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INCOLOY 800 is a form of INCOLOY alloy developed by Specialty Metals. Combining nickel, chromium, and iron with trace amounts of other metals, it is renowned for its strength, durability, and resistance to oxidation, carburization, and sulfidation corrosion.
Incoloy 800 alloy typically contains 15-25% chromium, 30-45% nickel, and small amounts of aluminum and titanium. After rapid cooling from high temperatures, 800 alloy remains in the austenitic monophase region, resulting in a single austenitic structure in service. The alloy's high chromium content and sufficient nickel content provide excellent high-temperature corrosion resistance, leading to widespread industrial applications.
INCOLOY 800 alloy resists corrosion in the harshest environments. It all comes down to its composition. INCOLOY 800 alloy's high nickel content provides good sulfidation resistance, iron reduces the risk of internal oxidation, and chromium provides excellent resistance to oxidation and general corrosion. Its key chemical balance results in excellent performance against a wide range of corrosion types. This includes scaling and stress corrosion cracking, particularly chloride stress corrosion due to the formation of metal chlorides.
1. Excellent corrosion resistance in extremely high temperature aqueous media up to 500°C
2. Good resistance to stress corrosion
3. Good workability
Metallographic structure of Incoloy 800H:
800H is a face-centered cubic lattice structure. Very low carbon content and increased Ti:C ratio increase structural stability and maximum resistance to sensitization and intergranular corrosion. A low-temperature annealing around 950°C ensures a fine-grained structure.
Corrosion resistance of Incoloy 800H:
800H can resist corrosion of many corrosive media. Its high nickel content makes it resistant to stress corrosion cracking in aqueous corrosion conditions. The high chromium content provides better resistance to pitting and crevice corrosion cracking. The alloy has good corrosion resistance to nitric acid and organic acids, but limited corrosion resistance in sulfuric acid and hydrochloric acid. Good corrosion resistance in oxidizing and non-oxidizing salts, in addition to the potential for pitting corrosion in halides. It also has good corrosion resistance in water, steam and mixtures of steam, air and carbon dioxide.
Grade | Ni | Cr | Fe≤ | Al | C | Mn | P≤ | Si≤ | S≤ | Al & Ti | Cu≤ |
Incoloy 800H | 30.0-35.0 | 19.0-23.0 | 39.5 | 0.15-0.60 | 0.05-0.10 | 1.5 | 0.045 | 1.00 | 0.015 | 0.30-1.20 | 0.75 |
Density:
7.95 g/cm³ (0.287 lb/in³)
Melting Range:
1350°C - 1400°C (2460°F - 2550°F)
Specific Heat Capacity (cₚ):
480 J/kg·K (0.115 Btu/lb·°F)
Thermal Conductivity (k):
11.8 W/m·K (6.8 Btu·in/h·ft²·°F)
Mean Coefficient of Thermal Expansion (α):
20 - 100°C: 14.4 µm/m·°C (8.0 µin/in·°F)
20 - 500°C: 15.7 µm/m·°C (8.7 µin/in·°F)
20 - 1000°C: 17.0 µm/m·°C (9.4 µin/in·°F)
Electrical Resistivity (ρ):
1.01 µΩ·m (101 µΩ·cm / 61 µΩ·in)
Modulus of Elasticity (Tension, E):
195 GPa (28.3 x 10⁶ psi)
Magnetic Permeability (µᵣ):
Typically < 1.01 (Essentially non-magnetic / paramagnetic in annealed state at 15.9 kA/m). May become slightly magnetic with severe cold work.
