Monel 400
Washers
UNS N04400
Monel 400 Washers — Why Matched Material Matters
Monel 400 (UNS N04400) is an annealed nickel-copper alloy with approximately 63–70% nickel and copper as the balance — one of the most corrosion-resistant alloys available for seawater, HF acid, and chloride service. In a bolted joint, every component that contacts an electrolyte is part of an electrochemical system. When a Monel 400 bolt contacts a 316L washer in seawater, the two different alloys create a galvanic cell. 316L is anodic to Monel 400 in chloride-containing electrolyte — it corrodes preferentially at the washer-nut contact interface, losing clamping load, causing crevice attack under the washer bearing face, and eventually seizing.
Using matched UNS N04400 Monel 400 washers throughout the assembly eliminates this failure path completely. Same alloy — no electrochemical potential difference, no galvanic cell, no accelerated corrosion. Akbar Fasteners Pvt. Ltd. supplies Monel 400 washers from the same ASTM B164 certified heat as the matching bolts and stud bolts, with one MTC and one COC covering the complete assembly.
For applications requiring higher strength (≥1000 MPa), consider our Monel K500 washers in age-hardened UNS N05500. The same galvanic compatibility principle applies — K500 washers must be used with K500 bolts. For strongly reducing acid service where Monel is not the specification, see our Hastelloy B3 washers.
| Element | Min % | Max % | Typical |
|---|---|---|---|
| Nickel + Cobalt | 63.0 | — | ~67% |
| Copper (Cu) | — | Balance | ~31% |
| Iron (Fe) | — | 2.5 | ~1.5% |
| Manganese (Mn) | — | 2.0 | ~1.0% |
| Carbon (C) | — | 0.30 | <0.15% |
| Silicon (Si) | — | 0.50 | <0.3% |
| Sulfur (S) | — | 0.024 | — |
Why Use Monel 400 Washers with Monel 400 Bolts
The instinct to save cost by using a stainless or carbon steel washer with Monel 400 fasteners is understandable — but in seawater, HF acid, or any conductive electrolyte environment, it is an engineering mistake that causes joint failure. The five reasons below explain precisely why Akbar Fasteners Pvt. Ltd. always recommends a fully matched Monel 400 assembly.
The same principle applies across our full range: we supply matched Monel K500 washers with K500 stud bolt sets, matched Hastelloy B3 washers with B3 stud bolt sets — from the same certified heat, under one documentation package. The material match is not optional in permanent seawater immersion or HF acid service.
Zero Galvanic Corrosion
Identical alloy throughout the joint means zero electrochemical potential difference — no galvanic cell forms between washer, nut, and bolt in seawater or chloride electrolyte.
No Crevice Attack Under the Washer
Monel 400 resists crevice corrosion in stagnant seawater under the washer bearing face — where oxygen depletion creates aggressive local chemistry that attacks 316L or carbon steel washers.
Sustained Clamping Load
Monel 400 washers resist embedding and creep under nut bearing faces in seawater service — dissimilar softer washers lose thickness over time, reducing bolt preload and causing joint leakage.
Single MTC — Complete Assembly
Washers, bolts, and nuts from the same certified UNS N04400 heat carry one mill test certificate and one PMI report — simplifying inspection and third-party documentation for the full assembly.
HF Acid Immunity Throughout
Monel 400 washers in HF alkylation unit assemblies are immune to HF vapour attack — unlike 316L washers that corrode rapidly in HF environments regardless of the bolt alloy used.
Monel 400 Washer Types & Configurations
All types manufactured from ASTM B164 certified UNS N04400 annealed bar stock. PMI-verified before machining. Full MTC and COC on every order.
Plain Flat Washers
Standard flat washers in Monel 400 to DIN 125A and DIN 125B / ISO 7089. The most widely used type — distributes bolt load over a greater bearing area under the nut and provides a corrosion-matched contact surface. Series A (tight ID) and Series B (clearance ID). M5–M100. Standard stock for all common sizes M5–M48.
Spring Washers
Split-ring (helical) spring washers in Monel 400 to DIN 127. Maintain bolt preload against vibration and thermal cycling in marine environments — critical in seawater pump casings, rotating equipment covers, and shipboard hardware subject to continuous vibration alongside chloride exposure. M5–M64.
