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Incoloy 800HT (UNS N08811, Werkstoff 1.4959) is a fully austenitic nickel-iron-chromium alloy containing 30–35% Ni, 19–23% Cr, and controlled additions of aluminium (0.25–0.60%) and titanium, with carbon fixed between 0.06–0.10%. It is designed for long-term service above 600°C (1112°F) and is the preferred grade for applications where creep strength, oxidation resistance, and resistance to carburisation are required simultaneously. It is governed by ASTM B407 (pipe/tube), ASTM B409 (plate/sheet), and ASTM B564 (forgings).
| Property | Value |
|---|---|
| UNS Designation | N08811 |
| Werkstoff Number | 1.4959 |
| Density | 8.02 g/cm³ (0.29 lb/in³) |
| Melting Range | 1,357–1,395°C (2,475–2,525°F) |
| Magnetic Properties | Non-magnetic (austenitic, FCC structure) |
| Curie Temperature | -115°C (-175°F) — well below room temperature |
| Max Service Temperature (creep-limited) | 815°C (1,500°F) |
| Max Service Temperature (oxidation-limited) | 1,100°C (2,012°F) intermittent; 1,150°C (2,102°F) continuous |
| Tensile Strength (min) | 450 MPa (65 ksi) |
| Yield Strength (min) | 170 MPa (25 ksi) |
| Elongation (min) | 30% |
800HT alloy has excellent creep strength above 1290°F. Alloy 800ht has similar high temperature properties to 800H alloy. Incoloy 800HT is resistant to a wide range of corrosive media. Its high nickel content makes it resistant to stress corrosion cracking in aqueous corrosive conditions. The high chromium content gives it better resistance to pitting and crevice corrosion cracking.
800HT has good corrosion resistance to nitric acid and organic acids, but limited corrosion resistance in sulfuric and hydrochloric acids. It has good corrosion resistance in both oxidizing and non-oxidizing salts, but pitting may be present in halides. It also has good corrosion resistance in water, steam, and mixtures of steam, air, and carbon dioxide.
Composition | Value |
Ni | 30.0-35.0 |
Cr | 19.0-23.0 |
Fe | ≥39.5 |
Al | 0.25-0.60 |
C | 0.06-0.10 |
Mn | ≤1.5 |
P | ≤0.04 |
Si | ≤1 |
S | ≤0.015 |
Al&Ti | ≤0.5-1.20 |
Cu | ≤0.75 |
Physical Properties | Value |
Density | 8.02 g/cm³ |
Specific heat | 460 J/Kg*K |
Intrinsic resistance | 99 μΩ·cm |
Thermal conductivity | 12.6 W/m*K |
Longitudinal elastic modulus | 19.7x104 MPa |
Curie point | -115 °C |
Magnetic properties | NO |
Melting point | 1357-1395 |
Physical Properties at High Temperatures
Temperatures | Thermal Conductivity (W/m*K) | Average Expansion Coefficient (10-6/℃) | Longitudinal Elastic Modulus (104 MPa) |
Normal Temperature | 12.6 | - | 19.7 |
100 °C | 14.1 | 14.6 | 19.3 |
200 °C | 16.1 | 15.9 | 18.7 |
300 °C | 17.8 | 16.4 | 18.0 |
400 °C | 19.3 | 16.8 | 17.3 |
500 °C | 20.6 | 17.0 | 16.7 |
600 °CC | 23.2 | 17.3 | 15.9 |
700 °C | 24.4 | 17.7 | 15.2 |
800 °C | 25.1 | 18.1 | 14.5 |
900 °C | 25.9 | 18.3 | 13.8 |
1000 °C | 26.7 | 18.6 | 13.1 |
Tensile, min, ksi[MPa] | Yield, min, ksi[MPa] | Elongation, %(min) |
65[450] | 25[170] | 30 |
Elevated Temperature Yield Strength
| Temperature (°C) | Yield Strength Rp0.2 (MPa) | Yield Strength Rp1.0 (MPa) |
|---|---|---|
| 100 | 205 | 230 |
| 200 | 180 | 205 |
| 300 | 165 | 190 |
| 400 | 155 | 180 |
| 500 | 150 | 175 |
| 600 | 145 | 170 |
| 700 | 135 | 160 |
| 800 | 120 | 145 |
High temperature resistance
Incoloy 800HT alloy has excellent high temperature resistance. It can maintain stability at high temperatures and is not easy to soften or flow. This ability makes it suitable for applications in various high temperature environments, such as furnace tubes, heating elements, annealing furnaces, heat treatment equipment and petrochemical units.
