Over the past 40 years or more this has become ever more important as subterranean
highways have become the dominant means of delivery of services to businesses and
residences. Furthermore, the past decade with the development of latest fibre optic
technologies has required even more use of the subsurface world, adding to that
already in use established networks for water, wastewater, gas, telecoms and electrical
power delivery.
Yet even today across the buried service industries there are reports of thousands of
utility strikes through excavations where operators have been unaware of the location
of existing services in the area. Even with the development of the detection and
mapping systems now available there are still many incidents recorded each year.
The increasing use of the family of trenchless technologies that serve the buried
service industries, with access being through small excavations, or existing manhole
or other accesses, has further required improved knowledge of what is already buried
nearby, what lies in the path of any new installation or what may be affected by the
trenchless operations being undertaken. But still strikes occur.
STRIKE REPORT
A recent report, ‘Utility Strikes – Causes, Costs & Developments’ from Professor Nicole
Metje of University of Birmingham who presented an IOSH Webinar: Managing
Underground Assets Safely, on 14 January 2021. (The full webinar presentation can be
viewed at: https://iosh.com/media/9192/utility-strikes-causes-costs-developments.pdf),
highlighted some interesting if potentially disturbing figures relating to strikes.
The webinar highlighted results from a test sample of incidents showing that in relation
to Causes and Reasons for strikes:
• Out of 255 incidents where pre-excavation CAT scans were carried out:
… 52% of the utilities were detected before the strike
… 48% failed to be detected before the stike
• Out of 187 incidents that indicated reviewing utility plans/drawings before
excavation:
… 48% of the utilities were on plans
… 52% were not shown on the plans
- Out of 89 incidents that were on plans:
… 16% indicated that the location of the utility shown was accurate
… 84% stated that the location of the utility struck was inaccurately plotted
Perhaps the most striking of these figures is that within the data used in the presentation
is that of the incidents studied a huge proportion of buried services were inaccurately
plotted on what are supposed to be accurate maps of existing utilities, not only to let
the utilities themselves know where their assets are but also to indicate this presence to
other utilities and or others that may need to operate/excavate in the same vicinity.
So, given the apparent evidence that the industry either does not know what is where
or at least to any great degree of accuracy, despite equipment long being available to
correct this situation, what is available?
LOCATION OPTIONS
The tool most used by working crews in the street is the Cable Avoidance Tool
(commonly known as C.A.T.). Essentially, a Cable Avoidance Tool is designed to pick up
the electromagnetic field created when an electrical current passes through a conductor
like a buried cable. The electromagnetic field forms in an area around the conductor
being at its strongest when the detector is directly above.
Where simple detection is achieved by passing the detector over the survey area this
known as Passive location. The downside of this type of survey is that if the service is not
carrying a current at the time of the survey, no electromagnetic field is generated so the service remains hidden.
For a stronger signal generation and therefore a more significant probability locating
a service, Active location is used by adding a specific signal onto a utility using a signal
transmitter/generator. Here, whether the conductor is carrying a current or not, the
generated signal will be located by the detector, allowing the route of the service to be
established irrespective of the service being active itself. There is usually a requirement
for this option that a physical connection needs to be made to the service at some
point, so a known starting location must be available to the survey to attach the signal
generator. The utility also needs to be constructed of a material tat will carry and
propagate the signal, usually a metal pipe.
If there is suspicion that a service exists but no known start location is available there is
the option to use a different form of signal generator to offer an Induced signal. Induction is a quick and simple way to apply a signal to a utility without the need to make any physical connection. An aerial pushes a magnetic field into the ground. Any buried metallic utilities routed within close proximity to the signal transmitter will be induced with the signal, allowing the utility to be located and traced with a cable locator.
The problem here of course is that many other than metal cable-based networks, modern services are now being installed, and have been for decades that do not use metal pipes or wiring. Water pipes have long been plastic, as have gas pipes. Fibre optic ducts and the cables themselves also are non-metallic. So, there is a need to ensure that these networks too are detectable when necessary.
