WO1999000679A1

WO1999000679A1 - Detecting underground pipes

Info

Publication number: WO1999000679A1
Application number: PCT/GB1998/001881
Authority: WO
Inventors: Andrew Biggerstaff Lewis
Original assignee: Radiodetection Limited
Priority date: 1997-06-26
Filing date: 1998-06-26
Publication date: 1999-01-07
Also published as: GB9713573D0

Abstract

Pressure waves are generated in a pipe (10) containing a dielectric fluid, by providing at least one electrode (11) adjacent to the pipe (10) and means (14) for applying a varying electric signal to the electrode (11) to generate a varying electric field in that pipe (10). The electric field is of a magnitude sufficient to create dipoles in the molecules of the dielectric fluid, and pressure waves are created by the creation and relaxation of these dipoles. A detector (20, 21, 22) detects the pressure waves in the pipe (10) at a point remote from the electrode (11), so enabling the pipe (10) to be detected underground.

Description

DETECTING UNDERGROUND PIPES

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates to the detection of a

pipe by means of pressure waves in the pipe.

SUMMARY OF THE PRIOR ART

US-A-5269335 discloses a method of detecting a

buried pipe, in which pressure waves were generated in

the pipe. Those pressure waves passed down the pipe and

outwardly of the pipe. They could therefore be detected

by sensors adjacent to the ground surface. By providing

two sensors, at spaced apart locations, it was possible

to determine the location of the pipe relative to the

sensors, and a reference sensor could be used to allow

distance measurement along the pipe by monitoring the

change in energy levels of the pressure waves detected.

In US-A-5269335, the pressure waves in the pipe were

generated by a valve which controlled the flow of water

in the pipe. Thus by causing the water to intermittently

flow and be shut off, a water hammer effect was generated

in the pipe, thereby generating the pressure waves.

This method has the disadvantages that a water flow

is needed in the pipe, and that the normal operation of the pipe has to be interrupted.

US-A-5553498, discloses a method of detecting a

buried pipe , in which it is the pipe itself which is

excited, by a vibration device attached to its wall. The

vibrating pipe is detected in a similar way to US-A-

5269335. Although this method does not require an

interruption of the normal operation of the pipe, it does

impose a large strain on the pipe at the vibration site.

SUMMARY OF THE INVENTION

The present invention proposes that a dielectric

fluid in a pipe made of insulating material is excited by

the generation of a pulsed or alternating electric field

in the pipe. The field is generated by at least one

electrode adjacent the pipe, to which is applied pulsed

or alternating electric signals. The preferred

dielectric fluid is fuel gas, although any other fluid

with appropriate dielectric properties could be carried

in the pipe to be located.

The electric field creates a dipole in the

molecules, which repel each other. This repulsion, which

is repeated due to the pulsing of the electric field,

causes pressure waves, e.g. acoustic waves, in the fluid

in the pipe which can be detected at a point removed from the location of the electrode. The detection arrangement

may be similar to that used in US-A-5269335, or any other

suitable detection arrangement. In this invention the

pressure waves are generated by the at least one

electrode.

The at least one electrodes are conveniently

provided in an assembly where they are encased in an

insulating material and insulated from each other, if

more than one is present. If a single electrode is used,

the signal is generated relative to ground, using the

part of the pipe not adjacent the electrodes as ground.

However, if more than one electrode is used to form an

electrode assembly, a signal return path may be defined

from the electrodes. The electrodes may be arranged

along the length of the pipe, or be arranged on opposite

sides of the pipe. With a plurality of electrodes, and

appropriate signal generation a travelling or

"peristaltic" wave can be set up in the fluid in the

pipe.

The electrode assembly may be of an suitable shape

to be placed adjacent the pipe, although one preferred

arrangement is for the assembly to be in the two-part

annular form which completely surrounds the pipe. The signal characteristics of the applied electric

signal are usually discrete pulses at regular intervals,

i.e. a square wave, with a frequency of about 300Hz.

However, the signal applied may take another form and/or

be modulated so that a different signal characteristic

may be assigned to each pipe which is to be located.

It should be noted that, where the dielectric fluid

is a gas, such as fuel gas, the magnitude of the electric

field should be less than that magnitude which would

cause electrical discharge in, or ionisation of, the gas.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be

described in detail, by way of example, with reference to

the accompanying drawings, in which:

Fig. 1 shows a schematic view of the operation of a

locator embodying the present invention;

Fig. 2 shows in more detail the electrode assembly

of Fig. 1; and

Fig. 3 shows an alternative construction of the

electrode assembly of Fig. 1; and

Fig. 4 shows in more detail the detector of the

embodiment of Fig. 1.

DETAILED DESCRIPTION Referring first to Fig. 1, a pipe 10 which is to be

located at a remote site A is accessed from an access

hole 16. This hole 16 may either be a standard access

hole or one excavated especially for the purpose of this

pipe location. An electrode assembly 11 is sited around

the pipe 10 at a transmission site B, in the hole 16.

The electrode assembly 11 may also be placed on a

standpipe or other similar pipe extending from the pipe

10 above the surface 15 of the ground. Another possible

arrangement is for the electrode assembly 11 to be fitted

to the pipe 10 before it is buried, with an electrical

connection point for the electrode assembly 11 to be

provided at a suitable location.

The electrode assembly 11 as illustrated is

connected to a signal generator 14. In operation, the

signal generator 14 sends a pulsed electric signal to the

electrode assembly 11, which generates a pulsed electric

field in the pipe 10. A signal return path from the

electrode assembly 11 to the signal generator 14 is also

present .

The pulsed electric field causes pressure waves in

the fluid in the pipe 10. Pressure waves therefore move

outwardly from the site B. The main path of transmission is through the fluid in the pipe 10 but some vibrational

energy will radiate outwardly from the pipe 10 along its

length.

