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UNS N08020, N08024 and N08026 Seamless Nickel Alloy Pipe
Dongmeng Group supplies seamless nickel-iron-chromium-molybdenum-copper alloy pipe and tube in UNS N08020, UNS N08024 and UNS N08026 for chemical processing, sulfuric-acid systems, pickling equipment, heat exchangers and other corrosive-service applications.
Products can be supplied hot finished or cold worked, with controlled heat treatment, material traceability, dimensional inspection and hydrostatic or nondestructive examination.
Important Standard Notice: ASTM B729-20 was withdrawn by ASTM International on March 12, 2026, without a replacement standard. New orders must identify whether the purchaser accepts the historical ASTM B729-20 requirements or requires another current project, ASME, engineering or customer specification. ASTM B829-24 remains an active general-requirements standard, but it does not independently replace ASTM B729-20.
What Are N08020, N08024 and N08026?
These three materials are corrosion-resistant iron-nickel-chromium alloys containing different levels of molybdenum, copper, niobium and nitrogen.
They are related by historical ASTM product coverage but should not all be described simply as "Alloy 20."
UNS N08020
UNS N08020 is the material commonly known as Alloy 20 or Carpenter 20Cb-3.
It contains approximately:
32–38% nickel
19–21% chromium
2–3% molybdenum
3–4% copper
Niobium plus tantalum stabilization
N08020 was developed for sulfuric-acid service and also provides useful resistance in environments containing chlorides, nitric acid and phosphoric acid.
Special Metals lists mixing tanks, heat exchangers, process piping, pickling equipment, pumps, valves and fittings among its representative applications.
UNS N08024
UNS N08024 contains higher nickel, chromium and molybdenum than N08020, with lower copper and a controlled niobium addition.
It should be identified by its exact UNS designation unless a traceable manufacturer trade name is shown on the material certificate.
Do not describe N08024 as "Alloy 20Cb-3." Carpenter Technology identifies 20Cb-3 as UNS N08020.
UNS N08026
UNS N08026 is commonly associated with Carpenter 20Mo-6.
It contains approximately 5.0–6.7% molybdenum together with chromium, nickel, copper and nitrogen.
Carpenter describes N08026 as resistant to hot, low-pH chloride environments, with good resistance to pitting, crevice corrosion and chloride stress-corrosion cracking. It is intended to complement N08020 where higher localized-corrosion resistance is required.
UNS N08020 / N08024 / N08026 Overview
Available Grades: UNS N08020 / N08024 / N08026
Product Forms: Seamless Pipe / Seamless Tube / Cut-Length Tube
Legacy Product Specification: ASTM B729-20
Current General Requirements: ASTM B829-24, where contractually applicable
Manufacturing Route: Hot Finished / Cold Worked / Cold Drawn
Heat Treatment: Stabilized Annealed / Solution Annealed / Annealed
Typical Pipe Range: OD 10.3–219.1 mm / Wall 1.2–12.7 mm
Typical Tube Range: OD 9.53–152.4 mm / Wall 0.889–8.56 mm
Length: Random Length / Fixed Length / Project-Specific Length
Ends: Plain / Deburred / Beveled / Machined
Surface: Pickled / Bright Annealed / Mechanically Finished
Testing: Hydrostatic / Eddy Current / Ultrasonic / PMI
Documents: EN 10204 3.1 MTC / NDT Report / Dimensional Report
Processing: Cutting / Beveling / Bending / Machining / Custom Marking
All dimensions and alloy availability must be confirmed against the selected mill, manufacturing route and project specification before order acceptance.
ASTM B729 Standard Status
ASTM B729-20 historically covered seamless, cold-worked or hot-finished pipe and tube in:
UNS N08020
UNS N08024
UNS N08026
The products were intended for general corrosive service.
ASTM officially withdrew B729-20 in March 2026 without publishing a direct replacement. It should therefore be described as a former or legacy specification, not as a current active ASTM standard.
