ground penetrating radar for the detection of water leakage in buried pipe
Post on 07-Jul-2018
217 Views
Preview:
TRANSCRIPT
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
1/60
Detecting Leakages in
Underground Buried Pipe
Dep ng artment of Mechanical Engineeri
National University of Singapore
Session 2009/2010
Name: Teo
Hwi
Bee
Matric Number: U067137N
Supervisor: Assoc Prof Chew Chye Heng
1
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
2/60
Summary
There is great difficulty in locating the exact location of leakages in water pipes.
Often, noise
created
due
to
sharp
bends
is
detected
instead.
In
this
project;
we
shall
try to differentiate noise created by leakage or bends in pipes. There is a need to
find out the frequency window at which turbulence is detected so we can eliminate
these frequencies.
In the first part of the experiment, the vibration‐frequency spectrum is obtained for
water flowing
through
a
pipe
without
any
leaks.
The
pipe
has
a
sharp
elbow
attached to it to create turbulence noise. The range of frequencies at which
turbulence occurs is noted.
In the second part of the experiment, a hole is drilled into the pipe to allow leakage
to occur. Similarly, the vibration‐frequency spectrum is obtained and certain ranges
of frequencies are eliminated. The ranges of frequencies which are omitted out are
those suspected to be due to noise created by turbulence. The only noise that
should be observed will be due to leakage in the pipes. In order to locate the exact
point of leakage, correlations were done.
Instead of using data logged from water piping system directly, a scaled down model
was set up to simulate this problem.
2
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
3/60
Acknowledgements
The author wishes to express sincere appreciation of the assistance given by my
supervisor, Assoc
Prof
Chew
Chye
Heng
in
advising
directions
of
the
project.
Not
forgetting the help rendered and assistance from the technicians of Dynamics Lab,
Air Conditioning Lab especially Mr Cheng and Mr Devan in carrying out the work
successfully.
3
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
4/60
Contents
Summary ................................................................................................................................... 2
Acknowledgements................................................................................................................... 3
List of Figures ............................................................................................................................ 6
List of Tables ............................................................................................................................. 7
List of Symbols .......................................................................................................................... 8
1. Introduction .......................................................................................................................... 9
1.1 Purpose ............................................................................................................................. 10
2. Project Directions................................................................................................................ 11
3. Theory ................................................................................................................................. 13
4. Experiment
Procedure ........................................................................................................ 14
4.1 Experimental Set Up 1 (Without Hole) ............................................................................. 15
4.2 Water Flow Rate ............................................................................................................... 16
4.2.1 Calculation of Water Flow Rate ..................................................................................... 17
4.2.2 Results for Different Water Flow Rate........................................................................... 18
4.3 General Observations ....................................................................................................... 19
4.3.1 Locating Turbulence for Different Locations of Accelerometers................................... 23
4.3.2 Locating Turbulence Frequency for Different Flow Rate ............................................... 26
4.4 Results for Set Up 1........................................................................................................... 27
5. Experiment Set Up 2 (With Hole)........................................................................................ 29
5.1 Results for Different Water Flow Rates ............................................................................ 31
5.2 Leakage Frequencies for Different Hole Sizes................................................................... 32
5.3 Locating consistency in leakage frequency....................................................................... 34
5.4 Locating Point of Leakage ................................................................................................. 35
6. Discussion............................................................................................................................ 38
6. 1
Limitations........................................................................................................................ 39
6.2 Other Possible Errors ........................................................................................................ 41
7. Conclusion........................................................................................................................... 42
8. Recommendations .............................................................................................................. 43
Appendix I‐ Spectrums for Different Flow Rates .................................................................... 44
