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Certifications: EN 10204 3.1 / 3.2 material test certificates, PMI and elevated-temperature mechanical testing, and complete export documentation packages.
Incoloy 800
(UNS N08800)
A world-class technical reference for EPC contractors, process and mechanical engineers, procurement heads, and TPI inspection agencies specifying Incoloy 800 / 800H / 800HT nickel-iron- chromium alloy — covering alloy metallurgy, the critical distinction between the 800/800H/800HT grade variants, high- temperature oxidation and carburization resistance, stress corrosion cracking performance, and the QC and documentation discipline required for critical petrochemical furnace and heat exchanger tube supply.
Key Properties
& Selection Logic
Incoloy 800 (UNS N08800) is a nickel-iron-chromium alloy engineered specifically for high-temperature service — resisting oxidation, carburization, and sulphidation while maintaining useful mechanical strength at temperatures where austenitic stainless steel loses adequate creep resistance and where fully nickel-based superalloys would be an unnecessary cost premium.
1.1 — What Incoloy 800 (UNS N08800) Is and Its Position in the Alloy Landscape
Incoloy 800 (a Special Metals Corporation registered trade name for UNS N08800, though the “Incoloy 800” designation is used generically across the industry regardless of specific manufacturer) is a nickel-iron-chromium alloy with a nominal composition of approximately 32% nickel, 21% chromium, and 46% iron, with the balance comprising minor alloying and residual elements. This composition places Incoloy 800 in an important intermediate position in the high-temperature alloy landscape: it contains substantially more nickel than standard austenitic stainless steel (304/316, which contain only 8–14% nickel) but less nickel than fully nickel-based alloys such as Inconel 600 (approximately 72% nickel) — this intermediate nickel content, combined with its specific alloying balance, gives Incoloy 800 excellent oxidation and carburization resistance at high temperature, good resistance to stress corrosion cracking in chloride and caustic environments where standard austenitic stainless steel is vulnerable, and adequate elevated-temperature strength for many process furnace and heat exchanger applications — all at a materially lower cost than fully nickel-based superalloys, making it the standard, cost-effective choice wherever its specific property combination matches the application’s requirements.
1.2 — Key Engineering Properties
High-Temperature Oxidation Resistance
Incoloy 800’s chromium content forms a protective chromium oxide surface layer that provides good oxidation resistance in air and combustion atmospheres up to approximately 1100°C (2000°F) for intermittent service, and somewhat lower for continuous long-term service — making it suitable for furnace tube, radiant tube, and other high-temperature process equipment exposed to oxidizing combustion gas atmospheres.
Carburization Resistance
Good resistance to carburization (carbon pickup from hydrocarbon-rich, carbon-monoxide-bearing, or other carbon-active process atmospheres at high temperature) — a specific and important property for petrochemical process applications such as ethylene cracking furnace tubes and steam reformer tubes, where carburization of the tube material over time causes embrittlement and reduced ductility that can lead to premature cracking failure.
Stress Corrosion Cracking Resistance
Incoloy 800’s nickel content provides substantially better resistance to chloride-induced stress corrosion cracking and caustic (alkaline) stress corrosion cracking than standard austenitic stainless steel (304/316) — a critical property for steam generator and heat exchanger tubing in power and process applications where SCC of standard stainless steel tubing has historically been a documented failure mode in certain water chemistry conditions.
Good Elevated-Temperature Mechanical Strength
Reasonable creep and stress-rupture strength at elevated temperature (particularly in the 800H and 800HT variants discussed in Section 1.3), suitable for pressure-containing tube and pipe applications operating at temperatures where standard austenitic stainless steel’s creep strength becomes inadequate for the required design life.
1.3 — Critical Distinction: 800 vs. 800H vs. 800HT
| Grade (UNS) | Carbon Content | Grain Size Control | Elevated-Temperature Creep Strength | Typical Application |
|---|---|---|---|---|
| 800 (N08800) | ≤ 0.10% | Standard, no specific requirement | Standard — adequate for moderate-temperature service | General corrosion-resistant service, moderate-temperature process equipment |
| 800H (N08810) | 0.05–0.10% (controlled range) | Coarser grain size specifically controlled (ASTM specified minimum) | Improved — higher carbon and controlled coarse grain size improve high-temperature creep-rupture strength | Furnace tubes, high-temperature pressure equipment requiring documented creep-rupture design allowables |
| 800HT (N08811) | 0.06–0.10% (controlled range) | Coarse grain size plus controlled aluminium + titanium content (0.85–1.20% combined) | Highest — optimised for maximum high-temperature creep-rupture strength | The most demanding high-temperature furnace tube and pressure equipment applications |
Product Forms
& Design Allowables
Incoloy 800/800H/800HT is manufactured across tube, pipe, plate, and bar product forms, each governed by a specific ASTM/ASME standard with elevated-temperature design allowable stress data published in the governing pressure equipment codes. Full detail on related nickel alloys is available across our standards reference library.
