Technical knowledge
Inconel 601 and 617 for elevated temperature fittings and ducting
Inconel 601 and Inconel 617 for furnace, exhaust and reformer piping: oxidation limits, creep strength, thermal fatigue behaviour and how to specify flanges and fittings for hot duty.
Which mechanism actually governs hot duty
Room temperature corrosion data is largely irrelevant above 600 C. The three mechanisms that decide the material are oxidation or scaling, creep rupture and thermal fatigue. A common mistake is to order a high PREN austenitic or nickel alloy because it looks impressive on a corrosion table, then lose the component to scale spalling or creep after two campaigns.
Inconel 601 and 617 compared
| Item | Inconel 601 | Inconel 617 |
|---|---|---|
| UNS number | N06601 | N06617 |
| Chromium | 21 - 25 % | 20 - 24 % |
| Key additions | Aluminium 1.0 - 1.7 % | Cobalt 10 - 15 %, molybdenum 8 - 10 % |
| Oxidation limit in air | About 1200 C | About 1100 C |
| Creep strength | Moderate | High, ASME code coverage for advanced designs |
| Typical use | Furnace muffles, radiant tubes, exhaust ducting | Reformer outlet piping, hot gas ducting, heat exchangers |
Design details that decide whether a hot joint survives
- Allow for thermal growth. Most hot joint failures are restraint failures. Expansion loops, sliding supports and correctly specified bolting matter more than a small difference in alloy creep strength.
- Bolting selection. Carbon steel studs lose preload and oxidise. Use ASTM A453 Grade 660 or a nickel alloy stud matched to the flange, and re-torque after the first thermal cycle.
- Gasket choice. Organic binders burn out. Use graphite or mica filled spiral wound gaskets to ASME B16.20 rated for the metal temperature, not the fluid temperature.
- Avoid thermal cycling through the sensitising range. Repeated heating and cooling through roughly 540 to 870 C can precipitate secondary phases and embrittle the joint.
How to specify hot service flanges and fittings
State the design metal temperature and the design life in hours rather than simply naming an alloy. Ask the supplier to confirm the solution annealing temperature, grain size and, where creep governs, the minimum creep rupture value used for the allowable stress. For welded assemblies in 617, request a weld procedure qualification that includes elevated temperature tensile or stress rupture testing of the joint.
Questions about this topic
Can Inconel 601 be welded without preheat?
Yes, both 601 and 617 are normally welded without preheat and without post weld heat treatment for oxidation service. Control heat input and interpass temperature, and use a matching filler such as ERNiCrCoMo-1 for 617 or ERNiCrFe-11 for 601.
Why does scale spall off hot ducting?
Spalling is usually caused by thermal cycling rather than by the alloy itself. A thick oxide grown at high temperature detaches when the coefficient of thermal expansion mismatch puts it into compression on cooling. Reducing the cycle severity and the peak metal temperature helps more than changing alloy.
Is 617 worth the extra cost over 601?
Yes when the component is pressure containing or creep limited, because 617 has substantially higher stress rupture strength and code recognised allowable stresses. For non pressure furnace internals and ducting, 601 is usually the more economical choice.
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.