Alloy 28 (UNS N08028) is a nickel-iron-chromium alloy with molybdenum and copper additions, engineered for exceptional resistance to aggressive acidic media and chloride-induced stress corrosion cracking. It is widely specified for phosphoric acid evaporators, sulfuric acid equipment, and sour gas production where conventional stainless steels are inadequate.
1. Product Specifications & AvailabilityAlloy 28 is available in tubular forms optimized for critical process applications. Forms: Instrument Tube, Precision Tube, Hydraulic Tube, Coiled Tube (seamless and welded executions). Certifications: ISO 9001 and AS9120 certified supplier. Support: Stock lists, free samples, and competitive quotes available upon request.
Chemical Composition| Element | Content (%) |
|---|
| Nickel | 30 - 34 | | Iron | 29 - 40.4 (Balance) | | Chromium | 26 - 28 | | Molybdenum | 3 - 4 | | Manganese | ≤ 2.5 | | Copper | 0.6 - 1.4 (typical) | | Others | Remainder |
Physical & Mechanical Properties| Property | Metric | Imperial |
|---|
| Density | 8.0 g/cm³ | 0.289 lb/in³ | | Tensile Strength (annealed) | 500 MPa | 72.5 ksi | | Yield Strength (annealed) | 214 MPa | 31 ksi | | Elongation at Break (cold worked) | 15-50% | 15-50% | | Modulus of Elasticity | 200 GPa | 29000 ksi | | Hardness (annealed) | 80-90 HRB | 80-90 HRB | | Hardness (cold worked) | 33 HRC max | 33 HRC max |
2. Operating Conditions & Selection CriteriaAlloy 28 is selected specifically for highly aggressive acidic and chloride-containing environments at elevated temperatures. Phosphoric Acid Resistance: Exceptional performance in wet process phosphoric acid (P₂O₅ production). Resists attack in reactor tanks, evaporators, and circulation pumps handling gypsum slurries and acid concentrations up to 54% P₂O₅. Sulfuric Acid Service: Suitable for hot sulfuric acid environments in concentrations typically encountered in chemical processing. Specified for heating equipment, reactor tanks, and inlet piping. Chloride Stress Corrosion Cracking: High nickel and chromium content provides superior resistance to chloride-induced SCC, making it ideal for sour gas production (downhole tubing, separators) and offshore platforms. Temperature Range: Maintains corrosion resistance and mechanical integrity across typical chemical processing temperatures. Suitable for continuous service in elevated temperature acidic environments. Oxidizing/Reducing Balance: Chromium provides resistance to oxidizing media; molybdenum and copper enhance resistance to reducing acids.
3. Fabrication Guidelines & Material ComparisonAlloy 28 can be fabricated using standard techniques with attention to its austenitic structure. Fabrication Guidelines: Welding: Good weldability using gas tungsten arc (GTAW/TIG) and gas metal arc (GMAW/MIG) processes. Use matching or overmatching filler metals to maintain corrosion resistance in the weld zone. Cold Working: Readily cold formed. The alloy work hardens; intermediate annealing may be required for severe forming operations. Annealing: Perform at 1020-1100°C (1870-2010°F) followed by rapid quenching to maintain corrosion resistance and restore ductility. Pickling: Scale removal should be followed by pickling in appropriate acid solutions to restore the passive surface.
Material Comparison: vs. Stainless Steel 317L: Alloy 28 offers significantly higher resistance to phosphoric acid and chloride SCC. The higher nickel and molybdenum content provides superior performance in aggressive media where 317L would corrode or crack. vs. Alloy 20: Alloy 20 (UNS N08020) is optimized for sulfuric acid service. Alloy 28 offers improved resistance to phosphoric acid and higher chromium content for better performance in oxidizing conditions. Alloy 28 is often preferred for phosphoric acid evaporators and sour gas service. vs. Nickel Alloys (e.g., C-276): Alloy 28 offers a cost-effective solution where the extreme corrosion resistance of high-nickel alloys is not required but performance exceeds standard stainless steels.
Primary Applications: Phosphoric acid production: reactor tanks, agitators, impellers, piping, cyclone evaporators, heat exchangers, circulation pumps Sulfuric acid equipment: heating elements, reactor tanks, inlet pipes Oil & gas: downhole tubing, separators, offshore platform equipment for sour gas service Chemical processing: acetic acid handling, vinyl chloride production Nuclear fuel reprocessing Acid production and pickling equipment
Contact & SupportFor detailed specifications, availability, and application guidance for Alloy 28, contact ZYTC Alloy. Our technical team provides material certification and engineering support for chemical processing, oil and gas, and acid-handling applications. Contact Us:Email:daisy@zytcsteel.com WhatsApp/WeChat: +86 17335753350 |
