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
Monel 400 Heavy Hex Nuts - UNS N04400 ASTM F467 / DIN 6915
Monel® 400 heavy hex nuts (also written Monel 400 2H nuts, UNS N04400 heavy hex nuts, Alloy 400 nickel-copper heavy hex nuts) are the flange-grade pattern specified when a stud bolt or heavy hex bolt is torqued onto a raised-face flange in HF alkylation service, NACE MR0175 sour gas, or seawater piping. Chemistry is covered by ASTM F467/F467M, marking F 467U (Ni 400) or F 467V (Ni 405). Inch dimensions come from ASME B18.2.2 Table 10; metric dimensions come from DIN 6915 (the structural heavy hex pattern). The nut is the F467 companion to the F468 bolting it clamps, so chemistry, proof load and hardness track the bolt one-for-one. Monel is a registered trademark of Special Metals Corporation; TorqBolt is not authorized by, affiliated with or endorsed by Special Metals.
Standard Hex vs Heavy Hex Nut Dimensions
Heavy hex nuts carry a wider seat and a thicker body than standard hex nuts of the same thread. The wider bearing surface spreads compressive load across the flange face and protects the gasket seat from local crushing. Source: ASME B18.2.2-2010 Table 4 (standard hex) and Table 10 (heavy hex). Width across flats follows F = 1.500D + 0.125 in for heavy hex; the standard hex pattern is narrower.
| Nominal Size | Standard Hex F (in) | Heavy Hex F (in) | Standard Hex H (in) | Heavy Hex H (in) |
|---|---|---|---|---|
| 1/2 | 3/4 | 7/8 | 7/16 | 31/64 |
| 5/8 | 15/16 | 1-1/16 | 35/64 | 39/64 |
| 3/4 | 1-1/8 | 1-1/4 | 41/64 | 47/64 |
| 7/8 | 1-5/16 | 1-7/16 | 3/4 | 55/64 |
| 1 | 1-1/2 | 1-5/8 | 55/64 | 63/64 |
| 1-1/8 | 1-11/16 | 1-13/16 | 31/32 | 1-7/64 |
| 1-1/4 | 1-7/8 | 2 | 1-1/16 | 1-7/32 |
| 1-1/2 | 2-1/4 | 2-3/8 | 1-9/32 | 1-15/32 |
Head Spec: ASME B18.2.2 Heavy Hex and DIN 6915
Inch-series Monel 400 heavy hex nuts conform to ASME B18.2.2-2010 Table 10. The Basic width across flats is F = 1.500D + 0.125 in, with thickness H = 1.000D - 0.016 + 0.012 in for the 1/4 to 1-1/8 in band, then 1.000D - 0.031 + 0.012 in for 1-1/4 to 2 in. Width across corners follows G = 1.1547 x Max F. The metric counterpart is DIN 6915, the heavy-pattern hex nut used with structural high-strength bolting (the same dimensional family as ISO 4775). Both patterns share the same role: pair with a heavy hex bolt or stud bolt head so the bearing diameter is identical across the joint.
Size Range Stocked
F467 covers 1/4 in through 1-1/2 in inclusive. Below the table are the metric equivalents that ship from Mumbai mill stock.
| Imperial Size | Metric Equivalent | UNC tpi | UNF tpi | Tensile Stress Area UNC (sq.in) |
|---|---|---|---|---|
| 1/2 | M12 | 13 | 20 | 0.1419 |
| 5/8 | M16 | 11 | 18 | 0.226 |
| 3/4 | M20 | 10 | 16 | 0.334 |
| 7/8 | M22 | 9 | 14 | 0.462 |
| 1 | M24 | 8 | 12 | 0.606 |
| 1-1/4 | M30 | 7 | 12 | 0.969 |
| 1-1/2 | M36 | 6 | 12 | 1.405 |
| (F468 forged equivalent) | M42, M48 | 4.5 (8UN) | n/a | n/a |
M42 through M48 are produced from ASTM B564 forging stock with a documented heavy hex dimensional equivalence and F467 mechanical retest on the finished nut. Heat number, melt cast and proof-load reading appear on the EN 10204 type 3.2 certificate.