4
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
5/60
Appendix II‐ Locating for consistency in turbulence frequency ............................................. 46
Appendix III‐ Leakage Frequency for 1 & 2 revolution water flow ......................................... 51
Appendix IV‐ Leak Frequency for 1mm hole........................................................................... 54
Appendix V
‐Leakage
Frequency
for
1.5mm
Hole................................................................... 57
Bibliography ............................................................................................................................ 60
5
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
6/60
List of Figures
1. Layout to determine the position of a leak from buried pipe water distribution
pipe
2. Schematic Diagram of Pipe Set Up
3. Close up view of valve and 90° elbow
4. Actual Experimental Set Up
5. Different Water Flow Rate Channel 1
6. Different Water Flow Rate Channel 2
7. Frequency
Spectrum
of
Pipe
8. Frequency Spectrum 1 revolution, 1m distance apart, channel 1
9. Frequency Spectrum 1 revolution, 1m distance apart, channel 2
10. Frequency Spectrum 1 revolution flow, 0.8m distance apart
11. Frequency Spectrum 1 revolution flow, 0.9m distance apart
12. Frequency Spectrum 1 revolution flow, 1m distance apart
13. Schematic
Diagram
of
Set
Up
2
14. Frequency of 1mm hole
15. Frequency of 1.5mm hole
16. Time spectrum for 1 revolution flow, 1mm hole
17. Time Spectrum for 1 revolution flow, 1.5mm hole, channel 1
18. Time Spectrum for 1 revolution flow, 1.5mm hole, channel 2
19. Vibration paused in between measurements
6
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
7/60
List of Tables
1. Water flow rate for different revolution of valve
2. Distance
with
comparison
to
range
of
turbulence
3. Water Flow rate and range of turbulence frequency
4. Range at which turbulence occurs
5. Range of Frequencies for 1 revolution and 2 revolution water flow
6. Range of Leak Frequency for 1mm and 1.5mm hole
7
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
8/60
List of Symbols
D1 Distance of the leakage point, m
c
wave speed,
m/s
time difference, s
8
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
9/60
1. Introduction
Today’s water utility operators have a range of equipments and techniques to
measure, analyse,
monitor
and
reduce
leakage
in
pipes.
In
recent
years
there
has
been a surge in development of tools and equipment to support this task.
However, there is still a big gap in such technologies, complementary technology
and equipment for locating and pinpointing leaks in hard to reach situations, such as
underground buried pipes. Thus systematic detection methods, exact water meter
reading and
fast
leak
repairs
are
essential
to
reduce
the
amount
of
leakages.
There are several conventional technologies for localizing, locating and pinpointing
leaks in distribution networks. The most commonly used method will usually involve
a 2 step approach. Firstly, water auditing is done, which monitors the night time
minimum flow rate in the inlet and outlet of a pipeline system. The audits cannot
find the precise location of the leaks but estimate the total leakage from the pipeline.
Next, acoustic method is used whereby sound or vibration by water leaking from
pipe is detected. Other conventional methods include tracer gas, thermography,
flow and pressure modeling.
There are also less conventional techniques which are invariably called on when the
other technologies fail:
‐ Correlation with low frequency hydrophones
‐ Inverse transient analysis
9
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
10/60
‐ Ground penetrating radar (GPR)
Low frequency hydrophones works on the same basis as acoustics. Hydrophones
have piezoelectric transducers that converts sound signal to electrical signal, since
sound is a pressure wave.
Inverse transient analysis is based upon pressure data collected during the
occurrence of transient events and minimization of the difference between the
observed data and the calculated pressures. In systems without leaks, important
phase shifts of the pressure wave occur at all sites within the pipe. For pipes with
leaks, pressure wave and transient event damping occurs and mathematical analysis
of this phenomenon allows the position of the leak to be determined.
Ground penetrating radar (GPR) is a rapid, high resolution tool for non‐invasive
subsurface investigation. GRP produces electromagnetic radiation that propagates
through the ground then returns to the surface. The radar waves are dependent
upon the dielectric constant due to changes in subsurface material. The travel time
of the electromagnetic wave from the emitted to reflected wave is a function of the
depth and electric properties of the media.
1.1 Purpose
Differentiate between noise created to due to turbulence and noise created due to
leakages
10
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
11/60
2. Project Directions
Initially, the intention of the project is to investigate the possibility of using ground
penetrating radar
to
replace
the
existing
acoustic
method
detection
system
in
which
PUB is using. As GRP also detects underground water content, it is a possible
alterative technology for leak detection. The use of GRP involves a worker to
manually navigate the device accordingly to the water distribution. Depending on
the antennae and the material properties of the soil, it can successfully penetrate
down
to
about
10m.
Data
are
stored
and
map
into
images
which
displays
the
water
content of the soil. The method is labour intensive as survey is needed to be done
throughout the whole network system.
After some discussion with PUB, acoustic logger system was decided eventually as
they have existing loggers around their water network system. They are currently
using the
Phocus2
System
and
Eureka
Digital
system
to
detect
leakages.
