Technical knowledge
Hastelloy C-276 flanges: the reference alloy for aggressive chemical duty
Hastelloy C-276 flanges and fittings to ASTM B564 and B366: composition, corrosion limits, thermal exposure risks, welding filler selection and what to state on the purchase order.
Composition and why each element is there
| Element | Range | Role |
|---|---|---|
| Nickel | Balance, about 57 % | Chloride stress corrosion cracking resistance |
| Chromium | 14.5 - 16.5 % | Oxidising species and passivity |
| Molybdenum | 15.0 - 17.0 % | Reducing acid and pitting |
| Tungsten | 3.0 - 4.5 % | Additional pitting resistance |
| Iron | 4.0 - 7.0 % | Cost and workability |
| Carbon | 0.01 % maximum | Limits carbide precipitation |
| Silicon | 0.08 % maximum | Limits intermetallic formation |
| Typical PREN | About 68 | Top tier pitting resistance |
The very low carbon and silicon limits are deliberate: they slow the formation of carbides and intermetallic phases during thermal exposure, which is the main metallurgical risk with this alloy.
Where C-276 is genuinely required
- Mixed acid streams. Where hydrochloric, sulphuric and oxidising contaminants coexist.
- Flue gas desulphurisation absorbers. High chloride, low pH and fluorides.
- Pharmaceutical and fine chemical reactors. Chlorinated solvents and catalyst residues.
- Pickling lines and acid regeneration. Hot, concentrated and contaminated acid.
- Waste incineration and scrubber outlet ducting. Condensing acidic species with chlorides.
The thermal exposure risk you must control
C-276 held between roughly 550 and 1100 C precipitates mu phase and other intermetallics at grain boundaries, which sharply reduces corrosion resistance even though strength and hardness look normal. This affects welding with excessive heat input, stress relieving that was not required, and hot forming performed outside the recommended window.
Tip Require corrosion testing or microstructural examination after any thermal cycle that was not part of the standard solution anneal. A tensile test will not reveal the problem.
Welding and ordering notes
Weld with ERNiCrMo-4 filler, control interpass temperature, and avoid stress relieving unless the design calls for full solution annealing afterwards. On the purchase order, state ASTM B564 for flanges and ASTM B366 for fittings, UNS N10276, the dimensional standard and class, the solution annealing requirement, NDT scope, and documentation: mill certificate to EN 10204 3.1 plus an SGS third party test report where independent verification is required.
Questions about this topic
Is Hastelloy C-276 weldable without filler metal changes across grades?
No. Use ERNiCrMo-4 for C-276 and do not substitute ERNiCrMo-3 from an Inconel 625 job. The weld metal chemistry will not match and the joint becomes the weak point in acid service.
Can C-276 flanges be stress relieved?
Only with care. Stress relieving in the precipitation range can damage corrosion resistance. If stress relief is required, either agree a cycle outside the critical range or plan a full solution anneal afterwards and re-test.
Is C-276 suitable for seawater?
It performs extremely well, but it is rarely economical for clean seawater. Inconel 625, super duplex 2507 or titanium will usually satisfy the duty at lower cost. C-276 earns its price in aggressive chemical streams.
Questions about our products
What products does Hangbo Alloy supply?
Four product families, all available in nickel-based alloys, titanium, duplex and special stainless steel: flanges, butt weld pipe fittings, elbows, and seamless tube and pipe. Flanges cover weld neck, long weld neck, slip-on, blind, socket weld, threaded and lap joint patterns. Fittings and elbows cover concentric and eccentric reducers, equal and reducing tees, caps, stub ends, and 45°, 90° and 180° returns in both long and short radius, plus 3D and 5D bends for piggable lines. Seamless tube and pipe is supplied cold drawn or hot finished from 6 mm to 630 mm outside diameter.
Which alloy grades are available for these products?
More than 90 grades are published in our grade library. The most requested are Inconel 625, 718, 600 and X-750, Hastelloy C-276, C-22 and B-2, Monel 400 and K-500, Incoloy 800H, 825 and 925, duplex 2205 and super duplex 2507, 316L, 904L and 254SMO stainless steel, and titanium Grade 2 and Grade 5. Nickel-based grades can also be supplied with VIM plus ESR double melting where cleanliness or fatigue life is critical.
What sizes, wall thicknesses and pressure classes can you supply?
Flanges run from NPS ½ to NPS 24 to ASME B16.5 and from NPS 26 to NPS 60 to ASME B16.47 Series A or B, in pressure classes 150 through 2500. Butt weld fittings and elbows run from NPS ½ to NPS 48 (DN 15 to DN 1200) in wall thickness Schedule 5S through XXS. Seamless tube and pipe covers 6 mm to 630 mm outside diameter, in random lengths of about 5 to 7 metres or fixed lengths up to 12 metres. Non-standard and intermediate sizes are quoted on request.
Which material and dimensional standards do you work to?
Forged flanges to ASTM B564, B381 and A182 with dimensions to ASME B16.5 and ASME B16.47. Butt weld fittings and elbows to ASTM B366 and A403 with dimensions to ASME B16.9 and MSS SP-43. Seamless tube and pipe to ASTM B444, B423, B622, B163, B167, B861, A312, A213 and A790. Marking follows MSS SP-25 and the applicable product standard. If your project is governed by EN, DIN, JIS or a company specification, send the document and we will confirm equivalence before quoting.
Is there a minimum order quantity?
There is no minimum for standard sizes and grades held in stock, and prototypes, spares and small trial batches are accepted. Made-to-order melts and special forgings carry a minimum weight that depends on the alloy and the route, typically from about 500 kg for special grades.
What inspection and certification is issued with the goods?
Every shipment carries an EN 10204 3.1 mill test certificate quoting the actual chemical and mechanical results for the specific heat lot, together with dimensional records and heat treatment data where applicable. Testing is carried out in house by optical emission spectrometry, tensile, impact and hardness testing, plus ultrasonic and eddy current examination, with hydrostatic pressure and intergranular corrosion testing to ASTM G28 or A262 Practice E where the specification requires it. Third party inspection by SGS or another recognised agency can be arranged, and their report is issued alongside the shipment.
What are typical lead times?
Standard stock items ship within days. Common production grades such as Inconel 625 or duplex 2205 are typically a few weeks. Special chemistries, larger forgings and items that require third party inspection take longer and are quoted individually against the requirement.
How are the products packed for export?
Flanges and fittings receive a rust preventive coating, are individually wrapped and are packed in plywood cases secured with steel banding. Tube ends are capped and bundles are strapped. Packing lists quote heat numbers so every case can be cross-checked against the mill certificate on arrival. We quote EXW, FOB, CFR, CIF and DAP, and mixed-alloy orders can be consolidated into one shipment with a single documentation package.
How do I request a quotation or a sample?
Send the grade or UNS number, the dimensions including schedule or wall thickness, the governing material and dimensional standards, quantity, any heat treatment or NDT scope and the certificate type you need; a drawing is ideal for special flanges and fittings. Email demi@nickel-alloy.com or message us on WhatsApp +86 15618279078 and we normally issue a formal quotation within 24 hours on working days. Samples and previous test reports can be arranged before the first order.
Talk to an engineer
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