Hastelloy B2
Stud Bolts
UNS N10665
Hastelloy B2 — Why No Chromium Is the Point
Hastelloy B2 (UNS N10665) is a Ni-Mo binary alloy — approximately 62% Ni with 26–30% Mo, strictly limited iron (≤2%) and cobalt (≤1%), and a deliberate near-absence of chromium (≤1%). This is the critical engineering decision in B2’s design: chromium is omitted precisely because it is not needed — and at high concentrations would actually reduce reducing acid resistance. In the Ni-Cr-Mo alloys (Hastelloy C276, C22), chromium provides oxidising acid resistance. B2 is designed exclusively for reducing acids, so the full alloy budget goes to molybdenum — the element that governs reducing acid corrosion resistance — at 26–30%.
In HCl at any concentration from dilute to anhydrous, in reducing H₂SO₄ below the azeotropic point, in acetic acid, in phosphoric acid, and in HF acid environments, B2’s high Mo content delivers corrosion rates that stainless steels, duplex grades, and even Ni-Cr-Mo alloys like C276 cannot match. B2 stud bolts are specified in: HCl synthesis equipment ASME B16.5 flanges, HCl storage tank manway bolting, acetic acid plant pressure flanges, phosphoric acid fertiliser plant connections, and acid recovery unit piping.
For new project design, the current-generation alloy is Hastelloy B3 (UNS N10675) — B3 adds Ti and tighter Fe/Si controls to eliminate B2’s grain boundary sensitisation at weld HAZ temperatures. For replacement procurement on existing B2-fitted equipment, these B2 stud bolts (UNS N10665) are the correct specification for galvanic compatibility and original equipment spec compliance. Both grades are available from Akbar Fasteners Pvt. Ltd. from the same ASTM B335 certified facility.
| 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 | — |
B2 Stud Bolt Configurations & Types
All configurations machined from ASTM B335 certified UNS N10665 solution-annealed bar. PMI-verified before production. Matched B2 heavy hex nuts from same heat on request — single MTC for the complete assembly.
Fully Threaded Stud Bolts
Thread runs the full length — ASME B16.5 standard for pressure flange joints. Class 150–2500. M12–M100, custom lengths to 3,000mm. The standard B2 stud bolt configuration for HCl, reducing H₂SO₄, acetic acid, and phosphoric acid ASME flanged process connections. Matched B2 heavy hex nuts from same certified heat for zero galvanic risk at nut bearing face.
Equal-End Double Stud
Equal thread length on both ends with plain centre section — for equipment where stud must be torqued from one end while the other is flush-mounted in a tapped bore. Used in HCl reactor body tapped hole connections, acid-resistant pump casing assemblies, and reducing acid pressure vessel covers where through-bolt is not possible.
Unequal-End Double Stud
Different thread lengths on each end — one end sized for engagement in a tapped flange or equipment body, the other end full engagement for heavy hex nut. For ASME B16.5 reducing acid flanges with integral stud boss where one end depth is fixed by the flange equipment specification.
Inch Thread Stud Bolts
UNC (coarse) and UNF (fine) inch thread stud bolts in B2 UNS N10665 for US chemical plant and HCl facility projects where metric is not specified. ¼”–4″. ASME B16.5 inch thread dimensions for Class 150–2500 flanges. Same ASTM B335 certified material as metric range. Matched B2 heavy hex nuts in inch thread available.
Metric Double-End Studs
DIN 939 (long-threaded end) and DIN 938 (short-threaded end) metric double-end studs in B2 for equipment tapped bore applications under DIN flanges in European chemical plant, acid synthesis facilities, and reducing acid recovery units specifying DIN rather than ASME B16.5 dimensional standard.
Custom Configurations
Left-hand thread, non-standard diameters (M14, M18, M22, M27), combined metric-inch dual thread, and drawing-specific configurations in B2 for proprietary acid plant equipment, chemical reactor internals, and specialised reducing acid process hardware. Email drawing to sales@akbarfasteners.in.
