FIELD OF THE INVENTION

The invention relates to a method and apparatus for assessing a pipe system.

Embodiments of the invention are particularly adapted for use in assessing pipe wall condition and/or condition of a valve within a pipe system.

BACKGROUND OF THE INVENTION

Pipe condition assessment plays an important role within the asset management cycle for water supply infrastructure. The condition assessments of water network

infrastructure can be challenging as major assets are often buried, placed adjacent to busy main roads, or supplying critical water demands where service disruptions are not desirable.

Condition assessment information that is useful for asset management includes the condition of seals on isolation valves, and pipe wall condition assessment.

There are several commercially available tools for condition assessment. Each of these suffers from its own limitations. These limitations include restrictions on pipe diameter, material type, flow conditions, network access, and service requirements. These techniques are typically short-range, sensitive to background noise, and/or require the pipe system to be shut down in order for them to be applied. For example, closed-circuit television techniques require the water system to be shut down to enable the camera to be moved through the pipe system.

Passive acoustic techniques involve listening for a 'hissing' sound that would indicate faulty valves. Effectively this requires the traffic near to the suspected defect to be shut down as the technique is sensitive to background noise. Restricting traffic flow has the potential to place significant cost onto the detection technique. The technique itself works reasonably well for concrete and steel pipes. However the technique does not work so well for plastic pipes as the plastic tends to attenuate the noise.

Other techniques involve 'smart balls'. They require the pipe system to be pressurised. Loss of the smart balls is not unknown. Such techniques take several hours to set up. A further technique is a 'listening stick'. A person listens for water whistling through a faulty valve. This technique is not so suitable for larger systems in which the valve must be almost totally turned off before a whistle can be detected. The test has to be operated in a quiet setting. One technique involves introducing small amplitude pressure signals into a pipe system. The physical characteristics of the system, such as the pipe wall condition and valve status, will affect the propagation of the pressure wave. Analysis of the wave

propagation within a system coupled with an understanding of transient flow behaviour can provide insights to the condition of a pipe system or its components. United States patent application publication US 2012/0041694 to Stephens et al/Adelaide Research & Innovation Pty Ltd describes a method and system for assessing the condition of a pipe carrying a fluid. The method generates a low frequency pressure wave in the fluid being carried along the pipe and detects a pressure wave interaction signal resulting from an interaction of the pressure wave with a localised variation in pipe condition. The method determines, from the timing of the pressure wave interaction signal, the location of the localised variation on pipe condition.

It is an object of preferred embodiments of the present invention to address some of the aforementioned disadvantages. An additional or alternative object is to at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a method of determining a pipe wall condition and/or pipe valve condition within a pipe system, the method comprising introducing a pressure signal at a frequency greater than 30 Hz to fluid at a first connection point at a local station within the pipe system, measuring propagation of the pressure signal through the fluid within the pipe system at a second connection point at a remote station within the pipe system, and/or measuring reflection of the pressure signal through the fluid within the pipe system at the first connection point at the local station within the pipe system; and determining a pipe wall condition and/or pipe valve condition at least partly from the propagated and/or reflected pressure signal.

Correlatively, the invention also relates to a pipe line assessment system comprising : a signal generating component configured to introduce a pressure signal at a frequency greater than 30 Hz to fluid at a first connection point at a local station within a pipe system; a first signal measuring component configured to measure propagation of the pressure signal through the fluid within the pipe system at a second connection point at a remote station within the pipe system, and/or measure reflection of the pressure signal through the fluid within the pipe system at the first connection point at the local station within the pipe system; and a pipe condition determiner configured to determine a pipe wall condition and/or a pipe valve determiner configured to determine a pipe valve condition at least partly from the propagated and/or reflected pressure signal.

The term 'comprising' as used in this specification means 'consisting at least in part of. When interpreting each statement in this specification that includes the term

'comprising', features other than that or those prefaced by the term may also be present. Related terms such as 'comprise' and 'comprises' are to be interpreted in the same manner.