As a result, sensors 20 and 21 at the detection site

A will be able to sense vibrational energy transmitted

from the pipe 10 through the ground. The sensors 20, 21

may thus be mounted close to the surface 15 of the

ground. The sensors 20, 21 pass signals to a detector

22, and the analysis of those signals enable an operator

to determine whether the pipe has been located correctly.

Whilst the presence of the pipe carrying the vibrational

energy can be detected by one sensor 20, 21, the use of

two sensors enables the location of the pipe 10 at the

detection site A to be determined more accurately. If it

is found that the sensors 20, 21 are aligned with the

pipe, and spaced along it, it may also be possible to

determine the distance between the detection site A and

the transmission site B by the change in vibrational

energy levels between the sensors 20, 21. Alternatively,

a further sensor (not shown) may be provided connected at

detector 22, but spaced between the detection site A and

the transmission site B.

The signal from the signal generator 14 may generate a simple pulsed electric signal, i.e. a square wave.

However, if desired, a modulation may be applied to

enable different pipes to be identified. In such

circumstances, it may be useful for the signal generator

14 to signal its modulation to the detector 22, shown by

arrow 23.

Fig. 2 illustrates a construction of the electrode

assembly 11. The assembly 11 contains three electrodes

13A, 13B, 13C which are encased in insulating material

12. The central electrode 13B receives the generated

signal from the signal generator 14, and the outer

electrodes 13A, 13C, which are electrically connected

together, form the start of the return path to the signal

generator 14. The insulating material 12 is thick enough

to prevent its dielectric breakdown on the application of

te electric signal across the electrodes 13A, 13B, 13C.

The assembly 11 is provided in a two part annular

form, designed to completely encompass the pipe 10. The

two parts are connected together by standard means such

that each of the electrodes 13A, 13B, 13C forms a

complete ring about the pipe 10. However, another or of

the electrode assembly envisaged is a flexible sleeve of

insulating material containing flexible electrodes, so that the electrode assembly can fit round pipes of ^~

varying diameters, being secured in place by straps or

the like.

Fig. 3 illustrates an alternative construction for

the electrode assembly 51. In this embodiment, the

assembly 51 has two parts 51A, 51B disposed diametrically

opposite each other, which are linked to the signal

generator 14 as in Fig. 2. The electric field produced

is therefore directed across the pipe 10 within the

length of the electrode assembly 51. Each of the two

parts 51A, 51B has one electrode 53A, 53B, encased in an

insulation layer 52A, 52B. The two parts 51A, 51B of the

electrode assembly 51 are of a suitable axial length to

produce the desired results.

The signal applied by the signal generator should

have a frequency preferably in the low audio hand e.g.

300Hz, and in the form of a pulsed signal, i.e. a square

wave. As mentioned above, the signal may be take another

form and/or modulated to make the location of a number of

pipes easier to di ferentiate. The size of the signal

may be any suitable voltage, although lOkV or more is

preferred.

Referring now to Fig. 4, the detector 22 has an analog input 41 connected to each of the sensors 20 ,^~ 21.

Each sensor 20, 21 includes a geophone 43. Only one

geophone 43 is shown in Fig. 3, but there will be one for

each sensor 20, 21. The geophone 43 passes signals to

the input 41, and from there to a processing unit 46.

Power for the detector 22 is obtained from a battery pack

47, power from which is passed by a power control unit 48

to the processing unit 46 and the input 41. The

processing unit 46 also controls the power control unit

48. The processing unit 46 uses a program stored in a

memory 49 to analyse the signals from the geophone 43 to

generate a display which displayed on a display unit 50

to indicate the results of the detection of the acoustic

waves. The processing unit 46 may also have as an input

the modulation 23 (not shown) applied by the signal

generator 14, so as to ensure the location of the correct

pipe. A key pad 51 permits the user to input commands to

the processing unit 46 and to the power control unit 48.

Claims

1. A device for generating pressure waves in a pipe

containing a dielectric fluid, comprising at least one

electrode located adjacent the pipe and means for

applying a varying electric signal to said electrode so

as to generate a varying electric field in the pipe, at

least the maximum value of the electric field being

sufficient to create dipoles in the molecular of the

dielectric fluid, the pressure waves being generated by

the creation and relaxation of these dipoles.

2. A device according to claim 1, having two

electrodes, with the signal being applied between the

electrodes .

3. A device according to claim 2 , wherein each of said

electrodes is curved so as to conform to the pipe, the

electrodes forming a broken annulus around the pipe.

4. A device according to claim 1 having a single

electrode, with the signal being applied between the

electrode and ground.

5. A device according to any one of the preceding

claims, wherein the at least one electrode is encased in

insulating material.

6. An apparatus for detecting a pipe comprising a device according to any one of the preceding claims^"

mounted on the pipe, and at least one detector for

detecting the pressure waves in the pipe at a point

remote from the electrode.

7. A method of generating pressure waves in a pipe

containing a dielectric fluid, in which a varying

electric signal is generated in the pipe so as to

generate a varying electric field in the pipe, at least

the maximum value of the electric field being sufficient

to create molecular dipoles in the dielectric fluid, so

that pressure waves are generated by the creation and

relaxation of those dipoles.

8. A method of detecting a buried pipe containing a

dielectric fluid, the method comprising:

generating pressure waves at a first point in the

pipe by generating a varying electric signal in the pipe,

so as to generate a varying electric field in the pipe,

at least the maximum value of the electric field being

sufficient to create molecular dipoles in the dielectric

fluid, so that so that pressure waves are generated by

the creation and relaxation of those dipoles; and

detecting the pressure waves in the pipe at a second

point remote from the first point.