Seamless Alloy 28 Pipe
What is a Seamless Alloy 28 Pipe?
Seamless Alloy 28 Pipe (UNS N08028, also known as Sanicro 28 or Incoloy 28) is a super-austenitic stainless steel containing 30–34 % nickel, 26–28 % chromium, 3.0–3.5 % molybdenum and about 1 % copper, produced from a solid billet without a welded seam.
This powerful chemistry was engineered for wet-process phosphoric acid service, where the combination of chlorides, fluorides and sulfuric acid destroys conventional stainless steels. The high chromium and molybdenum levels give Alloy 28 a PREN (pitting resistance equivalent) above 40, protecting against the most aggressive localized corrosion.
Manufactured to ASTM B668 with full solution annealing, Alloy 28 seamless pipe is the established material for phosphoric acid evaporators, sulfuric acid coolers and sour-gas handling systems worldwide.
Alloy 28 (Sanicro 28) vs Alloy 825 vs 904L: Wet-Corrosion Specialists
Alloy 28 shares its high-nickel, high-chromium, molybdenum-copper chemistry with the classic wet-corrosion alloys. The comparison shows where the 31 % chromium grade earns its place.
| Grade | Key Chemistry / Condition | Where It Fits |
|---|---|---|
| Alloy 28 / N08028 | 31Cr-27Ni-3.5Mo-1Cu | Outstanding in wet-process phosphoric acid and sulfuric acid; PREN above 40 |
| Alloy 825 | 21Cr-42Ni-3Mo-2Cu-Ti | Broader chemical duties, slightly lower chromium for concentrated phosphoric acid |
| 904L | 20Cr-25Ni-4.5Mo-1.5Cu | Cast-wrought super-austenitic alternative with good sulfuric performance |
| Alloy 625 | Ni 58 %, 20Cr-9Mo-Nb | Highest strength and seawater performance; premium alloying cost |
Product Specifications
Specification data for Seamless Alloy 28 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 B668 / ASME SB668 |
| Welded Tube | ASTM B704 / ASME SB704 |
| UNS Designation | N08028 |
| Werkstoff Number | 1.4563 |
| Common Trade Names | Sanicro 28, Incoloy 28, Nicrofer 3127 hMo |
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 | 0.65 | 3.02 | 0.81 |
| 1/2" | 21.3 | 2.77 | 1.29 | 3.73 | 1.65 |
| 3/4" | 26.7 | 2.87 | 1.72 | 3.91 | 2.24 |
| 1" | 33.4 | 3.38 | 2.55 | 4.55 | 3.3 |
| 1-1/4" | 42.2 | 3.56 | 3.46 | 4.85 | 4.55 |
| 1-1/2" | 48.3 | 3.68 | 4.13 | 5.08 | 5.52 |
| 2" | 60.3 | 3.91 | 5.54 | 5.54 | 7.62 |
| 3" | 88.9 | 5.49 | 11.51 | 7.62 | 15.57 |
| 4" | 114.3 | 6.02 | 16.38 | 8.56 | 22.75 |
| 6" | 168.3 | 7.11 | 28.8 | 10.97 | 43.38 |
| 8" | 219.1 | 8.18 | 43.36 | 12.7 | 65.88 |
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) | 30.0 | 34.0 |
| Chromium (Cr) | 26.0 | 28.0 |
| Molybdenum (Mo) | 3.0 | 3.5 |
| Copper (Cu) | 0.6 | 1.4 |
| Carbon (C) | — | 0.03 |
| Manganese (Mn) | — | 2.0 |
| Silicon (Si) | — | 1.0 |
| Phosphorus (P) | — | 0.03 |
| Sulfur (S) | — | 0.03 |
| Iron (Fe) | Balance | — |
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength, min | 500 MPa (72.5 ksi) |
| Yield Strength (0.2 % offset), min | 220 MPa (32 ksi) |
| Elongation in 2 in. / 50 mm, min | 30 % |
| Hardness (typical) | ≤ 210 HBW |
| Heat Treatment | Solution annealed 1020 – 1120 °C, rapid cooling |
Physical Properties
| Property | Value |
|---|---|
| Density | 8.00 g/cm³ |
| Melting Range | 1350 – 1400 °C |
| Elastic Modulus | 200 GPa |
| Coefficient of Thermal Expansion (20–100 °C) | 13.5 µm/m·°C |
| Thermal Conductivity (at 100 °C) | 11.5 W/m·K |
| Specific Heat Capacity | 500 J/kg·K |
Equivalent Grades
| Standard System | Designation |
|---|---|
| UNS | N08028 |
| Werkstoff Nr. | 1.4563 |
| EN | X1NiCrMoCu31-27-4 |
| Trade Name | Sanicro 28 |
Why Alloy 28 Rules Wet-Process Phosphoric Acid Plants
The chemistry of Alloy 28 was tuned for one of the harshest routine duties in the fertilizer industry: wet-process phosphoric acid, where a fluoride-, chloride- and sulfate-laden liquor at 80-90 °C destroys lesser stainless grades within months. Its 31 % chromium, 27 % nickel, 3.5 % molybdenum and 1 % copper combination delivers a pitting resistance number above 40 and a stable passive film that keeps heat-exchanger tubing in service for years — the reason it is also known as Sanicro 28.
Beyond fertilizer plants, the alloy performs in sulfuric acid at intermediate concentrations, in oilfield downhole service meeting NACE MR0175 sour-gas requirements, and in seawater-cooled heat exchangers. Our seamless Alloy 28 pipe is solution annealed at about 1050-1100 °C and rapid-quenched, with intergranular-corrosion testing per the governing standard available on every lot.
Manufacturing Process
Our seamless production route for Seamless Alloy 28 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 Alloy 28 Pipe is specified in the following industries and services:
- Phosphatic Fertilizer Industry: Evaporator tubing, agitators and transfer piping in wet-process phosphoric acid — the flagship application of Alloy 28.
- Sulfuric Acid Service: Acid coolers, heat exchangers and piping in concentrated and contaminated sulfuric acid systems.
- Oil & Gas (Sour Service): Downhole and surface piping meeting NACE MR0175 for H2S-rich wells.
- Chemical Processing: Mixed-acid systems, pickling plants and chlorinated solvent equipment.
- Seawater Cooling Systems: Heat-exchanger tubing resisting pitting in high-chloride cooling water.
- Nuclear Fuel Reprocessing: Piping exposed to aggressive oxidizing-reducing acid mixtures.
Quality Assurance, Testing and Documentation
Every length of Seamless Alloy 28 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. What makes Alloy 28 different from Alloy 825?
A: Both are Ni-Fe-Cr-Mo super austenitics, but Alloy 28 carries higher chromium (26–28 % vs about 21 %) and molybdenum (3.0–3.5 % vs about 3 %), giving it better resistance in wet-process phosphoric acid, while 825 is optimized for reducing acids and general chemical service.
Q2. Is Alloy 28 pipe qualified for sour oilfield service?
A: Yes. Its chemistry and hardness after solution annealing comply with NACE MR0175/ISO 15156 for H2S-bearing production environments.
Q3. How does Alloy 28 compare with 904L?
A: Alloy 28's higher chromium and molybdenum give it an advantage in oxidizing phosphoric acid, whereas 904L offers higher nickel for reducing-acid duties. Selection depends on the specific acid chemistry and temperature.
Q4. What documentation is supplied with Alloy 28 shipments?
A: EN 10204 3.1 certificates, NACE compliance statements when required, and full dimensional and NDT reports with heat traceability.
Ready to Request a Quotation?
Send us your size range, wall thickness/schedule, standard and quantity for Seamless Alloy 28 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.
