i
UNIVERSITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN STATUS TESIS ♦
JUDUL :
LEAK DETECTION AND LOCALISATION IN WATER
DISTRIBUTION NETWORK BY ACOUSTIC METHOD
SESI PENGAJIAN:
Saya,
2006 / 2007
HO JIANN CHYUAN
(HURUF BESAR)
mengaku membenarkan tesis (PSM / Sarjana / Doktor Falsafah)* ini disimpan di Perpustakaan
Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut:
1.
2.
3.
4.
Tesis adalah hakmilik Universiti Teknologi Malaysia.
Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan
pengajian sahaja.
Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara
institusi pengajian tinggi.
**Sila tandakan ( 9 )
√
SULIT
(Mengandungi maklumat yang berdarjah keselamatan atau
kepentingan Malaysia seperti yang termaktub di dalam
AKTA RAHSIA RASMI 1972)
TERHAD
(Mengandungi maklumat TERHAD yang telah ditentukan
oleh organisasi/badan di mana penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh
(TANDATANGAN PENULIS)
Alamat tetap
12, JALAN BENDERA 22
TAMAN BUKIT BENDERA
28400, MENTAKAB, PAHANG.
Tarikh:
CATATAN:
20 APRIL 2007
*
**
‹
(TANDATANGAN PENYELIA)
PM. IR. FATIMAH MOHD. NOOR
Nama Penyelia
Tarikh:
20 APRIL 2007
Potong yang tidak berkenaan.
Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/
organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu
dikelaskan sebagai SULIT atau TERHAD.
Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara
penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan penyelidikan, atau
Laporan Projek Sarjana Muda (PSM)
ii
“I hereby declare that I have read through this thesis and in my opinion, it has
fulfilled the scope and quality for the purpose of an award of degree in Bachelor of
Engineering (Civil).”
Signature
:
………………………………
Name of Supervisor :
Assoc. Prof. Ir. Fatimah Mohd. Noor
Date
20 April 2007
:
iii
LEAK DETECTION AND LOCALISATION IN WATER DISTRIBUTION
NETWORK BY ACOUSTIC METHOD
HO JIANN CHYUAN
This thesis report is submitted as partial fulfilment
of an award of a degree in
Bachelor of Engineering (Civil)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
APRIL 2007
ii
“I hereby declare that this thesis report is a result of my own research except for
each and every quotation and summarisation which I have stated its source.”
Signature
:
………………………………….
Name of Writer
:
Ho Jiann Chyuan
Date
:
20 April 2007
iii
DEDICATION
This thesis is specially dedicated to my
beloved parents and all my friends.
iv
ACKNOWLEDGEMENT
It is extremely delightful to have completed my final year project within the
time given. It is certain that this project would not be able to be completed smoothly
without the help and assistances from all parties. Therefore, I would like to take this
golden opportunity to express my gratitude and appreciation to the following parties.
First of all, I would like to address a million thanks to my beloved supervisor,
Assoc. Prof. Ir. Fatimah Mohd. Noor, who has been very dedicated in providing
advice and guidance during the entire process of my project. I’m feeling grateful that
I’ve learnt not only technical knowledge from her, but also important values in life. I
appreciate her great effort in taking care and nurturing me like her own child.
Appreciation is also addressed to Syarikat Air Johor (SAJ) Holdings and
Ranhill Water Services Sdn. Bhd. These two organisations have provided useful
materials and assistance for the completion of my project. A special thank you is
addressed to En. Amzari and En. Fadli for their kind cooperation during data
acquisition.
Lastly, thank you to people who had contributed to the completion of this
project, either directly or indirectly.
v
ABSTRACT
Water is crucial to human being. We use water for a wide variety of uses
daily. However, leakage has caused substantial water loss to our precious processed
water. The major contributor to non-revenue water in Malaysia is pipeline leakages.
The water industry in the nation has invested in equipment to detect and localise
leaks in water distribution systems. One of the equipment mentioned is acousticbased. The principle of acoustic is that whenever a leak is present in a pipeline, noise
is generated and will travel along the pipeline. The acoustic leak detection method is
then derived by calculating the distance travelled by this noise generated by the leak.
Different equipment based on acoustic theory are used for different types of leak
localisation, be it surface localisation, pinpointing leak on a stretch of pipe, or in the
water transmission mains. Acoustic based equipments are effective, but have
limitations on pipe size, materials, pipe length and also surrounding conditions. This
paper presents the study on the leak detection strategies in Johor, where a
comprehensive survey that includes zone measurement, pre-location and pinpoint
location survey is adopted. In addition, the accuracy of leak noise correlator in
pinpointing leaks in certain stretches of pipelines is studied. Analysis on the pipe
length and surrounding conditions factors to the accuracy of correlation are carried
out and it is found that both factors play significant roles in pinpointing leak in water
distribution pipelines. It is suggested that precautionary measures and steps to be
taken during correlation process so as to improve its reliability. More advanced
technology, especially the in-line detection technology is suggested to be developed
for better leak detection.
vi
ABSTRAK
Air merupakan elemen yang penting bagi manusia. Kita menggunakan air
dalam pelbagai activiti harian. Akan tetapi, kebocoran paip boleh menyebabkan
kehilangan air yang banyak. Punca utama yang menyumbangkan kepada masalah air
tak-berhasil di negara ini ialah kebocoran paip. Industri air dalam negara ini telah
melabur untuk alat pengesanan kebocoran. Salah satu daripada alat yang dilabur
merupakan peralatan berasaskan teori akustik. Prinsip yang digunakan dalam alat
pengesanan akustik adalah bunyi akan dihasilkan apabila terdapat kebocoran dalam
paip. Bunyi ini akan bergerak di sepanjang paip. Dengan mengirak jarak yang dilalui
oleh bunyi tersebut, alat pengesanan akustik dapat menjangka kedudukan kebocoran.
Alat pengesanan akustik yang berlainan telah digunakan untuk mengesan kebocoran
yang berbeza. Antaranya termasuk pengesanan atas permukaaan, pengesanan tepat,
dan pengesanan dalam saluran paip utama. Alat pengesanan akustik sangat berkesan,
tetapi masih bergantung kepada keadaan seperti saiz and bahan paip, panjang paip,
dan juga keadaan persekitaran. Kajian ini mempertengahkan strategi pengesanan
kebocoran di negeri Johor yang menyeluruh, di mana pengukuran zon, pengesanan
pra-lokasi dan pengesanan lokasi tepat telah digunapakai. Selain daripada itu,
kejituan korelator bunyi bocor yang digunakan dalam pengesanan kebocoran paip
juga dikaji. Analisis ke atas faktor panjang paip and keadaan persekitaran yang
menyumbangkan kepada kejituan korelator bunyi bocor juga telah dikaji. Kedua-dua
faktor ini didapati menyumbangkan kepada ketidakjituan korelator bunyi bocor
dalam pengesanan kebocoran. Adalah dicadangkan supaya pendekatan yang cermat
digunakan ketika penggunaan korelator bunyi bocor. Teknologi yang lebih canggih,
seperti teknologi pengesanan dalam-talian juga dicadang supaya dibangunkan untuk
tujuan pengesanan kebocoran yang lebih efektif.
vii
TABLE OF CONTENT
TITLE PAGE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENT
vii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF APPENDICES
xiii
CHAPTER
TITLE
I
INTRODUCTION
PAGE
1.0 General
1
1.1
Problem Statement
3
1.2
Objective and Scope of Project
5
viii
II
LITERATURE REVIEW
2.0 Introduction
6
2.1
7
Definition
2.2 Causes of Leakage
8
2.3
Impacts of Leakages
9
2.4
Control of Leakages
11
2.4.1
Water Audits
11
2.4.2
Leak Detection Surveys and Strategies
13
2.5
Methods of Leakage Detection
15
2.5.1
Acoustic Method
15
2.5.1.1
16
Factor Influencing the Effectiveness
of Acoustic Method
2.5.1.2
Ground Surface Listening Devices
17
2.5.1.3
Leak Noise Correlators
18
2.5.1.4
Leak Detection in Large Water
21
Transmission Mains
2.5.1.4.1
Limitations of Previously
21
Discussed Devices
2.5.1.4.2 In-line Acoustic Based
21
Leak Detection System
(Sahara)
2.5.1.4.3
Free-Swimming Leak
24
Detection Technology
2.5.2
Transient Pressure Method
27
2.5.3
Tracer Gas Technique
30
2.5.4
Thermography
31
2.5.5 Ground Penetrating Radar
32
ix
III
METHODOLOGY
3.0 Introduction
33
3.1
Site Locations of Correlations
34
3.2
Equipment
34
3.2.1
Leak Noise Correlators
34
3.2.2
Distance Measuring Wheel
38
3.3
IV
3.2.3 Sounding Stick
38
Data
39
3.3.1 Pipe Characteristics
39
3.3.2
Result of Correlation
39
3.3.3
Actual Leak Distance
40
3.3.4
Existing Environment and Network Alignment
40
3.4 Procedures of Testing
40
3.5
Limitations of Testing
42
3.6
Measures Taken to Overcome or Reduce Limitations
43
RESULTS AND ANALYSIS
4.0 Introduction
44
4.1 Leakage Detection and Localisation Methods
44
4.2
Correlation Analysis
45
4.2.1 Pipe Characteristics
46
4.2.2
Leak Distance
47
4.2.3
Calculations and Results
48
4.3
Discussion
50
4.3.1 Relationship between Accuracy and Pipe Length 50
4.3.2 Relationship between Accuracy and Surrounding 53
Conditions
x
V
CONCLUSIONS AND SUGGESTIONS
5.0 Introduction
56
5.1
Conclusions
57
5.2
Suggestions
58
BIBLIOGRAPHY
APPENDICES
61
63-70
xi
LIST OF TABLES
NO. OF
TITLE
PAGE
TABLE
1.1
Production capacity and water distribution in Malaysia
3
4.1
Results of calculations for difference of distance and
50
discrepancy
4.2
Relationship between tested pipe length and discrepancy for
each tested location
52
xii
LIST OF FIGURES
NO. OF
TITLE
PAGE
FIGURE
2.1
Flowchart for Non-Revenue Water Leakage Detection
14
2.2
Operators using different listening devices to locate leak
18
2.3
Schematic illustration of the cross-correlation method
19
2.4
Schematic diagram of Sahara system in operation
22
2.5
Schematic of a drogue in operation and visual representation
23
of a leak
2.6
Video and audio display of acoustic event generated by leak
26
2.7
Computer display depicting revolutions of the ball and
26
correlation to distance travelled
2.8
Pressure graphs showing presence of leak in a water tight
28
network by Fatimah MN (1995)
2.9
Pressure graphs for different leak size representations
28
2.10
Schematic diagram for study by Gally and Rieutord (1985)
29
2.11
Tracer gas leak detection technique
30
2.12
Thermography leak detection technique
31
3.1
Leak noise correlator
35
3.2
Set-up of transmitter at valve
35
3.3
Principal used in leak noise correlator
36
3.4
Typical display of leak noise correlator
37
3.5
Distance measuring wheel
38
3.6
Sounding sticks
38
4.1
Correlated leak distance
47
4.2
Illustration of symbols used in calculation
48
4.3
Relationship between pipe length and discrepancy
52
xiii
LIST OF APPENDICES
APPENDIX TITLE
PAGE
A
Specification of Leak Noise Correlators and Transmitters
63
B
Typical Correlation Display
65
C
Data of Tested Pipe Characteristics
66
D
Saved Correlation Displays for Tested Locations
67
E
Tabularised Correlation Results
68
F
Results of Calculation for Tested Locations
69
G
Remarks of Environment for Tested Locations
70
1
CHAPTER I
INTRODUCTION
1.0
General
Water, in its pure form, is one of the most essential elements on earth to all
known forms of life. Water exists abundantly on earth and is odourless, colourless
and tasteless. The United Nation Environment Programme estimates that there are
about 1400 millions cubic kilometres of water exist on earth. Water appears in
various forms and it never stays static. It can be water vapour and clouds in the sky;
waves and icebergs in the sea; glaciers and rivers in the mountains, aquifers in the
ground, runoff and many more. In a water cycle, where water goes through different
processes such as evaporation, condensation, transportation, precipitation,
infiltration and runoff, it transforms continuously from one form to another.
