TITLE OF THE INVENTION

[001 ] Method and system for testing fluid filled pipes, tubes and other such vessels using sound and vibration

TECHNICAL FIELD

[002] This invention relates to methods and systems for testing and assessing the wall conditions and properties of fluid filled pipes, tubes and other such vessels and distribution systems using controlled acoustic signals, measurement and analysis, and the measurement of key characteristics of the fluid in said vessels.

BACKGROUND ART

[003] As piped infrastructure systems deteriorate over time, leaks and breakages occur more frequently. Common failures for older pipes include decreased wall strength and loss of seal at joints, both of which produce leaks.

[004] Typically, fluid filled pipe networks are diagnosed using statistical methods based on trend analyses of failure rates. Because the service life of a pipe is governed by many uncontrollable variables, identical systems may deteriorate at different rates, this method does not provide specific or localized information on the state of elements in the pipe network in question.

[005] Currently, there are several methods by which one may inspect specific pipe wall conditions. Insertion of a physical probe, for example, provides detailed data on pipe conditions. The problem with these methods, however, is that they risk damaging the pipe, causing obstructions or contaminating the fluids within. In addition, they often require that pipe sections be bypassed or temporarily taken out of service, which creates service disruptions.

[006] Destructive testing of exhumed pipe segments is another common form of analysis familiar to those skilled in the art.

[007] There are also non-invasive methods of pipe analysis which include eddy current, or ultrasonic measurement such as those disclosed in US 6000288 (KWUN, H, et al.) December 14, 1999 and US 6568271 B2 (SHAH, V, et al.) May 27, 2003 as well as surface corrosion surveys. These methods require excavation around the pipe, however, and only reveal local features.

SUMMARY OF INVENTION

[008] The device and method disclosed herein overcome many of the drawbacks associated with traditional condition assessment by using acoustic waves to accurately determine characteristics of a subject fluid filled vessel's wall, including wall stiffness and wall mass.

[009] This is a non-invasive method which provides detailed and specific information that is directly tied to the serviceability of the tested item.

[010] By using a controlled, high-efficiency sound source along with sensors, for example sensors affixed to the pipe wall or appurtenance by way of magnets, epoxy, or other connective means one can measure the wave speed of sound in the pipe. The changes in this speed based on the frequency of the sound source tend to be functions of characteristics of the subject pipe, for example the wall stiffness, the pipe wall mass per unit length, and the bulk modulus of the fluid. [Oi l] The present method thus provides a cost-effective and non-invasive way to extract the relevant service information from a particular pipe system, rather than relying on statistical methods or invasive and expensive probes.

TECHNICAL PROBLEM

[012] Less invasive methods pipe wall assessment methods such as those disclosed in US 6561032 Bl (HUNAIDI, O) May 13, 2003, US 7328618 B2 (HUNAIDI, O, et al.) February 12, 2008, US 9097601 B2 (STEPHENS, M, et al.) August 4, 2015, and DE 202013012302 Ul (GUTERMANN) 2016.03.17, measure certain aspects of propagation of unsteady pressures in liquid filled conduits with elastic walls and to relate this information, in an approximate manner to pipe wall conditions.

[013] Methods such as those disclosed tend to overestimate or under estimate pipe thickness by large margins. This has been documented in reputable independent studies conducted by the EPA (NESTLEROTH, B., et.al., Field Demonstration of Innovative Condition Assessment Technologies for Water Mains: Acoustic Pipe Wall Assessment, Internal Inspection, and External Inspection. EPA/600/R-14/148. July 2014 p. 14, 72, 115-117.), Brabant Water (BEUKEN, R., et. AL, Mains Condition Assessment by Echopulse, a Validation of Results, pp. 1437 - 1444, Procedia Engineering 89, 2014) and Virginia Tech (BHEVIANADHUNI, S., SFNHA, S. K., Pilot Acoustic Condition Assessment of Water Distribution System, Virginia Tech, 2014 p 15).

