Hastelloy Alloy Selection Guide: C-276, C-22 and B-Series Performance in Severe Corrosion

Hastelloy is a trade family, not a single alloy, and the most expensive specification mistakes in chemical plant procurement happen when the family name is used instead of the grade. C-276, C-22, C-2000, C-4, B-2 and B-3 all carry the Hastelloy name, and they behave very differently in the same process stream. A reactor built for mixed acids will suffer in oxidising chlorides if it is made from a nickel-molybdenum grade, while a hydrochloric acid column lined with a chromium-rich grade will corrode faster than the carbon steel around it.

This guide is written from the supply side. We hold and ship the C-series and B-series grades in bar, plate, sheet, strip, seamless tube, welded tube, fittings and welding wire, and the questions we field every week are always versions of the same three: which grade suits the chemistry, which product form and standard to specify, and what documentation to require. The tables below cover family chemistry, the ASTM framework, a corrosion performance matrix, mechanical and physical data, and the fabrication limits that decide whether a grade will survive installation.

1. Mapping the Hastelloy Family

The family splits into three metallurgical groups, and the group always comes before the grade number in the selection logic. The C-series is nickel-chromium-molybdenum, designed for mixed oxidising and reducing service. The B-series is nickel-molybdenum, designed for strong reducing acids such as hydrochloric acid. The high-temperature grades such as Hastelloy X and Hastelloy S are a separate discussion, because they are selected for strength and oxidation resistance at temperature rather than for aqueous corrosion.

2. Chemistry of the C-Series and B-Series

The table below shows the specification chemistry ranges that matter commercially. Molybdenum and chromium are the two elements that decide the corrosion envelope; tungsten, copper and iron fine-tune it; carbon, silicon and phosphorus must be kept low because they drive grain-boundary precipitation and reduce corrosion resistance after welding.

The single most useful observation from this table is that the B-series contains almost no chromium. Chromium is what allows a nickel alloy to build a passive surface film in oxidising conditions, so removing it delivers outstanding performance in hydrochloric acid and very poor performance as soon as an oxidising species appears in the same stream. That is why the presence of dissolved oxygen, ferric or cupric ions, or hypochlorite instantly rules the B-series out.

3. Standards and Product Forms

4. Corrosion Performance Matrix

The matrix below is the practical heart of grade selection. Ratings are comparative within this family and assume material in the solution-annealed condition, correctly fabricated. They are not a substitute for project-specific corrosion testing, and no responsible supplier would present them as a certification.

5. Mechanical and Physical Properties

All of these grades are solid-solution alloys. They are not strengthened by heat treatment, and any quotation that offers them in a hardened condition is describing something else. Strength is increased only by cold work, which is why cold-drawn bar and cold-rolled sheet are harder than the annealed equivalents and why forming limits tighten as the temper rises.

6. Choosing Between C-276 and C-22

This is the decision most buyers face, because the two grades overlap in price and in general appearance while differing in specific environments.

The practical rule we give customers: if the stream is reducing and well established, order C-276 and use the deep stock availability to keep the schedule. If the stream is oxidising, or alternates between oxidising and reducing as it does in chlorination, bleaching, and many effluent systems, order C-22 and accept the narrower availability. If the stream chemistry is genuinely uncertain and cannot be pinned down, C-2000 covers the widest single-grade envelope, and a smaller quantity of the right grade is cheaper than a larger quantity of the wrong one.

7. The B-Series: Powerful, But Unforgiving

The nickel-molybdenum grades exist for one reason: they are the best wrought materials available for hydrochloric acid and for strongly reducing sulphuric and phosphoric acid streams. B-2 has been largely superseded by B-3 because B-2 is prone to forming a harmful nickel-molybdenum phase in the temperature range associated with welding and hot forming, which degrades both ductility and corrosion resistance. B-3 approaches the same corrosion performance with better thermal stability, which means more forgiving fabrication.

Three limitations decide whether a B-series specification is safe:

• No oxidising species. Dissolved oxygen, ferric or cupric ions, hypochlorite or nitric contamination will attack the alloy severely. A trace of air in a hydrochloric acid system is enough to change the answer.
• No high-temperature exposure beyond the qualified range. B-series material should not be held in the phase-formation temperature window unless the procedure and heat treatment have been qualified.
• Matching filler metal. Welding must use a compatible nickel-molybdenum filler, and the procedure should be qualified for the specific grade, because using a C-series filler on a B-3 joint defeats the purpose of the specification.

8. Fabrication and Heat Treatment

8.1 Welding

All of these grades are welded with processes similar to those used for austenitic stainless steel, but the discipline is stricter: clean, dedicated tooling, low heat input, controlled interpass temperature, and matching filler metal. For C-276 the standard filler is ERNiCrMo-4 and for C-22 it is ERNiCrMo-10. Surfaces must be free of sulphur, lead, zinc and shop contamination. Where the service is severe, the weld procedure qualification should include corrosion testing of the welded joint rather than only mechanical testing, because the heat-affected zone is where preferential attack appears first.

