Alloy 28 at a glance
- Designations: UNS N08028 · Werkstoff 1.4563 · trade name Sanicro 28, one grade, three names.
- Family: high-nickel super-austenitic stainless steel, solution-annealed and non-magnetic.
- Why it exists: a copper-bearing alloy with roughly 3.5% molybdenum, built to stand up to hot sulfuric and phosphoric (wet-process) acid.
- PREN ~38: one rung above 904L on the pitting-resistance ladder.
- ISO-scope specialty: Nandini Steel lists Alloy 28 / Sanicro 28 plate as a declared grade under its ISO 9001:2015 certified scope.
Nandini Steel holds ISO-scope certification for 904L, Alloy 28/Sanicro 28, Incoloy 800 and Hastelloy plate. Every piece of stock is genuine mill material, sourced from Aperam, Outokumpu, Jindal, POSCO, Nippon Steel or JFE. It ships ex-stock, so orders go out right away. Each one comes with an EN 10204 3.1/3.2 mill test certificate.
What is Alloy 28 (Sanicro 28)?
Alloy 28 is a high-nickel super-austenitic stainless steel, a fully austenitic grade alloyed well beyond standard 300-series levels to survive reducing acids that destroy 316L. Its ~31% nickel stabilizes the austenite and lifts chloride stress-corrosion-cracking resistance; ~3.5% molybdenum and ~27% chromium drive pitting and crevice resistance; and roughly 1% copper is the deliberate addition that gives the grade its signature performance in sulfuric acid.
"Sanicro 28" is Sandvik's trade name for this same material, not a separate alloy. On a purchase order or mill test certificate, Alloy 28, Sanicro 28, UNS N08028, and 1.4563 all point to the identical chemistry. High nickel content leads some buyers to call it "Inconel 28," but that grade doesn't exist; specify UNS N08028 instead, and receiving inspection won't flag anything. Alloy 28 belongs among the acid-service nickel-alloy grades, a step up from 904L and in the same company as Alloy 20 and Incoloy 825.
Chemical composition
Alloy 28 conforms to the UNS N08028 chemistry. Its low carbon ceiling (≤0.03%) keeps sensitization in check, so the heat-affected zone of a weld resists intergranular corrosion even without post-weld annealing.
| Element | Symbol | Content (wt%) |
|---|---|---|
| Carbon | C | ≤ 0.030 |
| Chromium | Cr | 26.0 – 28.0 |
| Nickel | Ni | 30.0 – 34.0 |
| Molybdenum | Mo | 3.0 – 4.0 |
| Copper | Cu | 0.6 – 1.4 |
| Manganese | Mn | ≤ 2.0 |
| Silicon | Si | ≤ 1.0 |
| Phosphorus | P | ≤ 0.030 |
| Sulfur | S | ≤ 0.030 |
| Iron | Fe | Balance |
Molybdenum fights off chloride pitting; copper keeps the general corrosion rate down in hot reducing acids. That pairing is the whole point of the alloy. Together, they turn Alloy 28 into a sulfuric- and phosphoric-acid grade, not some general-purpose stainless.
Mechanical properties
Values are typical minima for solution-annealed plate.
| Property | Value (metric) | Value (imperial) |
|---|---|---|
| Tensile strength | ≥ 500 MPa | ≥ 73 ksi |
| Yield strength (0.2% proof) | ≥ 214 MPa | ≥ 31 ksi |
| Elongation (A50) | ≥ 40% | ≥ 40% |
| Hardness | ≤ 90 HRB | ~ 200 HB |
Physical properties
| Property | Value |
|---|---|
| Density | 8.0 g/cm³ |
| Melting range | ~1350 – 1370 °C |
| Thermal conductivity (20 °C) | ~12 W/m·K |
| Mean coefficient of thermal expansion (20–100 °C) | ~14–15 µm/m·°C |
| Modulus of elasticity | ~195 GPa |
| Magnetic response | Non-magnetic (austenitic) |
Corrosion resistance and PREN
Alloy 28 was built to handle the acids that chew through lower grades. It resists hot sulfuric acid across a wide concentration range, and it holds up well in wet-process phosphoric-acid service, which explains why fertilizer and acid plants rely on it so heavily. Copper is what brings the corrosion rate down under these reducing conditions. Molybdenum and chromium, meanwhile, take care of the oxidizing and chloride-bearing side of the same job.