[014] The same applies to pipe wall strength, which is proportional to pipe wall thickness.

[015] Additionally, the zeroth order formulations claimed or cited in the aforementioned disclosures relate the pipe wall thickness (h _p ) to the measured propagation speed (c _w ) via h _p = o ^r similar expressions, where c ₀ is the natural speed of sound in the (unbounded)

liquid; p ₀ the density of the liquid, c _p the flexural wave speed of the pipe wall material, p _p the density of the pipe wall, a _p and b _p the inner and outer radii of the pipe.

[016] In the referenced inventions these parameters are required to be estimated or are not known with sufficient precision.

[017] In particular, c ₀ is known to be sensitive to the gas contents of the liquid. For composite pipes such as asbestos cement, concrete pressure pipes, and plastics the use of p _p c _p usually leads to invalid estimates of pipe wall thickness and or strength.

SOLUTION TO PROBLEM

[018] Realistic physics-based propagation models for unsteady pressures in fluid-filled conduits with elastic walls are described in the scientific literature, e.g. FEIT, D, JUNGER, MC, Sound, Structures, and Their Interaction. MIT Press, 1986, ISBN 0-262-10034-7 pp. 37-39 and 378-386, INGARD, K Uno. MORSE, P, Theoretical Acoustics, Princeton University Press, 1986, ISBN 0- 691-08425-4 pp. 666-668, KONDIS, A, Acoustical Wave Propagation in Buried Water Filled Pipes. MSCEE dissertation, Dept. Civil and Environmental Engineering, Massachusetts Institute of Technology, 2005.

[019] In general, the propagation speed c _w of unsteady pressures in fluid-filled conduits with elastic walls can be written as where c ₀ is the natural

speed of sound in the (unbounded) liquid; p ₀ the density of the liquid, c _p the flexural wave speed of the pipe wall material, p _p the density of the pipe wall, v _p is the Poisson's ratio of the pipe wall material, , e _p the damping constant of the pipe wall material, a _p and b _p the inner and outer radii of the pipe, Θ the temperature of the liquid, and / the acoustic frequency.

[020] This list of dependent variables is by not complete but suffices for homogenous walls.

[021] It will be appreciated by those skilled that c _w can be inferred from measurements that determine the time T taken for an acoustic signal to traverse a known distance L: c _w = L /T . The cross-correlation technique, also well known to those skilled, is the preferred, but not only possible method for determining T.

[022] The bulk modulus of the liquid K _Q is determined by means of an apparatus herein disclosed. The presence of gas diminishes the bulk modulus but has negligible influence on the fluid density p ₀ unless the liquid is 'bubbly' .

[023] From the speed of sound of the liquid is determined, as p ₀ which is a function

of temperature may be obtained from published data or weighing a known volume of fluid.

[024] Morse and Ingard (pp. 475-477) derive a model for plane waves in a duct based on the linearized equations of conservation of mass and momentum. It reduces to the telegraph equation:

[025] Here Z _p = R + iC is the impedance of the pipe wall, Q a loss factor associated with viscous wall effects and p the unsteady, acoustic pressure in the liquid. Ordinarily,

and is neglected in subsequent analysis. [026] The pipe wall impedance Z _p accounts for wall stiffness (K), wall mass ( ), and any material damping, absorption at the wall, as well as radiation losses to the exterior. It is understood that the impedance is a function of frequency.

[027] Those skilled in the art can select appropriate impedance models to suit the particular vessel being tested. A comprehensive library of model as can be found in MECHEL, F.P., Formulas of Acoustics, Springer, 2008, ISBN 978-3-540-76892-6 pp 287-346 and 595-792.

[028] In general, an acoustic pressure signal p(x, t) with frequency / propagating in the +x direction is proportional to

[034] The signals are dispersive and diminish in amplitude in the direction of propagation or reflection. Signal loss is due material damping, absorption by porous deposits on the wall (tuberculation), and sound transmission into the surrounding medium.

