A SUMMARY OF PIPE LOCATION TECHNOLOGIESCompiled on behalf of the Tonga Water Board

Harald ScholzelSOPAC Secretarial

August 1999 SOPAC Technical Report 272

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Table of Contents

1 SUMMARy ..........•.••..........••..••..••.••••............••••••...••••..••......••••....••••.••.•...•.••..•.•••.•.................................. 4

2 INTRODUCTION .••••••••....•.•.••••.•......•.••.................................................................................................. 5

2.1 BACKGROUND 52.2 ACKNOWLEDGEMENT 5

3 PIPE LOCATION TECHNOLOGY 6

3.1 ELECTRONIC METHODS 63.1.1 Physical Principles 63.1.2 Electronic Locators 73.1.3 Applying Pipe Location Techniques with Electronic Methods 83.1.4 Evaluation 10

3.2 ACOUSTIC METHODS 103.2.1 Physical Principle 113.2.2 Evaluation 11

3.3 GEORADAR 113.3.1 Physical Principle and Application 123.3.2 Pipe Location with Georadar 123.3.3 Evaluation 14

4 LOCATING OTHER SERVICE INSTALLATIONS 14

4.1 LOCATING SURFACE BOXES 144.1.1 Magnetic Surface Box Locators 144.1.2 Electric Surface Box Locators 15

APPENDIX 1: MANUFACTURERS ...•.....•.••........................................................•.•....•.••....•..•.....••••••••••..... 15

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Table of Figures

FIGURE I : EVALUATION OF PIPE LOCATION TECHNOLOGIES .4FIGURE 2: CREATION OF AN ELECTROMAGNETIC FIELD DURING THE PIPE LOCATION PROCESS 7FIGURE 3: INSTRUMENTS FOR PIPE LOCATION 8FIGURE 4: LOCATING FERROUS METAL PIPES WITH SEARCH COILS 9FIGURE 5: ACOUSTIC PIPE LOCATION, SOUND PULSES THROUGH THE GROUND TO THE SENSOR 11FIGURE 6: EQUIPMENT FOR ACOUSTIC PIPE LOCATION 12FIGURE 7: EXAMPLES OF GEORADAR RESULTS FROM SWEEP FOR PIPE LOCATION 14

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1 SummaryThe simplest way to trace pipes is by determining the approximate location of the pipe withthe help of visible parts such as valves, hydrants and service boxes etc. The exact locationcan than determined through search trenches. The advantage of this technique is that

- no further training is necessary to apply it,

- all types of pipes can be detected by that method.

The disadvantage is that it is costly since it is time consuming and ties up resources. It alsoalways bears the possibility of damaging the pipes or other utility lines (while excavating) andthe trenches disturb traffic etc. This technique will not be further discussed throughout thisstudy.

The research for suitable methods has identified three categories for pipe location:

1. Electronic methods (Section 3.1)

2. Acoustic methods (Section 3.2)

3. Ground penetrating radar or Georadar (Section 3.3)

In principle all three methods allow for the detection of PVC pipes if adapted to that particularapplication (as in the case for electronic methods). Electronic methods, through inductive orconductive coupling, can be seen as the most established technology while acousticmethods and georadar are relatively new. All three methods require more or less extensivetraining for utility personnel to make full use of the capabilities of the equipment with the mosttraining required for the georadar followed by the acoustic methods. However, four days oftraining is sufficient to successfully apply each of the methods. Figure 1 provides acomparison of the different equipment characteristics in terms of price, accuracy, trainingrequirements and suitability.

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Both the electronic and acoustic methods require access to the pipe to be traced at somepoint, preferably through a hydrant or service box, to place a device into the pipe. This devicecan be either a cable that is then traced by the locator or, as in the case of the acousticmethod, a sound wave generating "sonde". Georadar does not require access to the pipe.

If conditions are favourable and operating personnel are capable the best accuracy isprovided by the georadar since it could be used to create images of the detected pipes,cross-connections, boxes etc. Both acoustic and electronic methods can also determine thedepth of the located pipes. The accuracy here seems to be highly dependent on the qualityof the equipment and its price. Prices range from A$ 500 for the cheapest electronic deviceto more than A$ 55,000 for a fully equipped georadar. Similar observations can be madeabout the range of the respective methods where range is basically the distance betweenany sort of emitting transmitter and the actual locating device.