One option that allows C.A.T. systems to be used is the installation of detectable warning tapes. Warning tapes have been used for many years during open installations of pipes to highlight to excavator drivers that they are nearing a buried service. More recently however many of these tapes have been made available with in-built wiring which, if connected to a signal generator or using an induction signal generator, can be traced as if they were metallic pipes.
Many C.A.T. systems also now have depth approximation technology in-built to indicate the expected depth of the buried service. This can aid excavation operations by allowing the driver to know when to expect to be near an existing service or where a trenchless operation is planned to indicate the depth of any potential obstacle to that operation as it proceeds.
GROUND PENETRATING RADAR
Where the use of signal generation is not feasible, or the materials used for the buried service are metallic, Ground Penetrating Radar (GPR) is a geophysical survey method that uses pulses of electromagnetic radiation to image the subsurface. It provides a non-intrusive and non-destructive method of surveying. Consequently, it is a useful survey technique to investigate many materials. Examples include the ground, concrete, masonry, and asphalt.
A GPR transmitter emits pulses of electromagnetic energy into the subsurface. Changes in the sub-surface are detected based on differences in aspects like density. When a change in the sub-surface is encountered, some of the electromagnetic energy is reflected back to the surface. This is detected by a receiving antenna and variations in the return signal are recorded. The information is displayed on a radargram, which when correctly analysed can indicate utility routes, voids and buried obstacles.
Although Ground Penetrating Radar can detect changes in the sub-surface, it cannot determine their exact nature. Some features exhibit specific characteristics in the reflected wave pattern. For example, reflections from metallic surfaces have a high amplitude, while reflections from a void are reverse polarity. These help with the identification of the detected features. However, in some cases, it may be necessary to supplement a GPR survey with absolute data from boreholes, sample cores, trial pits, etc.
It is now common practice to include GPR in a utility detection survey, especially for the location of non-metallic pipes and cables where other technologies may struggle or fail.
A big leap forward in GPR technologies came in the early 90’s with the advent of portable computing with enough power to process GPR data immediately on site, thus enabling of cart based GPR systems, with an odometer for in-line positioning.
Another significant leap forward on the 2000’s was the advent on multi-channel systems, which can be of two types.
The first is where antennas of two distinct frequency bands are packaged together in one antenna, thus two or more different data sets can be acquired simultaneously each giving different depth of investigation and resolution and thus enabling improved interpretation of the data, thus removing the need to make a critical decision about which antenna frequency to use to facilitate the best chance of locating the utilities of size depth and position interest.
The second development was that of arrays of up to 20 antennas of the same frequency in a single box, which can be either vehicle mounted in the case of large arrays, or in a push cart for smaller arrays. In both cases, data can be accurately positioned from a GNSS or use of a total station. With this development the age of 3D GPR surveying began. The physical size of the antenna array means they cannot be used in every location but if the area to be surveyed is large enough and relatively clear of obstructions then their use allows a significant improvement in data quality, speed of survey, accuracy and ease of interpretation over a conventional single antenna system.
With all GPR systems there is a trade-off between data resolution and depth of investigation, so it is important to have a knowledge of the anticipated ground conditions, the size range and depth of utilities of interest, so the appropriate antenna frequency can be selected to give the best possibility of a successful detection survey.
OTHER OPTIONS
Gyroscopic Alignment Systems are based on an entirely different mapping technique
to more conventional systems which relay upon an emitted signal and as such are not
limited by depth, pipe material or the quality of signal and absence of interferences. The Gyroscopic Mapping system is passed through the subject pipeline, duct or sewer using a combination of propulsion methods and wheel arrangements and through the combination of on-board gyros, accelerometers, inclinometers and odometer sensors, are able to accurately plot the 3D alignment (X, Y, Z) of the pipe route between 2 fixed points of reference for example manhole chambers. Multiple surveys are usually conducted to ensure Quality Control Procedures and to maximise accuracy. The data obtained is then processed with averaging software to provide maximum accuracy for the plotted alignment. Gyroscopic Alignment techniques are unaffected by the external factors which would impact alternative techniques such as Electromagnetic Probing and would be the recommended minimum survey level for sewers of significant depth, size or importance.