Submit form, grade variant, size, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — Governing Standards
ASTM B163 / ASME SB-163 — Seamless Tube for Condensers and Heat Exchangers
Governs seamless nickel and nickel-alloy tube (including Incoloy 800/800H/800HT) for condenser and heat exchanger applications — the primary specification for tubing in shell-and-tube heat exchangers, steam generators, and similar heat transfer equipment.
ASTM B407 / ASME SB-407 — Seamless Pipe
Governs seamless nickel-iron-chromium alloy pipe — the primary specification for larger-diameter Incoloy 800/800H/800HT pipe used in process piping and larger pressure-containing pipe applications beyond the heat exchanger tube range.
ASTM B409 / ASME SB-409 — Plate, Sheet, and Strip
Governs flat-rolled Incoloy 800/800H/800HT product — plate for pressure vessel fabrication, sheet and strip for general fabrication and structural applications requiring the alloy’s high-temperature or corrosion performance.
ASTM B408 / ASME SB-408 — Rod and Bar
Governs rod and bar stock for machined components, forging billet, and fastener manufacture in Incoloy 800/800H/800HT — the base material for bolting and machined fittings in this alloy family.
ASME Section II / VIII — Design Allowable Stress Tables
ASME Section II Part D publishes the design allowable stress values by temperature for 800H/800HT (and, separately though generally lower, for standard 800) referenced by ASME Section VIII (pressure vessels) and B31.3 (process piping) for elevated-temperature pressure-containing equipment design — the specific grade variant (800 vs 800H vs 800HT) determines which allowable stress table applies, reinforcing the critical importance of the grade distinction discussed in Section 1.3.
NACE MR0175 / ISO 15156
For sour (H₂S-containing) service applications, NACE MR0175/ISO 15156 provides material qualification guidance for nickel alloys including the Incoloy 800 family, relevant where this alloy is specified for petrochemical process equipment with sour service exposure alongside its primary high-temperature application.
2.2 — Typical Mechanical and Chemical Composition Reference
| Element / Property | Incoloy 800 (N08800) | Incoloy 800H (N08810) | Incoloy 800HT (N08811) |
|---|---|---|---|
| Nickel | 30.0–35.0% | 30.0–35.0% | 30.0–35.0% |
| Chromium | 19.0–23.0% | 19.0–23.0% | 19.0–23.0% |
| Iron | Balance (~39.5–46%) | Balance | Balance |
| Carbon | ≤ 0.10% | 0.05–0.10% | 0.06–0.10% |
| Aluminium + Titanium | 0.30–1.20% (combined, general range) | 0.30–1.20% | 0.85–1.20% (specifically controlled) |
| Tensile Strength (annealed, MPa) | 450–600 | 450–600 | 450–600 |
| Yield Strength (annealed, MPa) | 170–280 | 170–280 | 170–280 |
| Elongation (%) | 30–40 | 30–40 | 30–40 |
Room-temperature mechanical properties are broadly similar across the three grade variants — the key differentiation is in elevated-temperature creep-rupture behaviour, governed by the carbon content and grain size controls discussed in Section 1.3, not by room-temperature tensile properties.
Corrosion Performance
& Alloy Comparison
Correct heat treatment is essential to achieving Incoloy 800/800H/800HT’s designed high-temperature performance, and the alloy’s specific corrosion resistance profile must be understood relative to alternative nickel alloys to confirm it is the correct material for the intended service.
3.1 — Solution Annealing Heat Treatment
Incoloy 800/800H/800HT is supplied in the solution-annealed condition — heated to a temperature (typically 980–1150°C, with the specific temperature and hold time tailored to achieve the required grain size for the specific grade variant, particularly the coarse grain requirement for 800H/800HT) sufficient to dissolve carbides and other secondary phases into solid solution, followed by rapid cooling (typically water quench for tube and pipe products) to retain this solutionised, single-phase austenitic microstructure. This heat treatment is essential to achieving the alloy’s designed corrosion resistance (avoiding sensitisation, similar in principle to the stainless steel sensitisation risk discussed in RR Hydraulic’s Carbon Steel and other material references, though the specific mechanism differs for this Ni-Fe-Cr alloy family) and its designed elevated-temperature mechanical properties. Any subsequent fabrication welding introduces a heat-affected zone that may require post-weld heat treatment or careful welding procedure control to avoid compromising the alloy’s corrosion and mechanical performance at the weld.
