Copper Nickel
Fasteners
Manufacturer India
Cu-Ni 90/10 and 70/30 — Seawater Corrosion, Biofouling, and System Compatibility
Copper-nickel alloys (Cu-Ni, CuNi, Cupro-Nickel) are the standard fastener material for marine seawater systems, offshore platform firewater systems, naval vessel seachest connections, and desalination plant raw seawater handling — any application where the fastener is in direct, continuous contact with seawater at operating conditions.
The seawater corrosion protection mechanism of Cu-Ni is unique: a thin, adherent cuprous oxide (Cu₂O) layer forms naturally in seawater within weeks of initial immersion. This layer is tenacious, self-repairing, and — critically — biologically active. The slow release of Cu²⁺ ions from the surface creates a mildly toxic microenvironment at the metal surface that prevents macrofouling organisms (barnacles, mussels, oysters, algae, tube worms) from settling and establishing permanent attachment. This is the biofouling resistance that makes Cu-Ni uniquely qualified for seawater piping flanges and heat exchanger connections where biofouling growth inside the system would restrict flow and accelerate localised corrosion.
Compared with stainless steel 316L for seawater service: 316L (PRE≈24) is susceptible to chloride pitting and crevice corrosion in stagnant seawater — the exact conditions of a bolted flange face where seawater is trapped in the gasket crevice. Monel 400 provides similar seawater immunity but has no biofouling resistance. Cu-Ni 90/10 provides the complete combination: seawater corrosion resistance, biofouling resistance, system galvanic compatibility with Cu-Ni piping and tubing, and lower cost than Monel K500 where the higher strength of K500 is not required.
90/10 CuNi
70/30 CuNi
Cu-Ni Fastener Types & Standards
90/10 (C70600) is the primary stocking grade — suitable for most seawater service. 70/30 (C71500) for higher-strength and higher-temperature seawater service, desalination RO pressure vessels, and naval firewater piping. M4–M36.
Stud Bolts
Fully threaded stud bolts in 90/10 (C70600) and 70/30 (C71500) for seawater pipeline flanges, offshore seachest flanges, desalination plant heat exchanger channel heads, and naval vessel firewater system connections. M6–M36, lengths to 500mm. Fe content verified by PMI before machining. MTC per ASTM B151.
Hex Bolts
Full thread and partial thread hex bolts in 90/10 and 70/30. M4–M36. Seawater intake screening systems, offshore pipeline tie-in connections, reverse osmosis plant process connections, and marine heat exchanger structural bolting where Cu-Ni system galvanic compatibility (matching the Cu-Ni piping and tube sheets) eliminates bimetallic corrosion at flange connections.
Hex Nuts
Standard hex nuts in 90/10 and 70/30. M4–M36. Matched from same ASTM B151 certified bar as stud bolts — single MTC for complete stud bolt assembly covering stud and nut from the same certified heat. Cu-Ni nuts for Cu-Ni stud bolts eliminate the galvanic couple at the thread engagement crevice — the critical interface for seawater crevice corrosion.
Washers
Plain flat washers in 90/10 C70600. M4–M36. For complete Cu-Ni seawater assembly documentation — stud bolt, nut, and washer from same certified heat. The washer-nut bearing face crevice is a seawater corrosion site; matching-alloy Cu-Ni washers eliminate the galvanic couple at this interface in seawater-immersed flange connections.
Socket Cap Screws
Hex socket cap screws in 90/10 and 70/30. M4–M24. Confined-access seawater system connections — heat exchanger internal baffle screws, seachest strainer plate screws, below-waterline instrument port screws, and all marine bolting where flush head access from one side and Cu-Ni system compatibility are both required.
Custom Cu-Ni / Naval
Non-standard dimensions, DEF STAN compliant Cu-Ni fasteners for naval vessel procurement, and drawing-specific configurations in 90/10 or 70/30. Naval defence contracts specifying DEF STAN 02-870 or equivalent Cu-Ni fastener specifications supplied with appropriate defence-standard documentation. Contact sales@akbarfasteners.in with specification number.
