FAILURE ANALYSIS OF CRACKED REDUCER FLANGE

摘要

A cracked reducer flange was analyzed for the cause of the failure. The flange was carefully cut in order to obtain samples for metallographic, x-ray, and Scanning Electron Microscopy (SEM) Examinations. The examinations revealed that the introduction of chloride ions in the operational service led to pitting corrosion in the inner surface of the flange. Chloride ions were probably the result of chemical contaminations, i.e., cleaning contamination during shutdown of the operation . The introduction of corrosion pits, caused unexpected load stress intensification and cracldng of the flange. Consequently, stress corrosion cracking emanated from the pits under the influence of chloride attack and operational pressure. Then the cracks propagated in a transgranular manner, in the radial direction of the flange, until the final failure occurred.