Technical knowledge
Inconel 600 vs Inconel 625: which alloy for your piping?
Composition, corrosion resistance, strength and cost comparison of Inconel 600 and Inconel 625 for flanges and fittings, with clear guidance on where each alloy is the right choice.
The composition difference that drives everything
| Item | Inconel 600 | Inconel 625 |
|---|---|---|
| UNS number | N06600 | N06625 |
| Nickel plus cobalt | 72 % minimum | 58 % minimum |
| Chromium | 14.0 - 17.0 % | 20.0 - 23.0 % |
| Molybdenum | Not specified | 8.0 - 10.0 % |
| Niobium plus tantalum | Not specified | 3.15 - 4.15 % |
| Iron | 6.0 - 10.0 % | 5 % maximum |
| Typical annealed yield | About 240 MPa | 414 MPa minimum |
| Typical PREN | About 17 | 45 - 51 |
Where Inconel 600 is still the better buy
- Caustic evaporators and digesters. High nickel content gives excellent resistance to concentrated sodium hydroxide, where 625 offers no meaningful advantage.
- Furnace and heat treat fixtures. Good oxidation and carburisation resistance at a lower alloy cost.
- Dry chlorine and hydrogen chloride. Useful up to several hundred degrees where no liquid water is present.
- Food and pharmaceutical processing. Cleanability, low iron and a long history of use.
Where Inconel 625 is clearly worth the premium
- Any wet chloride service. Seawater, brine, ballast and produced water all sit above the pitting threshold of 600.
- Sour oil and gas. 625 is listed in NACE MR0175 / ISO 15156; 600 is not commonly accepted for this duty.
- Higher design stress. The yield strength advantage allows a thinner section, which partly offsets the higher cost per kilogram.
- Welded fabrication. 625 tolerates weld thermal cycles without losing corrosion resistance and is widely used as an overlay on carbon steel.
Limits that apply to both alloys
Neither alloy should be selected on corrosion tables alone. Inconel 600 can suffer stress corrosion cracking in high temperature caustic and in polythionic acid formed during shutdown of sulphur bearing units; if that is a credible mechanism, Inconel 690 is usually the upgrade path. Inconel 625 loses toughness if held in the 540 to 870 C range for long periods, so confirm the thermal history for heated service.
Questions about this topic
Can Inconel 600 be used in seawater?
Not for immersed service. Without molybdenum its pitting threshold is low and crevice attack under gaskets and deposits starts quickly. Duplex 2205 or Inconel 625 are the usual alternatives depending on temperature and stagnation.
Is 625 always a safe upgrade from 600?
For corrosion, generally yes. For very high temperature oxidising or carburising duty the higher chromium of some other grades may be preferable, and 625 should not be used where long term exposure between 540 and 870 C is expected without checking toughness.
Do both alloys use the same filler metal?
No. 600 is typically welded with ERNiCr-3 and 625 with ERNiCrMo-3. Using the wrong filler leaves a weld metal that is weaker than the parent in the governing mechanism, which is where most service failures originate.
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
Share your duty conditions and we will shortlist candidate alloys within one working day.