By adding a full in-pipe LIDAR Survey to a Gyroscopic Alignment survey it enhances alignment accuracy and expands upon the lineal mapping of the pipeline route by adding 3D properties and confirming the internal extent of the structure which can be invaluable in informing the design of infrastructure and piling schemes around an existing underground asset. It is also common for internal structures to change shape and size along their route and the inclusion of full In-Pipe LiDAR survey will ensure that these deviations are captured accurately within the point cloud model. The quantity of internal data captured in one traverse will also ensure that the data is future proofed in the event that further information is required to inform later elements of a project or to confirm the presence of pre-existing defects for liability or monitoring purposes.
Electromagnetic (EM) Probe/Sonde surveys are another option. Here the probe or sonde is passed remotely through a pipeline, duct or sewer. This is traced using equipment similar to that used for C.A.T. surveys from surface to confirm the alignment and depth. Marked locations on the surface can be subsequently recorded using Topographic Survey methods and overlaid onto an existing survey drawing or OS Tile to provide a mapped representation of the pipe route with approximate depths where obtainable. Electromagnetic Probing presents a cost-effective remote mapping method within small, shallow pipelines. However, its reliability diminishes within increased asset diameter, depth or close proximity of adjacent utility infrastructure.
LOCATION SYSTEM MANUFACTURERS
There are a number of product manufacturers for the range of systems highlighted herewith so the following is but a small sample of the products available.
Allied Associates – Allied Associates Geophysical Ltd offers many solutions to this sector to include Utilityscan, Utilityscan DF and Utilityscan Pro by GSSI. Built for the utility locating professional to accelerate workflow from target detection to reporting, these Utilityscan products can be configured with an optional Linetrac® power detection module.
LineTrac is designed to identify and trace the precise location of underground electric and RF induced utilities with this data overlayed on a GPR scan. As this information is collected during a normal GPR survey this additional information comes without additional survey cost or time.
Other products in demand are GPR arrays, large multi-channel systems such as the 8
and 18 channel Raptor systems from Impulse Radar.
With the integration of RTK GPS or total stations, the surveyor’s workload is reduced
as traditional survey grids are now a thing of the past. Large survey areas can produce
very large data sets, normally an issue at processing time. Allied Associates caters for a
diverse client base supporting low- or high-end systems, post processing options, GPS
and even vehicles for acquisition of highway and off-road data collection.
C.Scope – The use of a Sonde and a depth-measuring Locator, such as C.Scopes
DXL4 Cable Avoidance Tool or MXT4 Locator to detect the exact position and depth of
sewers and drains is already well known in the drainage industry but there is perhaps
less knowledge surrounding the use of the same equipment to detect electricity cables
prior to excavation work commencing.
All C.Scope Cable Avoidance Tools, such as the DXL4 and MXL4 Locators are designed
for this critical task of ‘detecting to avoid,’ especially when used in conjunction with the
SGV4 Signal Generator.
To further support their cable avoidance activities, these C.Scope products have a
feature known as ‘data-logging’ which, put simply, means that a record is being kept of
exactly when and how they have been used. Another version even records where they
are being used. This feature is there primarily to provide reassurance that this essential
cable avoidance scanning work has actually taken place before any excavation work
commences but it is also useful to identify when refresher training courses might need
to be considered.
