Technical knowledge
Inconel 625 flanges to ASTM B564: properties, classes and ordering notes
Inconel 625 flanges to ASTM B564 and UNS N06625: chemistry, mechanical properties, ASME B16.5 class coverage, heat treatment, NDT scope and purchase order wording.
Which standards actually govern an Inconel 625 flange
Four documents define a 625 flange and they are frequently confused on purchase orders. ASTM B564 covers the nickel alloy forging material and its mechanical properties; ASME B16.5 (up to NPS 24) or B16.47 series A or B (above NPS 24) controls dimensions, facing and pressure class; ASME B16.20 covers the gasket; and MSS SP-25 covers marking. A flange can be compliant with all four and still fail in service if the purchase order did not state the heat treatment condition and the hardness limit.
For seamless tube and butt weld fittings in the same alloy the companion specifications are ASTM B444 or B829 for tube, ASTM B366 for wrought fittings and ASTM B443 for plate used in blind flanges or spades.
Chemistry and mechanical properties that matter
The alloy is strengthened in the annealed condition by molybdenum and niobium in solid solution rather than by precipitation hardening, which is why it welds without losing corrosion resistance and why post weld heat treatment is rarely required for corrosion service.
| Item | Value | Why it matters |
|---|---|---|
| Nickel | 58 % minimum | Chloride stress corrosion cracking immunity |
| Chromium | 20.0 - 23.0 % | Oxidising acid and scaling resistance |
| Molybdenum | 8.0 - 10.0 % | Pitting and crevice resistance |
| Niobium plus tantalum | 3.15 - 4.15 % | Stabilises against sensitisation |
| Yield strength, annealed | 414 MPa minimum | Setting for allowable stress |
| Tensile strength, annealed | 827 MPa minimum | Ductility margin |
| Typical PREN | 45 - 51 | Roughly double that of 316L |
| Density | 8.44 g/cm3 | Weight and cost per metre |
Where Inconel 625 outperforms duplex and stainless steel
- Stagnant or warm seawater. Duplex resists flowing seawater well but crevice attack starts under gasket faces when the line sits idle at elevated temperature.
- Hypochlorite dosing. Residual oxidant pushes stainless past its pitting threshold within weeks.
- Sour service. 625 is listed in NACE MR0175 / ISO 15156 in the annealed condition and is commonly used for wellhead and christmas tree components.
- Flue gas desulphurisation. The combination of chlorides, low pH and fluorides defeats most stainless grades.
- Mixed acid streams. Where both oxidising and reducing species are present the chromium and molybdenum balance of 625 covers a wider window than a straight molybdenum or straight chromium alloy.
What to state on the purchase order
- Material specification ASTM B564 and UNS N06625, plus the dimensional standard and pressure class, for example ASME B16.5 Class 300 weld neck, raised face.
- Heat treatment condition: solution annealed is the default for corrosion service; hot worked or stress relieved gives higher strength but lower corrosion margin.
- NDT scope: ultrasonic examination of the forging, dye penetrant on machined sealing surfaces, and PMI coverage percentage.
- Documentation: mill test certificate to EN 10204 3.1 quoting actual results from the heat lot, with an SGS third party test report where independent verification is required.
- Marking to MSS SP-25 so the heat number survives installation and future inspection.
Questions about this topic
Is Inconel 625 the same as Alloy 625?
Yes. Alloy 625, Inconel 625 and UNS N06625 refer to the same nominal composition. Inconel is a registered trademark of Special Metals Corporation, so procurement documents should use UNS N06625 or the ASTM designation to stay vendor neutral.
Can Inconel 625 flanges be used in seawater without coating?
Yes, and coating is usually discouraged because a damaged coating creates a small anode and a large cathode, which accelerates localised attack. Control crevice geometry and avoid dissimilar metal couples instead.
Does an Inconel 625 flange need post weld heat treatment?
Not for corrosion service. Stress relief is sometimes specified for dimensional stability of large machined assemblies, but unnecessary thermal exposure in the 540 to 870 C range can precipitate secondary phases and reduce toughness, so agree the cycle before it is applied.
Which filler metal should be used for welding 625 flanges to pipe?
ERNiCrMo-3 for matching welds and ENiCrMo-3 for covered electrodes. Where 625 is welded to carbon steel, butter the carbon steel face first with the same filler before the final joint so the dilution zone is controlled.
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.
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