BACKGROUND 
       [0001]    This disclosure relates to pipeline systems. More specifically the disclosure relates to leak detection systems utilized in pipeline systems. 
         [0002]    During the operation of pipeline systems the flow of the conveyed fluids is monitored using various sensors measuring parameters such as pressure, flow rate and temperature. Using these instruments the operator of the pipeline system can evaluate the health of the systems within the accuracy of the measurements and uncertainty of the flow parameters. It is, however, not possible to detect all potential leaks. Further instrumentation, therefore, providing a high level of sensitivity to potential problems can extend the safety of pipeline system operations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  shows an example wireless sensor node installed near a pipe. 
           [0004]      FIG. 2  shows example electrical architecture of the wireless sensor node of  FIG. 1 . 
           [0005]      FIG. 3  shows a wireless sensor node placed in proximity to a pipeline. 
           [0006]      FIG. 4  shows another embodiment of a wireless sensor node. 
           [0007]      FIG. 5  shows an embodiment of a sensor node having a hollow coupling rod. 
           [0008]      FIG. 6  shows an embodiment of a wireless sensor node including a pipeline warning sign. 
           [0009]      FIG. 7  shows a wake/sleep cycle for wireless sensor nodes illustrated with a flow diagram. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Referring to  FIG. 1 , a leak detection system  100  according to the present disclosure may be used with a pipeline system  101 . The pipeline system  101  may comprise a pipeline constructed to transmit a fluid from one location to another, or it may be a combination of pipes forming a network transmitting fluid to and from a plurality of locations. The pipeline system  101  is typically buried below the ground surface  106  in order the protect it from damage. 
         [0011]    Some non-limiting examples of pipeline systems include hydrocarbon pipelines, water distribution pipeline network systems, chemical pipelines, and sewer networks. 
         [0012]    In case of a containment failure in the pipeline system  101  causing a leak, it is important to detect such leak and begin corrective actions as soon as possible. The leak detection system  100  disclosed herein facilitates prompt detection of containment failure by locating a plurality of wireless sensor nodes  102  at various locations along the pipeline system  101 ; each wireless sensor node  102  being in proximity to the pipeline system  101 . The wireless sensor nodes  102  may be placed with small enough spacing between them such that each wireless sensor node  102  is in the wireless signal  104  range of at least one other wireless sensor node&#39;s  102  wireless signal  104 . The foregoing spacing between wireless sensor nodes  102  enables creating a wireless sensor network, for example a mesh network. The wireless sensor nodes  102  will be explained in more detail below with reference to  FIGS. 2 through 6 . 
         [0013]    Communication of commands and data in the wireless sensor network may be relayed from one wireless sensor node  102  to another. Also located in the wireless sensor network is a gateway node  105  which has a) connectivity with one or more wireless sensor nodes  102  in the wireless sensor network, and b) signal connectivity external to the wireless sensor network, for example, with an operations control center having equipment (not shown) therein for monitoring the wireless sensor network. The out-of-network connectivity may be established by various communication means for example and without limitation, cellular communication networks, Ethernet, optical fiber connection and satellite communication devices. 
         [0014]    Because the wireless sensor nodes  102  are typically not externally wired for electrical power, they may, for example, use battery and/or solar power. In some embodiments, the wireless sensor nodes  102  may be programmed to maintain a low-power “sleep” mode as much as possible to extend battery life. 
         [0015]    In an example embodiment of a monitoring scheme, all the wireless sensor nodes  102  in the wireless sensor network switch on (“wake up”) and make measurements, e.g., of ambient acoustic signals, to detect the possible presence of a leak in the pipeline system  101 . These measurements may be locally post-processed in each wireless sensor node  102  to minimize volume of data transfer on the wireless sensor network. For example, a wireless sensor node  102  may calculate the power of the signal measured and compare this to a locally stored threshold. If the signal power is determined to be more than the locally stored threshold, the wireless sensor node  102  will transmit these measurements to the wireless sensor network. Conversely, if the power of the locally measured signal is less than the threshold, the wireless sensor node  102  may be programmed not to transmit the measurements to conserve its own battery power and that of the other wireless sensor nodes  102  on the wireless sensor network. Following post-processing, each wireless sensor node  102  may have programmed therein a preselected duration window of time in which the wireless sensor node  102  may transmit its measurements and/or the results of its post-processing to another wireless sensor node  102  in proximity thereto (typically the closest or neighboring wireless sensor node  102 ). The transmitted data may then be relayed in the wireless sensor network from one wireless sensor node  102  to another until the data reach the gateway node  105 , which in turn communicates the data out of the wireless sensor network, e.g., to an operations control center. The determination of a leak by a wireless sensor node  102  is further described with reference to  FIG. 7 . 
