A South East Asian power plant was experiencing high vibration and cracking in the exhaust hood of one of its steam turbines.  Travel to the area was very limited due to the outbreak of the avian flu in 2005.  The typical troubleshooting approach is to travel to the site of the machinery, collect the data, analyze it at the home office, and provide a specific solution.  However, in order to meet the customer’s timing, technical, and other requirements, MSI agreed to implement a new remote problem solving approach.

exhaust_hood-300x225

Figure 1. Exhaust hood cracking created a reliability and safety concern.

Initially, MSI packaged and shipped test instrumentation including signal analyzers, accelerometers, pressure transducers, strain gages and shaft sticks to the job site.  An Internet Protocol (IP) phone and camera were also shipped to allow visual as well as verbal low cost communication.  The test hardware was installed under MSI’s oversight from 12,000 miles away. MSI’s advanced troubleshooting process was supported by local plant personnel based on very specific instructions in real time from MSI staff located at their New Jersey office.  Visual and voice communication was accomplished using the camera and IP phone, as an early version of MSI's Distance Communication Maintenance System.  MSI staff also remotely controlled the FFT 40-Ch analyzer through a broadband internet connection.

Remote data collection was supported by FEA analysis performed at MSI’s USA offices.  The FEA results were correlated to the test data (Figures 2 and 3) and were used to analyze potential fixes before recommending fixes that could be installed with confidence.

feavsods-300x225

Figure 2. Remote test data applied to computer generated model (Left) vs. FEA analysis results (Right). Testing model motion is slightly more exaggerated than the FEA model motion

steam-turbine-power-plant-animated-FEA-300x241

Figure 3.  FEA demonstrating turbine casing deflection.

The remote test data and FEA indicated a natural frequency of the exhaust hood with synchronous motion at both ends close to 50 Hz.  Figure 4 shows the motion of the natural frequency that coupled with an S-shaped rotor natural frequency also near 50 Hz.  The rotor mode was driving the bearing housing, which in turn drove the exhaust hood casing motion.

steam-turbine-power-plant-operating-deflection-shape-236x300

Figure 4. Operating Deflection Shape (ODS) and modal test data showing exhaust hood and shaft motion.

Follow-up testing performed on-site by MSI staff confirmed that the remote test data and FEA were accurate.  The ends of the exhaust hood were stiffened by adding additional support ribs and bolting thick metal plating across the casing ends, the vibration was reduced and the cracking stopped.  Costly trial and error problem solving was avoided.  The remote approach allowed MSI to respond very quickly and minimize travel related costs.

REAL-WORLD EXAMPLES AND CASE STUDIES

MSI In Action

Case Study

A Cure for the Common Cold – in Turbines

A steam turbine at a waste-to-energy facility in the Northeast underwent a scheduled repair, at which time the turbine bearings were reworked, after which the turbine periodically experienced very high amplitude shaft vibrations.

Case Study

BFP Fluid Drive Troubleshooting

A boiler feed pump (BFP) driven off of the main steam turbine via a fluid drive was experiencing high vibration levels leading to frequent replacement of the fluid drive bearings.

Case Study

Aeroderivative Gas Turbine Modifications to Solve a Problem

MSI was contracted to understand and help solve a high vibration problem on an aero-derivative gas turbine driven generator.