Inconel Pipe: Properties and Applications

Inconel is a family of nickel-chromium superalloys developed by Special Metals Corporation (now part of Precision Castparts). Inconel pipes are specified where extreme temperatures, aggressive corrosion, or both exceed the capabilities of stainless steel and duplex alloys.

The three most common Inconel pipe grades are Alloy 600, Alloy 625, and Alloy 718. Each targets different service conditions.

Key Inconel Grades

Property	Alloy 600	Alloy 625	Alloy 718
UNS	N06600	N06625	N07718
Ni (%)	72 min	58 min	50-55
Cr (%)	14-17	20-23	17-21
Mo (%)	-	8-10	2.8-3.3
Nb (%)	-	3.15-4.15	4.75-5.50
Fe (%)	6-10	5 max	Balance
Yield (min, annealed)	240 MPa	414 MPa	1034 MPa (aged)
Tensile (min, annealed)	550 MPa	827 MPa	1241 MPa (aged)
Max. service temp	~1090°C	~980°C	~705°C (aged)
ASTM pipe spec (seamless)	B167	B444	B637 (bar/forging)
ASTM pipe spec (welded)	B516	B705	-
Primary resistance	Oxidation, carburization	Pitting, crevice, acids	High-strength at temp

Alloy 600

Inconel 600 provides excellent resistance to oxidation and high-temperature corrosion. It maintains its structure at temperatures up to 1090°C. Primary applications:

• Furnace components and heat-treating equipment
• Chemical processing (caustic alkali environments)
• Nuclear engineering (steam generator tubing)
• Aerospace gas turbine components

Alloy 625

Inconel 625 is the most widely used nickel alloy pipe in oil and gas. The combination of nickel, chromium, molybdenum, and niobium provides outstanding resistance to:

• Seawater and marine environments
• Pitting and crevice corrosion (PREN > 50)
• Acid environments (HCl, H2SO4, HF)
• High-temperature oxidation (up to 980°C)

Applications include subsea flowlines, offshore wellhead equipment, flue-gas desulfurization systems, and chemical reactor piping.

Pro Tip

Inconel 625 is often used as a weld overlay (cladding) on carbon steel or low-alloy pipe rather than as solid alloy pipe. A 3-6 mm Alloy 625 overlay on a carbon steel substrate provides the corrosion resistance of Inconel at a fraction of the cost of solid alloy pipe.

Alloy 718

Inconel 718 is a precipitation-hardened alloy with exceptionally high strength at elevated temperatures. It is primarily used for components rather than piping: downhole tools, wellhead components, BOP parts, and aerospace turbine discs. Its high cost and specialized heat treatment (solution + aging) limit pipe applications.

Cost Considerations

Inconel pipe costs 5-15x more than equivalent carbon steel pipe and 2-5x more than stainless steel. Lead times for seamless Inconel pipe range from 12-26 weeks. Procurement should be initiated early in the project procurement cycle.

Material	Relative Cost (per kg, approximate)
Carbon steel (A106 Gr. B)	1x
316L stainless	3-4x
Duplex 2205	4-6x
Inconel 625	10-15x
Inconel 718	15-20x

Read the full guide to pipe types