Technical knowledge
Inconel 625 vs Hastelloy C-276: a selection method, not a preference
How to choose between Inconel 625 and Hastelloy C-276 using the actual stream chemistry, temperature and failure modes, with composition, PREN and cost boundary guidance for flanges and fittings.
Composition drives the decision
| Item | Inconel 625 | Hastelloy C-276 |
|---|---|---|
| UNS number | N06625 | N10276 |
| Nickel | 58 % minimum | Balance, about 57 % |
| Chromium | 20.0 - 23.0 % | 14.5 - 16.5 % |
| Molybdenum | 8.0 - 10.0 % | 15.0 - 17.0 % |
| Tungsten | Not specified | 3.0 - 4.5 % |
| Niobium plus tantalum | 3.15 - 4.15 % | Not specified |
| Typical PREN | 45 - 51 | About 68 |
| Density | 8.44 g/cm3 | 8.89 g/cm3 |
A three question decision rule
- Is the fluid an oxidising acid or a reducing acid? Oxidising acids such as nitric and chromic favour chromium, where 625 is competitive. Reducing acids such as hydrochloric and sulphuric at concentration favour molybdenum, where C-276 wins.
- Are chlorides present with an oxidising species? Seawater with hypochlorite, or process streams containing ferric or cupric ions, push both alloys toward their pitting threshold; C-276 has the larger margin but 625 is often adequate and cheaper.
- What is the temperature? Above roughly 60 C in chloride service, the margin of 625 narrows faster than that of C-276. That is where the extra cost usually justifies itself.
The cost view that decision makers actually need
Compare installed cost, not kilogram price. C-276 typically carries a significant premium over 625 and a higher density, which increases both material and freight cost. However, both are small compared with a single unplanned shutdown on a critical acid line. Where the duty is clearly within the 625 window, over-specifying C-276 buys little; where it is marginal, the premium is cheap insurance.
Fabrication differences worth knowing
- Welding. 625 with ERNiCrMo-3; C-276 with ERNiCrMo-4. Do not mix fillers.
- Heat treatment. Both are normally used in the solution annealed condition. C-276 is more sensitive to thermal exposure in the 550 to 1100 C range where secondary phases precipitate, so control the cycle and verify with impact or corrosion testing when required.
- Machining. Both work harden; C-276 is generally regarded as somewhat more demanding on tool life.
Questions about this topic
Is Hastelloy C-276 always better than Inconel 625?
No. In clean seawater, in sour service and in oxidising acid duty, 625 often performs as well or better at lower cost. C-276 is the stronger choice for reducing acids, mixed acids and hot contaminated chloride streams.
Can I substitute C-276 flanges on a 625 piping system?
You can, but check galvanic compatibility and welding. Dissimilar filler metals and a large cathodic area on a small anodic area can create problems, and the design allowable stresses differ, so confirm with the piping engineer before substituting.
Which alloy should I choose for flue gas desulphurisation scrubbers?
C-276 is widely used in the most aggressive zones of scrubbers, with 625 and C-22 also common depending on chloride concentration, pH and fluoride content. Base the choice on the actual absorber liquor analysis rather than on a general rule.
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 [email protected] 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
Share your duty conditions and we will shortlist candidate alloys within one working day.