Process and Prevention of Intergranular Corrosion of Aluminium Brass Condenser Tube Surfaces Infested with Barnacles
Ryusuke Kado, Ichiro Katsuyama, Hirohiko Kominami, Jiro Kittaka
The process of and prevention method for intergranular corrosion beneath attached barnacles on aluminium brass condenser tubes have been studied. Experiments were conducted to find when the corrosion starts and ends by using pieces of the tube with barnacles killed by freezing. The corrosion proceeded rapidly during the first two weeks after death, then lasted slowly or ended afterward. Depth of the corroded portion was deeper in barnacles of greater shell length. S was detected in basis and just beneath Fe coat at high levels by EPMA from the cross section through the blackened barnacle basis to the aluminium brass body. Whitish scale under some blackish scales appeared after 45 days only, indicating that the whitish scale were formed in aerobic condition following recovery after breakdown of the anaerobic condition. Mechanical removal test of barnacles also conducted with ordinary cleaning balls in the laboratory. The sponge and the carborundum ball were effective for smaller than 1mm size and 2 to 3mm size barnacles, respectively. However removal of 5mm size barnacles or larger could not be accomplished by these balls. Three times of a sponge ball-per-tube operation should be applied more than twice a week during the settling season to prevent the corrosion due to barnacles.