Seamless Inconel 690 Pipe
What is a Seamless Inconel 690 Pipe?
Seamless Inconel 690 Pipe is a high-chromium nickel alloy (Ni ≥ 58 %, Cr 27–31 %) tube produced from a solid billet with no welded seam. Registered as UNS N06690, this alloy was developed as an improvement over Inconel 600 specifically for nuclear and severely corrosive high-temperature service.
The elevated chromium content gives Alloy 690 exceptional resistance to oxidizing acids and — critically — to stress-corrosion cracking in high-temperature, high-purity water, the environment inside pressurized-water-reactor steam generators. Its low cobalt variant chemistry also minimizes activation in nuclear service.
Manufactured to ASTM B163, B167 and B829 with full solution annealing, Inconel 690 seamless pipe is the international reference material for nuclear steam-generator tubing and is equally valuable in nitric acid and other oxidizing chemical service.
Inconel 690 vs Inconel 600 vs Inconel 625: The Nickel-Chromium Line-Up
Within the nickel-chromium family, 690 occupies a deliberately specialized position. This comparison shows why nuclear and severe-corrosion projects moved from 600 to 690.
| Grade | Key Chemistry / Condition | Where It Fits |
|---|---|---|
| Inconel 600 | Ni ≥ 72 %, Cr 14-17 % | Classic nickel-chromium grade; excellent in caustic and dry chlorine, but susceptible to stress-corrosion cracking in high-temperature pure water |
| Inconel 690 | Ni ≥ 58 %, Cr 27-31 % | Raised chromium for a stable Cr2O3 film; the standard for PWR steam-generator tubing and nuclear waste processing |
| Inconel 625 | Ni 58 % min, Cr 20-23, Mo 8-10, Nb | Highest strength and pitting resistance of the three; heavier alloying, higher cost |
| Incoloy 800H | Fe-Ni-Cr balanced | Iron-nickel alternative for furnace and heat-treatment duty |
Product Specifications
Specification data for Seamless Inconel 690 Pipe is compiled from the governing ASTM/ASME/EN standards and our routine production records; typical values are shown where a standard leaves a limit open.
| Category | Standard / Designation |
|---|---|
| Seamless Pipe & Tube | ASTM B167 / B163 / ASME SB167 / SB163 |
| Billet & Bar Stock | ASTM B829 / B166 |
| UNS Designation | N06690 |
| Werkstoff Number | 2.4642 |
| Typical Application Code | ASME Boiler Code Section III (nuclear) |
Size and Weight Chart
| NPS | OD (mm) | SCH 40 WT (mm) | SCH 40 kg/m | SCH 80 WT (mm) | SCH 80 kg/m |
|---|---|---|---|---|---|
| 1/4" | 13.7 | 2.24 | 0.66 | 3.02 | 0.83 |
| 1/2" | 21.3 | 2.77 | 1.32 | 3.73 | 1.69 |
| 3/4" | 26.7 | 2.87 | 1.76 | 3.91 | 2.29 |
| 1" | 33.4 | 3.38 | 2.61 | 4.55 | 3.38 |
| 1-1/4" | 42.2 | 3.56 | 3.54 | 4.85 | 4.66 |
| 1-1/2" | 48.3 | 3.68 | 4.22 | 5.08 | 5.65 |
| 2" | 60.3 | 3.91 | 5.67 | 5.54 | 7.81 |
| 3" | 88.9 | 5.49 | 11.78 | 7.62 | 15.94 |
| 4" | 114.3 | 6.02 | 16.77 | 8.56 | 23.29 |
| 6" | 168.3 | 7.11 | 29.49 | 10.97 | 44.41 |
| 8" | 219.1 | 8.18 | 44.39 | 12.7 | 67.44 |
Weights are theoretical for seamless pipe (kg per metre) calculated from the nominal dimensions; actual weights vary within the dimensional tolerances shown below. Intermediate sizes and schedules between SCH 10S and SCH 160 are produced to order.