3.2 — Corrosion Performance in Specific Environments
| Environment | Performance | Notes |
|---|---|---|
| High-temperature oxidizing (air, combustion gas) | Excellent to ~1100°C intermittent | Chromium oxide film provides the primary protection mechanism |
| Carburizing atmosphere (hydrocarbon process, high temp) | Good — significantly better than standard austenitic stainless steel | Key property for petrochemical furnace/reformer tube applications |
| Chloride stress corrosion cracking | Good — substantially better than 304/316 stainless steel | Nickel content raises the SCC threshold compared to lower-nickel stainless grades |
| Caustic (alkaline) stress corrosion cracking | Good — a key differentiator vs. standard stainless steel | Specified for caustic evaporator and process equipment for this reason |
| Sulphidation (high-temperature sulphur-bearing atmosphere) | Moderate — inferior to higher-chromium or specialized sulphidation-resistant alloys | Verify specific sulphur content and temperature against alloy limits before specifying for sulphidizing service |
| Reducing acids (e.g., dilute sulphuric, hydrochloric) | Limited — not the alloy of choice for aggressive reducing acid service | Specify a higher-molybdenum nickel alloy (e.g., Hastelloy C-276) for aggressive reducing acid environments instead |
3.3 — Comparison to Related Nickel Alloys
Incoloy 800 vs. Incoloy 825 (UNS N08825)
Incoloy 825 contains higher nickel (~38–46%), added molybdenum (2–3%) and copper (1.5–3%), providing substantially better resistance to reducing acids and pitting/crevice corrosion in chloride environments than Incoloy 800 — but with lower high-temperature strength and oxidation resistance than the 800 family. Specify 825 for aggressive aqueous/chemical corrosion service at moderate temperature; specify 800/800H/800HT for high-temperature oxidation/carburization-resistant service.
Incoloy 800 vs. Inconel 600 (UNS N06600)
Inconel 600 contains substantially higher nickel (~72%) and lower iron than Incoloy 800, providing somewhat better high-temperature corrosion resistance and higher-temperature service capability in certain environments, at correspondingly higher material cost — Incoloy 800’s higher iron content makes it more economical while still meeting the requirements of many high-temperature process applications where the full nickel content of Inconel 600 is not necessary.
Incoloy 800 vs. Standard Austenitic Stainless Steel (304/316)
The fundamental comparison driving Incoloy 800 specification — standard austenitic stainless steel’s nickel content (8–14%) is inadequate for the highest-temperature oxidation/carburization service or for the most demanding chloride/caustic SCC resistance requirements; Incoloy 800’s higher nickel content (30–35%) addresses both limitations at a cost premium over stainless steel but well below fully nickel-based alloys.
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified nickel alloy heat to finished, tested, and packed Incoloy 800/800H/800HT component shipment. Chemical composition, grain size, and mechanical verification are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 / Documentation Requirements
| Certificate | Content | EPC Requirement | When Mandatory |
|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Not acceptable for critical high-temperature/pressure supply | Never for petrochemical furnace/heat exchanger critical supply |
| 3.1 (EN 10204) | Heat-traceable chemical + mechanical test report | Mandatory — all EPC supply | All process, furnace, and heat exchanger component supply |
| 3.2 (EN 10204) | 3.1 + TPI countersign | Critical / owner-specified critical items | Furnace tube, high-consequence pressure equipment |
4.3 — Applications by Industry
Petrochemical Furnace and Reformer Tubes
Incoloy 800H/800HT furnace tube for ethylene cracking, steam methane reforming, and other petrochemical high-temperature process applications — the alloy’s carburization resistance and documented elevated-temperature creep-rupture allowable stress data (per ASME Section II Part D) make it a standard specification for this critical, high-consequence equipment category.
Heat Exchanger and Steam Generator Tubing
Incoloy 800 tube for heat exchanger and steam generator applications where standard stainless steel’s stress corrosion cracking vulnerability in specific water chemistry conditions is a documented concern — the alloy’s improved chloride and caustic SCC resistance provides a meaningful reliability improvement over stainless steel tubing in these services.
Caustic Process Equipment
Incoloy 800 components for caustic evaporator and other alkaline process equipment where caustic stress corrosion cracking of standard stainless steel is a known failure mode — leveraging the alloy’s specific SCC resistance advantage discussed in Section 3.2.
4.4 — Export Packaging Specification
- Tube and pipe ends capped and bore-protected to prevent contamination and moisture ingress during transit, particularly important given the alloy’s typical use in high-purity or high-integrity process service
- Heat/lot number stamped or tagged on each item, cross-referenced to the accompanying material test certificate including grade variant (800/800H/800HT) confirmation
- Components segregated from carbon steel and other dissimilar materials during packing to avoid surface contamination affecting the alloy’s corrosion performance
- Documentation in a waterproof pocket: EN 10204 3.1/3.2 MTC, chemical composition report, grain size report (800H/800HT), mechanical properties report, PMI report, NDT reports, and packing list with grade/form/size breakdown per item
- ISPM-15 timber or export cartons for international shipment, with country of origin and HS tariff code documentation matched to the nickel alloy product category
Submit your form, grade variant, size, and quantity to RR Hydraulic for a complete, certified commercial offer.