[035] Controlled measurements utilizing the sound source disclosed herein form the basis for determining the propagation speed c _w and attenuation factor as functions of frequency. The bulk modulus apparatus disclosed herein is used to determine appropriate value

[036] It is evident that R and C can be determined with an appropriate system parameter identification algorithm that operates on the measured data set. System identification software is commercially available and most can be readily integrated into the data acquisition and analysis engine herein described.

[037] The parameters of the general physical model of a fluid conduit with elastic walls which may have absorptive porous surfaces are explicit functions of frequency as well material and geometric properties of the wall. The parameter identification algorithm returns the most likely values for wall thickness and strength which form the basis of condition assessment.

[038] The controlled sound source disclosed herein is used to inject a known signal into the pipe. Single tones are not suitable to determine the transit time T over a known distance L with the precision needed in the present application. However, when two tones which differ slightly in frequency are measured by sensors separated by a distance L their normalized cross-correlation

[039] The time shift of the signal envelope is

[040] Those skilled in the art will note that applying the Hilbert transform to the cross- correlation facilitates the determination of

[041] As the nominal signal frequency used in the calculations is

[042] The attenuation factor is determined from the ratio of the mean square of the signals measured by sensors separated by a known distance

ADVANTAGEOUS EFFECTS OF INVENTION

[043] The invention comprises a system and method for the measurement of the propagation speed of unsteady pressures in fluid filled conduits with elastic walls as a function of frequency. It reduces the number of unknown variables that determine that determine the characteristic of the wall of a fluid filled vessel, such as the wall thickness , to better evaluate the

serviceability of said vessel.

BRIEF DESCRIPTION OF DRAWINGS

[044] The following description references drawings, in which:

[045] FIG.1 illustrates an embodiment of a system for the non-destructive analysis of fluid filled pipes and other such vessels or distribution systems taken in a plane extending in the radial and longitudinal directions according to examples of the present disclosure.

[046] FIG. 2a illustrates a cross-sectional view of an embodiment of a sound source for fluid filled pipes and other such vessels or distribution systems taken in a plane extending in the radial and longitudinal directions according to examples of the present disclosure.

[047] FIG. 2b illustrates a view of an embodiment of a rotor plate with apertures for an embodiment of a sound source for fluid filled pipes and other such vessels or distribution systems taken in a plane extending in the radial direction and orthogonal to the longitudinal direction according to examples of the present disclosure.

[048] FIG. 2c illustrates an embodiment of motor connections and controls in an embodiment of a sound source for fluid filled pipes and other such vessels or distribution systems.

[049] FIG. 3 illustrates the effective aperture size over time for an embodiment of a sound source for fluid filled pipes and other such vessels or distribution systems.

[050] FIG. 4a illustrates a cross-sectional view of an embodiment of a device for determining the bulk modulus of a fluid extracted from a pipe or other such vessel or distribution systems, taken in a plane extending in the radial and longitudinal directions according to examples of the present disclosure.

[051] FIG. 4b illustrates a view of the housing and connections of an embodiment of a device for determining the bulk modulus of a fluid extracted from a pipe or other such vessel or distribution systems, taken in a plane extending in the radial direction and orthogonal to the longitudinal direction according to examples of the present disclosure;

[052] FIG. 5 illustrates a block diagram of a measurement system to determine the wall conditions of a fluid filled pipe or other such vessel or distribution system, according to examples of the present disclosure.

[053] FIG. 6 illustrates a computer based system with storage medium for storing instructions to determine the wall conditions of a fluid filled pipe or other such vessel or distribution system, as in FIG. 1, according to examples of the present disclosure.

DESCRIPTION OF EMBODFMENTS

[054] It should be understood that all references herein to a "computer" include not only to a desktop or notebook personal computer or workstation, but also mobile computing devices such smartphones, tablets, and wearables such as smart watches, digital signal processing units of any configuration, a server and any other device, capable of comparable functionality to said devices.

