The tube leak occurred in a 300MW, Foster Wheeler boiler, equipped with 8 metalborne waveguides and sensors. The sensors on this unit cycle with load.  That is, the signal level increases whenever the load increases, and decreases when load decreases.  On Sunday evening, 10/21 the unit came down in load, but  the signal level for channel 2 remained high.  On Monday morning, as load was increased, channel 2 signaled an alarm.  A short time later channels 4 and 6 also signaled an alarm.

There were no other indications of a leak.

Sootblowers were shut down to eliminate sootblower noise as the cause of the increased signal.  The noise level remained high.  While walking the boiler, operations heard a leak noise by a boiler door near Sensor #2.  Operations decided to schedule an outage for Friday evening, so the leak could be repaired over the weekend. 

Throughout the week, the noise levels on channels 2, 4, 6 continued to increase.  By Wednesday, water usage had begun to trend higher and channel 8 went into alarm.

The leak was found in a partition wall tube. The tube had a bent support bracket for a reheat tube bundle.  The partition leak cut one reheat tube in the supported bundle.  The station suspects the bracket may have been bent by the air bags used to spread the reheat tube bundles during maintenance operations.