Generally, water has a chemical formula of H2O, which means one molecule
of water is composed of two hydrogen atoms and one oxygen atom. Water appears
mostly in the oceans as saltwater and polar ice caps. These two forms of water body
comprise of 99% of total water quantity on earth. Despite the fact that seawater is
crucial in transportation, goods delivery system and in tourism sectors, it has no
significant contribution to the living of mankind. It just cannot simply be consumed
as drinking water unless it has undergone the desalination process in order to get rid
of its salt content. The remaining 1% of the water body is mainly of underground
water. Therefore, it could be concluded as water which can be extracted to support
our daily consumption is rather limited and scarce.
2
The dependence of human being on water makes water indispensable in
human lives. As human, we mainly consume water for drinking purpose. About 72%
of the fat free mass of a human body is made of water. To function properly, the
body requires between one and seven litres of water a day to avoid dehydration; the
precise amount depends on the level of activity, temperature, humidity, and other
factors. Although it is undeniable that clean water supply for drinking purpose is the
most vital utilisation in our daily lives, we should not ignore other forms of water
utilisations. Washing, cleaning and cooking, which support substantially a human’s
life are also water-consuming activities.
Water usage is not limited to individuals, it also plays a major role to the
modern civilised world in various sectors. Water is prominent in sectors, for
instances, agriculture, aquaculture, power generation, transportation, recreational
activities and for aesthetic purpose. Other than direct contributions, water also serves
importantly in nearly all forms of industries which are running machines on water.
Very often, water is being utilised as industrial solvent or as coolant in machines.
Albeit being useful to mankind, like every other element on earth, water also has its
own dark sides. The strike of floods and droughts are always the major concerns of
human being. And when these disasters come, it always cost thousands of lives.
In Malaysia, the excessive amount of rainfall is always taken as granted and
that water shortage is perceived impossible. However, our experience had proved us
wrong with the water crisis faced by most residents in the centre region of the
country during 1998. Due to the increasing demand of water, an efficient water
distribution network is the key to prevent the repetition of such water crisis. Sadly,
statistic has shown that the non-revenue water is a major problem in this country. As
shown in the Table 1.1 (Mushaliza, 2001), it is clearly seen that over a ten-year
stretch period, the situation of non-revenue water has not been improved
tremendously. It was recorded that non-revenue water accounted to 43% and 38% in
year 1990 and 2000 respectively.
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Table 1.1
Production capacity and water distribution in Malaysia
Year
1990
2000
Production Capacity
6,103
11,800
National
80
95
Urban Area
96
99
Rural Area
67
83
Non-Revenue Water
43
38
(Ml/day)
Distribution (%)
Climate change has resulted in greater difficulty in weather forecast. A
nation like Malaysia, which is so used to exploit the excessive annual rainfall, is
now longer able to guarantee a sufficient water supply in the future. Unprecedented
severe droughts are expected to strike the country without prior warning. Thus,
uncontrolled water loss due to various reasons will only be the nails in the already
alarming water crisis’s coffin. Consumers of water supply in this country should
always remember and reflect the disruption and financial loss caused during the
period of water crisis in 1998. Consumers can no longer take water supply for
granted, because the increase of global temperature due to global warming is
certainly promising us more come back of droughts which dry major water sources
in the country.
1.1
Problem Statement
Early detection of water leakages in water distribution system has always
been a challenge in the water industry as most water pipelines are laid foot
underground, which are normally unseen to human naked eyes until water starts to
flow out from roads and creates puddles. Over the past few centuries, various
equipments had been improvised in order to aid the related body to detect and locate
leakages in water distribution system. These equipments are developed based on
4
different scientific theories, for instances, transient pressure, thermal detection and
also acoustic method.
Acoustic method is currently the most common method adopted in detection
and localisation of leaks. However the existing acoustic methods and equipments are
generally considered by most professionals as effective only if the sound pitch
induced by the leaks is high enough to be distinguished from the noises generated
from the environment. Theoretically, leaks maybe easy to be detected in laboratory.
However, when acoustic-based equipment is utilised at site, readings may not be
satisfying as the equipment will also capture ambient noises, for example, the
interfering traffic control signals, pedestrians, traffic, etc.
Sounds induced by leaks differ according to the leak sizes. For leak size
which is too small, the sound induced is too low a pitch and it will not be able to be
captured by equipment developed based on the acoustic theory. For leak size which
is too big, the sound induced is also too low a pitch to be captured at all. The ability
to detect leaks accurately is further deterred by the existence of the branches in a
stretch of water distribution system. The sound induced by leak will tend to
attenuate whenever branches of water distribution system exist in the stretch of
distribution system being tested. Besides, sounds generated by leaks in different pipe
materials will also influence the accuracy as pipe materials are also a factor
influencing the sounds generated from leaks.
In summary, to accurately pinpoint a leak in water distribution system by
using acoustic-based testing equipments is hard and it may sometimes depends on
luck. Various factors as mentioned in the previous paragraph play their roles in
affecting the detection capability of these equipments.
5
1.2
Objectives and Scope of Project
The main objective of this research is to study non-revenue water caused by
leakage problem in the water distribution system. This research will focus on the use
of acoustic method in leakage detection and localisation. Leak noise correlator,
equipment which was developed based on acoustic theory and is aimed to accurately
detect leakages in water distribution system will be utilised throughout the entire
study. The main scopes of this study are:
1. To collect data in field leakages detection by utilising leak noise correlator in
leak-present pipelines by studying the environment conditions and pipelines
layouts, and by measuring the actual leaks locations in eight different
stretches of pipeline system in both Kulai and Senai areas.
2. To carry out analysis on the accuracy of leak noise correlator in localising
leakages in water distribution system by comparing data generated from the
above activities.
The objectives of this research are:
1. To look into the methods and equipments used in the water industry in Johor
in detecting leakages in water distribution system.
2. To study the accuracy of acoustic method, particularly the utilisation of leak
noise correlator, in leakage detection and localisation in water distribution,
by testing the equipment on eight different stretches of water pipeline in
Kulai and Senai areas.
3. To draw conclusions on the accuracy of the utilisation of leak noise
correlator and make recommendations on the current practice of leakage
detection.
6
CHAPTER II
LITERATURE REVIEW
2.0
Introduction
Leakage occurs in different components of the distribution system;
transmission pipes, distribution pipes, service connection pipes, joints, valves, and
fire hydrants. Leaks waste both money and a precious natural resource, and they
create a public health risk. The primary economic loss is the cost of raw water, its
treatment, and its transportation. Leakage leads to additional economic loss in the
form of damage to the pipe network itself, e.g., erosion of pipe bedding and pipe
breaks, and to the foundations of roads and building. Risk to public health can be
caused by contaminants entering the pipe through leak openings if water pressure in
the distribution system is lost.
Economic constraints, concern over public health risk and the need to
conserve water all motivate water system operators to implement leakage-control
programs. Systematic leakage-control programs have two main components which
are water audits and leak-detection surveys. In recent years, significant efforts have
been made to develop water audit procedures and leak-detection methods. As a
result, water system operators now have several well established procedures and
modern equipment to help them control water loss.
In this study, the focus is placed on the causes of leakages in water
distribution system, the effects of leakages and the various controlling measures
under taken to reduce the occurrence of leakages. Attention is also given to the
7
development of various equipments based on different theories which is lead us to
the study of this research; the accuracy measurement of the utilisation of acoustic
method, particularly the use of leak noise correlator.
2.1
Definition
There are various techniques to gauge the loss of water. For instances,
unaccounted water or non-revenue water, water loss index, supervising and testing
of meter and also complains from consumers. Among all the techniques, nonrevenue water can be considered as the profoundly popular technique.
This
indicator shows the discrepancy between quantity of water supply and also quantity
of used water being recorded by meter. Non-revenue water is generally being
utilised in a legal and effective way such as by the use of fire fighting, road cleaning
purpose and flushing of drainage system or it can be used illegally such as water
theft and squatter areas. Commonly, non-revenue water is expressed in percentage,
which is:
Non-Revenue Water =
Production - Metered Use
× 100%
Production
2.1
There are two types of water losses; apparent water losses and real water
losses. Apparent water losses are the amount of water which is not captured
correctly or not captured at all. These are the caused by inaccuracy of water counters,
by losses caused by a very low flow or by theft. Real water losses are the amount of
water which is lost by defects and operating mistakes (SebaKMT Training Manual).
Leakages in pipelines between production point and water counters are examples of
real water losses. Real water losses are also known as physical losses.
Water loss can occur due to various causes. For example, corrosion of
pipelines, material defects, faulty installation, and also ground movement. Indeed,
water loss need to be controlled properly as it not only cause huge amount of
8
economy loss to the water industry, it also poses health hazard as pollutant may
easily enter into the water supply distribution system through leakage. In order to
control water loss more efficiently, many efforts has been put in especially in
targeting the leakage problem.
2.2
Causes of Leakages
There are many causes which contribute to the leakage problem in pipeline
system. Among the causes as suggested by Lahlou (2001) and Fatimah (1997) are:
a. Corrosion. Corrosion is not only contributing to the leakage problem, it also
affects the quality of water being transmitted. Corrosion can occur inside or
outside a pipe and causes the pipe to become weaker in supporting the outer
force exerted on it. Corrosion which happens outside of the pipe is mainly due
to the environmental effect while water quality and corrosion protection layer are
the factors affecting corrosion happens in the inside of the pipe.
b. Material defects.
Material of the pipeline used may not comply with the
standard requirements. This means that it may not able to sustain the designed
water pressure and designed traffic loads. Therefore it stands a high potential to
get burst and causes leakage problem.
c. Faulty installation. Every pipe need to be installed properly so that they can
take up the water pressure and traffic loads designed. Poor workmanship on the
pipes installation will greatly reduce the capability of pipes to take up loads
exerted on it and eventually causes leakage problem.
d. Excessive water pressure. Excessive water pressure resulting pipes with small
thickness to be easily burst and causes leakage problem.
9
e. Ground movement.
Ground movement is usually caused by drought or
freezing. The arrangement of pipes will differ from its original position either
horizontally or vertically after ground movement and this will lead to the non
uniform distributed load on the pipes.
