What is Alloy 20 Seamless Pipe
Alloy 20 is an austenitic corrosion-resistant alloy containing nickel, chromium, molybdenum and copper, with niobium stabilization. It is considered for sulfuric-acid and other chemically compatible process piping. UNS N08020 identifies the grade; the product specification and inspection requirements must be separately stated.
The grade sits alongside the pure nickel grades on the Nickel and Nickel Alloy Seamless Pipes page, where selection considerations are compared.
Product Specification and Delivery Condition
Alloy 20 seamless pipe and tube are ordered against ASTM B729. The applicable edition, delivery condition and any supplementary requirements must be identified in the enquiry and confirmed in the quotation and purchase order. The tables below set out the composition, mechanical property and equivalent-grade references stated for UNS N08020.
Product Specifications and Data
1. Equivalent Grade
The table below maps Nickel Alloy 20 (UNS N08020) to its equivalent designations in EN/DIN, JIS, ISO, and other international material classification standards.
| Grade | UNS | GB (ISC) | GB (NEW) | JIS | ISO | DIN / EN | GOST |
|---|---|---|---|---|---|---|---|
| Alloy 20 | N08020 | — | — | — | NiCr20CuMo | 2.4660 | — |
2. Chemical Composition
The table below provides the full elemental composition of Nickel Alloy 20. The copper content gives it reducing acid resistance, while niobium stabilizes the alloy against intergranular corrosion after welding. All values are weight percentage (wt%).
| Grade | C | Mn | P | S | Si | Ni | Cr | Mo | Cu | Nb+Ta | Fe |
|---|---|---|---|---|---|---|---|---|---|---|---|
| UNS N08020 | ≤0.07 | ≤2.0 | ≤0.045 | ≤0.035 | ≤1.00 | 32.00 – 38.00 | 19.00 – 21.00 | 2.00 – 3.00 | 3.00 – 4.00 | 8 × C – 1.00 | BAL |
Grade N08020 to standard B729. The niobium addition stabilizes the alloy against sensitization, and the copper addition provides resistance in reducing acid environments.
3. Mechanical Properties
The mechanical values below apply to Nickel Alloy 20 pipe and tube in the solution-annealed condition. This is the standard delivery state for acid corrosion service.
| Grade | Standard | Tensile Strength (Min) | Yield Strength (Min) | Elongation (Min) |
|---|---|---|---|---|
| N08020 | B729 | ≥550 MPa (80 ksi) | ≥240 MPa (35 ksi) | ≥30 % |
Important Specification Status
ASTM lists B729-20 as withdrawn in 2026, with no replacement. A legacy project may reference a historical edition, but its use must be explicitly accepted by the purchaser, supplying mill and relevant project requirements. Do not assume that an existing ASTM reference establishes compliance with a current specification or an ASME construction code.
For a new enquiry, provide the engineering specification, intended service and required code basis. The quotation must identify the agreed acceptance basis, heat treatment, dimensions, testing and documents. An alternative specification must not be substituted without confirming that it covers the actual grade and product form.
Acid-Service Selection
Alloy 20 is associated with sulfuric-acid resistance, but acid concentration alone does not define suitability. Include temperature, contaminants, chloride content, aeration, flow conditions and any corrosion-rate limit. Avoid treating a stated concentration range as an unconditional operating envelope.
Fabrication Considerations
Niobium stabilization supports resistance to sensitization. Welding procedures, filler selection and any post-weld requirements must follow the project requirements and qualified fabrication practice. Seamless construction does not guarantee immunity to localized corrosion or a higher pressure rating.
Primary Applications
Alloy 20 seamless pipe is used in the following services.
Sulfuric Acid Plants
Absorption towers, acid coolers, heat exchanger shells and tubes, and pump casings in contact-process and dual-absorption H2SO4 plants handling concentrated acid at temperatures from ambient to 100°C.
Pharmaceutical Manufacturing
Reactor vessels, transfer piping, and centrifuge components in pharmaceutical synthesis processes that use sulfuric acid as a catalyst or reactant. Preventing product contamination from metallic dissolution is a primary concern.
Pickling and Acid Cleaning Systems
Immersion tanks, fume hoods, and overflow piping in hot dilute H2SO4 pickling baths used for steel mill scale removal and metal preparation.
Synthetic Fiber Production
Acid recovery piping, spinning bath heat exchangers, and process vessels in viscose rayon and nylon manufacturing where concentrated sulfuric acid and zinc sulfate solutions coexist at elevated temperatures.
Explosives and Fertilizer Industry
Nitration and neutralization process piping in the production of ammonium sulfate, ammonium nitrate, and nitric acid-sulfuric acid mixed acid streams. Alloy compatibility with fluctuating acid composition is required.
Frequently Asked Questions
Is ASTM B729 still an active standard?
ASTM lists B729-20 as withdrawn in 2026 with no replacement. Confirm the current project acceptance basis before placing an order.
Can a legacy project still request B729-20?
The request must be reviewed and explicitly accepted against the contract and engineering requirements. The quotation should state the historical edition rather than describe it as current.
Is Alloy 20 automatically suitable for sulfuric acid service?
No. The temperature, concentration, contaminants and required corrosion performance must be evaluated together.
Can Alloy 20 be supplied under another ASTM number?
Only after the scope, grade coverage, product form and acceptance requirements have been verified and accepted. A different standard number is not an automatic substitute.
Technical References
Specification status: ASTM B729-20 official record. Material background: Carpenter Technology 20Cb-3 Alloy 20 information. A trade name does not establish the manufacturer or origin of the supplied pipe.
Specification Control and Dimensions
The quotation and purchase order must identify the material grade, product specification and edition, delivery condition, dimensions and acceptance requirements. Chemical analysis, mechanical test results and dimensional inspection must be assessed against the agreed requirements for the supplied heat and product form.
Available dimensions are confirmed for the requested grade, outside diameter, wall thickness, length and delivery condition. Catalogue dimensions are not a guarantee that every size combination is available or held in stock. Dimensional tolerances, straightness, wall basis and cut-length tolerances are confirmed against the ordered specification.
Inspection and Traceability
State the inspection document type and any supplementary inspection in the enquiry. The agreed documentation should link the supplied material and heat marking to the material test results. Hydrostatic testing, nondestructive examination and supplementary tests are governed by the product specification and purchase order; test methods, coverage and acceptance criteria must be stated rather than assumed.
PMI can support alloy identification but does not replace the full chemical analysis or the material test certificate. Where carbon content distinguishes the ordered grade, use a chemical analysis method capable of measuring carbon. Specify any EN 10204 3.1 or 3.2 documentation and third-party witnessing before order confirmation; availability and scope are subject to agreement.
Design and Service Assessment
Seamless construction means the product has no longitudinal weld seam. It does not establish a universal pressure rating or corrosion guarantee. Design pressure, temperature and service life depend on the applicable code, dimensions, allowable stress, corrosion allowance, joint details and operating conditions. Typical material data must not be used as design allowable stresses.
Request a Quotation for Pipe
Send the grade and UNS designation; product specification and edition; NPS and schedule with the applicable dimensional standard, or actual OD and wall thickness; quantity; length; delivery condition; end finish; required inspection documents; and delivery destination. Include the operating medium, concentration, temperature and pressure when service suitability needs assessment. State the required delivery date so supply options can be reviewed.
Supplier Information
Wenzhou Xinzhe Tech Co., Ltd. is a China-based stockist and supplier of seamless stainless steel, duplex, super duplex, and nickel alloy pipes and tubes. Supply scope, specification, inspection documents and delivery terms are confirmed in the quotation.
