Choose Hastelloy C-22 for mixed oxidizing/reducing environments and bleach systems; C-276 for pure reducing acids (HCl, H2SO4) with no oxidizers present; B-3 only for concentrated HCl with zero oxidizer contamination; and G-30 for phosphoric acid and fluoride-containing fertilizer production environments. C-276 is the most famous Hastelloy but it is the wrong choice wherever oxidizers are present — its low chromium (16%) makes it vulnerable to oxidizing acid attack that C-22 (22% Cr) handles with ease. The wrong grade choice does not just reduce corrosion resistance — it causes premature equipment failure.
If you've ever had to specify a Hastelloy alloy for a project, you've probably found yourself staring at a table of grades wondering: which one do I actually need? C-276 is the most famous — it's what most engineers reach for first. But there are important reasons to choose C-22, B-3, or even G-30 instead. And if you pick the wrong one, your equipment won't last.
I've been supplying Hastelloy alloys for over 30 years across the oil & gas, chemical processing, and pharmaceutical sectors. This guide is a practical decision framework — not just a chemistry table — based on what actually works in the field.
The starting question is almost never "which Hastelloy?" — it's "what's the actual process environment?" Once you know the acid type, concentration, temperature, and presence of chlorides or oxidizers, the right grade usually becomes clear. This guide walks you through that decision process.
1. The Four Grades at a Glance
Hastelloy is a family of nickel-molybdenum-chromium alloys, each optimized for different corrosion environments. The four most commonly supplied grades are:
| Grade | Primary Type | PREN | Best For | Avoid When |
|---|---|---|---|---|
| C-276Alloy C-276, UNS N10276 | Low-carbon, W-stabilized | ~69 | Reducing acids, mixed acids, chloride-rich environments | Strong oxidizers (hot concentrated HNO₃) |
| C-22Alloy C-22, UNS N06022 | Higher Cr, W+V stabilized | ~74 | Both oxidizing AND reducing environments, wet Cl₂ | Highly reducing, very high Mo-demand environments |
| B-3Alloy B-3, UNS N10675 | High Mo, low Cr | ~55 | Hot HCl, H₂SO₄, phosphoric acid — pure reducing acids | Any oxidizing agent, even mild; wet chlorine service |
| G-30Alloy G-30, UNS N06030 | High Cr, moderate Mo, Nb-stabilized | ~52 | Phosphoric acid, sulfuric acid, nitric acid mixtures, fertilizer production | Pure HCl at high temperature |
PREN (Pitting Resistance Equivalent Number) = Cr + 3.3Mo + 16N — higher PREN generally means better resistance to pitting and crevice corrosion in chloride-containing environments. But PREN is not the only metric: Cr content drives oxidizing acid resistance, Mo content drives reducing acid resistance. The balance matters.
2. C-276: The Default Choice — and When It's Wrong
C-276 is the most widely stocked, most commonly quoted, and most well-known Hastelloy grade. It's the sensible default when you don't know exactly which grade you need. But "default" doesn't mean "optimal."
Where C-276 Performs Best
- Hot hydrochloric acid (HCl) at all concentrations up to 20%: excellent resistance. C-276's high Mo content makes it one of the best choices for HCl service.
- Mixed reducing acids — sulfuric acid + HCl mixtures, formic acid, acetic acid: C-276 handles these well.
- Chloride-rich environments: seawater, brine, chloride brines — C-276's PREN of ~69 gives it strong pitting resistance.
- Weld overlay and cladding: C-276 weld overlays on carbon steel equipment are extremely common in chemical plants. The weld metal stays corrosion-resistant.
- Chemical waste incinerator scrubbers: where complex acid mixtures with chlorides are present.
Where C-276 Struggles
- Hot concentrated nitric acid (HNO₃): C-276's low Cr relative to its Mo content means it has poor oxidizing acid resistance. In concentrated HNO₃ above 50%, C-276 can corrode at 1–2 mm/year. Use 316L or 904L instead, or C-22 for a wider envelope.
- Wet chlorine gas (Cl₂): C-276's performance in wet Cl₂ is borderline — some heat-treated conditions in the HAZ can show accelerated corrosion. C-22 was specifically developed to solve this problem.