Phocus2 system is an acoustic logger system. An area is surveyed by installing a
number of loggers at available hydrants and valves, Phocus2 records acoustic noise
over a selected period. Eureka Digital system is a leak noise correlator. Transmitters
are placed at 2 points on a suspected leak position. The noise correlator operates by
comparing the
noise
detected
at
2
different
points
in
the
pipeline.
11
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
12/60
Both systems basically works along the same principle and both operates with an
integrated accelerometer. The main problem that arises with such loggers is that it is
difficult to
differentiate
between
noise
created
due
to
turbulence
or
due
to
leak.
12
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
13/60
3. Theory
A typical measurement layout to determine the location of a leak in a buried pipe is
shown in
figure
1.
Figure
1:
Layout
to
determine
the
position
of
a
leak
from
buried
pipe
water
distribution
pipe
If a leak is suspected, the acoustic sensors, typically accelerometer are places either
side of the leak. The aim is to determine the position of the leak, which in this case is
the distance D1 from transmitter A. This distance is related by the equation below:
Where is the wave speed
is the time difference
Thus to determine the leak, these variables need to be known. The wave speed c,
can be measured experimentally by tapping on the pipe, then measuring the time at
which the sound travel. To estimate , the cross‐correlation of the signals from the
sensors is generally used. However the quality of this estimate depends upon the
type and positioning of the sensors and the processing of the signals.
13
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
14/60
4. Experiment Procedure
2 set ups are done to investigate noise created due to turbulence and leakage. In
this experiment,
instead
of
using
the
actual
piping
used
in
water
works,
a
1
inch
copper pipe is used to simulate actual behavior.
Copper pipe of 1 inch diameter was used to get the frequencies of vibration when
the pipe is with or without hole. Accelerometers are placed at both ends of the pipe
to obtain the vibration motion of the pipe and distances at which accelerometers
are placed
on
the
pipe
are
varied.
A
90°
elbow
bend
was
placed
to
create
some
form
of turbulence. 2 experiments are conducted to investigate the vibration spectrum of
the pipe. First set up was when water flow through a normal copper pipe and the
turbulence frequency is investigated. As for the second experiment, a hole was
drilled into the pipe to simulate water leakage while the other end of the pipe is
sealed. Hence,
leakage
frequency
is
investigated.
14
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
15/60
4.1 Experimental Set Up 1 (Without Hole)
Set Up 1: To get frequency spectrum for water flow in copper pipe
1.3m pipe
CH2 CH1
Accelerometer 1
valve
Accelerometer 2
90° elbow
Figure 2: Schematic Diagram of Pipe Set Up
Figure 3: Close up view of valve and 90 degree elbow
15
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
16/60
Figure 4: Actual Experimental Set Up
4.2 Water
Flow
Rate
Water flow rate is controlled by the number of revolutions done by the tap. A
marker was used to give a rough estimate of the water flow rate. Time is recorded
to get the average flow rate.
Table 1: Water flow rate for different revolution of valve
Revolutions Time taken/s Average Time/s Volume Flow rate/ m3s‐1
1 49.23 48.35 48.79 2.07 10‐4
2 25.5 25.45 25.475 3.96 x 10‐4
3 24 24.93 24.465 4.13 x 10‐4
Channel 1Channel 2
16
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
17/60
4.2.1 Calculation of Water Flow Rate
1 inch = 0.0254m
Time taken for water to flow through the pipe is estimated to be slowest at 3.17s.
Hence, when obtaining frequency spectrum for the pipe, real time capture of
approximately 5s was done. A real time capture of 5s should be sufficient to collect
17
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
18/60
vibrations data made by the pipe. The frequencies made by the pipe should be
relatively low and of low amplitude.
4.2.2 Results for Different Water Flow Rate
Comparing figure 5 and 6, it can be seen that a higher water speed results in greater
vibration magnitude. This is expected of greater water speed. Sound created will be
louder and of higher magnitude. Another observation that we can see below is that
most
of
the
peaks
are
grouped
at
a
low
frequency
range
for
all
3
water
flow
rate.
For the power spectra obtained from channel 2, there is an anomaly for 1 revolution
water speed. The magnitude should be lower compared to a faster water speed.
