Hastelloy B2
Nuts
UNS N10665
B2 Nuts — Matched Heat · Zero Galvanic · Anti-Galling
When Hastelloy B2 stud bolts (UNS N10665) are specified for HCl, reducing H₂SO₄, acetic acid, or phosphoric acid service, the nut material is not a secondary decision — it is the primary corrosion risk point in the entire fastener assembly. The nut-stud thread engagement zone and the nut-washer bearing face are in direct contact with the stagnant reducing acid trapped in the crevice geometry of the flange joint. A dissimilar-alloy nut — stainless steel, duplex, or even C276 — creates a galvanic couple that will preferentially corrode the less noble material at the thread interface within a plant maintenance cycle.
Akbar Fasteners Pvt. Ltd. supplies B2 hex nuts from the same ASTM B335 certified UNS N10665 heat as the matching stud bolts. Same bar stock, same heat number, same PMI XRF confirmation. The mill test certificate covers stud bolt and nut under a single document. For EPC and TPI documentation, matched-heat assembly simplifies vendor document submission — single MTC, single COC, single PMI report for the complete stud bolt set including nuts.
Galling caution: Hastelloy B2 nuts in the solution-annealed condition have a higher galling tendency at the thread interface than Ni-Cr-Mo alloys like C276 or 316L stainless. Molybdenum-rich alloys are inherently susceptible to adhesive wear (galling) when dry metal-to-metal contact occurs during torquing. Always apply a suitable nickel-based anti-seize compound (Molykote, Jet-Lube Nickel, or equivalent) to the stud thread and nut bearing face before assembly. Lubrication factor must be applied to the ASME PCC-1 torque calculation.
| Element | Min % | Max % | Typical |
|---|---|---|---|
| Nickel (Ni) | Balance | — | ~62% |
| Molybdenum (Mo) | 26.0 | 30.0 | ~28% |
| Iron (Fe) | — | 2.0 | ~1% |
| Cobalt (Co) | — | 1.0 | — |
| Chromium (Cr) | — | 1.0 | <0.5% |
| Manganese (Mn) | — | 1.0 | — |
| Carbon (C) | — | 0.02 | — |
| Silicon (Si) | — | 0.10 | — |
Hastelloy B2 Hex Nut Types & Standards
All types machined from ASTM B335 certified UNS N10665 solution-annealed bar. PMI-verified before production. Supplied from same certified heat as stud bolts on request — single MTC covers the complete assembly.
Standard Hex Nuts
Standard-height hex nut per DIN 934 / ISO 4032 in B2 UNS N10665 for all reducing acid flange and equipment bolting where ASME B18.2.2 heavy hex is not specified. M6–M100. The most common B2 nut form for chemical equipment cover bolting, agitated vessel body connections, and non-pressure-flange structural bolting in HCl, reducing H₂SO₄, acetic acid, and phosphoric acid service. Apply nickel anti-seize before assembly. Matched from same ASTM B335 heat as B2 bolts on request.
Heavy Hex Nuts
Wider across-flats and greater height than DIN 934 — the ASME B16.5 standard nut form for pressure flange stud bolt sets. M12–M100. Paired with B2 fully threaded stud bolts for ASME B16.5 Class 150–2500 flanges in HCl piping, reducing acid process equipment, and acetic acid plant. Wider bearing face reduces bearing stress on gasket and flange face. Supplied from same certified B2 heat as stud bolts — single MTC for the complete stud bolt set.
Coupling Nuts (Barrel Nuts)
Long hex nuts for joining two threaded rods or extending a stud bolt — used in HCl synthesis equipment expansion joints, acid plant equipment jacking arrangements, reducing acid plant structural tie-rod extensions, and wherever two sections of B2 threaded rod must be joined in reducing acid service. Length approximately 3× hex width. M6–M100. From same ASTM B335 certified B2 heat.
Non-Standard Nuts
Inch UNC/UNF thread nuts for US chemical plant projects, left-hand thread, and drawing-specific configurations in B2 UNS N10665. Flange nuts (DIN 6923), slotted nuts, and castle nuts for specialised reducing acid reactor and acid recovery unit applications. Contact sales@akbarfasteners.in with drawing or specification.
Preventing Galling on Hastelloy B2 Hex Nuts
Galling is the signature failure mode of solution-annealed Ni-Mo alloy fasteners during assembly — and B2 is more susceptible than B3 (which has tighter Si controls) and significantly more susceptible than Ni-Cr-Mo alloys like C276. Galling occurs when the high molybdenum content creates adhesive metal-to-metal contact under the interface pressures generated during nut torquing. The result is thread damage that prevents the fastener from being de-tensioned without cutting — a critical problem in reducing acid plant where bolted joints must be opened regularly for inspection, gasket replacement, and equipment maintenance.
The four assembly practices listed opposite eliminate B2 nut galling in reducing acid plant service. These are standard requirements for all B-grade Ni-Mo alloy fastener assemblies. The anti-seize product selected must be compatible with the reducing acid service environment — most nickel-based anti-seize compounds are resistant to HCl and reducing H₂SO₄. Confirm with the anti-seize manufacturer for specific acid concentrations and temperatures before use.
Apply Nickel-Based Anti-Seize
Coat the stud thread and nut bearing face with nickel-based anti-seize (Molykote P-37, Jet-Lube Nickel 63, Bostik Never-Seez, or equivalent) before assembly. Copper-based anti-seize introduces galvanic risk in reducing acid — use nickel-based only. Apply generously to the full thread engagement length.
