The tube leak occurred in a 102MW, tangent tube boiler equipped with 20 metalborne waveguides and sensors.  The metalborne waveguides are mounted on 4” x 4” waveguide plates that attach to the boiler.  The waveguide plates act as a collection point for acoustic activity.  The amplitude of the signal increases with the noise generated by the steam leak.

The signal for Sensor 11, located in the Upper Primary Superheater, begins to trend upward and very quickly crosses the alarm threshold (92dB) in a 24-hour period.  The signal continues to increase over the next four days and reaches 112dB before shutdown.  The 30-Day Trend for Sensor 11 shows the rapid increase as the leak grows.  The level remains high, even when the unit is at low load.

The 10-Day Group Trend shows the high readings for the sensors near the leak.  Sensor 11 demonstrates the highest response to the leak, followed by Sensor 9, which is located on the same wall.  Sensors 10 and 12, the pair sensors for 9 and 11 located on the opposite wall at matching elevations, also show high signals.  The high readings, along with multiple sensor involvement help to diagnose the tube leak.

The leak was located on the East Side in the primary superheater outlet tube, 10 tubes from the east about two feet from the top of the superheat assembly.