How New Orders Should Be Specified
A new purchase order should state one of the following:
ASTM B729-20 legacy requirements accepted by the buyer
Current ASME/BPVC specification and edition
Customer material specification
Approved engineering data sheet
Alternative current material and pipe standard
Additional requirements based on ASTM B829-24
For pressure-equipment projects, the buyer must confirm that the selected material specification is permitted by the applicable design code.
ASTM B829-24 contains active general requirements for nickel and nickel-alloy seamless pipe and tube, including dimensional, inspection and testing provisions. However, it is a general specification and does not itself define the alloy-specific product requirements previously contained in B729.
Alloy Comparison
| Item | UNS N08020 | UNS N08024 | UNS N08026 |
| Common Identification | Alloy 20 / 20Cb-3 | Specify by UNS number | 20Mo-6 |
| Nickel | 32.0–38.0% | 35.0–40.0% | 33.0–37.2% |
| Chromium | 19.0–21.0% | 22.5–25.0% | 22.0–26.0% |
| Molybdenum | 2.0–3.0% | 3.5–5.0% | 5.0–6.7% |
| Copper | 3.0–4.0% | 0.5–1.5% | 2.0–4.0% |
| Stabilizing Addition | Nb + Ta | Nb | Nitrogen |
| Historical Heat Treatment | Stabilized annealed | Annealed | Solution annealed |
| Main Selection Direction | Sulfuric-acid and mixed chemical service | Higher-alloy composition with Nb stabilization | More severe chloride and localized-corrosion conditions |
The table is a preliminary comparison only. Final material selection requires corrosion data for the actual process solution.
Chemical Composition
| Element | UNS N08020 | UNS N08024 | UNS N08026 |
| Carbon, max. | 0.07% | 0.03% | 0.03% |
| Manganese, max. | 2.00% | 1.00% | 1.00% |
| Phosphorus, max. | 0.05% | 0.04% | 0.03% |
| Sulfur, max. | 0.04% | 0.04% | 0.03% |
| Silicon, max. | 1.00% | 0.50% | 0.50% |
| Nickel | 32.00–38.00% | 35.00–40.00% | 33.00–37.20% |
| Chromium | 19.00–21.00% | 22.50–25.00% | 22.00–26.00% |
| Molybdenum | 2.00–3.00% | 3.50–5.00% | 5.00–6.70% |
| Copper | 3.00–4.00% | 0.50–1.50% | 2.00–4.00% |
| Niobium + Tantalum | 8 × C to 1.00% | 0.15–0.35% Nb | - |
| Nitrogen | - | - | 0.10–0.16% |
| Iron | Balance | Balance | Balance |
These are the historical ASTM B729-20 composition limits. Final acceptance must follow the heat-specific MTC and the specification stated in the purchase order.
Historical Heat-Treatment Requirements
Under former ASTM B729-20, the three grades had different required material conditions.
| Grade | Historical Delivery Condition | Recommended Annealing Range |
| UNS N08020 | Stabilized annealed | 982–1010°C |
| UNS N08024 | Annealed | 1052–1079°C |
| UNS N08026 | Solution annealed | 1121–1204°C |
The material was to be water quenched or rapidly cooled by another suitable method after annealing.
Heat-treatment records should identify:
Furnace batch
Heating temperature
Holding time
Cooling method
Material heat number
Tube dimensions
Final material condition
The heat-treatment ranges above come from the withdrawn ASTM B729-20 requirements and must not be applied automatically to another governing specification.
Historical Minimum Mechanical Properties
Former ASTM B729-20 specified the following minimum room-temperature properties for the covered grades:
| Property | Historical Minimum |
| Tensile Strength | 550 MPa |
| 0.2% Yield Strength | 240 MPa |
| Elongation | 30% |
These values are historical product-specification minima rather than universal design values.
