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ASTM B668 is the standard specification for "UNS N08028 Seamless Tube". (In industrial contexts, "tube" and "pipe" from this standard are often used for pressure piping applications). This standard defines the requirements for seamless, cold-worked, or hot-finished pipes/tubes made from UNS N08028, an austenitic stainless steel designed for extreme corrosive environments. UNS N08029 is a closely related, enhanced version of N08028 and is often accepted or specified within the framework of this standard due to its superior properties. The standard governs the chemical composition, mechanical properties, dimensions, and testing for these pipes.
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Alloy 28 seamless pipes and tubes, including grades UNS N08028 and UNS N08029, are advanced nickel-iron-chromium alloys specifically developed for demanding industrial environments where conventional stainless steels may experience premature corrosion failure.
Featuring a balanced combination of nickel, chromium, molybdenum, and copper, these high-performance alloys provide exceptional resistance to sulfuric acid, phosphoric acid, chloride-bearing solutions, seawater exposure, sour gas media, and other highly corrosive process conditions.
The enhanced alloy chemistry offers outstanding protection against localized corrosion mechanisms such as pitting, crevice attack, and chloride-induced stress corrosion cracking, making Alloy 28 a preferred material for critical process equipment and long-term service applications.
Why ASTM B668 Alloy 28 Pipes Are Preferred in Corrosive Industries
Products chemical requirements
Products tensile requirements
Key Characteristics and Composition
The core difference lies in the optimized chemistry of N08029, which enhances its performance.
| Feature | UNS N08028 (Alloy 28) | UNS N08029 (Alloy 29) |
|---|---|---|
| Key Composition | ~31% Ni, 27% Cr, 3.5% Mo, ~1% Cu | ~31% Ni, 26% Cr, 4.0% Mo, ~1% Cu |
| Key Additions | ~0.02% N | ~0.25% N |
| PREN | ~38 | ~42 |
| Key Characteristics | Excellent resistance to sulfuric acid, phosphoric acid, and good chloride resistance. | An upgrade to N08028 with higher Mo & N, resulting in better strength and pitting resistance. |
| Primary Advantage | A proven, cost-effective solution for severe sulfuric acid service. | Improved pitting/crevice resistance and higher mechanical strength than N08028. |
| Relationship | The original/base alloy. | A modern, enhanced version with optimized chemistry. |
Why the Nitrogen (N) in N08029 is Critical:
The significant addition of 0.25% Nitrogen provides two major benefits:
Solid Solution Strengthening: Dramatically increases yield and tensile strength in the annealed condition.
Enhanced Pitting Resistance: Directly boosts the PREN value, making it more resistant to chloride-induced pitting and crevice corrosion.
Machining Performance Analysis
ASTM B668 UNS N08028 Seamless Pipes offer reliable and consistent machining performance when processed using appropriate tooling and optimized cutting parameters. Due to the alloy's high nickel, chromium, and molybdenum content, machining operations typically require lower cutting speeds, rigid machine setups, and high-performance carbide tooling to achieve optimal results.
With proper machining practices, Alloy 28 pipes can be fabricated into precision components while maintaining excellent dimensional accuracy and surface integrity.
Superior Alternative to 316L Stainless Steel
Compared with conventional 316L stainless steel, Alloy 28 (UNS N08028) offers significantly enhanced resistance to chloride-induced corrosion and acidic attack. This makes it the preferred material choice for chemical processing plants, fertilizer production facilities, offshore systems, seawater applications, and other demanding environments where standard stainless steels may fail prematurely.
As a result, ASTM B668 UNS N08028 seamless pipes provide a reliable, long-term solution for critical process systems requiring maximum corrosion resistance, operational safety, and lifecycle cost efficiency.
ASTM B668 UNS N08028 Pipe Specifications
| Type | Seamless Pipe / Seamless Tube |
|---|---|
| Outer Diameter | 6mm – 630mm |
| Wall Thickness | 0.5mm – 40mm |
| Length | Up to 12m |
| Surface Finish | Annealed / Pickled / Bright |
| End Type | Plain End / Beveled End / Threaded |
| Manufacturing | Cold Drawn / Cold Rolled |
| Tolerance | ASTM / ASME Standard |
| Testing | UT / ET / Hydrostatic / PMI |
Applicable Standards
| Standard | Description |
|---|---|
| ASTM B668 | Nickel Alloy Seamless Pipe & Tube |
| ASME SB668 | Boiler & Pressure Vessel Specification |
| ASTM B829 | General Requirements for Nickel Alloy Pipe |
| ASTM E112 | Grain Size Testing |
| ASTM E8 | Tensile Testing |
FAQ
What is ASTM B668 UNS N08028 seamless pipe?
ASTM B668 UNS N08028 is a high alloy nickel-iron-chromium seamless pipe designed for highly corrosive industrial environments involving acids and chlorides.
What is Alloy 28 pipe used for?
Alloy 28 seamless pipes are widely used in chemical processing, offshore systems, seawater handling, FGD systems, and phosphoric acid plants.
Is UNS N08028 better than 316L stainless steel?
Yes. UNS N08028 provides significantly better resistance to pitting corrosion, chloride SCC, and acidic corrosion compared with 316L stainless steel.
Can ASTM B668 Alloy 28 pipes be welded?
Yes. Alloy 28 pipes have excellent weldability using TIG, MIG, and orbital welding methods.
What sizes are available for ASTM B668 seamless tubes?
Standard sizes range from 6mm to 630mm OD with custom wall thicknesses available according to project requirements.
Do you provide third-party inspection?
Yes. SGS, BV, TUV, and other third-party inspections are available before shipment.
Can you manufacture custom dimensions?
Yes. We support customized pipe dimensions, lengths, surface finishes, and special project requirements.
What certificates can you provide?
We can provide EN10204 3.1 certificates, MTC, PMI reports, hydro test reports, and export inspection documentation.
Contact Us
Xi'an Dongmeng Group Co., Ltd
Professional Supplier of ASTM B668 UNS N08028 / N08029 Seamless Pipe & Tube
Phone / WhatsApp / WeChat: +8615769214734
Email: office@dongmjd.com
Products: Nickel Alloy Pipe, Tube, Plate, Bar, Coil & Custom Fabrication
Service: OEM / ODM / Global Export Supply
Contact us today for technical support, pricing, and fast quotations for your industrial corrosion resistant alloy projects.
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