Copper-nickels are the benchmark seawater alloys. They combine good general corrosion resistance in salt water with two properties very few other materials offer together: high resistance to chloride stress-corrosion cracking, the mechanism that limits austenitic stainless steel in warm seawater, and inherent resistance to macrofouling — barnacles, mussels and algae do not settle readily on them, so condenser tubing and seawater piping stay clean without chlorination. The 1.0–1.8% iron in 90/10 and 0.40–1.0% in 70/30 are deliberate additions, not impurities: iron is what forms the adherent protective film. Beyond the marine pair this family diverges sharply — it also contains a Constantan-type electrical resistance alloy, a high-strength aluminium-manganese grade, and a spinodally hardened Cu-15Ni-8Sn alloy reaching 1138 MPa. Exotic Alloy manufactures C71500 fasteners to ASTM F468 and F467.
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Copper-nickels have a flow velocity ceiling, and exceeding it is the most common way they are misapplied. Above a critical velocity the protective film is stripped faster than it reforms and the alloy suffers erosion-corrosion — impingement attack, typically showing as horseshoe-shaped pits pointing downstream. Design limits are conventionally about 3.0–3.5 m/s for 90/10 (C70600) and 4.0–4.5 m/s for 70/30 (C71500). Those are figures for clean seawater in well-made pipework, and local velocity matters more than bulk velocity: partly closed valves, sharp bends, weld penetration protruding into the bore, and entrained air or sand all create conditions far worse than the nominal flow.
Stagnation during commissioning is the classic failure case. A new copper-nickel seawater system needs time with clean, flowing, aerated seawater to develop its protective film — weeks to months for full maturity. A system hydrotested with seawater and then left full and still during fit-out goes anaerobic, sulfides form, and the film never establishes properly. Commission with clean seawater at design flow, or drain and dry completely between tests; never leave the system wet and stagnant. Separately, sulfide-polluted seawater from stagnant harbour water, anaerobic mud or decaying organic matter produces a black, non-protective corrosion product in place of the proper film, and attack can be rapid.
Iron content is a specification issue, not a formality. The 1.0–1.8% iron in C70600 and 0.40–1.0% in C71500 are deliberate additions that form the protective film. Material at the bottom of the range, or with iron tied up as coarse precipitate rather than in solution, performs measurably worse in flowing seawater. Read the heat analysis rather than assuming. Note particularly that C71580 permits up to 0.50% iron but sets no minimum at all, so it is not a drop-in substitute for C71500 in high-velocity duty.
Specify the welding grade when the part will be welded. ASME SB-466 states that C70620 and C71520 “are intended for product that will be subsequently welded.” They are the same 90/10 and 70/30 compositions with carbon capped at 0.05%, phosphorus at 0.02% and sulfur at 0.02% — the three elements that cause porosity and hot cracking in copper-nickel welds, and on which the standard grades carry no limit at all. Mechanical requirements are identical, so there is no property penalty for specifying the welding grade. Keep weld bores free of penetration and spatter: a protruding root bead in a seawater line creates exactly the local turbulence that initiates impingement attack.
Only C71500 has a fastener standard behind it. ASTM F468 and F467 list C71500 as Cu 715 — but C70600 is not among them, and neither is any other grade here. Where a certified copper-nickel bolt, cap screw, stud or nut is required, specify C71500 (70/30). On strength, annealed 70/30 is 345 MPa minimum against 830 MPa for an A325 structural bolt — these are corrosion materials, not structural ones. The exception is C72900, the spinodal Cu-15Ni-8Sn alloy, at up to 1138 MPa. Finally, note that two grades on this list are not copper-nickels at all — see the table footnote below.
The copper-nickels carry a CDA machinability rating of 20, the same as pure copper — tough and gummy, work hardening ahead of the tool, producing long continuous swarf with a strong tendency to build up on the cutting edge. Sharp positive-rake tooling kept genuinely sharp, rigid setups, a positive feed that keeps the tool cutting rather than rubbing, moderate speeds and generous lubricant are all needed. Cold and hot forming are both rated Good, though the alloys work harden faster than pure copper and need interstage annealing for severe work. Welding is where this family is genuinely exceptional among copper alloys: CDA rate C71500 Excellent for soldering, brazing, gas-shielded arc, coated metal arc, spot, seam and butt welding — a clean sweep no pure copper approaches, because the nickel lowers thermal conductivity enough that a weld pool can actually be established.
