CS23: Resolution of Steam Turbine High Vibration Due to Rotor Rub

Abstract

This case study presents a high vibration trip incident experienced on a SP steam turbine which was overhauled, during re-start The machine tripped 3 times on high vibration just before 1st critical The problem was identified quickly through vibration analysis and issue resolved without needing to re-open the turbineThe problem was suspected to be rubbing of the shaft and the labyrinth during acceleration which resulted in a thermal bow of the turbine shaft During detailed troubleshooting, a hold-down bolts on the turbine Drive-end casing was found to be excessively tight This restrained the normal thermal growth of the casing which caused a minor distortion as more steam was being introduced into the turbine The distortion resulted in a rub which thermally bowed the shaft and resulted in the high 1X vibrationThis case study will present the problem encountered, vibration analysis done and the resolution implemented