Hastelloy B2
Washers
UNS N10665
B2 Washers — Completing the Reducing Acid Assembly
When Hastelloy B2 (UNS N10665) stud bolts and bolts are specified for HCl, reducing H₂SO₄, acetic acid, or phosphoric acid service, the washer under the nut is the most critical component from a galvanic corrosion standpoint. The washer-nut bearing face sits in stagnant electrolyte trapped in the crevice geometry between the washer and the flange face — the highest-risk location for accelerated corrosion in any reducing acid bolted joint. Using a stainless steel washer under a B2 nut creates a galvanic couple that will corrode the washer preferentially in reducing acid media within a plant maintenance cycle.
Akbar Fasteners Pvt. Ltd. supplies B2 washers from the same ASTM B335 certified UNS N10665 heat as the matching B2 stud bolts — the same bar, the same heat treatment, the same mill test certificate. A single MTC, single PMI report, and single COC covers the complete assembly: stud bolt + heavy hex nut + washer. For procurement engineers preparing TPI hold plan documentation and vendor document packages, matched-heat assemblies simplify documentation and eliminate the multi-supplier traceability chain.
For existing equipment already fitted with Hastelloy B3 stud bolts (UNS N10675) — the current-generation Ni-Mo alloy — matched B3 washers from same heat are available separately. For new project design, B3 is the preferred alloy. For replacement procurement on existing B2-equipped plant, these B2 washers ensure full galvanic compatibility with the existing B2 fastener assembly.
| 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 | — |
| Manganese (Mn) | — | 1.0 | — |
| Carbon (C) | — | 0.02 | — |
| Silicon (Si) | — | 0.10 | — |
Why B2 Washers with B2 Bolts
The reducing acid environments where Hastelloy B2 fasteners are specified — HCl gas and liquid, reducing H₂SO₄, acetic acid, phosphoric acid, and HF acid — are the very environments where washer material selection most critically affects assembly service life. A stainless steel washer under a B2 nut in HCl will corrode preferentially within months, losing bearing thickness and progressively reducing bolt preload until flange leakage occurs.
The four specific failure modes listed opposite explain why procurement engineers who specify B2 stud bolts and bolts should complete the assembly with B2 washers from the same certified heat — and why Akbar Fasteners Pvt. Ltd. supplies washers as part of the same matched assembly from the same ASTM B335 certified lot.
Zero Galvanic Corrosion at Bearing Face
B2 washer under a B2 nut — identical Ni-Mo alloy, identical electrochemical potential. No galvanic cell at the bearing interface in HCl, reducing H₂SO₄, acetic acid, or phosphoric acid electrolyte.
No Crevice Attack Under Washer
B2’s 28% Mo provides outstanding crevice corrosion resistance in the stagnant reducing acid trapped in the washer-flange face crevice — the highest-risk location in the reducing acid bolted joint assembly.
Maintained Bolt Preload Over Service Life
A corroding stainless washer loses bearing thickness over time, progressively reducing bolt preload and eventually causing flange leakage. A matched B2 washer maintains dimensional integrity throughout service life in reducing acid.
Single MTC for Complete Assembly
Stud bolt + nut + washer from the same UNS N10665 certified heat — one mill test certificate, one PMI XRF report, one COC. Simplifies TPI hold plan documentation and vendor document submission for EPC reducing acid plant projects.
Hastelloy B2 Washer Types & Standards
All types machined from ASTM B335 certified UNS N10665 solution-annealed sheet or bar. PMI-verified before production. Full MTC and COC on every order.
Plain Flat Washers
Standard flat washers to DIN 125A and DIN 125B / ISO 7089 — distributes bolt load over greater bearing area and provides a corrosion-matched contact surface under the nut in HCl, reducing H₂SO₄, acetic acid, and phosphoric acid flange assemblies. Series A (tight ID) and Series B (clearance ID). M5–M100. Standard stock for common sizes M5–M48.
Spring Washers
Split-ring helical spring washers to DIN 127 in B2 UNS N10665 — maintains bolt preload against vibration and thermal cycling in chemical plant equipment handling reducing acids: HCl synthesis reactors, acid regeneration units, and acetic acid process equipment with pump-induced pulsation. M5–M64. Matches B2 stud bolt sets in vibration-prone reducing acid flanges.
Large OD Washers
Extra-large outer diameter washers in B2 for reducing acid plant connections through soft substrates, FRP-lined vessel nozzle connections, rubber-lined equipment covers, and acid-resistant composite structural connections where a standard OD washer would pull through. M6–M64. Available in same B2 alloy as stud bolts for fully matched reducing acid assemblies.