Large OD Washers
Extra-large outer diameter (fender) washers in Monel 400 for soft marine substrates: GRP (fibreglass) hull fittings, composite structural connections, timber marine structures, and equipment bases in tidal zones. The large OD prevents pull-through and distributes bolt load over a much greater bearing area. M6–M64.
Custom Profile Washers
Non-standard OD/ID combinations, reduced thickness, square washers, and bevelled washers cut from Monel 400 sheet or machined from certified bar. Used in bespoke offshore structural connections requiring specific bearing area calculations. Send drawing to sales@akbarfasteners.in.
DIN 125 Monel 400 Flat Washer Dimensions
Standard dimensions per DIN 125 / ISO 7089. All sizes in mm. DIN 127 spring washer and large OD dimensions on request to sales@akbarfasteners.in.
| Bolt Size (M) | Washer ID (d1) | Std OD (d2) | Large OD (d2) | Thickness (h) | Standard | Material | Condition |
|---|---|---|---|---|---|---|---|
| DIN 125 / ISO 7089 — PLAIN FLAT WASHERS (UNS N04400 · ASTM B164) | |||||||
| M5 | 5.3 | 10 | 15 | 1.0 | DIN 125A | N04400 | Annealed |
| M6 | 6.4 | 12 | 18 | 1.6 | DIN 125A | N04400 | Annealed |
| M8 | 8.4 | 16 | 24 | 1.6 | DIN 125A | N04400 | Annealed |
| M10 | 10.5 | 20 | 30 | 2.0 | DIN 125A | N04400 | Annealed |
| M12 | 13.0 | 24 | 37 | 2.5 | DIN 125A | N04400 | Annealed |
| M16 | 17.0 | 30 | 44 | 3.0 | DIN 125A | N04400 | Annealed |
| M20 | 21.0 | 37 | 60 | 3.0 | DIN 125A | N04400 | Annealed |
| M24 | 25.0 | 44 | 72 | 4.0 | DIN 125B | N04400 | Annealed |
| M30 | 31.0 | 56 | 92 | 4.0 | DIN 125B | N04400 | Annealed |
| M36 | 37.0 | 66 | 110 | 5.0 | DIN 125B | N04400 | Annealed |
| M42 | 45.0 | 78 | Custom | 7.0 | DIN 125B | N04400 | Annealed |
| M48 | 52.0 | 92 | Custom | 8.0 | DIN 125B | N04400 | Annealed |
| M56 – M100 | Custom | Custom | Custom | Custom | Custom | N04400 | Annealed |
* DIN 127 spring washer, SAE flat washers, and inch sizes on request. Non-standard OD/ID to drawing — contact sales@akbarfasteners.in
Standards We Manufacture & Test To
Same quality system as our Hastelloy B3 stud bolts and all exotic alloy fasteners. Full heat traceability from mill certificate to dispatch.
Monel 400 Washer Applications
Wherever Monel 400 bolts and nuts are specified — the washer must be Monel 400 too. These are the service environments that drive the matched material requirement.
Marine & Seawater
seawater pipe flanges
Desalination Plants
brine equipment washers
Offshore Platforms
splash zone assemblies
HF Alkylation Units
acid service joints
Chemical Processing
brine handling equipment
Pump & Rotating Equipment
seawater pump covers
Naval & Shipbuilding
naval non-mag assemblies
GRP / Marine Composites
composite hull fittings
Complete Documentation Package
Heat & Lot Traceable
Conformance
100% Lots Verified
Tensile · Hardness
TÜV · BV · Lloyds
Matched Monel 400 & Alloy Components
Order washers with bolts, stud bolts, and nuts from the same certified UNS N04400 heat — one MTC, one PMI report, zero galvanic risk throughout the assembly.
Monel 400 Fasteners
Full Monel 400 range — hex bolts, stud bolts, hex nuts, socket screws — all annealed, all from same certified heat as these washers.
View Page →Monel K500 Washers
Age-hardened K500 washers for higher-strength assemblies. ≥1000 MPa. Same matched-material principle as these Monel 400 washers, but for K500 bolt sets.
View Page →Hastelloy B3 Washers
Matched washers for Hastelloy B3 stud bolt sets in HCl and strongly reducing acid service. Same galvanic compatibility principle applied to the B3 alloy family.
View Page →Hastelloy B3 Stud Bolts
For HCl and reducing acid service where Monel 400 is not the specification. ASME B16.5 Class 150–2500. Matched B3 nuts and washers from same heat.
View Page →Need Monel 400
Washers Now?
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