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UNS N08028 | W.Nr. 1.4563 | NS1403 | ASTM B709 / B668
Alloy 28, commercially known as Incoloy 028 or Sanicro 28, is an ultra-low-carbon iron-nickel-chromium-molybdenum-copper austenitic alloy. The synergistic addition of high chromium, molybdenum, and copper provides exceptional resistance to both oxidizing and reducing acids, chloride pitting, crevice corrosion, and stress corrosion cracking (SCC). It is a workhorse in chemical acid processing, flue gas desulfurization, seawater handling, and sour oil & gas applications, and is fully compliant with ASME pressure vessel codes.
1. Standard Grade Cross Reference
| Standard System | Designation |
|---|---|
| UNS Number | N08028 |
| Commercial Names | Incoloy 028, Sanicro 28, Alloy 28 |
| European EN Number | 1.4563 (X1NiCrMoCu31-27-4) |
| Chinese GB Standard | NS1403 |
| ASTM Plate/Sheet/Strip | B709 / ASME SB709 |
| ASTM Seamless Tube | B668 / ASME SB668 |
| ASTM Bar & Forgings | B409, B462 |
| EN Standard | EN 10088-3 |
2. Chemical Composition (wt%, ASTM Standard Range)
| Element | Range (wt%) | Key Function |
|---|---|---|
| Fe | Balance | Austenitic matrix base |
| Ni | 29.5 – 32.5 | Stabilizes austenite; resists SCC and reducing acid attack |
| Cr | 26.0 – 28.0 | Forms dense Cr₂O₃ passive film; foundation of pitting and oxidation resistance |
| Mo | 3.0 – 4.0 | Enhances resistance to pitting and crevice corrosion in chloride media |
| Cu | 0.6 – 1.4 | Significantly boosts resistance to sulfuric acid and phosphoric acid |
| C | ≤0.030 | Ultra-low carbon prevents intergranular corrosion after welding |
| Si | ≤1.00 | Deoxidation element |
| Mn | ≤2.50 | Deoxidation and microstructure stabilizer |
| P | ≤0.030 | Strict impurity control for hot workability |
| S | ≤0.030 | Prevents hot cracking |
| N | ≤0.11 | Auxiliary pitting resistance reinforcement |
3. Physical Properties (Solution-Annealed Condition)
| Property | Typical Value | Unit |
|---|---|---|
| Density | 8.0 | g/cm³ |
| Melting Range | 1311 – 1366 | °C |
| Mean CTE (20 – 100 °C) | 17.2 × 10⁻⁶ | /°C |
| Thermal Conductivity (20 °C) | ~12.5 | W/(m·K) |
| Modulus of Elasticity | 195 | GPa |
| Maximum Continuous Service Temperature | ≤593 °C | — |
| Magnetic Property | Non-magnetic* | — |
Note: Long-term exposure above 593 °C can cause microstructural embrittlement. Alloy 28 is not recommended for high-temperature structural applications.
4. Mechanical Properties (Minimum Guaranteed, Solution-Annealed)
| Property | Minimum Value |
|---|---|
| Ultimate Tensile Strength (Rm) | ≥500 MPa |
| 0.2% Yield Strength (Rp0.2) | ≥214 MPa |
| Elongation (A%) | ≥40% |
| Brinell Hardness | ≤230 HB |
5. Core Corrosion Advantages
- Superior Dual Acid Resistance – The Cu-Mo synergy delivers excellent performance in both oxidizing media (nitric acid) and reducing environments (sulfuric, phosphoric, and mixed acids).
- High PREN Value – Outstanding pitting and crevice corrosion resistance in seawater, brine, and chloride-laden process streams, far exceeding standard 316L and 904L stainless steels.
- Immunity to Chloride SCC – Exceptional resistance to chloride-induced stress corrosion cracking under even severe evaporative conditions.
- No Post-Weld Sensitization – Ultra-low carbon content (≤0.03%) eliminates intergranular corrosion risk in as-welded condition; no solution anneal is required for general corrosion service.
- Sour Gas & Flue Gas Resistance – Performs reliably in environments containing H₂S, SO₂, and acidic condensates.
6. Heat Treatment & Fabrication Guidelines
6.1 Standard Heat Treatment (Solution Annealing)
- Heat to 1093 – 1149 °C, hold until uniformly soaked, then rapid air cool or water quench. This produces a fully austenitic structure with maximum ductility and restored corrosion resistance.
