Effect of Ammonia and Sulphide Environment on 90/10 and 70/30 Cupronickel Alloy
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TECHNICAL ARTICLE—PEER-REVIEWED
Effect of Ammonia and Sulphide Environment on 90/10 and 70/30 Cupronickel Alloy D. C. Agarwal Æ A. M. Bapat
Submitted: 4 March 2009 / Accepted: 22 July 2009 / Published online: 22 August 2009 Ó ASM International 2009
Abstract Copper nickel alloys 90/10 and 70/30 are used extensively in saltwater systems operating on marine platforms and offer high corrosion and biofouling resistance. However, systems using these materials were reported to fail prematurely. Preliminary investigations revealed pollution of harbor waters with tangible levels of ammonia and sulphides which was reported to be the primary cause of failure. The present author(s) have performed laboratory and field investigations to identify the stress-material-environment interaction of the copper nickel alloys extensively in use on seawater system of marine platforms. Results obtained point to the fact that polluted seawaters can affect the material properties of the alloy leading to premature failure(s) of systems at stresses well below the designed stress. The paper presents the correlation of the results of the laboratory and field tests of 90/10 and 70/30 copper–nickel alloys in seawaters polluted with ammonia and sulphide pollutants. Keywords Accelerated corrosion testing Brittle fracture Mechanical property estimation Environmentally assisted cracking SEM Stress corrosion cracking Embrittlement Laboratory simulations
D. C. Agarwal (&) A. M. Bapat Defence Institute of Advanced Technology, Girinagar, Pune 411025, Maharashtra, India e-mail: [email protected]; [email protected]; [email protected] A. M. Bapat e-mail: [email protected]
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Introduction Copper–nickel (Cu–Ni) alloys are widely accepted materials for seawater piping applications because of their superior corrosion resistance [1]. However, this material too has been reported to have failed well before their expected lifetime [2]. Investigations had revealed that a majority of these failures occurred when the pipes in question were subjected to widely varying fluid flow rates and were exposed to polluted seawaters. Investigations on failed pipes revealed that SCC was the operative failure mechanism under the influence of ammonia and sulphide reducing the load bearing capacity of the material. It is well known that copper nickel alloy forms protective films of cuprous oxide which were modified by the incorporation of nickel and iron causing decrease in ionic conductivity [3]. Exposure of Cu–Ni alloys to quiet and clean seawaters showed minimal corrosion and biofouling due to progressive development of protective films causing corrosion rates to fall to negligible rates [4]. However, copper nickel alloys have been known to show increased rates of corrosion in polluted seawaters. Seawaters in harbor are known to contain ammonia and sulphides [2]. Tests conducted on condensor tubes made of 90/10 Cu–Ni and 70/30 Cu–Ni when exposed to waters containing ammonia had shown susceptibility to impingement attack, crevice corrosion, and SCC [5]. Detailed
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