8.2 Machining

These alloys work harden rapidly and have low thermal conductivity, so they machine in a way that rewards rigidity and punishes dwelling. Use sharp positive-rake carbide inserts, moderate surface speeds compared with stainless steel, heavy and consistent feeds, and generous coolant. Never let the tool rub: a work-hardened skin on the surface makes every subsequent pass more difficult and can also affect the corrosion performance of a finished part if it is left in a stressed condition.

8.3 Forming and heat treatment

Cold forming is practical with intermediate anneals for severe deformation. Solution annealing is carried out at high temperature followed by rapid cooling, and it is the correct treatment after hot forming or before service where a stressed surface would be vulnerable. For C-4 the metallurgy was specifically designed to retain corrosion resistance after exposure in the sensitising temperature range, which is why it remains in specifications for equipment that cannot avoid such exposure.

9. Stock Forms and Procurement Essentials

Because these grades carry a high unit cost, the commercial difference between a good and a poor purchase is usually in the specification detail, not in the price per kilogram. State the grade with its UNS number, the standard, the product form and size tolerance, the condition (solution annealed is normal), the surface finish, any intergranular corrosion test required, and the certification level. Where the equipment is safety-critical, add third-party inspection and a corrosion test requirement to the weld procedure qualification. For small quantities, a stock-based supplier can often cut plate or bar to size quickly; there is no technical reason to buy a full mill plate to obtain a small part.

10. Frequently Asked Questions

What is the difference between Hastelloy C-276 and Hastelloy C-22?

Both are nickel-chromium-molybdenum alloys, but C-22 contains more chromium and slightly less molybdenum and tungsten. That shift improves performance in oxidising environments such as wet chlorine, hypochlorite and ferric chloride, where C-276 is only moderately resistant. In reducing acids both perform well, and C-276 has the deeper stock availability and longer track record.

Can Hastelloy B-3 be used when the acid contains dissolved oxygen?

No. The B-series relies on a virtually chromium-free composition for its exceptional resistance to reducing acids, and oxidising species attack it rapidly. If oxygen, ferric or cupric ions, or hypochlorite can enter the stream, a C-series grade or a different alloy family must be specified instead. This is one of the most expensive selection errors in chemical plant procurement.

Is Hastelloy suitable for seawater service?

The C-series grades are used in seawater for pumps, valves, fasteners and heat exchangers, and they resist chlorides far better than stainless steels. Crevice and deposit conditions still need attention, and the environment should be evaluated for the specific temperature and oxygen content. The B-series is not suitable for seawater at all.

Which filler metal should be used to weld C-276?

The standard consumable is a matching nickel-chromium-molybdenum filler of the ERNiCrMo-4 family. For C-22, ERNiCrMo-10 is normally used. Do not substitute a stainless steel filler on the basis of convenience; the weld metal would then be the corrosion-limiting feature of the whole fabrication.

Do these alloys need post-weld heat treatment?

Generally no. Solution annealing is used after hot forming and before service in severe duty, and it must be carried out correctly with rapid cooling. C-4 was developed specifically for applications where exposure to a sensitising temperature range cannot be avoided, because it retains corrosion resistance better than C-276 in that condition.

What documentation should accompany a delivery?

An EN 10204 Type 3.1 mill test report that names the heat, the UNS number and the standard, with chemistry and mechanical results. For severe service, add intergranular corrosion test results such as the ASTM G28 method where the end user requires them, plus positive material identification at goods-in and heat-number traceability on every piece.

Why is Hastelloy more expensive than stainless steel, and how can I reduce the cost impact?

The alloying content is the main reason: substantial molybdenum, and in the C-series significant chromium and tungsten, on a nickel base. Cost can be managed by ordering the correct grade rather than an over-specified one, by using thinner gauges made possible by higher strength, by keeping the fabricated design simple to reduce weld length, and by buying cut-to-size stock rather than full mill lots. Selecting a cheaper grade that fails early is the most expensive option of all.

11. Summary

Hastelloy grades are selected by environment first and availability second. Reducing acids point to the B-series, provided that oxidising species can be excluded absolutely. Mixed and variable streams, and anything involving chlorination, point to the C-series, with C-22 preferred for oxidising duty and C-276 as the established default. Phosphoric acid has its own grades. Once the grade is right, the remaining work is specifying the standard and the product form correctly, welding it with matching consumables, and verifying the delivery with the certificate, an identity test and traceable heat numbers.

Send us the stream chemistry, the product form, the size, the quantity and the documentation you require, and our technical sales team will confirm the closest available stock and the condition in which it is held.