| Property | Temperature °C (°F) | Value (Metric) | Value (Imperial) |
|---|---|---|---|
| Specific Heat (cₚ) | 100°C (212°F) | 520 J/kg·K | 0.124 Btu/lb·°F |
| 500°C (932°F) | 690 J/kg·K | 0.165 Btu/lb·°F | |
| 1000°C (1832°F) | 760 J/kg·K | 0.182 Btu/lb·°F | |
| Thermal Conductivity (k) | 100°C (212°F) | 15.3 W/m·K | 8.8 Btu·in/h·ft²·°F |
| 500°C (932°F) | 21.5 W/m·K | 12.4 Btu·in/h·ft²·°F | |
| 1000°C (1832°F) | 30.5 W/m·K | 17.6 Btu·in/h·ft²·°F | |
| Mean Coeff. Thermal Exp. (α) | 20-200°C (68-392°F) | 14.8 µm/m·°C | 8.2 µin/in·°F |
| 20-400°C (68-752°F) | 15.4 µm/m·°C | 8.6 µin/in·°F | |
| 20-600°C (68-1112°F) | 16.0 µm/m·°C | 8.9 µin/in·°F | |
| 20-800°C (68-1472°F) | 16.6 µm/m·°C | 9.2 µin/in·°F | |
| 20-1000°C (68-1832°F) | 17.0 µm/m·°C | 9.4 µin/in·°F | |
| Electrical Resistivity (ρ) | 100°C (212°F) | 1.06 µΩ·m | 63.5 µΩ·in |
| 500°C (932°F) | 1.11 µΩ·m | 66.4 µΩ·in | |
| 1000°C (1832°F) | 1.20 µΩ·m | 72.2 µΩ·in | |
| Modulus of Elasticity (E) | 100°C (212°F) | 189 GPa | 27.4 x 10⁶ psi |
| 500°C (932°F) | 168 GPa | 24.4 x 10⁶ psi | |
| 800°C (1472°F) | 142 GPa | 20.6 x 10⁶ psi | |
| 1000°C (1832°F) | 110 GPa | 16.0 x 10⁶ psi |
Incoloy 800H retains useful strength from cryogenic temperatures to 1,000C. At room temperature the minimum yield strength is 170 MPa (UTS 450 MPa); at 900C it retains approximately 25 MPa yield and 115 MPa UTS. The 100,000h creep rupture strength of approximately 83 MPa at 900C is the key figure for reformer tube and steam superheater design -- approximately 4x higher than 316H stainless steel at the same temperature.
Property | Metric | Imperial | Standard |
Tensile Strength, UTS (minimum) | 450 MPa | 65 ksi | ASTM B409 / ASME SB409 |
Yield Strength, 0.2% offset (minimum) | 170 MPa | 25 ksi | ASTM B409 / ASME SB409 |
Elongation in 50mm or 4D (minimum) | 30% | 30% | ASTM B409 |
Hardness (maximum) | 90 HRB | 90 HRB | ASTM E18 |
ASTM Grain Size | 5 or finer (mandatory) | 5 or finer (mandatory) | ASTM E112 |
Density | 7.95 g/cm3 | 0.287 lb/in3 | ASTM B409 |
Magnetic Permeability (max) | 1.02 | 1.02 | ASTM A342 |
Temperature | 0.2% Yield Strength | UTS | Elongation | Notes |
20C / 68F (RT) | 170 | 450 | 30 | Mill test certificate minimum values; |
200C / 392F | 150 | 415 | 28 | Feedwater preheating range; |
400C / 752F | 130 | 390 | 26 | Typical superheater outlet temp; |
500C / 932F | 115 | 365 | 25 | Subcritical steam conditions; |
600C / 1,112F | 105 | 340 | 24 | Supercritical steam (SC/USC); |
700C / 1,292F | 80 | 280 | 22 | A-USC conditions; reformer |
750C / 1,382F | 65 | 240 | 20 | Ethylene reformer outlet; |
800C / 1,472F | 50 | 195 | 18 | Ethylene reformer tubes; |
850C / 1,562F | 38 | 155 | 16 | Pyrolysis furnace conditions; |
900C / 1,652F | 25 | 115 | 14 | Key design temperature for |
950C / 1,742F | 15 | 80 | 12 | Primary reformer crown temperature; |
1,000C / 1,832F | 8 | 50 | 10 | Maximum continuous oxidizing service; |
Temperature | 10,000h Rupture | 100,000h Rupture | 1,000,000h Estimated | ASME B31.3 Allowable |
700C / 1,292F | 140 | 100 | ~70 | 55 MPa |
750C / 1,382F | 110 | 83 | ~58 | 45 MPa |
800C / 1,472F | 83 | 60 | ~42 | 34 MPa |
850C / 1,562F | 60 | 42 | ~28 | 20 MPa |
900C / 1,652F | 42 | 28 | ~18 | 14 MPa |
950C / 1,742F | 28 | 18 | ~10 | 7 MPa |
1,000C / 1,832F | 18 | 10 | ~5 | N/A |
Note: ASME B31.3 Class 1 allowable stress = 2/3 of minimum yield at temperature, OR 1/3 of minimum UTS at temperature, OR 100,000h rupture strength x 0.67 -- whichever is lowest. For 900C: allowable = min(170x2/3, 450x1/3, 83x0.67) = min(113, 150, 56) = 14 MPa.
Incoloy 800H has LIMITED but USEFUL resistance in sulfuric acid, primarily in oxidizing conditions at intermediate temperatures. It is NOT the preferred alloy for H2SO4 storage or cooling applications -- but it IS a proven and widely used material in Sulfuric Acid Alkylation (SAU) furnace tubes and high-temperature process piping where the combination of strength and oxidation resistance matters more than pure acid corrosion resistance.
