Incoloy 800 vs 800H vs 800HT: Complete Temperature Range Guide & Material Selection Reference

Incoloy 800 is suitable for continuous service up to 593°C (1100°F). Incoloy 800H extends this ceiling to 899°C (1650°F) through controlled carbon and grain size. Incoloy 800HT pushes further to 982°C (1800°F) via a tighter aluminium + titanium specification. All three are iron-nickel-chromium alloys governed by ASTM B409/B514 and ASME Code Case approvals, but each targets a distinct thermal duty. Choosing the wrong grade is the leading cause of premature creep failure in high-temperature process equipment.

Incoloy 800 vs 800H vs 800HT

The Incoloy 800 family is among the most widely specified iron-nickel-chromium alloys in process industries worldwide. At first glance, the three grades-Incoloy 800, Incoloy 800H, and Incoloy 800HT-appear nearly identical: same base chemistry, same product forms, sometimes even the same price per kilogram. Yet their elevated-temperature performance differs dramatically. Selecting the wrong variant for a high-temperature application can shorten equipment service life from decades to years.

This guide provides a definitive, data-driven comparison of all three grades. It is structured to answer three practical questions engineers face every day:^[1,4]

What temperature range is each grade designed for?

What are the chemical and microstructural differences that drive those temperature limits?

Which grade should I specify for my application?

Whether you are designing a steam methane reformer, specifying superheater tubing for a heat recovery steam generator (HRSG), or sourcing material for an ethylene cracking furnace, this article gives you the numbers, standards references, and decision logic you need.

All three grades share the same nominal iron-nickel-chromium base: approximately 32–35 wt% Ni, 19–23 wt% Cr, and the balance iron. This combination produces a stable austenitic (face-centred cubic) matrix that resists high-temperature oxidation and carburisation. The grades were developed progressively by Special Metals Corporation (now part of Precision Castparts Corp.) to meet increasingly demanding thermal service requirements.^[1]

The critical engineering differentiators are not the bulk chemistry but rather the controlled carbon content, grain size, and the aluminium + titanium (Al + Ti) balance-three variables that together determine creep strength and microstructural stability at elevated temperatures.^[4,6]

Incoloy 800 was introduced in the 1940s as a weldable, corrosion-resistant heat-exchanger alloy. By the 1960s, demand for higher-temperature petrochemical processing drove the development of 800H, which mandated a coarser grain size (ASTM No. 5 or coarser) to improve creep resistance. 800HT followed, adding a tighter Al+Ti specification (0.85–1.20 wt% vs. the broader 0.30–1.20 wt% of 800 and 800H) to further stabilise the austenitic matrix against sigma-phase formation and carbide coarsening above 800°C.^[1,4,5]

The ASTM B409 (plate/sheet) and ASTM B514 (welded tube) standards define the following nominal compositions. Key differentiating elements are highlighted.^[1,2]

Element / Property	Incoloy 800	Incoloy 800H	Incoloy 800HT	Engineering Significance
Ni (wt%)	30.0–35.0	30.0–35.0	30.0–35.0	Core austenite stabiliser
Cr (wt%)	19.0–23.0	19.0–23.0	19.0–23.0	Chromia scale; oxidation resistance
Fe (wt%)	Balance	Balance	Balance	Matrix element
C (wt%)	≤ 0.10	0.05–0.10	0.06–0.10	KEY: carbide former; creep strength driver
Al (wt%)	0.15–0.60	0.15–0.60	0.25–0.60	Oxide scale adherence
Ti (wt%)	0.15–0.60	0.15–0.60	0.25–0.60	TiC precipitation; grain boundary pinning
Al + Ti (wt%)	0.30–1.20	0.30–1.20	0.85–1.20 ★	KEY: 800HT tighter minimum
Mn (wt%, max)	1.50	1.50	1.50	Deoxidiser
Si (wt%, max)	1.00	1.00	1.00	Deoxidiser
S (wt%, max)	0.015	0.015	0.015	Hot-workability control
Cu (wt%, max)	0.75	0.75	0.75	Corrosion modifier
Grain Size	Not controlled	ASTM 5 or coarser	ASTM 5 or coarser	KEY: coarse grain = better creep

Table 1. Chemical composition ranges for Incoloy 800, 800H, and 800HT per ASTM B409/B514. ★ denotes the tighter 800HT minimum. [1,2]

Key Insight: The minimum carbon floor of 0.05 wt% in 800H and 800HT is what separates them from standard 800. Without a minimum carbon, grain boundaries lack the M₂₃C₆ carbide network that pins dislocations under creep loading. A higher carbon floor plus a controlled coarse grain size is the metallurgical foundation of the elevated temperature rating.