The pipes will start to crack and
eventually resulting in leakage.
f. Excessive loads and vibration from road traffic. Pipes are often designed to
sustain certain amount of traffic loads. Pipes which have been put in used for a
very long time may not have the ability to sustain excessive increment of the
traffic loads and therefore will crack and contribute to leakage problem.
g. Old and poorly constructed pipelines. This is due to the long term usage of
pipelines which is no longer sufficient in providing its service to water supply.
h. Poorly maintained valves and mechanical damage.
Mechanical damage
usually will cause the pipelines system to not function in its optimum level
which matches the quantity of water supply and the water pressure. In serious
cases, it will result in the occurrence of leakage.
2.3
Impacts of Leakages
According to Goh, Zakaria and Chin (2006), water loss due to leakages in
water distribution system is generating more than just financial loss. Some of the
potential impacts of uncontrolled leakages in water distribution system are:
a. Loss of revenue. Every state in the country spent an immense amount of
cash in treating raw water and to deliver the treated water to its final
consumer, which are the community and the industry. Whenever leak
presents is distribution system, the money spent will be lost and it is not
recoverable. Observing the current leakages problem across the country, a
10
state’s government is anticipated to be able to cut its operating cost to half or
double its revenue should there is an efficient water detection survey.
b. Optimum energy consumption cannot be achieved. Pressure need to be
increased in a water distribution system in order to deliver the water in the
supply network system whenever leak occurs. This is because leakages will
usually cause a significant plunge in pressure and thus the delivery of this
energy will not be efficient.
c. Risk of contamination. Water pipelines are normally laid several feet
underneath the massively developed and densely populated cities. These
cities are usually exposed to numerous forms of pollutions. Leakages in
water network system will increase the risk of contamination to treated water
supply through seepage of pollutants from environment into the piping
network.
d. Damage to infrastructure. As in the aforementioned impact, leakages tend
to overflow from underground to road surface. Water is famously known for
its destructive behaviours such as damaging the road structure and also
causing landslide. Besides, the presence of water at road surface will also
cause skidding effect of vehicles which is definitely an effect that could
endanger the lives of road users.
e. Inefficient fire-fighting capabilities. Due to the failure to maintain
optimum pressure in the water distribution system servicing hydrants, firefighting capabilities may be reduced and becomes inefficient. This situation
is certainly going to increase the number of lives and properties lost due to
the presence of leaks in water distribution system.
f. Jeopardising public confidence. Complaints from the public which is more
accurately to be addressed as consumers, is inevitable whenever there is a
disruption in water supply. State water authorities are expected to be
11
bombarded with numerous complaints from end consumers. This will not
only increase the work loads of state water authorities, it will also jeopardise
the public relations between consumers and the authorities and generate
unnecessary negative image among public.
g. Delayed capacity expansion. Leakage problem will increase the operating
cost of state water authorities to treat more water as to meet the demand;
increase the amount spent in network maintenance; and reduced revenue
from inefficient water supply system. The decrease in revenue will prevent
the state water authorities to expand its network capacity to serve more
people.
2.4
Control of Leakages
Leakages pose destructive impacts to end consumers, to state water
authorities and to the environment by damaging the infrastructure. Therefore, an
effective and efficient control of leakages is crucial. Systematic leakage control
programmes have two main components which are the water audits and leakdetection surveys. Over the years, significant efforts have been invested to develop
water audit procedures and leak detection methods. Therefore, there are many well
established procedures and modern equipment to help the water industry to control
water loss nowadays. In the coming discussion in this study, each and every method
developed over the centuries are to be scrutinised.
2.4.1
Water Audits
As mentioned by Hunaidi (2000), the main aim of water audits is to
determine the amount of water loss in the distribution system. Basically, water
audits can be performed on a network-wide basis or district by district. Network-
12
wide audits are able to provide the overall image of water losses in the distribution
system. These audits require detailed accounting of water flow into and out of the
distribution system. This is usually done by referring to the past meter records and
flow meter accuracy checks. The comprehensive nature of network-wide audits
entails significant efforts, especially for large system.
On the other hand, the distribution system in a district audits is divided into
small districts or zones having approximately 20 to 30 km of water mains. These
districts are isolated individually by turning off the appropriate valves except at
control points where portable flow meters are installed to measure water flow over a
24-hour period. By comparing the ratio between the night time minimum rate and
the average daily rate of water flow to the “normal” ratios or previously measured
ratios of the same district, excessive leakage can be determined. Alternatively, if all
service connections in the water system are metered, more accurate information
about leakage can be obtained by monitoring water flow and usage in the isolated
district over an extended time period.
Areas of excessive leakage in a district can be bracketed by “step testing”.
Step testing is a method where the district is being subdivided into smaller zones and
then flow rates are measured while turning off the valves to cut off different
subdivisions in succession. A significant lower flow rate indicates excessive leakage
in the last subdivision which has been cut off. Since district audits are performed at
night, as in the day, they tend to be more labour intensive and costly. To solve this
problem, a new trend has emerged in recent years. By installing permanent flow
meters that are connected telemetrically to a SCADA system, flow rate data can be
transmitted and are automatically analysed to detect unusual increase in flow
patterns. Based on the experience with the water system, it can then determine
whether an increase in flow rate is due to new leaks.
Although district audits and step testing help to identify areas of distribution
system that have excessive leakage, they do not provide information needed by the
repair crews on the exact location of leaks. Therefore, leak detection surveys are
required.
13
2.4.2
Leak Detection Surveys and Strategies
In areas that have been identified to have excessive leakage, the exact
location of the leakage will be pinpointed by using acoustic or non-acoustic methods.
All the methods being practiced in the water industry will be further discussed in the
preceeding paragraphs. The primary objective of these leakage detection surveys and
strategies is to reduce and maintain losses at the long term economic level based on
the assessment of costs, resources, demand levels and any regulatory requirements.
The reduction of physical losses is mainly concerned with the carrying out of
several different activities such as the management of pressures, the monitoring of
flows, actively detecting and repairing leaks, the reduction of apparent losses, and
the reduction of physical losses. All these activities require manpower which has the
adequate knowledge on the detection and repair of leakage. Therefore, training
programmes are always carried out to train and motivate staff engaged in the nonrevenue water activities. Other strategies being practiced are replacement of assets
and also distribution network modelling.
Figure 2.1 is a flowchart that generally summarises the flow of non-revenue
water detection which combine both the water audits and also the leak detection
survey (Goh, Zakaria and Chin, 2006). It can be seen from the flowchart that both
the water audits and also leak detection survey are repetitive processes. The aim of
this repetitive procedure is to locate the leaks so that the amount of water lost from
the leakage is equal to the excessive night flow measured.
14
First-pass leak detection survey
(daytime correlation and sounding)
Do leak found equals
excess night flow?
Yes
Follow repair procedure
No
Carry out night leak survey
Do leak found equals
excess night flow?
Yes
Follow repair procedure
No
Is a step test worthwhile?
No
Yes
Carry out step test
planning procedure
Are valves operable?
No
Repair valves
Yes
Carry out step test
Analysis results
Leak location required?
No
Repair leaks found
Yes
Figure 2.1
Flowchart for Non-Revenue Water Leakage Detection
15
2.5
Methods of Leaks Detection
Various methods have been developed in order to detect pipeline leakage in a
more effective way. Among all the methods being developed, acoustic method is
the one gaining much popularity compared to other methods such as tracer gas,
ground-penetrating radar, infrared imaging and also thermography method. The
acoustic method is popular because it is easy to adopt and effective in detecting
leakage. Other than the aforementioned methods, pressure point analysis, wave alert,
SCADA-based system, radioactive tracing and many more techniques are also
common practices. These practices are described in the following paragraphs.
2.5.1
Acoustic Method
Acoustic devices are the principal equipments used by the water industry to
locate leaks in the distribution system nowadays. The adoption of acoustic-related
devices is not uncommon since 1980s. In fact, the simple to understand, easy to
operate, and most importantly high accuracy nature of this method has actually
accelerated the technology development and advancement of acoustic devices.
Today, other then simple listening devices such as listening rods, sounding stick and
aquaphones, sophisticated equipments that utilising acoustic theory to locate leaks at
more diversified water distribution network, for example, leak noise correlator and
Sahara leak detection system, had also been developed and are tested to be able to
locate leaks efficiently.
The theory used behind the acoustic methods is sound will be induced by
water as it escapes from pipes under pressure. Leak sounds are transmitted through
the pipe itself over significant distances (depending on the pipe size and type), and
through the surrounding soil into the immediate area of leak. By utilising simple
devices to listen for this sound, leaks can be detected easily. Although acoustic
method is widely practiced by the water industry, the detection and localisation of
16
leaks are not always fruitful due to the several factors that may influence the
listening process.
2.5.1.1 Factors Influencing the Effectiveness of Acoustic Method
Factors that are influencing the effectiveness of acoustic methods are pipe
size, type and depth; soil type and water table level; leak type and size; system
pressure; interfering noise; and sensitivity and frequency range of the equipment
(Hunaidi, 2000; SebaKMT Training Manual) . All these factors are actually dealing
with the fundamental of acoustic methods, which is the sound or noise generated
from leak in a pipeline. The significance of each factor is discussed as follows:
a. Pipe size, type and depth. The attenuation of leak signals in a pipe depends
greatly on the pipe materials and also the pipe diameter. For instance, leak signal
is travelling farther in metal pipe than in plastic ones. The greater the diameter of
the pipe, the greater the attenuation, which means the harder it is to detect the
leak. Besides, the pipe material and diameter also affect the predominant
frequencies of leak signals. Leak signals are more susceptible to interference
from low-frequency vibrations, such as from pumps and road traffic, if the
diameter of the pipe is large and the pipe is less rigid, due to the lower
predominant frequencies.
b. Soil type and water table level. In general, leak sounds are more audible on
sandy soils than on clayey ones; and on asphalt or concrete surface than on grass.
Besides, leak signals become weaker when the pipe is below the water table
level.
c. Location and size of leaks. Leaks occur at different part of a pipe will generate
different frequency of noise. Splits and corrosion pits in pipe walls usually
induce stronger leak signals and higher frequencies than leaks in joints or valves.
Leaks which are too small may be too hard to induce leak signal significant
17
enough to be detected. Therefore, the larger the leak, the stronger the leak
signals. But this may not true for very large leaks.
d. Pipe pressure. The higher the pipe pressure, the stronger the leak signals and
thus the easier to locate a leak. However, increase pressure in pipe may reduce
the efficiency of distribution network. The sudden increment of pipe pressure
may also cause damage to piping system.
e. Sensitivity and frequency range of equipment. Indeed, the more sensitive the
leak sensors, the higher the signal-to-noise ratio of the equipment, which means
the smaller the leaks that can be detected. Filters and amplifiers may be
incorporated to make leak signals more significant.
2.5.1.2 Ground Surface Listening Devices
There are several ground service listening devices as mentioned by Hunaidi
(2000), which have been put in use for quite sometime. These include listening rods,
aquaphones, and geophones or ground microphones. To detect leaks in pipeline
system, leak detection crew first roughly bracket leaks in the system by listening on
all accessible contact points in the distribution system such as fire hydrants and
valves. Whenever suspected leaks are identified, the leak detection crew will start to
pinpoint the leaks by listening on the ground surface at very close intervals (usually
about 1m) with the aforementioned devices. Although the operation of listening
device is usually straightforward, their effectiveness depends greatly on the
experience of the user. If the crew was inexperienced, then it is very likely that he
will miss out the possible leak location. Besides, the noise generated is louder only
when the leak is closer to the listening device. Thus, the crew may miss out a leak if
he is further away from the leak.