For H2SO4 applications below 260C, Alloy 20, Hastelloy C276, or Hastelloy C22 are the preferred materials.
Sulfuric Acid Corrosion Performance of Incoloy 800H
H2SO4 Concentration | Temperature | Incoloy 800H Performance | Preferred Alternative | Why 800H Is/Is Not Preferred Here |
< 0.01% (deionized water | Up to 200C | EXCELLENT | 316L or 800H itself | Essentially no corrosion; 800H suitable |
0.01 - 0.10% | Up to 150C | GOOD | 316L, 904L | 800H is over-specified and costly; |
0.1 - 10% | Up to 100C | ACCEPTABLE | 904L or 254 SMO | 800H marginal; 904L or Alloy 20 preferred; |
10 - 50% | Up to 100C | LIMITED | Alloy 20 (780825) | Alloy 20 is standard; 800H not recommended |
50 - 85% | 100-260C | ACCEPTABLE | For absorption section | In SAU furnace firebox (oxidizing), |
85 - 98% | 100-300C | POOR | Silicon bronze (C69400) | High-temperature concentrated H2SO4 |
98 - 99.8% | 150-300C | LIMITED to MODERATE | 904L, 254 SMO | For acid plant absorption towers; |
Sulfuric Acid Alkylation is a petroleum refining process that converts isobutane and light olefins (propylene, butylene) into alkylate, a high-octane gasoline blending component. The process uses concentrated 98.5% H2SO4 as a catalyst at temperatures of 30-80C in the reactor, but the feed to the furnace is preheated to 150-260C (300-500F) before entering the reactor.
This preheat is done in the SAU furnace, and the furnace tubes operating in the firebox (exposed to flame radiation at 800-1,000C tube skin temperature) are made from Incoloy 800H.
Service Parameter | Typical Value in SAU Furnace | Why 800H Works Here |
Tube skin temperature | 800-900C (in firebox radiation zone) | 800H creep rupture adequate; |
Process stream temperature | 150-260C inlet / 260-350C outlet | 800H has excellent strength at these temps; |
H2SO4 concentration | 98.5% (alkylation acid) | Concentrated H2SO4 is oxidizing; |
Acid mist and vapor | Present in acid settling tanks | 800H adequate for acid mist; proper |
Furnace tube size (typical) | 2-6 inch OD, sch-80 to sch-160 | 800H is cost-effective at these thicknesses; |
Campaign life | 3-7 years typical | 800H SAU tubes typically last 5-8 years; |
Alternative alloy | 316H or 310S for lower-T sections | For the cooler end (< 200C tube skin) |
Other Sulfuric Acid Applications for Incoloy 800H
· Sulfuric acid regeneration (SAR) plants -- regenerating spent acid at 400-650C; 800H used in the regeneration furnace for acid preheat coils where both acid vapor corrosion and high temperature strength are present.
· Sulfur burning acid plants -- where SO2/SO3 gas mixtures are processed at 400-700C; 800H furnace tubes for the sulfur burner and converter inlet preheaters.
· Metal pickling lines -- 800H used in sulfuric acid pickling coils for steel strip and wire; the combination of hot dilute acid and mechanical vibration requires both corrosion resistance and strength; 800H replaces carbon steel and 316L here.
· Electrolytic metal refining -- 800H anodes and process piping in copper and zinc electrowinning circuits where sulfuric acid media at moderate temperatures is present.
· Phosphate fertilizer production -- wet-process phosphoric acid circuits use 50-55% H2SO4 at 70-90C; 800H can be used for the hottest sections (acid preheaters); 904L or Alloy 31 is preferred for most of the circuit.
WERKSTOFFNR. | UNS | JIS | BS | GOST | AFNOR | EN | OR |
1.4958 / 1.4876 | N08810 | NCF 800H | NA 15(H) | ЭИ670 | Z8NC33-21 | X5NiCrAlTi31-20 | XH32T |
| Product | Standards | Show |
| Incoloy 800H Rods/Bars | ASTM B408, EN 10095 |  |
| Incoloy 800H Sheet/Plate | ASTM A240/ A480/B409/ B906 |  |
| Incoloy 800H Seamless Pipe/Tube | ASTM B829/ B407 |  |
| Incoloy 800H Welded Pipe/Tube | ASTM B829/ B407 |  |
| Incoloy 800H Welded Fittings | ASTM B366 |  |
| Incoloy 800H Forgings | ASTM B564/DIN 17460 |  |
Chemical and Petrochemical Processing—process equipment for theproduction of ethylene, ethylene dichloride, acetic anhydride, ketene,nitric acid and oxy-alcohol
Petroleum Refining—steam/hydrocarbon reformers andhydrodealkylation units
Power Generation—steam super-heaters and high temperature heatexchangers in gas-cooled nuclear reactors, heat exchangers andpiping systems in coal-fired power plants
Thermal Processing Fixtures—radiant tubes, muffles, retorts andfixtures for heat-treating furnaces
Incoloy 800H is the dominant high-temperature nickel alloy in chemical processing -- it has been specified in refinery and petrochemical furnace tubes since the 1970s and now accounts for over 60% of global reformer tube installations by tonnage.