In a particular embodiment the pipe wall condition corresponds to the thickness of the pipe wall.

In other embodiments, the determination of the pipe wall condition may notably consist in a diagnosis of valve sealing, or the identification of air-pockets or the identification of obstructions.

Preferably, the method and/or the signal generating component further comprise a piezo-electric actuator introducing the pressure signal to the first connection point within the pipe system. Preferably the piezo-electric actuator is adapted to generate a pressure signal to the fluid at a frequency within the range of 100 Hz to 44 kHz.

Preferably the piezo-electric actuator is adapted to generate a pressure signal to the fluid at a frequency within the range of 500 Hz to 44 kHz.

Preferably the piezo-electric actuator is adapted to generate a pressure signal to the fluid at a frequency within the range of 1 kHz to 44 kHz.

Preferably the piezo-electric actuator is adapted to generate a pressure signal to the fluid at a frequency within the range of 100 Hz to 3.5 kHz. Preferably the piezo-electric actuator is adapted to generate a pressure signal to the fluid at a frequency within the range of 500 Hz to 3.5 kHz.

Preferably the piezo-electric actuator is adapted to generate a pressure signal to the fluid at a frequency within the range of 1 kHz to 3.5 kHz. Preferably, the method further comprises selecting the pressure signal such that the pressure signal is distinct from background noise within the pipe system.

Correlatively, the signal generating component may be configured to select the pressure signal from a signal types database such that the pressure signal is distinct from background noise within the pipe system. Preferably, the method further comprises selecting the pressure signal from a group of signal types comprising constant frequency sine wave, repeating frequency sweep signal, pseudo random binary signal, randomised time and frequency signal, and white noise.

Correlatively, the signal generating component may be configured to select the pressure signal from a signal types database in which is stored a plurality of signal types from a group of signal types comprising constant frequency sine wave, repeating frequency sweep signal, pseudo random binary signal, randomised time and frequency signal, and white noise.

Preferably, the method further comprises introducing a plurality of pressure signals to the fluid at a predetermined interval. Correlatively, the signal generating component may be configured to introduce a plurality of pressure signals to the fluid at a predetermined interval.

Preferably, the method further comprises introducing the plurality of pressure signals to the fluid at a predetermined interval selected from the range of 5 seconds to 15 seconds.

Correlatively, the signal generating component may be configured to introduce the plurality of pressure signals to the fluid at a predetermined interval selected from the range of 5 seconds to 15 seconds.

Preferably, the method further comprises introducing the plurality of pressure signals to the fluid at a predetermined interval comprising 10 seconds.

Correlatively, the signal generating component may be configured to introduce the plurality of pressure signals to the fluid at a predetermined interval comprising 10 seconds. Preferably the plurality of pressure signals comprises the same signal type.

Preferably the first connection point and the second connection point respectively comprise one of a fire hydrant, a service point, and a supply connection.

Preferably, the method and/or the the signal measuring component further comprise a pressure transducer measuring the propagated pressure signal at the second connection point within the pipe system.

Preferably propagation of the pressure signal through the fluid within the pipe system comprises measuring a magnitude of the pressure signal at the remote station.

Correlatively, the signal measuring component may be configured to measure a magnitude of the pressure signal at the remote station.

Preferably, the location of the local station and a location of the remote station is such that the pipe system includes an inline valve positioned between the local station and the remote station.

Preferably, the method further comprises: introducing the pressure signal to the fluid at the local station and measuring the magnitude of the propagated pressure signal at the remote station while the inline valve is in a substantially open position; introducing the pressure signal to the fluid at the local station and measuring the magnitude of the propagated pressure signal at the remote station while the inline valve is in a substantially closed position; comparing the measured amplitudes of the pressure signal at the remote station when the inline valve is in a substantially open position and in a substantially closed position respectively; determining the expected magnitudes of the pressure signal at the remote station when the inline valve is in a substantially open position and in a substantially closed position respectively at least partly from the comparison of the measured amplitudes; determining a pipe valve condition of 'poorly sealed' if the measured amplitude of the pressure signal substantially exceeds the expected magnitude of the pressure signal when the inline valve is in a substantially closed position; and determining a pipe valve condition of 'well sealed' if the measured amplitude of the pressure signal does not exceed the expected magnitude of the pressure signal when the inline valve is in a substantially closed position.