C.Scope utility location products are designed such that they do not require a periodic
servicing or calibration regime to be set up once purchased. The C.Scope DXL4 and
MXL4 Locators have an automatic, daily self-test feature that checks the Locators ability
to detect the signals it is designed to detect. The SGV4 Signal Generator, uniquely,
also has the same feature, but this time it is checking the SGV4s ability to transmit the
signals it is designed to transmit. These self-tests are also recorded in the units’ data
files meaning that there is a record available to the owner that indicates the operating
performance of the product. These tests are available to the owner at all times and at
no cost.
C.Scope’s utility detection training courses are now renowned throughout the industry
and allow the very most benefit to be gained from the use of this underground pipe
and cable detection equipment.
GeoMatrix – Alongside its many other geophysical survey systems, GeoMatrix offers a
range of Ground Penetrating Radar options from manufacturer ImpulseRadar.
These include three models of the Crossover range. The Crossover1760 can be used
in a variety of conditions and can be configured as a single channel (low or high
frequency) or dual channel depending on your application. Its middle range antenna
frequencies allow the operator to apply/ use the ground penetrating radar system
in a variety of environmental, archaeological, UXO and civil projects. Used to image
the near surface at high resolutions, at a medium depth range. The Crossover1760 is
available in a cart and sled configuration, enabling the user to access restricted, uneven
terrain and other surface types, whilst maintaining an easy-to-use comfortable design
which you can adjust/transport within the field.
The Crossover4080 is an ultra-wide bandwidth dual channel GPR system, which can be
used in a pull or push cart configuration. The system itself can be operated as a dual or
single channel (depending on your application the system can be upgraded to a dual
channel) and has two high frequency antennas, 400MHz (Low frequency channel) and
800MHz (High frequency channel).
The Crossover730 is the largest system within the Crossover series and is only available
in a pulling arrangement, however the design can be adjusted and re-customised to
suit the comfort of the user. The system uses low frequency antennas 70 MHz (Lowest
Frequency) to 300 MHz (Highest Frequency) to prospect to deeper levels beneath
the surface. Each of the channels are available as a single channel to which can be
upgraded to dual channel system. The design of this GPR product allows the user
to collect data in rough, barely accessible terrain throughout the field working day,
covering large survey areas.
RETURN TO CONTENTS INSPECTION, DETECTION & MAPPING 32
GeoMatrix also offers the PinPoint R system. Specifically designed to meet the
requirements of the utility detection industry, the PinPointR GPR system combines
ImpulseRadar’s real-time sampling (RTS) technology with a 400 MHz and 800 MHz
set of antennae to provide unquestionable data fidelity and resolution. The dual
channel electronics permit both frequency antenna to be recorded simultaneously and
targets picked from either channel on the fly. The compact all-in-one design means
the systems can be stored and transported complete so that it is ready for use at a
moment’s notice.
Completing the GeoMatrix offering is the Raptor range. The Mini Raptor offers a
set of High speed GPR systems which use real time sampling (RTS) technology to
obtain accurate and fast results in a variety of applications. The cart configuration
can be used as an 8-channel arrangement for the 450 MHz antenna, up to a
12-channel array for the 800 MHz antenna. The raptor cart can easily be constructed,
transported and stored by one person for use on a number of project sites especially
in constricted areas. In terms of the data collection, the data acquired over each
survey line can be combined with DGPS data improving the accuracy and gathering
process. Furthermore, its modular design allows the user to make their own channel
arrangement (from 4 to 30) depending on their requirements.
The Vehicle Raptor offers a set of High speed GPR systems which use real time
sampling (RTS) technology to obtain accurate and fast results in a variety of
applications. The Vehicle carrier option allows the operator to choose between an
18-channel arrangement for the 450 MHz antenna up to a 280-channel array for the
800 MHz antenna.
IDS GeoRadar – IDS GeoRadar, part of Hexagon, offers a full range of non-intrusive
utility detection and mapping products which exploit the most advanced ground
penetrating radar technologies and methodologies. The company is a worldwide
leading provider of Ground Penetrating Radar (GPR) solutions committed to delivering
best-in-class performance for Utility Location and Underground Mapping.