Actual properties may vary with:
Alloy grade
Hot- or cold-finished condition
Tube dimensions
Heat-treatment procedure
Amount of cold work
Test-piece geometry
Applicable project standard
For reference, Special Metals publishes typical annealed N08020 values of approximately 620 MPa tensile strength, 300 MPa yield strength and 40% elongation, but these typical figures are not substitutes for contractual minimum requirements.
Recommended Product Specifications
| Parameter | Available Requirement |
| Product | Seamless pipe or seamless tube |
| Grades | N08020, N08024 and N08026 |
| Historical Product Standard | ASTM B729-20, withdrawn |
| General Requirements | ASTM B829-24, when contractually applicable |
| Pipe Ordering Method | NPS and schedule or specified OD and wall |
| Tube Ordering Method | OD × average or minimum wall thickness |
| Typical Pipe OD | 10.3–219.1 mm |
| Typical Pipe Wall | 1.2–12.7 mm |
| Typical Tube OD | 9.53–152.4 mm |
| Typical Tube Wall | 0.889–8.56 mm |
| Length | Random, fixed or drawing-specific |
| Manufacturing | Hot finished, cold worked or cold drawn |
| Surface | Pickled, bright annealed or mechanically finished |
| Ends | Plain, deburred, beveled or machined |
| Inspection | Hydrostatic or nondestructive examination |
| Documentation | MTC, heat-treatment record and inspection report |
Do not publish the current page's unsupported statements of:
6–610 mm seamless tube
1/8–30 inch pipe
Schedule 5 through Schedule 160 for every grade
unless each range is supported by an identified production mill and current manufacturing route.
N08024 and N08026 are significantly less common than N08020, so their size range and minimum production quantity should be confirmed before quotation.
Pipe vs Tube Ordering
Seamless Pipe
Pipe is generally ordered using:
Nominal pipe size
Schedule or specified wall
Length
End preparation
Test method
Applicable piping code
Example:
UNS N08020, NPS 2, Schedule 40, 6 m, beveled ends
Seamless Tube
Tube is normally ordered using:
Actual outside diameter
Average or minimum wall thickness
Length
Dimensional tolerance
Surface condition
NDT requirement
Example:
UNS N08020, 38.1 × 2.77 × 6000 mm seamless tube
Former ASTM B729 required the purchaser to identify pipe by standard pipe size and schedule, and tube by outside diameter with average or minimum wall thickness.
Manufacturing Process
A typical seamless nickel-alloy tube manufacturing route includes:
Alloy billet and heat-number verification
Billet conditioning and heating
Hot piercing or extrusion
Hot rolling or pilger processing
Pickling and intermediate cleaning
Cold drawing or cold pilgering when required
Final annealing or solution treatment
Rapid cooling
Straightening
Dimensional calibration
Surface finishing
Hydrostatic or nondestructive testing
Final inspection and marking
Export packaging
Special Metals notes that cold-worked seamless nickel-alloy tubing can be manufactured through tube reduction or cold drawing according to the alloy, size and required finish.
Hydrostatic and Nondestructive Testing
Under the former B729 requirements, every pipe or tube had to receive either:
A hydrostatic test; or
A nondestructive electric test
The manufacturer could select the method unless the purchase order specified otherwise.
The historical specification required:
One chemical analysis per lot
One mechanical-property test per lot
Hydrostatic or electric examination on every piece
ASTM B829-24 remains the active general-requirements specification for seamless nickel and nickel-alloy pipe and tube and can provide the agreed test framework when contractually referenced.
Available project inspection can include:
Hydrostatic testing
Eddy-current testing
Ultrasonic testing
Positive Material Identification
Outside-diameter measurement
Wall-thickness inspection
Straightness inspection
Surface inspection
End-preparation inspection
Third-party witnessing
The purchase order should state the selected NDT method and acceptance level.
Corrosion-Resistance Considerations
Sulfuric Acid
N08020 was specifically developed for sulfuric-acid environments.
