All About Hastelloy C276

Inconel is a brand name of a group of nickel-chromium superalloys designed to work where ordinary steels and stainless steels fail to work  in severe heat, violent corrosion, and high-level stress fatigue conditions. Having over a dozen commercial grades, each with its own unique composition and performance profile, incorrect choice of Inconel grade may result in premature failure, unjustified expense or over-specification that adds weight and cost but does not offer any advantage.

This is a guide to the larger grades of Inconel employed in piping and process equipment industry, their compositions, temperature extremes, corrosion resistance, plus the type of service that each grade was specified to perform with, so you can reasonably be sure of selecting the correct alloy to your circumstances.

Types of Inconel Grades: Grade-by-Grade Breakdown

The grades below represent the most widely specified Inconel alloys in industrial piping, pressure vessels, heat exchangers, and structural applications. Each section links to the matching Kalpataru product page for full specifications and dimensional data.

Inconel 600 (UNS N06600 / DIN 2.4816)

Inconel 600 is the original nickel-chromium alloy, the baseline grade against which all others are measured. With approximately 72% nickel and 16% chromium, it offers excellent resistance to oxidation and corrosion across a wide temperature range, from cryogenic service up to 1177°C (2150°F).

•       Outstanding resistance to chloride-ion stress-corrosion cracking — a common failure mode for austenitic stainless steels.
•       Resistant to carburisation and nitriding atmospheres, critical in furnace and heat-treatment equipment.
•       Good mechanical properties at both low and elevated temperatures; non-magnetic.
•       Does not contain molybdenum, not optimised for pitting resistance in aggressive chloride media. For those environments, specify Inconel 625.

Primary industries: Nuclear fuel processing, heat-treatment furnace components, chemical processing, food industry equipment, and alkaline service.

Kalpataru Product Page: Inconel 600 Pipes & Tubes  →  /inconel-600-seamless-pipes-tubes-supplier-exporters/ 

Inconel 601 (UNS N06601 / DIN 2.4851)

Inconel 601 is a nickel-chromium alloy with a significant aluminium addition (1.0–1.7%), which forms a tightly adherent, protective aluminium oxide scale that dramatically improves oxidation resistance at temperatures above 1000°C. It is the preferred Inconel grade where cyclic thermal exposure, repeated heating and cooling, would cause spalling in other alloys.

•       Superior oxidation resistance in both continuous and cyclic service up to 1200°C (2200°F).
•       High resistance to nitriding, carburising, and sulphidising atmospheres.
•       Good resistance to scaling and hot-gas corrosion, used extensively in combustion environments.
•       Moderate aqueous corrosion resistance, not the primary selection for room-temperature chemical service.

Primary industries: Industrial furnaces, radiant tubes, heat-treating baskets and fixtures, gas turbine combustion hardware, catalytic reformer equipment.

Kalpataru Product Page: Inconel 601 Pipes & Tubes  →  /inconel-601-seamless-pipes-tubes-supplier-exporters/

Inconel 617 (UNS N06617 / DIN 2.4663)

Inconel 617 is a nickel-chromium-cobalt-molybdenum alloy designed specifically for the most extreme high-temperature structural applications. Cobalt (10–15%) and molybdenum (8–10%) additions provide exceptional solid-solution strengthening, giving 617 the highest strength retention of any commercial Inconel grade at temperatures above 980°C.

•       Retains significant strength and creep resistance up to 1093°C (2000°F), one of the highest rated commercial alloys.
•       Excellent oxidation resistance; aluminium addition promotes a protective oxide scale.
•       Used in next-generation gas turbines, including land-based power generation units at advanced steam conditions.
•       Approved for ASME Boiler and Pressure Vessel Code Section I and Section VIII service up to 982°C.

Primary industries: Advanced gas turbines, aerospace jet engines, high-temperature process heaters, steam reformers, industrial furnace components operating above 1000°C.

Inconel 625 (UNS N06625 / DIN 2.4856)

Inconel 625 is the most widely specified Inconel grade in the oil and gas, marine, and chemical processing industries. Its combination of high molybdenum (8–10%) and niobium (3.15–4.15%) content produces outstanding resistance to pitting, crevice corrosion, and chloride stress-corrosion cracking  without any precipitation hardening heat treatment.

