ground penetrating radar for the detection of water leakage in buried pipe

8/18/2019 Ground Penetrating Radar for the Detection of Water Leakage in Buried Pipe

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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

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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.

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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.

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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

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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

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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

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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

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List of Symbols

D1 Distance of the leakage point, m

c

wave speed,

m/s

time difference, s

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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

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‐ 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

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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.

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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.

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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.

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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.

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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

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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

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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

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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.

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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.

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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.

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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

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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.

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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

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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.

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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.

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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.

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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.

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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


4th


5th


ID5 (1 rev, 0.9m) 5seconds 1.248 kHz 1.84 kHz

1st

second ‐ ‐

2nd


3rd


4th


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.

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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

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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.

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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.

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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

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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.

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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.

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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

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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

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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.

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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.

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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

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‐ 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

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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.

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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.

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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.

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Appendix I- Spectrums for Different Flow Rates

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Appendix II- Locating for consistency in turbulence frequency

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Appendix III- Leakage Frequency for 1 & 2 revolution water flow

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Appendix IV- Leak Frequency for 1mm hole

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Appendix V- Leakage Frequency for 1.5mm Hole

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Bibliography

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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

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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

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Acoustic

Signal

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