- Strong oxidizing chlorides like ferric chloride (FeCl₃) and cupric chloride (CuCl₂): C-276 can experience unexpected attack. C-22 handles these better.
- Long-term service above 677°C: C-276 can form secondary phases (sigma, mu) during prolonged high-temperature exposure, reducing toughness and corrosion resistance.
Stock availability: C-276 is by far the most readily available Hastelloy grade. Plate, sheet, bar, and pipe are commonly stocked in thicknesses from 3mm to 50mm. If you're in a hurry, C-276 is usually the fastest to source.
3. C-22: The Upgrade, and When It Earns Its Premium
C-22 was developed primarily to solve two problems with C-276: intergranular corrosion in the weld HAZ during certain exposures, and poor performance in wet chlorine environments. It achieved this by increasing the chromium content from ~16% to ~22% while maintaining high molybdenum and adding a small amount of tungsten.
Where C-22 Outperforms C-276
Wet Chlorine Gas / Chlorine Dioxide
C-22's higher Cr gives it passivation ability in oxidizing chloride environments that C-276 simply doesn't have. This makes it the standard for bleach plants, chlor-alkali processing, and any wet Cl₂ service.
Oxidizing Acid Mixtures
Where C-276 is strong in reducing acids but weak in oxidizing, C-22 maintains corrosion resistance across a wider range — from strongly reducing to moderately oxidizing. Mixed acid environments favor C-22.
Ferric / Cupric Chloride Solutions
FeCl₃ and CuCl₂ solutions are strong oxidizing chloride environments. C-276's resistance in these media is inconsistent; C-22 handles them reliably.
Weld HAZ in Restricted Geometries
In tight welds with restricted cooling, C-276's HAZ can show accelerated corrosion in certain environments. C-22's composition is more stable in the HAZ. For complex fabrications with many weld passes, C-22 reduces risk.
When C-22 Is Not the Right Answer
- Pure high-temperature HCl: if the environment is purely reducing and chloride-rich with no oxidizer, C-276's higher Mo content gives it an edge. C-22 is better across a wide range, but not necessarily the best in this specific niche.
- Very high Mo-demand environments: some highly specific process conditions require maximum molybdenum content. For these, the older C-4 or even B-2/B-3 grades may be more appropriate.
- Cost-sensitive projects with simple environments: C-22 costs roughly 20–30% more than C-276. If the process is purely reducing acid with no oxidizers and no chlorides, C-276 is adequate and C-22 is an unnecessary expense.
4. B-3: The Expert's Choice for Pure Reducing Acids
B-3 (UNS N10675) is a nickel-molybdenum alloy with minimal chromium content (~1.5% Cr). Its composition is dominated by nickel (~65%) and molybdenum (~30%), making it exceptional in pure reducing acids but essentially helpless in oxidizing environments.
Where B-3 Excels
- Hot hydrochloric acid (HCl) at all concentrations, including above 200°C: B-3 has the highest corrosion resistance to HCl of any commercially available alloy. If you have a process with pure HCl at elevated temperature, B-3 is the right answer.
- Sulfuric acid (H₂SO₄) across a wide concentration and temperature range: B-3 is excellent in H₂SO₄ up to 70% concentration and 100°C+.
- Phosphoric acid: B-3 has good resistance in phosphoric acid across most concentrations and temperatures.
- Formic acid and acetic acid: B-3 performs well in these organic acids at elevated temperature.
The Critical Limitation: No Oxidizers Allowed
B-3 will fail catastrophically if any oxidizer enters the system. Even trace amounts of nitric acid, ferric ions, cupric ions, or dissolved oxygen can cause rapid, localized attack. If your process has any possibility of oxidizer contamination — even intermittently — do not specify B-3. C-276 or C-22 will be more tolerant.
Hot Pure HCl (No Oxidizers)
Up to 20% HCl at 100°C+, B-3 corrodes at less than 0.1mm/year. This is the premier application for B-3.
HCl with Trace Oxidizers
Even 0.1% HNO₃ contamination or 100ppm Fe³⁺ can cause rapid pitting. Switch to C-276 or C-22 immediately.
5. G-30: The Phosphoric Acid Specialist
G-30 (UNS N06030) is the newest of the four grades, developed primarily for the phosphoric acid and fertilizer industries. It has the highest chromium content (~30%) among the Hastelloy grades and lower molybdenum (~13%) than the others.
