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 Heavy Hex Nuts
Incoloy 800H heavy hex nuts to ASME B18.2.2 are the US-spec matched nut for Incoloy 800H heavy hex bolts and stud bolts on high-temperature ASME Section VIII pressure-vessel flange assemblies. TorqBolt machines heavy hex nuts from ASTM B408 round bar in inch range 1/2 inch through 2 inch with metric equivalents M12-M52 on call-out. The heavy hex nut carries a larger across-flats and a thicker nut height than the standard hex nut (DIN 934 / ASME B18.2.4) to deliver higher bearing area under torque-controlled tightening. Internal threads are tapped to class 2B per ASME B1.1 (inch) or class 6H per ISO 965 (metric). Every heavy hex nut ships with EN 10204 type 3.1 mill test certificate documenting heat number, ASTM B408 chemistry, solution-anneal cycle and ASTM grain size 5 verification. Heavy hex nuts are the standard nut for petrochemical refinery flange bolting where bolt-up torque exceeds the bearing capacity of standard-pattern hex nuts.
Heavy Hex Nut Dimensions (ASME B18.2.2)
| Size designation | Across flats / OD | Head / nut height | Thread pitch | Standard reference |
|---|---|---|---|---|
| 1/2 inch | 0.500 inch thread | A/F 7/8 inch; Nut height 31/64 inch | 13 tpi UNC | ASME B18.2.2 |
| 5/8 inch | 0.625 inch thread | A/F 1-1/16 inch; Nut height 39/64 inch | 11 tpi UNC | ASME B18.2.2 |
| 3/4 inch | 0.750 inch thread | A/F 1-1/4 inch; Nut height 47/64 inch | 10 tpi UNC | ASME B18.2.2 |
| 7/8 inch | 0.875 inch thread | A/F 1-7/16 inch; Nut height 55/64 inch | 9 tpi UNC | ASME B18.2.2 |
| 1 inch | 1.000 inch thread | A/F 1-5/8 inch; Nut height 63/64 inch | 8 tpi UNC | ASME B18.2.2 |
| 1-1/8 inch | 1.125 inch thread | A/F 1-13/16 inch; Nut height 1-7/64 inch | 7 tpi UNC | ASME B18.2.2 |
| 1-1/4 inch | 1.250 inch thread | A/F 2 inch; Nut height 1-7/32 inch | 7 tpi UNC | ASME B18.2.2 |
| 1-1/2 inch | 1.500 inch thread | A/F 2-3/8 inch; Nut height 1-15/32 inch | 6 tpi UNC | ASME B18.2.2 |
| 1-3/4 inch | 1.750 inch thread | A/F 2-3/4 inch; Nut height 1-23/32 inch | 5 tpi UNC | ASME B18.2.2 |
| 2 inch | 2.000 inch thread | A/F 3-1/8 inch; Nut height 1-31/32 inch | 4.5 tpi UNC | ASME B18.2.2 |
Manufacturing Route at TorqBolt
Heavy hex nut manufacture follows the same CNC turn-mill route as standard hex nuts with larger across-flats and thicker nut height per ASME B18.2.2:
- Receive Incoloy 800H bar to ASTM B408; PMI verification on each heat.
- Cut bar into heavy nut-height slugs on horizontal saw.
- CNC mill the 6-sided heavy hex profile per ASME B18.2.2 schedule.
- Drill the through-hole to thread-tap minor diameter.
- Tap the internal thread to class 2B per ASME B1.1 (inch) or class 6H per ISO 965 (metric).
- Solution anneal at 1149 deg C plateau followed by rapid quench; ASTM grain size 5 verified.
- Hardness band 120-184 HB; thread plug gauge verification.
- Visual + dimensional + PMI inspection 100 percent.
- Pack matched with stud or heavy hex bolt from same heat batch; CoC + EN 10204 cert.
Heavy Hex Nut Sizes Stocked and Lead Times
| Diameter range | Length range | Stock status | Lead time |
|---|---|---|---|
| 1/2 inch - 1 inch | Per ASME B18.2.2 | Stock + ex-stock | 7 working days |
| 1-1/8 inch - 1-1/2 inch | Per ASME B18.2.2 | Made-to-order from stock bar | 10 to 14 working days |
| 1-3/4 inch - 2 inch | Per ASME B18.2.2 | Made-to-order, large bar | 3 to 5 weeks |
| Above 2 inch | Per print | Forged blank required | 5 to 7 weeks |
Inspection and Heat Marking
Heavy hex nut specific inspections cover the larger across-flats geometry, nut-height tolerance and class 2B thread compliance:
- Heavy hex across-flats verified per ASME B18.2.2 schedule with go / no-go gauge.
- Nut height per ASME B18.2.2 tolerance band.
- Internal thread verified with class 2B plug gauge full-traverse.
- Hardness band 120-184 HB on first piece and one per batch.
- ASTM E112 grain-size etch verification.
- PMI by X-ray fluorescence on first piece and one per batch.
- Visual inspection for thread damage, washer-face flatness and chamfer integrity.
- Heat number traceable to bar; matched-pair batch CoC.
Typical Service Conditions
Heavy hex nuts are the standard nut form on US-spec pressure-vessel and refinery flange bolting where high torque is applied:
- Matched assembly with heavy hex bolts on US-spec petrochemical flange bolting.
- Matched assembly with stud bolts on ASME Section VIII flange joints.
- ASME Section VIII pressure-vessel manhole cover bolting.
- Heat exchanger tubesheet stud bolting on hydrocracker and coker units.
- Ethylene cracker radiant-section header bolting on US-spec scope.
- Steam superheater final-stage flange bolting on waste-heat boilers.
Incoloy 800H Alloy Considerations on This Fastener Form
Companion Fasteners and Related Pages
- Hex Nuts: standard-pattern DIN 934 alternative for European-spec scope.
- Lock Nuts: prevailing-torque variant for vibration-resistance.
- Castle Nuts: cotter-pin retention variant.
- Coupling Nuts: extended hex variant for threaded-rod joining.
- Stud Bolts: matched studs for heavy hex nut assemblies.
Frequently Asked Questions
Q. What is the difference between heavy hex and standard hex nuts?
Heavy hex nut has larger across-flats and thicker nut height than standard hex nut (ASME B18.2.2 vs ASME B18.2.4 or DIN 934 vs DIN 934). The larger nut delivers higher bearing area under torque-controlled tightening and is the US-spec standard on pressure-vessel flange bolting.
Q. Are Incoloy 800H heavy hex nuts qualified to ASTM A194 grade 8M?
No. A194 grade 8M is 316 stainless. Incoloy 800H heavy hex nuts are machined from B408 bar to A194 dimensional geometry but the material certificate references ASTM B408 chemistry, not A194 chemistry.
Q. Are heavy hex nuts available in metric sizes?
Yes. Standard supply is inch (1/2 inch - 2 inch). Metric M12-M52 to DIN 6915 (German heavy hex nut) is machined to print on PO call-out from the same B408 bar.
Q. What is the thread tap class supplied?
Class 2B per ASME B1.1 default for inch supply. Class 6H per ISO 965 default for metric supply. Class 5H or 6H on PO call-out for special applications.
Q. Do you supply heavy hex nuts with washer face both sides?
Yes on PO call-out. Default supply is washer face one side per ASME B18.2.2. Washer face both sides (ASME B18.2.6 heavy double-chamfered) is machined on call-out.
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