Erosion corrosion of copper-10% nickel alloy revisited

Hodgkiess, T. and Vassiliou, G. (2003) Erosion corrosion of copper-10% nickel alloy revisited. In: International Symposium on Corrosion Science in the 21st Century, University of Manchester, 6-11 July 2003,

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In the past, erosion corrosion of copper-nickel alloys has received considerable attention but the main focus has been on obtaining estimates of the maximum-permissible velocities, especially with regard to condenser tubes, together with investigations of the constitution of the protective-surface films. Rather less effort has been devoted to the mechanisms of erosion corrosion. This paper describes findings from a study of the erosion-corrosion behaviour of Cu/10Ni under liquid impingement conditions in saline water at 19°C. Experiments were conducted at zero, 2.4, 4.5, 17 and 86 m/s; i.e. pertinent to the practical use of Cu/Ni alloys but also extended to much higher velocities for the purposes of mechanistic studies. The experimental protocol included measurement of total weight loss, both under free-corrosion conditions and during the application of cathodic protection, electrochemical monitoring to yield the pure corrosion rates, and microscopical examination. The results indicated complex dependencies of total weight loss as a function of time at constant impingement velocities and as a function of velocity at constant time of exposure. Another finding was of significant-to-large contributions to the overall material loss from pure erosion and from synergisitic, or interactive, mechanisms. However, the main focus of this paper is on the detailed study of the velocity-dependence and time-dependence of the pure electrochemical component of the damage process. Detailed analysis of the anodic and cathodic polarisation curves and trends in free-corrosion potential supports the view that, for a small range of velocities where the corrosion rate was observed to increase with velocity, the corrosion rate of this alloy is under mixed diffusion/charge transfer control. This is essentially the same mechanism that has been suggested by previous workers in relation to the behaviour of pure copper. However, the observed corrosion rate/velocity relationships at higher velocities are rationalised in terms of film formation and breakdown mechanisms. For a fixed velocity of 17 m/s, the results indicated that the corrosion rate was cycling between low and high values over a 70-hour test period. Again these trends are discussed with reference to the detailed analysis of the Tafel plots, which correlated well with linear-polarisation monitoring. The relevance of the observations to conventional notions of active/passive cells occurring on copper-nickel alloys in flowing systems is discussed.

Item Type:Conference Proceedings
Glasgow Author(s) Enlighten ID:Hodgkiess, Dr Trevor
Authors: Hodgkiess, T., and Vassiliou, G.
Subjects:T Technology > TA Engineering (General). Civil engineering (General)
College/School:College of Science and Engineering > School of Engineering > Systems Power and Energy

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