Corrosion resistance
Incoloy 800HT alloy has good corrosion resistance and can resist corrosion from a variety of corrosive media. It has good resistance to acidic solutions, alkaline solutions and chlorides. In addition, it can also maintain good corrosion resistance in oxidizing environments.
Based on these characteristics, 800HT alloy is widely used in chemical, petrochemical, oil refining, power and nuclear energy industries. It is used to manufacture reactors, pipelines, heat exchangers, storage tanks, pipelines and pickling equipment.
Anti-oxidation performance
Incoloy 800HT alloy has excellent anti-oxidation properties and can remain stable in high temperature and oxidizing environments. It can form a dense oxide film to effectively prevent the material from being oxidized. Therefore, it can be used to manufacture high temperature furnaces, burners and other high temperature equipment.
Crack and stress corrosion resistance
Incoloy 800HT alloy has good crack and stress corrosion resistance. It can remain stable in high temperature and corrosive environments and is not prone to cracks and stress corrosion cracking. This makes Incoloy 800HT alloy an important material in the oil refining, chemical and nuclear energy industries.
Manufacturing and processing
Incoloy 800HT alloy can be manufactured by conventional processes such as smelting, forging, heat treatment and cold working. During the manufacturing process, the composition and processing temperature of the alloy need to be strictly controlled to ensure the best performance and microstructure.
Processing processes include forging, hot rolling, cold drawing, welding, etc. During the welding process, appropriate welding materials and welding processes should be selected to avoid welding defects and stress corrosion cracking.
STANDARD | WERKSTOFF.NR. | UNS | JIS | BS | GOST | EN | OR |
Incoloy 800HT | 1.4959 / 1.4876 | N08811 | NCF 800HT | NA 15(HT) | ЭИ670 | X8NiCrAlTi32-21 | XH32T |
Product | Standard | Show |
Incoloy 800ht rod bars | ASTM B408, EN 10095 |  |
Incoloy 800ht plate/sheet/strip | ASTM A240, A480, ASTM B409, B906 |  |
Incoloy 800ht pipe tubes | ASTM B407 |  |
Incoloy 800ht fittings | ASTM B366 |  |
Incoloy 800ht forgings | ASTM B564, DIN 17460 |  |
Ethylene furnace quench boilers
Incoloy 800HT is selected for ethylene furnace quench boilers because it provides outstanding resistance to carburization and oxidation at temperatures up to 1100°C. It maintains excellent creep-rupture strength in the extremely hot, carbon-rich environment of ethylene cracking furnaces, preventing premature failure and ensuring long service life.
Hydrocarbon cracking
In hydrocarbon cracking processes, Incoloy 800HT is used due to its superior high-temperature strength and excellent resistance to carburization and nitridation. These properties allow it to withstand the aggressive, high-temperature atmospheres where hydrocarbons are cracked into lighter products without suffering from embrittlement or rapid degradation.
Industrial furnaces
Industrial furnaces require materials that can endure prolonged exposure to high temperatures and oxidizing or carburizing gases. Incoloy 800HT is preferred because of its stable microstructure, high creep strength, and outstanding oxidation resistance, which keep furnace components (such as radiant tubes and hangers) reliable and maintenance-free for extended periods.
Heat-treating equipment
In heat-treating equipment, Incoloy 800HT is chosen for its ability to resist thermal fatigue, oxidation, and carburization at elevated temperatures. It retains good mechanical properties even after repeated heating and cooling cycles, making it ideal for fixtures, baskets, and furnace internals that must perform consistently in heat-treatment operations.
Chemical and petrochemical processing
Incoloy 800HT is widely used in chemical and petrochemical processing because it offers excellent resistance to a wide range of corrosive environments at high temperatures, including organic acids, sulfur compounds, and chloride-containing media. Its high creep strength ensures structural integrity in reactors, piping, and other process equipment under demanding operating conditions.
Superheaters and re-heaters in power plants
Superheaters and reheaters in power plants operate at very high steam temperatures and pressures. Incoloy 800HT is selected for these components due to its exceptional creep-rupture strength, resistance to steam oxidation, and long-term microstructural stability, which prevent tube failures and extend the life of the power generation system.
