Failure analysis of heat exchanger tubes used in a lithium bromide central air-conditioning unit

Absorber heat exchanger tubes of central air-conditioning unit of a company are made of pure copper. After running for one and a half years, many corrosive holes were found on these exchange tubes. The heat exchanger was of the bayonet type with cooling water inside the tubes and lithium bromide solution at the shell side. In order to investigate the failure mechanism, macroscopical inspection, chemical composition analysis, corrosion production analysis with Energy-Dispersive X-ray spectroscopy (EDX), cooling water impurity measurement were carried out. The study revealed that the corrosion cracking of the tube is corrosive pitting, The main reason is due to the cracking of the absorber shell during operation, lots of oxygen and carbon dioxide leaked into the exchanger and destroyed the passive film, further more, the hardness of recycle cooling water is higher, the impurity in the water was easy to accrete on surface and made solution there concentrate, which speeded up the local corrosion of the tube, To avoid such pitting corrosion, precautions should be taken to prevent the oxygen and carbon dioxide leak into the exchanger and keep the impurities in cooling water within the ordinary value.