Chemical Composition
| Element | Min (%) | Max (%) |
|---|---|---|
| Nickel (Ni) | 58.0 | — (min) |
| Chromium (Cr) | 27.0 | 31.0 |
| Iron (Fe) | 7.0 | 11.0 |
| Carbon (C) | — | 0.05 |
| Manganese (Mn) | — | 0.50 |
| Silicon (Si) | — | 0.50 |
| Copper (Cu) | — | 0.50 |
| Sulfur (S) | — | 0.015 |
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength (typical, annealed) | 710 MPa (103 ksi) |
| Yield Strength (0.2 % offset, typical) | 350 MPa (51 ksi) |
| Elongation in 2 in. / 50 mm (typical) | 41 % |
| Hardness (typical) | ≤ 95 HRB |
| Heat Treatment | Solution annealed 1040 – 1120 °C, rapid cool; thermal-treatment variants per nuclear specs |
Physical Properties
| Property | Value |
|---|---|
| Density | 8.19 g/cm³ |
| Melting Range | 1345 – 1380 °C |
| Elastic Modulus | 211 GPa |
| Coefficient of Thermal Expansion (20–100 °C) | 14.1 µm/m·°C |
| Thermal Conductivity (at 100 °C) | 14.9 W/m·K |
| Specific Heat Capacity | 450 J/kg·K |
| Electrical Resistivity | 118 µΩ·cm |
Equivalent Grades
| Standard System | Designation |
|---|---|
| UNS | N06690 |
| Werkstoff Nr. | 2.4642 |
| EN | NiCr29Fe |
| ASTM | B163 / B167 / B829 |
Why Inconel 690 Is the Nuclear and Severe-Corrosion Standard
Inconel 690 was engineered specifically to defeat the stress-corrosion cracking that affected Alloy 600 tubes in pressurized-water-reactor steam generators. Its 27-31 % chromium forms a tenacious, protective chromium-oxide film even in lithiated, hydrogenated primary water at 300 °C and above, and thermally treated (TT) conditions — a controlled 700-750 °C heat treatment — further deplete grain-boundary chromium in a way that has proven crack-resistant over decades of reactor service.
Outside the nuclear island, the same chemistry excels in hot caustic, sulfuric acid environments and nitrate-bearing media, and in coal-gasification and spent-fuel reprocessing equipment where boiling nitric-hydrofluoric acid mixtures destroy lesser alloys. Supplied seamless and solution annealed at about 1050-1100 °C with rapid quench, our Inconel 690 pipe carries full melt traceability and EN 10204 3.1/3.2 certification.
Manufacturing Process
Our seamless production route for Seamless Inconel 690 Pipe follows these documented stages:
- Premium Melt Practice: Primary nickel, chromium and iron are vacuum- or AOD-melted with strict control of tramp elements; ingots are forged and ultrasonically inspected.
- Hot Extrusion: Billets are sheathed and hot-extruded into seamless shells, preserving the single-phase structure essential for nickel-alloy performance.
- Cold Reduction: Cold drawing and pilgering bring the shell to final dimensions with close tolerance on OD and wall.
- Solution Annealing: Annealing at 1050-1150 °C with rapid water quench keeps alloying elements in solid solution and optimizes grain size for corrosion and creep performance.
- Descaling & Finishing: Careful acid descaling (with controlled alkaline pre-soak for high-Cr grades) yields the uniform surface the alloys are known for.
- Testing & Release: Every length receives eddy-current or ultrasonic examination, mechanical and intergranular-corrosion testing where specified, and full certification.
Surface Finish Options
- Pickled: Standard descaled condition for chemical-process piping.
- Bright Annealed: For instrumentation, heat-exchanger and high-purity applications.
- Mechanically Polished: Up to 600-grit for hygienic and visible installations.