However, it can be suspected that it may be due to noise from the environment
during recording or outlet noise from the pipe. It can be observed that there are
clusters of
peaks
of
higher
frequencies
in
the
graph
of
channel
2
but
not
channel
1.
18
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
19/60
Figure 5: Different Water Flow Rate Channel 1
Figure 6: Different Water Flow Rate Channel 2
4.3 General Observations
After analyzing many spectrums, there are some consistent observations that can be
brought up. These observations can be applied to both experiment 1 and 2.
19
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
20/60
Figure 7: Frequency Spectrum of Pipe
First observation is that most spectrums has initial spike at 0 frequency, therefore it
is difficult to analyse the rest of the spectrum at higher frequencies. This may be due
to incorrect timing at which measurements are taken. The initial spike may be due
to low turbulence frequency at which is caused either by the valve or the elbow.
There is a large initial change in momentum. This occurrence is common for many
graphs and when this happens, we shall omit and focus on the peaks due to
turbulence.
20
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
21/60
Figure 8: 1 revolution, 1m distance apart, channel 1
Figure 9: 1 revolution, 1m distance apart, channel 2
As we compare the results between channel 1 and 2 and zoom into one of the peaks
in channel 1 which happens at 1.488 kHz having a magnitude of 8.53E‐03 Vrms and
21
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
22/60
channel 2 at 1.488 kHz having a magnitude of 6.02E‐03 Vrms. There is a decrease in
magnitude due to lost of energy when wave passes through a distance. The peak
magnitude was
chosen
as
it
is
due
to
the
turbulence
caused
by
the
90°
elbow.
Zooming into the circled out frequencies above at figure 8, it can be deduced that
these high magnitudes are noises caused by the turbulence of the elbow. Compared
to channel 2, at these frequencies, the magnitudes are slightly lower due to energy
losses.
Figure 9 has a circled out region and we can see that there are usually high
magnitudes at higher frequencies. This should not be the case and we can suspect
that these high magnitudes are due to the outlet noise, noise created when water
gushes out of the pipe. Since channel 2 accelerometer is nearer to the outlet, it is
able to pick up the loud noises when water is escaping.
Hence, second observation is that initial peaks are due to turbulence or leakages.
Third observation is that peak at high frequencies for channel 2 is due to outlet
noise.
22
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
23/60
4.3.1 Locating Turbulence for Different Locations of
Accelerometers
Ideally, accelerometers
are
to
be
placed
at
a
certain
distance.
Since
the
pipe
is
about
1.3m long, the accelerometers are placed about 1m apart. It cannot be placed any
further as it will collect noise from the environment for channel 2 and for channel 1,
it will directly collect noise from the 90 degree elbow.
Distance at which accelerometers are placed are varied from 1m to 0.8m. Placing
the accelerometers
too
close
is
not
favourable
as
well
because
the
sound
collected
will attune such that both are recording the same thing. In this case, we are trying to
get the maximum distance at which sound dies off so the accelerometers will not be
placed at that particular distance. Below are some of the distances varied from 0.8m
to 1m.
Figure 10: 1 revolution, 0.8m distance apart
23
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
24/60
When accelerometers are placed 0.8m distance apart, the turbulence frequency
occurs at a range of 1.328 kHz to 1.584 kHz.
Figure
11:
1
revolution
flow,
0.9m
distance
apart
The accelerometers are placed 0.9m distance apart, we now observe a similar trend,
the initial peaks at low frequencies for channel 1 is due to turbulence, these peaks
decreases at channel 2. Hence, we can interpret that turbulence which is the boxed
out region occurs at 1.248 kHz to 1.840 kHz. There are lots of peaks at 1.92 kHz
onwards. These peaks are due to noise created by the outlet.
24
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
25/60
Figure 12: 1 revolution, 1m distance apart
From the graph above, it is observed that the range at which turbulence occurs over
816Hz to 1.97 kHz.
Table 2: Distance with comparison to range of turbulence
Distance at which accelerometers are placed Range of turbulence frequency/ kHz
1m 0.816 – 1.97
0.9m
1.248 –
1.84
0.8m 1.323 – 1.584
From table 2, at all distances in which accelerometers are placed, vibration can be
detected. Accelerometers cannot be placed any further due to the short pipe length.
