Failure Investigation was carried out on a fractured Weld neck flange of an 8”discharge pipeline of an ethylene compressor in a Petrochemical complex. The Investigation was carried out with the aim of determining the root cause of the failure. In the course of this investigation, Metallurgical techniques including micrography and fractography as well as stress analysis of the piping were carried out on the failed part. The root cause of the failure was identified as vibration induced fatigue enhanced by the non-homogeneity of the microstructure of the flange due to incorrect normalizing practice after forging. Remedial measures to prevent a reoccurrence were proffered.