Technical knowledge
Incoloy 800H vs 800HT: what the extra letters actually buy
The real difference between Incoloy 800H and 800HT: carbon content, titanium and aluminium limits, grain size requirement, allowable stresses and how to specify the correct variant for hot piping.
What H and HT mean in practice
| Requirement | 800 | 800H | 800HT |
|---|---|---|---|
| UNS number | N08800 | N08810 | N08811 |
| Carbon | 0.10 % maximum | 0.05 - 0.10 % | 0.06 - 0.10 % |
| Grain size | Not specified | ASTM 5 or coarser | ASTM 5 or coarser |
| Titanium plus aluminium | Not combined | Not combined | 0.85 - 1.20 % combined |
| Elevated temperature allowable stress | Not permitted | Permitted | Higher than 800H |
| Typical annealing | About 1150 C | About 1150 C | About 1150 C |
Why grain size is a purchasing requirement
Creep deformation at elevated temperature is strongly influenced by grain boundary area. A coarse grain structure reduces the boundary area available for grain boundary sliding and therefore improves creep rupture life. This is why the ASTM specification for 800H and 800HT states a grain size requirement rather than leaving it as an optional attribute.
Tip Require grain size to be reported on the certificate. Without it there is no evidence that the material qualifies for the elevated temperature allowable stresses used in the design.
Typical duty for 800H and 800HT components
- Steam reformer outlet and transfer piping. The classic application for 800H.
- Ethylene cracking furnace coils and pigtails. Carburisation and thermal fatigue resistance.
- Heat treating and nitriding equipment. Resistance to nitriding atmospheres.
- Nuclear and high temperature heat exchanger tubing. Where the design temperature exceeds the range of stainless steel.
Buying notes
State the exact UNS number, not simply Incoloy 800. Require a solution annealing temperature appropriate to developing the coarse grain size, report the grain size result, and confirm intergranular corrosion testing where the specification calls for it. For welded assemblies use a matching filler and verify the weld metal creep properties for long term hot service.
Questions about this topic
Can I use 800H where 800 is specified?
Usually yes, because 800H meets the 800 chemistry and adds requirements. The reverse is not true: substituting plain 800 for an 800H design removes the grain size and carbon controls that justify the elevated temperature allowable stress.
Is 800HT always better than 800H?
For creep limited designs at the highest temperatures, yes, because the combined titanium and aluminium requirement raises stress rupture strength. For lower temperature applications the difference may not be worth the extra procurement effort.
What happens if the material is fine grained?
It will still meet the chemistry but will not achieve the creep rupture life assumed in the design. This is a documentation and verification failure rather than a visible defect, which is why the certificate must show the grain size result.
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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