18
Figure 2.2
Operators using different listening devices to locate leak.
Geophones (left), ground microphones (centre) and listening rods (right).
2.5.1.3 Leak Noise Correlators
Alternatively, suspected leaks can be pinpointed automatically by adopting
the use of modern leak noise correlators which have become popular in recent years.
Normally, leak noise correlators are more efficient and more accurate than listening
devices. Leak noise correlators are the state-of-art portable computer based devices
that can pinpoint leaks automatically, but it is not based on listening to the noise
transmitted through the ground to the surface, like the principle adopted by listening
devices. The operation of the leak noise correlator is by measuring vibration or
sound at two points that bracket the location of a suspected leak. Figure 2.3 shows
how leak noise correlators is put into operation (Hunaidi, 2000). In this method,
acoustic leak signal are measured with vibration sensors (normally accelerometers)
or hydrophones are placed at two pipe contact points (usually fire hydrants or valves)
that bracket the location of a suspected leak. Vibration or sound signals are
transmitted wirelessly from the sensors to the correlators.
The leak is in most cases located asymmetrically between measurement
points and consequently there is a time lag between the measured leak signals. As to
pinpoint a suspected leak, a correlator first determines the time lag between
measured leak signals by calculating cross-correlation function. The location of the
leak is calculated based on an algebraic relationship between the time lag, the
19
sensor-to-sensor distance, and the propagation velocity of sound waves in the pipe.
Normally, the distance between sensors is measured on site or read from distribution
system maps. Propagation velocities for various pipe types and sizes are usually
available in most commercial devices, or they can be measured easily on site.
Figure 2.3
Schematic illustration of the cross-correlation method for
pinpointing leaks in water pipes
The calculations involved in the acoustic method with symbols as indicated
in the Figure 2.3 as follows:
Arrival time of signal (1), T1 = L1 / V
2.2
Arrival time of signal (2), T2 = L2 / V
2.3
Time lag between signals (1) and (2), ∆T = T2 – T1 = (L2-L1) / V
2.4
Where, V = Sound propagation velocity in pipe.
The technology of leak noise correlators is no stranger to most of the water
industry around the globe. As early as 1980s, the water industry in the United
20
Kingdom had purchased correlator and in the first week of operation, they had found
a leak which they suspected and had investigated for a year. The success of the
operation saved the water industry 270,000 gallons of water per day. Five years later,
another United Kingdom water authority operated a microprocessor correlator over a
period of six weeks with a total of 48 correlation attempts, found a total of 48 leaks
successfully (Halliday, 1985).
In the late 1980s, water authority of Nagoya city occupied a series of water
leak detection works in the city which also incorporated leak noise correlator in their
operation, had successfully increased the efficiency of water supply in the city
(Teruo Sonobe, 1989). After years of operations, the Nagoya city water authority
had summarised its operation as having less number of leakage repairs and an
increased of the effective rate and accountable water rate. The overall effectiveness
of water supply in the city was reported to be nearly 100%. The water authority also
concluded that measures for leak prevention by mean of ‘sound’ should be
developed more rigorously. Thus we can conclude that the utilisation of leak noise
correlator is capable in locating pipeline leaks and increase efficiency of water
distribution.
Although leak noise correlator is capable in locating leaks in pipeline, it is
not always providing accurate results, especially while being tested on plastic pipes,
to the water industry for subsequent excavation and repair works. Hunaidi et al.
(2000) had performed a test to determine the best testing methods to detect leaks in
plastic pipeline. The test concluded that leaks in plastic pipe are able to be located
by leak noise correlators. But several difficulties had been giving the method
challenges. Professional leak detection teams in this test found out that when
operated in automatic and manual mode, leak noise correlator was rarely succeed in
locating leak signals as the range of frequency selected was usually too high for
plastic pipes which has frequency range of mostly below 50Hz. The teams
concluded that the leak noise correlators may yield a better result if the automaticmode algorithms are revised. In the test, it was found that non-acoustic methods
appeared to be more promising.
21
2.5.1.4
Leak Detection in Large Water Transmission Mains
2.5.1.4.1
Limitations of Previously Discussed Devices
When utilising listening devices, the distance from the leak location to the
listening sensor is a critical factor deciding the accuracy the detection of leak’s
location. In general, the deeper in the ground that the leak occurs, the harder it is to
detect. The type of soil and soil conditions can also be a factor, as sound attenuation
or the reduction in intensity of a sound is greater in clay soils versus sandy soils. To
effectively detect a leak, listening devices need to be placed almost directly over a
leak location. Thus, ground surface listening device, or even ground penetrating rods,
which are historically proven to be effective in detecting leaks on distribution
pipelines that are buried relative shallow are unsuitable for the detection of large
diameter pipelines, due to the long distance of these pipelines and also the various
uncertainties as to where the pipelines actually run underground.
Another leak detection device, the leak noise correlator, which is also widely
used in leak detection, is not suitable for the leak detection carried out at large
diameter transmission mains. The availability of accessible appurtenances on which
to attach the accelerometer becomes a limiting factor to the use of the noise
correlator, which required accelerometers to be attached to a relatively close space.
Besides, identification of leaks can be limited by the physics of acoustic attenuation
and propagation of the acoustic activity in large diameter pipeline.
2.5.1.4.2
In-Line Acoustic Based Leak Detection System (Sahara)
In-line acoustic based leak detection system, which also known as the Sahara
system, is one of the newer non-destructive technologies developed with the aim to
detect leaks in pipeline system. Sahara system not only pinpoints the location of leak,
it also estimates the magnitude of leaks. This system of leak detection is used in
water transmission mains. The Sahara system uses a highly sensitive acoustic
22
detector unit (known as drogue), which is inserted into the main at any tap point of
two-inch or greater in diameter while the pipeline remains under pressure (between
3 and 200 psi or 0.3 and 13.8 bar) (Larsen et al., 2005). Other than the acoustic
detector unit, the operating unit also consists of a cable which incorporates with a
retractable guide which protects the cable from damage as it passes into the pipe, a
winch which forces the umbilical into the pipe against water pressure and withdraws
the umbilical from the pipe upon completion of the survey, and cable drum which
control the deployment and retrieval of the umbilical.
Figure 2.4
Schematic diagram of Sahara system in operation
During operation (as illustrated in Figure 2.4), the system is carried along the
pipe by the flow water. In order to carry the system, flow rate in transmission mains
must be greater than 1ft/sec or 0.3m/s. The detector head will continuously record
for distinctive noise of a lead that is generated by the escape of under-pressure water
as the system travels through the pipe. Once a leak is detected, the sensor head can
be stopped at the precise location of the leak. An operator can then estimate the
magnitude of the leak through quantification of the acoustic signal recorded by the
sensor, which is then presented in visual data output through the conversion of audio
data. The location of the leak is then surface located using a precision locator unit
and accurately marked for subsequent excavation and repair.
23
Figure 2.5
Schematic of a drogue in operation (left) and visual
representation of a leak (right).
Sahara system was commissioned to detect leaks in pre-commissioned
pipelines in the Lake Fork Transmission Main near Dallas, Texas in the United
States, when the 11.3 kilometres pipeline had failed a series of hydrostatic pressure
tests (Larsen et al., 2005). Before the Sahara system is adapted, attempts were made
to locate the leak using both visual inspections (internal and external) and correlators.
However, neither of these methods detected leaks successfully. By using the Sahara
system, the contractor of the project managed to determine two leaks and four
anomalies, which could be described as “leaking faucet”. The presence of the leaks
was verified with the subsequent excavation and repair work. It was found out that
both main leaks were happened to be at joint locations.
In the United Kingdom where the Sahara leak detection system was first
developed, Thames Water Utilities Limited, which is the largest water and
wastewater services company in the United Kingdom, concluded that the Sahara
leak location system was the most accurate and cost effective way of detecting and
locating trunk main leaks, after its eight years of investigations which were
successfully detected and located over 960 leaks from the over 960 completed
surveys (Mergelas, Bond and Laven, 2006). The organisation also reported that after
comparing a range of new and traditional leak detection methods, with parameters
included cost of operation, sensitivity of detection and accuracy of locations, the
Sahara leak detection system had provided the organisation sufficient useful
24
information to repair an average leak of approximately 0.15Ml/day, with near 100%
accuracy record.
Although this in-line acoustic based system is effective in detecting leaks in
large diameter water transmission mains, it has a very significant shortcoming. This
system is tethered by a cable during its operation. The most significant limitation of
a tethered system is just like what its name suggests – it is tethered. How far can the
system be extended was always the main concern of the operator. Under optimum
condition, it may be stretched to a mile length. However, when the inspection is to
be carried out for several miles, the setting up and dismantling of the system may
sound too cumbersome and time consuming and therefore could be inefficient. The
presence of in-line valves, sharp bends, and changes in elevation may affect the
length of the tethered cable that can be deployed.
2.5.1.4.3
Free-Swimming Leak Detection Technology
Free-Swimming (non-tethered) leak detection technology is invented and
designed after the recognition of the value offered by acoustic lead detection
technology and the realisation of the limitations associated with current leak
detection technologies applicable to large diameter water transmissions mains. FreeSwimming leak detection technology is developed with the goal to enable operators
and engineers to survey pipelines which are not previously possible or logistically
challenging.
David W. Kurtz (2004) had set up a research and development programme to
develop a free-swimming acoustic leak detection device targeting at large dimension
transmission mains. The device was developed as a leak detection device that could
be propelled with the water flow over long distances while recording signals
generated by leaks as it travelled through the pipeline. The incorporation of the
ability of this device to propel with water flow is due to the state of large water
mains which run for long distances and do not offer much in the way of intermediate
access point. One of the chief challenges in designing this device was to provide for
25
the sensitive detection of the acoustic signal generated by a leak. The advantage of
this free-swimming acoustic leak detection device is the ability of placing a sensor
very near to the leak which is no further than a pipe diameter. However, the
interference from noise generated by the movement of the device as it traverses
along the pipeline may greatly affect the accuracy of leak detection.
In the recognition of shortcomings of design, the device had finally been
created as a device that provides a foam ball that envelopes an aluminium, watertight sphere containing sensitive acoustic instruments. The foam ball is inserted into
pipeline and released to allow the flow to carry the ball downstream. While the ball
is traversing the pipeline, it makes a continuous recording of all the acoustic activity
in the pipeline. Once the ball has travelled the desired pipe length, which is
depending of the battery in the device, it is retrieved with a net assembly and
extracted from the pipeline. The acoustic data is then evaluated to determine the
presence and location of any leaks in the pipeline.
As any other acoustic leak detection technology developed, the freeswimming technology utilises several features in combination as to accurately locate
a leak in a pipe. These include:
a. Transponders which are periodically placed along the pipeline to track the
location and movement of the ball and acoustic instrument by detecting pulses.
b. Counting revolutions. The ball may roll along the bottom of the pipe without
skidding or any extra revolutions. A general indication of where a leak is
achieved by counting the number of times the ball has rolled. It can also be
utilised to confirm other locating algorithms.
c. A miniature transponder placed inside the sphere emits a coded ping that allows
a GPS based logger on the surface to identify the ball as it passes.
d. Internal monitoring and recording of temperature and temperatures changes can
denote inlet/outlet along the pipeline.