Pressure vessels
Incoloy 800HT is ideal for pressure vessels operating at elevated temperatures because it combines high creep and rupture strength with excellent resistance to oxidation and general corrosion. It meets stringent design codes for high-temperature service while providing reliable performance and safety in pressurized, hot environments.
Heat exchangers
Heat exchangers made from Incoloy 800HT perform reliably in high-temperature service because the alloy offers superior thermal stability, resistance to oxidation and carburization on both process and utility sides, and high creep strength. This ensures efficient heat transfer and prevents tube wall thinning or cracking over long operating periods.
Incoloy 800HT is suitable for high-temperature dry sulfur-containing flue gas environments (300–650°C) with a corrosion rate of 0.04–0.09 mm/year, but it is not recommended for aqueous sulfuric acid service, especially dilute condensing sulfuric acid below 200°C, where its corrosion rate can reach 1–2 mm/year due to the absence of molybdenum and copper. For aqueous H₂SO₄ service, Incoloy 825 or Alloy 20 is the correct choice.
Sulfuric acid is one of the most widely used industrial chemicals, and its corrosive behavior varies dramatically with concentration, temperature, and phase state (liquid vs. vapor). Understanding where Incoloy 800HT fits in sulfur-containing environments requires distinguishing between high-temperature dry sulfur-bearing gas and aqueous sulfuric acid.
In flue gas desulfurization (FGD) systems, sulfuric acid plants, and refinery furnace stacks, Incoloy 800HT excels in the high-temperature dry gas zone where sulfur compounds exist as SO₂ and SO₃ vapor rather than liquid acid. The alloy's chromium and aluminum content forms a stable oxide scale that resists sulfidation and high-temperature corrosion.
| Environment | Temperature Range | Corrosion Rate (mm/year) | Performance Rating |
|---|---|---|---|
| Dry flue gas containing SO₂/SO₃ | 300–650°C | 0.04–0.09 | Excellent (≥15 year life) |
| Refinery furnace gas (sulfur-bearing) | 600–900°C | 0.15 | Good |
| Dilute H₂SO₄ (5%) at 50°C (liquid) | 50°C | 0.51 | Marginal |
| Condensing dilute H₂SO₄ (5–10%) | 120–200°C | 1.0–2.0 | Not recommended |
| Concentrated H₂SO₄ (>40%) | ≥80°C | >1.0 | Not recommended |
Important Boundary: The critical transition occurs at the sulfuric acid dew point (approximately 120–150°C depending on SO₃ concentration). Above the dew point, dry sulfur gas is manageable for 800HT. Below the dew point, sulfuric acid condenses as a dilute liquid that aggressively attacks 800HT because the alloy lacks molybdenum (for reducing-acid passivation) and copper (specific inhibitor for H₂SO₄ active dissolution).
| Service Zone | Temperature | Recommended Material | Rationale |
|---|---|---|---|
| High-temperature dry gas zone (FGD inlet, furnace) | 300–650°C | Incoloy 800HT | Best creep strength + sulfidation resistance; cost-effective for ≥15-year life |
| Acid dew point zone (heat exchanger inlet) | 120–200°C | Incoloy 926 / 254SMo / Hastelloy C-276 | Mo-containing grades resist condensing dilute H₂SO₄ |
| Aqueous H₂SO₄ (dilute, <10%) | ≤80°C | Incoloy 825 / Alloy 20 | Cu + Mo provide specific H₂SO₄ resistance; rate < 0.1 mm/year |
| Aqueous H₂SO₄ (10–40%) | ≤80°C | Incoloy 825 / Alloy 20 | 825 rate < 0.1 mm/year; Alloy 20 similar with higher Cu |
| Aqueous H₂SO₄ (40–70%) | ≥80°C | Hastelloy C-276 / C-22 | 825/Alloy 20 degrade above 70% or >90°C; switch to Ni-Cr-Mo |
| Concentrated H₂SO₄ (>70%) | Any | Hastelloy C-276 / Silicon iron / Tantalum | Extreme service; requires specialty materials |
Use Incoloy 800HT in the hot, dry gas section of sulfur-containing systems. For any zone where liquid sulfuric acid may condense or exist as a process fluid, switch to Mo- and Cu-bearing grades (825, Alloy 20, C-276). This is the single most common material specification error in sulfuric acid plant design.
The following case studies illustrate real-world applications of Incoloy 800HT in chemical and petrochemical processing environments, demonstrating both its strengths and its application boundaries.
