For flange buyers, the choice also affects the material specification, kaynak prosedürü, companion piping materials and purchasing documents. This guide explains the selection logic without assigning a universal concentration or temperature limit.

Hastelloy B2 and C276 Are Different Nickel Alloys

Hastelloy B2 is a nickel-molybdenum alloy identified as UNS N10665. Hastelloy C276 is a nickel-chromium-molybdenum-tungsten alloy identified as UNS N10276. Their different chromium and molybdenum balances are central to how they behave in reducing and oxidizing environments.

The official HASTELLOY C-276 alloy page identifies UNS N10276 and describes its broad corrosion resistance. The producer’s corrosion-resistant alloy specifications page lists product-form specifications for B-2 and C-276. These are screening and specification references, not project-specific approval.

Why Hydrochloric Acid Service Needs More Than a Grade Name

Hydrochloric acid is strongly reducing, but real process streams may also contain ferric or cupric salts, chlorine, hypochlorites, nitric acid, dissolved oxygen or other oxidizing species. Those contaminants can shift the selection away from what a clean-acid chart might suggest. Dilution, shutdown, cleaning and startup can also expose the flange to conditions that differ from normal operation.

Define at least these conditions before selecting either alloy:

• normal, minimum and maximum hydrochloric acid concentration;
• normal, cleaning and upset temperatures;
• oxidizing contaminants, chlorides, solids and other process chemicals;
• aeration, akış hızı, stagnant zones and crevice geometry;
• welding, ısıl işlem, pickling and field contamination controls; Ve
• acceptable corrosion allowance, design life and inspection plan.

A flange joint adds gasket contact, bolting loads and crevice conditions. Data from a simple coupon or a different process state should not be treated as automatic approval for the complete joint.

When Hastelloy B2 May Be the Better Candidate

B2 may deserve priority when the documented service is strongly reducing and substantially free of oxidizing contaminants. Its high molybdenum content supports resistance in many hydrochloric-acid environments. The low chromium content that helps define the alloy also means oxidizing species must be evaluated carefully.

Do not extend clean-acid performance data to an aerated or contaminated process without review. Confirm the complete pressure boundary, welds, gasketed crevices, cleaning chemicals and abnormal operating states.

When Hastelloy C276 May Be the Better Candidate

C276 may be the more robust candidate when the process includes mixed chemistry or plausible oxidizing contamination. Chromium and tungsten contribute to its broad resistance profile, while molybdenum supports performance in reducing environments. This wider envelope can be valuable where feed composition or operating states vary.

C276 is not a universal solution. Concentration, sıcaklık, kirleticiler, velocity, crevices and fabrication condition still control the decision. If representative corrosion data do not cover the actual process, a qualified materials review or testing program is needed.

B2 vs C276 Flange Selection Table

What ASTM B564 Defines for Forged Flanges

Forged or rolled nickel-alloy flanges are commonly specified to ASTM B564 where its scope and listed grade apply. The purchase order should identify the exact UNS grade—N10665 for B2 or N10276 for C276—together with the project-adopted edition. Do not order by the trade name alone.

The material specification does not complete the flange description. State the dimensional standard, such as ASME B16.5 where applicable, plus nominal size, basınç sınıfı, flanş tipi, karşı karşıya, bore or matching pipe schedule, tolerances and required supplementary examination. Confirm compatibility with the adjoining pipe, gasket, bolting and welding procedure.

Eight Details to Include in the RFQ

1. Material identity: UNS N10665 veya UNS N10276, not only a trade name.
2. Malzeme özellikleri: applicable ASTM specification and project-adopted edition.
3. Geometry: flanş tipi, nominal boyut, bore or pipe schedule and quantity.
4. Pressure connection: boyut standardı, class and facing.
5. Service: hydrochloric acid concentration range, temperatures and operating states.
6. Contaminants: oxidizing species, chlorides, solids and cleaning chemicals.
7. Quality requirements: izlenebilirlik, MTC, PMI or additional testing only where the order requires them.
8. Commercial scope: inspection points, destination, required schedule and approved deviations.

Do not infer stock, sertifikasyon, test scope or lead time from a material page. These points must be confirmed against the exact flange schedule and purchase requirements.

Sıkça Sorulan Sorular

What are the key differences between Hastelloy B2 and C276?

B2 is a nickel-molybdenum alloy focused on reducing environments. C276 adds substantial chromium and tungsten for a broader balance across reducing and oxidizing conditions. Their UNS designations are N10665 and N10276 respectively.

Which is better for hydrochloric acid, B2 or C276?

B2 is often screened for clean reducing hydrochloric acid, while C276 may be preferred when oxidizing contamination or mixed chemistry is possible. Neither can be selected safely without concentration, temperature and contaminant data.

Is Hastelloy C276 resistant to hydrochloric acid?

C276 has useful resistance in many hydrochloric-acid environments, but it is not immune under every concentration, temperature or contamination condition. Use representative data for the actual service.

What is Hastelloy B2?

Hastelloy B2 is a nickel-molybdenum corrosion-resistant alloy designated UNS N10665. It is commonly evaluated for reducing chemical environments, including defined hydrochloric-acid service.

Can B2 and C276 flanges be substituted for each other?

Not automatically. They have different compositions, UNS designations and corrosion behavior. Any substitution requires engineering approval and confirmation of the material specification, design basis, welding and service conditions.

What ASTM specification applies to forged B2 and C276 flanges?

ASTM B564 is commonly used for forged or rolled nickel-alloy flanges where the selected grade and product form are within scope. Confirm the UNS grade, project-adopted edition and all dimensional requirements on the purchase order.

References checked 10 October 2026. Producer and standards references are screening resources; they do not replace project-adopted specifications or a qualified corrosion assessment.