- Alloy 28 is not age-hardenable; strength can only be increased by cold working.
6.2 Hot & Cold Working
- Hot Working – Forge at 1150 – 950 °C; finishing temperature must be above 950 °C to avoid brittle phase precipitation.
- Cold Forming – Good ductility; moderate work hardening rate. Heavy deformation (e.g., deep drawing) requires intermediate solution annealing to restore ductility.
6.3 Welding
- Applicable Processes: GTAW (TIG), GMAW (MIG), SMAW.
- Recommended Filler Metal: ERNiCrMo-3 / ENiCrMo-3 (also suitable for dissimilar welding with 316L, 904L, Alloy 59, etc.).
- Post-Weld Heat Treatment: Generally unnecessary for standard corrosion service. Optional stress relief at 760 – 800 °C for thick-wall high-pressure components.
6.4 Non-Destructive Testing (NDT)
- Routine UT (Ultrasonic Testing) and PT (Liquid Penetrant Testing) for surface and sub-surface integrity; additional RT or PMI upon request.
7. Typical Applications
- Chemical & Fertilizer Plants – Sulfuric/phosphoric acid reactors, nitric acid coolers, pickling equipment, acid evaporators.
- Flue Gas Desulfurization (FGD) – Scrubbers, outlet ducts, waste acid recovery, industrial wastewater treatment.
- Oil, Gas & Geothermal – Sour gas injection lines, brine heat exchangers, sand screen base pipes, high-chloride downhole components.
- Marine & Desalination – Seawater cooling piping, MSF/MED heat exchangers, offshore platform corrosion-resistant fittings.
- Pharmaceutical & Food Processing – High-purity acid delivery lines, sanitary reactors, mixing vessels.
8. Comparative Analysis with Other Corrosion Alloys
| Feature | Alloy 28 (N08028) | 904L (N08904) | Alloy 59 (N06059) | C22 (N06022) |
|---|---|---|---|---|
| Nickel Base | Fe-Ni (30% Ni) | Fe-Ni (25% Ni) | Ni-base (59% Ni) | Ni-base (56% Ni) |
| Key Strengths | High Cr, Mo, Cu – superior in H₂SO₄/H₃PO₄ | Cost-effective for mild acid/chloride | Best in concentrated HCl & oxidizing acids | Excellent oxidizing & crevice corrosion |
| Chloride SCC Resistance | Outstanding | Very Good | Excellent | Excellent |
| Typical Use | Chemical acid process, seawater, sour gas | General acid piping, heat exchangers | Strong mixed acids, severe chlorides | Highly oxidizing media, pharma |
| Cost Position | Mid-range, high value for H₂SO₄ service | Lower cost | Premium nickel alloy | Premium nickel alloy |
Summary: Alloy 28 offers an optimal cost-performance balance for sulfuric, phosphoric, and mixed acid environments containing chlorides, filling the gap between high-performance stainless steels and expensive nickel-base alloys.
9. Our Product Range – Alloy 28 (UNS N08028)
We leverage our integrated manufacturing capabilities to supply a full spectrum of Alloy 28 pressure components and semi-finished products:
- Seamless Pipes & Tubes – Per ASTM B668, custom OD/WT, available with EN 10204 3.1 certification.
- Plates, Sheets & Strips – ASTM B709, thickness from 0.5 mm to 50 mm, cut-to-size service.
- Forged Flanges & Fittings – WN, SO, BL, SW per ASTM B462, pressure Class 150–2500.
- Butt-Weld Fittings – Elbows, tees, reducers per ASTM B462/B366 equivalent, SCH10S–SCH80S.
- Round Bars & Forgings – Per ASTM B409, ready for machining of custom components.
All products are supported by full PMI spectral analysis, mechanical testing, and multi-standard NDT reports.
For Alloy 28 (UNS N08028 / 1.4563) — the cost‑effective bridge between super stainless and nickel alloys in H₂SO₄, H₃PO₄ and seawater service — choose C&N / HONGCHENG. Full ASTM B709/B668 range: pipes, plates, flanges, fittings, bars. 3.1 certified, full‑batch traceable. Contact Us for inventory and engineering support.