Compositions and physical data from the Copper Development Association alloy records. Specified minimums for C70600, C70620, C71500 and C71520 are from ASME SB-466 / ASTM B466 Table 2, annealed O60 temper.
| Grade | Type | Nickel | Iron | Annealed Strength | Velocity Limit | ASTM F468 | Chosen For |
|---|---|---|---|---|---|---|---|
| C70600 | 90/10 cupronickel | 9.0–11.0% | 1.0–1.8% | 262 MPa | 3.0–3.5 m/s | No | The marine workhorse |
| C70620 | 90/10 — welding grade | 9.0–11.0% | 1.0–1.8% | 262 MPa | 3.0–3.5 m/s | No | Welded 90/10 fabrication |
| C71500 | 70/30 cupronickel | 29.0–33.0% | 0.40–1.0% | 345 MPa | 4.0–4.5 m/s | Yes — Cu 715 | Certified fasteners; high velocity |
| C71520 | 70/30 — welding grade | 29.0–33.0% | 0.40–1.0% | 345 MPa | 4.0–4.5 m/s | No | Welded 70/30 fabrication |
| C71580 | 70/30 — low Fe and Mn | 29.0–33.0% | 0.50% max, no min | On request | Not established | No | Controlled-chemistry variant |
| C72150 | Constantan-type | 43.0–46.0% | 0.10% max | On request | Not applicable | No | Electrical resistance — not marine |
| C72420 | High-strength Cu-Ni-Al-Mn | 13.5–16.5% | 0.7–1.2% | On request | Not established | No | Higher load than 90/10 or 70/30 |
| C72900 | Cu-15Ni-8Sn spinodal | 14.5–15.5% | 0.50% max | 441–1138 MPa | Not applicable | No | High-strength bearings and bushings |
| Alloy 130 | Silver-bearing copper* | 0.05% max — impurity | — | 234–393 MPa | Not applicable | No | Softening resistance at 98% IACS |
| Alloy 191 | High copper alloy* | 0.9–1.3% | 0.20% max | 248–717 MPa | Not applicable | No | Free machining, heat treatable |
*Two grades on this list are not copper-nickels. The Copper Development Association classifies Alloy 130 (C13000) under Wrought Coppers — it is a silver-bearing tough pitch copper whose 0.05% nickel is an impurity ceiling, not an alloying addition, and it carries none of the seawater behaviour of the C7xxxx grades. Alloy 191 (C19100) is genuinely nickel-bearing at 0.9–1.3% but CDA place it under Wrought High Copper Alloys; it is a free-machining, precipitation-hardenable Cu-Ni-P-Te alloy with no deliberate iron addition. Both are built here because they appear on this category list, and both carry the classification note on their own pages. Neither should be specified for seawater service — use C70600 or C71500 for that. Note also that the family diverges sharply beyond the marine pair: C72150 at 43–46% nickel is a Constantan-type electrical resistance alloy for precision resistors, strain gauge foil and thermocouple negative legs, not a piping material; and C72900 is strengthened by spinodal decomposition rather than precipitation, which means — unusually — heavy sections do not suffer the property fall-off that quench rate imposes on a precipitation-hardening alloy.
We are committed to delivering zero-defect copper-nickel fasteners and components. All products undergo rigorous testing including PMI (Positive Material Identification), chemical analysis with iron and manganese reported explicitly on the 90/10 and 70/30 grades, mechanical verification against the specified temper and product form, dimensional inspection and full traceability with EN 10204 3.1 certification. Iron within the specified range is what makes the protective seawater film work, so it is never left to assumption.
Exotic Alloy exports copper-nickel fasteners, tube, fittings and components to marine, offshore, desalination, shipbuilding, power generation and heat exchanger clients worldwide. Our dedicated logistics team ensures secure export packaging and timely deliveries by sea and air freight with full customs documentation support.