Detection of Broken Blade on Compressor

Abstract

A sudden step change in vibration was observed on a 7400 rpm compressor with direct amplitude from 43 um pp to over 62 um pp (trip level) at NDE, thus tripping the unit Vibration reached over 120 um pp at 4000 rpm, compared to normally 20 um pp during coast down Vibration excursion was dominantly due to the 1 X component It was noticed that thrust probe gap readings started to fluctuate 6 months prior to the vibration trip A sudden change in unbalance was diagnosed, followed by an inspection It appeared that a balance pipe started to leak earlier, causing the axial thrust force to fluctuate, as indicated by fluctuating thrust gap It was possible that a piece of damaged fragments entered the gas flow and hit the 3 rd stage blade, thus breaking the blade to lead to a sudden change in unbalance.