documentation (upon special order); RCC-M compliance; NACE MR0175 / ISO 15156 hardness certification; and third-party inspection reports from Bureau Veritas, Lloyd's Register, TÜV SÜD, DNV, SGS, or client-nominated agencies.
As a high-chromium, nickel-based specialty alloy, Inconel 690 / UNS N06690 flanges are priced at a premium over standard stainless steel or lower-alloy Inconel grades. Pricing is driven by current nickel and chromium commodity markets, flange type, NPS, pressure class, heat treatment requirements, and quantity.
Tesco Steel & Engineering offers competitive factory-direct pricing with full traceability documentation. Please use the Inquiry Form or contact our technical sales team via WhatsApp at +91 92233 66922 for a detailed, item-level quotation with current lead time. We respond within 24 hours.
Countries We Export Inconel 690 Flanges To: Kuwait, UAE, Saudi Arabia, Germany, West Africa, Dubai, Iraq, Congo, Mexico, Bahrain, Canada, Philippines, Thailand, Kenya, Oman, Malaysia, Turkey, Qatar, Sudan, Netherlands, Nigeria, Lithuania, Gabon, Russia, Vietnam, Angola, Bolivia, Indonesia, UK, Yemen, Italy, United States, Venezuela, Spain, Iran, Estonia, Kazakhstan, Algeria, Jordan, Ecuador, Portugal, Colombia, Libya, Chile, Peru, South Africa, Bangkok, Namibia, Jeddah, Afghanistan, Israel, Zambia, Macau, Morocco, Denmark, Taiwan, Norway, Belarus, Lebanon, Sri Lanka, Bulgaria, Ukraine, Belgium, Finland, Romania, France, Brazil, Trinidad & Tobago, Fiji, Tunisia, Gambia, Hungary, Zimbabwe, Mongolia, Ghana, Egypt, Czech Republic, Azerbaijan, Poland, Greece, New Zealand, Croatia, Tanzania, Somalia, Australia, Singapore, Japan, South Korea.
Domestic Supply — Inconel 690 Flanges in India: Mumbai, Delhi, Bangalore, Hyderabad, Ahmedabad, Chennai, Kolkata, Surat, Pune, Jaipur, Lucknow, Kanpur, Nagpur, Visakhapatnam, Indore, Thane, Bhopal, Pimpri-Chinchwad, Patna, Vadodara, Ghaziabad, Ludhiana, Coimbatore, Agra, Andhra Pradesh, Arunachal Pradesh, Assam, Bihar, Chandigarh, Chhattisgarh, Goa, Gujarat, Haryana, Himachal Pradesh, Jammu & Kashmir, Jharkhand, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Manipur, Meghalaya, Mizoram, Nagaland, Odisha, Punjab, Rajasthan, Sikkim, Tamil Nadu, Telangana, Tripura, Uttar Pradesh, Uttarakhand, West Bengal.