Stream UP is a cutting-edge GPR solution comprising a multi-channel, multi-frequency,
double-polarised and lightweight GPR system which is specifically designed to perform
utility mapping on extensive areas.
Stream UP, designed for easy assembly and mounting on a normal vehicle, can operate
in urban environments without slowing down traffic (up to 150 km/h or 93 mile/h, with
a suggested acquisition speed of 60 km/h or 37 mile/h), dramatically reducing the time
for data acquisition and traditional maintenance operations thanks to the total absence
of contact with the ground.
Stream Up can be combined with GNSS+INS technology by NovAtel in the APS (Accurate
Positioning System) solution. APS is the turn-key accurate positioning solution to
minimise time and cost for data collection and extraction process. It is able to obtain
the most accurate radar information in poor or no satellite coverage scenarios, ranging
from urban canyons to tree-lined roads, to tunnels and underpasses.
Besides hardware solutions, IDSGeoRadar offers software solutions for advanced GPR
data analysis such as IQMaps, a post-processing software application providing fast
interfacing between the user and the GPR data. IQ Maps allows underground assets’
detection and mapping for real-time processing with advanced target management
and 3D visualisation. IQMaps provides a step-by-step approach to guide the user in
performing the best and the quickest data analysis; with the help of a customisable
processing and analysis tool with functionalities for 3D mapping of sinkholes, inspection
chambers or even archaeological sites.
When performing mapping on extensive areas, the amount of data available in a short
amount of time can be huge and the workload for processing and analysis of radar data
becomes a challenging activity for professionals. With AiMaps, IDS GeoRadar’s latest
software solution leverages Artificial Intelligence and processing and interpretation
of acquired radar data is performed in the Cloud through deep learning algorithms.
AiMaps provides an intelligent view of underground utilities, quickly highlighting areas
where, with a high probability, hidden underground utilities lie. By doing so AiMaps can
significantly reduce risks in underground detection while decreasing time, workload and
costs for the utility analysis and extraction process.
Radiodetection – An established and trusted name in the industry, Radiodetection
provides knowledge and equipment to locate, survey, maintain and protect critical
buried infrastructure.
Radiodetection focuses on enabling its customers to identify and trace underground
infrastructure thanks to a range of superior detection tools. These include:
• Cable and Pipe Locators
• Pipeline Integrity and Corrosion Control
• Plastic Water Pipe Locators
• Time Domain Reflectometers (TDR)
• Cable Test
• Network Analysis
Schondstedt is another company in the Radiodetection family, and is a worldwide
leader in the design and manufacture of metal and magnetic locators as well as cable
and pipe locators.
Lastly, Sensors & Software expands Radiodetection’s Ground Penetrating Radar (GPR)
offering.
Flagship products include precision pipe and cable locators that are widely used
around the world to identify buried utilities. Radiodetection’s RD8200(G)® is claimed
to be the most advanced precision locator in its range, offering accurate and reliable
location in the most challenging of situations as well as mapping. In addition, the
RD7200® is an all-industry locator offering a versatile, high-quality solution that is
suitable for a wide variety of locating tasks, enabling accurate cable and pipe locating.
Radiodetection also has a focus on data solutions that comprise:
• C.A.T Manager® Online – which provides automatic field data retrieval as well as
storage into a secure cloud database and web-based usage analysis
• eCert™ (for remote locator calibration with no downtime)
• RD Map™, which enables users to create detailed utility maps in real time with
external third-party GPS.
• PCMx Manager Mobile allows users to create measurement graphs automatically
and in real time to facilitate emailing survey reports directly from the field.
Furthermore, when Radiodetection launched the Cable Avoidance Tool (C.A.T), it was
the first commercially available electromagnetic locator. The latest C.A.T. models are
the C.A.T4® and Genny4® products. The C.A.T4 is the standard model of the range.
Using it with the Genny4 transmitter, experienced operators will be able to find more
buried utilities, faster.
