Abstract
Ant-nest corrosion is a type of premature and localized failure, which is observed in Cu tubes used mainly in air-conditioning and heat exchanger units, induced by the presence of organic matter. Leakage takes place within a short period of time after unit installation and frequently causes pipeline and equipment damage accompanied with loss of refrigerant liquid. In the present paper, case histories concerning such type of insidious corrosion phenomena are presented. Metallographic examination on cross-sections revealed that a particular pitting corrosion mechanism is activated, driving to a tunnelling-type “tortuous” pit propagation, causing rapid metal tube perforation and leakage.
Highlights
Copper is the first member of Group IB of the Periodic Table having atomic number 29 and electronic configuration [Ar]3d104s1
Higher magnification observation was carried out using a FEI XL40 SFEG Scanning Electron Microscope (SEM) under 20 kV accelerating voltage, coupled with an EDAX Energy Dispersive X-ray Spectroscopy (EDS) Apollo XF Silicon Drift Detector (SDD) of 60 mm2 area
Ant-nest corrosion most commonly appears in the copper tubing of air conditioning or refrigeration equipment and is mostly found in Cu-DHP, which is the main material of construction
Summary
Copper is the first member of Group IB of the Periodic Table having atomic number 29 and electronic configuration [Ar]3d104s1. The loss of the outermost s-electron produces the cuprous ion Cu+ and a second electron may be lost from the filled d-shell to form the cupric ion Cu2+. The availability of the d-electrons for coordination allows copper to readily form complexes with such species as NH3 and CN [1]. As copper is not an inherently reactive element, it is not surprising that the rate of corrosion is usually low. Due to its high thermal conductivity is frequently used in unit installations such as air conditioners and refrigerators. Copper tubes from different applications exhibit various types of corrosion: pitting corrosion [2,3], erosion-corrosion [4], microbiological influenced corrosion [5] etc
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