Its nickel, chromium, molybdenum and copper content provides resistance across many sulfuric-acid concentrations and temperatures. However, corrosion performance changes according to concentration, temperature, aeration, contaminants, velocity and heat-transfer conditions.
Chloride Environments
N08020 provides useful resistance to chloride stress-corrosion cracking compared with conventional 300-series stainless steel.
N08026 contains substantially more molybdenum and controlled nitrogen, making it the stronger preliminary candidate where pitting, crevice corrosion and hot, low-pH chloride exposure are the main concerns.
Phosphoric and Mixed Acids
N08020 and N08026 may be considered for selected phosphoric-acid and mixed chemical environments.
Material selection must use corrosion data that represents the actual:
Acid concentration
Temperature
Contamination
Oxidation potential
Flow velocity
Deposits
Crevice geometry
Heat-transfer surface
Do not select an alloy from the acid name alone.
N08020 vs N08026
| Selection Factor | N08020 | N08026 |
| Nickel | 32–38% | 33–37.2% |
| Chromium | 19–21% | 22–26% |
| Molybdenum | 2–3% | 5–6.7% |
| Copper | 3–4% | 2–4% |
| Nitrogen | Not specified | 0.10–0.16% |
| Main Strength | Sulfuric-acid and general chemical resistance | Increased localized-corrosion resistance |
| Typical Concern | Severe hot chloride pitting may require higher alloy | Higher material cost and lower availability |
| Commercial Availability | More widely available | More limited |
N08026 complements N08020 rather than universally replacing it. Carpenter describes 20Mo-6 as intended for service requiring stronger pitting and crevice-corrosion performance than 20Cb-3.
Fabrication and Welding
N08020 can be formed and welded using suitable nickel-alloy fabrication practices.
Its niobium stabilization helps reduce carbide-related sensitization, allowing many correctly welded fabrications to enter corrosive service without a separate post-weld anneal. This does not remove the need for a qualified welding procedure.
Welding requirements should specify:
Base-alloy UNS number
Qualified WPS and PQR
Filler-metal designation
Heat input
Interpass temperature
Joint cleaning
Shielding gas
Back purging
Heat-tint removal
Pickling or passivation
Final NDT
Special Metals lists nickel-alloy welding consumables for N08020, including several nickel-chromium-molybdenum filler systems. Final filler selection must be made by the project welding engineer.
Do not weld N08020, N08024 and N08026 using one generic procedure without confirming the exact base material and service requirements.
Typical Applications
These alloys may be considered for:
Sulfuric-acid process piping
Chemical process plants
Pickling equipment
Acid transfer lines
Heat exchangers
Mixing tanks
Distillation equipment
Pharmaceutical production
Fertilizer processing
Phosphoric-acid systems
Petroleum processing
Pumps and valves
Flue-gas scrubber equipment
Solvent and organic-chemical production
Custom corrosion-resistant piping assemblies
Special Metals identifies process piping, heat exchangers, mixing tanks, pickling equipment, pumps, valves and fittings as representative N08020 applications.
N08026 may be considered for more severe chloride, scrubber and wet-process phosphoric-acid environments, subject to project-specific corrosion evaluation.
Quality Control
Inspection can be arranged according to the approved purchase specification and inspection and test plan.
Available controls include:
Heat-number and material-grade verification
Chemical-composition review
PMI testing
Heat-treatment record verification
Tensile and yield testing
Elongation testing
Outside-diameter measurement
Wall-thickness inspection
Ovality and straightness inspection
Surface and end inspection
Hydrostatic testing
Eddy-current or ultrasonic testing
Final marking inspection
Third-party witnessing
Available Documentation
EN 10204 3.1 Mill Test Certificate
Chemical analysis report
Mechanical test report
Heat-treatment record
Hydrostatic test report
Eddy-current test report
Ultrasonic test report
PMI report
Dimensional inspection report
Certificate of Conformity
Heat-number list
Third-party inspection report
Packing list
The required documentation package must be confirmed before production.