26
The device was put in test at Tucson, Arizona and had traversed a length of
approximately 3.77 miles, by a two-man crew in a matter of hours (Kurtz, 2006).
The result of the test shows that the device was able to capture clearly acoustic
signal generated by a one gallon per minute leak. The acoustic signal was picked up
about ten to fifteen feet on either side of the leak location, as the signal built to a
very well defined acoustic crescendo as it passed nearby by the leak. Figure 2.6
shows the test result which can be captured both audibly and graphically.
Figure 2.6
Video and audio display of acoustic event generated by leak.
Besides successfully locating the leak, the device had also reaffirmed the
various tracking methods which are greatly contributing to the detection of leaks.
These include counting revolutions of the ball and positioning and timing from the
surface mounted transponders, as demonstrated in Figure 2.7.
Figure 2.7
Computer display depicting revolutions of the ball and
correlation to distance travelled.
27
Subsequent testing was performed and they had reinforced the reliability of
the device to identify acoustic signals associated with a leak event in a pipeline by
utilising proven acoustic technologies. Other than leak detection accuracy, the
ability of the device to travel in long distance which therefore increases the
efficiency of the testing verifies the cost effectiveness offered by it to detect leaks in
large diameter water transmission mains.
2.5.2
Transient Pressure Method
Over the years, many researchers had carried out researches based on the
utilisation of transient pressure theory. Generally, in a hydraulic system, transient
pressure occurs whenever there is a change in flow condition, resulting pressure
waves to propagate through the system until a steady state is achieved. Similarly, a
leak will generate reflected waves that will continue to attenuate when a pressure
wave is initiated in the system. Thus, researchers use this theory to make detection
of leaks possible by measuring the pressure variation between leak-presence system
and water tight system. Figure 2.8 shows the result obtained from the leak detection
study by using transient pressure of Fatimah, Azmahani and Ng (1995).
The researchers of this study carried out simulation using computer software
SURGE. The steady state of a water tight sample network was disturbed with on-off
operation of valves in the network. From Figure 2.8, it is obvious that the presence
of leak in a pipeline will result a different transient wave profile than a transient
wave profile of a pipeline without any presence of leak. The superposition of these
two profiles gives the researchers a very vivid finding that by comparing transient
pressure in leak present system and water tight system, the presence of leak in
pipeline system can be detected. Besides detecting leak, the researchers also carried
out study on the wave profiles of different leak sizes and the results are shown as
followed. From Figure 2.9, it is clearly seen that the larger the leak size, the fastest
the attenuation of pressure inside a pipeline.
28
Figure 2.8
Pressure graphs showing presence of leak in a water tight
network by Fatimah MN (1995)
Figure 2.9
Pressure graphs for different leak size representations
29
The previous study of the two researchers was actually modified from a
study by Gally and Rieutord (1985). In this study, oil is utilised instead of water. It
was assumed in the study that the presence of transient pressure occurs when there is
a sudden disturbance, for example, presence of a leak in the system. Two pressure
recorders were installed at the upstream and downstream of the system as to record
the time needed for pressure generated to reach each measurement point. After that
the location is determined with the equation generated from the time difference of
the arrival of pressures.
Figure 2.10
Lx =
Schematic diagram for study by Gally and Rieutord (1985)
c (t1 − t 2 ) + L
2
where, c
Lx
2.5
= velocity of wave
= distance of leak from either one of the recorders
(t1 – t2) = difference of time arrival
L
= distance between two recorders
The estimation of leak’s location is pretty similar to the one used in a leak
noise correlator. However, instead of measuring pressure, the leak noise correlator
measures the propagation of noise generated by the leak. Comparing these two
30
methods, it is seen that the utilisation of acoustic method is providing a better
approach to locate a leak. As mentioned, pressure yielded in a network due to an
abrupt disturbance will tend to attenuate along the pipeline. The size of the leak will
also greatly contribute to the attenuation of the pressure. Thus, it is generally more
difficult to capture the pressure generated accurately. On another hand, noise
generated from a leak can propagate through a longer stretch of pipeline and the
attenuation of the noise is less important since noise travel at very high speed.
Besides, it is easier to distinguish a noise generated by a disturbance than to detect a
difference in pressure due to presence of leak. Therefore, it can be concluded that
the utilisation of acoustic method is able to yield a better result in the localisation of
leak in a pipeline system.
2.5.3
Tracer Gas Technique
Figure 2.11: In tracer gas method, a portable gas sensor is used to detect
monotoxic gas as it escaped through leaks in pipe and rises through the
surrounding soil to the ground surface.
In this method, as discussed by Hunaidi et al. (2000) and Stafford and
William (1996), a non-toxic, water-soluble and lighter-than-air gas is injected into
an isolated segment of a water pipe. Gases usually being used are helium and
hydrogen. After the gas has been injected into the isolated pipe, it will escape at a
leak opening and then, being lighter than air, permeates to the surface through the
31
soil and pavement. Therefore, wherever there is a leak in the pipelines, a higher
concentration of the gas injected will accumulates around the leaks areas. By
scanning the ground surface directly above the pipe with a highly sensitive gas
detector, the leak can be located, as in Figure 2.11. Although the method is rather
simple to be adopted, the minimum detectable leak level depends on upon the
installation, pipeline product, and the sampling detector sensitivity.
2.5.4
Thermography
Figure 2.12: Thermography techniques detect thermal infrared radiation by
focusing the camera system directly above a leak and display it as visible
images
Water leaking from an underground pipe changes the thermal characteristics
of the adjacent soil (Hunaidi et al., 2000). In many situations, a pipeline will create a
temperature disturbance in the environment surrounding the pipe. For example, in
pressurised pipelines, the escaping water will generate a cold zone in the
environment surrounding the pipe and thus making the pipe a more effective heat
sink than the surrounding dry soil.
This is the principle used behind the
thermography concept or the temperature profile technique, as in Figure 2.12. The
resulting thermal anomalies above pipes are detected with handheld, or vehicle or
airplane-mounted infrared cameras.
There is also some more advanced and
intensive ways to detect the thermal difference by acquiring distributed temperature
32
sensors. Two major technologies compete in this temperature sensing area are multi
sensor electrical cable and optical time domain reflectometry (OTDR) using fibre
optic cable (Stafford and William, 1996). However these two technologies are
usually costly and complex. There are more common being used in detecting leaks
in gas pipelines.
2.5.5
Ground Penetrating Radar
To locate leaks in buried water pipes, radar can be used either by detecting
voids in the soil created by leaking water as it circulates near the pipe, or by
detecting segments of pipe which appear deeper than they are because of the
increase in the dielectric constant of adjacent soil saturated by leaking water
(Hunaidi et al., 2000). Ground penetrating radar waves are partially reflected back
to the ground surface when they encounter an anomaly in dielectric properties, for
example, a void or pipe. The size and shape of the object is formed as an image by
radar time-traces obtained by scanning the ground surface. The time lag between
transmitted and reflected radar waves determines the depth of the reflecting object.
33
CHAPTER III
METHODOLOGY
3.0
Introduction
In order to study the effectiveness and efficiency of the adoption of acoustic
method in leak detection and localisation, a study on the utilisation of leak noise
correlator in the localisation of leakages of the water industry in Johor has been
carried out. The related leak noise correlator studies are carried out with cooperation with the Non-Revenue Water Division of Ranhill Water Services Sdn.
Bhd. The works involved are mainly field visits and testing of the equipment at
various sites where leaks were predicted to have occurred, based on the observation
from visual inspection and step-test technique. Besides, discussion with water
industry authority on the various methods of leakage detection and localisation had
also been carried out.
This chapter will detail out the equipment used in the study and the
influences that may cause these equipments to obtain data inaccurately, the
procedures and types of measurements taken during the studies. In addition, various
obstacles and decision making activities involved in the process and mitigating
measures involved are also discussed in this chapter.
34
3.1
Site Locations of Correlations
Testing have been carried out in nine different locations around Kulai and
Senai areas for the purpose of checking the accuracy of leak noise correlator and the
effectiveness of adoption acoustic method in detecting and localising leaks. The site
locations of the nine correlations are as follows;
i.
Jalan Aman, Kampung Sri Aman, Senai
ii.
Jalan Sinaran 6, Senai
iii.
Jalan Sinaran 3, Senai
iv.
Jalan Sentul 1, Kulai
v.
Jalan Bunga Kertas 2 , Kulai
vi.
Jalan Bunga Rose, Kulai
vii.
Jalan Susur Kulai, Kulai
viii.
Jalan Seruling 2, Kulai
ix.
Jalan Santaria, Kulai
3.2
Equipment
3.2.1
Leak Noise Correlator
Leak noise correlator as shown in Figure 3.1 (with its specifications as
attached in Appendix A) used in this study consists of three components, i.e. two
transmitters namely orange (A) and yellow (B), and also a digital correlator.
Transmitters are positioned and installed at two different points, such as valves and
water meter. Transmission from the transmitters will be sent to the digital correlator
located in between once the whole unit is put into operation. The digital correlator
allows user to configure several options before starting the correlation process.
These options include pipe material, pipe size and pipe length. Since the accuracy of
35
leak localisation based on acoustic method varies between different pipe materials,
pipe sizes and pipe lengths, the provision of these options are therefore crucial.
Figure 3.1
Leak noise correlator central digital correlator (left) and two
transmitters
Figure 3.2
A set up of transmitter at a valve during correlation
36
The principle of this correlator is that it detects and memorises the noises
pattern propagated to transmitter A and B, with a time difference. The digital
correlator is then compares the two signals and matches the signals by shifting the
signals in the time base. Whenever two signals are matched, a correlation is said to
have been found. The time difference is measured and a calculation of the leak
position can be done. This principle of correlation is illustrated in Figure 3.3.
Figure 3.3
Signals matched (below) from signals from transmitter A (upper
left) and signals from transmitter B (upper right)
After the whole set of leak noise correlator is put into an operation,
transmission signals are sent continuously from both the transmitters to the digital
correlator. A user can observe a correlation display on the screen of digital correlator,
as shown in Figure 3.4, during the operation. The details of this correlation display
can be referred to in Appendix B. One thing worth mentioned in this correlation
display is the display of coherence spectrum. This coherence spectrum serves as a
very important function in the correlation process as it allows users to make
adjustment to filter out unnecessary noise, thus provides a more accurate reading.
Usually the filtering process is carried out when the no satisfactory result is obtained.
37
As stated in the user’s manual of this leak noise correlator, there are certain
situations where a correlator may face difficulty to accurately localise a leak. These
influences are size of the leak, pressure in the pipe when correlation is carried out,
kind of soil and density of the soil, ambient noise, pipe material and dimension. In
order to educate user regarding possible doubt of correlation, the digital correlator
may display three different messages in the status bar. These messages and their
respective explanation are as follows;
i.
Attention: correlation doubtful. The correlation information is very uncertain
as the value of the correlation keeps jumping during the measurement.
ii.
