What b167 ni-cr-fe alloy tube solutions are available for aerospace exhaust systems?

Aerospace exhaust systems push materials to their absolute limit. Inside a turbofan tailpipe or a business-jet exhaust mixer, skin temperatures can swing from sub-zero on the ramp to over 1,000 °C in cruise, while exhaust gases carry unburned fuel residues, sulfur compounds, and chloride-laden moisture from ground operations. For engineers specifying the tube sections that route these hot gases, drain offboard bleed, or feed sensors through the duct wall, ASTM B167 Ni-Cr-Fe alloy tube is one of the most reliable choices in the nickel-alloy family. The question most buyers ask is simple: what B167 Ni-Cr-Fe alloy tube solutions are actually available for aerospace exhaust systems, and how do you pick the right one?

This article walks through the realistic product options EZ Steel Industrial supplies under the B167 specification, the grade-by-grade trade-offs that matter for exhaust service, the dimensional and testing envelope buyers should expect, and a short sourcing checklist for project-based procurement.

Why B167 Ni-Cr-Fe alloy tube is specified for exhaust service

Exhaust ducts on civil and military aircraft sit in a narrow material window. They need:

Sustained oxidation resistance from roughly 600 °C up to 1,095 °C in intermittent peaks, without spalling of the protective oxide layer.
Resistance to chloride-ion stress-corrosion cracking, which becomes a real risk when salty runway moisture condenses on cooler duct sections during descent.
Stable mechanical properties across thermal cycling, so the tube does not creep or sag against its supports after thousands of flight hours.
A seamless microstructure with no longitudinal weld, because a weld seam in an exhaust flow path is a fatigue and crack-initiation concern under vibration.

The Ni-Cr-Fe alloy family covered by B167 Ni-Cr-Fe alloy tube meets all four points. With a nickel matrix above 72%, the austenitic structure stays stable from cryogenic ground conditions to the upper creep range, while 14–30% chromium forms a self-healing chromium oxide film that resists oxidation, sulfidation, and carburization. Iron at 6–10% keeps the alloy cost-effective compared with higher-nickel alternatives, which is one reason B167 is preferred over B163 or B407 grades for many exhaust line sections rather than for the heat-exchanger core.

B167 grade options for aerospace exhaust systems

B167 is not a single material; it is a specification that covers several UNS designations. For exhaust service, three grades carry most of the workload:

UNS N06600 (Inconel 600) — the baseline exhaust tube

N06600 is the workhorse. It offers oxidation resistance up to about 1,095 °C in continuous service and short peaks closer to 1,200 °C, with the chloride stress-corrosion immunity that B167 is known for. In an aerospace exhaust system, N06600 is typically used for:

Tailpipe extension tubes and augmenter liners.
Exhaust gas recirculation (EGR) lines on turboprop and small turbofan installations.
Sensor boss tubes that penetrate the duct wall to host thermocouple and pressure probes.
Bleed-air dump tubes downstream of the turbine section.

Minimum mechanical properties in the annealed condition are 550 MPa tensile strength and 205 MPa yield at 0.2% offset, with 30% minimum elongation. Solution annealing at 925–1,040 °C followed by rapid cooling keeps the grain structure clean and the oxide film adherent.

UNS N06601 — for sulfur-bearing exhaust streams

N06601 raises the chromium content to roughly 22–23%, which strengthens the passive film against sulfidation attack. Aviation fuel traces containing organic sulfur, combined with sulfate deposits from ground air, can aggressively attack lower-chromium nickel alloys at 700–900 °C. N06601 is the right call for exhaust sections that see prolonged exposure to those conditions, such as auxiliary power unit (APU) exhaust lines and ground-test-cell ducting.