•       Service temperature range: cryogenic (-196°C) to 982°C (1800°F), the broadest of any standard Inconel grade.
•       No post-weld heat treatment required, simplifies fabrication of complex piping systems and offshore structures.
•       ASTM B444 / ASME SB444 seamless pipe and tube; ASTM B705 welded pipe.
•       Available in Grade 1 (annealed- higher room-temperature strength) and Grade 2 (solution annealed, better creep resistance above 593°C).
•       Saudi ARAMCO approved; widely used in subsea, FPSO, and offshore riser applications.

Primary industries: Offshore oil and gas, subsea pipelines, chemical processing, aerospace ducting, flue gas desulfurisation, marine seawater piping, pharmaceutical heat exchangers.

Kalpataru Product Page: Inconel 625 Pipes & Tubes  →  /inconel-625-pipes-tubes-supplier-exporters/ 

Inconel 686 (UNS N06686 / DIN 2.4606)

Inconel 686 is a premium corrosion-resistant alloy with one of the highest molybdenum contents (15–17%) among the Inconel family, combined with tungsten (3.0–4.4%). It was developed specifically to outperform Hastelloy C-276 and Inconel 625 in the most aggressive mixed-acid and oxidising-plus-reducing environments encountered in chemical and pollution-control applications.

•       Exceptional resistance to sulfuric acid, hydrochloric acid, and mixed-acid environments, particularly where oxidising and reducing conditions alternate.
•       High PREN (Pitting Resistance Equivalent Number), superior to Inconel 625 in concentrated chloride media.
•       Used where Hastelloy C-276 shows borderline performance, the step-up alloy for severe chemical service.

Primary industries: Flue gas desulfurisation (FGD) scrubbers, chemical reactors handling mixed acids, pharmaceutical and specialty chemical manufacturing, pulp and paper bleaching lines. 

Inconel 718 (UNS N07718 / DIN 2.4668)

Inconel 718 is the highest-strength Inconel grade available in standard commercial form — achieving tensile strengths above 1,270 MPa in the precipitation-hardened (aged) condition. Its strength derives from the controlled precipitation of gamma-prime (γ’) and gamma-double-prime (γ”) phases through a two-stage heat treatment (solution anneal + aging). This makes 718 the dominant alloy in gas turbine rotating components and high-strength fasteners.

•       Tensile strength up to 1,276 MPa (185 ksi), approximately 50% stronger than Inconel 625 at room temperature.
•       Excellent fatigue, creep, and rupture strength up to 649°C (1200°F) and above this temperature strength drops sharply.
•       Requires post-weld heat treatment (solution annealing + aging) to restore full strength after welding.
•       Good weldability for a precipitation-hardened alloy, less susceptible to strain-age cracking than Inconel X-750.
•       ASTM B983 (pipe/tube), AMS 5596 (sheet/plate), AMS 5662/5663 (bar), stringent aerospace material certifications available.

Primary industries: Gas turbine discs, compressor blades and shafts, aerospace fasteners and structural components, nuclear reactor spacer grids, downhole oil and gas completion tools.

Kalpataru Product Page: Inconel 718 Pipes & Tubes  →  /inconel-718-seamless-pipes-tubes-supplier-exporters/ 

Inconel X-750 (UNS N07750 / DIN 2.4669)

Inconel X-750 is a precipitation-hardenable nickel-chromium alloy strengthened by titanium and aluminium additions, similar in concept to Inconel 718 but optimised for spring and fastener applications where high relaxation resistance at elevated temperature is the critical requirement. It is widely used in gas turbine hot section components and nuclear reactor core structures.

•       High relaxation resistance that is it retains clamping force in bolted joints and spring elements at temperatures up to 700°C.
•       Excellent oxidation resistance up to 980°C.
•       Three heat treatment conditions: equalized & aged, annealed & aged, solution treated & aged — each producing a different strength/ductility balance.
•       Used in applications where Inconel 718 is over-specified for temperature or where a spring-quality alloy is required.

Primary industries: Gas turbine springs, retaining rings, and seals; nuclear reactor fuel spacer grids; high-temperature bolting; aircraft exhaust systems.

Inconel Chemical Composition Table: ASTM Specification Limits

The table below lists the chemical composition limits for each Inconel grade as defined in the applicable ASTM and AMS standards. All values are in weight percent (wt%). These are the specification minima and maxima, individual heats are certified to these limits on the Material Test Report (MTR); actual heat chemistry will fall within the ranges shown.

