ASTM B729 UNS N08020 Alloy 20 Seamless Nickel Alloy Pipe with Corrosion Resistance and Stabilized Annealed Treatment

ASTM B729 UNS N08020 Alloy 20 Seamless Pipe is a nickel-iron-chromium-molybdenum-copper alloy pipe designed for demanding corrosive service. UNS N08020 is commonly known as Alloy 20 or Carpenter 20, and is particularly associated with process environments involving sulfuric acid and other aggressive chemical media.

The seamless construction provides a continuous pipe wall without a longitudinal weld seam, making it suitable for process piping systems where corrosion resistance, dimensional integrity and material traceability are important.

Our Alloy 20 seamless pipes can be supplied according to ASTM B729 requirements, with customized outside diameter, wall thickness, length, end preparation and inspection requirements.

Material note: UNS N08020 is Alloy 20 / Carpenter 20. It should not be classified as Hastelloy.

Alloy 20 is a nickel-iron-chromium alloy containing molybdenum and copper. Its alloying system is designed for resistance to a range of corrosive chemical environments.

The addition of chromium contributes to general corrosion and oxidation resistance, while molybdenum and copper are important for resistance to localized and sulfuric-acid-related corrosion conditions.

The material is commonly selected for process piping where conventional stainless steels may not provide sufficient corrosion resistance.

Related Material Designations:

• UNS N08020
• Alloy 20
• Carpenter 20
• 20Cb-3
• Nickel-Iron-Chromium-Molybdenum-Copper Alloy

ASTM B729 covers seamless nickel-iron-chromium-molybdenum-copper alloy pipe and tube for general corrosive service.

For UNS N08020, the material is supplied in a stabilized annealed condition to meet the applicable material requirements.

Important standard-status note: ASTM B729-20 was withdrawn in 2026 and currently has no replacement standard listed by ASTM International. For new projects, the applicable purchase specification and current project requirements should therefore be confirmed before ordering.

Alloy 20 seamless pipe is manufactured through a seamless tube/pipe production route followed by heat treatment, sizing and finishing operations.

Typical production sequence:

• Billet Preparation
• Hot Piercing
• Seamless Rolling
• Heat Treatment
• Sizing
• Straightening
• Surface Treatment
• Cutting
• Inspection
• Marking
• Packaging

The manufacturing route can be adjusted according to pipe size, wall thickness, dimensional tolerance and final inspection requirements.

Inspection requirements can be tailored to the project specification.

Typical inspection items include:

• Chemical composition analysis
• Mechanical property testing
• Tensile testing
• Hardness testing where specified
• Hydrostatic pressure testing
• Nondestructive testing
• 100% ultrasonic testing when required
• Dimensional inspection
• Outside diameter and wall thickness measurement
• Visual and surface inspection
• PMI / Positive Material Identification
• Heat number traceability
• EN 10204 3.1 Material Test Certificate

For projects requiring enhanced quality control, third-party inspection can also be arranged.

Alloy 20 seamless pipe is typically considered for piping systems exposed to corrosive chemical environments.

• Chemical Processing - Used for process piping, transfer lines and equipment connections handling aggressive chemical media.
• Sulfuric Acid Service - The nickel-chromium-molybdenum-copper composition makes Alloy 20 a commonly considered material for sulfuric acid-related applications.
• Chemical Storage & Transfer - Suitable for selected storage, transfer and circulation systems where corrosion resistance is a major material-selection factor.
• Process Equipment - Can be used in piping connected to reactors, tanks, pumps, heat exchangers and other chemical-process equipment.
• Corrosive Process Piping - Applicable to customized piping systems where conventional stainless steel grades may require additional corrosion resistance.