Attention: possible centre correlation. This message is to warn user that leak
is not necessary located in the middle of the testing section. Instead, it may
be caused by an interfering signal which is captured on both transmitters.
iii.
Attention: leak possibly outside of field. A correlation peak will also be
indicated in the closest transmitter to the leak in this case as to warn user that
there might be a leak located outside the testing section.
Figure 3.4
A typical correlation display of leak noise correlator
38
3.2.2
Distance Measuring Wheel
Figure 3.5
Distance Measuring Wheel (left) and its meter up-close shoot
(right)
Figure 3.5 shows the meter tape used in the study. This meter tape consists of
a roller, a holding stick and a meter attached to the side of the roller. The meter tape
is a reset available one. The reading of the meter tape can be set to the initial value,
which is usually zero, once a new measurement is to be taken. To use this equipment,
the user is only required to roll on road pavement. A reading can be captured once
the rolling process is finished.
3.2.3
Sounding Stick
Figure 3.6
Sounding Stick
39
Sounding stick, as shown in Figure 3.6, is a stick that will accentuate the
noise generated by leak. This equipment is put in use only when the reading from
correlator is not providing a vivid and satisfactory result.
3.3
Data
Data are taken during testing for analysis. Data are taken in every study
including pipe material, pipe diameter, pipe length, the result of correlation, the
existing environment condition, and also the alignment of water distribution network.
All these data will be discussed in the following sub-topics.
3.3.1
Pipe Characteristics
As being discussed in literature review, the material of pipes, the size of pipe
and the length the pipeline being investigated play very important roles in the
localisation of a leak. All these data are crucial as they will become the input to
digital correlator before a correlation can be carried out. Usually all these data are
obtained from the existing schematic diagram of the related water distribution
network. The reading for these data are tabled (Appendix C).
3.3.2
Result of Correlation
Result of correlation in each area is saved after the correlation is completed.
The result saved in the digital correlator is then transferred to computer before it is
printed out. The saved correlation file is identical to the screen display of the digital
correlator, indicating an estimation of the possible location of a leak. These saved
correlations are attached in Appendix D.
40
3.3.3
Actual Leak Distance
In calculating the discrepancies between reading from correlator and the
actual location of a leak, the actual location of the leak needs to be measured.
Measurements are taken from the point of transmitters’ position during correlation,
after contractor has carried out excavation and repair work. Usually contractor will
work on the possible leak site two to three days after the correlations have been
carried out.
3.3.4
Existing Environment and Network Alignment
It is important to observe the existing environment where correlation is being
carried out. This is because the environmental conditions may contribute to the
pattern of water usage and the possible ambient noise that will affect the process of
correlation. Besides, network alignment should also be kept in record. It is noted that
the more branches a stretch of pipeline have, the harder it is to capture an accurate
reading with digital correlator. This is mainly because noise that propagates along
the pipeline may attenuate.
3.4
Procedures of Testing
The procedures of testing consist of two parts, i.e. the night correlation
process and the day contractor’s works. The procedure to acquire data for correlation
is mentioned as follows:
1) Transmitter A and transmitter B are positioned and sensors of both
transmitters are fastened to valve mechanism or hydrant. Both transmitters
are turned on and antennas of both transmitters are raised for the purpose of
correlation.
41
2) Digital correlator is turned on and positioned in between both transmitters.
3) Distance between both transmitters is measured by rolling meter tape on the
road between the transmitters. The distance is recorded for later use.
4) Pipe material and pipe size are obtained from existing schematic diagram of
the water distribution network. All three data, pipe material, pipe size, and
pipe length as measured from 3) are keyed into digital correlator.
5) Digital correlator is set to correlation mode. Correlation is continued for
several minutes until a steady state of correlation is achieved. A steady state
is said to be achieved if a particular reading is repeated frequently. If steady
state is hard to achieve, filtering option is chosen until satisfactory result is
obtained.
6) Satisfactory result is saved in digital correlator. Saved data is loaded into
computer after operation is finished.
7) Observation to the existing environment, especially visual inspection of
suspected water flow caused by leakage in pipeline is made and recorded.
Observation to the existing network is made and recorded based on the
information from schematic diagram. Both records are kept for the use of
future reference.
The following procedure is used to acquire data for contractor’s works:
1) Contractor is called by the water authority for excavation and repair works.
Repair works are carried out by contractor based on the finding from
correlation.
42
2) After repair works are finished, update is made to the water authority. Based
on the information provided by contractor, measurement of the distance to
previous installed transmitters’ locations is made. Data is recorded.
3.5
Limitations of Testing
Throughout the whole process of data acquisition, the following constraints
and limits are observed:
1) Several areas of the testing locations are located in residential area. Although
testing of correlator was done at night, the occasional water usage by local
resident was inevitable. Thus, the reading obtained from correlation process
was affected.
2) Schematic diagram where pipe material and pipe size are obtained is not upto-date. This increases the uncertainty of accuracy of existing water
distribution network, thus making record observation difficult.
3) Due to the working nature between night testing and contractor’s work,
several days of time lag occurred. This increases the inaccuracy of reading
taken as it is generally harder to trace the exact location of leak.
4) Ambient noise is inevitable during the testing. Thus, reading from correlation
may be affected.
43
3.6
Measures Taken to Overcome or Reduce Limitations
In order to obtain satisfactory data from all the testing, the following
measures had been taken;
1) Based on the observation of digital correlator display, whenever usage of
water was suspected in a test location, especially when testing was carried
out in residential area, which was common in this study, testing was
terminated and re-run as to make sure no testing is carried out whenever
there is a usage of water.
2) Information of pipe, including its size and material, was obtained from the
latest possible schematic diagram in order to ensure no inaccurate data
becomes input of correlation which will eventually resulting in an inaccurate
finding.
3) Contractor’s work was carried out as soon as possible after correlation was
carried out. This is achieved by effective communication and coordination
with the water authority.
4) Testing was carried out with minimal possible traffic interference and
ambient interruption.
44
CHAPTER IV
RESULTS AND ANALYSIS
4.0
Introduction
As stated in the first chapter of this report, the main objective of this research
is to study the leakage detection and localisation methods used by the water industry
in the state of Johor. This also includes the use of acoustic method, focusing
particularly on the accuracy of leak noise correlator in localising leak in water
distribution pipeline, and finally constructive recommendations are made for better
practice in the leakage localisation process with the aid of leak noise correlator. In
this chapter, analysis will be carried out based on the data obtained from field tests.
Several factors which may contribute to the inaccuracy of correlation are discussed.
In addition, the leakage detection and localisation methods used by Johor water
industry are also be presented.
4.1
Leakage Detection and Localisation Methods
In Johor, all water supplies production and management are under the
jurisdiction of Syarikat Air Johor (SAJ) Holdings, a subsidiary of Ranhill Utilities
Berhad. However, the task to execute testing and repair works on faulty pipelines is
not under its responsibility. Instead, all the leakage testing and repair works are fall
under the responsibility of Service and Maintenance Department of Ranhill Water
Services Sdn. Bhd. The leak detection teams in this company carry out regular
45
checking on existing pipelines. They also carry out investigation whenever they
receive complains or reports from the public regarding disruption of water supply.
This company has invested in quite a number of equipment in order to
effectively localise leakage and carry out subsequent repair work as soon as possible
to reduce the loss of money due to excessive non-revenue water. The equipment
include, noise loggers, leak noise correlators, and sounding sticks. Noise loggers and
leak noise correlators are currently the main equipment used in localising a possible
leak. The authority usually uses noise loggers in zone measurement where a set of
about ten units of noise loggers will be placed at sites to continuously collect data on
several sections of pipelines. This procedure is categorised as pre-location leak
detection procedure. Noise logger is helping the authority to bracket the possible
leak area, after which, visual inspections with the aid of sounding stick are carried
out by the maintenance force. It is usually at this time that the detection team is able
to pinpoint possible leak locations. For non-visible leaks, leak noise correlators are
used. Both visual inspections and the utilisation of leak noise correlators are
categorised as pinpointing leak detection procedure.
Besides relying on high-tech equipments, the water authority also performs
step tests whenever the area of inspection is too large. This procedure is called the
zone management leak detection. Step test is usually performed to narrow down the
area of possible leak occurrence. Although the water industry has a rather complete
and effective leakage detection and localisation plan when dealing with local water
distribution network, it does not have equipment of higher-end technology, for
instance, Sahara system or free-swimming acoustic system, to investigate the
condition of faulty pipelines in water transmission mains.
4.2
Correlation Analysis
As mentioned in Chapter III, nine correlations were carried out at nine
different locations in Kulai and Senai areas. In the following discussions, the
46
analysis of the results obtained is presented. The analysis is mainly focused on the
accuracy of correlations by leak noise correlator comparing to the exact leak
locations measured after the repair works. Factors influencing the accuracy of
correlations are scrutinised as to give a more comprehensive impression on the
effectiveness and efficiency of leak noise correlator. The results of correlations are
attached in Appendix E.
4.2.1
Pipe Characteristics
From previous discussions, the characteristics of correlated pipe, for
instances, pipe materials, pipe size, pipe length, and number of branches play an
important role in determining the accuracy of correlation. Unfortunately, in this
study, the nine locations tested have the same characteristics in terms of pipe size
and pipe materials. This is mainly due to the reason that tests were carried out
mostly at residential areas in which the water industry usually receives complaints
from end users. In these nine tested locations, the pipes are made of asbestos cement,
and the sizes are all 150 mm in diameter. With this information of pipe material and
pipe size, the generated leak noise travelling velocity was set as 1029 m/s by the
leak noise correlator automatically. This means that correlations carried out in all
nine tests were based on detection of leak noise travelling at this velocity. As there is
no special reference to this configuration, this value used automatically by the leak
noise correlator was not verified.
The length of the tested pipe sections in this study were measured by
distance measuring wheel. The accuracy of the distance measured was to one
decimal point, which is sufficient to be used as an input to leak noise correlator. The
data input capacity of leak noise correlator for pipe length was also up to one
decimal point. The data for pipe characteristics and date of tests are tabled
(Appendix C).
47
4.2.2
Leak distance
There are two leak distances which are crucial in this analysis; the correlated
leak distance by using leak noise correlator, and the actual leak distance measured
after repair work has been carried out by appointed contractor. In the correlation
process, both distances from transmitter A and transmitter B to the correlated leak
were indicated in leak noise correlator. However, only one of the two distances was
used in analysis. As to maintain the consistency of analysis, only the correlated leak
distances from transmitter A, Lc, for all nine test locations are tabled. Similarly, for
actual leak distance, La, measured after repair work, only distances from the leak to
the position of transmitter A are measured and recorded. Figure 4.1 shows the
reading of correlated leak distance from transmitter A, Lc, in a typical correlators’
display. The results for both distances are tabled (Appendix E).
Correlated
leak distance
Figure 4.1
Correlated leak distance from transmitter A (as circled in red)
48
4.2.3
Calculations and Results
The objective of this study is to measure the accuracy of leak noise correlator
in localising a leak in a pipeline system. Therefore the calculation of the difference
between correlated leak distance and exact leak distance is crucial. The calculations
of these differences were based on the equation 4.1. Besides, the difference of
distance is also converted into percentage form and is known as discrepancy. The
calculation for this discrepancy is based on equation 4.2. Figure 4.2 illustrates the
symbols used in the calculation.
