Failure Analysis on Cracking of an Aluminum Alloy Flange for Current Transformer

Multiple cracking was found on an aluminum flange used for the current transformer in coastal region of Fujian province. Means such as macro examination, chemical composition analysis, metallographic analysis, scanning electron microscope and energy spectrum analysis, and so on were utilized to investigate the causes for the cracking. The results show that all the cracks initiated from the bolt holes, and the failure of the flange was stress corrosion cracking (SCC) under the coaction of corrosive environment and stress. The high tightening force of the bolts, the high Cl^- concentration of the service environment and the high sensitivity to SCC of the aluminum alloy were the main causes for the cracking of the flange. Finally, preventive measures were put forward according to the cracking causes of the flange.