Monel K500
Washers
UNS N05500
Monel K500 Washers — The Galvanic Case
A bolted joint in seawater is an electrochemical system. When a washer made of a different alloy contacts a Monel K500 stud bolt and nut, a galvanic cell forms at the contact interface. In seawater — a highly conductive electrolyte — this galvanic couple drives accelerated corrosion of whichever metal is anodic in the pair. A 316L washer against a K500 stud is particularly aggressive: 316L corrodes rapidly in the crevice at the washer-nut interface while the K500 fastener remains intact, but the corroded washer loses clamping load, allows joint leakage, and eventually seizes or fails in service.
Using matched UNS N05500 Monel K500 washers throughout eliminates this galvanic couple completely. The washer, stud bolt, and nut are all the same alloy — no electrochemical potential difference, no preferential corrosion path, no crevice attack at the bearing faces. In permanent seawater immersion, splash zones, and desalination plant environments, this principle is mandatory for long-service joint integrity.
Beyond galvanic compatibility, K500 washers provide the same age-hardened strength (≥1000 MPa UTS) as the stud bolts they accompany — preventing embedding and load loss under the nut bearing face that would occur with a softer washer material. Akbar Fasteners Pvt. Ltd. supplies K500 washers from the same ASTM B865 certified heat as the matching bolts, with a single documentation package covering the complete assembly.
| Element | Min % | Max % | Typical |
|---|---|---|---|
| Nickel + Cobalt | 63.0 | — | ~65% |
| Copper (Cu) | — | Balance | ~30% |
| Aluminium (Al) | 2.30 | 3.15 | ~2.7% |
| Titanium (Ti) | 0.35 | 0.85 | ~0.6% |
| Iron (Fe) | — | 2.0 | ~1.5% |
| Manganese (Mn) | — | 1.5 | — |
| Carbon (C) | — | 0.25 | — |
| Silicon (Si) | — | 0.50 | — |
| Sulfur (S) | — | 0.010 | — |
| Ultimate Tensile Strength | ≥ 1000 MPa |
| 0.2% Proof Stress | ≥ 690 MPa |
| Elongation | ≥ 20% |
| Hardness | ≤ 35 HRC |
| Condition | Age Hardened |
Monel K500 Washer Types & Configurations
All types manufactured from ASTM B865 certified UNS N05500 bar stock, age-hardened in-house, PMI-verified. Compare with our Hastelloy B3 washers for corrosive acid environments.
Plain Flat Washers
Standard flat washers in Monel K500 to DIN 125 and ISO 7089. The most common type — distributes the bolt load over a larger bearing area on soft substrate materials and provides a corrosion-matched contact surface under the nut. M5–M100.
Spring Washers
Split-ring (helical) spring washers in Monel K500 to DIN 127. Maintain bolt preload against vibration and thermal cycling in marine environments. Critical in pump casing covers and rotating equipment that experiences constant vibration alongside seawater exposure.
Large OD (Fender) Washers
Extra-large outer diameter washers in Monel K500 for soft flange facings, composite materials, and GRP (fibreglass) structural connections in marine applications. Large OD prevents pull-through and distributes load over a much greater bearing area. M6–M64.
Custom Profile Washers
Non-standard OD/ID combinations, reduced thickness, bevelled, and square washers cut from Monel K500 sheet or machined from bar. Used in structural offshore connections requiring specific bearing area calculations. Send drawing to sales@akbarfasteners.in.
DIN 125 Monel K500 Flat Washer Dimensions
Standard dimensions per DIN 125 / ISO 7089. All sizes in mm. Custom OD, ID, and thickness on request to sales@akbarfasteners.in.
