Standard ETP copper is an excellent electrical and thermal conductor, but it is soft and it degrades quickly in two very different environments: sustained heat and fast-moving seawater. Engineers facing either condition normally choose between two specialist materials that are often confused with each other, chromium-zirconium copper and copper-nickel 90/10. They are not interchangeable, and using one where the other belongs is a guaranteed early failure.
Two Completely Different Failure Modes
The first failure mode is softening. A pure copper spot-welding electrode tip begins to soften at roughly 200 deg C. Beyond that temperature the tip mushrooms, loses its profile and sticks to the workpiece, so welds become inconsistent and the electrode has to be dressed or replaced. The alloy answer is to raise the temperature at which the material recrystallises.
The second failure mode is erosion-corrosion. When seawater is pumped through a copper tube, turbulence continuously strips the protective surface layer. Pure copper tolerates flow velocities of well under 1 m/s before metal loss accelerates; the alloy answer is a chemistry that rebuilds its own protective film in service.
C18150 Chromium-Zirconium Copper: The Heat-Resistant Option
C18150 adds small amounts of chromium and zirconium to copper. The two elements form fine precipitates that pin the grain structure so that recrystallisation is pushed to a much higher temperature. The alloy therefore keeps its hardness even when it is running hot.
| Property | Typical value | Engineering meaning |
|---|---|---|
| Softening temperature | about 525 deg C | Hardness retained under welding heat |
| Electrical conductivity | about 80% IACS | High current without self-heating |
| Hardness | 75-83 HRB | Withstands electrode force |
| Magnetic behaviour | Non-magnetic | Safe for instrument and welding environments |
Typical applications are resistance-welding caps and electrode holders, contacts in high-temperature equipment, high-current switchgear parts and engine components that see a high heat flux. One practical point governs quality: caps must be produced from wrought, drawn or forged stock. Cast bar is cheaper but has a coarser structure and lower hardness, and it fails earlier in service. Surface cleanliness also matters, because oxide scale and contamination raise contact resistance and reduce the effective conductivity of the tip.
C70600 Copper-Nickel 90/10: The Seawater Option
C70600, also written CuNi 90/10, contains roughly 10% nickel with deliberate iron and manganese additions. In seawater it forms a complex, self-healing oxide film that stays intact even where flow is turbulent, which is why it is the default material for marine piping and heat exchangers.
| Item | Typical value | Comment |
|---|---|---|
| Nickel | 9.0-11.0% | Principal alloying element |
| Iron | 1.0-1.8% | Essential for erosion-corrosion resistance |
| Manganese | 1.0% max | Improves castability and film stability |
| Electrical conductivity | about 10-12% IACS | Adequate for thin-wall heat transfer |
| Seawater velocity tolerance | up to about 3.5 m/s | Against well under 1 m/s for plain copper |
The iron content deserves particular attention. International tube standards require approximately 1.0-1.8% iron, and without it the protective film is far less stable and erosion-corrosion resistance falls sharply. Tubes and fittings are commonly ordered to ASTM B111/B111M, with EN 12451 and JIS H3300 used for European and Japanese projects. Typical applications are ship seawater intake and discharge lines, offshore platform fire-fighting systems, desalination plant tubing, condenser and heat-exchanger tubes, water boxes and brake tubing.
Side-by-Side Comparison
| Feature | C18150 (CrZrCu) | C70600 (CuNi 90/10) |
|---|---|---|
| Primary strength in service | Resists softening at high temperature | Resists seawater erosion-corrosion |
| Electrical conductivity | about 80% IACS | about 10-12% IACS |
| Softening temperature | about 525 deg C | Not used as a hardness material |
| Seawater performance | Poor; the alloying elements do not build a protective film | Excellent; self-healing oxide film |
| Magnetic | No | No for 90/10; the 70/30 grade is very slightly magnetic |
| Colour | Reddish copper | Silvery white |
| Typical service | Welding electrodes, hot contacts, high-current parts | Marine piping, condensers, desalination |
Selection Rules and Verification
Choose by failure mode, not by conductivity alone. If the part must survive repeated welding heat, take C18150; if it must survive seawater, take C70600.
Do not force one material to do the other's job. A copper-nickel electrode tip will soften and deform under welding load, and a chromium-zirconium tube will suffer rapid erosion-corrosion in a seawater line.
Verify chemistry on every heat. Chromium and zirconium must be within the specified range for C18150, and iron must be within the 1.0-1.8% band for C70600.
Check product form as well as grade. Welding caps should be wrought, not cast, and tubes should be supplied with an eddy-current test report and a hydrostatic or pneumatic test as applicable.
Confirm dimensions against the drawing or tube standard, including wall thickness tolerance, which controls both pressure rating and heat-transfer performance.
FAQ
Q: Can C18150 be used in seawater?
No. Chromium-zirconium copper does not develop the protective oxide film that copper-nickel alloys form, so it corrodes quickly in flowing seawater. C70600 is the correct choice for that environment.
Q: Can C70600 be used as a welding electrode?
No. Its softening temperature and hardness are far too low for resistance-welding duty, and it would deform under electrode force within a short production run.
Q: Why does the iron content of C70600 matter so much?
Iron stabilises the protective surface film that resists erosion-corrosion. Tubes made without the specified iron range can lose much of their seawater resistance, so iron must be verified spectrometrically rather than assumed.
Q: What does "softening temperature" mean for C18150?
It is the temperature at which the alloy begins to lose hardness through recrystallisation. For C18150 that is about 525 deg C, compared with roughly 200 deg C for pure copper, which is why it survives repeated welding cycles.
Q: Which standards apply?
Copper-nickel tubes are commonly ordered to ASTM B111/B111M, EN 12451 or JIS H3300, while electrode and contact copper is specified by chemistry and hardness to the relevant bar and rod specification.
Q: Is either alloy magnetic?
Neither C18150 nor C70600 is magnetic in normal use. Only the 70/30 copper-nickel grade shows very slight magnetic behaviour.