         [0016]    In some wireless sensor networks, the wireless sensor nodes  102  may be programmed to operate at a low power level sleep mode during standby until detection of a wireless signal transmission from another wireless sensor node  102 . Detection of such signal transmission triggers the wireless sensor node  102  to wake up and initiate wireless communication and/or other functions of the wireless sensor node  102 . 
         [0017]    The information communicated by each wireless sensor node  102  may be raw sensor data, compressed data, or results of post-processing which may indicate a leak being present. 
         [0018]    During the time when any one or more wireless sensor nodes  102  are “awake”, the operator of the wireless sensor network may be enabled to send commands to each wireless sensor node  102  to acquire sensor data or send new software or parameters using the gateway node  105 . 
         [0019]    It may be desirable to synchronize timing between wireless sensor nodes  102  during some or all wake up intervals so that subsequent wake up triggering events are better timed for the wireless sensor network. 
         [0020]    It may be desirable to place a wireless sensor node  102  such that it is in the range of both adjacent wireless sensor nodes  102  and further wireless sensor nodes adjacent to the adjacent wireless sensor nodes  102 . Such spacing of the wireless sensor nodes  102  may provide a desirable signal communication redundancy to ensure that a communication failure in any one wireless sensor node  102  is unlikely to interrupt communication within the wireless sensor network. 
         [0021]    Because typical pipeline systems are substantially linear, it may be practical to use an antenna  103  for each wireless sensor node  102  that is directional and have its highest gain aligned along the principal direction of the pipeline system  101 . The antenna  103  may be disposed above the ground surface  106  to facilitate wireless communication. 
         [0022]    Referring to  FIG. 2 , the electrical architecture of each wireless sensor node  102  may include a controller  200  electrical assembly. The controller  200  may consist of, including and without limitation a microcontroller, microprocessor, field programmable gate array (FPGA) application specific integrated circuit (ASIC) or other programmable integrated circuitry and some form of data storage or memory (volatile and/or non-volatile). The controller  200  may include real-time clock circuitry (not shown), for example, a global positioning system satellite signal receiver, and interfaces to transmit data to and from other devices within the wireless sensor node  102 . 
         [0023]    The wireless sensor node  102  may be powered by a power source  204 . Some non-limiting examples of power sources are batteries such as lithium batteries, supercapacitors, photovoltaic cells, thermoelectric generators, vibration energy harvesters, fuel cells, thermal batteries or any combination of the foregoing power sources. 
         [0024]    The controller  200  may be in signal communication with the antenna  103  to increase the signal strength of transmitted and received signals from other wireless sensor nodes  102  and/or the gateway node  105 . 
         [0025]    The leak detection system ( 100  in  FIG. 1 ) may use acoustic measurements to detect the presence of fluid discharge from the pipeline system  101 . The wireless sensor node  102  may include two sensors for this purpose: an acoustic sensor  201  and an ambient sensor  202 . The acoustic sensor  201  may be acoustically coupled with the pipeline system ( 101  in  FIG. 1 ) to detect acoustic waves propagating through the pipeline system ( 101  in  FIG. 1 ). While the ambient sensor  202  may have some acoustic coupling with the pipeline system  101 , such coupling is to a lesser degree and therefore the ambient sensor  202  may be used to sense the background acoustic environment. By using an acoustic sensor  201  and an ambient sensor  202 , it is possible to substantially determine if an acoustic wave is received from the pipeline system ( 101  in  FIG. 1 ) or another source in the ambient. 
         [0026]    The typical source of the acoustic waves in a leaking pipeline system is from fluids, which are under pressure in the system, escaping to the environment. The acoustic waves normally propagate through the pipeline system ( 101  in  FIG. 1 ) the fluid contained in the pipeline system, and the medium surrounding the pipeline system. 
         [0027]    The acoustic sensor  201  can detect fluid escape sound traveling through the soil covering the pipeline system. The range of the measurement of such sound by the acoustic sensor  201  is enhanced by the presence of pipeline system  101  because pipes create an effective waveguide allowing for the acoustic waves to propagate much further than they do in soil. 
         [0028]    The controller  200  filters the analog signal generated by the acoustic sensor  201  and the ambient sensor  202  and converts the analog signal to a digital signal using one or more analog to digital converters (not shown separately) which may form part of the controller  200 . The digital signals may in turn be processed by the controller  200  or any other processor (not shown) in the wireless sensor node  102  to analyze detected acoustic energy for the presence of leaks. 