Where G-30 Is the Standard Choice
- Phosphoric acid production: particularly in the wet process phosphoric acid (WPA) loop, where impurities like HF and fluoride ions are present. G-30's high Cr and Nb content give it excellent resistance to fluoride-attack that C-276 and C-22 cannot match.
- Fertilizer production: ammonium phosphate plants, urea synthesis, mixed acid environments with nitrate and sulfate.
- Nitric-phosphoric acid mixtures: G-30 handles oxidizing acid mixtures better than the other Hastelloys. If you have a process involving both HNO₃ and H₃PO₄, G-30 is worth evaluating.
- Sulfuric acid with chloride contamination: G-30's high Cr gives it good resistance to oxidizing conditions in H₂SO₄.
G-30 Limitations
- Pure HCl at high temperature: G-30's lower Mo content makes it inferior to C-276 and B-3 in pure HCl. For pure reducing HCl service, don't use G-30.
- Weldability: G-30 has higher Nb content for stabilization, which makes it slightly more prone to heat-affected zone cracking than C-276. Weld procedure qualification is essential.
- Availability: G-30 is less commonly stocked than C-276 and C-22. Lead times for plate and bar are typically longer. Confirm availability before specifying.
6. Side-by-Side: Key Data at a Glance
| Property | C-276 | C-22 | B-3 | G-30 |
|---|---|---|---|---|
| UNS Number | N10276 | N06022 | N10675 | N06030 |
| Ni (%) | ~57 | ~56 | ~65 | ~43 |
| Cr (%) | ~16 | ~22 | ~1.5 | ~30 |
| Mo (%) | ~16 | ~13 | ~30 | ~13 |
| W (%) | ~4 | ~3 | — | ~2.5 |
| Fe (%) | ~6 | ~3 | ~1.5 | <13 (Bal) |
| Nb (%) | — | — | — | ~0.8 |
| PREN (approx) | ~69 | ~74 | ~55 | ~52 |
| Max Service Temp (°C) | 677 | 677 | 427 | 677 |
| Weldability | Good | Good | Fair (requires care) | Fair (Nb-stab, needs WPS) |
| Stock availability | ★★★★★ | ★★★★ | ★★★ | ★★★ |
7. Decision Framework: How to Choose
Hastelloy Grade Selection Flowchart
8. Common Selection Mistakes to Avoid
Mistake 1: Specifying C-276 for Every Application
- C-276 is not the best choice for oxidizing environments
- It costs more than necessary when C-22 isn't needed
- It may not be the best choice for phosphoric acid
Mistake 2: Confusing B-3 with C-276
- B-3 has almost no chromium — it has NO oxidizing acid resistance
- Specifying B-3 for a process with intermittent oxidizer contamination is a serious engineering error
- Always confirm no oxidizers before specifying B-3
Mistake 3: Ignoring Weld HAZ Performance
- All Hastelloys require low-heat-input welding procedures
- B-3 is the most sensitive to welding — must use ERNiMo-2 filler
- C-276 and C-22 are more forgiving, but must still be welded correctly
- Always qualify the WPS before production welding
Mistake 4: Choosing Based on Price Alone
- C-276 is often cheaper than C-22, but if C-22 is the right grade, the savings are false economy
- Equipment failure costs far more than the material premium
- When in doubt, get an independent corrosion engineering assessment
9. How Findsteel Can Help
We supply all four Hastelloy grades in plate, sheet, bar, pipe, and weld overlay form, with full mill certification and traceability documentation.
- C-276, C-22, B-3, G-30 in stock or on fast lead time
- Plate from 3mm to 80mm, sheet from 0.5mm to 3mm
- Round bar from 10mm to 300mm, hex bar, and forged shaft available
- Weld overlay service on request — C-276/C-22 weld overlay on carbon steel
- Corrosion data consultation — provide your process conditions and we'll recommend the right grade
- PMI (positive material identification) on all deliveries to ensure material grade compliance
Not Sure Which Hastelloy Grade You Need?
Send us your process conditions — acid type, concentration, temperature, and any oxidizers present. We'll recommend the right grade with justification.
Get a Grade Recommendation →