Impeller High cycle fatigue failure on a Natural Gas Pipeline Compressor Following Choked Flow Operation

Case StudyThe impeller of a natural gas pipeline compressor failed at the junction between the blade trailing edge and the hub. A root cause analysis showed the machine had been operated beyond the compressor map right limit during short periods, in recent unit history (after 60000 hours of operation). The impeller interference diagram analysis revealed the presence of a potentially critical interference at 100% speed, between an impeller trailing edge mode and an impeller/vaneddiffuser aerodynamic synchronous excitation. The metallurgical analysis and crack investigations confirmed the High Cycle Fatigue failure mode. A reduced choke flow operational limitation was implemented based on unsteady aerodynamic simulation results