ASTM B167 Inconel 718 pipe (UNS N07718, W.Nr. 2.4668) is a precipitation-hardening nickel-chromium-iron-molybdenum superalloy pipe designed for extreme temperatures from cryogenic service to approximately 704 °C. It is renowned for exceptional strength, high corrosion resistance and excellent weldability with resistance to post-weld cracking, making it a critical material in aerospace, gas turbine and nuclear industries.
Key Takeaways
Composition: Ni 50-55%, Cr 17-21%, Fe balance, Al 0.2-0.8%, C max 0.08%.
Mechanical: tensile 135,000 psi (930 MPa), yield 75,000 psi (482 MPa), elongation 45%.
Seamless pipe 1/2-16 NB and welded 1/2-24 NB; OD 6.00-914.4 mm.
Inconel 718 work-hardens rapidly; machining needs rigid setups and controlled parameters.
What Is Inconel 718 Pipe?
Inconel 718 pipe is a nickel-based alloy pipe with excellent corrosion resistance, weldable in both annealed and precipitation-hardened states and easy to process with correct technique. It offers outstanding creep resistance and some of the highest tensile strengths available in piping alloys, serving temperatures from cryogenic levels to over 650 °C in aerospace and nuclear engines.
Specification Summary
Standards are ASTM B167 and ASME SB167 for seamless pipe, with B517/SB517 for welded pipe; dimensional standards follow ANSI/ASME B36.19M and B36.10M. Seamless sizes run from 1/2 NB to 16 NB, welded from 1/2 NB to 24 NB, with outside diameters from 6.00 mm up to 914.4 mm and schedules from SCH 5 to XXS. Pipe ends are plain, beveled or threaded, and value-added services include cutting, beveling, polishing, threading and ultrasonic testing.
Chemical Composition
Weight percent limits are carbon up to 0.08%, manganese up to 0.35%, silicon up to 0.35%, iron balance, sulfur up to 0.01%, chromium 17.0-21.0%, aluminum 0.2-0.8% and nickel 50.0-55.0%, with niobium and molybdenum completing the precipitation-hardening system.
Mechanical Properties
Density is 8.2 g/cm³, melting point about 1350 °C, tensile strength 135,000 psi (930 MPa), yield strength 75,000 psi (482 MPa) and elongation 45%. The material work-hardens during processing, so machining requires rigid setups, sharp tools and controlled speeds, feeds and coolant.
Pressure Ratings
Working pressure rises with wall thickness: for 1/8-inch OD tube, 7,900 psig at 0.028-inch wall and 10,100 psig at 0.035-inch; for 1/2-inch OD, 2,300 psig at 0.035-inch up to 4,400 psig at 0.109-inch; and for 1-inch OD, 2,200 psig at 0.065-inch up to 4,300 psig at 0.120-inch. Confirm the rating against the design code and temperature.
Applications
ASTM B167 718 pipe serves railway engines and coaches, defense components, aerospace structures, textile machinery, heavy engineering, oil and gas facilities, agricultural equipment, conveyor shafts and cold-headed components, where strength, corrosion resistance and temperature capability are required.
Frequently Asked Questions
Q: What is ASTM B167?
The standard governing seamless nickel alloy pipe and tube, covering Inconel 718 for extreme-temperature service.
Q: Does Inconel 718 work harden?
Yes. Its high toughness, low thermal conductivity and work-hardening tendency make it difficult to process without rigid setups.
Q: What strength does 718 pipe provide?
Tensile strength of 135,000 psi (930 MPa), yield of 75,000 psi (482 MPa) and 45% elongation.
Q: What sizes are available?
Seamless 1/2-16 NB and welded 1/2-24 NB, with OD from 6.00 mm to 914.4 mm.
Q: What is the temperature range?
From cryogenic temperatures to approximately 704 °C.
Q: Can 718 pipe be welded?
Yes, in annealed or precipitation-hardened states, with resistance to post-weld cracking.