Case 1: Ethylene Cracking Furnace Quench Boiler Tubes
Industry: Petrochemical | Location: China | Operating Temperature: 900–1,100°C | Service Life: 15+ years
Challenge: Ethylene cracking furnaces operate at 900–1,100°C with cyclic thermal loading. Conventional austenitic stainless steels (304H, 310S) suffer from carburization, thermal fatigue cracking, and excessive creep deformation within 3–5 years. The quench boiler (TLE) tubes must simultaneously resist high-temperature oxidation, carburization from hydrocarbon atmosphere, and thermal shock from rapid temperature changes during decoking.
Solution: Incoloy 800HT (UNS N08811) was selected for TLE tube bundles. The alloy's controlled Al+Ti content (0.85–1.20%) provides gamma-prime precipitation strengthening that maintains creep resistance at 900°C+. The coarse grain structure (ASTM 5) achieved by solution annealing at 1,149°C ensures maximum stress-rupture life. The 30–35% Ni content resists carburization by forming a stable, slow-growing oxide scale.
Result: Tube life extended from 3–5 years (310S) to 15+ years (800HT). No carburization-related failures observed. ASME Code allowable stress at 900°C is 50% higher than 304H. Estimated savings: $2.5M per furnace over a 15-year cycle.
Case 2: 500,000 t/y Ethylbenzene/Styrene Unit — High-Temperature Process Piping
Industry: Petrochemical | Location: China | Operating Temperature: 600–855°C | Welding: GTAW + SMAW
Challenge: A 500,000-ton/year ethylbenzene/styrene unit required high-temperature process piping operating at 600–855°C. The piping must maintain creep-rupture integrity for a 20-year design life while being field-welded into a complex pipeline network. The material needed to be weldable without requiring post-weld solution annealing (impractical in the field).
Solution: Incoloy 800HT pipe (ASTM B407) was specified. Welding was performed using GTAW for the root pass (ERNiCr-3 filler, 99.99% argon backing gas) followed by SMAW fill passes (ENiCrFe-3 electrodes). Key parameters: interpass temperature ≤100°C, low heat input (10–18 kJ/cm), stringer bead technique. For service above 855°C, a stress-relief PWHT at 900°C ±10°C for 2 hours was applied using electric resistance furnaces for overall heat treatment.
Result: First-pass welding qualification rate of 99%. RT (radiographic testing) pass rate: 98.5%. No creep-related failures in 12+ years of service. The unit achieved design life without unplanned shutdowns for piping replacement.
Case 3: Hydrogen Reformer Outlet Manifold and Pigtails
Industry: Petrochemical / Refining | Operating Temperature: 750–900°C | Design Life: 100,000 hours
Challenge: Steam methane reformer (SMR) furnaces operate with catalyst tubes at 850–950°C. The outlet manifold and pigtail connections must collect and transport 850°C hydrogen-rich gas at 30–40 bar pressure. The manifold experiences creep, thermal cycling during start/stop, and oxidation from both the inner process gas and outer furnace atmosphere. Material failure causes unplanned furnace shutdowns costing $50,000–$100,000 per day in lost production.
Solution: Incoloy 800HT was selected for the outlet manifold, pigtail tubes, and header connections. The alloy's ASME Code allowable stress at 850°C is among the highest of any wrought alloy in its cost class. The Al+Ti-strengthened microstructure maintains creep ductility over 100,000+ hours. Field welding used ERNiCr-3 filler with strict interpass temperature control (≤93°C) and low heat input.
Result: Manifold and pigtail system achieved >100,000-hour creep-rupture life at design conditions. No stress-relief cracking or sigma phase embrittlement detected. Reforming unit achieved 5-year turnaround cycles without manifold replacement.
Case 4: Flue Gas Desulfurization (FGD) High-Temperature Duct Section
Industry: Power Generation | Location: Coal-fired Power Plant | Temperature: 350–550°C inlet → 120°C outlet
Challenge: A coal-fired power plant's FGD system experienced rapid corrosion of the inlet duct section (350–550°C), where hot flue gas containing SO₂ and SO₃ caused sulfidation and oxidation of 316L stainless steel ductwork within 2 years. The existing 316L showed corrosion rates >0.5 mm/year, with through-wall penetration at welded joints.