Apply Lubrication Factor K to Torque
The ASME PCC-1 torque calculation for dry (unlubricated) B2 studs must be corrected by the K factor for the anti-seize product used — typically K = 0.13–0.17 for nickel-based anti-seize versus K = 0.20–0.22 dry. Failure to apply K will over-torque the stud and cause thread yield or galling.
Torque in Incremental Cross-Pattern
Tighten in three incremental passes at 30%, 70%, and 100% of target torque in a cross-bolt pattern (ASME PCC-1 Appendix F) to ensure uniform gasket compression. Do not run a B2 nut to full torque in a single pass — the rapid thread engagement at high torque rate increases galling probability.
Replace Stud and Nut If Galling Occurs
If a B2 nut galls during assembly and requires force to turn, do not attempt to salvage by re-lubrication. Galled threads are work-hardened above the NACE MR0175 hardness limit. Replace both the stud bolt and the nut — using a new matched B2 pair from the same ASTM B335 certified heat.
DIN 934 / ASME B18.2.2 B2 Hex Nut Dimensions
Standard dimensions per DIN 934 / ISO 4032 and ASME B18.2.2 heavy hex. All in mm. Coupling nut DIN 6334 and inch thread dimensions on request to sales@akbarfasteners.in.
| Size (M) | Thread Pitch | Std Hex AF (s) mm | Std Height (m) mm | Heavy Hex AF mm | Heavy Hex Ht mm | Material | Condition |
|---|---|---|---|---|---|---|---|
| HEX NUTS — UNS N10665 · ASTM B335 · SOLUTION ANNEALED · NACE MR0175 · APPLY Ni ANTI-SEIZE BEFORE ASSEMBLY | |||||||
| M6 | 1.0 mm | 10.0 | 5.2 | — | — | N10665 | Sol. Ann. |
| M8 | 1.25 mm | 13.0 | 6.8 | — | — | N10665 | Sol. Ann. |
| M10 | 1.5 mm | 17.0 | 8.4 | — | — | N10665 | Sol. Ann. |
| M12 | 1.75 mm | 19.0 | 10.8 | 21.0 | 11.1 | N10665 | Sol. Ann. |
| M16 | 2.0 mm | 24.0 | 14.8 | 26.9 | 15.9 | N10665 | Sol. Ann. |
| M20 | 2.5 mm | 30.0 | 18.0 | 33.5 | 19.8 | N10665 | Sol. Ann. |
| M24 | 3.0 mm | 36.0 | 21.5 | 40.4 | 23.8 | N10665 | Sol. Ann. |
| M30 | 3.5 mm | 46.0 | 25.6 | 50.8 | 28.6 | N10665 | Sol. Ann. |
| M36 | 4.0 mm | 55.0 | 31.0 | 60.3 | 34.9 | N10665 | Sol. Ann. |
| M42 | 4.5 mm | 65.0 | 34.0 | 71.0 | 38.1 | N10665 | Sol. Ann. |
| M48 | 5.0 mm | 75.0 | 38.0 | 82.6 | 42.9 | N10665 | Sol. Ann. |
| M56–M100 | Custom | Custom | Custom | Custom | Custom | N10665 | Sol. Ann. |
* Inch UNC/UNF, DIN 6334 coupling, custom — sales@akbarfasteners.in
Standards We Manufacture & Test To
Same quality system as our Hastelloy B3 stud bolts and complete B2 fastener range. Full heat traceability from mill certificate to dispatch.
Industry Applications
Wherever B2 stud bolts or bolts are specified — the nut must be B2 too. These are the reducing acid environments where a dissimilar nut corrodes at the thread interface and nut-bearing face first.
HCl Gas & Liquid Plant
anhydrous HCl nut sets
Chemical Processing
acid process equipment nuts
HF Acid Systems
fluoride acid flange nuts
Acetic Acid Plant
anhydride process nuts
Phosphoric Acid
fertiliser acid process nuts
Acid Recovery Units
spent acid treatment nuts
Pharmaceutical
HCl process vessel nut sets
Oil Refining
crude oil acidising nuts
Complete Documentation Package
Heat & Lot Traceable
Conformance
100% Lots Verified
Tensile · HB Hardness
TÜV · BV · Lloyds
Related B2 Fasteners
Matched B2 stud bolts, washers, and the complete B2 fastener range from the same certified ASTM B335 heat — single MTC for the complete assembly.
Hastelloy B2 Stud Bolts
Fully threaded B2 stud bolts for ASME B16.5 pressure flanges, Class 150–2500, M12–M100. Order B2 heavy hex nuts from the same certified heat — single MTC for the complete stud bolt set.
View Page →Hastelloy B2 Washers
Flat and spring washers in B2 from same certified heat — complete the B2 assembly (stud bolt + nut + washer) with zero galvanic potential at all bearing interfaces in reducing acid service.
View Page →Hastelloy B2 Bolts
Hex bolts, heavy hex, socket cap, and flanged hex in B2 for reducing acid equipment cover and structural bolting. Matched B2 DIN 934 hex nuts from same heat on request.
View Page →Hastelloy B3 Stud Bolts
Current-generation Ni-Mo for new reducing acid design. Eliminates B2’s HAZ sensitisation. B3 heavy hex nuts available from same certified heat. For new projects — specify B3 over B2.
View Page →Need Hastelloy B2
Nuts Now?
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