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- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Incoloy 800H High-Temperature Strength
Incoloy 800H (UNS N08810) retains useful tensile and yield strength to 982 deg C (1800 deg F) and is qualified for sustained pressure-vessel service to 815 deg C (1500 deg F) under ASME Section VIII Division 1 design tables. The strength envelope is split into three regimes by temperature. Below 540 deg C (1000 deg F) the allowable design stress is tensile-controlled at approximately one-third of the room-temperature ultimate tensile. From 540 deg C to 649 deg C (1000 to 1200 deg F) the controlling property switches to 0.2 percent yield divided by 1.5 with the ASME factor. Above 649 deg C the design stress drops onto the creep-rupture surface and is governed by the 100,000-hour rupture stress divided by the safety factor specified in ASME Section II Part D. This page presents the tensile, yield and ASME allowable stress at the four standard design points 540, 650, 815 and 982 deg C with the strength basis identified for each.
Hot Tensile + 0.2 Percent Yield at the Four Design Points
| Temperature | UTS (MPa / ksi) | 0.2 percent yield (MPa / ksi) | Elongation (percent) | Test method |
|---|---|---|---|---|
| 540 deg C (1000 deg F) | 420 / 61 | 145 / 21 | ~44 | ASTM E21 hot tensile |
| 650 deg C (1200 deg F) | 380 / 55 | 140 / 20 | ~49 | ASTM E21 hot tensile |
| 760 deg C (1400 deg F) | 290 / 42 | 135 / 19.5 | ~62 | ASTM E21 hot tensile |
| 815 deg C (1500 deg F) | 210 / 30 | 130 / 19 | ~72 | ASTM E21 hot tensile |
| 870 deg C (1600 deg F) | 165 / 24 | 105 / 15 | ~80 | ASTM E21 hot tensile |
| 925 deg C (1700 deg F) | 125 / 18 | 83 / 12 | ~86 | ASTM E21 hot tensile |
| 982 deg C (1800 deg F) | 97 / 14 | 65 / 9.5 | ~96 | ASTM E21 hot tensile |
Typical values from the Special Metals INCOLOY alloys 800H/800HT technical bulletin Table 4. Confirm against the heat-specific mill test certificate for design use.
ASME Section II Part D Allowable Design Stress (Section VIII Division 1)
| Design temp (deg F) | Design temp (deg C) | S (ksi) | S (MPa) | Controlling property |
|---|---|---|---|---|
| 1000 | 538 | 15.5 | 107 | Yield-controlled (Sy / 1.5) |
| 1100 | 593 | 15.0 | 103 | Yield-controlled |
| 1150 | 621 | 13.8 | 95 | Transition yield to creep-rupture |
| 1200 | 649 | 12.0 | 83 | Creep-rupture-controlled (Sr 100,000 hr / 1.5) |
| 1250 | 677 | 10.0 | 69 | Creep-rupture-controlled |
| 1300 | 704 | 7.7 | 53 | Creep-rupture-controlled |
| 1350 | 732 | 6.0 | 41 | Creep-rupture-controlled |
| 1400 | 760 | 4.7 | 32 | Creep-rupture-controlled |
| 1450 | 788 | 3.5 | 24 | Creep-rupture-controlled |
| 1500 | 815 | 2.5 | 17 | Creep-rupture-controlled (ASME Section VIII maximum for 800H) |
Indicative ASME Section II Part D Table 1A values for SB-407 / SB-408 / SB-409 / SB-564. Section VIII Division 1 design limit for Incoloy 800H is 815 deg C (1500 deg F). Above 815 deg C the design path is Incoloy 800HT under Code Case 2196 to 899 deg C (1650 deg F).
Three Strength Regimes by Temperature
- Tensile-controlled (below 540 deg C): the allowable design stress is approximately one-third of the room-temperature ultimate tensile divided by the ASME safety factor. The room-temperature 450 MPa UTS floor sets a comfortable design margin for low- and intermediate-temperature ASME Section VIII vessels.
- Yield-controlled (540 to 649 deg C): the allowable design stress is governed by the 0.2 percent yield at temperature divided by 1.5. This is the regime where 800H delivers comparable stress to 304H and 316H stainless at a roughly equivalent material cost premium.