The optimum distance at which accelerometers should be placed is probably at a
distance of 0.9m. The distance of 0.8m may be too close. The range of turbulence
frequency obtained when accelerometers are placed closely is too narrow.
25
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
26/60
4.3.2 Locating Turbulence Frequency for Different Flow Rate
Ideally, a slower flow rate will be better in locating turbulence and leakage. As there
is little excitation on the pipe, the noise made will be smaller. Turbulence and
leakage peaks will be more obvious.
Below is the table at which different flow rate is used and the corresponding
estimated turbulence frequency. Comparing different flow rates, the slowest water
speed give the most appropriate range at which turbulence occurs. For a higher
water speed, the range at which turbulence occur is too widespread.
Table 3: Water Flow Rate and Range of Turbulence
Ranges at which turbulence occurs
ID5 (1 rev, 0.9m) 1.248 kHz 1.84 kHz
ID6 (2 rev, 0.9m) 368Hz 1.87kHz
ID7 (3 rev, 0.9m) 688 Hz 1.54 kHz
Refer to Appendix I for the spectrums above.
26
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
27/60
4.4 Results for Set Up 1
Readings were recorded by the tape recorder and signals are sent through the
oscilloscope. Time capture of 5s of vibration is recorded and the frequency spectrum
range is up to a frequency of 6.48 kHz. Any frequencies above that are undetectable
and the noise magnitude is very small. Averages of 20 are done.
Revolutions of the valves and distance at which the accelerometers are placed are
varied. In order to check the consistency in our deduction we noted the frequencies
of peaks for channel 1 and channel 2. Note that we will eliminate the outlet noise
picked up by channel 2 and estimate the peak frequency for channel 2 which is
created due to turbulence. Another condition is that the magnitude at which this
occurs for channel 2 must be lower than channel 1. Since 1 revolution water flow
speed gives a better range, analysis will be carried out for this spectrum. The time
capture of
5s
will
be
broken
up
into
1s
interval
of
5
parts
to
check
if
the
turbulence
frequency is consistent.
27
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
28/60
Table 4: Range at which turbulence occurs
Ranges at which turbulence occurs
ID2 (1 rev, 1m) 5seconds 1.22 kHz 1.48 kHz
1st
second 1.28 kHz 1.41 kHz
2nd
second 928 Hz 1.36 kHz
3rd
second 928 Hz 1.46 kHz
4th
second 1.38 kHz 1.41 kHz
5th
second 928 Hz 1.07 kHz
ID5 (1 rev, 0.9m) 5seconds 1.248 kHz 1.84 kHz
1st
second ‐ ‐
2nd
second 1.22 kHz 1.58 kHz
3rd
second 1.02 kHz 1.87 kHz
4th
second 1.34 kHz 1.41 kHz
5th
second 1.15kHz 1.46 kHz
Refer to appendix II for the spectrums
From the table above, we get the averages for channel 1 and channel 2 respectively.
Frequency turbulence occurs at a range from 1.15 kHz to 1.48 kHz. Though there are
certain anomalies, like ID5 spectrum for the 1st
second whereby we are unable to
spot the turbulence frequency range because it does not fulfill the condition that
magnitude of vibration of channel 1 is higher than channel 2. This occurrence can be
due to various reasons. The reasons will be discussed later. If we take note of these
range at
which
turbulence
occurs,
we
should
be
able
to
effectively
spot
where
leakages occur b eliminating such frequencies.
28
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
29/60
5. Experiment Set Up 2 (With Hole)
1.3m pipe
CH2 CH1
valve
sealed
0.5m
hole
0.7m 0.3m
Copper pipe of 1 inch diameter was used to get the frequencies of vibration when
the pipe is with hole. Accelerometers are placed at both ends of the pipe to obtain
the vibration
motion
of
the
pipe
and
distances
at
which
accelerometers
are
placed
on the pipe are varied. A 1mm hole was drilled to stimulate water leakage. The hole
is drilled 0.5m away from the elbow. 1mm hole was chosen as it is the smallest hole
that is possible with the available equipments. Initially, a bigger hole was drilled and
the pipe was vibration visibly hard thus the whole experiment was redone by drilling
a
smaller
hole.
The
end
of
the
pipe
is
sealed
so
noise
made
by
the
pipe
should
only
be due to the leak only. In this second part of the experiment, we are to investigate
the frequency range of leakage.