The C.A.T4+ offers the same locating performance as the C.A.T4 but with addition of
Depth measurement, allowing better identification of the route of buried utilities.
With the gC.A.T4+, this model adds GPS positioning to the usage data recorded.
Bluetooth connectivity allows seamless transfer of usage data to the C.A.T Manager
Online cloud-based system for near real-time monitoring of operators’ performance.
The Genny4’s patented simultaneous dual-frequency signal output facilitates location
of small diameter cables such as telecoms and street lighting, including spurs. All
C.A.T4 locator models have patented technology to detect both signals simultaneously.
The power boost function in Genny4 enables the locate signal to travel further and
deeper, and couple onto utilities more easily.
Ground Penetrating Radar (GPR) solutions from Sensors and Software offer
application-focused GPR including:
• LMX® for utility-locating
• CONQUEST® 100 for concrete scanning
• FINDAR® for forensics
• IceMap™ for measuring ice thickness
• RESCUE RADAR® for Search & Rescue
• EKKO_Project for advanced GPR software.
Schonstedt’s magnetic locators are used by surveyors and utility contractors to
accurately locate buried ferrous metal objects such as cast iron and steel, water and
gas pipes. These locators are trusted by private contractors and NGOs in munitions
response operations around the globe.
‘Alternative’ Technology
In line with the foregoing, it has also been noted that some utility companies are
starting to utilise new mapping software in conjunction with their mapping and
tracking operations to aid field operatives to pinpoint locations once surveys have
been completed. Thames Water is one such example.
In November 2021 the company announced that it using the ‘what3words’ app.
Described as a mobile-first app, the software provides a detailed overview of London’s
vast trunk sewer network and has been adopted by Thames Water as part of its
industry-leading digital transformation.
SymTerra allows the Strategic Pumping & Trunk Sewer team at more than 1,000
locations across the capital to record and access all aspects of a job, whether remotely
or on-site.
With ‘what3words’ embedded across all features of the app, communication and safety
is improved by enabling engineers to record the location and condition of assets and
generate real-time updates of progress and issues.
A fully searchable cloud-based photo and knowledge library can also be created that
integrates with Thames Water’s existing mapping and modelling systems, making it
quicker, easier and cheaper to plan for future work.
So, where does this leave the detection and mapping sector? Basically, in a very strong
position. The technology is there that will detect and allow display on modern digital
maps. There is also now software that will assist in the locating of these assets once
plotted for those in the field.
What is however clear from some of the figures reported above is that, even with this
technology available, there is still the problem of just how accurate some of the utility
plans are that are deemed to show the whereabouts of long-established services. This
brings rise to two points.
Firstly, more needs to be done to find what is already there and new build,
replacement or renovation operations need to ensure that up-to-date accurate data
on location is provided as part of any such operation. There is of course the question
of resources here from the utility owner view-point. But the question has to be raised
as to whether the costs of completing the data update will outweigh the costs and
inconvenience to customers when their services are interrupted when the utility gets
struck during someone else’s project.
Secondly, for those carrying out what might be termed third-party works in the vicinity
of buried services, there is a need to understand that the plans they are being given
simply may not be accurate enough for the purpose in hand and that they themselves
as the excavator need to confirm the positionings shown before work commences and
not just with a simple C.A.T. survey, as there is far more ‘down there’ today than a few
cables that need to be avoided.
CONDITION ASSESSMENT
There is little profit in simply knowing where an asset runs unless its state of repair is
known and how this changes, over time.
Only when the engineer understands the full extent of an asset’s condition can a full
and effective plan be put together to make best use of it and replace it in a timely
fashion as and when required.
Obtaining this information is not however always easy. Where access is available it may
be possible to get the required data by using a man-entry team to go and look. But,
with modern Health & Safety concerns, the need for confined space training and setup on site does usually make this a less than desirable option.