- Creep-rupture-controlled (above 649 deg C): the allowable design stress drops onto the 100,000-hour rupture stress divided by the safety factor in ASME Section II. This is where 800H opens the gap against 300-series stainless and where the procurement decision shifts decisively to 800H or 800HT. See the dedicated creep-rupture strength page for the time-dependent stress tables.
Strength Comparison at the Three Critical Design Temperatures
| Alloy | UTS at 540 deg C (MPa) | UTS at 815 deg C (MPa) | UTS at 982 deg C (MPa) | ASME Section VIII ceiling (deg C) |
|---|---|---|---|---|
| 304H stainless | ~380 | ~140 | not qualified | 815 |
| 316H stainless | ~395 | ~150 | not qualified | 815 |
| 321H stainless | ~370 | ~140 | not qualified | 815 |
| 310H stainless | ~410 | ~170 | ~80 | 815 |
| Incoloy 800H | 420 | 210 | 97 | 815 |
| Incoloy 800HT | 420 | 220 | 105 | 899 (Code Case 2196) |
Test Methods + Cert Practice
Hot tensile + yield are reported to ASTM E21 with the test temperature held to plus or minus 3 deg C and the strain rate to plus or minus 25 percent of the nominal value. The test specimen is preheated to the test temperature and soaked for 30 minutes minimum before loading. Elongation is reported on the same 4D gauge length as the room-temperature test. Hot hardness is not a B-series specification floor but is reported to ASTM E92 (Vickers) on call-out for surface engineering and tribology design. ASME pressure-vessel certification requires the heat-specific room-temperature tensile + yield + elongation + grain size on the EN 10204 type 3.1 mill test report; high-temperature data above 540 deg C is taken from the ASME Section II Part D allowable stress tables unless a specific high-temperature mill test is called for on the order.
Engineering Implications
- Below 540 deg C the allowable design stress is the same order as 304H and 316H stainless; the cost premium of 800H is hard to justify unless the design temperature will rise during the life of the asset.
- From 540 to 815 deg C the allowable design stress for 800H is approximately 25 to 50 percent higher than 304H / 316H at the same temperature, and the gap widens with temperature.
- Above 815 deg C the alloy is no longer ASME Section VIII qualified in the 800H grade, the design path is 800HT under Code Case 2196.
- The yield-to-tensile ratio rises from 0.40 at room temperature to approximately 0.65 at 815 deg C, so piping flexibility analysis is governed by yield, not tensile.
- For pressure-vessel design, the 800H allowable stress at 815 deg C of 17 MPa is approximately one-twelfth of the room-temperature allowable, wall thickness scales accordingly.
- See the oxidation resistance, carburization resistance and thermal expansion pages for the environmental and dimensional design data that pair with these strength values.
Frequently Asked Questions
What is the ASME Section VIII allowable stress at 815 deg C?
Approximately 2.5 ksi (17 MPa) per ASME Section II Part D Table 1A for SB-407 / SB-408 / SB-409 / SB-564 in the 800H grade. The value is creep-rupture controlled.
At what temperature does the design stress switch from yield to creep control?
Between 593 and 649 deg C (1100 to 1200 deg F) for Incoloy 800H. Below 593 deg C the design stress is yield-controlled (Sy / 1.5). Above 649 deg C it is creep-rupture controlled (Sr 100,000 hr / 1.5).
Is hot hardness reported on the mill test certificate?
Not by default. Room-temperature Brinell hardness is reported to ASTM E10 per ASTM B408 paragraph 9. Hot Vickers hardness to ASTM E92 at a specified test temperature is supplied on call-out.
What is the difference between hot tensile and creep rupture in the design tables?
Hot tensile (ASTM E21) measures the load-to-failure under continuous loading at temperature in 30 minutes or less. Creep rupture (ASTM E139) measures the time-to-failure at constant stress at temperature over hundreds to hundreds-of-thousands of hours. ASME allowable design stress above 649 deg C is governed by the 100,000-hour creep-rupture value, not the hot tensile.
Can Incoloy 800H be used above 815 deg C for ASME Section VIII vessels?
Not in the 800H grade. ASME Section VIII Division 1 caps 800H at 815 deg C (1500 deg F). For sustained service above 815 deg C, the design path is 800HT (UNS N08811) under Code Case 2196 to 899 deg C (1650 deg F).
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