On consideration of the advantages and disadvantages of each technology it isrecommended that the Tonga Water Board should purchase pipe location equipment basedon the electronic method mainly because of its versatility i.e. it can be used to locate metallicpipes and utility lines without having any physical access to the pipe. That should be of greathelp if any sort of excavation is to be carried out.

2 Introduction

2.1 Background

The present desk study on available and suitable pipe location technologies is the result of arequest brought forward by the Tonga Water Board at the 27th Annual Session of SOPAC inOctober 1998.

Presently the Tonga Water Board has very few reliable maps to indicate the course of watersupply pipes and no system is in use for on-site location of pipes. If maintenance work isrequired, pipes are usually approximately traced with the help of visible parts such ashydrants, valves, service boxes etc. The exact location is then determined by searchtrenches. This approach is time consuming and costly, mainly because of the heavy-dutyequipment required for excavation.

The present desk study aims at identifying available technologies for exact pipe locationconsidering the special circumstances and difficulties in Tonga namely the detection of PVCpipes in an underground partly saturated with seawater.

The outline of this study in electronic, acoustic and georadar methods may appear somewhatartificial since all instruments use electronic equipment to get results. However, the literaturedistinguishes the different physical principles into these categories.

2.2 Acknowledgement

Special credit for this desk study has to be given to Rolf G. Niemeyer, Klaus P. Gilles andBernard Riggers' for their Research Report "Reduction of Water Losses in Drinking WaterSupply Systems in Developing Countries'". The part on pipe location with electronicinstruments has been taken out of this report and only slightly modified.

1 Niedermeyer, R. G. et al (1996): Reduction of Water Losses in Drinking Water Supply Systems, ResearchReports of the Federal Ministry for Economic Cooperation and Development, Volume 120, Weltforum Verlag,K61n.

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3 Pipe Location Technology

3.1 Electronic Methods

Pipe location with electronic instruments is based on the principle of induction inelectromagnetic fields and was originally developed for locating metal pipes. In order tolocate non-metallic pipes (PE, PVC, asbestos cement) it is advisable to lay non-metallictogether with a metal search-line, e.g. a cable of 2 to 4 mrn", location and warning strip.

3.1.1 Physical Principles

If an electric current flows through a conductor, a magnetic field is created. Its lines of forceare concentric circles perpendicular to the conductor's axis. If an alternating current flowsthrough the conductor, an alternating field is created. The strength of the magnetic fielddepends on the current and the distance between the test point and the centre of theconductor. The voltage depends on the position and orientation of the coil or the pipe locatorin the magnetic field. The effects of induction are used for pipe location. The generatedelectromagnetic field can be measured and, by scanning the electromagnetic field withlocators (coils) at the surface, the position of the pipe can be precisely determined. Figure 2gives a general overview about the technology.

In the case of non-metal pipes, a metallic cable or a transmitter can be introduced into thepipe. This can be done using a fibreglass rod (diameter 6 mm, length up to 120 m) with ametal core. The fibreglass rod is rolled off a reel and introduced into the open end of the pipewhose course is to be traced. With the help of a transmitter mounted on the tip of the rod, thetip can be pinpointed with an accuracy in the range of centimetres.

The electromagnetic field surrounding the pipe is created by inductive or conductivecoupling.

Inductive Coupling

In the case of inductive coupling without direct contact, a detectable alternating current isinduced in the pipe that is to be located by means of a frame coil or transmitter tong. Thetransmitter generates an electromagnetic field whose lines of force penetrate the pipe with acertain frequency and are focussed due to the low longitudinal resistance. The secondarycurrent induced creates a secondary field surrounding the pipe. This secondary field can bescanned with the search coil of the receiver.

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Conductive Coupling

In the case of conductive coupling, a direct electric connection between the pipe and thetransmitter is established. The alternating current generated by the transmitter creates anelectromagnetic field surrounding the pipe. This field can be scanned with the search coil andthus allows the pipe to be located.

3.1.2 Electronic Locators

Sophisticated locators for different purposes are available on the market (see Figure 3). Theinstruments consist of a transmitter and search coils (receivers). The transmitters used forelectronic location have an infinitely variable output of 2 to 25 watt and several frequencyranges of around 1 to 10kHz. The transmitters usually have settings for continuous andpulsed output.

