Introduction
ASTM B729 Alloy 20 Seamless Pipe (UNS N08020), also known as Carpenter 20, is a high-performance nickel-iron-chromium austenitic alloy pipe developed for superior corrosion resistance in sulfuric acid and chloride-rich environments. DLSS offers seamless pipes in 101.6 mm OD × 16.15 mm WT × 2616.2 mm length, manufactured to ASTM B729, featuring heavy wall thickness for high-pressure service and a bright annealed surface for enhanced cleanliness and corrosion resistance.
Thanks to its balanced chemical composition, Alloy 20 Seamless Pipe is widely used in chemical plants, petrochemical industries, refineries, and marine environments, where ordinary stainless steels may not perform reliably.
What is Alloy 20 (UNS N08020)?
Alloy 20 is an advanced corrosion-resistant material designed to bridge the gap between stainless steels and higher-cost nickel alloys. Its key composition includes:
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Nickel (Ni): 32–38%
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Chromium (Cr): 19–21%
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Iron (Fe): balance
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Copper (Cu): 3–4%
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Molybdenum (Mo): 2–3%
Key Advantages
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Excellent resistance to sulfuric acid across a wide concentration range
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Protection against chloride stress corrosion cracking
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Resistance to phosphoric acid, nitric acid, and seawater
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Heavy wall thickness provides enhanced durability under high pressure
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Balanced cost-to-performance ratio compared with other nickel alloys
Specifications
| Item | Details |
|---|---|
| Standard | ASTM B729 |
| Material | Alloy 20 (UNS N08020) |
| Type | Seamless Pipe |
| Size | 101.6 mm OD × 16.15 mm WT × 2616.2 mm Length |
| Wall Type | Heavy Wall Thickness |
| Surface Finish | Bright Annealed |
| Condition | Solution Annealed |
| Applications | Sulfuric acid plants, heat exchangers, reactors, marine piping, power generation |
Key Features of ASTM B729 Alloy 20 Seamless Pipe
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Heavy Wall Thickness – suitable for high-pressure, severe service conditions.
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Bright Annealed Finish – smooth, oxide-free surface improves corrosion resistance.
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Sulfuric Acid Resistance – one of the most effective alloys for H₂SO₄ applications.
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Chloride Stress Corrosion Resistance – performs well in seawater and brine.
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Durability – combines strength with corrosion protection for long service life.
Applications
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Chemical Processing Plants – sulfuric and phosphoric acid equipment.
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Petrochemical Industry – reactors, scrubbers, and high-pressure piping.
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Power Generation – condensers and boiler piping exposed to aggressive media.
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Marine & Offshore – seawater cooling and desalination systems.
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Pharmaceutical & Food Industry – clean alloy suitable for sterilization and acidic service.
Alloy 20 vs 904L vs Hastelloy C276 – Comparison
| Item / Material | Alloy 20 (UNS N08020) | 904L Stainless Steel (UNS N08904) | Hastelloy C276 (UNS N10276) |
|---|---|---|---|
| Standard | ASTM B729 / B464 / B468 | ASTM A312 / A213 / A240 | ASTM B622 / B619 / B626 |
| Base Composition | Ni 32–38%, Cr 19–21%, Cu 3–4%, Mo 2–3%, Fe balance | Ni 23–28%, Cr 19–23%, Mo 4–5%, Cu ~1.5%, Fe balance | Ni (balance), Cr 15–17%, Mo 15–17%, W ~3.5%, Fe 4–7% |
| Corrosion Resistance | Excellent in sulfuric acid, phosphoric acid, chlorides | Good resistance to chlorides and sulfuric acid, better than 316L | Outstanding in reducing acids and aggressive chemicals |
| Stress Corrosion Cracking | Good resistance in chloride service | Moderate, improved over conventional stainless steels | Excellent, highly resistant to chloride SCC |
| Temperature Range | Effective up to ~550°C | Effective up to ~450°C | Stable up to ~1250°C |
| Cost Level | Medium | Lower (more affordable than Alloy 20 or Hastelloy) | High |
| Typical Applications | – Sulfuric acid service – Heat exchangers – Chemical reactors – Marine piping |
– Marine piping – Storage tanks – Food & pharma equipment – Heat exchangers |
– Chemical reactors – Pollution control – Flue gas scrubbers – Offshore oil & gas |
| Summary | Best choice for sulfuric acid & mixed acids | Cost-effective upgrade from stainless steels | Best for the harshest reducing environments |
Professional Summary
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Alloy 20 – the optimal choice for sulfuric acid handling and mixed acid service, balancing cost and performance.
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904L Stainless Steel – economical upgrade from 316L, suitable for moderate chloride environments.
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Hastelloy C276 – premium alloy for the most aggressive reducing acids and offshore chemical service.
Choose Alloy 20 for sulfuric acid and high-pressure chemical systems.
Choose 904L for a cost-effective stainless alternative.
Choose C276 where maximum corrosion resistance is essential.
Why Choose DLSS?
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Expertise in supplying nickel alloy seamless pipes including Alloy 20, Incoloy, Inconel, Monel, Hastelloy.
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Strict Quality Control – Eddy Current, Hydrostatic, Ultrasonic, and PMI testing.
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Third-Party Certification – SGS, BV, TUV available.
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Export Packaging – capped, wrapped, ISPM-15 wooden cases.
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Global Projects – supplied to sulfuric acid plants, refineries, desalination, and marine cooling systems.