Dimensional Tolerances
Delivered dimensions are verified against the tolerances below; tighter tolerances can be negotiated for instrumentation and precision applications.
| Dimension | Tolerance |
|---|---|
| OD, tube ≤ 25.4 mm (cold worked) | ± 0.10 mm |
| OD, tube 25.4 – 38.1 mm | ± 0.15 mm |
| OD, tube 38.1 – 50.8 mm | ± 0.20 mm |
| OD, hot-finished pipe ≥ 50.8 mm | ± 1 % of OD |
| Wall thickness | - 12.5 % under-tolerance (min-wall basis) |
| Straightness | ≤ 1 mm per metre |
| Cut length | + 10 / - 0 mm (fixed lengths) |
Common Industrial Applications
Because of its characteristic property profile, Seamless Inconel 690 Pipe is specified in the following industries and services:
- Nuclear Power Plants: Steam-generator tubing, pressurizer components and reactor coolant system piping — the primary worldwide application of Alloy 690.
- Nitric Acid Plants: Tubing and piping for concentrated nitric acid service where oxidizing attack destroys stainless steels.
- Petrochemical Reformers: Furnace components requiring combined carburization resistance and high-temperature strength.
- Power Generation (Fossil): Superheater tubing in aggressive coal-ash corrosion environments.
- Waste Treatment & Vitirification: Molten-glass and off-gas handling hardware in radioactive waste processing.
- Chemical Processing: Oxidizing chemical service and caustic evaporators where lower-chromium alloys fail.
Quality Assurance, Testing and Documentation
Every length of Seamless Inconel 690 Pipe passes through a documented quality-control chain before dispatch:
- Material Certification: EN 10204 3.1 mill test certificates are issued for every heat; 3.2 certification with third-party witness (TUV, SGS, BV) is available on request.
- Chemical & Mechanical Testing: Heat-level chemical analysis plus tensile, hardness and, where applicable, flattening, flaring and reverse-flattening tests per the governing standard.
- Non-Destructive Examination: 100 % eddy-current or ultrasonic testing and hydrostatic or pneumatic pressure testing in line with the standard's supplementary requirements.
- Dimensional & Visual Inspection: Full OD, wall thickness, ovality and length verification with visual surface inspection after pickling or finishing.
- Traceability & Marking: Heat numbers stenciled or banded on every length, maintaining complete melt-to-pipe traceability.
Export and Packaging
Pipes are bundled with steel strapping and fitted with plastic or steel end caps, then packed in seaworthy wooden cases or crates and secured in containers for long-distance ocean freight. Standard export documentation — commercial invoice, packing list, certificate of origin, mill test certificates and, where required, third-party inspection reports — accompanies every shipment. Container-load and bulk project orders receive priority production slots and consolidated shipping documentation.
Frequently Asked Questions
Q1. Why did nuclear plants replace Alloy 600 tubing with Alloy 690?
A: Field experience showed Alloy 600 tubing could suffer stress-corrosion cracking in the high-temperature water of PWR steam generators. Alloy 690's higher chromium content (27–31 % vs about 15 %) essentially eliminated that failure mode, making it the modern standard.
Q2. What is the difference between Inconel 690 and Inconel 625?
A: Alloy 690 is a Ni-Cr-Fe alloy optimized for oxidizing media and SCC resistance, while Alloy 625 adds molybdenum and niobium for superior pitting resistance and higher strength. They serve different environments rather than replacing each other.
Q3. Is Inconel 690 pipe available with nuclear-quality documentation?
A: Yes. Supply with ASME Section III material requirements, NQA-1 quality-system documentation and third-party witnessing can be arranged for nuclear projects.
Q4. What non-destructive examination is applied to 690 tubing?
A: 100 % ultrasonic and eddy-current testing per ASTM B163 supplementary requirements, plus hydrostatic or pneumatic pressure testing, with full digital records.
Ready to Request a Quotation?
Send us your size range, wall thickness/schedule, standard and quantity for Seamless Inconel 690 Pipe, and our engineering team will respond with a detailed technical and commercial offer within 24 hours. Custom sizes, third-party inspection and full export documentation are part of our standard service.