Difference of distance, ∆L = | Lc – La |
Discrepancy =
where
Figure 4.2
ΔL
× 100%
Lc
Lc = Correlated leak distance from transmitter A
La = Actual leak distance from transmitter A
Illustration of symbols used in calculation
4.1
4.2
49
As to facilitate readers to better understanding, a sample calculation for Jalan
Aman case is presented as follows;
Tested pipe length, L
= 113.0 m
Correlated leak distance, Lc = 56.5 m
Actual leak distance, La
= 20.9 m
Difference of distance, ∆L
= | Lc – La |
4.1
= | 56.5 – 20.9 |
= 35.6 m
Discrepancy
=
ΔL
× 100%
Lc
=
35.6
× 100%
56.5
4.2
= 63 %
Based on the above sample calculation, discrepancies for the other eight tests
were carried out by using the same manner. Table 4.1 summarises the results of
calculations for the difference in distance and their respective discrepancies for the
nine tested locations.
50
Table 4.1
Results of calculations for difference of distance and
discrepancy
No.
4.3
Location
Difference
Discrepancy
ΔL (m)
(%)
1
Jln. Aman
35.6
63.0
2
Jln. Sinaran 6
54.5
73.6
3
Jln. Sinaran 3
0.3
75.0
4
Jln. Sentul 1
0.0
0.0
5
Jln. Bunga Kertas 2
0.0
0.0
6
Jln. Bunga Rose
3.0
17.0
7
Jln. Susur Kulai
3.0
15.8
8
Jln. Seruling 2
1.5
14.3
9
Jln. Santaria
3.0
20.0
Discussions
It is quite unfortunate that variance in pipe material and pipe size are not
possible in this study. Fortunately however, pipe lengths and the surrounding
conditions referring to number of branches in the stretch of pipeline tested and its
surrounding environment, of each tested locations were different. Therefore, the
discussion of results for the accuracy of leak noise correlator used in the tests will be
discussed in these two perspectives, namely, pipe length and environmental
condition.
4.3.1
Relationship between Accuracy and Pipe Length
Theoretically, the generation of a leak location by leak noise correlator in a
longer pipe will become less accurate. In the user manual of the leak noise correlator
used, it is suggested that the ideal tested pipe length should be limited to less than
51
100 m. Indeed, it is suggested also that the shorter the distance, the more accurate
the correlation analysis will be. However, the limitation of 100 m is not always
easily achieved. There were many situations where the correlation to be carried out
for a stretch of pipeline which exceeded the 100 m limitations, for example, fire
hydrants or valves were not available to position the transmitters. In this study,
however, such limitation was not met. However, the pipe length tested in two of the
locations studied in this research were set to be more than 100 m intentionally, so as
to give an idea on the relationship between correlation accuracy and pipe length
tested. These two locations are at Jalan Aman and Jalan Sinaran 6.
Table 4.2 shows the comparison between tested pipe length and accuracy of
correlation for each tested locations. The same results obtained are translated into
graphical form, as demonstrated in Figure 4.3. From both the table and graph, it can
be generally seen that the longer the tested pipe length, the higher the discrepancy,
although there is no absolute pattern showing that the discrepancy increases with the
increased pipe length. From the results, it is notable that both locations of Jalan
Aman and Jalan Sinaran 6, with tested pipe length of more than 100 m, showed a
significant increase in discrepancies. For Jalan Aman which has a tested pipe length
of 113 m, the discrepancy is reported to be 63%. Meanwhile for Jalan Sinaran 6, a
discrepancy of 73.6% is recorded for a tested pipe length of 148 m. From these two
readings, it clearly shows that increase in tested pipe length results in an increase of
inaccuracy.
From the results, there are three exceptional cases for the tested pipe length
theory. The first case is Jalan Sinaran 3, which has a tested pipe length of 12 m, the
shortest among the nine tested locations, the discrepancy reported is a whopping
75%, the highest discrepancy reported in all nine locations. The main reason for this
occurrence is due to the leak distances used in the calculation of discrepancy. The
correlated leak distance from transmitter A recorded is only 0.4 m, whereas the exact
leak location recorded is 0.7 m. The difference between these two readings is 0.3 m.
It can be seen that in this case, a difference between correlated leak distance and
exact leak distance from transmitter A, although is short, will result in a very high
52
Table 4.2
Relationship between tested pipe length and discrepancy for
each tested location
No.
Location
Pipe Length (m)
Discrepancy (%)
1
Jln. Aman
113.0
63.0
2
Jln. Sinaran 6
148.0
73.6
3
Jln. Sinaran 3
12.0
75.0
4
Jln. Sentul 1
52.6
0.0
5
Jln. Bunga Kertas 2
35.5
0.0
6
Jln. Bunga Rose
36.1
17.0
7
Jln. Susur Kulai
39.1
15.8
8
Jln. Seruling 2
22.0
14.3
9
Jln. Santaria
27.0
20.0
Pipe Length Tested (m)
Relationship between Tested Pipe Length
and Discrepancy
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
Discrepancy (%)
Figure 4.3
Relationship between tested pipe length and discrepancy
80
53
discrepancy. If the discrepancy for the case of Jalan Sinaran 3 is calculated based on
the correlated leak distance and exact leak distance from transmission B, which are
11.6 m and 11.3 m respectively, the discrepancy yielded is only 2.6%. Therefore, it
can be concluded that for leak distance less than 1.0 m, the calculated discrepancy
may not able to provide a reliable accuracy of accuracy.
For cases in Jalan Sentul 1 and Jalan Bunga Kertas 2, both locations reported
a 0% discrepancy. From the observation to the correlation graphs of these two
locations, it is found that both correlation graphs clearly indicating the presence of
leaks in both stretches of pipeline. It is actually possible for a leak noise correlator to
pinpoint exactly the location of leak under ideal conditions and in these two cases, it
shows that those are of ideal cases. The indication of the word ‘ideal’ means that the
leak is generating a very distinctive noise that could be easily detected by leak noise
correlator. The noise should also be clear enough to be distinguished from other
interferences, such as traffic and nearby mechanical system noise. Of course, the
ideal condition also includes interference from water usage during the correlation
operation. In this case, the leak noise correlator also generated a very certain
correlation graph. However, the indication from the graph is not referred to, and
should not be taken as correlated leak distance. The distance and graph shown in this
case simply refer to the location of water flow to consumers.
4.3.2
Relationship between Accuracy and Surrounding Condition
During the tests, various remarks had been recorded for future reference.
This is important in the localisation of leakage using the acoustic method. When
talking about acoustic method, the interference caused from other sources, for
instance, the environment, the soil condition, and the network distribution, play very
important role in determining accurate correlation. The remarks for each location are
tabled (Appendix G). In the following sections, discussion on several surrounding
conditions encountered during correlation process is discussed.
54
One of the main obstacles that will hinder a digital leak noise correlator from
accurately locating a leak in a tested pipe length is credited to the characteristics of
the existing water distribution network. At least this is what had been shown from
the nine testing locations. For the Jalan Aman case, the test was carried out on an
inclined pipeline and distance was taken likewise. However, the transmitters send
transmissions to leak noise correlator horizontally. This will result in a form of
discrepancy in reading. Besides pipeline orientation, the number of connections
from main pipe and whether transmitters were placed on these connections during
correlation also contributed to the inaccuracy of correlation. For example, in Jalan
Sinaran 6 case, connections from main pipe were numerous due to the number of
connections. This scenario increases the opportunity of water usage during
correlation and also helps the attenuation of leak noise travels in the pipe. Thus,
reading from correlation would become unreliable.
Besides the number of connections, the problem of positioning transmitters
on connections instead of directly on main pipe can cause problem to accuracy of
correlation too. Transmitters are usually placed at connections instead due to the
absence of hydrants or valves which are suitable to position transmitters. This
problem in most cases of in this study. The main concern of this problem is leak
noise is not detected by transmitters in a straight direction, but after alteration of
direction, which also causes attenuation of leak noise signal. Besides, connections
from main pipe are usually made of different materials. Since the correlation is set to
be based on homogenous material, the readings of correlation where transmitters are
placed on connections from main pipe are not accurate.
From the tests also, it is found that ambient noise does affect the accuracy of
the correlation. Taking the case of Jalan Susur Kulai and Jalan Santaria, where these
two site locations are at shop lots near to main traffic passageway, the discrepancies
reported both exceeded 15%. The reason for the inaccuracy is partly due to the
traffic interference during the correlation process. For the case of Jalan Santaria, the
disruption from the surrounding environment was worse, as there was an airconditioning mechanical system constantly generating noise. This was also the
reason why Jalan Santaria reported a higher discrepancy of 20% than Jalan Susur
55
Kulai of 15.8%. The latter was free from mechanical system’s noise interference
during the correlation process.
To conclude, accuracy of leak noise correlator in localising a leak in a stretch
of pipeline is affected by the following surrounding condition factors:
1. Pipeline orientation
2. Number of connections from main pipe
3. Positioning of transmitter on connections instead of main pipe
4. Ambient noise
56
CHAPTER V
CONCLUSIONS AND SUGGESTIONS
5.0
Introduction
Undoubtedly, non-revenue water is no longer strange to all the water
authorities around the world. Every year, the financial loss from non-revenue water
has greatly reduced the ability of water industry to expand their network and provide
efficient water supply service to the consumers. Among all forms of non-revenue
water, leakages pose the greatest loss to the water industry. Leakages are not only
causing the loss of revenue in term of unbilled treated water to water industry, but
also greatly reduces the profit margin for investigation and repair works. Leakages
in water pipeline pose a lot of disadvantages and dangers to the whole water industry;
the provider and the end users, as mentioned in Section 2.3. In order to minimise the
impacts of pipeline leakages, it is therefore crucially important for the water industry
authority to set up measures to mitigate this problem.
Studies were done on the current leakage investigation methods adopted by
the Johore water authority. Beside that, a field study was also carried out to
determine the accuracy and effectiveness of digital leak noise correlator in localising
pipeline leaks in water distribution network. Digital leak noise correlator is one of
the equipment belonging to Ranhill Water Services Sdn. Bhd., the authority
responsible for leakage investigation. Tests were carried out in the nine locations
listed in Section 3.1, which are located in both Senai and Kulai area. Analysis on the
results obtained based on the various factors influencing the accuracy of correlation.
In this chapter, conclusion will be made based on the aforementioned studies.
57
5.1
Conclusions
From the visits to Ranhill Water Services Sdn. Bhd., it has been found that
leakage detection and localisation in water distribution system is definitely more
than just simply installing any equipment at site and testing the pipeline. It required
a thorough and comprehensive study on the existing water distribution network.
Leak detection and localisation survey is a combination of visual inspection,
utilisation of testing equipments, and also a constantly effective water audit. In the
Johore water industry, whenever a leak is suspected, or whenever a complaint from
consumer is received, the investigation crew will carry out daytime sounding test,
which involves the listening activity with sounding stick at every meter stand. When
leak was not successfully located, noise loggers will be used, or in some cases, step
test will be carried out to bracket the leak area. The final stage would be to carry out
correlation with digital leak noise correlator. For every leak found or detected,
Ranhill Water Services Sdn. Bhd. will have appointed contractor to carry out repair
work.