The table below condenses the most specification-critical data points for quick reference during material selection.

Parameter	Incoloy 800	Incoloy 800H	Incoloy 800HT	Source / Note
UNS Designation	N08800	N08810	N08811	[1,2]
W. Nr. / EN designation	1.4876	1.4876	1.4876	[3]
Carbon specification	≤ 0.10 wt%	0.05–0.10 wt%	0.06–0.10 wt%	[1,2]
Al + Ti minimum	0.30 wt%	0.30 wt%	0.85 wt% ★	[1,2]
Grain size (ASTM)	Not specified	No. 5 or coarser	No. 5 or coarser	[4]
Solution anneal temperature	980–1000°C	1120–1180°C	1120–1180°C	[1]
Max continuous service temp.	593°C (1100°F)	899°C (1650°F)	982°C (1800°F)	[5]
ASME BPVC Section I, VIII-1	✓ Approved	✓ Approved	✓ Approved	[8]
ASME max allowable temp. (P.V.)	538°C	899°C	982°C	[8]
Creep-rupture life (relative)	1× (Baseline)	~2× 800	~3–4× 800	[4,6]
Typical cost premium over 800	Baseline	+8–15%	+15–25%	Market indicative
Primary applicable standard	ASTM B409/B514	ASTM B409/B514	ASTM B409/B514	[1]

Table 2. Side-by-side specification summary for Incoloy 800, 800H, and 800HT. ★ = tighter specification in 800HT. [1,2,4,5,8]

Understanding how yield strength and ultimate tensile strength (UTS) decline with rising temperature is essential for pressure vessel and piping design. The data below is drawn from Special Metals technical publications and ASME Section II, Part D.^[7,8]

Grade	Test Temp.	0.2% YS (MPa)	UTS (MPa)	Elongation (%)	Creep-Rupture Life	Source
Incoloy 800	RT	207 min	517 min	30 min	Baseline	[1,7]
Incoloy 800	500°C	~138	~379	~35	Baseline	[7]
Incoloy 800	593°C	~117	~345	~38	Baseline	[7]
Incoloy 800H	RT	170 min	448 min	30 min	~2× 800	[1,7]
Incoloy 800H	649°C	~138	~310	~40	~2× 800	[7]
Incoloy 800H	816°C	~97	~228	~45	~2× 800	[7]
Incoloy 800HT	RT	170 min	448 min	30 min	~3–4× 800	[1,7]
Incoloy 800HT	760°C	~124	~276	~42	~3–4× 800	[7]
Incoloy 800HT	982°C	~62	~172	~50	~3–4× 800	[7]

Table 3. Elevated-temperature mechanical properties. 'min' = ASTM minimum; other values are typical published data. [1,7,8]

Note: Values marked 'min' are guaranteed ASTM minimums. Typical values exceed minimums. Creep-rupture life comparisons are indicative ratios based on 1,000-hour rupture strength at the respective maximum service temperature.^[4,7]

The following table is the central decision tool of this article. For each temperature band, it identifies which grade is suitable, provides representative applications, and explains the engineering rationale. Use this table as the first filter in your material selection process.

incoloy 800 vs 800h vs 800ht Temperature Range

Temp. Range	Typical Applications	800	800H	800HT	Selection Guidance
< 500°C	Water heaters, food processing	✓ 800	✓ 800H	✓ 800HT	Cost drives selection; 800 is most economical
500 – 600°C	HRSGs, heat exchangers	✓ 800	✓ 800H	✓ 800HT	800 adequate; 800H preferred for longer design life
600 – 760°C	Superheater tubes, reformer piping	✗ Marginal	✓ 800H	✓ 800HT	800H optimal; ASME P-No. 45 approved
760 – 900°C	Ethylene cracking, radiant coils	✗ Avoid	✓ 800H	✓ 800HT	800H upper limit; 800HT preferred for > 820°C
900 – 982°C	Steam reformer furnaces, annealing furnaces	✗ Avoid	✗ Marginal	✓ 800HT	800HT is the engineered solution
> 982°C	Short-term, intermittent service	✗ Avoid	✗ Avoid	⚠ Review	Consult specialist; consider Inconel 601/602CA