Correlatively, in a particular embodiment of the system of the invention : the signal measuring component is configured to measure the magnitude of the propagated pressure signal at the remote station while the inline valve is in a

substantially open position and while the inline valve is in a substantially closed position, and compare the measured amplitudes of the pressure signal at the remote station when the inline valve is in a substantially open position and in a substantially closed position respectively; and the pipe valve determiner is configured to determine a pipe valve condition of 'poorly sealed' if the measured amplitude of the pressure signal substantially exceeds an expected magnitude of the pressure signal when the inline valve is in a substantially closed position, and configured to determine a pipe valve condition of 'well sealed' if the measured amplitude of the pressure signal does not exceed the expected magnitude of the pressure signal when the inline valve is in a substantially closed position

Preferably, the method further comprises determining an expected wave speed of the pressure signal.

Preferably, the method further comprises determining the expected wave speed of the pressure signal at least partly from one or more of pipe nominal diameter, expected pipe wall thickness, and material elastic modulus.

Preferably, the method further comprises determining the pipe nominal diameter, expected pipe wall thickness and/or material elastic modulus from at least one manufacturing code. Preferably, the method further comprises determining the distance of the at least part of the pipe system between the local station and the remote station at least partly from spatial data comprising one or more of as built drawings, GIS, and onsite surveys.

In another aspect, the invention relates to a computer-readable medium having stored thereon computer-executable instructions that, when executed by a processor, cause the processor to perform at least part of the method described above. In another aspect, the invention relates to a pipe line assessment system comprising a storage device, a display anda processor programmed to perform at least part of the method described above.

The term 'connected to' includes all direct or indirect types of connection or

communication, including physical connection, wired and wireless, via a cellular network, via a data bus, or any other computer structure. It is envisaged that they may be intervening elements between the connected integers. Variants such as 'in

communication with', 'joined to', and 'attached to' are to be interpreted in a similar manner. Related terms such as 'connecting' and 'in connection with' are to be

interpreted in the same manner.

The invention in one aspect comprises several steps. The relation of one or more of such steps with respect to each of the others, the apparatus embodying features of construction, and combinations of elements and arrangement of parts that are adapted to affect such steps, are all exemplified in the following detailed disclosure.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

In addition, where features or aspects of the invention are described in terms of Markush groups, those persons skilled in the art will appreciate that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

As used herein, Xs)' following a noun means the plural and/or singular forms of the noun.

As used herein, the term 'and/or' means 'and' or Or' or both.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9, and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5, and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents or such sources of information is not to be construed as an admission that such documents or such sources of information, in any jurisdiction, are prior art or form part of the common general knowledge in the art.

Although the present invention is broadly as defined above, those persons skilled in the art will appreciate that the invention is not limited thereto and that the invention also includes embodiments of which the following description gives examples.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred forms of the method and apparatus for detecting defects in a pipe system will now be described by way of example only with reference to the accompanying figures in which :

Figure 1 shows a preferred form system 100 for assessing the condition of a pipe and/or pipe fitting within a pipe system; Figure 2 shows a preferred form apparatus for introducing a pressure signal to the pipe system and/or measuring propagation of the pressure signal through the pipe system;

Figure 3 shows additional components of the system of figure 2;

Figure 4 shows a simplified block diagram of a device forming at least part of a computing device on which one or more of the components of Figure 3 are implemented; Figure 5 shows a preferred form method for determining a pipe valve condition;

Figure 6 shows an example data display of a valve in good condition;

Figure 7 shows an example data display of a valve in poor condition; Figure 8 shows a preferred form method for assessing pipe wall condition; Figure 9 shows an example of an input signal generated by the signal generating component of figures 2 and 3;

Figure 10 shows an example of the time series data measured at the local station; Figure 11 shows an example of the time series data measured at the remote station;

Figure 12 shows a graphical example of the correlation strength of the signal with time at the local measurement station; and

Figure 13 shows a graphical example of the correlation strength of the signal with time at the remote measurement station.