Figure 10: Schematic Diagram of Set Up 2
29
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
30/60
From the results of set up 1, a slower flow rate is more appropriate when measuring
excitation of the pipe due to leakage. Therefore, our analysis shall be limited to 1 to
2 revolution
of
water
flow
speed.
Ideally,
the
range
at
which
leakage
occurs
should
be smaller than turbulence frequency. The excitation due to turbulence is greater
than leakage.
30
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
31/60
5.1 Results for Different Water Flow Rates
Analysis is done in comparison for 1 revolution and 2 revolution water speed. The
distance at which the accelerometers are varied from 1m to 0.8m distance, it will
not really affect the frequency obtain as ideally range of frequency for leakage
should be roughly consistent for same water flow rate.
Table 5: Range of Frequencies for 1 revolution and 2 revolution water flow
Range of frequency at which leakage occurs/ kHz
ID1 (1
rev,
1m
dist)
0.944
1.28
ID5(1 rev, 0.9m dist) 0.848 0.900
ID8 (1 rev, 0.8m dist) 0.480 0.804
ID3 (2 rev, 1m dist) 0.144 0.368
ID6 (2 rev, 0.9m dist) 0.688 0.704
ID9 (2 rev, 0.8m dist) 0.480 0.702
Refer to appendix III for the spectrums
From the data above, it looks like the results are very inconsistent. We are not able
to distinguish a difference between noise created by turbulence or leakage. Most of
the time, we have to assume that the leak frequency is low. Often, the magnitude of
channel 1 and channel 2 coincides.
31
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
32/60
5.2 Leakage Frequencies for Different Hole Sizes
1mm hole was decided as it is the smallest possible hole that can be drilled into the
pipe. The hole is supposed to be as small as possible in order to simulate little
excitation to the pipe. Whereas noise made by turbulence is much higher than the
leak. In the experiment, a comparison was done between 2 hole sizes, 1mm and
1.5mm hole respectively.
Figure 11: Frequency of 1mm hole
32
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
33/60
Figure 12: Frequency of 1.5mm hole
From the 2 spectrums above, 1mm hole has an estimated leak frequency of 1 kHz to
1.58 kHz. Though the magnitude of channel 1 is not higher than 2 but it is also highly
impossible that the leak frequency is 2.5 kHz. The assumption here is that the pipe
length is relatively short so there is little damping effect. This same assumption is
assumed for
figure
14.
The
leak
frequency
is
from
688
Hz
to
1.37
kHz.
The spectrums results are different from what we are expected of. The bigger hole
leakage should occur at a higher frequency compared to the smaller hole leakage.
Moreover, the vibration magnitude for the smaller hole is greater than a larger hole
which defies expectation.
33
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
34/60
5.3 Locating consistency in leakage frequency
In order to check if the leakage frequency is less than 1 kHz, we will analyse the time
capture spectrum in per second interval. The slowest water flow rate is used for
analysis.
Table 6: Range of Leak Frequency for 1mm and 1.5mm hole
Range of leak frequency/ kHz
ID1 (1 rev, 1mm hole, 1m dist)
1st
second 0.128
2nd second
0.048
0.208
3rd
second 0.048
4th
second 0.064
5th
second 0.048
ID26 (1 rev, 1.5mm hole,0.9 dist)
1st
second 0.528 0.704
2nd
second 0.480 0.688
3rd second
0.528
0.672
4th
second 0.528 0.816
5th
second 0.528 0.688
Refer to Appendix IV for 1mm hole spectrums.
Refer to Appendix V for 1.5mm hole spectrums.
From the analysis, the average frequency at which 1mm hole leakage is 67.2 Hz to
208
Hz. Whereas
the
leakage
for
the
bigger
1.5mm
hole
is
from
a
range
of
412
Hz
to
714 Hz which is higher than the smaller hole. As what we have analysed here is
different from what we have found out earlier on. Perhaps, for lower frequency we
have to use a time capture for a smaller interval to obtain a more reliable result.
