Acoustic Monitoring and Traditional Methods of Detecting Boiler Tube Leaks
Acoustic monitoring is little known outside the power industry. Even some engineers consider it redundant high technology and are not ready to consider it because of concerns of the costs involved.
For detecting boiler tube leaks, plant operating engineers constantly monitor boiler furnace vacuum, which is maintained between a -10 to -20 mm water column, feed water flow to the boiler drum from the feed pump, which must not abruptly increase, the de-aerator level, the quantity of makeup water, and hissing sounds emitted by leaking steam detected by human ears at the boiler floor physically.
Boiler furnace vacuum generally gets disturbed and starts fluctuating if a sufficient amount of steam leakage occurs. There are also increases in feed water consumption, which is monitored by feed flow instruments provided in the unit control board. The de-aerator level and make up water to the hot well is also monitored by instruments provided at the UCB. Boiler tube leaks must be detected very early, otherwise leaking steam may further damage adjacent costly parts due to its heavy impact.
Units allowed, through negligence, to run for a long time without maintenance results in great loss to the boiler such as costly water wall tubes and headers, superheaters, furnace refractory, and even boiler structure beams which share boiler loads have had to be replaced due to damage or bending. Structural beams at the top share full load, so leaking steam can cause bending and deformation there as well.
The furnace refractory is like a protective layer. When leaking steam strikes refractory, it becomes damaged, too.
Maintenance costs due to secondary damage from boiler tube leaks are very high, and repairing the damage takes a very long time.
Traditional leak detection systems, such as hearing hissing noises or detecting vacuum fluctuations, are not reliable or sensitive enough to detect small tube leaks in the early stages. These conventional methods may detect a tube leak- if it’s big enough- and getting big enough could take as much as 72 hours! There are many instances in which thermal power plants have been allowed to run for extended times with undetected tube leaks due to confusion in the absence of advanced monitoring systems.