DETAILED DESCRIPTION

Figure 1 shows a preferred form system 100 for assessing the condition of a pipe and/or pipe fitting within a pipe system. The pipe system typically includes a main transmission pipe 105.

The pipe system includes a plurality of connection points. These connection points are typically spaced approximately 100 metres from each other. Connection points typically include one or more of a fire hydrant, a service point, and a supply connection. Figure 1 shows a first connection point 110 and a second connection point 115. Both connection points are shown as fire hydrants. It will be appreciated that one or both connection points could alternatively comprise a service point or supply connection.

Attached to one or both connection points 110 and 115 is a riser pipe or respective riser pipes. The connection points are typically subterranean. The riser pipes extend upwardly from the connection points above the surface. Figure 1 shows riser pipe 120 fitted to first connection point 110 and riser pipe 125 fitted to second connection point 115. In one embodiment, riser pipe 120 and/or riser pipe 125 are permanently mounted to connection point 110 and/or connection point 115 respectively. In another embodiment riser pipe 120 and/or riser pipe 125 is/are removably mounted to connection point 110 and/or connection point 115. In an embodiment the main transmission pipe 105 includes at least one pipe fitting. An example of a pipe fitting includes an inline valve. In one embodiment the locations of the first connection point 110 and the second connection point 115 are selected so that the pipe system includes an inline valve 130 positioned within the pipe system between the first connection point 110 and the second connection point 115. Main transmission pipe 105 includes a fault 135. A fault is typically a section of pipe having a reduced wall thickness due to pipe age or degradation. Other examples of faults include blockages, air pockets, and burst sections.

As will be more particularly described below, a pressure signal is introduced to fluid at the first connection point 110. The propagation of the pressure signal through fluid within the pipe system is measured at the second connection point 115. It will be appreciated that the pressure signal is alternatively introduced at the second connection point 115 and measured at the first connection point 110. The connection point at which the pressure signal is introduced is notionally referred to as a local station. The connection point at which propagation of the signal is measured is notionally referred to as a remote station.

Figure 2 shows a preferred form apparatus for introducing a pressure signal to the pipe system and/or measuring propagation of the pressure signal through the pipe system. The preferred form apparatus 200 includes one or both of a signal generating component 205 and a signal measuring component 210. In one embodiment, apparatus 200, 205, and/or 210 is/are removably connected to the first connection point 110 and/or the second connection point 115 of Figure 1. In another embodiment apparatus 200, 205, and/or 210 is/are removably connected to riser pipe 120 and/or riser pipe 125.

The signal generating component 205 includes a piezo-electric actuator 215, an amplifier 220, and a data logger 225. Component 205 is configured to generate a customised pressure signal within the pipe system. The signal is preferably chosen such that it is distinct from any background noise within the pipe system. Another factor in choosing a signal is the ability to transmit the signal a suitable distance within the pipe system.

The preferred form signal has a frequency greater than 30 Hz. In various embodiments, component 205 is configured to generate a pressure signal to the fluid within the pipe system at a frequency within one of more of the following ranges:

• 100 Hz to 44 kHz

• 500 Hz to 44 kHz

• 1 kHz to 44 kHz · 100 Hz to 3.5 kHz

• 500 Hz to 3.5 kHz

• 1 kHz to 3.5 kHz. In one embodiment signal generating component 205 is configured to select a pressure signal from a group of signal types comprising constant frequency sine wave, repeating frequency sweep signal, pseudo random binary signal, randomised time and frequency signal, and white noise. These signal types are further described below: constant frequency sine wave - a single frequency signal repeating frequency sweep (chirp) signal - the sweep rate is either positive or negative. In various embodiments it is linear, quadratic or logarithmic.