Grade / ASTM Standard	Ni %	Cr %	Mo %	Nb+Ta %	Co %	W %	Al %	Ti %	Fe %	C % max	Mn % max	Si % max	S % max	Cu % max
Inconel 600 UNS N06600 ASTM B167 / B168 / B163	72.0 min	14.0–17.0	—	—	—	—	—	—	6.0–10.0	0.15	1.00	0.50	0.015	0.50
Inconel 601 UNS N06601 ASTM B167 / B168 / B163	58.0–63.0	21.0–25.0	—	—	—	—	1.0–1.7	—	Balance	0.10	1.00	0.50	0.015	1.00
Inconel 617 UNS N06617 ASTM B167 / B168 / ASME SB-167	Bal. (44.5 min)	20.0–24.0	8.0–10.0	—	10.0–15.0	—	0.8–1.5	0.6 max	3.0 max	0.05–0.15	1.00	1.00	0.015	0.50
Inconel 625 UNS N06625 ASTM B444 / B446 / B443	58.0 min	20.0–23.0	8.0–10.0	3.15–4.15	1.00 max	—	0.40 max	0.40 max	5.0 max	0.10	0.50	0.50	0.015	—
Inconel 686 UNS N06686 ASTM B622 / B619 / B626	Bal. (57.0 min)	19.0–23.0	15.0–17.0	—	—	3.0–4.4	—	0.02–0.25	5.0 max	0.010	0.75	0.08	0.020	—
Inconel 718 UNS N07718 ASTM B637 / AMS 5596 / AMS 5662	50.0–55.0	17.0–21.0	2.80–3.30	4.75–5.50	1.00 max	—	0.20–0.80	0.65–1.15	Balance (~17%)	0.08	0.35	0.35	0.015	0.30
Inconel X-750 UNS N07750 ASTM B637 / AMS 5542 / AMS 5598	70.0 min	14.0–17.0	—	0.70–1.20	1.00 max	—	0.40–1.00	2.25–2.75	5.0–9.0	0.08	1.00	0.50	0.010	0.50

Notes: All values in weight percent (wt%). Highlighted columns (Ni, Cr, Mo, Nb+Ta) represent the primary alloying elements that determine corrosion resistance and solid-solution strengthening. Additional controlled elements not shown: Boron (B) 0.006 max for Inconel 617 and 718; Phosphorus (P) 0.015 max for Inconel 625 and 718, 0.04 max for Inconel 686. “Balance” indicates the remainder after all specified elements are accounted for. Specification limits shown are per the applicable ASTM/AMS standard listed; individual heats are certified to these limits on the Material Test Report (MTR). For procurement, always cross-reference the project specification (NACE, API, ASME) for any additional chemistry or testing requirements.

Inconel Grade Comparison Table

Use the table below to make a first-pass selection. For detailed chemical composition, mechanical properties, and dimensional specifications, follow the product page links in each grade section above.

 

Grade	UNS	Key Alloying Elements	Max Service Temp	Strengthening Mechanism	Best Application
Inconel 600	N06600	Ni 72%, Cr 16%	1177°C (2150°F)	Solid solution	Furnace components, alkaline service, nuclear
Inconel 601	N06601	Ni 60%, Cr 23%, Al 1.4%	1200°C (2200°F)	Solid solution + Al₂O₃ scale	Cyclic oxidation, radiant tubes, heat treatment
Inconel 617	N06617	Ni 54%, Cr 22%, Co 12%, Mo 9%	1093°C (2000°F)	Solid solution (Co + Mo)	Advanced gas turbines, highest-temp structural
Inconel 625	N06625	Ni 58%, Cr 21%, Mo 9%, Nb 3.6%	982°C (1800°F)	Solid solution (Mo + Nb)	Offshore, subsea, chemical, marine, FGD
Inconel 686	N06686	Ni 57%, Cr 21%, Mo 16%, W 3.7%	1038°C (1900°F)	Solid solution (Mo + W)	Severe mixed-acid chemical environments
Inconel 718	N07718	Ni 52%, Cr 19%, Nb 5.1%, Mo 3%	649°C (1200°F)	Precipitation hardening (γ” phase)	Gas turbines, aerospace, high-strength structural
Inconel X-750	N07750	Ni 73%, Cr 15%, Ti 2.5%, Al 0.7%	700°C (1290°F)	Precipitation hardening (γ’ phase)	Springs, fasteners, nuclear spacers

 

Inconel vs Hastelloy: Which Alloy Family to Choose?