UNS N06690 — high-chromium option for oxidizing exhausts

N06690 pushes chromium to roughly 30%, giving the best resistance to intergranular attack and oxidizing hot-gas environments. It is heavier in nickel content and therefore more expensive, but for exhaust zones that run hot, lean, and oxidizing for long durations — for example, the tailcone of high-bypass turbofans — it offers a longer inspection interval between overhauls. It is also a sensible crossover choice for projects that need the same alloy to serve both exhaust and adjacent heat-exchanger tubing, since N06690 is the standard nuclear steam-generator grade under RCC-M specifications.

UNS N06693, N06025, N06045 — specialized grades

These precipitation-hardenable and high-chromium variants are reserved for very specific high-temperature, carburizing, or sulfidizing environments. They are typically specified only when the exhaust stream carries unusual chemistry — for instance, exhaust from auxiliary power units burning contaminated fuel or test-stand rigs with simulated corrosive inlet air. For most civil aerospace exhaust builds, N06600 and N06601 cover the practical envelope.

Tube forms and dimensions typically supplied

B167 Ni-Cr-Fe alloy tube for exhaust service is supplied in a tightly defined envelope. EZ Steel Industrial routinely produces the following forms:

Cold-worked seamless tube — the preferred form for exhaust ducting sections. Outside diameters typically range from 6 mm to 114 mm, with wall thicknesses from 0.5 mm to 12 mm depending on diameter. Cold pilgering or cold drawing delivers the tight OD and wall tolerances that flaring, bending, and welding operations downstream require.
Hot-finished seamless tube — used for larger diameter exhaust manifolds and augmenter inlets, generally above 100 mm OD, where hot working is more cost-effective than cold drawing.
U-bend tubes — for exhaust heat-recovery loops and exhaust-gas-to-air interchanger sections where the tube must reverse direction inside a tight envelope. U-bends are produced to a controlled bend radius and undergo post-bend solution annealing to restore corrosion resistance in the heat-affected zone.
Finned tubes — for exhaust sections that double as heat-recovery surfaces, combining an N06600 or N06601 base tube with embedded or wrapped fins to dump heat into a secondary fluid stream.

Standard mill lengths run to about 6 m for cold-worked tube and up to 12 m for hot-finished tube. For aerospace ducting, fabricators usually order cut-to-length pieces with end-prep machining (bevel, flare, or boss form) already done at the mill to reduce shop-floor welding time.

Manufacturing route that matters for exhaust service

Not every B167 tube on the market is made the same way, and the manufacturing route directly affects how the tube performs in a vibrating, thermally cycled exhaust line. The credible route for aerospace buyers is:

Vacuum induction melting (VIM) of the heat, with optional secondary refining by electroslag remelting (ESR) or vacuum arc remelting (VAR) for cleaner inclusion population.
Hot forging or hot rolling of the ingot into a billet, followed by hot piercing or extrusion to form a hollow shell.
Cold pilgering or cold drawing for the final dimensional and surface finish.
Solution annealing at 925–1,040 °C with rapid water quench, then pickling or bright annealing to restore the passive oxide layer.
Non-destructive testing on every tube — typically eddy current plus ultrasonic, backed by hydrostatic test at up to 1,000 psi (6.9 MPa) where specified.

Each of these steps leaves a traceable record in the mill test certificate. For aerospace exhaust builds, the MTC should include the heat number, full chemical composition, room-temperature tensile results, grain size, NDT report, and the heat treatment chart. The absence of a complete MTC is a clear red flag.

How B167 compares with related aerospace tube specifications

A common sourcing question is when to specify B167 versus B163 or B407. The short version:

ASTM B167 covers seamless Ni-Cr-Fe alloy pipe and tube for general high-temperature and corrosive service. It is the right call for exhaust ducting, sensor bosses, and structural hot sections.
ASTM B163 focuses on nickel alloy condenser and heat-exchanger tubes with tighter surface and dimensional requirements. If the same exhaust line includes a heat-recovery section that acts as a heat exchanger, B163 nickel alloy tube may be specified for that section instead.
ASTM B407 covers the Incoloy 800 family (Ni-Fe-Cr), which trades some nickel for cost. B407 Incoloy 800 tube is a reasonable choice where the exhaust temperature is below about 800 °C and the operating environment is less aggressive.