[055] References to "sensor" should be understood to encompass, microphones, hydrophones, accelerometers, and pressure sensors of any kind.

[056] With reference to FIG 1, an embodiment of the present invention is provided, comprising a sound source 102, transmitter and controller 103, a first sensor 104 and transmitter 105, a second sensor 106, and receiver 107, a bulk modulus measurement apparatus (not shown) in operation with a fluid filled pipe 101, a computer with a receiver/controller 108, a writable data storage medium 109, and an acoustic analysis engine 110, which together determine the speed of propagation of acoustic waves and therefore the pipe system's properties.

In the embodiment shown in FIG. 1, the high efficiency sound source and two sensors are separated by a distance L along the pipe 111.

[057] Skilled persons will appreciate that any basic commercially available sensors may be used in conjunction with the sound source and further than an alternative number or configuration of sensors may be used in some embodiments of the present invention. The sound source component of the present invention tends to be a high efficiency sound source, such as a controlled, hydro-dynamic sound source based on the principle of periodic mass injection. This is the same principle used in air-horns or loud warning sirens. In addition, 'electro-pneumatic transducers' may be included to generate acoustic power on the order of 10 ⁴ watts.

[058] Persons of skill will appreciate that other sound sources could be used in the present invention. Two important features of a controlled sound source for wall pipe assessment are portability and energy efficiency.

[059] The principal elements of the sound source depicted in FIGs 2a, 2b, and 2c are as follows: a valved connection that attaches the sound source to a fluid filled vessel or intermediary body 201; a plenum 202; at least two discharge openings in the plenum 206; two rotors 205 with one or more apertures which can be configured to generate any desired waveform (see FIG. 2b) aligned with the discharge openings 206; a increasing geared transmission of two or more gears 204A and 204B, connecting via a bearing 204C, each rotor 205 to electric motors 203A and 203B, controlled by a servo-electric speed selector 208 and feedback controller 209A and 209B and supplied by a portable power supply 207 such as a rechargeable lithium ion or other battery.

[060] These components may sit in a common housing, including a thermally insulated watertight housing, for encasement or protection as the case may be, and may be further supplemented by the use of thermal sensors and tachometers for the motors to provide operating information to the user and safety shutoff capability. Those skilled in the art would appreciate that other variable speed drives and transmissions including purely mechanical ones, may be used to provide the motive force for the rotors.

[061] Light-weight, fractional horsepower, brushless DC motors would tend to be preferred for the sound source, as when coupled with common, commercial servo controllers, a wide range of RPM and frequencies are available

[062] Flow from the source vessel which enters the plenum at 201 is therefore controlled by rotating the disks 205 which cover the outlets 206, minimizing flow when the outlets are covered and maximizing it, when the aperture is rotated into position.

[063] The regular modulation in flow from the discharge generates unsteady flow and acoustic waves in the fluid which are detectable by the sensors 104 and 106 which can then be used to calculate c _w .

[064] For present purposes as it is preferable to have two tones of equal sound pressure but slightly different frequency; separate motors 203A and 203B drive each rotor 205 at slightly different rates of rotation. This permits an operator finer control over the frequency and frequency ratio of the tones to achieve optimal signal strength at the sensors 104 and 106.

[065] This process can be controlled via the feedback controllers 209A and 209B with the speed selector 208 which can be controlled by the system wide controller 108 in response to measurements from the sensors 104 and 106.

[066] With reference to FIG 3, a graphical depiction of the effective aperture size of the discharge opening over time is provided. The figure illustrates the periodicity with which the discharge aperture, and thereby fluid flow, can be controlled. This modulation in the fluid flow generates the acoustic wave that allows an operator to analyze the pipe system or vessel.