Of course, the first non-man-entry option is the CCTV survey. A quick overview of the
types of CCTV inspection systems available include:
• Zoom cameras – where an access is not too deep there are systems available that can be lowered into the pipe horizon from a manhole or similar access with a CCTV
camera attached that can view using zoom several meters into a pipeline with images
being recorded at surface for later inspection and classification.
- Small rod-based CCTV systems – it is also possible from a drainage point of view for
wastewater pipes to be viewed from inside a building using small diameter camera
systems on extendable rods, either through a plug hole or around a U-Bend. This tends
to be utilised more in the plumbing profession that main and lateral drainage sectors. - Rod-based CCTV – This is a simple to use and quick CCTV option in (usually) shallow
sewers, however the cameras may be limited to smaller diameter pipes, up to a
maximum of 150 mm (6 in). The length of a survey is limited by the length of rod carried on the dispenser carriage which is today normally in the form of a flexible coiled ‘rod’ which also houses the power/data cables. Rod mounted systems usually utilise selflevelling cameras which retain an upright (correct view) image of the inside of the
pipe irrespective of the orientation of the camera head in the pipe. Images are usually
recorded at surface on the machine with data today being available direct to the client via WiFi or internet connection almost as soon as the survey is completed. - Crawler-mounted – In larger diameter pipes probably the most widely use CCTV
configuration with the CCTV camera mounted on a self-propelled tractor unit that can
be remotely-controlled by the surveyor from a single access point whilst monitoring
and recording images on a TV screen/storage system. The speed of survey is very
controllable. Advances in current camera and lighting technology now permits surveys in
pipes of over 2 m diameter. Pipes do not have to be thoroughly cleaned but it helps. Also, camera heads may be Pan & Tilt, some with zoom, which allows the operator to view more closely potential defect sites. - Digital Scanning – Sometimes known as SETT, Digital Scanning uses a digital, highresolution scanner to produce a forward image of the pipeline under inspection, as
well as a 360° image of the interior wall of the sewer at 90o to the survey route. A
360° scanning camera is mounted on a robotic, remote-controlled, wheeled tractor
which travels through the pipe at a constant speed. The camera continuously scans
the pipe’s inner surface creating a series of adjacent section views covering the pipe’s
circumference. Specially developed computer software processes these scanned sections
and stores them for further analysis as a single complete record of the survey run. - Lateral inspection – Where laterals join into a mainline pipe it is possible to some extent to utilise Pan & Tilt cameras to look into the lateral pipe but this can have limitations. Some companies have developed lateral inspection systems that can extend the camera head off the main crawler body and steered into the lateral to complete an inspection over in some cases several metres to provide a much clearer and detailed survey of the lateral connection.
In some cases, it is not just the requirement to ‘see’ what the inside of the pipe looks
like but to also understand if any deformation has occurred. For this the laser line
survey was developed. This shines a ring laser light around the circumference of the
pipe in question which is viewed and recorded as the ‘visual’ CCTV is carried out. The
laser ring ‘flexes’ as the pipe shape changes. Measuring these flex changes against
the known starting profile shows the degree of deformation at any point along the
pipeline. This can be advantageous when looking at the planning of rehabilitation or
other subsequent pipeline actions.
Where a pipe may not be able to be fully cleaned and desilted and may even have
continuous flows during a survey, a sonar-based survey system may be used in
conjunction with the visual survey. This aims sound waves into the invert which are
reflected to show any defects or deformation below any silt level as well as monitoring
the silt level itself.
Once all this information is collected it can be stored for future reference, usually
electronically for quick and easy access. Some CCTV software providers also now have
the capacity to enable storage of this information directly to GIS mapping systems
so that as a problem/question arises at a specific location the currently available
information can be viewed directly. This also enables any new survey to be compared
with the previous one to highlight any substantial changes that may have occurred.
This is also where condition monitoring comes into play. Comparative CCTV surveys
will allow engineers to see how pipeline condition progresses, but where this option is
not available there are other means of assessing pipeline conditions in the present and
over time.
