Inconel 718 Welded Pipe

Inconel 718 (UNS N07718 / W.Nr. 2.4668) is a precipitation-hardening nickel-chromium superalloy. While alternative superalloys rely primarily on aluminum and titanium for strengthening, Inconel 718 uses a unique combination of niobium (Nb) and iron (Fe). This specific chemistry fundamentally alters how the metal behaves during fabrication and welding. HT PIPE is a inconel 718 seamless and welded pipe supplier with 15+ export experience. Contact us for more information and quotes for free!

ASTM B163 UNSN07718 Pipe Specifications

Specification	ASTM B163 / ASME SB163, SAE AMS 5589, SAE AMS 5590
Standard Specification	EN, AMS, JIS, ASTM, ASME, GB, DIN, DTD, AISI
Seamless pipe Size	15 NB to 150 NB IN
	1/2" OD - 12" OD
Welded pipe Size	1/2" OD - 12" OD
	Guage: 25 SWG - 10 SWG
Length	Upto 30 meters, Single Random, Double Random & Required Length End: Plain End, Beveled End, Treaded, or Custom Cut Lengths
WT	0.40 mm - 12.70 mm
Schedule	5, 10S, 10, 30, 40S, 40, 80, 80S, XS, 160, XXH
Manufacturing techniques	LSAW, Seamless, ERW, Welded, DOM, Fabricated, EFW, CEW, Seam-Welded, CDW

 

Chemical Composition

The performance of a welded pipe starts with the precise chemistry of the master coil strip. Minor deviations can alter weld puddle behavior and high-temperature performance.

Nickel (Ni) + Cobalt (Co): 50.00% – 55.00% (Provides the austenitic matrix and high-temperature toughness)

Chromium (Cr): 17.00% – 21.00% (Ensures exceptional oxidation and scaling resistance)

Niobium (Nb) + Tantalum (Ta): 4.75% – 5.50% (The critical driver for precipitation hardening)

Molybdenum (Mo): 2.80% – 3.30% (Enhances resistance to pitting and crevice corrosion)

Iron (Fe): Balance (Acts as the structural base stabilizing cost and grain structure)

 

Formability and Seam Alignment

The process begins with high-purity flat-rolled sheets or strips compliant with ASTM B670 or ASTM B906. The strip passes through continuous forming rolls that shape it into a cylindrical profile. Because Inconel 718 work-hardens rapidly compared to standard steel, the forming equipment must apply uniform pressure to prevent structural spring-back and maintain exact roundness.

 

Advanced Welding Technologies

To prevent high-temperature cracking and alloy segregation, manufacturers use low-heat-input autogenous or filler-added welding processes.

Gas Tungsten Arc Welding (GTAW / TIG): The industry standard for heavy-wall pipes. Modern mills use a pulsed-current GTAW technique. Pulsing the current refines the solidification structure within the weld pool and restricts niobium segregation, minimizing the risk of hot cracking.

 

Laser Beam Welding (LBW) & Electron Beam Welding (EBW): Increasingly used for thin-walled precision tubing. The highly concentrated energy beam produces a narrow heat-affected zone (HAZ), reducing grain-boundary melting and eliminating the microfissuring often seen in wider welds.

 

Comparative Analysis: Welded vs. Seamless

Parameter	Inconel 718 Welded Pipes (ASME SB516 / ASTM B516)	Inconel 718 Seamless Pipes (ASME SB163 / ASTM B163)
Dimensional Tolerance	Concentric, uniform wall thickness throughout the run.	Variations in wall eccentricity can occur due to extrusion dynamics.
Surface Quality	Smooth internal and external finish derived from cold-rolled strip.	Can exhibit minor internal scaling or scoring from the piercing mandrel.
Size Availability	Readily produced in large diameters (up to 1200+ mm) and long continuous lengths.	Generally restricted to smaller outer diameters due to heavy extrusion press limits.
Production Cost	Significantly lower processing cost and shorter production lead times.	Higher production cost due to multi-stage hot piercing, drawing, and machining.
Weld Joint Factor	0.85 to 1.00 depending on full radiography verification (NDT).	1.00 (inherent absence of a longitudinal seam).

 

Mechanical Performance (Room vs. Elevated Temperatures)

In the fully age-hardened condition, Inconel 718 welded pipes reach a room-temperature minimum tensile strength of 930 MPa and a minimum yield strength of 482 MPa.

 

The alloy truly shines at high operating temperatures. It retains its high creep-rupture strength up to 704°C (1300°F), making it highly resistant to plastic deformation under constant load. At the other end of the spectrum, its stable austenitic structure prevents low-temperature embrittlement, allowing it to maintain high impact toughness down to cryogenic temperatures.

 

Crucial Standards to Verify

ASME SB516 / ASTM B516: Standard specification specifically governing nickel-chromium-iron-niobium-molybdenum welded tubes.

 

AMS 5590: The primary aerospace material specification outlining strict dimensional, chemical, and structural requirements for welded 718 piping.

 

Non-Destructive Testing (NDT) Checklist

To ensure the longitudinal weld seam performs reliably under high pressure, global procurement teams must mandate a comprehensive testing program from the manufacturer:

Ultrasonic Testing (UT) / Radiographic Testing (RT): Complete volumetric inspection of the weld seam to find any hidden internal voids, microfissures, or inclusions.

Hydrostatic Pressure Testing: Validates the structural integrity of the pipe under pressures exceeding standard field operating levels.

Positive Material Identification (PMI): Spectrometric analysis to verify the exact alloy composition before dispatch, preventing material mix-ups.

EN 10204 3.1 Certification: Provides full component traceability from the raw melting batch to the final product.

 

 

 

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