RESOLVING INTERMITTENT VIBRATION
SPIKES ON STEAM TURBINES
Rajakumar Thiagarajan Sankar Ganesh
Rotating Equipment Engineer Lead MDS Engineer
Ashraf Abdelrahim
Specialist - Condition Monitoring
Contents
Background
Machine description
Data analysis
Initial Analysis & Recommendations
Machine Inspection results
Subsequent Mechanical Failure Analysis
Conclusions
Lessons Learned
Background
Six Fresh Cooling Water Pumps:
4 Steam Turbines and 2 Motor driven pumps
Critical pumps in LNG production
Intermittent vibration spikes - Proactive detection on three
steam turbines using expert systems
The condition deteriorated and sporadic steam turbine trip.
Plant vulnerable to production loss
Sea
Water
Out
Sea Water FCW Pump A - F
In Tank Pump A - F
Make up
Schematic Diagram of Fresh Cooling Water System
Machine Description
PUMP
ST
Turbine Type: Back pressure (5 stage)
Bearings: Tilting pad
Seals: Mechanical Labyrinth
Coupling: Diaphragm
Power: 3840KW
Speed: 3602 RPM
Data Analysis
Process parameters Turbine vibration
Green plot Vibration Black, White, Red & Blue plots Process parameters
Overall Vibration vs. Process data
Increasing Vibration Trend & High vibration Trip
No correlation with the process parameters
Data Analysis Contd..
Polar Plot 1X Amplitude & Phase Angle
Turbine NDE-X Turbine NDE-Y
Turbine DE-X Turbine DE-Y
Abnormal Behavior Significant Phase Angle
Change During Steady State (All Over 3600)
Data Analysis Contd..
Direct Orbit Review During Vibration Excursion
Turbine NDE Turbine DE
Flattened Orbit Truncated Time waveform
Flat Orbit & Truncated Time Waveform due to
Rub
Data Analysis Contd..
Direct Orbit Overlay Comparison of Low & High
Vibration Amplitudes
Turbine NDE Turbine DE
Direct Orbit Becomes circular when
the vibration is at maximum
Orange plot when vibration is at minimum
Blue plot when vibration is at maximum
Significant change in the Orbit Shape &
Amplitude (Change in Balance Condition
Due to Thermal Bow)
Data Analysis Contd..
Thermal Bow Effect of Rub
0 High Spot 0 Rubbing Spot
mr2 mr2
1X Orbit
Heavy Spot
Seal
Effective A New High Spot
0
0 Unbalance and Rubbing
Location
mr2 mr2
1X Orbit Increased
1X Orbit
Data Analysis Contd..
Vibration Trend and Polar Plot Reviewed for 2nd Steam
Turbine
Intermittent vibration spikes Phase angle change all through 360 degree
Similar Behavior - Intermittent vibration
Amplitude & Change in Phase Angle
Data Analysis Contd..
Vibration Trend and Polar Plot Reviewed for 3rd Steam
Turbine
Intermittent vibration spikes Phase angle change all through 360 degree
Similar Behavior But Less Severity - Intermittent
vibration Amplitude & Change in Phase Angle
Initial Analysis & Recommendations:
Expert Analysts at site concluded the Rubbing Issue
is most likely due to
Carbonized oil buildup in the oil deflector / seal
area.
Recommended Action Items:
Inspect oil/steam seal areas for rubbing marks
due to deposit built-up / carbonized oil.
Machine Inspection Results
Oil Seal Area at Non Drive End Bearing of 1st Turbine
Carbonized deposits at NDE seal area Rubbing Marks on the shaft
Rubbing Marks at the seal area due to oil
carbonization is evidenced.
Machine Inspection Results Contd..
Rotor Internals of 1st Turbine
No abnormalities noticed on the Rotor
internal components.
Machine Inspection Results Contd..
Oil Seal Area at Non Drive End Bearing of 2nd & 3rd Turbine
Seal Area of 2nd Turbine Seal Area of 3rd Turbine
Oil Carbonization deposits and Rubbing Marks
at the seal area
Based on the inspection results of 1st Turbine,
no internal checks carried out for the 2nd & 3rd
Machines
Subsequent Mechanical Failure Analysis
Oil leak and migration to
steam end
Sealing Air
Design issue pressure low
Breather LO Supply
clogging Pressure high
Carbonization
Outside Operating
condition
Ejector poor Gland fins
performance clearance high
Heavy Steam Leak from
steam gland
Conclusions
Primary Causes:
Low seal air pressure - Oil leakage, migration at steam gland
Contributed Causes:
Breather clogging - Oil leakage due to vapor accumulation
and high lube oil pressure inside the bearing housing
Design issues
Back pressure on the common return header - Wrong
elevation of breather on the Gearbox drain line
Oil shelter in close vicinity to the steam gland
Action Items:
Installed Pressure Gauge
Breather cleaning task - Equipment Strategy.
Modify the Breather elevation
Lessons Learned
Reduced Maintenance Cost and Down Time
Prognostic approach on the issues and accurate
analysis through experts helped early detection of
machine malfunctions.
Findings on one steam turbine assisted to minimize the
maintenance activities on other two steam turbines.
Presence of online diagnostic system helped to plan the
machine shutdown for the maintenance without impact
on the production.
Design issues A lesson for future projects.
Absence of seal air pressure monitoring
Close vicinity of oil seal and steam gland
Wrong elevation of breather location on
the Gearbox