[067] In the embodiment shown, the sound source generates two tones and

only differ by a few Hertz. The zeroes of the envelope of the combined signal: occur at

regular time intervals and are easily identified, giving rise to a determination of the wave speed associated with the frequency. The signal detected by the first sensor is proportional to 5(t), while a second sensor, located a distance L (111) downstream, detects a signal that is proportional to where c _w is the wave speed. Using the wave speed and the effective frequency of

the sound source one can then determine the wall stiffness and the wall mass per

unit length of the pipe if the bulk modulus of the fluid is also known.

[068] The bulk modulus (K _w ) of the fluid in a pipe, tube or other such vessel is a characteristic used in determining pipe wall stiffness, mass per unit length, and overall serviceability of the pipe system. Some operators attempt to deduce the effective bulk modulus by measuring the wave speed in another "reference" pipe, the properties of which are assumed to be known precisely. The problem with this method is that, as discussed, there are many variables which may affect a pipe system's deterioration, and therefore the measurement of the bulk modulus from a reference pipe will be skewed by differences between the reference pipe's integrity and the one to be tested.

[069] The present invention therefore includes a bulk modulus tester to be used in conjunction with the high efficiency sound source to accurately assess serviceability in a pipe system.

[070] The bulk modulus of a liquid may be deduced by observing changes in absolute pressure when the volume is changed by a known amount. One of the common obstacles in such measurements is the fact that the walls of any vessel will yield a small amount when subjected to pressure. This obstacle can be overcome if the test vessel is placed in a container with the same liquid and at the same initial pressure.

[071] With reference FIG 4 an embodiment of a bulk modulus tester, comprises an inner cylinder 401, and outer cylinder 402 which are set into common end plates and fitted with a thermal insulating sleeve 411. The smaller cylinder 401 is the test volume and is positioned such that its side walls are fully surrounded by the same fluid as in the outer cylinder 402.

[072] Flow into and out of the chambers is controlled by a series of valves, gates or membranes. The apparatus is filled by opening valves 403, 404, 405A and 405B, while closing 405A and 405 B pressurizes the unit. Closing 403 isolates the chambers from the common supply attached to 403 and closing 404 prevents exchange of fluid between 401 and 402.

[073] A static pressure sensor 410 is used to measure the pressure P in 401 and the fluid's temperature is measured by thermometer or other temperature probe 409 which in one possible embodiment transmits this data to the analysis engine 110 through a transmitted using the same means and protocols devised for the acoustic sensors.

[074] A piston 407 moves a flexible, fluid-tight impermeable membrane 406 into the test chamber 401 by means of a lead screw 408. changing the volume of 401 from V. This

in turn increases the pressure from

[075] The operational definition of bulk modulus K ₀ is given by the equation so

[076] The embodiment's measurement of pressure and temperature thereby allows an operator to more accurately measure the bulk modulus of a fluid, which in turn permits greater accuracy in assessing the wall characteristics of the pipe, tube or other such fluid filled vessel under investigation.

[077] By using measurements enabled by the high efficiency sound source along with the bulk modulus tester, a more accurate model can be used to calculate pipe wall parameters than is typically possible with "static wave" and "inverse transient" sound analysis methods used in conventional systems and methods.

[078] In an embodiment of use, the steps to inspect a pipe segment or other such vessel of interest using the systems and methods described herein comprise the following first steps: a. Gather pipe/vessel information such as:

i. diameter at installation,

ii. wall material, depth of cover (if applicable)

iii. original wall thickness

iv. year of installation.

[079] It will be appreciated by those skilled in the art that not all of these will be available and thus the theoretical propagation model against which actual measured values can be compared will vary according to the quantity and quality of information gathered at this preliminary step.

