ASTM B729 UNS N08020 Alloy 20 Seamless Pipe & Tube
We manufacture and supply UNS N08020 Alloy 20 seamless pipes and tubes for chemical processing, sulfuric acid service, heat exchangers and other corrosive industrial applications.
Alloy 20, also known as N08020, Alloy 20Cb-3 or W.Nr. 2.4660, is an iron-nickel-chromium alloy containing copper and molybdenum. It was specifically developed to provide excellent corrosion resistance in many sulfuric-acid-containing environments.
Standard and customized pipe dimensions can be supplied according to project specifications, drawings and required inspection standards.
ASTM B729 Alloy 20 Seamless Pipe
ASTM B729 historically covered UNS N08020 seamless, cold-worked or hot-finished pipe and tube intended for general corrosive service.
Important Standard Update: ASTM B729-20 was withdrawn by ASTM International in March 2026 with no direct replacement.
For existing projects that specifically reference ASTM B729, the applicable contract edition should be confirmed. For new projects, the current material and piping specification required by the engineering design should be verified before production.
Alloy 20 Pipe Supply Range
| Product | Typical Supply |
|---|---|
| Material | UNS N08020 / Alloy 20 |
| Equivalent Designation | Alloy 20Cb-3 / W.Nr. 2.4660 |
| Product | Seamless Pipe / Seamless Tube |
| Legacy Standard | ASTM B729 / ASME SB-729 |
| Typical Size Range | 1/2″–16″ |
| Typical Wall | SCH 10–SCH 160 |
| Manufacturing | Cold Worked / Hot Finished |
| Condition | Stabilized Annealed |
| Length | Random / Fixed / Cut-to-Length |
| Certification | MTC / EN 10204 3.1 available |
The above dimensions represent our typical manufacturing and supply range rather than the dimensional limits of ASTM B729. Larger or special dimensions can be evaluated according to project requirements.
What Is Alloy 20 UNS N08020?
Alloy 20 is an iron-nickel-chromium-molybdenum-copper corrosion-resistant alloy designed particularly for chemical environments containing sulfuric acid.
The combination of nickel, chromium, molybdenum and copper provides resistance to general corrosion and helps improve performance against localized corrosion in demanding chemical environments.
Niobium stabilization also helps reduce susceptibility to intergranular corrosion after fabrication and welding.
Key characteristics include:
- Excellent resistance to many sulfuric acid environments
- Good resistance to phosphoric acid
- Useful resistance in nitric-acid-containing environments
- Resistance to pitting and crevice corrosion
- Good resistance to chloride-related corrosion
- Good weldability and fabrication performance
- Suitable for chemical process piping and equipment
Alloy 20 Chemical Composition
Typical composition limits for UNS N08020 are:
| Element | Composition, wt.% |
|---|---|
| Nickel (Ni) | 32.0–38.0 |
| Chromium (Cr) | 19.0–21.0 |
| Molybdenum (Mo) | 2.0–3.0 |
| Copper (Cu) | 3.0–4.0 |
| Carbon (C) | 0.07 max |
| Manganese (Mn) | 2.00 max |
| Silicon (Si) | 1.00 max |
| Phosphorus (P) | 0.045 max |
| Sulfur (S) | 0.035 max |
| Nb + Ta | 8 × C min, 1.00 max |
| Iron (Fe) | Balance |
The final chemical composition must comply with the specified material standard and purchase specification.
Alloy 20 Pipe Mechanical Properties
Legacy ASTM B729 requirements for UNS N08020 include the following minimum room-temperature mechanical properties:
| Property | Minimum Requirement |
|---|---|
| Tensile Strength | 80 ksi / 550 MPa |
| 0.2% Yield Strength | 35 ksi / 240 MPa |
| Elongation | 30% |
Actual certified values are provided on the material test certificate supplied with the order.
Corrosion Resistance of Alloy 20
The most important application advantage of Alloy 20 pipe is its performance in sulfuric-acid-containing process environments.
Copper contributes to resistance in sulfuric acid, while chromium and molybdenum improve resistance to oxidizing environments and localized corrosion.
Alloy 20 can therefore be considered for equipment handling:
- Sulfuric acid
- Phosphoric acid
- Selected nitric acid environments
- Chloride-containing process fluids
- Chemical process solutions
- Pickling solutions
Material suitability must always be evaluated according to acid concentration, temperature, chloride level, flow conditions and process chemistry.
Alloy 20 Pipe Applications
UNS N08020 seamless pipes and tubes are widely used in:
- Chemical processing plants
- Sulfuric acid production and handling
- Phosphoric acid systems
- Chemical process piping
- Heat exchangers
- Pickling equipment
- Pharmaceutical processing
- Food processing equipment
- Pumps and valves
- Process vessels
- Petrochemical equipment
Inspection & Certification
Alloy 20 seamless pipes can be supplied with complete inspection and material documentation according to project requirements.
Available inspection and certification include:
- EN 10204 3.1 Material Test Certificate
- Chemical composition analysis
- Mechanical property testing
- Dimensional inspection
- Visual inspection
- Hydrostatic testing when specified
- Nondestructive electric testing when required
- PMI testing
- Third-party inspection by customer-appointed agencies
Frequently Asked Questions
What is ASTM B729 Alloy 20 pipe?
ASTM B729 Alloy 20 pipe refers to seamless UNS N08020 pipe historically manufactured according to ASTM B729 for general corrosive service. The specification covered both cold-worked and hot-finished seamless pipe and tube.
Is ASTM B729 still active?
No. ASTM B729-20 was withdrawn in March 2026 with no direct replacement. Existing projects may still reference older editions, but new orders should confirm the governing material standard with the project engineer.
What is Alloy 20 pipe mainly used for?
Alloy 20 pipe is particularly associated with sulfuric acid and chemical-processing applications. It is also used for phosphoric acid systems, heat exchangers, pickling equipment and other corrosive process environments.
Is Alloy 20 better than 316L for sulfuric acid?
Alloy 20 was specifically developed for improved resistance in many sulfuric acid environments and may outperform 316L under certain conditions. However, material selection depends on acid concentration, temperature, contaminants and process conditions, so the alloys should not be compared only by grade name.
Related Products
- ASTM B366 Alloy 20 Pipe Fittings – UNS N08020 elbows, tees, reducers and other corrosion-resistant fittings.
- ASTM B462 Alloy 20 Flanges – UNS N08020 forged flanges for chemical and process piping.
- Alloy 20 Plate & Sheet – N08020 plate and sheet for chemical equipment fabrication.
- Incoloy 825 Pipe & Tube – Nickel-iron-chromium alloy for sulfuric acid, phosphoric acid and corrosive process service.
- Inconel 625 Pipe & Tube – Nickel-chromium-molybdenum alloy for highly corrosive and high-strength applications.
- 904L Stainless Steel Pipe – High-alloy austenitic stainless steel for selected sulfuric acid and chemical applications.
Alloy 20 Pipe Manufacturer
We supply UNS N08020 Alloy 20 seamless pipes and tubes for chemical processing and corrosion-resistant piping projects.
Custom dimensions, fixed lengths, inspection requirements and project-specific documentation can be supplied according to customer drawings and purchase specifications.
For quotation, please specify the material grade, applicable standard and edition, pipe size, wall thickness or schedule, length, quantity and inspection requirements.