         [0029]    Some non-limiting examples of the acoustic sensor  201  and ambient sensor  202  are geophones, hydrophones, microphones and accelerometers. 
         [0030]    The controller  200  may process acoustic measurements from the acoustic sensor  201  concurrently with processing signals from the ambient sensor  202  and previous measurements made at the location of the wireless sensor node  102  since other acoustic sources near the wireless sensor node  102  may lead to a false positive identification of a leak. The ambient sensor  202  is desirable to use in the process of detecting leaks however it is not essential. The process of detecting leaks with and without the ambient sensor  202  is described further with reference to  FIG. 7 . 
         [0031]    The electrical architecture of the gateway node ( 105  in  FIG. 1 ) may be similar to that of the wireless sensor node  102 . However, in addition to the controller  200  of the wireless sensor node  102 , the controller  200  of the gateway node ( 105  in  FIG. 1 ) may include capability to communicate out-of-network, as previously explained, typically to an operations monitoring center for the pipeline system ( 101  in  FIG. 1 ). The gateway node  105  may contain an acoustic sensor  201  and an ambient sensor  202  similar to those in any or all of the wireless sensor nodes  102  and such sensors may be used to detect leaks in a similar manner to a wireless sensor node  102 . Alternately, the gateway node  105  may not contain such sensors and may function merely as a communication link to connect communication from the wireless sensor nodes  102  to any one or more systems outside of the network. 
         [0032]    Other sensors may also be used on the wireless sensor node  102  to detect leaks. Some examples of other sensors are temperature sensors, optical cameras, infrared cameras, infrared sensors, resistivity sensors and electrochemical sensors. 
         [0033]    Referring to  FIG. 3 , the wireless sensor node  102  is placed in proximity to the pipeline system  101 . The controller  200  may be placed in a sealed enclosure  301  in the wireless sensor node  102 . The acoustic sensor  201  is placed in close proximity to the pipeline system  101  in order to increase its sensitivity to acoustic waves propagating along the pipes. The acoustic sensor  201  is in signal communication  300 , e.g., by electrical and/or optical signal conduction to the controller  200 . The ambient sensor  202  is placed in a similar manner; however, it may be placed at a greater distance away from the pipeline system to have less sensitivity to acoustic waves propagating in the pipes. 
         [0034]    As illustrated in  FIG. 3 , the wireless sensor node  102  may be placed in proximity of the pipeline system  101  without requiring significant excavation. This is useful design feature of the leak detection system ( 100  in  FIG. 1 ) as its installation thereby creates only a small risk of damage to the pipeline system  101 . 
         [0035]    Referring to  FIG. 4 , in another embodiment of the wireless sensor node  102 , in order to obtain better acoustic coupling between the acoustic sensor  201  and the pipeline system  101  a coupling rod  401  may be used. The coupling rod  401  may be inserted until it makes contact with the pipeline system  101 . Once the remainder of the wireless sensor node  102  is installed the coupling rod  401  may be urged against the pipeline system  101  by a biasing device such as a spring  402 . 
         [0036]    The acoustic sensor  201  may be affixed to the coupling rod  401  with mechanical means such as a screw and/or an adhesive to increase the acoustic coupling between the coupling rod  401  and the acoustic sensor  201 . 
         [0037]    It is also possible to place the acoustic sensor  201  in contact with the pipeline system  101  and use the coupling rod  401  to urge the sensor  201  against the pipeline system  101 . 
         [0038]    Referring to  FIG. 5 , in another embodiment a hollow coupling rod  401  may be used to connect the acoustic sensor  201  to the pipeline system  101 . A conduit  501  may pass through the interior of the coupling rod  401  to minimize the load required for inserting the coupling rod  401 . This also minimizes the load placed on the pipeline system  101 , especially during the final stages of the insertion. After the coupling rod  401  is inserted, an adhesive  502  such as an epoxy may pumped through the conduit  501  and placed between the coupling rod  401  and the pipeline system  101 , effectively increasing the acoustic coupling between the foregoing components. In other embodiments, one or more magnets (not shown) may be used on the coupling rod  401  to establish a connecting force between the coupling rod  401  and the pipeline system  101 . 
         [0039]    Referring to  FIG. 6 , in another embodiment the wireless sensor node  102  may include a pipeline warning sign  600  disposed above the ground surface  106 . A warning sign may consist of a post and a plate containing warning message affixed to the post. In other embodiments, the warning message may be written on the post. Pipeline warning signs are normally placed proximate to a buried pipeline to warn people with visual indication  601  of the presence of the pipeline  101  underground, reducing the chance of accidental damage to the pipeline  101  caused by nearby excavation or construction. Typical installation spacing of the warning signs  600  may be similar to that of the wireless sensor nodes  102 . Therefore it may be advantageous to connect the warning sign  600  to above-ground components of each wireless sensor node  102  to minimize cost and increase functionality. Furthermore the warning sign  600  may encase some of the necessary components of the wireless sensor node  102 , such as the antenna  103  as illustrated in the figure, or other sensors. It may be advantageous to place the antenna  103  at a higher elevation to maximize its range, especially in geographic areas where heavy snow cover is expected. In some embodiments, the height of the warning sign  601  may be used to place the antenna  103  on or in the sign. 
