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Alloy 66 / Alloy 67 Seamless Pipe and Tube
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Alloy 66 and Alloy 67 are iron-nickel-chromium-molybdenum alloys with a 6% molybdenum addition, supplied as seamless pipe and tube for corrosive and heat-resisting service. Both are austenitic grades with no precipitation-hardening treatment, which makes them straightforward to weld and form. This page covers the seamless form manufactured to ASME SB-690.
Specification Coverage
ASME SB-690 covers iron-nickel-chromium-molybdenum alloys UNS N08366 and UNS N08367 in the form of cold-finished annealed or hot-finished annealed seamless pipe and tube intended for special corrosive service and heat-resisting applications. General requirements for pipe and tube, including dimensional tolerances and the definition of minimum wall thickness used for allowable stress calculation, follow ASME B829.
Related product forms you may need alongside seamless pipe:
- ASME SB-691 — rod, bar and wire in the same two UNS numbers
- ASME SB-688 — plate, sheet and strip
- ASME SB-366 — factory-made wrought fittings; UNS N08367 is listed in Table 2 with markings CRNIC and WPNIC
- ASME SB-675 / SB-676 — welded pipe and welded tube for UNS N08367
- ASME SB-462 — forged flanges and forged fittings, which list UNS N08367
Grade Comparison
| Grade | UNS | Ni | Cr | Mo | N | Key Characteristic |
|---|---|---|---|---|---|---|
| Alloy 66 | N08366 | 23.50-25.50 | 20.00-22.00 | 6.00-7.00 | — | General 6% Mo austenitic |
| Alloy 67 | N08367 | 23.50-25.50 | 20.00-22.00 | 6.00-7.00 | 0.18-0.25 | Nitrogen-strengthened, higher strength |
| Alloy 31 | N08031 | 30.0-32.0 | 26.0-28.0 | 6.00-7.00 | 0.20-0.30 | Higher Ni and Cr content |
| Alloy 926 | N08926 | 24.00-26.00 | 19.00-21.00 | 6.00-7.00 | 0.15 max | Low carbon austenitic 6% Mo |
The distinguishing feature between Alloy 66 and Alloy 67 is the nitrogen addition. N08367 carries 0.18-0.25% nitrogen while N08366 has no nitrogen requirement, and that single change raises the yield strength substantially without altering the chromium or molybdenum corrosion behaviour.
Chemical Composition (ASME SB-690 Table 1)
| Element | UNS N08366 (%) | UNS N08367 (%) | Limit Type |
|---|---|---|---|
| Carbon | 0.035 max | 0.030 max | max |
| Manganese | 2.00 max | 2.00 max | max |
| Silicon | 1.00 max | 1.00 max | max |
| Phosphorus | 0.040 max | 0.040 max | max |
| Sulfur | 0.030 max | 0.030 max | max |
| Chromium | 20.00-22.00 | 20.00-22.00 | range |
| Nickel | 23.50-25.50 | 23.50-25.50 | range |
| Molybdenum | 6.00-7.00 | 6.00-7.00 | range |
| Nitrogen | — | 0.18-0.25 | range |
| Copper | — | 0.75 max | max |
| Iron | remainder | remainder | by difference |
Mechanical Properties (ASME SB-690 Table 2)
| Condition | Alloy | Tensile, min ksi (MPa) | Yield 0.2%, min ksi (MPa) | Elongation, min % |
|---|---|---|---|---|
| Cold-worked annealed | N08366 | 75 (517) | 30 (206) | 30 |
| Cold-worked annealed | N08367 | 100 (690) | 45 (310) | 30 |
| Hot-worked annealed | N08366 | 75 (517) | 30 (206) | 30 |
| Hot-worked annealed | N08367 | 95 (655) | 45 (310) | 30 |
Product Forms and Size Range
Outside diameters, wall thicknesses and length tolerances follow the B829 dimensional tables, and the minimum wall thickness used for allowable stress is the specified wall thickness less the permissible minus wall tolerance. Hydrostatic test is required unless otherwise agreed; when so agreed, the material may be treated to 1.5 times the allowable fiber stress. A nondestructive electric test to ASME A450/A450M may replace or supplement the hydrostatic test when specified by the purchaser.
Applications
The 6% molybdenum content drives pitting and crevice corrosion resistance, so these grades suit chloride-bearing process and cooling water service:
- Seawater cooling and heat exchanger tube service
- Desalination pre-treatment and brine handling
- Chemical processing equipment, especially acid and oxidising service
- Pulp and paper mill bleach plant piping
- Flue gas desulphurisation systems
- Oil and gas produced-water service
Certification and Inspection
Material is supplied with a mill test certificate per EN 10204 3.1 unless otherwise specified. Available inspection items include:
- Product (check) analysis per ASME B880 when required by the purchaser
- Hydrostatic test, or nondestructive electric test to ASME A450/A450M
- Tensile testing with test reports
- Intergranular corrosion testing to ASTM A262 where specified
- Non-destructive examination including eddy current and ultrasonic examination
- Third-party inspection by an internationally recognised agency
Ordering Information
Please include the following when requesting a quotation:
- Alloy: UNS N08366 or N08367
- Product form: seamless pipe or seamless tube
- Condition: cold-worked annealed or hot-worked annealed
- Outside diameter, wall thickness and length (or state cut-to-length requirements)
- Quantity and delivery schedule
- Certification: MTC per EN 10204 3.1, and any supplementary requirements
- Inspection and testing requirements, including whether third-party witness is required
- Shipping terms and destination port
Tell us the grade, the size and the service condition, and we will confirm availability and an FOB quotation.
Related specifications and products. Alloy 66 and Alloy 67 are listed among the nickel alloy forgings covered by SB-564. See the round pipe and tube product family Alloy 30 plate and fittings the nickel alloy grade cross-reference for the dimensional and material basis behind this page.
