Steam Turbine High Axial Displacement due to Governor Actuator Filter Clog

Abstract

The governor actuator for a steam turbine was observed to be hunting and failed to maintain stable operating speed. The steam turbine is used to drive a centrifugal compressor for H2 service in a recycle loop. The extent of speed oscillating was exaggerating over time and caused excessive turbine axial movement. The unit was forced to shut down to prevent secondary damage due to turbine high axial movement. The steam turbine was overhauled approximately 9 months prior to the incident. Oil flushing was performed, lube oil was changed out and main oil filters were replaced as part of machinery overhaul scope. The main oil filter elements were inspected during troubleshooting of this event and were badly fouled with blackish substance. The governor actuators were inspected and the internal filters for the oil supply line were clogged with soft, blackish substance. Foulant analysis was performed using Energy Dispersive X-ray (EDX) which identified the main component to be Carbon. De- gassing tank oil was drained out and observed layer of blackish substance. EDX identified the main component to be identical to that found in main oil filter. Water sample from de-gassing tank bottom drain was tested and the pH was 3-4 (i.e. acidic). Further troubleshooting revealed that fine carbon particles were carried over from upstream and mixing with the process gas prior to the unit shut down for the compressor train overhaul. The presence of carbon particles had contaminated the seal oil and control oil circuit which then clogged up the actuator internal fine filters (~40um). This case study presents the unusual phenomenon, troubleshooting tools, recovery process and key learnings which provide user operating with similar service a reference.