Steam Turbine Reoccurring Rubs, Troubleshooting and Corrective Action

Abstract

Rubs in steam turbines can be especially difficult to diagnose because the vibration signature can manifest differently depending on the location, severity, rotordynamics, machine design and bear similarities to other common causes of elevated vibration. This case study presents the information gathering, engineering analyses and site testing performed to diagnose a 22 stage condensing steam turbine with an intermittent rub. On-stream troubleshooting allowed the vibration to be largely mitigated until the next maintenance opportunity and proper scope development to address stuck pedestal sliding surfaces distorting the casing and causing the rub.