Case study: Energy steam turbine
CRITICAL MECHANICAL LOOSENESS IN STEAM TURBINE– DRIVEN FORCED DRAFT FAN
EnergyServices provided
Vibration AnalysisProducts used
Machine Sentry Fixed MSF2 Machine Sentry Mobile MSM2 Machine Sentry Next Generation Software
Working to Achieve
Improved asset reliability and early fault detection on a steam turbine–driven forced draft fan through ad hoc vibration analysis supported by Machine Sentry®, following reports of excessive operational noise.
The Challenge
The forced draft fan is used in the site’s power station to supply controlled airflow to the boiler’s combustion chamber. It is driven by a steam turbine via a reduction gearbox. If this fan were to fail unexpectedly, the boiler would trip offline, requiring another boiler to be fired up to maintain site-wide steam
demand, causing production disruption, excess fuel costs, and potential safety implications.
Our Approach
AVT Reliability holds a full-time monitoring contract on site, conducting monthly vibration surveys across all operational areas using the Machine Sentry® platform. This case fell outside routine survey cycles and was actioned ad hoc at the request of the site engineering team. Fixed Machine Sentry® sensors were already installed on the asset, enabling quick data collection. Given the reported symptoms, AVT suspected a gear or bearing defect. Data was analysed on the same day and findings were immediately reported to the site engineering distribution lis, ensuring rapid response and informed decision-making.
Our Findings
AVT carried out vibration measurements and identified a significant step change in readings across the gearbox input and steam turbine high-speed shaft.
Vibration amplitudes breached secondary alarm thresholds, with multiple harmonics of running speed present, strongly indicating mechanical looseness or excessive clearance between rotating components. These patterns are typically associated with issues such as worn journal bearings. AVT advised the immediate removal of the asset from service for inspection before catastrophic damage could occur.
The Solution
The turbine was isolated and brought offline for detailed inspection. Investigation revealed that the fault originated from an ineffective locking tab, which had allowed the retaining nut on the high-speed shaft to work loose. This created axial float, leading to turbine blade contact with the reversing segments and resulting in blade damage. Repairs were carried out on the high-speed shaft, and damaged turbine blades were replaced. The issue was confirmed to be
mechanical looseness and resolved without gearbox damage.
Follow-Up
Following repairs, AVT was mobilised to collect a new baseline dataset. Post-repair analysis confirmed that vibration levels had dropped significantly, returning to within acceptable alarm limits. No further signs of mechanical defect were detected. Without this early intervention, the failure could have escalated, potentially damaging the gearbox and causing a full boiler outage, resulting in extended downtime and high repair costs.
At a Glance
- INDUSTRY: Energy / Utilities
- PROCESS: Steam generation, Forced Draft Fan
- EQUIPMENT: Steam turbine, reduction gearbox, forced draft fan
- PRODUCTS: Machine Sentry® Sensors
- SERVICES: Ad hoc vibration analysis, fault diagnosis, baseline verificationfollow-up