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The search coil is used to scan intensity and direction of the electromagnetic fieldsurrounding the pipe that is to be located. The search coil can be inclined, its inclination isvisible from the outside and it can be engaged at an angle of 0°,45° or 90°, so that themaximum and minimum intensity of the field can be measured for the location of pipe courseand laying depth.

The signal is picked up, amplified, and acoustically transmitted to headphones or aloudspeaker and displayed on the instrument. Frequencies around 10kHz, which the humanear can hardly pick up, are transformed into frequencies around 1 kHz, which are moreaudible. The receiver must be precisely adjustable to the frequency of the transmitter or haveautomatic tuning.

In addition to the transmitter and the receiver, the equipment also includes rod probes of 30to 60 em length that are pushed into the ground, as well as clamps, cables, and headphones.

3.1.3 Applying Pipe Location Techniques with Electronic Methods

Location equipment can only be successfully used by qualified personnel. Training shouldinclude the main physical principles. This is the only way to avoid imprecise locations andfailures. Safe use of the equipment is possible only if its operational safety is supervised andthe manufacturer's instructions are followed under all circumstances.

The overwhelming majority of pipe location is being done applying electronic methods. Theconcrete application procedure of this technology is therefore described in this chapter.However, this chapter can be also used as a guideline for the application of acousticmethods.

3.1.3.1 Location with the Minimum-Maximum-Method

Regardless of the type of coupling used, the instrument registers either a maximum or aminimum directly above the pipe, depending on the position of the search coil (horizontalposition = maximum, vertical position = minimum). The minimum-method is more suitable forpinpointing, since it is far easier for the human ear to determine the point at which a signalvanishes than to determine the point of its highest intensity.

If the minimum-method is used for locating a pipe, its position is registered as an audibleminimum or displayed on the instrument. The search coil in its vertical position is movedback and forth. It is simultaneously moved along the suspected course of the pipe.

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If the maximum-method is used for locating a pipe, its position is registered as an audiblemaximum or displayed on the instrument. The search coil in its horizontal position is movedback and forth. It is simultaneously moved along the suspected course of the pipe. Theprinciple of detecting the signal is shown in Figure 4. The maximum current is induced andthe maximum registered when the search coil is directly above the pipe and the lines of forceintersect the search coil longitudinally.

Recommended Use

In the case of inductive coupling, the location of the pipe at the starting point has to be knownto set up the frame coil. If absolutely no information about the location of the pipe isavailable, the maximum-method can be used to approximately locate a starting point. Evenwhen the transmitter is set to maximum output, however, a successful pipe location is not tobe expected if the transmitter is more than 8 to 10m away from the pipe.

If a frame coil is used for inductive coupling in the vicinity of several pipes, there is thedanger of currents being induced in pipes that are not supposed to be located. This can leadto incorrect locations. In the case of pipes with small diameters (e.g. service pipes), selectiveinduction in the pipe that is supposed to be located is possible by means of a bipartite coil(transmitter tong). The danger of incorrect locations can thus be reduced.

In the case of conductive coupling, the cables connecting the transmitter and contact point ofthe pipe to be located (e.g. hydrant, gate valve, etc.) have to be placed far enough from thesearch coil and the pipe to avoid interference. The transitional resistance at the contactpoints should be minimised. Therefore, the contact points have to be cleaned and corrosiondeposits removed. Since every test circuit has its own specified resistance, the output of thetransmitter must be adjusted to the individual test circuit before measurements are taken.

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If it is not possible to establish two contact points on the pipe, one of the contacts can bereplaced by an earthing plug (rod probe) at the end of the course to be traced. In order tominimise the resistance between the earthing plug and the pipe, the plug should be placednear the pipe and in an area of low electric soil resistance.

Whether the inductive or the conductive method produces faster or better results depends onlocal conditions. The inductive method can be efficiently used when circumstances aresimple and pipe courses accessible. In urban areas, the conductive method is more usefuldue to the vast number of different pipes and cables.