Solution: The high-temperature duct section (inlet to heat exchanger, 300–650°C) was re-fabricated in Incoloy 800HT plate (ASTM B409). The low-temperature tail section (below acid dew point, <150°C) was upgraded to a Mo-bearing grade (Alloy 926) to resist condensing dilute sulfuric acid. This dual-material approach matched each section's environment to the correct alloy chemistry.
Result: 800HT duct section: corrosion rate 0.04–0.09 mm/year — projected life ≥15 years. No sulfidation or scale spallation observed after 5 years of inspection. The total replacement cost was 40% lower than a full C-276 solution while achieving equivalent service life in the hot zone.
Case 5: Nitric Acid Cooling Coil in Nuclear Fuel Dissolver
Industry: Nuclear / Chemical | Operating Temperature: 80–105°C | Medium: Boiling HNO₃ + traces of H₂SO₄ and NaOH (sequential)
Challenge: A nuclear fuel dissolver processes sequentially through sulfuric acid, nitric acid, and sodium hydroxide in the same vessel. The heating coils must survive alternating oxidizing (HNO₃) and reducing (NaOH) environments, plus the mixed-acid phase. Most austenitic stainless steels fail rapidly in the mixed-acid transition.
Solution: Incoloy 800HT was selected for the cooling/heating coil due to its 19–23% chromium content, which provides excellent resistance to nitric acid (oxidizing), and its high nickel content (>30%), which provides resistance to caustic (NaOH). The sequential processing avoids prolonged exposure to concentrated H₂SO₄, keeping 800HT within its performance envelope.
Result: Coil life extended to 10+ years (previous 304L coils lasted 18 months). No intergranular corrosion observed due to Ti-stabilized microstructure. The alloy's non-magnetic properties were also beneficial for the instrument environment.
What is Incoloy 800HT?
Incoloy 800HT is a nickel-iron-chromium alloy (UNS N08811) designed for high-temperature structural applications requiring excellent oxidation resistance, carburization resistance, and creep rupture strength. It offers enhanced mechanical stability and improved high-temperature strength compared with standard Incoloy 800 grades.
What is Incoloy 800HT used for?
Incoloy 800HT is widely used in heat exchangers, furnace components, petrochemical processing equipment, pressure vessels, and power generation systems. Its excellent resistance to oxidation and high-temperature creep makes it suitable for demanding industrial environments.
What is the difference between Incoloy 800H and Incoloy 800HT?
The main difference between Incoloy 800H and Incoloy 800HT lies in the chemical composition control of carbon, titanium, and aluminum. Incoloy 800HT provides better creep rupture strength and superior performance in elevated temperature applications, making it more suitable for long-term service under high thermal stress.
Is Incoloy 800HT suitable for high-temperature service?
Yes, Incoloy 800HT is specifically developed for long-term exposure to temperatures above 600°C. It provides excellent oxidation resistance, structural stability, and creep strength, making it ideal for high-temperature service environments.
What are the main properties of Incoloy 800HT?
Incoloy 800HT offers excellent oxidation resistance, carburization resistance, high creep rupture strength, and good metallurgical stability at elevated temperatures. These properties make it a reliable alloy for high-temperature structural applications.
What standards does Incoloy 800HT comply with?
Incoloy 800HT conforms to UNS N08811 and is commonly supplied according to ASTM B409, ASTM B163, ASTM B407, and ASTM B564 standards, depending on the product form and application requirements.
In what forms is Incoloy 800HT available?
Incoloy 800HT is available in a variety of product forms, including plate, sheet, pipe, tube, round bar, flanges, and forgings. These forms are widely used in industries requiring reliable high-temperature alloy materials.
What is the difference between Incoloy 800, 800H, and 800HT?
Incoloy 800 (N08800) has lower carbon (max 0.10%) and is a general-purpose grade. Incoloy 800H (N08810) has carbon controlled to 0.05–0.10% with a coarse grain structure (ASTM 5 or coarser) for improved creep strength. Incoloy 800HT (N08811) further tightens carbon to 0.06–0.10% and requires Al+Ti to be 0.85–1.20%, providing the highest creep and stress-rupture strength of the three grades for service above 600°C (1112°F).
Can Incoloy 800HT be used in sulfuric acid service?
Incoloy 800HT has limited resistance to sulfuric acid. It performs acceptably in dilute sulfuric acid (up to 5% concentration) at temperatures below 50°C, with a corrosion rate of approximately 0.51 mm/year. For higher concentrations or temperatures, grades containing molybdenum and copper, such as Incoloy 825 or Alloy 20, are strongly recommended. Incoloy 800HT excels in high-temperature dry flue gas containing sulfur compounds (300–650°C), where its corrosion rate is 0.04–0.09 mm/year, but it should not be used in condensing dilute sulfuric acid environments below 200°C.