Table 4. Temperature range selection guide. ✓ = Suitable ✗ = Not recommended ⚠ = Evaluate with specialist. [1,4,5,8]

Critical Engineering Rule: Never use Incoloy 800 (UNS N08800) as a cost-saving substitute for 800H or 800HT in applications exceeding 600°C. Its uncontrolled carbon and fine grain structure produce creep rates up to four times higher than 800HT at 760°C, violating ASME allowable stress limits and potentially causing catastrophic vessel failure.

Incoloy 800 is the workhorse grade for moderate-temperature service where cost matters more than ultimate creep strength. Its excellent aqueous corrosion resistance, combined with solid oxidation resistance up to approximately 593°C, makes it the standard specification for:^[1,5]

Heat exchanger tubing and shells in chemical plants (service fluid temperatures below 500°C)

Sheathing for industrial heating elements (typically 400–550°C)^[9]

Food processing equipment where austenitic corrosion resistance and temperature stability are simultaneously required

Domestic hot water cylinders and indirect heating coils operating below 300°C

Low-pressure steam superheater tubing in industrial boilers rated below 540°C

Incoloy 800H is the primary grade for mid-to-high temperature pressure-containing components where creep is the governing failure mode. It dominates petrochemical and power generation applications:^[1,4,5]

Heat Recovery Steam Generator (HRSG) superheater and reheater tubing in combined-cycle power plants (600–850°C flue gas temperatures)

Ethylene cracker transfer-line exchangers (TLEs) operating at 650–820°C^[6]

Steam methane reformer (SMR) outlet manifolds and pigtail tubing at 700–850°C

Industrial furnace retorts and muffles in the 700–880°C range

Ammonia plant process piping handling hydrogen-nitrogen mixtures at elevated temperature and pressure

Incoloy 800HT is the premium grade for the highest continuous service temperatures within the 800 family. Its tighter Al+Ti specification (minimum 0.85 wt%) ensures superior resistance to sigma-phase embrittlement and better creep-rupture life at temperatures where 800H begins to approach its limits:^[1,4,5]

Steam methane reformer radiant coils at 850–982°C (the highest-temperature application for the 800 family)

Hydrogen production plant reforming tubes operating at outlet temperatures of 800–900°C

Continuous annealing and normalising furnace components where temperatures cycle between 850°C and 980°C

Gas turbine exhaust systems and recuperators in the 800–950°C range

Nuclear steam generator tubing in certain reactor designs requiring combined corrosion and temperature resistance^[10]

All three grades are governed by the same family of ASTM and ASME standards, but the codes impose different maximum allowable temperature limits that track the service temperature ratings summarised in Section 6.

Standard / Code	Product Form	Grade Coverage	Application Scope
ASTM B409	Plate, Sheet, Strip	All three grades	Mechanical properties and composition
ASTM B514	Welded Tube	All three grades	Same composition; longitudinally welded
ASTM B515	Welded Pipe	All three grades	Larger diameter welded pipe
ASTM B163	Seamless Tube (condenser)	800/800H/800HT	Heat exchanger / condenser tubing
ASTM B407	Seamless Pipe and Tube	800/800H/800HT	Pressure piping service
ASTM B408	Rod and Bar	800/800H/800HT	Fasteners and machined components
ASME SB-409	Pressure Vessel Plate	All three grades	BPVC Section VIII Div. 1
ASME SB-514	Welded Tube	All three grades	BPVC Section I (power boilers)
ASME P-No. 45	Weld Procedure Grouping	All three grades	Simplifies WPS qualification
EN 10217-7	Welded Tubes (European)	1.4876 (equiv.)	European pressure equipment
DIN 17459	Seamless Tubes (German)	NiCr33Fe equiv.	German industrial furnace code

Table 5. Applicable standards and code approvals for the Incoloy 800 family. [1,3,8,11]

Use the following matrix as a secondary filter after applying the temperature range guide in Section 6. Tick the criteria relevant to your project and follow the recommendation in the right-hand column.

