A study of acoustic characteristics of leakage from boiler tubes

Acoustic monitoring of leakage from HP steam pipelines of utility-boiler heat exchangers is an important means for early fault detection and is of major significance for the rational arrangement of maintenance schedule and the enhancement of equipment availability. A theoretical analysis and experimental study were conducted of the jet flow noise from a relatively small leakage hole. A spectrum analysis and characteristics pick-up were performed of the jet flow noise signal actually measured. The analytic results show that the self-correlated power spectrum density distribution of the jet flow noise exhibits an obvious peak-value phenomenon and the peak-value frequency will decrease with an increase of the jet-flow hole diameter. For an under-expanded small hole jet flow at a pressure ratio below the critical one, when the jet-flow hole diameter increases from 1 mm to 4 mm, the peak value of the noise power spectrum Sr number will go up from 0.05 to 0.13. Such a feature can be used to estimate the leakage hole size. In the meanwhile, a proposal has been made for signal-wave filtering on the basis of the power spectrum distribution of high-temperature steam small-hole jet-flows.