common.
Monitoring Guidelines for Steam and Gas Turbines
Figure 3.3a Steam Turbine Blading
Vibration Collection and Analysis: Due to their criticality, most steam and gas turbines have dedicated vibration monitoring systems consisting of either case-mounted accelerometers or non-contacting proximity probes at each bearing including every thrust bearing. If a significant change in overall vibration amplitude or thrust position is reported by the monitoring system, a detailed frequency analysis is performed in an attempt to identify the nature of the malady. Critical monitoring systems usually have capabilities of generating trend plots, spectral comparisons, orbits, etc.
Inspection frequency: Additional monthly and quarterly inspections are often conducted by a technician to determine if any changes from the baseline have occurred.
Figure 3.3b Gas Turbine Power Recovery Buckets
Temperature Monitoring: Due to their criticality, steam turbines and gas turbines typically have thermocouples or RTDs embedded in the bearing Babbitt near the location of the maximum expected bearing temperature. The proper placement of thermocouples and RTDs in the bearing allows accurate and repeatable bearing metal temperature measurements that can better track changing load and lubrication conditions.
Inspection frequency: At the same time the vibration data is taken.
Oil Analysis: Periodic oil analyses are typically performed on steam turbines and gas turbines. These analyses can help detect oil contamination, oil breakdown, and bearing deterioration issues.
Inspection frequency: Monthly and quarterly inspection intervals are common.
Pressure Pulsation Analysis: This type of analysis is usually not conducted on steam turbines or gas turbines.
Inspection frequency: Only required when issues arise
Piping Vibration: This type of analysis is usually not conducted on steam turbines or gas turbines.
Inspection frequency: Only required when issues arise
Performance Monitoring: Performance monitoring can be conducted on steam turbines and gas turbines, but is both extremely complex and beyond the scope of this book. Usually this type of analysis is conducted by outside personnel with detailed knowledge of these machines.
Inspection frequency: Annual performance evaluations are common.
Additional Inspections: Due to the extreme conditions inside steam and gas turbines it is common to perform internal inspections at prescribed time intervals or “fired hours” intervals. This timing is because there are known failure modes that are not detectable with current online inspection methods. The original equipment manufacturer is a good starting point for recommended tear down inspection intervals for optimum reliability.
Monitoring Guidelines for Gear Boxes
Vibration Collection and Analysis: Due to their criticality, most large gear boxes have dedicated vibration monitoring systems consisting of either case-mounted accelerometers, non-contacting proximity probes at each bearing, or both types of sensors. Proximity probes are employed on units with fluid film bearings as a means of monitoring shaft vibration whereas case mounted accelerometers are used to monitor the condition of the gears.
Critical monitoring systems usually have capabilities of generating trend plots, spectral comparisons, orbits, etc. If a significant change in overall vibration amplitude is reported by the monitoring system, a detailed frequency analysis is performed in an attempt to identify the nature of the malady. Due to the sensitivity of gear dynamics to horsepower loading, it is particularly important to note power load levels when vibration data are collected.
Inspection frequency: Additional monthly and quarterly inspections are often conducted by a technician to determine of any changes from the baseline have occurred.
Figure 3.4 Double Herringbone Gears
Temperature Monitoring: Due to their criticality, large gear boxes typically have thermocouples or RTDs embedded in the bearing Babbitt near the location of the maximum expected bearing temperature. The proper placement of thermocouples and RTDs in the bearing allows accurate and repeatable bearing metal temperature measurements that can better track changing load and lubrication conditions.
Inspection frequency: At the same time the vibration data is taken.
Oil Analysis: Periodic oil analyses are typically performed on gear boxes. These analyses can help detect oil contamination, bearing deterioration issues, and gear degradation.
Inspection frequency: Monthly and quarterly inspection intervals are common.
Monitoring Guidelines for Fans
Figure 3.5 Typical Process Fan
Vibration Collection and Analysis: Most fan vibration levels are monitored on a periodic basis using “walk around” data collection programs. Assessments are made by placing a vibration sensor, usually an accelerometer, with a magnetic base, onto the bearing housings at specified locations. Overall vibration amplitudes are trended to see if any changes are occurring. If a significant change in overall amplitude is observed, a frequency analysis is performed in an attempt to identify the nature of the malady.
Inspection frequency: Monthly and quarterly inspection intervals are common.
Temperature Monitoring: Bearing temperatures can be taken at the same time vibration data is collected. Assessments may be either absolute or relative criteria. For example, you may decide that if a bearing temperature exceeds 200°F (93.3°C) you will shut down (this is an absolute criterion). Or if you see a 20°F (6.7°C) increase in bearing temperature from one inspection to the next, you will investigate. (This is an example of a relative analysis criterion.)
Inspection frequency: At the same time the vibration data is taken.
Oil Analysis: Many fans utilize greased bearings and are not conducive to periodic lubricant analysis. However, if the fan has a circulating lubrication oil system, periodic oil analysis is recommended.
Oil inspection frequency: Monthly and quarterly inspection intervals are common.
Pressure Pulsation Analysis: This type of analysis is rarely applied to fans.
Inspection frequency: Only required when issues arise
Piping or Ducting Vibration: This type of analysis rarely applies to fans.
Inspection frequency: Only required when issues arise
Performance
