2005 Volume 54 Issue 11 Pages 520-525
A heat exchanger for vaporizing liquefied natural gas (LNG) is made of aluminum alloy tubes, and the way of protecting the tubes from corrosion in sea-water is to form a sacrificial anode layer by thermal-spray coating of Al-Zn alloy on aluminum alloy tubes.
However, corrosion damage has been sometimes found in the lower part of heat exchangers exposed to near frozen sea-water. The purpose of this study is to investigate the corrosion behavior of Al-2mass%Zn alloy thermalspray coating in freezing sodium chloride solution and to examine a possibility of electrochemical impedance spectroscopy for monitoring of the corrosion process of heat exchanger. The Al-2mass%Zn thermal-spray coating corrodes at 253K in freezing sodium chloride solution. The characteristic of polarization change a mixed control at this temperature. The corrosion rate obtained by the measurement of electrochemical impedance spectroscopy didn't change with immersion time, corresponding with the corrosion rate obtained by the weight loss method.
It was found that this technique is a convenient tool for monitoring of the corrosion processes of heat exchanger in near frozen sea-water.