Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Incoloy 800H Bolt Dimensions
This reference page consolidates imperial and metric thread tables for Incoloy 800H (UNS N08810, Werkstoff 1.4876) bolting in the size range commonly supplied by TorqBolt for ASME Section VIII flange make-up, ethylene cracker and reformer access-cover bolting, fired-heater radiant-section hangers and ASME B16.5 / API 6A flange joints from NPS 1/2 inch through 24 inch. The data covers thread pitch, nominal major diameter, pitch diameter, minor diameter, stress area and root area for the UNC (Unified National Coarse) and 8UN (Eight-thread) series per ASME B1.1, and for the standard metric coarse thread series per ISO 68-1. Stress-area values are computed per the formula in ASME B1.1 paragraph 1.4 (As = (pi/4) x ((d - 0.9743 x p)/2 + d - 1.0825 x p)/2) for imperial threads and ISO 898-1 for metric, and form the basis for the tightening-torque calculation and the bolt-tensile-strength check in the ASME B16.5 flange make-up procedure. For the parent-material yield, UTS and creep-rupture data needed for the bolt-tensile-strength check, see mechanical properties and creep rupture strength.
Imperial UNC Thread Table (ASME B1.1)
| Nominal size | TPI | Pitch (in) | Pitch dia (in) | Minor dia (in) | Stress area (in2) | Root area (in2) |
|---|---|---|---|---|---|---|
| 1/4 inch UNC | 20 | 0.0500 | 0.2175 | 0.1959 | 0.0318 | 0.0269 |
| 3/8 inch UNC | 16 | 0.0625 | 0.3344 | 0.3073 | 0.0775 | 0.0676 |
| 1/2 inch UNC | 13 | 0.0769 | 0.4500 | 0.4167 | 0.1419 | 0.1257 |
| 5/8 inch UNC | 11 | 0.0909 | 0.5660 | 0.5266 | 0.2260 | 0.2018 |
| 3/4 inch UNC | 10 | 0.1000 | 0.6850 | 0.6417 | 0.3345 | 0.3020 |
| 7/8 inch UNC | 9 | 0.1111 | 0.8028 | 0.7547 | 0.4617 | 0.4193 |
| 1 inch UNC | 8 | 0.1250 | 0.9188 | 0.8647 | 0.6057 | 0.5510 |
| 1-1/8 inch 8UN | 8 | 0.1250 | 1.0438 | 0.9897 | 0.7895 | 0.7286 |
| 1-1/4 inch 8UN | 8 | 0.1250 | 1.1688 | 1.1147 | 0.9954 | 0.9276 |
| 1-3/8 inch 8UN | 8 | 0.1250 | 1.2938 | 1.2397 | 1.2236 | 1.1474 |
| 1-1/2 inch 8UN | 8 | 0.1250 | 1.4188 | 1.3647 | 1.4737 | 1.3893 |
| 1-3/4 inch 8UN | 8 | 0.1250 | 1.6688 | 1.6147 | 2.0398 | 1.9398 |
| 2 inch 8UN | 8 | 0.1250 | 1.9188 | 1.8647 | 2.6927 | 2.5856 |
| 2-1/4 inch 8UN | 8 | 0.1250 | 2.1688 | 2.1147 | 3.4325 | 3.3147 |
| 2-1/2 inch 8UN | 8 | 0.1250 | 2.4188 | 2.3647 | 4.2592 | 4.1310 |
| 2-3/4 inch 8UN | 8 | 0.1250 | 2.6688 | 2.6147 | 5.1730 | 5.0337 |
| 3 inch 8UN | 8 | 0.1250 | 2.9188 | 2.8647 | 6.1740 | 6.0235 |
Sizes 1-1/8 inch through 3 inch use the 8UN (eight-thread) series per ASME B1.1 - the canonical bolting series for large-diameter ASME B16.5 flange make-up.
