Complete Buyer Guide for Hastelloy Alloys: How to Select Between C276, C22, B2, B3 and C4 for Corrosive Process Conditions

Hastelloy alloys are not interchangeable. Choose the wrong grade and your equipment may fail in weeks instead of years - not because the alloy is low quality, but because it was matched to the wrong environment. This guide compares Hastelloy C276, C22, B2, B3, and C4 across chemical composition, corrosion resistance, welding performance, and service temperature. You will learn which alloy handles oxidizing acids, which handles reducing acids, which is best for welded structures without post-weld heat treatment, and which mistakes cause the most expensive field failures. Use the selection table below to match your medium, temperature, and fabrication method to the right alloy - in 60 seconds.

Short answer - match the alloy to your corrosion environment, not the other way around:

The single rule that prevents 90% of selection mistakes: identify whether your environment is oxidizing or reducing before you look at any alloy.

• Oxidizing (nitric acid, ferric chloride, cupric chloride, wet chlorine, hypochlorite) → need chromium. Choose C276, C22, or C4.
• Reducing (hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid) → need molybdenum. Choose B2, B3, or C276.
• Both oxidizing and reducing (mixed acids, flue gas desulfurization, chemical process with varying conditions) → need chromium + molybdenum. Choose C276, C22, or C4.

The critical warning: B2 and B3 contain no chromium. If any oxidizing species enters your system - nitric acid, ferric ions, cupric ions, dissolved oxygen in high concentration - the corrosion rate of B2/B3 increases dramatically. This is the single most common cause of Hastelloy B-series field failures. If you cannot guarantee the absence of oxidizers, choose C276 or C22 instead.

Hastelloy C276 (UNS N10276)

• Core feature: Higher molybdenum & tungsten content; excellent resistance to chloride‑triggered pitting & crevice corrosion.
• Best‑fit scenarios: Wet chlorine, flue‑gas desulfurization(FGD), ferric‑chloride pickling solution, mixed acid containing chloride ion, seawater cooling equipment.
• Not suitable: Strong pure oxidizing media (high‑concentration nitric acid); pure hot concentrated hydrochloric acid.

Typical C276 applications: FGD absorber towers, chemical reactors, heat exchangers, pickling equipment, seawater piping. For production-grade C276 plate, bar, pipe, and wire, see our Hastelloy C276.

Hastelloy C22 (UNS N06022)

• Core feature: Higher chromium content than C276; outstanding anti‑oxidation capacity; excellent heat‑affected‑zone corrosion resistance after welding; no mandatory post‑weld heat treatment required for many cases.
• Best‑fit scenarios: Nitric‑sulfuric mixed oxidizing acid, incinerator flue‑gas equipment, welding‑heavy pressure vessels, fluctuating oxidizing‑reducing alternating environment.
• Not suitable: Pure high‑temperature concentrated hydrochloric acid.

Typical C22 applications: pharmaceutical equipment, bleaching plants, seawater desalination, welded pressure vessels. For C22 in all product forms, see our Hastelloy C22.

Hastelloy C4 (UNS N06455)

• Core feature: Great metallurgical thermal stability; highly resistant to sensitization and intergranular corrosion in welding & 650‑1040 ℃ thermal exposure; tungsten‑free formula; no need post‑weld solution annealingHaynes Int....
• Best‑fit scenarios: Equipment suffering repeated welding & thermal upset condition, agro‑chemical reactor, halogen‑containing process, equipment cannot perform post‑weld heat treatment.
• Not suitable: Severe high‑chloride pitting condition (inferior local corrosion resistance compared with C276).

Typical C4 applications: welded chemical equipment, FGD components, pulp and paper bleaching. For C4 plate, sheet, bar, and wire, see our Hastelloy C4.

Hastelloy B2 (UNS N10665)

• Core feature: Nickel‑molybdenum alloy without chromium; superior performance in pure reducing acid.
• Best‑fit scenarios: Pure hydrochloric acid, dilute non‑oxidizing sulfuric acid, phosphoric acid without oxidant addition.
• Critical limitation: Sensitive to thermal exposure of 500‑900 ℃; brittle intermetallic phase precipitates; strictly forbidden in any oxidizing medium containing ferric ion / cupric ion / nitric acid. Mostly used for legacy‑equipment replacement today.

Typical B2 applications: hydrochloric acid reactors, pickling equipment, heat exchangers. For B2 pipe, bar, and plate, see our Hastelloy B2.