F467 Class and the 25 HRC Hardness Ceiling
F467 marks Ni 400 nuts as F 467U; the free-machining Ni 405 grade is marked F 467V. Hardness minimum from Table 2 is 75 HRB for F 467U. The hardness ceiling is governed by the sour-service rule, not by F467 directly: NACE MR0175 / ISO 15156-3 caps nickel-copper bolting at 35 HRC. TorqBolt manufacturing keeps actual readings below 25 HRC, which clears the NACE limit with a 10-point margin and matches the F468 bolt hardness cap of 25 HRC. Source: ASTM F467 Table 2 and NACE MR0175 / ISO 15156-3.
| Marking | Alloy | UNS | Hardness min | Hex Nut Proof Stress min (ksi) | Heavy Hex Nut Proof Stress min (ksi) |
|---|---|---|---|---|---|
| F 467U | Ni 400 Class A | N04400 | 75 HRB | 80 | 86 |
| F 467V | Ni 405 Class B | N04405 | 60 HRB | 70 | 76 |
Companion Stud Bolts (F468) and Structural Washers (F436)
A Monel 400 heavy hex nut is half a joint. The standard mate is a Monel 400 stud bolt in the same chemistry to ASTM F468, double-end pattern, length sized from the flange spec (ASME B16.5 raised face, ASME B16.47 series A or B). The bolt clears the nut bearing surface and engages a second F467U heavy hex nut on the far side. Hardened structural washers (ASTM F436 in plain carbon, or the Monel 400 equivalent in nickel-copper) sit under the nut to spread the bearing load further and prevent gasket pinch. The heavy hex bolt variant replaces the stud where a fixed-length, single-head fastener is preferred.
For a complete Monel 400 bolting assembly, match the bolt chemistry (F468 Class A or B) to the nut chemistry (F467 F 467U or F 467V). Mixed-chemistry assemblies break galvanic continuity in the clamped joint and are rejected on most refinery bolting specs.
Applications: HF Lines, Sour Service, Naval Bulkhead
Three application bands dominate Monel 400 heavy hex nut consumption. First, HF alkylation flange bolting at refineries operating Phillips-type or UOP HF alky units, per API RP 751 inspection regime; nickel-copper resists hydrofluoric acid across the alky concentration band (70 to 95 percent) where austenitic stainless and copper alloys lose section. Second, NACE MR0175 sour service piping at upstream wellheads, gas-processing trains, and pipeline manifolds where H2S partial pressure exceeds 0.05 psi (0.0003 MPa) and chloride is present; the F467 hardness regime keeps the nut inside the ISO 15156-3 Annex A.4 window. Third, naval and offshore bulkhead bolting on minesweepers, FPSO topsides and seawater piping, where the magnetic permeability of Monel 400 (below 1.005) and resistance to flowing-seawater pitting select it over stainless variants.
Detail on HF acid resistance, marine applications, and general corrosion resistance covers the metallurgical case in full.
NACE MR0175 / ISO 15156-3 Cross-Reference
Monel 400 bolting (bolts plus nuts) is listed in ISO 15156-3 Annex A as an acceptable nickel-based alloy for sour service, subject to the 35 HRC maximum hardness rule and the chloride / H2S exposure envelope. F467 caps F 467U at the manufacturing minimum 75 HRB and TorqBolt maintains a maximum cap of 25 HRC, both well inside the sour-service window. Sour-service shipments ship with EN 10204 type 3.2 mill test certificate plus a NACE compliance statement that cites the hardness reading per heat, the H2S partial pressure rating, and the chloride concentration the heat was qualified against. Cross-reference: NACE MR0175 page on this site.
FAQ
What is the difference between F 467U and F 467V? F 467U is Ni 400 Class A (Monel 400 weldable chemistry, sulfur 0.024 percent max). F 467V is Ni 405 Class B (Monel R-405 free-machining chemistry, sulfur 0.025 to 0.060 percent). Sour-service flange nuts ship as F 467U; F 467V is reserved for joints that stay unwelded and need higher machining throughput.
Are inch and metric heavy hex nuts interchangeable? No. ASME B18.2.2 inch heavy hex and DIN 6915 metric heavy hex are dimensionally distinct (the metric pattern is keyed to ISO metric threads, M-series). The bolt thread system and the nut thread system must match.
Do you supply 2H heat markings? ASTM A194 grade 2H is the carbon-steel heavy hex pattern; the nickel-copper analogue is ASTM F467 F 467U. The two are sometimes called interchangeably in field specs but the standards are distinct. TorqBolt supplies F 467U on Monel 400 heat-traced lots; the marking is F 467U, heat code, and the manufacturer mark.
What certification is included? EN 10204 type 3.2 mill test certificate is standard on sour-service and HF-acid shipments. Type 3.1 ships on general flange-service orders. Both cite chemistry (ladle + product), hardness, proof load result, dimensional inspection, and full heat traceability back to the B564 or wrought F467 source bar.
Related
See also Monel 400 nuts (overview), hex nuts, heavy hex bolts, stud bolts, ASTM F467 spec, NACE MR0175 sour service.
Request for Quote
Send thread, length under the head you are pairing with, applicable spec (F467 marking, NACE callout) and quantity to info@torqbolt.com or WhatsApp +91-22-66157017. Ex-Mumbai price and lead time returned within one working day. Domestic India 3 to 7 working days; export through JNPT.
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