3.1 .3.3 Establishing Laying Depth

In order to establish laying depth, the position or the pipe is to be marked. A minimum pointis determined on either side of the pipe with the minimum-method and a search coil inclinedat exactly 45°. The distance between the minimum point and the point marked directly abovethe pipe equals the distance between the surface and the central axis of the pipe.

Establishing a minimum point on both sides is necessary in order to reduce inevitableinaccuracies by averaging. Parallel pipes or cables can falsify results. The transmitter shouldbe set up 20 to 30 m away from the test point while the laying depth is being established.

If the surface is inclined, the result may have to be arithmetically corrected.

In addition to the method described, it is possible to establish laying depth with automaticinstruments. Their accuracy is in the range of decimetres.

3.1.3.4 Longitudinal Electric Conductivity

Welded steel pipes, cast iron pipes and steel pipes with caulking sockets, as well as pipeswith soldered connections of lead or copper have sufficient longitudinal electric conductivityfor a detectable field along the pipe. This is not always the case with rubber packing joints(e.g. screwed sockets and tyton connections), nor with flanged joints if screws and flangersare provided with a corrosion protection coating. Flanged joints with packing rings made ofnon-conductive material may also prevent the creation of an electromagnetic field along thepipe. In the case of conductive coupling, the chances of success can be increased by usinghigher frequencies. In the case of inductive coupling no such improvement can be expected.

Older water pipes often have a certain conductivity. If necessary, conductivity can beprovided for the period of location by introducing a wire or cable into the pipe.

In the case of newer pipes, especially plastic pipes, location can be made possible by meansof auxiliary devices, such as location strips, cables for remote measurements and control.

3.1.4 Evaluation

Pipe location with electronic methods is a well established technology with a wide variety ofrelatively cheap equipment available. It is widely used to locate utility lines throughout theworld. Its disadvantage with respect to locating PVC pipes is that there has to be somephysical access to the pipe which limits the effective search range to about 150 m of thataccess.

However, because of its advantages of requiring relatively little training, its affordable natureand its variety of applications, it is recommended that this method for pipe location in Tongabe used.

3.2 Acoustic Methods

Pipe location with acoustic methods is based on the principle that sound travels at differentspeed through different media. The arrival of sound pulses emitted into the pipe is detectedby sensors which allows calculation of the relative position of the pipe. Figure 5 shows theconfiguration used to pick up the signal.

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3.2.1 Physical Principle

The Acoustic Pipe Locator works by putting a series of sound bursts into the pipe to belocated. These sound pulses travel down the length of the pipe and into the surrounding soil.Sensors on the ground detect the pulses and record their arrival time. The microprocessorcalculates the position of the pipe relative to the sensors based on the difference in arrivaltime of each pulse.

A variation is that a sonde is connected to the pipe that generates a "gentle" water hammer.The pressure variations within the pipe can be located by a geophone. It can only be appliedto pressure pipes.

3.2.2 Evaluation

Both methods within this technology regime require physical access to the pipe. Theexcitation of the pipe is mainly used to locate house connections while the excitation of thewater columns is used to locate pressure pipes up to a distance of 1000 meters away fromthe access point. The application of acoustic methods requires some practice. Figure 6shows a set of equipment used for acoustic pipe location.

3.3 Georadar

Ground-Penetrating Radar (GPR) systems are used to find and image things buried in theground, but also objects in walls or reinforcing bars in concrete. Unlike many methods, GPRcan find non-metallic objects: plastic pipe, dead bodies, even voids. The only requirement isthat the material has different electrical properties than the host material. Ground PenetratingRadar can be used to locate:• Buried utilities, reinforcing bars

• Plastic, cement, asbestos, clay or metal pipes• Underground storage tanks and service lines• Hazardous waste and buried drums, even plastic ones• Archaeological sites: foundations, burial sites, privys, chambers• Forensic targets: bodies, weapons, drugs• Topsoil characteristics and shallow geologic structure• Dinosaur fossils, animal burrows

• UXO: unexploded ordnance, plastic land mines

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3.3.3 Evaluation

The technology has a wide variety of possible applications and enables the creation of 3-Dimages of buried items. It could also be used for geophysical explorations such as location offreshwater lenses The interpretation of the results doubtlessly requires some experience ofthe operating personnel. An application in areas where saltwater might be encountered closeto the surface is not recommended.

