- 90-10 Cu-Ni is a single phase alloy with a melting point above 1100C.
- In the case of a hydrocarbon fire, copper nickel does not generate toxic fumes. It will not show degradation in an uncontrolled manner.
- Cu-Ni has inherent high resistance to biofouling. Chlorination can be reduced or, in some instances, avoided.
- Cu-Ni can be recycled. It can be 100% remelted and reused.
- Leaching: Development of a protective film reduces fouling and the release of copper.
- Touch Contact: Nickel can cause allergic reactions in susceptible people. Cu-Ni in coins and other articles is transient and therefore rarely a problem.
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Copper is naturally present in aquatic environments and is an essential element in the life of aquatic organisms. Experience has shown that copper-nickel surface films generally have low biofouling.The protective films also resist corrosive attack from cooling waters.
In general, the film consists of copper oxides and other elements whose chemical composition depends primarily on water quality. Initial film formation in oxygen containing waters takes place at exponential reaction rates, the biggest portion being formed in a few hours (accompanied by the dissolution of copper oxides into adjacent water). Once the mature surface corrosion film has formed, the amount of released copper becomes very small, often difficult to detect by normal methods of analysis and quickly diluted in aquatic environments. The small remainder of film is formed within the next few weeks or months. Consequently, a short-term increase in copper concentration at the cooling water outlet will be noticed only during initial start up of the heat exchanger. This concentration decreases with time.
Released copper ions near the protective film surface inhibit the attachment and growth of a “slime” layer of microorganisms (“microfouling”). Further, the inhibition of the formation of this slime seems to make the surface uninviting to a large number of marine macro-organisms because they prefer to settle elsewhere. This keeps heat exchangers free of fouling so that the calculated effective heat transfer is maintained.
The copper released both in the course of film formation and during service is available in two different forms:
- Biologically active / "bioavailable" copper (e.g. ionic copper)
- Biologically inactive (e.g., copper bound to natural organic matter in the water)
It is important to make this distinction rather than refer to the total copper content because ionic copper is the form available to organisms and potentially available to cause toxicity. Since analytical testing and apparatus may contaminate the water samples being tested, proper sampling and testing practices should be employed particularly in regard to sample storage and method of analysis.
Copper release or leaching data for multi-stage flash desalination units indicates:
- Deaerated Brine Tubing: Copper in brine blow down in modern desalination plants with good process control can be expected to be less than 0.1ppm.
- Copper in Distillate: For acid and additive dosed desalination plants, the copper content is expected to be less than 0.1ppm; in most cases being below 0.035ppm.
Applicable water quality standards for copper can be as low as 0.002 ug/L in some jurisdictions, so care should be taken to ensure compliance of discharges to surface waters. Fortunately, standards based on bioavailble copper have been adopted in the US, EU and other countries; these newer bioavailable copper standards often yield local standards that are much higher than standards based on older toxicity data.
Touch ContactNickel has the ability to sensitize individuals and cause an allergic reaction when there is exposure to a sufficient amount of solubilized nickel ions. This is explained in a thorough overview of Nickel Allergic Nickel Dermatitis (ACD) on the Nickel Institute Website.
Notably the REACH Regulation Annex XVII (previously the European Union's Nickel Directive 94/27/EC; amended by Directive 2004/96/EC) prohibits the use of nickel in products intended for close and prolonged skin contact which will result in solubilization of nickel at a rate exceeding 0.5 micrograms per square centimetre per week.
Copper-nickel alloys contain nickel in solid form which when in prolonged contact with sweat can produce nickel ions. If the concentration of nickel ions becomes high enough, there is potential for NACD in nickel-sensitized individuals and for sensitizing non-nickel-sensitized individuals. Most of the studies related to copper-nickel alloys have involved coinage rather than engineering alloys, as these have the most public exposure. For example, in the UK, 50p coins are currently 75Cu and 25Ni; 20p coins are 84Cu and 16Ni. New 5p and 10p coins are now nickel plated steel but there are still original 75Cu-25Ni versions in circulation. If the new or old versions are tested in artificial sweat, all will release nickel at a rate greater than the 0.5ug/cm2/week specified in the Directive REACH Regulation Annex XVII. However, because of the transient nature of the contact, the handling of coins rarely causes NACD. Also, used coins have been shown to have lower levels of nickel release than coins when coins first enter circulation, probably because of surface dirt, oils and fats from the skin, and products of corrosion (e.g. nickel oxide).
Similarly for non-coinage articles, contact of copper-nickel with skin per se is not the direct cause of NACD but it is the soluble nickel products resulting from the corrosion of the metal by sweat. This requires a lapse of a period of time for the concentration of the soluble nickel corrosion products to reach a critical dose. Thus, transient contact of these alloys with skin is rarely damaging. For longer exposures, the rate of reaction may differ markedly between persons as a result of differences in the corrosivity of their sweat. Menné (1994) concluded that elicitation is unlikely below 15 μg Ni/cm2 non-occluded exposure of solubilized nickel ions. Prolonged exposure copper-nickel coinage alloys will require protection or avoidance of skin contact.
For further information on contact dermatitis, see the Nickel Institute.
- An Assessment of the Biofouling Resistance and Copper Release Rate of 90-10 Copper-Nickel Alloy, Michel, J., H. Michels, H., and Powell, C., Paper 11352, , Corrosion 2011, Houston, NACE, .
- Environmental Aspects of Corrosion in MSF and RO Desalination Plants, Oldfield, J. W., & Todd, B., Desalination, Vol. 108, 1-3, pp 27-36, , Second Annual Meeting of the European Desalination Society on Desalination and the Environment, Genoa, Italy, .
- Literature Review on the Effects on Aquatic Environments of Copper in Cooling Water from Copper Alloy Condensers, International Copper Association, .