In this study, nine correlations had been carried out to investigate the
accuracy and effectiveness of digital leak noise correlator in pinpointing a leak. It is
very unfortunate that correlations were not possible on pipeline with material other
than asbestos cement, and with pipe size other than 150 mm diameter. It is
acknowledged earlier that pipe material and pipe size are two very important factors
in determining the accuracy of digital leak noise correlator. However, correlations
were carried out on different pipe lengths and under different surrounding conditions.
From the analysis, it can be concluded that the increase in pipe length
reduces the accuracy of digital leak noise correlator’s ability to pinpoint a leak. This
is especially true when pipe lengths exceeded 100 m. For Jalan Aman and Jalan
Santaria 6, where the tested pipe lengths were 113.0 m and 148.0 m respectively, the
reported range of discrepancy was between 60% to 80%. Although discrepancy of
0% was obtained from the nine studies, it is concluded that this requires ideal
condition.
58
For surrounding environmental conditions, it is concluded from the studies
that pipe orientation and number of connections to a main pipe has the most
significant effects to the accuracy of correlation. It is also found that ambient noise
such as traffic interference and from mechanical system noise do affect the reading
of digital leak noise correlator as they will be captured by transmitters and will be
sent as noise signal to correlator. Therefore, it is concluded that, correlation process
will only yield an accurate estimation to a leak location if and only if the correlation
is carried out under an ideal condition. This means that the tested pipeline is straight
and has few connections in between, and the environment is quiet and tranquil.
5.2
Suggestions
Using acoustic devices to detect and localise leaks in water distribution
system should be employed. However, in this study, acoustic method does not seem
to substitute the need for leak detection crew. But the accuracy of acoustic-based
equipments is improvable. In this section, suggestions will be specifically focused
on the possible improvement to the digital leak noise correlator in localising a leak,
and also improvement on the detection and localisation of leakages in water
distribution network as a whole.
Suggestions to improve the digital leak noise correlators are listed as follows;
1. Perform correlation on pipe lengths not exceeding 100 m. The shorter the
tested pipe length, the better the result of correlation.
2. A Roadblock is suggested to be set up while testing pipeline in order to
reduce the traffic interference. Traffic interruption from the setting up
roadblock is expected to be minimal since correlation is carried out at night.
59
3. Correlation is suggested to be carried out by experienced user. An
experienced user is more capable in distinguishing a sound and logical
correlation than a newbie to the equipment. Training of inexperienced users
should be guided by experienced users.
4. Notice of intermittent water supply to be distributed to residents regarding
correlation analysis in their area as to avoid water usage during correlation.
5. Update schematic diagram in acceptable intervals so that it is always up-todate for the retrieval of information for correlations.
Suggestions to improve the detection and localisation of leak in the water
distribution network as a whole are listed as follows;
1. Develop free-swimming acoustic technology for local water distribution
system. The development of free-swimming acoustic method has been
proven to be effective in leak localisation in water transmission main.
Therefore, it is suggested that the technology be modified for local water
distribution network with smaller pipe diameters.
2. Water industry authority is suggested to provide easier means for public to
lodge leakage complaints more time-effectively. This can help build up a
good relationship with the public regarding leakages.
3. Local water authorities should organise training and study trips overseas to
learn the technology developed in foreign countries instead of just buying
their equipment. This is because technologies developed by foreign countries
are usually more practical and applicable in their home countries. Local
water industries should collaborate with higher institutions for the
development of advanced technologies that aim at the need of the local
market.
60
4. The development of new township in the future should take into the
consideration of pipeline leakage detection. The design of the piping network
is suggested to facilitate future detection work by providing more accessing
points for pipeline investigation.
5. Water authorities are suggested to co-organise conference regarding pipeline
inspection and leakage detection as a means to gather all resources for
knowledge and technology exchange to improve the overall leak detection
and localisation survey in Malaysia.
61
BIBLIOGRAPHY
1. David W. Kurtz (2006). Developments in a Free-Swimming Acoustic Leak
Detection System for Water Transmission Pipelines. The Pipeline Division
Specialty Conference 2006. July 30 – August 2, 2006. Chicago, Illinois, USA.
ASCE, CD-ROM.
2. Dr. Brian Mergelas, Anthony Bond and Kevin Laven (2006). Financial Benefits
from Seven Years of Water Loss Control Utilizing the Sahara System at Thames
Water in the United Kingdom. The Pipeline Division Specialty Conference 2006.
July 30 – August 2, 2006. Chicago, Illinois, USA. ASCE, CD-ROM.
3. Eric Goh, Muhd. Sobri Zakaria, and Peter Chin Joo Negan (2006). Water
Leakage Detection – Impact, Innovations and Economic Benefits. The Ingenieur.
Vol.32, 16-20
4. Fatimah M. N., Azmahani A.A., and Ng S.T. (1995). Detection of Leaks in
Water Distribution Systems – Using the Technique of Transient Pressure.
Malaysian Science and Technology Congress ’95. 22 – 25 August 1995.
5. Fatimah Mohd. Noor (1997). Pengesahan Kebocoran Dalam Talian Paip Air –
Pendekatan Tekanan Transien. Universiti Teknologi Malaysia: MEng. Thesis.
6. Gally M. and Rieutord E. (1985). Detection et Localisation de Fuites en
Ecoulment Instationnaire Application aux Oleoduces et Gazoduces. Journess
S.F.M. – S.H.F. sur la Mechanoque des Fluides. Paris, October. 61 – 65
62
7. George Kent and SebaKMT (2005). Water Leak Detection Equipment Training
to Ranhill Water Services, Johor. Training Manual.
8. Gorden E. Halliday (1985). Leak Detection in a Water Distribution System.
Journal of the I.W.W.A, Vol. XVI, No. 1
9. M. Stafford and N. Williams (1996). Pipeline Leak Detection Study. London:
Bechtel Limited.
10. Mike Larsen, Brian Mergelas, Brad Bengtsson, Lee Lawrence, and Rogers
Thomas (2005). Using In-Line Acoustic to Identify Leaks in Pre-Commissioned
Pipelines. The Pipeline Division Specialty Conference 2005. August 21- 24,
2005. Houston, Texas, USA. ASCE, CD-ROM.
11. Mushaliza bt. Mustar (2001). Mengesan Kebocoran Paip Menerusi Persamaan
Tenaga. Universiti Teknologi Malaysia: BEng. Thesis
12. Osama Hunaidi (2000). Detecting Leaks in Water-Distribution Pipes.
Construction Technology Update No. 40.
13. Osama Hunaidi, Wing Chu, Alex Wang, and Wei Guan (2000). Detecting Leaks
in Plastic Pipes. Journal AWWA. 92(2): 82-94.
14. Teruo Sonobe (1989). Water Leak Detection Works of the city of Nagoya. Water
Nagoya ’89, ASPAC IWSA
15. Zacharia M. Lahlou (2001). Tech Brief: Leak Detection and Water Loss Control.
National Drinking Water Clearinghouse, West Virginia University. unpublished.
63
APPENDIX A
Specification of leak noise correlators and transmitters
64
65
APPENDIX B
Typical Correlation Display
66
APPENDIX C
Data of tested pipe characteristics
Date of
No.
Location
Pipe Diameter
Tested Pipe
Testing
Pipe Material
(mm)
Length (m)
1
Jln. Aman
6/1/2007
Asbestos
150
113.0
2
Jln. Sinaran 6
6/1/2007
Asbestos
150
148.0
3
Jln. Sinaran 3
6/1/2007
Asbestos
150
12.0
4
26/1/2007
Asbestos
150
52.6
5
Jln. Sentul 1
Jln. Bunga Kertas
2
26/1/2007
Asbestos
150
35.5
6
Jln. Bunga Rose
26/1/2007
Asbestos
150
36.1
7
Jln. Susur Kulai
26/1/2007
Asbestos
150
39.1
8
Jln. Seruling 2
26/1/2007
Asbestos
150
22.0
9
Jln. Santaria
26/1/2007
Asbestos
150
27.0
67
APPENDIX D
Saved correlation display for tested locations
68
APPENDIX E
Tabularised correlation results
Date of
No.
Location
Pipe Diameter
Tested Pipe
Correlated Leak Distance
Exact Leak Distance
Testing
Pipe Material
(mm)
Length (m)
from Transmitter A, Lc (m)
from Transmitter A, La (m)
1
Jln. Aman
6/1/2007
Asbestos
150
113.0
56.5
20.9
2
Jln. Sinaran 6
6/1/2007
Asbestos
150
148.0
74.0
19.5
3
Jln. Sinaran 3
6/1/2007
Asbestos
150
12.0
0.4
0.7
4
26/1/2007
Asbestos
150
52.6
9.6
9.6
5
Jln. Sentul 1
Jln. Bunga Kertas
2
26/1/2007
Asbestos
150
35.5
6.5
6.5
6
Jln. Bunga Rose
26/1/2007
Asbestos
150
36.1
17.6
14.6
7
Jln. Susur Kulai
26/1/2007
Asbestos
150
39.1
19.0
16.0
8
Jln. Seruling 2
26/1/2007
Asbestos
150
22.0
10.5
9.0
9
Jln. Santaria
26/1/2007
Asbestos
150
27.0
15.0
18.0
69
APPENDIX F
Results of Calculation for tested locations
Correlated Leak Distance
No.
Location
Difference
Discrepancy
from Transmitter A, Lc (m)
Exact Leak Distance
from Transmitter A, La
(m)
ΔL (m)
(%)
1
Jln. Aman
56.5
20.9
35.6
63.0
2
Jln. Sinaran 6
74.0
19.5
54.5
73.6
3
Jln. Sinaran 3
0.4
0.7
0.3
75.0
4
Jln. Sentul 1
9.6
9.6
0.0
0.0
5
Jln. Bunga Kertas 2
6.5
6.5
0.0
0.0
6
Jln. Bunga Rose
17.6
14.6
3.0
17.0
7
Jln. Susur Kulai
19.0
16.0
3.0
15.8
8
Jln. Seruling 2
10.5
9.0
1.5
14.3
9
Jln. Santaria
15.0
18.0
3.0
20.0
70
APPENDIX G
Remarks of environment for tested locations
No.
Name of Place
1 Jln. Aman
Remarks
Tested pipeline is inclined
Flow of suspected leaked water was not from main pipe
2
Jln. Sinaran 6
Too many meters at that area, compacted residential
area
Reading on correlator was not consistent
Water usage was suspected during correlation process
3
Jln. Sinaran 3
Flow of leaked water was clearly seen from drain
4
Jln. Sentul 1
Correlation result is near to flow of suspected leaked
water
5
Jln. Bunga Kertas 2
Leak was suspected inside residential house (connected
pipe)
Trasmitters are placed on connected pipes
Flow of suspected leaked water was from inside
residential house
Transmitter was placed at connected pipe instead of on
main pipe
6
Jln. Bunga Rose
7
Jln. Susur Kulai
Location is at shop lot
Correlation was performed next to main road, traffic
interference
8
Jln. Seruling 2
Wet spot on the road was found during day time
9
Jln. Santaria
Pipe consists of PVC and Asbestos
Air-conditioning nearby was in operation during
correlation
Not confident to the reading of correlator
Location is at shop lot