34
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
35/60
5.4 Locating Point of Leakage
In order to locate point of leakage, a time capture of spectrums at the exact same
time interval is needed. Next, we have to sieve out a common pattern between both
spectrums from channel 1 and 2 to obtain the time difference. This is also known as
correlation. By noting the time delay and multiplying it with the speed of sound in
copper pipe, we can locate the leakage point. Distance between the 2
accelerometers need to be noted as well. Through some analysis, we zoomed into
the time
capture
spectrum
to
the
clearest
possible
view.
peak due to leakage
Figure 13: Time spectrum for 1 revolution flow, 1mm hole
Above
is
the
time
based
spectrum
for
1mm
hole
at
1
revolution
water
flow
rate,
from 0.53s to 0.55s interval. It seems like a similar pattern cannot be found, thus
unable to obtain the time delay. By zooming into the peaks, we noticed that the
peak occurs at an earlier time in channel 2 compared to channel 1 and this should
35
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
36/60
not be the case as channel 1 is nearer to the leakage. Channel 1 should detect the
leakage first. Hence, further explains that this result is wrong. Different timings of
the spectra
is
investigated
as
well
but
there
are
no
convincing
results.
Figure 14: Time Spectrum for 1 revolution flow, 1.5mm hole, channel 1
Figure 15: Time Spectrum for 1 revolution flow, 1.5mm hole, channel 2
36
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
37/60
For 1.5mm hole, by comparing the above 2 time based spectrums, we can estimate
to shift the spectra for channel 2 along this direction to obtain the same pattern as
channel 1.
Hence,
there
will
be
a
time
delay
of
0.02s.
Speed
of
sound
in
copper
is
3901m/s, hence the hole is estimated to be at a distance of 78.02m, which is very
incorrect.
Through several analysis, we zoomed in the time capture spectrum to the smallest
possible available scale. However, we are still unable to correlate or find any similar
pattern in
both
channel
1
and
2.
If
there
are
no
similar
pattern
available,
we
cannot
obtain the time delay neither can we calculate the exact leakage point. Hence,
locating leak point is not really possible through this experiment set. There are far
too much variation in water pressures, hence determining the peak due to leakage is
difficult. There are many reasons can attribute to this occurrence. Further
explanation
will
be
elaborated
below
under
the
discussion.
37
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
38/60
6. Discussion
Generally, most spectrums have a great range and lots of them are chosen due to
many assumptions. Many spectrums have initial spike in attenuation and therefore
we focus on the area which we think are significant.
For the first experiment, the turbulence frequencies hover around 1kHz. However,
there were much inconsistencies in the experimental results. Generally, channel 2
has a higher magnitude than channel 1. There is a suspicion that channel 2 collected
outlet noises when water is gushing out of the pipe. The peaks spectrum for both
channel 1 and 2 are not consistent. Unknown peaks at certain high and low
frequencies range are spotted.
For the second experiment, it is difficult to sieve out the leakage frequency. Either
the frequency is too low since the whole set up is scaled down or that
environmental noises are recorded. Below are some of the limitations of the
experiments.
38
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
39/60
6. 1 Limitations
Numerous limitations were faced when gathering the data presented in this report.
Many limitations
affected
the
repeatability
of
the
data
collected
in
various
ways.
Lack of equipment to mimic the actual conditions of water piping systems also
resulted in a loss of accuracy of the results.
The limitations are listed below:
‐ The length of the pipe is too short; a longer pipe will be more reliable. Wave
travels too quickly and pipe gets excited by surrounding vibrations very easily.
‐ Length of pipe is only 1.3m so there can be very little variation in the
distancing the 2 accelerometers
‐ Water flow speed may not be slow enough to detect difference in turbulence
and leakages.
‐ Noises in the environment may be louder than the noise created by the
turbulence and pipes itself.
‐ Water pressure may not be consistent during measurements
‐ Equipments may not be sensitive enough to capture low frequencies
measurements
‐ Turbulence
may
be
caused
by
the
half
opened
valve
rather
than
90
degree
elbow
39
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
40/60
‐ Pipes are freely supported and not fully support along its axis will result in
higher vertical amplitude to the pipe axis are not ideal for leakage location
because they
are
narrow
band
in
character
and
propagation
velocity
may
vary with frequency.
‐ Vibration is not captured fully by the accelerometers at times (see figure 18
below)
As the results are badly affected by the limitations, filtering and conditioning of the
signals has
to
be
done
in
order
to
see
any
correlation.
These
factors
are
also
why
the
results presented may appear seemingly unconvincing and inconsistent.
Figure 16: Vibration paused in between measurements
40
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
41/60
6.2 Other Possible Errors
Though there are many limitations could affect the results of both experiment,
there may be other possible errors that resulted in unreliable results.
