- Inconel (nickel-chromium) is chosen for high temperature; Incoloy (nickel-iron-chromium) is the cheaper heat- and acid-resistant option.
- Monel (nickel-copper) is best for sea water, brine, caustic and hydrofluoric acid.
- Hastelloy (nickel-molybdenum-chromium) handles the most aggressive chemicals: hot chlorides, wet chlorine and mixed acids.
- Always specify the UNS number (e.g. N06625 for Inconel 625), not just the trade name.
When stainless steel is not enough, engineers reach for nickel alloys, the "percentage items" of the steel trade. The four names that come up most are Inconel, Incoloy, Monel and Hastelloy. They are trade names, not grades, and each family contains several alloys. This guide explains what each family is good at, how they differ, and how to choose.
The four families at a glance
| Family | Main elements | Known for | Common alloys | Relative cost |
|---|---|---|---|---|
| Inconel | Nickel, chromium (some with Mo, Nb) | Strength and oxidation resistance at high temperature | 600, 601, 617, 625, 718 | High to very high |
| Incoloy | Nickel, iron, chromium | Economical heat and acid resistance (an iron-rich cousin of Inconel) | 800, 800H/HT, 825 | Medium-high |
| Monel | Nickel, copper | Sea water, brine, hydrofluoric acid, caustic | 400, K-500 | High |
| Hastelloy | Nickel, molybdenum, chromium | Severe wet corrosion: hot acids, chlorides, mixed chemicals | C-276, C-22, B-2 | Very high |
Inconel, Incoloy and Monel are trademarks of Special Metals Corporation; Hastelloy is a trademark of Haynes International. The alloys themselves are made by many mills under their UNS numbers, which is what you should specify on a drawing. Our nickel alloy pages list UNS and Werkstoff numbers for each.
Inconel: heat first
Inconel alloys are nickel-chromium alloys that hold their strength and resist scaling in hot gases. Where stainless 310S gives up at around 1,100 °C, Inconel 600 and 601 work in furnaces, heat-treatment fixtures and exhaust systems at similar or higher temperatures for far longer. Inconel 625 adds molybdenum and niobium, which gives it excellent corrosion resistance too, so it is used in sea water, flue-gas scrubbers and chemical plants as well as hot sections. Inconel 718 is a precipitation-hardened alloy with very high strength, used for shafts, fasteners, gas-turbine parts and oil-and-gas tooling.
Choose Inconel when the problem is heat, or heat plus corrosion, and the budget allows.
Incoloy: heat and acids at a lower price
Incoloy alloys contain more iron and less nickel than Inconel, which makes them cheaper while keeping much of the performance. Incoloy 800 and its high-carbon variants 800H and 800HT are the standard materials for furnace tubes, heat-exchanger tubes and steam-reformer pigtails at 600–1,000 °C. Incoloy 825 adds molybdenum and copper and is tuned for wet corrosion: sulphuric and phosphoric acid, sour gas and pickling plants.
Choose Incoloy when you need better heat or acid resistance than 316L or 310S but Inconel is more than the job requires.
Monel: sea water and hydrofluoric acid
Monel is about two-thirds nickel and one-third copper. That combination is almost immune to sea water, brine and most alkalis, and it is one of very few metals that resist hydrofluoric acid. Monel 400 is used for pump shafts, valve trim, sea-water piping, heat-exchanger tubes and chemical equipment handling fluorides. Monel K-500 is the age-hardened version with roughly three times the strength, used for pump shafts and fasteners.
Monel is not a high-temperature alloy; keep it below about 500 °C, and note that it is not suitable for oxidising acids such as nitric acid.
Choose Monel when the environment is sea water, brine, caustic or hydrofluoric acid.
Hastelloy: the most severe chemical service
Hastelloy C-276 and C-22 are nickel-molybdenum-chromium alloys with tungsten. They resist a wider range of aggressive chemicals than any other common alloy: hot chlorides, wet chlorine gas, hypochlorite, mixed acids, and the unpredictable streams found in pharmaceutical, agrochemical and dye plants. C-276 is the workhorse; C-22 handles oxidising conditions slightly better and is often chosen for new reactors where the process may change.
Choose Hastelloy when 316L and 904L have already failed, or the process stream is too aggressive or too variable to risk anything less.
Composition compared
| Alloy | UNS | Ni | Cr | Mo | Fe | Cu | Other |
|---|---|---|---|---|---|---|---|
| Inconel 600 | N06600 | 72 min | 14–17 | — | 6–10 | 0.5 max | — |
| Inconel 625 | N06625 | 58 min | 20–23 | 8–10 | 5 max | — | Nb 3.15–4.15 |
| Incoloy 800 | N08800 | 30–35 | 19–23 | — | 39.5 min | — | Al, Ti |
| Incoloy 825 | N08825 | 38–46 | 19.5–23.5 | 2.5–3.5 | 22 min | 1.5–3 | Ti |
| Monel 400 | N04400 | 63 min | — | — | 2.5 max | 28–34 | — |
| Hastelloy C-276 | N10276 | Balance | 14.5–16.5 | 15–17 | 4–7 | — | W 3–4.5 |
The full chemistry of all 17 alloys we supply is on the chemical composition chart.
Selection guide by problem
| Your problem | First choice | Alternative |
|---|---|---|
| Furnace parts, heat-treatment fixtures above 900 °C | Inconel 601 / 600 | Incoloy 800HT, SS 310S (lower temperature) |
| Heat-exchanger and reformer tubes at 600–1,000 °C | Incoloy 800H / 800HT | Inconel 600 |
| Hot and corrosive: flue-gas, scrubbers, sea-water heat exchangers | Inconel 625 | Super duplex 2507, 254 SMO |
| High-strength shafts, bolts, downhole tools | Inconel 718 | Monel K-500 (sea water) |
| Sulphuric / phosphoric acid, sour gas | Incoloy 825 | Alloy 20, SS 904L |
| Sea water, brine, caustic soda | Monel 400 | Super duplex 2507 |
| Hydrofluoric acid | Monel 400 | — |
| Hot chlorides, wet chlorine, mixed or changing acids | Hastelloy C-276 | Hastelloy C-22 |
| Caustic soda above 300 °C, chlorine gas (dry) | Nickel 200 / 201 | Monel 400 |
What they cost, roughly
Nickel alloys are priced per kg and move with the nickel and molybdenum markets. As a rule of thumb, with SS 304 as 1: Incoloy 800 is around 4–6 times, Monel 400 and Inconel 600 around 6–9 times, Inconel 625 and Incoloy 825 around 8–12 times, and Hastelloy C-276 around 12–18 times. The ratios shift from month to month, so treat them as a guide to the order of magnitude, not a quote. For today's rate on a specific size, send us the alloy, form and quantity.
Common mistakes
- Over-specifying. Hastelloy in a job that 316L or 904L handles wastes money. Ask what actually failed before upgrading.
- Buying by trade name only. Write the UNS number on the order and check it on the mill test certificate.
- Wrong filler wire. Each alloy needs a matching or over-alloyed filler (for example ERNiCrMo-3 for Inconel 625, ERNiCrMo-4 for C-276). Welding with a stainless filler undoes the corrosion resistance at the joint.
- Mixing Monel with oxidising acids. Monel is excellent in reducing media and poor in nitric acid.
We stock and source Inconel, Incoloy, Monel, Hastelloy, Nickel 200/201, Alloy 20, 254 SMO and super duplex in sheet, plate, bar, pipe and flanges, with mill test certificates, and deliver all over India. Start with the alloy pages or ask us which alloy fits your service.