         [0040]    Referring to  FIG. 7 , leak detection is made using the measurements from the acoustic sensor  201 , and the ambient acoustic sensor  202 . In  FIG. 7 , a typical wake  700 -sleep  707  cycle of the wireless sensor node  102  is illustrated with a flow diagram. The wireless sensor nodes  102  are typically operated in two modes: awake and sleep modes. In the sleep mode, some of the circuitry in the node  102  is turned off in order to conserve battery power. In awake mode, the nodes  102  acquire data, transmit and receive data and/or commands on the wireless sensor network. In the present embodiment after waking  700  from sleep mode, the wireless sensor node  102  acquires data from the acoustic sensor  201  and the ambient acoustic sensor  202 . In this acquisition the acoustic sensor  201  is sampled N number of times and a discrete-time signal represented by a(k) is acquired, where k is the time index of the signal and ranges between 1 and N. Similarly the ambient acoustic sensor  202  is sampled to obtain a discrete-time signal represented by b(k). In the next step  702 , average power of each discrete-time signal a(k) and b(k) is calculated. The average power of a discrete-time signals x(k) may be defined as P x =(1/N) Σ k=1   N [x (k)] 2 . P a  and P b  represent the average power of signals a(k) and b(k), respectively. The average power of the two signals are used to determine if a leak alert needs to be issued by the wireless sensor node  102  by first conducting Test A  703  and then Test B  704 . In one embodiment Test A consists of comparing P a  and P b  against threshold values T a (t) and T b (t) respectively. The threshold values are predetermined and may be stored in a non-volatile memory space in the wireless sensor node  102 , e.g., in flash memory. The threshold values are time-dependent as they account for expected background noise at the location of the particular wireless sensor node at a given time. For example, if traffic noise from a nearby highway is present at the wireless sensor node location, the threshold value during rush hour will be different than the threshold value at other times. In the present embodiment Test A is found to be true if P a &gt;T a (t) and P b &lt;T b (t). Otherwise Test A is false. Test B is typically utilized to avoid taking up wireless sensor network bandwidth based on a single calculation. An errant calculation may be caused by a local disturbance such as a train or a vehicle passing near the wireless sensor node  102  and it is beneficial to avoid false leak alerts based on these local events. In this embodiment Test B is the found to be true if P a &gt;T a (t) and P b &lt;T b (t) at the previous wake-sleep cycle. Otherwise Test B is false. Even though the same criteria may be used on Tests A and B, since Test B tests for the criteria at the previous wake-sleep cycle, it can be used to screen for temporary disturbances if the wake-sleep cycle frequency is low enough (for example once every 10 minutes). If Test B is true, then the wireless sensor node  102  transmits a leak alert and the acquired data associated with this leak alert, and a(k) and b(k) through the wireless sensor network to the operation control center. At the operation control center, the user can determine an appropriate response to a leak alert by evaluating the acquired data further. Even though this completes the evaluation necessary for determining a local leak at a wireless sensor node  102 , the wireless sensor node may need to remain in awake mode further to relay data or commands transmitted from other nodes on the network. Once this step ( 706 ) is complete, the node  102  goes to sleep mode  707 . 
         [0041]    In another embodiment the wireless sensor node  102  calculates  702  a reduced noise signal, c(k) based on the measurements from the acoustic sensor  201  and the ambient acoustic sensor  202  by using the formula c(k)=a(k)−K C ·b(k), where K C  is the coupling constant typically with value between 0 and 1. In this step it also calculates the average power of the noise reduced signal, P c . In this embodiment Test A is true if P c &gt;T c (t), where T c (t) is a time-dependent threshold. Otherwise it is false. Test B utilizes the same criteria on the previous wake-sleep cycle measurements. 
         [0042]    In another embodiment, the ambient acoustic sensor  202  is not utilized. Test A is true if P a &gt;T a (t). Otherwise it is false. Test B utilizes the same criteria on the previous wake-sleep cycle measurements. 
         [0043]    In the present description, the following definitions may be used for certain terms used therein: 
         [0000]    ACOUSTICALLY COUPLED: Means a set of conditions wherein oscillations of matter in one body can lead to oscillations of matter in another body. The two bodies can be directly in contact with one another or there may be other intermediate bodies in between. The acoustically coupled and intermediate bodies may be solid or fluid. For example an earphone is acoustically coupled with an eardrum of the user as the oscillations of the earphone is transmitted to the eardrum. In this example the intermediate bodies are the air medium in between the two bodies and tissues near the ear.
 