Cu-Ni 90/10 vs Monel 400 vs 316L — Seawater Grade Matrix
Cu-Ni fills the gap between 316L (insufficient seawater resistance) and Monel 400 (no biofouling resistance, higher cost). This matrix identifies when 90/10 is the correct and cost-effective seawater fastener alloy.
| Criterion | Cu-Ni 90/10 This Page | SS 316L | Monel 400 | Duplex 2205 |
|---|---|---|---|---|
| SEAWATER PERFORMANCE | ||||
| Continuous seawater immersion | ✔ Excellent | Pitting risk | ✔ Excellent | Good (PRE≈35) |
| Crevice corrosion (flange face) | Good | ✗ Fails | ✔ Excellent | Good |
| Biofouling resistance | ✔ Excellent (Cu²⁺ toxic) | None | None | None |
| Flow velocity tolerance | Good (to ~2.5 m/s) | Poor | ✔ Excellent | Good |
| SYSTEM COMPATIBILITY | ||||
| Galvanic match with Cu-Ni piping | ✔ Perfect match | Galvanic couple | Good (Monel pipe) | Galvanic couple |
| Non-magnetic | ✔ Yes | ✔ Yes | ✔ Yes | Slightly magnetic |
| COST POSITION | ||||
| Relative cost vs 316L | 2–3× 316L | Baseline 1× | 5–7× 316L | 1.5–2× 316L |
| Best position | Cu-Ni piping systems | Not for seawater | HF acid or H.strength | Stainless spec seawater |
High-strength seawater: Monel K500 (≥1000 MPa) · System pipes: Cu-Ni & Copper alloys
Cu-Ni Fasteners Application Areas
Seawater systems in offshore, naval, desalination, and marine industries — wherever the fastener is part of a Cu-Ni piping or heat exchanger system and galvanic compatibility with the system alloy is required.
Offshore Platforms
seachest connection bolts
Naval Vessels
naval firewater fasteners
Desalination Plants
heat exchanger channel bolts
FPSO / Floating Platforms
utility seawater pipe flanges
Marine Heat Exchangers
channel head stud sets
Power Station Cooling
condenser cooling flanges
Aquaculture / Fish Farm
seawater cage hardware
Harbour / Port Infrastructure
tidal zone structural
Cu-Ni Standards Coverage
Same ISO 9001:2015 quality system as our complete fastener range. PMI on all Cu-Ni orders confirms nickel content and — critically — iron content ≥1.0% (90/10) which governs seawater film protection quality.
Complete Documentation Package
ASTM B151 Traceable
Conformance
Ni% / Cu% Confirmed
Tensile · Hardness
TÜV · BV · Lloyds
Related Marine Fastener Alloys
Cu-Ni for Cu-Ni piping systems and biofouling resistance. Monel K500 for high-strength seawater. Silicon bronze for boat hull bolting. SS Duplex 2205 for structural marine.
Monel K500 Fasteners
When seawater strength exceeds Cu-Ni’s capability — Monel K500 (age-hardened, ≥1000 MPa) provides the highest-strength seawater fastener in commercial engineering. For propeller shaft connections, high-pressure seawater injection systems, and subsea structural applications requiring Cu-Ni seawater immunity with significantly greater mechanical strength.
View K500 →Monel 400 Fasteners
When the seawater system uses Monel piping (not Cu-Ni piping) — Monel 400 provides galvanic compatibility with Monel 400 piping and valves. Monel 400 also handles HF acid service that Cu-Ni cannot. For Monel system galvanic compatibility, specify Monel 400 fasteners rather than Cu-Ni.
View M400 →Silicon Bronze / Al Bronze
For marine structural bolting in wood, FRP, and composite hulls — silicon bronze C65500 provides below-waterline dezincification-resistant fasteners for boat construction. Aluminium bronze C63000 for high-load marine structural where Cu-Ni’s lower strength is insufficient.
View Copper Range →Super Duplex 2507
For seawater service where a stainless steel specification is mandatory (rather than Cu-Ni) — Super Duplex 2507 (PRE≈43) provides the highest seawater pitting resistance of any standard stainless steel, with superior strength to Cu-Ni. For stainless-specified offshore seawater systems.
View SS Range →Need Cu-Ni
Fasteners?
Grade (90/10 or 70/30) · product form · size · application · standard (ASTM / DEF STAN). Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Export: +91 8696 32 4646 · Support: +91 800 9315 333 · export@akbarfasteners.in