[080] The second step comprises measuring the properties of the fluid in the pipe or other vessel to be tested, by drawing a sample from said pipe or vessel into the claimed bulk modulus measurement device, to measure and record the bulk modulus of said fluid according to the formula

[081] The third step involves instrumenting the test vessel with the sensors placed at a known or measured distance from the sound source to measure and attaching the sound source to the vessel or an intermediary vessel or connection. And connecting these sensors to a storage media and digital controller via cable or wireless connection

[082] The fourth step involves operating the sound source and using the sensors to measure the propagation speed of the introduced tones according to a procedure such as :

a. measure cross-spectral densities recorded by sensors

b. record wave files (on storage media)

c. signal average recorded files (using a computer)

d. extract dispersive wave speeds from appropriate pipe wall model (using a computer) e. identify any reflected signals with weighted time windows (using a computer)

f. numerically propagate signal averaged data in forward and backward directions to determine transmission loss parameters (using a computer)

g. solve parameter matrix for pipe wall thickness distribution at specified intervals (using a computer)

h. compare measured signal data with pipe wall model propagation data stored in database (using a computer)

i. update database with new signal data (using a computer)

j . solve tuberculation dispersion and attenuation models selected by computer program from database matches to estimate tuberculation (using a computer)

k. output results

[083] Persons of skill will appreciate that additional steps, alternative ordering of steps, or a subset of these steps could be used in other embodiments of use. While the invention has been described and illustrated in connection with preferred embodiments, many variations and modifications, as will be evident to those skilled in the relevant arts, may be made without departing from the spirit and scope of the invention; and the invention is thus not to be limited to the precise details of methodology or construction set forth above as such variations and modifications are intended to be included within the scope of the invention.

[084] Except to the extent necessary or inherent in the processes themselves, no particular order to steps or stages of methods or processes described in this disclosure, including the Figures, is implied. In many cases the order of process steps may be varied without changing the purpose, effect, or import of the methods described.

[085] Persons of skill will appreciate that wall characteristic information, including the geographic or relative location of localized variations in wall conditions can be expressed and displayed in a variety of formats according to the needs of the particular operator. INDUSTRIAL APPLICABILITY

[086] The present invention is of particular use in the management of piped infrastructure systems such as drinking water distribution networks, steam or water based district heating systems, snow-making systems, petrochemical pipelines, and fuild distribution systems in factories, food and chemical processing plants, textile steel and pulp and paper mills, or any other such place where an understanding of current pipe wall conditions would improve asset management decision making and planning.

CITATION LIST

[087] Patent Literature

US 6000288 (KWUN, H, et al.) December 14, 1999

US 6561032 Bl (HUN AID I, O) May 13, 2003

US 6568271 B2 (SHAH, V, et al.) May 27, 2003

US 7266992 B2 (SHAMOUT, M, et al.) September 11, 2007

US 7328618 B2 (HUN AID I, O, et al.) February 12, 2008

US 9097601 B2 (STEPHENS, M, et al.) August 4, 2015

US 20160370325 Al (YUSUF, S, et al.) December 22, 2015

DE 202013012302 Ul (GUTERMAN) 2016.03.17

[088] Non-Patent Literature

BEUKEN, R., et al., Mains Condition Assessment by Echopulse, a Validation of Results, Procedia Engineering 89, 2014 pp. 1437 - 1444

BHFMANADHUNI, S., SFNHA, S. K., Pilot Acoustic Condition Assessment of Water Distribution System, Virginia Tech, 2014, pp

FEIT, D., JUNGER, M.C., Sound, Structures, and Their Interaction, MIT Press, 1986, ISBN 0- 262-10034-7 pp. 37-39, pp. 378-386,

INGARD, K., Uno. MORSE, Philip, Theoretical Acoustics, Princeton University Press, 1986, ISBN 0-691-08425-4 pp 666-668

KONDIS, A., Acoustical Wave Propagation in Buried Water Filled Pipes. MSCEE dissertation, Dept. Civil and Environmental Engineering, Massachusetts Institute of Technology, 2005 passim MECHEL, F.P, Formulas of Acoustics, Springer, 2008, ISBN 978-3-540-76892-6

NESTLEROTH, B., et al., Field Demonstration of Innovative Condition Assessment Technologies for Water Mains: Acoustic Pipe Wall Assessment, Internal Inspection, and External Inspection. EPA/600/R-14/148. July 2014 p. 14, 72, 115-117