Introduction

ASTM B668 Seamless Nickel Alloy Pipe is the standard specification for iron-nickel-chromium-molybdenum alloy seamless pipe and tube, covering Alloy 28 (UNS N08028 / Sanicro 28 / W.Nr. 1.4563) and UNS N08029 in cold‑finished and hot‑finished forms. This general corrosive service alloy contains 30–32% nickel, 26–28% chromium, 3–4% molybdenum, and 0.6–1.4% copper, delivering excellent corrosion resistance to sulfuric acid, phosphoric acid, and chloride‑containing environments. With a minimum PRE number of 38, it offers high resistance to pitting and crevice corrosion. This corrosion resistant nickel alloy tube is the preferred material for chemical processing, heat exchangers, oil and gas, pollution control equipment, and acid production systems. Available in cold‑finished and hot‑finished conditions, custom size, Schedule 40/80, and large diameter options.

Specifications & Process Options

Applications

1. Chemical Processing & Acid Production

• In sulfuric acid plants, phosphoric acid evaporators, and acid production facilities, ASTM B668 Alloy 28 pipe for chemical processing delivers exceptional resistance to both reducing and oxidizing acids. The molybdenum and copper combination in this iron-nickel-chromium-molybdenum alloy pipe provides outstanding protection against localized attack such as pitting and crevice corrosion.

• For sulfuric acid pickling equipment and acid handling systems, UNS N08028 seamless pipe is especially effective when acids are contaminated by chlorides and fluorides. It outperforms standard stainless steels in hot, concentrated acid service.

• ASTM B668 nickel alloy tube is also specified for reactors, distillation columns, and heat exchanger tubing in chemical processing and petrochemical plants.

2. Oil & Gas / Offshore Engineering

• For downhole production tubing, casing, and liners in deep sour gas wells, Sanicro 28 pipe for oil and gas provides excellent resistance to stress corrosion cracking in H₂S and chloride‑containing environments. Its high alloy content ensures reliable performance in aggressive downhole conditions.

• For offshore platforms and subsea equipment, Alloy 28 seamless tube withstands seawater, brine, and chloride attack while maintaining mechanical strength.

3. Heat Exchangers & Pollution Control Equipment

• For shell‑and‑tube heat exchangers in severely corrosive conditions with high chlorides, ASTM B668 pipe for heat exchangers offers excellent resistance to pitting and crevice corrosion. Seawater‑cooled heat exchangers and marine applications benefit from its high resistance to localized attack.

• For flue gas desulfurization systems and pollution control equipment, UNS N08029 seamless pipe withstands low‑pH, high‑chloride environments while maintaining structural integrity.

4. Nuclear Fuel Reprocessing & General Industrial Service

• For nuclear fuel reprocessing equipment and radioactive waste handling, ASTM B668 seamless tube provides the corrosion resistance needed for demanding nuclear applications.

• For general industrial corrosive service and process piping, corrosion resistant alloy pipe delivers long‑term reliability in chemical plants, fertilizer production, and industrial equipment.

FAQ – ASTM B668 Alloy 28 Pipe

Q: What is the difference between Alloy 28 and Alloy 825?

A: Alloy 28 seamless pipe (UNS N08028) is an iron-nickel-chromium-molybdenum alloy with higher molybdenum (3–4%) and chromium (26–28%) content, giving it superior localized corrosion resistance and a higher PREN (≥38). Alloy 825 seamless pipe (UNS N08825) has a higher nickel content (38–46%) with titanium stabilization, providing better resistance to stress corrosion cracking in severe sour brine environments. Alloy 28 is generally more cost‑effective for sulfuric and phosphoric acid service; Alloy 825 is preferred for applications requiring higher nickel content and SCC resistance.

Q: What is the maximum operating temperature for ASTM B668 Alloy 28 pipe?

A: Alloy 28 seamless tube maintains excellent corrosion resistance at elevated temperatures up to approximately 400°C (750°F). Its high chromium and molybdenum content provides resistance to oxidation and high‑temperature corrosion. For continuous service above 400°C, higher nickel alloys such as Inconel 625 or Hastelloy are recommended.

Q: Can ASTM B668 pipe be welded, and does it require post‑weld heat treatment?

A: Yes. ASTM B668 seamless pipe can be welded using common welding techniques. For optimal corrosion resistance in the heat‑affected zone, solution annealing (PWHT) at 1040–1120°C followed by rapid quenching may be required. A heat input of <1.0 kJ/mm and interpass temperature of <150°C (300°F) is recommended for welding Sanicro® 28. In many applications, the alloy can be used in the as‑welded condition.

Q: What is the difference between ASTM B668 and ASME SB668?

A: ASTM B668 is the material specification published by ASTM, covering chemical composition, mechanical properties, and testing for iron‑nickel‑chromium‑molybdenum alloy seamless pipe. ASME SB668 is the ASME adoption of the same specification for pressure vessel and boiler applications, listed in the ASME Boiler and Pressure Vessel Code. Materials meeting both standards can carry the SB‑668 designation for code‑stamped pressure equipment.

We are a trusted ASTM B668 Seamless Nickel Alloy Pipe Supplier and Alloy 28 Pipe Manufacturer, China‑based, serving chemical processors, oil and gas contractors, heat exchanger manufacturers, and pollution control equipment builders worldwide. All products comply with ASTM B668 / ASME SB668 with EN 10204 3.1 mill certificates, PMI verification, hydrostatic and eddy current test reports. We offer cold‑finished and hot‑finished Alloy 28 pipe in custom sizes, Schedule 40/80, and large diameter options. Contact us at info@monokj.com for size chart, pricing, or custom requirements.