Custom Profile Washers
Non-standard OD/ID combinations, reduced thickness, and square washers machined from B2 UNS N10665 sheet for specialised reducing acid process equipment. SAE flat washer sizes and inch bolt sizes available. Drawing-specific configurations for HCl plant and acid recovery unit flanges. Contact sales@akbarfasteners.in.
DIN 125 Hastelloy B2 Flat Washer Dimensions
Standard dimensions per DIN 125 / ISO 7089. All in mm. DIN 127 spring and large OD dimensions on request to sales@akbarfasteners.in.
| Bolt Size (M) | Washer ID (d1) mm | Std OD (d2) mm | Large OD (d2) mm | Thickness (h) mm | Standard | Material | Condition |
|---|---|---|---|---|---|---|---|
| DIN 125 / ISO 7089 — PLAIN FLAT WASHERS (UNS N10665 · ASTM B335 · SOL. ANNEALED) | |||||||
| M5 | 5.3 | 10 | 15 | 1.0 | DIN 125A | N10665 | Sol. Ann. |
| M6 | 6.4 | 12 | 18 | 1.6 | DIN 125A | N10665 | Sol. Ann. |
| M8 | 8.4 | 16 | 24 | 1.6 | DIN 125A | N10665 | Sol. Ann. |
| M10 | 10.5 | 20 | 30 | 2.0 | DIN 125A | N10665 | Sol. Ann. |
| M12 | 13.0 | 24 | 37 | 2.5 | DIN 125A | N10665 | Sol. Ann. |
| M16 | 17.0 | 30 | 44 | 3.0 | DIN 125A | N10665 | Sol. Ann. |
| M20 | 21.0 | 37 | 60 | 3.0 | DIN 125A | N10665 | Sol. Ann. |
| M24 | 25.0 | 44 | 72 | 4.0 | DIN 125B | N10665 | Sol. Ann. |
| M30 | 31.0 | 56 | 92 | 4.0 | DIN 125B | N10665 | Sol. Ann. |
| M36 | 37.0 | 66 | 110 | 5.0 | DIN 125B | N10665 | Sol. Ann. |
| M42 | 45.0 | 78 | Custom | 7.0 | DIN 125B | N10665 | Sol. Ann. |
| M48 | 52.0 | 92 | Custom | 8.0 | DIN 125B | N10665 | Sol. Ann. |
| M56 – M100 | Custom | Custom | Custom | Custom | Custom | N10665 | Sol. Ann. |
* DIN 127 spring, SAE flat, inch bolt sizes — 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 bolts and stud bolts are specified for reducing acid service — the washer must be B2 too. These are the environments where a dissimilar washer will corrode first.
HCl Gas & Liquid Plant
hydrochloric acid storage
Chemical Processing
mixed acid process joints
HF Acid Systems
fluoride acid plant flanges
Acetic Acid Plant
anhydride system joints
Phosphoric Acid
fertiliser plant connections
Acid Recovery Units
spent acid reconcentration
Pharmaceutical
HCl reaction vessel flanges
Oil Refining
crude oil acidising systems
Complete Documentation Package
Heat & Lot Traceable
Conformance
100% Lots Verified
Tensile · Hardness
TÜV · BV · Lloyds
Related B2 & Hastelloy Fasteners
Complete the matched B2 assembly — stud bolts, nuts, and washers from one certified source. Or compare B3 for new project design.
Hastelloy B2 Fasteners
Complete B2 fastener range — stud bolts, hex bolts, hex nuts, threaded rods, and socket screws from the same certified ASTM B335 heat. One MTC covers the full assembly.
View Page →Hastelloy B3 Stud Bolts
The current-generation Ni-Mo alloy for new reducing acid projects — eliminates B2’s sensitisation risk. For replacement procurement on existing B2 equipment, use matched B2 washers instead.
View Page →Hastelloy C276 Washers
Matched washers for C276 stud bolt sets in mixed acid and chlorinated solvent service — same matched-material principle applied to the C276 Ni-Cr-Mo alloy assembly.
View Page →Hastelloy Fasteners India
Complete Hastelloy range — six grades, all product forms including washers. Grade selection guidance for your specific reducing or mixed acid corrosion environment.
View Range →Need Hastelloy B2
Washers Now?
Type · bolt size · quantity · matched set requirement. Akbar Fasteners Pvt. Ltd. responds within 24 hours with full pricing and documentation list.