For the hottest sections of a modern high-bypass turbofan exhaust — typically the augmentor liner and the tailpipe just downstream of the turbine — B167 in N06600 or N06690 is the default specification. For cooler sections such as the bypass duct, B407 or even stainless steel may be sufficient, which is why most airframe builders run a multi-material exhaust design rather than a single alloy throughout.

Quality control and documentation buyers should expect

Aerospace exhaust programs demand documentation that goes well beyond a standard commercial shipment. At minimum, each B167 Ni-Cr-Fe alloy tube lot should arrive with:

Mill test certificate (MTC) to EN 10204 3.1, with heat number, full chemical composition, and mechanical test results.
NDT report covering 100% eddy current or ultrasonic inspection, plus hydrostatic test data where applicable.
Heat treatment chart showing actual furnace temperature and quench medium timing.
Dimensional inspection report against the agreed tolerances, including ovality and wall eccentricity.
Surface finish and pickling report, with confirmation that the passive oxide layer has been restored after any cold-working operation.
Positive Material Identification (PMI) results when multiple alloy grades are present in the same work package.

Independent third-party inspection — for example, by SGS, BV, or TÜV — is recommended for first-article qualification on a new program. Once a heat, size, and grade combination is approved, incoming inspection can usually be reduced to dimensional and PMI checks against the original qualification data.

Sourcing checklist for project-based exhaust builds

Lead times for B167 Ni-Cr-Fe alloy tube typically run 8–16 weeks from order to delivery, depending on grade, size, and quantity. A few practical points shorten that window and reduce risk:

Confirm whether the supplier is the actual manufacturer or a trading company. Direct mills offer tighter traceability and faster technical response.
Check for in-house NDT and mechanical testing laboratories, since subcontracted testing adds calendar days and handoffs.
For multi-discipline exhaust packages, look for a supplier that can also deliver matching pipe fittings, pipe flanges, and gaskets to keep alloy chemistry consistent across the assembly.
Ask for a pre-production sample of the actual heat and size, then run a sample weld procedure and a metallographic mount to verify the microstructure before releasing the full order.
Agree on packaging that protects the passive surface — usually individual plastic sleeves, desiccant, and sealed wooden crates — because any surface contamination from unprotected storage can delay downstream pickling and passivation.

EZ Steel Industrial supply scope for B167 aerospace exhaust tube

EZ Steel Industrial Co., Ltd. supplies B167 Ni-Cr-Fe alloy tube in UNS N06600, N06601, N06690, and the related UNS designations covered by the specification, in cold-worked and hot-finished seamless forms. The company's three-site manufacturing footprint — Cangzhou for alloy inventory and custom fittings, Yangzhou for large-scale carbon and alloy pipe production, and Lishui for stainless and copper-nickel corrosion-resistant materials — supports project packages that combine B167 exhaust tube with the matching fittings, flanges, gaskets, stud bolts, and industrial valves from the broader ezindustrialtube.com product line.

Quality management is certified to ISO 9001, with API 5L and API 5CT product certifications available for pipeline-scope work, and PED compliance for European pressure equipment. Production control spans more than 12 quality checkpoints, from raw material PMI through final hydrostatic and ultrasonic testing, and every shipment leaves with a full mill test certificate. For aerospace exhaust programs, EZ Steel Industrial supports sample qualification, custom size runs, bundled project packaging, and multilingual technical documentation to streamline cross-border procurement.

To discuss a B167 Ni-Cr-Fe alloy tube requirement for an aerospace exhaust system, contact the EZ Steel Industrial engineering team at export@ezsteelpipe.com or +86 731 8870 6116, or visit the B167 product page for the standard size range and current data sheets.