Alloy 28 – UNS N08028
27Cr-31Ni-3.5Mo-Cu super-austenitic stainless steel
Alloy 28 (UNS N08028, W.Nr. 1.4563) is a high-Cr, high-Ni super-austenitic alloy with Mo and Cu, for strong acids (wet-process phosphoric, sulfuric) and media with chlorides and H2S. It is also sold as Sanicro® 28 (Alleima). Excellent resistance to stress corrosion and intergranular corrosion; used in OCTG tubing for sour wells.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | N08028 |
| W.Nr./EN | 1.4563 (X1NiCrMoCu31-27-4) |
| DIN | X1NiCrMoCu31-27-4 |
| Trade names | Alloy 28; also sold as Sanicro 28 (Alleima) |
| Others | SS 2584 |
Standards by product form
| Form | Standard |
|---|---|
| Bar/billet | EN 10088-3 (1.4563) |
| Plate | ASTM B709 |
| Tube | ASTM B668 / ASME SB-668 |
| Sour service | NACE MR0175 / ISO 15156-3 |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7222.30.00 | 7222.30 | 7222.30.0024 | 7222 30 51 |
| Hot-rolled bar | 7222.11.00 | 7222.11 | 7222.11.0059 | 7222 11 11 |
| Plate (> 10 mm, width ≥ 600 mm) | 7219.21.00 | 7219.21 | 7219.21.0020 | 7219 21 10 |
| Seamless pipe | 7304.41.90 | 7304.41 | 7304.41.6045 | 7304 41 00 |
| Welded pipe | 7306.40.00 | 7306.40 | 7306.40.5085 | 7306 40 80 |
Tariff class: stainless steel (by chemical composition, under the Chapter 72 Notes and Section XV Note 5). Fe-Ni-Cr alloy in which iron predominates by weight: under Section XV Note 5 and Chapter 72 Note 1(e) it is classified as stainless steel (7219, 7222, 7304), not as a Chapter 75 nickel alloy.
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM B668
| Element | Range (%) |
|---|---|
| C | ≤ 0.030 (Alleima Sanicro® 28: ≤ 0.020) |
| Mn | ≤ 2.50 |
| P | ≤ 0.030 |
| S | ≤ 0.030 |
| Si | ≤ 1.00 |
| Cr | 26.0 – 28.0 |
| Ni | 30.0 – 34.0 |
| Mo | 3.0 – 4.0 |
| Cu | 0.6 – 1.4 |
| Fe | balance |
Mechanical properties
Solution annealed (ASTM B668; Alleima in parentheses)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 214 MPa (Alleima: ≥ 220) |
| Tensile strength | ≥ 500 MPa (Alleima: 500 – 750) |
| Elongation | ≥ 40% (Alleima: ≥ 35%) |
| Hardness | ≤ 220 HB (Alleima) |
| Impact | ≥ 60 J at –196 °C (Alleima) |
Typical physical properties
| Property | Value |
|---|---|
| Density | 8.0 g/cm³ (typical) |
| Modulus of elasticity | ≈ 200 GPa (typical) |
| Thermal conductivity (20 °C) | ≈ 11 W/m·K (typical) |
| Thermal expansion (20–100 °C) | ≈ 15 µm/m·K (typical) |
| Electrical resistivity | ≈ 1.0 µΩ·m (typical) |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | Cryogenic (–196 °C) up to ≈ 427 °C in pressure vessels (ASME)*; the main application is corrosion at moderate temperature. |
| Heat treatment | Solution annealing 1,080 – 1,150 °C with rapid water quench. |
| Welding | Good. Over-alloyed consumable AWS ER383 (27.31.4.LCu) or ERNiCrMo-3; low heat input. |
| Machining | Machinability lower than carbon steel: it work hardens quickly; use sharp tools, positive rake, constant feed without 'rubbing' and abundant coolant. Behavior close to that of nickel alloys. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Production tubing (OCTG) in wells with H2S, CO2 and chlorides
- Wet-process phosphoric acid production
- Sulfuric acid and evaporators
- Heat exchangers in acidic chloride media
- Replacement of bimetallic or clad tubes
Alternatives: 904L in less severe media (cheaper); 254 SMO for seawater; G-3, 625 or C-276 when H2S and temperature exceed N08028.
Alloy 28: complete guide
What Alloy 28 (UNS N08028) is
Alloy 28 is the generic name of UNS N08028 (W.Nr. 1.4563); the same material is also sold as Sanicro® 28 (Alleima). It belongs to the family of special stainless steels, in the high-chromium, high-nickel super-austenitic group. It is more alloyed than 904L in chromium and nickel and less in molybdenum than the 6Mo alloys, which positions it as a phosphoric acid and oil-well sour service material.
Chemical composition and role of the elements
The high chromium (26 – 28%) gives resistance to oxidizing media and raises the PREN; nickel (30 – 34%) ensures the austenitic structure and resistance to stress corrosion in chlorides and H2S; molybdenum (3 – 4%) is essential for pitting resistance; copper (0.6 – 1.4%) improves behavior in sulfuric and phosphoric acid. Iron is the balance, about 33 – 37%.
Corrosion and limits of use
With a PREN of 36 to 41, it resists chlorides, phosphoric acid contaminated with fluorides and chlorides, dilute sulfuric acid and well environments with H2S, CO2 and chlorides, with NACE MR0175 / ISO 15156 qualification.
Applications
Oil and gas well production tubing and accessories in sour service (OCTG), phosphoric acid and fertilizer production equipment, dilute sulfuric acid exchangers and piping, pulp plant components and machined parts for severe chloride media.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, solution annealing in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of Alloy 28?
Per ASTM B668: C ≤ 0.030 (Alleima Sanicro® 28: ≤ 0.020); Mn ≤ 2.50; P ≤ 0.030; S ≤ 0.030; Si ≤ 1.00; Cr 26.0 – 28.0.
Which standards cover Alloy 28?
Bar/billet: EN 10088-3 (1.4563). Plate: ASTM B709. Tube: ASTM B668 / ASME SB-668. Sour service: NACE MR0175 / ISO 15156-3.
Up to what temperature can Alloy 28 be used?
Cryogenic (–196 °C) up to ≈ 427 °C in pressure vessels (ASME)*; the main application is corrosion at moderate temperature.
Which materials can replace Alloy 28?
904L in less severe media (cheaper); 254 SMO for seawater; G-3, 625 or C-276 when H2S and temperature exceed N08028.
Are Alloy 28 and Sanicro 28 the same material?
Yes. Alloy 28 is the generic name of UNS N08028 (W.Nr. 1.4563); Sanicro® 28 is Alleima's trade name for the same composition. Purchase orders should state the UNS number and the product standard (e.g. ASTM B668 for tube), not only the trade name.