Packaging and Traceability
Nickel-alloy seamless tubes can be packed with:
Plastic end caps
Waterproof wrapping
Individual sleeves
Foam or paper separators
Steel or wooden support frames
Reinforced wooden cases
Desiccant for sea shipment
Heat-number identification
Grade and dimension tags
Customer-specific shipping marks
The heat number should remain traceable between:
Pipe marking
MTC
Heat-treatment record
NDT report
Packing list
Bundle identification
Why Choose Dongmeng Group?
Dongmeng Group supports corrosion-resistant alloy projects with:
N08020 seamless pipe and tube supply
N08024 and N08026 project sourcing
Legacy-standard technical review
Custom OD and wall-thickness inquiries
Fixed-length cutting
End beveling and machining
PMI and NDT coordination
Heat-number traceability
Third-party inspection
Project documentation packages
Export seaworthy packaging
FOB, CFR, CIF and DDP shipping support
Every inquiry should be reviewed against the current project specification before material is offered as ASTM-, ASME- or code-compliant.
Request a Technical Quote
Please provide:
Required UNS grade
Governing specification and edition
Confirmation of legacy ASTM B729-20 acceptance
Pipe or tube
NPS and schedule or actual OD × wall
Average or minimum wall requirement
Length
Quantity
Manufacturing condition
Heat-treatment requirement
Surface finish
End preparation
Hydrostatic or NDT requirement
Design code
Design temperature
Process fluid and concentration
Required documentation
Destination port or delivery address
Company: Dongmeng Group
Email: office@dongmjd.com
Phone / WhatsApp: +86 157 6921 4734
Website: www.cndmmetal.com
Frequently Asked Questions
Is ASTM B729 still active?
No. ASTM B729-20 was withdrawn on March 12, 2026, without a replacement. It can only be used as a historical or contractually accepted legacy specification.
Does ASTM B829 replace ASTM B729?
No. ASTM B829-24 is an active general-requirements standard for nickel-alloy seamless pipe and tube. It does not independently provide all alloy-specific requirements formerly contained in B729.
Can material still be supplied to ASTM B729-20?
A manufacturer may contractually produce material to the historical technical requirements if the buyer, design authority and applicable code permit it. The order should clearly state the 2020 edition and all supplementary requirements.
Is N08024 the same as Alloy 20Cb-3?
No. Carpenter identifies 20Cb-3 or Alloy 20 as UNS N08020. N08024 should be specified using its exact UNS designation unless a traceable proprietary name is confirmed.
What is N08026?
N08026 is commonly associated with 20Mo-6, a higher-molybdenum alloy designed for stronger pitting, crevice-corrosion and chloride-environment performance than conventional Alloy 20.
Are all three alloys called Alloy 20?
No. N08020 is the grade generally called Alloy 20. N08024 and N08026 have different chemical compositions and should be identified by their exact UNS numbers.
What was the minimum tensile strength under ASTM B729-20?
The historical minimum tensile strength was 550 MPa, with minimum yield strength of 240 MPa and minimum elongation of 30%.
Was every pipe hydrostatically tested?
Former ASTM B729 required every piece to receive either a hydrostatic test or a nondestructive electric test. The manufacturer selected the method unless the purchase order specified otherwise.
Is N08020 suitable for sulfuric acid?
N08020 was developed for sulfuric-acid environments, but suitability depends on acid concentration, temperature, aeration, contaminants, velocity and heat-transfer conditions.
When should N08026 be considered?
N08026 can be considered where higher molybdenum and stronger localized-corrosion resistance are required, particularly in hot, low-pH chloride environments. Final selection requires project corrosion data.
Can you supply beveled or machined ends?
Yes. Plain, deburred, beveled and drawing-specific machined ends can be reviewed according to tube dimensions and order quantity.
What documents can be supplied?
Available documents include MTC, heat-treatment records, hydrostatic or NDT reports, PMI, dimensional inspection, Certificate of Conformity and third-party inspection reports.
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