What is the maximum service temperature of Incoloy 800HT?
Incoloy 800HT is designed for long-term service above 600°C (1112°F). Its maximum temperature for structural/creep-limited applications is approximately 815°C (1500°F). For oxidation-limited applications, it can withstand temperatures up to 1,100°C (2,012°F) for intermittent service and 1,150°C (2,102°F) for continuous service.
What welding consumables are recommended for Incoloy 800HT?
The recommended filler metal is ERNiCr-3 (AWS A5.14) for service below 787°C. For maximum high-temperature mechanical strength above 787°C, ERNiCrCoMo-1 (Alloy 617) is preferred. Matching composition filler metals (ERNiFeCr-1) may also be used. Never use stainless steel fillers such as 308L or 309L, as they create dilution zones prone to hot cracking and sigma phase embrittlement.
Is Incoloy 800HT magnetic?
No. Incoloy 800HT is a fully austenitic alloy with a face-centered cubic (FCC) crystal structure. It is non-magnetic in the annealed condition, with a Curie point of approximately -115°C (-175°F), well below room temperature. It will not attract a permanent magnet at ambient temperature.
What is the difference between Incoloy 800HT and Inconel 625?
Incoloy 800HT (N08811) is a nickel-iron-chromium alloy (30–35% Ni, 19–23% Cr, balance Fe) optimized for high-temperature creep strength and oxidation resistance. Inconel 625 (N06625) is a nickel-chromium-molybdenum alloy (58% min Ni, 20–23% Cr, 8–10% Mo) optimized for aqueous corrosion resistance, especially in chloride and acidic environments. 800HT is better for high-temperature structural service; 625 is better for aggressive chemical corrosion service.
What ASTM standards apply to Incoloy 800HT products?
Incoloy 800HT products are covered by ASTM B407 (seamless pipe and tube), ASTM B408 (bar), ASTM B409/B906 (plate, sheet, and strip), ASTM B564 (forgings), ASTM B366 (welded fittings), and ASTM A240/A480 (plate for pressure vessels). ASME code cases include SB-407, SB-408, SB-409, and SB-564.
Does Incoloy 800HT require post-weld heat treatment (PWHT)?
For typical piping thicknesses up to 50mm, PWHT is generally not required. However, for heavy-wall sections or components operating in the creep range (above 538°C), a full solution annealing at 1,149–1,177°C (2,100–2,150°F) followed by rapid cooling is recommended. For service above 855°C, a stress-relief heat treatment at 900°C ±10°C for a minimum of 2 hours is recommended to eliminate residual stresses and prevent grain boundary cracking.
What is the minimum order quantity (MOQ) for Incoloy 800HT products?
The MOQ depends on product form and stock availability. For standard stock items (common pipe sizes, plate thicknesses), we can supply from 1 piece. For custom-cut or made-to-order items, the MOQ is typically 100kg. Contact our sales team with your specific requirements for a detailed quotation.
How long is the delivery time for Incoloy 800HT?
For items in stock, delivery is 3–7 days for domestic orders and 7–15 days for international shipments. For made-to-order products, the lead time is typically 15–30 days depending on quantity, product form, and specifications. Mill test certificates (EN 10204 3.1) are provided with every shipment.
Why does Incoloy 800HT have higher creep strength than Incoloy 800?
The higher creep strength of 800HT comes from three factors: (1) tighter carbon control (0.06–0.10%) ensures sufficient dissolved carbon for solid-solution strengthening; (2) Al+Ti combined at 0.85–1.20% promotes gamma-prime (Ni₃(Al,Ti)) precipitation that strengthens grain interiors; (3) solution annealing at ≥1,149°C produces a coarse grain structure (ASTM 5 or coarser) that resists grain boundary sliding at high temperature.
Can Incoloy 800HT be used for ASME pressure vessel construction?
Yes. Incoloy 800HT (N08811) is approved under ASME Section VIII Division 1 with Code Case 1325. Allowable stress values are published up to 899°C (1,650°F). The material must be solution annealed with a grain size of ASTM 5 or coarser, verified on the mill test certificate, to qualify for the higher allowable stress values.