Metric ISO Coarse Thread Table (ISO 68-1)
| Nominal size | Pitch (mm) | Pitch dia (mm) | Minor dia (mm) | Stress area (mm2) | Root area (mm2) |
|---|---|---|---|---|---|
| M6 | 1.0 | 5.35 | 4.77 | 20.1 | 17.9 |
| M8 | 1.25 | 7.19 | 6.47 | 36.6 | 32.8 |
| M10 | 1.5 | 9.03 | 8.16 | 58.0 | 52.3 |
| M12 | 1.75 | 10.86 | 9.85 | 84.3 | 76.2 |
| M14 | 2.0 | 12.70 | 11.55 | 115.0 | 104.7 |
| M16 | 2.0 | 14.70 | 13.55 | 157.0 | 144.1 |
| M20 | 2.5 | 18.38 | 16.93 | 245.0 | 225.2 |
| M24 | 3.0 | 22.05 | 20.32 | 353.0 | 324.3 |
| M30 | 3.5 | 27.73 | 25.71 | 561.0 | 519.0 |
| M36 | 4.0 | 33.40 | 31.09 | 817.0 | 759.3 |
| M42 | 4.5 | 39.08 | 36.48 | 1121.0 | 1045.0 |
| M48 | 5.0 | 44.75 | 41.87 | 1473.0 | 1377.0 |
| M52 | 5.0 | 48.75 | 45.87 | 1758.0 | 1652.0 |
| M56 | 5.5 | 52.43 | 49.25 | 2030.0 | 1905.0 |
| M64 | 6.0 | 60.10 | 56.64 | 2676.0 | 2519.0 |
Tightening Torque Calculation
The standard short-form torque-tension equation for bolted-flange make-up is T = K x F x D, where T is the applied torque, K is the nut factor (typically 0.20 for as-supplied threads or 0.15 for lubricated threads), F is the target preload (typically 50 to 70 percent of bolt-material yield x stress area), and D is the nominal bolt diameter. For the bolt-material yield input to the calculation, use the elevated-temperature yield from mechanical properties at the service temperature, NOT the room-temperature yield. At 540 deg C service the yield drops to approximately 70 percent of room-temperature value; at 650 deg C it drops to approximately 55 percent.
Bolt Stress Relaxation at High Temperature
Incoloy 800H bolts in long-duration service above 540 deg C exhibit stress relaxation: the initial bolt preload decays over time as creep accommodates the elastic strain. Re-torque on a periodic schedule (typically annually for service above 540 deg C, every 6 months for service above 650 deg C) is supplied as part of the turnaround maintenance programme. The stress-relaxation behaviour is documented in the Special Metals technical bulletin and can be modelled with the Larson-Miller parameter approach using creep-rupture data from creep rupture strength.
Related References
Product pages: Incoloy 800H fasteners (stud bolts, hex bolts, heavy hex bolts, nuts, washers). Standards: ASME B1.1 (imperial), ISO 68-1 (metric), ASME B18.2.1 (square + hex bolts), ASME B18.2.2 (nuts), ASTM A193 / A194 (fastener bolting families) - see 800H vs A193 B16 comparison. Material data: mechanical properties, high-temperature strength.
Bolt Dimensions FAQ
Q. Why does ASME use the 8UN series for bolts above 1 inch instead of UNC?
The 8UN series fixes the thread pitch at 8 TPI (0.125 inch pitch) for all diameters above 1 inch. This delivers a higher tensile stress area than the increasingly coarse UNC pitch would, and gives a consistent torque-tension relationship across the bolt size range typically used for ASME B16.5 flange make-up.
Q. What is the difference between stress area and root area?
Stress area (As) is the effective cross-sectional area used for the bolt tensile-strength calculation; it is computed from the average of the pitch and minor diameters and is typically 8 to 15 percent larger than the root area. Root area (Ar) is the cross-sectional area at the minor diameter (thread root) and is the strict minimum area for yield calculation. Both are tabulated above.
Q. Can I use 800H bolts on a Class 1500 / Class 2500 ASME B16.5 flange?
Yes for service temperatures within the 800H design envelope (815 deg C max for ASME Section VIII). Below 540 deg C, ASTM A193 B16 (chrome-moly-vanadium) bolts are normally specified for high-pressure flanges because they cost less than 800H at similar tensile strength. Above 540 deg C, 800H delivers the necessary creep resistance that B16 cannot provide.
Q. What torque should I apply to an M30 800H bolt at 600 deg C service?
For an M30 bolt at 600 deg C service, use the 600 deg C yield from the mechanical-properties page (typically 110 to 130 MPa for solution-annealed 800H - verify against the heat certificate). Target preload F = 0.6 x 120 MPa x 561 mm2 = 40,400 N. Tightening torque T = 0.20 x 40,400 N x 0.030 m = 242 N.m. The calculation should be re-done using the heat-specific certificate for the actual project.
Q. Do you supply 800H bolts to NACE MR0175 sour-service?
Yes. 800H bolts in solution-annealed condition meet NACE MR0175 / ISO 15156 hardness limits (22 HRC max for Ni-Fe-Cr alloys, 237 HV equivalent). The NACE MR0175 compliance statement is added to the EN 10204 certificate.
Request a Quote on Incoloy 800H Bolting
Send the bolt size, thread series (UNC / 8UN / ISO metric), grade (800H or 800HT), quantity, certification class (3.1 or 3.2) and any NACE MR0175 / NACE TM0177 / pre-tensioning add-ons to our sales desk.
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