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Introduction
Alloy 28 (UNS N08028) is a super austenitic stainless steel, specifically designed for sulfuric and phosphoric acid applications, even when contaminated by chlorides and fluorides. The high nickel content improves stress corrosion cracking resistance, while the combined chromium and molybdenum additions drastically increase localized corrosion resistance. N08028 Alloy performs much better than Alloy 825 and can replace the more expensive Alloy 625 in some applications, including sour gas fields.
Alloy 28 seamless pipe and welded tube are widely used in heat exchangers and chemical processing. Alloy 28 round bar, sheet, plate, strip, wire, forgings, flanges, and fittings are also available. N08028 OCTG tubing and casing are common for oil and gas downhole service. The alloy meets ASTM B668, B709, and NACE MR0175 standards for sour gas environments.
Chemical components(%)
Composition | C | Si | Mn | P | S | Cr | Ni | Mo | Cu |
Min | \ | \ | \ | \ | \ | 26.00 | 30.00 | 3.00 | 0.60 |
Max | 0.03 | 1.00 | 2.50 | 0.03 | 0.03 | 28.00 | 34.00 | 4.00 | 1.40 |
Mechanical properties
Rigidity | Tensile strength | Yield strength | Elongation |
HB≤200 | ≥600MPa | ≥300MPa | ≥40% |
Physical properties
Density | Melting points | Specific heat | Magnetism | Resistivity | Thermal conductivity | Linear expansivity |
8.0g/cm3 | 1390-1420℃ | 455J/(Kg.℃） | \ | 1.0Ω·m(20℃) | 14.3W/(m.k)(100℃) | 15.6×10-6/K(0-100℃) |
Alloy 28 (UNS N08028) Available Products and Standard
1. ASTM B668 (Standard Specification for UNS N08028 Seamless Pipe and Tube)
Grade: UNS N08028 / Alloy 28 / Sanicro 28 / 1.4563
Type: Seamless Pipe / Seamless Tube
Size Range:
Seamless Pipe: 6 – 610 mm OD
Seamless Tube: 15.9 – 127 mm OD × 1.65 – 12.70 mm wall thickness
Surface: Annealed, Bright, Pickled
Testing: Chemical analysis, tension test, flaring test, hydrostatic or nondestructive test, dimensional inspection-1
2. ASTM B709 (Standard Specification for UNS N08028 Plate, Sheet, and Strip)
Grade: UNS N08028 / Alloy 28 / Sanicro 28 / 1.4563
Type: Plate / Sheet / Strip (solution-annealed condition)
Size Range:
Plate: 5 – 180 mm thick
Sheet: 0.5 – 5.0 mm thick
Strip: 0.05 – 5.0 mm thick × 5 – 500 mm wide
Surface: Annealed, Pickled, Bright, Polished
Testing: Chemical analysis, mechanical test (tensile strength, yield strength, elongation), hardness test, dimensional inspection-11
3. ASTM B829 (Standard Specification for General Requirements for Nickel Alloy Seamless Pipe and Tube)
Grade: UNS N08028 / Alloy 28 / Sanicro 28 / 1.4563
Type: Seamless Pipe / Seamless Tube / Welded Tube
Size Range: Custom sizes available upon request
Surface: Annealed, Pickled, Bright, Ground
Testing: Chemical analysis, mechanical test (tensile, yield, elongation), hydrostatic test, eddy current test, dimensional inspection
Advantages
(1)Excellent acid resistance: Alloy 28 seamless pipe and welded tube perform exceptionally well in sulfuric and phosphoric acid environments, even when contaminated by chlorides or fluorides.
(2)High stress corrosion cracking resistance: With 31% nickel content, Sanicro 28 round bar and sheet resist chloride-induced stress corrosion cracking, making them ideal for sour gas and offshore applications.
(3)Superior localized corrosion resistance: The combination of 27% chromium and 3.5% molybdenum gives N08028 plate and strip outstanding pitting and crevice corrosion resistance.
(4)Cost-effective alternative: Alloy 28 OCTG tubing and casing perform much better than Alloy 825 and can replace more expensive Alloy 625 in many sour gas fields.
(5)Versatile product forms: Incoloy 028 forging, flanges, fittings, wire, and round bar are readily available to meet various project requirements.
(6)Proven in harsh environments: UNS N08028 seamless pipe meets ASTM B668 and NACE MR0175 standards, ensuring reliable service in chemical processing, petrochemical, and offshore engineering.
Applications
(1)Sulfuric and phosphoric acid production – Alloy 28 seamless tube and pipe are widely used in heat exchangers, evaporators, and reactor vessels handling hot concentrated acids.
(2)Sour gas fields (OCTG) – N08028 OCTG tubing and casing are specified for downhole service in very sour gas environments, where high H₂S and chloride levels require superior corrosion resistance.
(3)Chemical processing industry – Sanicro 28 plate and sheet are used in flue gas desulfurization (FGD) scrubbers, ductwork, and stack liners for power plants and incinerators.
(4)Offshore and marine engineering – Alloy 28 round bar and forgings serve in seawater piping, platform risers, and subsea components requiring resistance to chloride attack.
(5)Petrochemical and refining – Incoloy 028 flanges, fittings, and welded tube are applied in high-pressure process lines, amine treating units, and sour water strippers.
(6)Replacement for higher-cost alloys – Alloy 28 strip and wire are often chosen over Alloy 625 for cost savings without compromising performance in moderately aggressive environments.
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