·Table of Contents ·Industrial Plants and Structures | Acoustic Emission Detection of Underground Pipeline LeakageShifeng Liu, Luming Li, Jian Cui, Tie LiDepartment of Mechanical Engineering, Tsinghua University, Beijing, China Bang Xian Li, Center of Boiler and Pressure Vessel Inspection and Research, Beijing, China Aihong Dong, Beijing Organic Chemical Plant, Beijing China Contact |
Acoustic emission is one of underground pipeline leakage detection methods investigated[2]. The sensitivity and the ability of location for acoustic emission method at moment are not so satisfied by the application users. Miller and Pollock etc. investigated the acoustic emission method for underground pipeline leakage detection and gave a very encourage result. The accuracy of the location is about 1 foot and the sensitivity is about 25 feed sensor spacing in their field trials. In our investigation some signal processing technologies (FFT, wavelet analysis, fractal and AR spectrum) were used for extract weak leakage acoustic emission signals for improving the sensitivity. A model of energy-attenuation was established for better location accuracy. Further a pulse-enlarge method was designed to enlarge the leakage signal and then improve sensitivity.
c:wavelet(db3) and fractal, left for noise and right for leakage, x:level of coefficients, y:value of the coefficient above:low frequency part, below:high frequency part,Kis the fractal number |
Fig 1: Signal analysis results, a: waveform and FFT of noise, b:waveform and FFT of leakage C:wavelet and fractal, d:AR spectrum |
Dia,spacing | 20m | 86m | pressure(Kg/cm^{2}) |
1mm gas | -1.7~ -3.1 | -2.0~ -3.3 | 32 |
1mm gas | -1.1~ -3.1 | -2.4~ -3.1 | 58 |
1mm liquid | -1.2~ -2.8(2m) | -1.7~ -3.1(26m) | 130 |
1mm liquid | -1.3~ -2.7 | -1.6~ -3.0 | 80 |
Table 1a: results of fractal analysis for dia 1mm leakage |
Dia, soacing | 20m | 86m | pressure(Kg/cm^{2}) |
2mm gas | -1.9~ -3.3 | -2.1~ -3.1 | 32 |
2mm gas | -1.6 ~ -3.4 | -2.8 ~ -3.3 | 56 |
2mm liquid | -1.3~ -2.5(2m) | -1.7~ -3.1(26m) | 130 |
2mm liquid | -1.4~ -2.5 | -1.8~ -3.2 | 80 |
Table 1b: Results of fractal analysis for dia 2mm leakage |
Noise | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
[15 40] | -0.3984 | -1.0127 | -0.7419 | -1.0218 | -0.9820 | -0.5044 | -1.0520 | -0.7433 |
[15 50] | -1.3417 | -1.6633 | -1.4123 | -1.6000 | -1.7222 | -1.3862 | -1.6146 | -1.3528 |
Table 2: fractal numbers for noise signals(8 groups of noise signals) at different windows of frequncies |
Attenuation curve | Real location | Measure location | error | |
1/x | 8.2/23.6m = 0.3475 | 0.2348 | 32% | |
No compensate | Exp(-0.0442x) | No location | ||
Simple compensate | 0.251 | 27% | ||
Complicate compensate | Exp(-0.088x) | 7.8/24.0=0.325 | 6% | |
Table 3: Location accuracy improving results. |
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