Pseudo random binary signal (PBRS) - various embodiments are such that each pulse within the signal comprises a fixed frequency or a chirp function for a random or fixed length of time. The 'off component of the PBRS contains no generated signal or can include an inverted pulse.

Randomised time and frequency signal - the signal sweeps between randomly selected frequencies within specified bounds across randomly selected time intervals within specified bounds. White noise - the signal comprises white noise filtered within specified frequency bounds.

One or more of the above signal types is generated for a fixed or predetermined length of time. In a further embodiment a plurality of pressure signals is introduced to the fluid at a predetermined interval. Repeating transmission of the signals in this way improves signal-to-noise ratios and assists with signal processing and analysis. As described above, the signal measuring component 210 is configured to measure propagation of the pressure signal through the fluid. The pressure signal is introduced at the local station and is measured at the remote station.

A preferred form signal measuring component 210 includes a pressure transducer 230, a filter 235, and a data logger 240. Component 210 is configured to record pressure measurements at a suitably high sampling rate to ensure the full bandwidth of the signal can be accurately captured. It will be appreciated that filter 235 is an optional component of measuring component 210. In an embodiment, signal filtering and processing is performed by a processor remote from measuring component 210.

Additional filtering is optionally performed by filter 235. The partially filtered and/or raw signal measurements are stored in data logger 240 for subsequent retrieval.

Figure 3 shows additional components of the system. Signal generating component 205 is connected to a signal types database 300 in which is stored a plurality of signal types. As described above, suitable signal types are selected from the signal types database 300 which are then introduced to the pipe system by signal generating component 205.

Signal measuring component 210 is connected to a plurality of components. It will be appreciated that one or more of these components in one embodiment is/are

implemented as computer executable instructions that are executed by a general purpose processor. The components are described as logical modules characterised by their respective functions.

A signal processor 320 is configured to perform analysis on the data measured by the signal measuring component 210. In an embodiment, the signal processor 320 is configured to apply one or more of the following techniques:

• Band pass filtering

• cross correlation, match filtering.

These techniques are described in more detail below. The signal measuring component 210 is configured to measure the strength of the signal transmission as well as the transmission time of the signal. Both the measured strength and the transmission time are stored for example in data logger 240.

The wave speed calculator 325 determines the wave speed of the signal. In an embodiment the wave speed calculator 325 determines the wave speed at least partly from the distance the pressure signal travels and the recorded time for the pressure signal to travel that distance. The recorded time comprises the measured signal transmission duration.

The distance between the local station and the remote station is determined in one embodiment at least partly from spatial data. Examples of spatial data include as built drawings, GIS, and onsite surveys.

The functions of the pipe condition determiner 330 and the pipe valve determiner 335 are more particularly described below. In an embodiment the pipe condition determiner 330 determines or at least infers a pipe wall condition. In an embodiment the pipe valve determiner 335 determines a pipe valve condition. In one embodiment the signal types database 300 and at least part of the signal generating component is maintained on computing device 340. In another embodiment one or more of the signal processor 320, wave speed calculator 325, pipe condition determiner 330, and pipe valve determiner 335 is/are maintained on computing device 345.

In another embodiment the one or more of the components maintained on computing devices 340 and/or 345 are alternatively or additionally maintained on computing device 350.

In another embodiment one or more of the components is/are implemented within a microprocessor located within, or at least connected to, the signal measuring component 210 and/or the signal measuring component 210. Figure 4 shows a simplified block diagram of a device forming at least part of a computing device on which one or more of the components of Figure 3 are implemented.

Sets of computer executable instructions are executed within device 400 that cause the device 400 to implement the components described above. The device may also include any other machine capable of executing a set of instructions that specify actions to be taken by that machine. These instructions can be sequential or otherwise.

A single device 400 is shown in Figure 4. The term "computing device" also includes any collection of machines that individually or jointly execute a set or multiple sets of instructions to perform any one or more of the methods described above.