The three most critical application areas are ethylene/olefin production, sulfuric acid alkylation, and ammonia/methanol synthesis -- all of which require the combination of high-temperature creep strength, resistance to specific process chemistry, and the ability to operate without post-weld heat treatment.
Application: Primary reformer furnace tubes, 10-inch OD, 15mm wall, 12-meter length
Service conditions: Natural gas/ethane feed, outlet temperature 870C (1,600F), pressure 2.5 MPa, campaign length 3 years
Quantity: 480 tubes, total 28 tonnes of Incoloy 800H
Why 800H was specified:
· The primary reformer outlet temperature of 870C is at the upper limit for 316H and 310S stainless steel -- their 100,000h creep rupture strength at 900C is insufficient for the required design life of 3 years at this temperature
· 800H ASTM 5 grain size gives approximately 83 MPa 100,000h rupture strength at 870C (interpolated), providing a design margin of approximately 2x over the calculated hoop stress
· 800H is significantly cheaper than 800HT for this temperature range (870C is below the threshold where 800HT becomes mandatory), and significantly stronger than standard 800
· The furnace operates in a mixed oxidizing/reducing atmosphere (steam/methane/CO2/CO/H2), which is within 800H's approved service range
Performance after 3 years:
· Tube skin temperatures remained stable throughout the campaign; no measurable creep sag detected in any tube
· Wall thickness survey after 3 years showed oxidation allowance consumed approximately 1.8mm (within the 2mm design margin), confirming the 3mm oxidation allowance was correctly specified
· All tubes passed PMI verification and grain size verification on selected samples (ASTM 5 confirmed)
· Tubes replaced at scheduled turnaround; no forced outages due to tube failure
Application: SAR furnace preheat coil, 4-inch OD, sch-80, 6-meter length
Service conditions: Spent acid (82% H2SO4 + organic contaminants) sprayed into furnace at 450C, acid regeneration to 96% H2SO4 at outlet; furnace firebox temperature 1,000C tube skin
Quantity: 120 tubes, total 3.2 tonnes of Incoloy 800H
Why 800H was specified:
· The combination of concentrated H2SO4 vapor at 450C process temperature and tube skin temperatures of 800-900C in the firebox requires an alloy with both corrosion resistance in hot acid AND creep strength at high temperature -- 800H is the standard choice; 316L would fail in less than 6 months in this service
· 904L and Alloy 20 lack the creep strength at these temperatures; Hastelloy C276 has adequate corrosion resistance but costs 3x more than 800H and offers no creep advantage.
· The SAR furnace operates continuously for 18 months between decokes; the tube must survive thermal cycling between 450C (process) and 900C (firebox) without cracking -- 800H's good ductility at temperature (elongation approximately 20% at 900C) accommodates this.
Performance after 18 months:
· One tube showed localized erosion-corrosion at the acid spray nozzle zone (not creep-related); replaced during scheduled decoke shutdown
· Oxidation thickness loss approximately 1.2mm (within design); internal acid vapor corrosion minimal
· All tubes confirmed to be within wall thickness tolerance; campaign extended to 24 months
· Cost comparison: if Hastelloy C276 had been specified, material cost alone would have been $1.2M higher for the same quantity
Application: Primary reformer outlet pigtail tubes and synthesis gas preheat coil
Service conditions: Reformer outlet temperature 820C, synthesis gas (H2/N2/NH3/Ar/CH4) at 35 MPa pressure; 4-year campaign
Quantity: 24 tonnes of Incoloy 800H (bimetallic with 316H transition layer for thermal expansion)
Why 800H was specified:
· The synthesis gas preheat coil operates at the highest combined temperature-pressure conditions in the ammonia plant: 820C at 35 MPa is well within 800H's approved range (ASME B31.3 Class 1)
· NACE MR0175 / ISO 15156 compliance was required because the natural gas feedstock contains 50 ppm H2S; 800H is approved for sour service at these conditions
· The transition joint between the 800H coil and the 316H downstream piping required ERNiCrMo-3 filler (dissimilar metal weld); this was executed per a qualified WPS
Performance after 4 years:
· Zero tube failures; all tubes passed hydrostatic test at the turnaround shutdown
· Synthesis gas-side corrosion negligible; no H2S-related attack detected on any tube
· Creep sag in two coils (approximately 3-4mm measured by laser profile) -- within acceptable limits; coils monitored for continued behavior
· Replacement coils ordered for next turnaround; estimated remaining life 1-2 years for the affected coils
All three alloys are solid-solution strengthened Ni-Fe-Cr austenitic alloys with excellent oxidation and sulfidation resistance up to 1,000C. The differences are in carbon control, Al+Ti level, and mandatory grain size -- and these small metallurgical differences translate to significant performance differences at high temperature.