| Bolt Size (M) | Washer ID (mm) | Std OD (mm) | Large OD (mm) | Thickness (mm) | Standard | Material | Condition |
|---|---|---|---|---|---|---|---|
| DIN 125 / ISO 7089 — PLAIN FLAT WASHERS (UNS N05500) | |||||||
| M5 | 5.3 | 10 | 15 | 1.0 | DIN 125A | N05500 | Age Hard. |
| M6 | 6.4 | 12 | 18 | 1.6 | DIN 125A | N05500 | Age Hard. |
| M8 | 8.4 | 16 | 24 | 1.6 | DIN 125A | N05500 | Age Hard. |
| M10 | 10.5 | 20 | 30 | 2.0 | DIN 125A | N05500 | Age Hard. |
| M12 | 13.0 | 24 | 37 | 2.5 | DIN 125A | N05500 | Age Hard. |
| M16 | 17.0 | 30 | 44 | 3.0 | DIN 125A | N05500 | Age Hard. |
| M20 | 21.0 | 37 | 60 | 3.0 | DIN 125A | N05500 | Age Hard. |
| M24 | 25.0 | 44 | 72 | 4.0 | DIN 125B | N05500 | Age Hard. |
| M30 | 31.0 | 56 | 92 | 4.0 | DIN 125B | N05500 | Age Hard. |
| M36 | 37.0 | 66 | 110 | 5.0 | DIN 125B | N05500 | Age Hard. |
| M42 | 45.0 | 78 | Custom | 7.0 | DIN 125B | N05500 | Age Hard. |
| M48 | 52.0 | 92 | Custom | 8.0 | DIN 125B | N05500 | Age Hard. |
| M56 – M100 | Custom | Custom | Custom | Custom | Custom | N05500 | Age Hard. |
* DIN 127 spring washer and large OD dimensions on request. Inch sizes (SAE flat washers) available. Non-standard OD/ID/thickness manufactured to drawing — contact sales@akbarfasteners.in
Six Reasons to Use K500 Washers with K500 Bolts
Engineers sometimes specify Monel K500 stud bolts and nuts with 316L or Duplex washers to reduce cost. In laboratory environments or atmospheric service this may be acceptable — but in any application involving seawater immersion, splash zones, or HF acid exposure, this decision causes failures. The six reasons below explain why Akbar Fasteners Pvt. Ltd. always recommends matching all components in the bolted joint to the same alloy.
The same principle applies across our entire range — we supply matched Hastelloy B3 washers with Hastelloy B3 stud bolt sets, and matched Monel 400 washers with Monel 400 bolt sets, from the same certified heat with a single documentation package.
Eliminates Galvanic Corrosion
Identical alloy = zero electrochemical potential difference. No galvanic cell, no accelerated corrosion at the washer-nut contact interface in seawater or chloride electrolyte.
Prevents Crevice Attack
Monel K500 resists crevice corrosion in stagnant seawater under the washer bearing face — where oxygen depletion creates aggressive local chemistry that would attack 316L or duplex.
Maintains Clamping Load
Age-hardened K500 washers (≤35 HRC) resist embedding under nut bearing faces. Softer dissimilar washers creep under load, reducing preload and causing joint leakage.
Single Documentation Package
Washers, bolts, and nuts from the same UNS N05500 heat carry one MTC and one PMI report — simplifying inspection and NACE MR0175 compliance documentation for the full assembly.
HF Acid Immunity
Monel K500 washers in HF alkylation unit assemblies are immune to HF attack at any concentration — unlike stainless steel washers that corrode rapidly in HF vapour environments.
Non-Magnetic Throughout
K500 washers maintain low magnetic permeability — critical for naval minesweeper hardware and MRI facility structural assemblies where ferromagnetic washers would cause interference.
Standards We Manufacture & Test To
Same quality process as our complete Monel K500 fastener range. Full heat traceability — mill certificate to dispatch.
Monel K500 Washer Applications
Everywhere Monel K500 bolts and nuts are specified — the washer must also be K500 to maintain galvanic compatibility and NACE compliance of the complete assembly.
Marine & Offshore
seawater pipe connections
Seawater Systems
heat exchanger flanges
Subsea Equipment
subsea manifold joints
Oil & Gas
FPSO riser clamps
HF Alkylation Units
HF immune assemblies
Naval & Defence
minesweeper fittings
Pump & Rotating Equipment
marine pump casings
GRP / Composite Joints
offshore structure bolts
Complete Documentation Package
Heat & Lot Traceable
Conformance
100% Lots Verified
Tensile · Hardness
TÜV · BV · Lloyds
Matched Monel K500 & Alloy Components
Order washers, bolts, stud bolts, and nuts together from the same certified UNS N05500 heat — one order, one documentation package, one PMI report.
Monel K500 Fasteners
Complete range — hex bolts, hex nuts, socket screws — all in age-hardened K500 from the same certified heat as these washers.
View Page →Monel K500 Stud Bolts
Fully threaded and double-end stud bolts. Class 150–2500. M12–M100 up to 3,000mm. Supply with matching K500 washers from same heat.
View Page →Hastelloy B3 Washers
For HCl, H₂SO₄ and reducing acid environments where Monel K500 washers are not specified. Same matched-material principle, different alloy family.
View Page →Monel 400 Fasteners
Annealed Ni-Cu for lower-strength marine applications. Monel 400 washers available when K500 bolt loads are not required.
View Page →Need Monel K500
Washers Now?
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