The example computing device 400 includes a processor 405. One example of a processor is a central processing unit or CPU. The device further includes read-only memory (ROM) 410 and random access memory (RAM) 415. Also included is a Basic Input/Output System (BIOS) chip 420. The processor 405, ROM 410, RAM 415 and the BIOS chip 420 communicate with each other via a central motherboard 425.

Computing device 400 further includes a power supply 430 which provides electricity to the computing device 400. Power supply 430 may also be supplemented with a rechargeable battery (not shown) that provides power to the device 400 in the absence of external power.

Also included are one or more drives 435. These drives include one or more hard drives and/or one or more solid state flash hard drives. Drives 435 also include optical drives. Computing device 400 may also comprise a sound and/or graphics card 445 to support the operation of the data output device 460 described below. Computing device 400 further includes a cooling system 450 for example a heat sink or fan. Computing device 400 includes one or more data input devices 455. These devices include a keyboard, touchpad, touchscreen, mouse, and/or joystick. The device(s) take(s) input from manual keypresses, user touch with finger(s) or stylus, spoken commands, gestures, and/or movement/orientation of the device. Data output device(s) 460 include(s) a display and/or printer. Device(s) 460 may further include computer executable instructions that cause the computing device 400 to generate a data file such as a PDF file.

Data port 465 is able to receive a computer readable medium on which is stored one or more sets of instructions and data structures, for example computer software. The software causes the computing device 400 to perform one or more of the methods or functions described above. Data port 465 includes a USB port, Firewire port, or other type of interface. The computer readable medium includes a solid state storage device. Where drives 435 include an optical media drive, the computer readable medium includes a CD-ROM, DVD-ROM, Blu-ray, or other optical medium. Software may also reside completely or at least partially within ROM 410, within erasable non-volatile storage and/or within processor 405 during execution by the computing device 400. In this case ROM 410 and processor 405 constitute computer-readable tangible storage media.

Figure 5 shows a preferred form method 500 for determining a pipe valve condition. An example pipe valve is the inline valve 130 shown in figure 1. The valve is set 505 to a fully open position. At least one pressure signal is introduced 510 into the pipe system at the local station while the valve is fully open. The transmission strength of the pressure signal is measured 515 at the remote station.

The valve is set 520 to a fully closed position. Steps 510 and 515 are repeated. These steps are shown at 525 and 530 respectively.

It will be appreciated that steps 520, 525, and 530 in one embodiment are performed after steps 505, 510 and 515. In a further embodiment steps 520, 525, and 530 are performed before steps 505, 510, and 515. It will also be appreciated that any one or more of these steps is able to be repeated.

It is expected that the transmission strength of the pressure signal will be greater when the valve is fully open than when the valve is fully closed. The difference between the two measurements is known as the transmission reduction. The transmission reduction is determined 535 as the difference between the transmission strength measured at 515 and the transmission strength measured at 530.

The pipe valve condition is then determined 540 at least partly from a comparison of the transmission reduction determined at 535 and an expected transmission reduction.

A valve that will not fully shut allows water to pass through even when the valve is set to a fully closed position. Such a poorly sealed valve will maintain a hydraulic connection through the valve face. Water and pressure signals will transmit through the valve. A well-sealed valve on the other hand will provide no hydraulic mechanism for water or pressure signals to pass. Signal transmission through the valve will therefore be minimal .

Figure 6 shows an example of a valve in good condition. Shown at 600 is the measured transmission strength at the remote station when the valve is in a fully open position.

Shown at 605 is the measured transmission strength when the valve is in a fully closed position. It can be observed that there is no significant measured transmission of the pressure signal. The transmission reduction is significant leading to a determination that the pipe valve is in good condition.

Figure 7 shows an example of a valve in poor condition. Shown at 700 is the measured transmission strength at the remote station when the valve is in a fully open position. The measured transmission strength pattern is similar to that shown at 600 in figure 6.

Shown at 705 is the measured transmission strength when the valve is in a fully closed position. There is no significant transmission reduction. This leads to a determination that the pipe valve is in poor condition. Figure 8 shows a preferred form method 800 for assessing pipe wall condition. At least one pressure signal is introduced 805 into the pipe system at the local station. The transmission duration of the pressure signal is measured 810 at the remote station.