Selection Criterion	800	800H	800HT	Recommendation & Notes
Design life < 10 yr	✓	✓	✓	800 adequate if temp < 600°C
Design life > 30 yr	⚠	✓	✓	800H/HT ensure creep margins
Operating temp > 700°C	✗	✓	✓	Mandatory upgrade to 800H or 800HT
Operating temp > 900°C	✗	✗	✓	800HT only
ASME BPVC pressure service	✓	✓	✓	All three code-approved; verify temp limits
Cyclic thermal loading	✓	✓	✓	800HT best due to Al/Ti balance
Oxidising atmosphere	✓	✓	✓	Cr₂O₃ scale on all three; 800HT superior > 900°C
Carburising/nitriding	⚠	✓	✓	Higher C in 800H/HT aids resistance
Cost optimisation priority	✓	⚠	✗	800 lowest cost; 800HT carries premium
Weldability	✓	✓	✓	All readily weldable with matching filler

Table 6. Material selection decision matrix. ✓ = Meets criterion ✗ = Does not meet criterion ⚠ = Conditional / review required. [1,4,5,8]

Q1: Can I substitute Incoloy 800H for 800HT to save cost?

Only if the service temperature remains below 870°C and the design life is under approximately 30 years. Above 870°C, 800H's lower Al+Ti content leads to faster grain boundary degradation and higher creep rates. The cost premium for 800HT is typically 10–15% over 800H, which is negligible compared with the cost of a premature furnace tube replacement campaign.^[4,6]

Q2: Are Incoloy 800H and 800HT dual-certified?

Yes. Because 800HT (UNS N08811) is essentially a subset of the 800H (UNS N08810) composition range-with tighter Al+Ti and a narrower carbon band-it is common for mills to supply material that simultaneously meets both specifications. Dual certification reduces inventory complexity for distributors and end users. Always request the full mill test report (MTR) to verify both sets of limits are satisfied.^[1]

Q3: What welding filler metal is recommended?

AWS A5.14 ERNiFeCr-1 (matching composition) or ERNiCr-3 (Inconel 82) are the standard filler metal choices for all three grades. Post-weld heat treatment (PWHT) is generally not required for aqueous service, but a stabilising anneal at 1120°C may be specified for 800H/HT components destined for high-temperature service to restore the controlled grain size and carbide distribution.^[1,12]

Q4: What is the difference between Incoloy 800 and stainless steel 310S?

Both are high-chromium austenitic alloys with good oxidation resistance, but they serve different purposes. SS 310S (UNS S31008) contains approximately 25% Cr and 20% Ni and is optimised for oxidation resistance in intermittent service up to about 1040°C. Incoloy 800HT contains 30–35% Ni and is optimised for sustained creep strength under pressure at elevated temperature. Where pressure containment and long-term creep life at 700–900°C are requirements, the 800-family consistently outperforms 310S.^[7]

Q5: Does Incoloy 800HT resist carburisation?

Yes. The combination of a protective Cr₂O₃ / Al₂O₃ scale and the higher carbon content (which pre-saturates the matrix against further carbon ingress) gives 800H/HT better carburisation resistance than lower-nickel austenitic steels. In severely carburising atmospheres above 950°C, however, alloys with higher nickel content such as Incoloy 803 or Inconel 601 may be preferred.^[5,6]

Q6: What is the density and thermal expansion of these alloys?

All three grades share essentially the same physical properties: density ≈ 7.94 g/cm³ (0.287 lb/in³), mean coefficient of thermal expansion from 20°C to 700°C ≈ 16.0 × 10⁻⁶ /°C (8.9 × 10⁻⁶ /°F), and thermal conductivity at 700°C ≈ 18.0 W/(m·K). These shared physical properties simplify stress analysis when upgrading from one grade to another.^[7]

When ordering Incoloy 800-family products, specify the following on your purchase order to avoid receiving non-conforming material:

UNS Number: N08800 (800), N08810 (800H), or N08811 (800HT). Do not rely on trade name alone.

ASTM Standard and Grade: e.g., ASTM B409, Grade UNS N08811.

Grain Size Certification: For 800H and 800HT, request documentary proof of ASTM No. 5 or coarser per ASTM E112.