‐ Time window selected for analyzing of data. As data captured may have
possible pauses in between. A wrong time interval is selected when analyzing.
‐ Assumption at which frequency of turbulence and leakage occurs may be
wrong. As always, our analysis may be wrong and thus results are incorrect. Some
possible factors and details may be left out due to lack in experience
‐ Human reaction time error when recording vibration. Number of averages
taken may be insufficient.
‐ It is difficult to come up with a theoretical spectrum of the water flowing in a
pipe, hence little comparison can be done. Water flowing through the pipe is
turbulent.
‐Valve
and
90
degree
elbow
are
close
together,
hence,
difficult
to
identify
vibration due to valve or elbow.
41
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
42/60
7. Conclusion
From this project, there is a better understanding in detecting leakages in pipe. It is
evident that a range of frequency was obtained for both leakage and turbulence.
Though some of the experimental results do not concur with theoretical expectation
but there were many limitations and error throughout the whole experimental
process. Much effort is done in trying to reduce such errors, however, results may
not be very convincing unless more testing is done.
Perhaps, one of the more significant findings is that turbulence frequency ranged
around 1kHz and that leakage frequency is around 100 to 800 Hz. Leakage frequency
is dependent on hole size. Another finding is that high water flow speed is not good
in determining both leakage and turbulence frequency range. A much longer pipe is
needed to space out the accelerometer.
Lastly, in order to obtain better results, further improvements could be done to this
experiment. We believe that through continual efforts, we are able to correctly
determine and distinguish between turbulence and leak frequency.
42
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
43/60
8. Recommendations
The recommended solutions are arranged in order of ease of implementation:
1) Installing an additional/larger accelerometer to check consistency of data.
2) Note down timings at which the environmental conditions are more
favorable, quietest period to conduct data collection. Experiments could
possibly be conducted at night.
3) Increase number of data collected.
4) If the limitations of fluctuating pressure cannot be avoided, we can install a
pressure gauge meter on the pipe to record the pressure when the
experiment to plot a 3‐D graph for better correlation.
5) Longer pipe, bigger diameter pipe could be used. Actual public water system
would be preferred.
6)
Collect result
of
pipe
buried
in
ground
rather
than
pipe
which
is
freely
supported.
7) Ensure pressure of water is constant throughout the whole experiment. Have
a proper valve or digital system of measuring water flow rate, input of flow
meter.
8)
Fluids should
not
contain
any
other
substances
such
as
air
bubbles
or
small
particles.
9) Measure the ideal water flow rate which results in the least vibration of the
pipe.
43
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
44/60
Appendix I- Spectrums for Different Flow Rates
44
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
45/60
45
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
46/60
Appendix II- Locating for consistency in turbulence frequency
46
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
47/60
47
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
48/60
48
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
49/60
49
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
50/60
50
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
51/60
Appendix III- Leakage Frequency for 1 & 2 revolution water flow
51
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
52/60
52
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
53/60
53
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
54/60
Appendix IV- Leak Frequency for 1mm hole
54
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
55/60
55
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
56/60
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
57/60
Appendix V- Leakage Frequency for 1.5mm Hole
57
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
58/60
58
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
59/60
59
-
8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe
60/60
Bibliography
Dunegan, H. (2004). Location of Leaks in Pipe by Use of Acoustic Emission Model Ratio
Techniques.
Liston, D. L. (1992). Leak detection techniques. Journal of the New England Water Works
Association , 103‐108.
M.J Brenna, P. J. Some Recent Research Results on the use of Acoustic Methods to Detect
Water Leaks in Buried Plastic Water Pipes. Institute of Sound and Vibration Research,
University of Southhampton.
R. Long, M. L. (2003). Attenuation characteristics of the fundamental modes that propagate
in buried iron water pipes. Ultrasonics 41 , 509‐519.
Riehle, H.
V.
(1991).
Ten
Years
of
Experience
with
Leak
Detection
by
Acoustic
Signal
Analysis.
Applied Acoustic 33 , 1‐19.
Seung Yeup Hyun, Y. S.‐Y.‐S. (2007). The laboratory scaled down model of a ground
penetration radar for leak detection of water pipes. Measurement Science and Technology
18 , 2791‐2799.
top related