Remediation of a vibration problem

Three-axis accelerometer in place on the bump-stop

Station:

A 400MW single-shaft combined-cycle plant, including a 150MW three-pressure HRSG with reheat

Problem:

Irregular movement of a reheater header at maximum load, with potential for reduced fatigue life of tube-to-header welds

Approach:

Team approach with the prime contractor, OEM and operator
Design review; plant instrumentation and monitoring
External observation during operation; internal inspection off-load
Investigation of the effect of operational parameters

Benefits:

Flow induced vibration of tube-bank identified as prime cause, being predicted to generate displacements and frequencies comparable to those observed
Addition of tube spacers implemented, leading to elimination of problem and allowing operation at full power to be resumed
Secondary effect of attemporator performance identified as requiring further investigation

Variation in reheater attemporator flow

Publication:

Brear, J.M. and Jarvis, P.
“Tracing a vibration problem back to source”
ETD Int Conf ‘Heat Recovery Steam Generator Technology’, Woburn House, London, 10-12 Nov 2003

Plant Integrity