When stainless steel is not enough, engineers turn to nickel alloys. Enquiries for Inconel, Monel and Hastelloy pipes, fittings and flanges are smaller in tonnage but much higher in value — and the buyers expect real technical knowledge. This guide on Inconel vs Monel vs Hastelloy gives you the essentials to quote confidently.
Why nickel alloys?
Nickel-based alloys keep their strength at very high temperatures and resist corrosion where stainless steels fail — hot acids, chlorides, seawater, sour gas and oxidising atmospheres. They are used in:
- chemical and petrochemical plants,
- offshore oil and gas,
- power generation and pollution control (FGD scrubbers),
- marine engineering,
- aerospace and furnace components.
Note: Inconel, Incoloy and Monel are trademarks of Special Metals Corporation; Hastelloy is a trademark of Haynes International. In trade, buyers usually refer to the UNS number or alloy number, such as "Alloy 625".
Inconel: heat and oxidation resistance
Inconel alloys are nickel–chromium based. Chromium gives oxidation resistance at high temperature.
| Grade | UNS | Key features |
|---|---|---|
| Inconel 600 | N06600 | Ni 72% min, Cr 14–17%; furnace parts, heat treatment, chemical processing |
| Inconel 625 | N06625 | Ni-Cr-Mo-Nb; excellent strength and seawater/acid resistance; offshore, chemical |
| Inconel 718 | N07718 | Age-hardenable; very high strength; aerospace, fasteners, wellhead parts |
Inconel 625 is the most requested for piping because it combines strength, weldability and corrosion resistance.
Monel: seawater and hydrofluoric acid
Monel alloys are nickel–copper based.
| Grade | UNS | Key features |
|---|---|---|
| Monel 400 | N04400 | Ni about 63% min, Cu 28–34%; seawater, brine, hydrofluoric acid, marine pumps and valves |
| Monel K500 | N05500 | Age-hardenable version with aluminium and titanium; shafts, springs, fasteners |
Monel 400 is famous for resisting seawater and hydrofluoric acid. You will see it in desalination, marine hardware, HF alkylation units and offshore piping.
Hastelloy: strong acids and chlorides
Hastelloy alloys are mainly nickel–molybdenum–chromium based, designed for the most aggressive chemical environments.
| Grade | UNS | Key features |
|---|---|---|
| Hastelloy C276 | N10276 | Ni balance, Mo 15–17%, Cr 14.5–16.5%, W 3–4.5%; wet chlorine, hot acids, FGD |
| Hastelloy C22 | N06022 | Higher chromium; better in oxidising media; very versatile |
| Hastelloy B3 | N10675 | Ni-Mo; hydrochloric acid at all concentrations |
C276 is the "go-to" grade for pollution control, pickling lines and chemical reactors where pitting and stress corrosion cracking are concerns.
Don't forget Incoloy
Incoloy alloys (nickel–iron–chromium) sit between stainless and full nickel alloys:
- Incoloy 800/800H/800HT (N08800/N08810/N08811): high-temperature furnace and heat exchanger tubing.
- Incoloy 825 (N08825): Ni 38–46%, Cr 19.5–23.5%, Mo 2.5–3.5%, Cu 1.5–3%; sulphuric and phosphoric acid, sour oil and gas.
Quick comparison
| Need | First choice |
|---|---|
| High-temperature oxidation | Inconel 600/601, Incoloy 800H |
| Strength + seawater + acids | Inconel 625 |
| Seawater, HF acid | Monel 400 |
| Hot chlorides, wet chlorine, mixed acids | Hastelloy C276 / C22 |
| Hydrochloric acid | Hastelloy B3 |
| Sulphuric/phosphoric acid, sour gas | Incoloy 825 |
Common ASTM specifications
- Seamless pipe and tube: ASTM B167 (600), B444 (625), B165 (Monel 400), B622 (C276, C22), B423 (825), B407 (800/800H).
- Welded pipe: ASTM B705, B619, B775 depending on alloy.
- Butt weld fittings: ASTM B366 (with grade designations such as WPNCMC for 625 and WPHC276 for C276).
- Forged flanges and fittings: ASTM B564.
- Plate and sheet: ASTM B168, B443, B127, B575, B424.
Always include both alloy name and UNS number in quotations — for example, "ASTM B444 UNS N06625 seamless pipe". Our ASTM vs EN vs IS standards guide explains how these specs fit together.
Verifying nickel alloys
Because these alloys cost many times more than stainless steel, buyers almost always ask for:
- EN 10204 3.1 certificates from the original mill (see EN 10204 3.1 vs 3.2),
- PMI testing of every piece — read our PMI testing guide,
- heat number traceability on every item,
- sometimes third-party inspection.
Pricing tips
Nickel alloy prices move with nickel, molybdenum and cobalt markets and depend heavily on product form and size availability. Quote with a clear validity period (often 7 days) and state the origin of the mill. Weight-based pricing needs accurate density — nickel alloys are denser than steel (around 8.4–8.9 g/cm³). Our pipe weight calculator lets you pick the material for correct weights.
Frequently asked questions
Is Inconel better than stainless steel?
For high temperatures and aggressive corrosion, yes. For general service, stainless steel is far cheaper and perfectly adequate.
Which is more corrosion resistant, Inconel 625 or Hastelloy C276?
Both are excellent. C276 generally performs better in strongly reducing acids and wet chlorine, while 625 offers higher strength and very good all-round resistance.
Is Monel magnetic?
Monel 400 is slightly magnetic at room temperature, which is normal for this alloy.
Can nickel alloys be welded?
Yes, with matching filler metals such as ERNiCrMo-3 for 625 and ERNiCrMo-4 for C276, using controlled heat input.
Key takeaways
- Inconel = nickel–chromium, best for heat and oxidation.
- Monel = nickel–copper, best for seawater and HF acid.
- Hastelloy = nickel–molybdenum–chromium, best for the harshest acids and chlorides.
- Always quote alloy name, UNS number and ASTM specification together.
High-value alloy enquiries reward suppliers who reply fast and accurately. QuoteMitra helps you send a clean, professional quote in minutes.