Carbon Content (MTR): Verify the certified carbon is within the grade-specific range, especially the 0.05 wt% minimum for 800H and 0.06 wt% for 800HT.

Al + Ti Sum: For 800HT, confirm Al + Ti ≥ 0.85 wt% on the mill test report.

Heat Treatment Condition: Confirm solution-annealed condition (1120–1180°C for 800H/HT) to ensure code-compliant creep properties.

Third-Party Inspection: For critical service (pressure vessels, reformer tubes), specify third-party inspection to ASME or EN requirements.

Dual Certification (if required): Explicitly request N08810+N08811 dual certification if needed for procurement flexibility.

The Incoloy 800 family-800, 800H, and 800HT-occupies a critical niche in high-temperature alloy engineering. The three grades are superficially similar but engineered for fundamentally different thermal duties. To summarise:

Incoloy 800 (UNS N08800): up to 593°C. Cost-effective for moderate heat-exchanger and heating-element service.

Incoloy 800H (UNS N08810): up to 899°C. The standard for HRSG superheaters, ethylene crackers, and reformer outlet piping. Creep life approximately twice that of 800.

Incoloy 800HT (UNS N08811): up to 982°C. The premium grade for radiant reformer coils and continuous high-temperature furnace service. Creep life three to four times that of 800.

Selecting the right grade at the design stage costs nothing. Replacing under-specified tubing in an operating furnace or reactor costs tens of millions of dollars in plant downtime, repair labour, and lost production. The information in this guide-grounded in ASTM standards, ASME code limits, and published metallurgical data-provides the technical foundation to make that selection correctly, first time.

Contact Our Technical Team: We supply certified Incoloy 800, 800H, and 800HT in plate, sheet, seamless tube, welded tube, pipe, bar, and strip forms. All material is accompanied by full mill test reports and, on request, third-party inspection certificates. Contact our technical sales team to discuss your application requirements.

References

[1] ASTM B409-22. Standard Specification for Nickel-Iron-Chromium Alloy Plate, Sheet, and Strip. ASTM International, West Conshohocken, PA, 2022.

[2] ASTM B514-22. Standard Specification for Welded Nickel-Iron-Chromium Alloy Pipe. ASTM International, 2022.

[3] EN 10217-7:2019. Welded Steel Tubes for Pressure Purposes - Technical Delivery Conditions - Part 7: Stainless Steel Tubes. European Committee for Standardization (CEN), Brussels, 2019.

[4] Lai, G.Y. High-Temperature Corrosion and Materials Applications. ASM International, Materials Park, OH, 2007. Chapter 8: Iron-Nickel-Chromium Alloys, pp. 221–248.

[5] Special Metals Corporation. Incoloy® Alloy 800H/800HT Technical Data Sheet. Publication SMC-047. Huntington Alloys, Huntington, WV, 2016.

[6] Norton, J.F., ed. High Temperature Materials Corrosion in Coal Gasification Atmospheres. Elsevier Applied Science, London, 1984. Chapter on Alloy 800H creep-rupture data, pp. 105–130.

[7] ASM Handbook, Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials. ASM International, 2020. Table on Elevated-Temperature Tensile Properties of Nickel and Iron-Nickel Alloys.

[8] ASME Boiler and Pressure Vessel Code, Section II, Part D: Properties (Customary), 2023 Edition. ASME International, New York. Table 1A - Allowable Stress Values for Nonferrous Alloys.

[9] Resistance Heating Technical Committee. Alloy Selection Guide for Electrical Resistance Heating Elements. Electrical Resistance Heater Association (ERHA), Cleveland, OH, 2019.

[10] IAEA Safety Reports Series No. 82. Integrity of Reactor Pressure Vessels in Nuclear Power Plants: Assessment of Irradiation Embrittlement Effects. International Atomic Energy Agency, Vienna, 2009.

[11] DIN 17459:1992. Seamless Circular Tubes of Heat-Resisting Nickel Alloys. Deutsches Institut für Normung (DIN), Berlin, 1992.

[12] AWS A5.14/A5.14M:2018. Specification for Nickel and Nickel-Alloy Bare Welding Electrodes and Rods. American Welding Society, Miami, FL, 2018.