Inconel and Hastelloy are both nickel-based superalloys which are produced by Special Metals (since renamed PCC). The significant difference lies in the fact that they are intended to be used with a different purpose:

• The inconel grades are usually optimised in the high-temperature strength and oxidation resistance with good corrosion resistance as secondary property. The exception is Inconel 625 which is on the head in terms of corrosion resistance.
• The Hastelloy alloys (especially C-276, C-22, and C-2000) are designed with the highest possible level of corrosion resistance over the broadest possible spectrum of hostile media – both the highly oxidising and the highly reducing. To do this, they trade off some of the high temperature strength.
• Inconel 625 is often the more viable option than Hastelloy C-276 in mixed-service applications (high temperature, as well as aggressive corrosion), as it is easier to fabricate, does not require PWHT, and is cheaper.
• Hastelloy C-276 or C-22 is still the choice when subjected to the most severe chemical conditions – concentrated hydrochloric acid, wet chlorine gas, mixed acid streams.

How to Select the Right Inconel Grade for Your Application

Material selection for nickel superalloys is driven by four primary variables. Work through these in order:

Step	Question to Answer	Grade Direction
1 — Operating Temperature	What is the maximum continuous service temperature?	Above 980°C → 601 or 617 | 650–980°C → 625 (Gr.2) or 686 | Below 650°C → 600, 625 (Gr.1), or 718
2 — Corrosion Environment	Is the medium aqueous, acidic, chloride-bearing, or oxidising at temperature?	Seawater/chloride → 625 or 686 | Mixed acid → 686 | Alkaline/mildly corrosive → 600 | Oxidising high-temp gas → 601 or 617
3 — Strength Requirement	Is maximum tensile/yield strength the design driver (e.g., structural, fasteners)?	Maximum strength → 718 (PH) | High strength + corrosion → 625 | Spring/relaxation → X-750
4 — Fabrication Method	Is welding involved? Is post-weld heat treatment feasible?	No PWHT possible → 625 or 600 | PWHT available → 718 or X-750 | Cyclic thermal shock → 601

 

Kalpataru Inconel Products 

Kalpataru Piping manufactures and supplies pipes, tubes, flanges, fittings, bars, fasteners, and plates across the complete Inconel alloy family. Each product family below links to full specifications, dimensional data, and chemical/mechanical property tables:

•       Inconel 600 Pipes & Tubes  →  /inconel-600-seamless-pipes-tubes-supplier-exporters/
•       Inconel 601 Pipes & Tubes  →  /inconel-601-seamless-pipes-tubes-supplier-exporters/
•       Inconel 625 Pipes & Tubes  →  /inconel-625-pipes-tubes-supplier-exporters/
•       Inconel 718 Pipes & Tubes  →  /inconel-718-seamless-pipes-tubes-supplier-exporters/
•       Explore our complete Inconel Products range  →  /inconel-products/

Conclusion 

No single Inconel grade is universally superior. The low price point of mild high-temperature and chemical service is Inconel 600. Inconel 601 and 617 are used in the applications of extreme oxidation and cyclic thermal service. Inconel 625 prevails in every case of aqueous corrosion, chloride or complicated offshore fabrication. When the structural strength of 1000Mpa or higher is required, then the only option available is Inconel 718. Inconel X-750 is used in the spring and fastener applications which are not applicable with 718.

The strongest specification mistake in factory procurement is the defaulting to Inconel 625 on all nickel alloy demands. Although the most popular grade is 625 due to its versatility, 718 when required by strength or 601 when required by cyclic oxidation will be higher performance at a reduced overall cost.

You can take your project specification and ask Kalpataru Piping technical team to look and consult on grade, schedule, standard and certification and Kalpataru Piping technical team can review your operating conditions to suggest the right alloy and supply format. 

→  Need Help Selecting the Right Inconel Grade for Your Project?      Submit a Specification Enquiry  |  export@kalpatarupiping.com  |  +91 022-66337137