ACOUSTIC PROXIMITY: A set of conditions wherein two devices are acoustically coupled at their respective locations.
 
ACOUSTIC SENSOR: A sensor that measures acoustic waves propagating in a medium in which the sensor is placed. Some non-limiting examples of the acoustic sensor are geophones, hydrophones, microphones and accelerometer.
 
AMBIENT ACOUSTIC SENSOR: An acoustic sensor that is utilized to measure the acoustic environment in which a wireless sensor node is placed and typically has small or no acoustic coupling to a pipeline system.
 
COUPLING ROD: A component placed in between a wireless sensor node and a pipeline system to enhance the acoustic coupling between the pipeline system and the acoustic sensor, as illustrated in  FIGS. 3-5 .
 
GATEWAY NODE: A node on a wireless sensor network which has a) connectivity with one or more wireless nodes in the network, and b) connectivity out of this network, typically with an operation center monitoring this network. Out-of-network connectivity can be established by various communication means such as cellular networks, Ethernet, satellite communications.
 
GEOPHONE: An acoustic sensor that measures ground movement. It is typically constructed by a spring mounted magnetic mass that oscillates through a wire coil, generating a voltage on the coil with the motion of the mass.
 
PIPELINE SYSTEM: A fluid transmission or conduit system devised to transmit fluid between two or more locations. Some non-limiting examples of pipeline systems are hydrocarbon pipeline, water distribution pipeline network system, chemical pipeline, and sewer network.
 
PIPELINE WARNING SIGN: A visual warning device placed in proximity to a buried pipeline to warn people of the existence of the pipeline system.
 
WIRELESS SENSOR NETWORK: A communications network of wireless sensors in which communication of commands and data is relayed from one wireless sensor node to another. Also located in this network is a gateway node, which has a) connectivity with one or more wireless nodes in the network, and b) connectivity out of this network. The out-of-network connectivity can be established by various communication means such as cellular networks, Ethernet and satellite communications.
 
WIRELESS SENSOR NODE: A node on a wireless sensor network that has radio communication with one or more nodes on the network. While a particular node may be in the range of a gateway node, which allows out-of-network communication, this is not essential to establish the communication. The wireless nodes can communicate with other nodes that are in their radio signal range and relay communications along the network until the gateway node is reached.
 
         [0044]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
A robust pipeline leak detection system allows the operator to take timely corrective action to the problem, minimizing leakage of the fluids contained in the pipeline to the environment. The wireless sensor network system disclosed in this invention detects the presence of a leak by various sensors including acoustic sensors distributed along a pipeline system. The sensors are connected to the wireless sensor network. An advantage of this system is that it is possible to deploy the leak detection system on existing buried pipelines without significant excavation.