Its pitting resistance equivalent number (PREN = Cr + 3.3 × Mo + 16 × N) is approximately 38, placing it above 904L (~34) and above standard 316 (~24) for resistance to chloride pitting and crevice corrosion. On the orderable PREN ladder it reads: 316 (~24) < 904L (~34) < Alloy 28 (~38), with Alloy 20 (~30) below and Incoloy 825 spanning a ~31–40 band. For sour-gas duty, Alloy 28 can be supplied against NACE MR0175 / ISO 15156; cite the requirement on the order so the heat is delivered in the qualified condition.
Equivalent grades and designations
| System | Designation |
|---|---|
| UNS | N08028 |
| Werkstoff (W.-Nr.) | 1.4563 |
| EN | X1NiCrMoCu31-27-4 |
| Trade name | Sanicro 28 |
| AISI / JIS | No direct common equivalent |
Alloy 28 vs the alternatives
Alloy 28 overlaps with three neighboring acid-service grades. Which one you pick comes down to the specific acid, its temperature, and the chloride load.
| Grade | PREN | Choose it when… |
|---|---|---|
| Alloy 28 (N08028) | ~38 | Hot phosphoric and sulfuric acid together with a chloride pitting risk. |
| Alloy 20 (N08020) | ~30 | Sulfuric-acid pumps, valves and vessels where chloride pitting is secondary. |
| 904L (N08904) | ~34 | Sulfuric acid and high chloride at lower cost, one rung down the ladder. |
| Incoloy 825 (N08825) | ~31–40 | Mixed reducing-and-oxidizing acids and sour service. |
Compare the closest sibling, Alloy 20, when the duty is dominated by sulfuric-acid pump and valve service; step down to 904L super-austenitic when the acid runs cooler and cost matters; and reach for Incoloy 825 when the stream mixes reducing and oxidizing acids or turns sour.
Available forms and sizes
| Form | Availability |
|---|---|
| Plate (lead product) | Ex-stock, immediate dispatch |
| Sheet | Ex-stock, immediate dispatch |
| Pipe & tube (seamless / welded) | Ex-stock, immediate dispatch |
| Round bar | Ex-stock, immediate dispatch |
| Forged fittings & flanges | Ex-stock, immediate dispatch |
All Alloy 28 / Sanicro 28 stock we hold is genuine mill material, kept on the shelf and ready to go out the door the moment an order comes in. Send us your thickness, width, length or bore schedule with an inquiry, and we'll come back with exact sizes and live pricing.
Standards and specifications
- ASTM B709, N08028 plate, sheet and strip.
- ASTM B668, N08028 seamless tube.
- NACE MR0175 / ISO 15156, qualification for sour (H2S) service, supplied on request.
Testing and certification
Every Alloy 28 order ships with an EN 10204 3.1/3.2 mill test certificate reporting the heat chemistry and mechanical results against the applicable standard. Positive material identification (PMI) confirms the grade. Intergranular-corrosion testing to ASTM A262 can be performed where service conditions call for it. Heat and cast numbers carry through to give full material traceability.
Applications
- Fertilizer and wet-process phosphoric-acid plants, digesters, evaporators, filters and heat exchangers exposed to hot phosphoric acid; see fertilizer and acid service.
- Sulfuric-acid service, coolers, piping and vessels that handle hot, concentrated sulfuric acid.
- Oil & gas and pollution control, sour-service components and scrubber internals, where reducing acids and chlorides work together against the metal.
FAQ
What is Alloy 28 used for?
Is Alloy 28 the same as Sanicro 28?
How does Alloy 28 compare with 904L?
Does Alloy 28 come with a mill test certificate?
Request a quote
Nandini Steel keeps Alloy 28 / Sanicro 28 (UNS N08028) on hand as plate, sheet, pipe, tube, round bar, fittings and flanges. It's genuine mill material, ex-stock, ready for immediate dispatch. Every order ships with an EN 10204 3.1/3.2 mill test certificate. Send your grade, form and sizes, and we'll get you live pricing.
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