A further advantage with respect to pipe location is that no physical access to the pipe isnecessary, though a rough idea of where the pipe should be seems advisable. However, thehigh price of about A$ 55,000 does not seem to justify its application to pipe location only.The purchase of a ground penetrating radar could be justified for countries whereunexploded ordnance represents a risk while undertaking any sort of earth work. But even inthis case electronic instruments should provide a more efficient solution.

4 Locating other ServiceInstallationsSurface installation can also be hard to detect. This is the case in many Pacific IslandCountries where both fast growing vegetation and human activity make it sometimesimpossible to locate valves or meter boxes.

4.1 Locating Surface Boxes

Magnetic and electric surface box locators are used to locate surface boxes. Magneticsurface box locators only detect ferrous metals. Electric surface box locators are able todetect any type of metal.

4.1.1 Magnetic Surface Box Locators

Magnetic surface box locators contain a magnetic needle suspended vertically (vertical axisof rotation), which orients itself vertically under the influence of the earth's magnetic field andcounterweights. A north-arrow visible on the instrument housing has to remain orientedtowards the north. If the instrument is moved into the vicinity of a surface box, the needleregisters the distortion of the earth's magnetic field at this point.

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Another technique makes it possible to locate elongated ferrous metal objects verticallyburied in the ground (e.g. slide rods) directly by means of a magnetically sensitive probe. Themagnetic surface box locator is held about 2 cm above the surface. As soon as theinstrument is in the vicinity of a surface box, the needle is deflected. The surface box can bepinpointed by approaching it from different sides.

If a larger area has to be scanned with the instrument, it is advisable to divide the area intostrips about 30 cm wide along the north-south-axis and pace out these strips, as themagnetic needle is more easily deflected from the north-south-axis than from the east-west-axis.

Several surface boxes lying close together can lead to wrong readings, since their combinedmass tends to form its own north and south pole and the magnetic needle only detects thesouthern most surface box.

Magnetic surface box locators require the earth's magnetic field to be as undistorted aspossible. Their use is thus limited to areas free of large pieces of iron (e.g. railroad tracks,sheet piles). Since the earth's magnetic field is comparatively weak and the location rangedepends on the mass of the surface box, these instruments can locate surface boxes only upto a depth of 40 cm.

4.1.2 Electric Surface Box Locators

In an electric surface box locator, the transmitting coil and the receiving coil are insulated, sothat no induction occurs. The coils get coupled only if the electromagnetic field generated bythe transmitting coil is distorted by pieces of metal. The current induced triggers anacoustical and/or optical signal.

The electric surface box locator is held about 2 cm above the surface. At the point at whichthe signal is triggered, the surface box is located. The surface box can be pinpointed byapproaching it from different sides.

The electric locators have a greater depth range than the magnetic instruments.Unfortunately, however, smaller objects, such as slide rods without surface boxes, are onlydetected if the instrument is directly above them, whereas the needle of a magneticinstrument is also deflected if the object is approached sideways. Sources of interference,such as nails, tin foil or blasting furnace slag, may lead to incorrect locations with this type ofinstrument.

The maximum depth range for locating surface boxes is 80 cm.

Appendix 1: Manufacturers

General

(Severin) Australia Foster Test Equipment Pty Taylor Made PlasticsLtd. 20 S .Unit 1 35 Faundry Road 3. outh Manatee Ave. Arcadia,

, . . Florida 34266Seven.Hllls, N.S.W. 2147, Australia Phone: +1-800-928-1218Phone. 0061-2-96742244 F 1 941 9939953Fax: 0061-296746604 ax . + . - -

E-mail: tmplastlcs@desoto.net

Aquaduct Trading Pty Ltd.

Neva Court Mt. Waverly VictoriaAustralia 3149Phone +61 398861616Fax: +61 398868177E-mail: aguaduct@diesel.net.au

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GeoradarGeoRadar Inc. Emrad Ltd.

19623 Via Escuela Drive Fleet Business Park, Sandy Lane Church,Saratoga, CA 95070 U.S.A. Crookham, HampshirePhone +1 408-867-3792 GU13 OBFEngland.Fax +1 408-867-4900 Phone: +44 1252628880E-mail: dcrice@georadar.com Fax: +44 1252625556

E-mail: enguries@emrad.com

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