Hastelloy B3 (UNS N10675)

• Core feature: Upgraded iteration of B2; optimized impurity control and element ratio; largely eliminates brittleness risk in intermediate temperature range while preserving excellent reducing‑acid corrosion resistance.
• Best‑fit scenarios: New‑project hydrochloric‑acid reactor, heat exchanger, piping, where welding and thermal processing are required. First choice for modern B‑series application.
• Not suitable: Any oxidizing‑agent containing medium.

Typical B3 applications: hydrochloric acid plants, acid regeneration, pickling equipment. For B3 in all product forms, see our Hastelloy B3.

• Flue‑gas desulfurization scrubber with high chloride: C276
• Reactor handling nitric‑sulfuric mixed acid, many welding joints: C22
• Equipment subject to repeated welding where post‑weld annealing cannot be executed: C4
• Brand‑new hydrochloric acid synthesis equipment, welding fabrication required: B3
• Old‑plant maintenance for legacy B‑2 equipment: prefer upgrade to B3, keep B‑2 only for exact spare‑part replacement.

• Always specify full UNS number besides commercial grade name, avoid confusion of similar‑named alloys.
• Require Mill Test Report(MTR), PMI/XRF inspection report for every batch, verify chemical composition against ASTM standard.
• Confirm delivery condition: C‑series and B‑series Hastelloy material should be supplied under solution‑annealed state.
• B‑series alloy cannot contact oxidizing impurity inside process fluid, otherwise corrosion rate surges sharply.
• For welded construction: C4 & C22 have better as‑weld performance; C276 recommends stabilizing heat treatment after welding; B2/B3 must control welding heat input strictly.

Pitfall 1: Using B2 or B3 where oxidizing species are present.
This is the single most common and most expensive mistake. B2/B3 contain no chromium. If ferric or cupric ions enter a hydrochloric acid system, they act as oxidizers and cause rapid corrosion of B2/B3. If you cannot guarantee the absence of oxidizers, choose C276 or C22.

Pitfall 2: Assuming C276 and C22 are interchangeable.
C276 has higher molybdenum (15–17% vs 12.5–14.5%) for better chloride resistance. C22 has higher chromium (20–22.5% vs 14.5–16.5%) for better oxidizing resistance. Choose based on whether your environment is dominated by chlorides (C276) or oxidizing acids (C22).

Pitfall 3: Ignoring weld heat-affected zone performance.
C22 and C4 offer superior weld HAZ corrosion resistance compared to C276. If you are welding large structures and cannot perform post-weld heat treatment, C22 or C4 may be the better choice even if C276 has higher base-metal corrosion resistance.

Pitfall 4: Specifying B2 for a new project.
B2 has been largely superseded by B3. B3 offers better thermal stability and weldability with equivalent corrosion resistance. For new projects, specify B3 instead of B2. B2 is only appropriate for legacy replacement where the original specification calls for it.

Pitfall 5: Overlooking C4 for welded equipment.
C4 is the most sensitization-resistant alloy in the Ni-Cr-Mo family. It does not require post-weld solution treatment for most applications. If welded structures are central to your design, C4 may reduce fabrication cost and complexity.

Pitfall 6: Buying on certificate alone.
Two suppliers can both provide a certificate of compliance while their material differs in grain size, precipitate distribution, and actual corrosion performance. Request measured corrosion data, PMI verification, and heat treatment records.

Whether you need C276 for mixed acids and chlorides, C22 for oxidizing environments, B2 or B3 for pure hydrochloric acid, or C4 for welded structures, the right choice depends on your specific medium, temperature, and fabrication requirements.

Explore our Hastelloy products → [Hastelloy C276] | [Hastelloy C22] | [Hastelloy B2] | [Hastelloy B3] | [Hastelloy C4]

Or contact our technical team with your medium type, concentration, temperature, and welding requirements - we will recommend the right alloy and supply condition.

Q1: What is the difference between Hastelloy C276 and C22?

A: C276 has higher molybdenum (15–17% vs 12.5–14.5%) for better chloride and pitting resistance. C22 has higher chromium (20–22.5% vs 14.5–16.5%) for better oxidizing acid resistance and superior weld HAZ performance. Choose C276 for chlorides and mixed acids; choose C22 for oxidizing acids and welded structures.

Q2: What is the difference between Hastelloy B2 and B3?

A: B3 is the improved version of B2 with better thermal stability. B3 resists Ni₄Mo precipitation in the 600–800°C range, so it maintains ductility after welding and can be used in the as-welded condition for many applications. For new projects, choose B3 over B2.