At 815 the observed wave speed is determined. In one embodiment the wave speed calculator 325 from figure 3 determines the observed wave speed as:

L

dt

In the above equation :

a is the average measured wave speed for the pipe section, L is the length of pipe, and

dt is the transmission duration.

Comparison of the observed wave speed with the theoretical wave speed enables condition of the pipeline to be determined in terms of the change in the pipe wall thickness or the elastic modulus of the pipe materials.

In an embodiment, a theoretical wave speed is determined by:

In the above equation :

K is the fluid bulk modulus,

p is the fluid density,

E is the elastic modulus of the pipe material,

D as the pipe diameter,

e is the pipe wall thickness, and

cl is a constant which accounts for pipe fixity conditions.

The pipe wall condition is determined 825 by the pipe condition determiner 330 of figure 3. Wave speed is governed by the structural integrity of the pipeline. Significant differences between the observed wave speed and the expected wave speed indicate impairment to the structural integrity of the pipeline.

The following table provides examples.

Observed Wave speed Expected wave speed

Assessed condition

(m/s) (m/s)

431 +/- 2.3 387 - 460 Good

380 +/- 2 387 - 460 Good

396 +/- 11.6 387 - 460 Good

848 +/- 0.3 1059 - 1070 Poor

1022 +/- 0.7 1059 - 1070 Poor 1019 +/- 0.6 1059 - 1070 Poor

1055 +/- 0.4 1059 - 1070 Reduced

1002 +/- 0.0 1059 - 1070 Poor

925 +/- 0.4 967 - 978 Poor

1009 +/- 0.5 972 - 984 Good

1044 +/- 0.6 972 - 984 Good

1055 +/- 1.2 972 - 984 Good

1079 +/- 0.8 1311 - 1395 Poor

989 +/- 0.8 1311 - 1395 Poor

1095 +/- 1.1 1199 - 1329 Poor

Figure 9 shows an example of an input signal generated by the signal generating component 205. In this embodiment the signal is a randomised time and frequency domain signal. The signal is repeated at 10 second intervals to improve the signal to noise ratio and improve signal processing capabilities.

In one embodiment the local station includes both a signal generating component 205 and a signal measuring component 210.

Figure 10 shows an example of the time series data measured at the local station.

Figure 11 shows an example of the time series data measured at the remote station.

The measurements shown in figures 10 and 11 include generated and background noise components.

As described above, in one embodiment the local station and the remote station each include both a signal generating component 205 and a signal measuring component 210. Referring to figure 1, the first connection point 110 and the second connection point 115 have positioned between them a main transmission pipe 105. In one embodiment a riser pipe 120 is attached to first connection point 110. In another embodiment a riser pipe 125 is attached to the second connection point 115. In a further embodiment both the first connection poi nt 110 and the second connection point 115 have respective riser pipes attached to them .

In one embodiment the signal processor 320 is configured to perform a cross correlation method to determine the transmission duration between the local station and the remote station . A preferred form correlation function is given by : c(m) = [R _xy {m - N)]™ ^~

in the a bove equation :

x and y a re two time dependent inputs

R _xy (m) s given by :

The cross correlation is normalised i n one embodiment by the val ue of the a uto correlation of the i nput signal at a zero lag . In another embodiment the cross correlation is normalised by the product of the standard deviation of X and y, σ _χ σ _ν .

Figure 12 shows a graphical example of the correlation strength of the signal with time at the local measurement station .

Figure 13 shows a g raphical example of the correlation strength of the signal with time at the remote measurement station .

The difference in time lag between correlations is identified by the time to the fi rst spike in the cross correlation between the input signal and the remote response. Figure 14 shows a graphical exam ple of the signal time lag to the remote station .

The foregoing descri ption of the invention i ncl udes preferred forms thereof. Modifications may be made thereto without departing from the scope of the invention .