800H is the most widely used global workhorse for reformer tubes and steam superheaters at 800-925C; 800HT is specified when tube skin exceeds 925C or campaign life exceeds 5 years; 800 is for general furnace use below 800C or where creep is not a design constraint.
Parameter | Incoloy 800 | Incoloy 800H | Incoloy 800HT | Practical Implication |
Carbon (C) | max 0.10% | 0.05-0.10% | 0.06-0.10% | 800H and HT: controlled C ensures |
Al + Ti combined | 0.30-1.20% | 0.30-1.20% | 0.85-1.20% | HT min 0.85% is the defining |
ASTM Grain Size | Not specified | 5 or finer | 5 or finer | Fine grain = key to 800H and HT |
100,000h Rupture | ~65 MPa | ~130 MPa | ~150 MPa | 800H has 2x the creep strength |
100,000h Rupture | ~35 MPa | ~83 MPa | ~100 MPa | 800H is 2.4x stronger than 800; |
100,000h Rupture | ~15 MPa | ~38 MPa | ~50 MPa | 800HT preferred above 900C; |
Max Continuous | 800C in air | 1,000C in air | 1,050C in air | HT for highest temperature; |
Sigma Phase Risk | Lower risk | Moderate risk | Lower risk | HT preferred for campaigns |
Typical Cost | Baseline | +10-15% over 800 | +20-30% over 800H | 800H is the sweet spot: |
Typical Applications | Furnace radiant tubes, | Reformer tubes, steam | Pyrolysis coils at 900-1,050C, |
Is Incoloy 800H suitable for sulfuric acid service?
Incoloy 800H has LIMITED resistance in sulfuric acid and is NOT the preferred alloy for most H₂SO₄ applications — but it IS a proven, standard material in Sulfuric Acid Alkylation (SAU) furnace tubes where the combination of high-temperature creep strength and oxidizing acid conditions matters more than pure acid corrosion resistance.
What is the difference between Incoloy 800, 800H, and 800HT?
All three share the same Ni–Fe–Cr base. The practical rule: 800 for general furnace use below 800°C; 800H for reformer tubes and steam superheaters to 925°C; 800HT for pyrolysis coils and the hottest sections to 1,050°C.
What is Incoloy 800H approved for under NACE MR0175 and ISO 15156?
Yes — Incoloy 800H is listed in NACE MR0175 / ISO 15156-3:2020 Table C.4 for sour gas and petroleum refinery service. The material must be in the annealed condition with hardness not exceeding 90 HRB (which annealed 800H naturally meets). Post-weld heat treatment is NOT required for corrosion resistance.
What is the maximum service temperature of Incoloy 800H?
Conclusion: Incoloy 800H is approved for continuous service up to 1,000°C (1,830°F) in oxidizing atmospheres and up to 925°C (1,700°F) in steam and steam–gas mixtures.
What welding filler metal is used for Incoloy 800H?
ERNiCr-3 (AWS A5.14) is the standard filler metal for welding Incoloy 800H to itself, using GTAW (TIG) or GMAW (MIG). ERNiCrMo-3 is used for dissimilar welds between 800H and stainless or carbon steel.
What is the creep rupture strength of Incoloy 800H, and why does grain size matter?
Incoloy 800H has a 100,000-hour creep rupture strength of approximately 83 MPa at 900°C and approximately 38 MPa at 1,000°C — approximately 4× higher than 316H stainless steel at the same temperatures. The ASTM 5 or finer grain size is the metallurgical reason for these values: fine grain boundaries act as obstacles to dislocation climb, the dominant creep mechanism at 600–900°C. Coarse-grain 800H (ASTM 3–4) has approximately 20–30% lower creep rupture strength at 900°C. The fine grain is achieved by a controlled low-temperature anneal at approximately 950°C after hot working.
Is Incoloy 800H magnetic at room temperature?
No — Incoloy 800H is essentially non-magnetic at room temperature, with magnetic permeability below 1.02.