Hastelloy B2 vs B3 Stud Bolts — Selection Table
Both B2 (N10665) and B3 (N10675) are Ni-Mo alloys for reducing acid ASME B16.5 pressure flange service. The selection depends entirely on whether the application is new project design or replacement on existing B2-fitted equipment. Both available from Akbar Fasteners Pvt. Ltd., same certified Mumbai facility.
| Selection Criterion | B2 (N10665) This Page | B3 (N10675) — Preferred for New |
|---|---|---|
| New Project / Greenfield Design | Specify B3 instead | ✔ Preferred Choice |
| Replacement on Existing B2 Equipment | ✔ Required for Compatibility | Not compatible spec |
| Contractually Mandated UNS N10665 | ✔ Only Valid Choice | Cannot substitute |
| Weld HAZ Sensitisation Risk | Risk at 200–650°C slow cool | ✔ Eliminated by Ti addition |
| HCl Resistance (Away from Weld) | ✔ Excellent — Same as B3 | ✔ Equal or Better |
| Reducing H₂SO₄ Resistance | ✔ Excellent — Same as B3 | ✔ Equal or Better |
| Acetic Acid Resistance | ✔ Excellent | ✔ Equal |
| NACE MR0175 Sour Service | ✔ Compliant (≤241 HB) | ✔ Compliant (≤241 HB) |
| ASTM Standard | ASTM B335 (N10665) | ASTM B335 (N10675) |
| Available Sizes (ASME B16.5) | M12–M100, Class 150–2500 | M12–M100, Class 150–2500 |
For grade selection guidance: B2 Fastener Range · B3 Stud Bolts
B2 Stud Bolt Lengths — ASME B16.5 Class 150 to 2500
Stud bolt lengths per ASME B16.5 / ASME B16.47. Dimensions in mm. Inch thread and non-standard lengths on request to sales@akbarfasteners.in.
| Size (M) | Thread Pitch | Class 150 | Class 300 | Class 600 | Class 900 | Class 1500 | Class 2500 | Material |
|---|---|---|---|---|---|---|---|---|
| ASME B16.5 FULLY THREADED STUD BOLTS — UNS N10665 · ASTM B335 · SOLUTION ANNEALED · NACE MR0175 | ||||||||
| M12 | 1.75 mm | 75 | 100 | 110 | 130 | 155 | 200 | N10665 |
| M16 | 2.0 mm | 90 | 115 | 130 | 155 | 185 | 240 | N10665 |
| M20 | 2.5 mm | 105 | 140 | 160 | 195 | 235 | 305 | N10665 |
| M24 | 3.0 mm | 120 | 160 | 185 | 225 | 275 | 360 | N10665 |
| M30 | 3.5 mm | 145 | 195 | 225 | 280 | 340 | 450 | N10665 |
| M36 | 4.0 mm | 165 | 225 | 265 | 335 | 410 | 535 | N10665 |
| M42 | 4.5 mm | On order | On order | On order | On order | On order | On order | N10665 |
| M48 | 5.0 mm | On order | On order | On order | On order | On order | On order | N10665 |
| M56–M100 | Custom | Custom length on order — contact sales@akbarfasteners.in | N10665 | |||||
All lengths in mm. Tolerances per ASME B16.5. * Non-standard lengths — sales@akbarfasteners.in
Standards We Manufacture & Test To
Same quality system as our Hastelloy B3 stud bolts and complete ASTM B574 Hastelloy fastener range. Full heat traceability from mill certificate to dispatch.
Industry Applications
Reducing acid pressure flanges where stainless steels fail by uniform corrosion within months and Ni-Cr-Mo alloys lack sufficient molybdenum for the specific reducing acid chemistry.
HCl Gas Plant
anhydrous HCl equipment
Chemical Processing
acid process piping joints
HF Acid Systems
HF acid generation
Acetic Acid Plant
anhydride process joints
Phosphoric Acid
fertiliser acid process
Acid Recovery Units
spent acid treatment
Pharmaceutical
HCl reaction vessel flanges
Oil Refining
crude oil acidising systems
Complete Documentation Package
Heat & Lot Traceable
Conformance
100% Lots Verified
Tensile · HB · Charpy
TÜV · BV · Lloyds
Related B2 & Hastelloy Fasteners
Complete the matched B2 assembly from one certified source — or compare B3 for new project design.
Hastelloy B2 Fasteners
Full B2 range — hex bolts, hex nuts, washers, threaded rods, socket screws. Matched from same ASTM B335 certified heat as stud bolts for single MTC coverage of the complete assembly.
View Range →Hastelloy B2 Washers
Plain flat (DIN 125), spring (DIN 127), and large OD washers in B2 from the same certified heat — zero galvanic potential at the washer-nut bearing face in all reducing acid environments.
View Page →Hastelloy B3 Stud Bolts
Current-generation Ni-Mo alloy preferred for new reducing acid project design. Eliminates B2’s sensitisation risk. Same ASME B16.5 configurations, Class 150–2500, M12–M100.
View Page →Hastelloy Fasteners India
Complete Hastelloy range — six grades, all product forms. Grade selection guidance for reducing, mixed, and oxidising acid service from ISO 9001:2015 certified Mumbai facility.
View Range →Need Hastelloy B2
Stud Bolts Now?
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