Q3: Can I use Hastelloy B2 in oxidizing environments?

A: No. B2 contains no chromium and must NOT be used in oxidizing media or where oxidizing contaminants (ferric or cupric ions) are present. If oxidizers enter a hydrochloric acid system, B2 corrosion rate increases dramatically. For oxidizing environments, use C276 or C22.

Q4: What is the difference between Hastelloy C276 and C4?

A: C4 has lower carbon (≤0.015% vs ≤0.01%) and titanium stabilization (≤0.70%), giving it better resistance to sensitization and intergranular corrosion after welding. C4 does not require post-weld solution treatment for most applications. C276 has higher molybdenum and tungsten, offering higher reducing acid resistance and higher maximum service temperature. Choose C4 for welded structures; choose C276 for maximum reducing acid resistance.

Q5: Which Hastelloy alloy should I choose for hydrochloric acid?

A: For pure hydrochloric acid with no oxidizers, choose B2 (cost-effective) or B3 (better thermal stability, modern choice). For hydrochloric acid with possible oxidizing contaminants or mixed acids, choose C276 or C22 - B2/B3 will fail in the presence of oxidizers.

Q6: Which Hastelloy alloy should I choose for oxidizing acids?

A: Choose C22 for oxidizing acids (nitric acid, nitric + sulfuric acid mixtures, nitric + hydrofluoric acid mixtures). C22's higher chromium content (20–22.5%) provides superior oxidizing resistance. C276 can also handle oxidizing media but with lower chromium content.

Q7: Which Hastelloy alloy is best for welded structures?

A: C4 is the best choice for welded structures because it has the lowest sensitization tendency in the Ni-Cr-Mo family and does not require post-weld solution treatment for most applications. C22 is also excellent for welded structures due to its superior weld HAZ corrosion resistance.

Q8: Can I substitute C276 for B2?

A: Not directly. C276 contains chromium and is designed for mixed oxidizing/reducing environments. B2 contains no chromium and is designed for pure reducing acids. C276 can handle oxidizing media that would destroy B2, but C276 has lower molybdenum content and may not match B2's performance in pure hydrochloric acid. Match the alloy to your specific environment.

Q9: Can Hastelloy B2 or B3 be used for nitric‑acid containing environment?

A: No. B‑series nickel‑molybdenum alloys contain zero chromium. Any oxidizer such as nitric acid, ferric ion or cupric ion will cause severe accelerated corrosion. In this condition you should select C‑series grades such as C276, C22 or C4.

Q10: How do I avoid procurement pitfalls when buying Hastelloy?

A: Key checks:

• Match the alloy to your environment - oxidizing vs reducing.
• Verify the grade - confirm UNS number and equivalence.
• Request the Mill Test Certificate - confirm chemical composition and mechanical properties.
• Check heat treatment condition - solution annealed for optimal corrosion resistance.
• Request PMI verification - confirms material authenticity.
• Confirm weld procedure - especially for B2/B3 which require interpass temperature control.
• Request corrosion data - measured values, not just datasheet numbers.

Q11: What is the one-line rule for choosing Hastelloy?

A: Oxidizing environment → C22 or C276. Reducing environment → B2 or B3. Both oxidizing and reducing → C276 or C22. Welded structures without post-weld heat treatment → C4. If unsure, C276 is the safest default.

Q12: What is the difference between Hastelloy C4 and C276? Should I replace C276 with C4?

A: C4 has far better anti‑sensitization performance after welding and thermal cycling and can skip post‑weld heat‑treatment. However, C276 provides stronger resistance for chloride‑induced pitting and crevice corrosion. You cannot substitute blindly: choose C4 if post‑weld heat treatment is impossible; choose C276 if chloride local‑corrosion risk is your primary threatHaynes Int....

Q13: Can I use C22 to take place of C276?

A: It depends on service medium. C22 performs better under oxidizing mixed acid and welding‑heavy equipment. C276 excels in high‑chloride reducing‑mixed condition. Direct substitution without engineering assessment may trigger unexpected corrosion failure.

Q14: Why should new hydrochloric‑acid project pick B3 instead of B2?

A: B2 will form brittle Ni₄Mo phase when staying within 500‑900 ℃ temperature range during welding or thermal processing, leading to toughness drop and stress‑corrosion risk. B‑3 optimizes composition to mitigate this flaw while keeping equivalent hydrochloric‑acid resistance, which is the mainstream modern selection for new projects.