In particular it may be necessary establish the condition of pipelines, often metallic
pipes, to measure for example corrosion, loss of wall thickness, reduction in stiffness
or other effects of stresses.
Examples of such systems are:
• Remote Field Eddy Current (RFT) is a method of non-destructive testing using lowfrequency AC to find and measure defects in metallic pipes.
• Near Field Eddy Current (BEM or NFT) technology uses two coils, a transmitter and
a receiver. Typically, the receiver coil is close to the transmitter coil, taking advantage
of the transmitter’s near-field zone, that is the zone where the magnetic field from
the transmitter coil induces strong eddy currents, axially and radially, in the pipe wall.
• Magnetic flux leakage or MFL (also known as TFI or Transverse Field Inspection
technology) is a magnetic method of non-destructive testing used to detect corrosion
and pitting in metallic pipes. The principle uses a powerful magnet to magnetise the
steel in the structure. Using an MFL tool a magnetic detector is placed between the
poles of the magnet to detect the leakage field. At areas where there is corrosion or
missing metal, the magnetic field ‘leaks’ from the metal. Trained specialists interpret
the recording of the leakage field to identify damaged areas and to estimate the
depth of metal loss.
• Ultrasonic non-destructive testing is also a method of characterising the thickness
or internal structure of a structure under test using high frequency sound waves.
The frequencies used for ultrasonic testing are many times higher than the limit of
human hearing, most commonly in the range from 500 kHz to 20 MHz. Ultrasonic
testing is widely used on metals, plastics, composites, and ceramics.
LEAK DETECTION
Whilst understanding the structural condition assessment and the visual inspection of
pipes may be a necessity for water and sewerage engineers, leakage is pretty much at
the top of the list of the problems the water companies need to sort out according to
public opinion.
However, given that across all the Water companies in England and Wales there are
some 346,455 km of water pipes, it is no surprise that leakage is a problem and is likely
to continue to be for some time to come even if losses continue to fall year on year.
This situation has of course led to the development of significant leakage detection
technology.
Modern technologically based systems include:
• In-pipe systems – where a listening device is passed through a pipe suspected of
having leaks. As the device passes any leak a microphone picks up the distinctive
sound created by pressurised water passing through the defect. Tracking from
surface using a transmitter sonde and receive aerial on surface then allows the leak
location to be marked for further investigation and repair.
• Volume measuring – this can be done on a local or area spread whereby monitoring
stations are set up to check flows at specific points in the network which are then
cross-referenced to see if there are measurable losses between points that are
unexpected, which could indicate a leak in a specific part of the network which needs
further pinpoint investigation.
• Acoustic monitoring – in similar fashion to the volume monitoring set-up area
‘listening devices’ can be set-up across a network to pick up the characteristic noises
of leakage that run through pipes. By picking up and recording these noises and
cross-referencing them it is possible to locate the possible source of the noise/leak
and locate it to a smaller area for further investigation and repair.
This is a very simplistic view of the leak detection systems available but generally
covers the options available.
This of course does not take into account any leakage from foul sewers that may be
in need of rehabilitation or replacement which could lead to contamination of ground
water and other water courses. As yet however, other than the previously discussed
inspection options there is little in the way of technology that can pin-point and record
these sorts of leaks. They are generally addressed by the ongoing and long-term
rehabilitation and replacement programmes within the water companies.
To conclude then, engineers in the buries service industries need to know first where
their service is and where it runs and what it does (water, wastewater, gas, power,
telecoms etc.). Without this knowledge the likelihood of it being damage by third
parties is high and the likelihood of not being able to find it easily to maintain or repair
it is low.
Once this knowledge is available there is the need to know just how well it is operating,
so condition assessment is required.
Only when all the available data is in the engineers hands will it be possible to manage
the asset effectively in terms of cost to the owner, convenience of service to the
customer and benefit to the environment.
