Patent Publication Number: US-2017356870-A1

Title: Remote communication and powering of sensors for monitoring pipelines

Description:
BACKGROUND 
     Buried metallic pipelines are protected by a coating supplemented with cathodic protection. An impressed current cathodic protection system for a pipeline consists of a DC power source, often an AC powered transformer rectifier, and an anode or array of anodes buried in the ground. The DC power source would have up to  50  amperes and  50  volts, depending upon several factors such as the size of the pipeline and coating quality. The positive DC output terminal would be connected via cables to the anode array, while another cable would connect the negative terminal of the rectifier to the pipeline, preferably through junction boxes to allow measurements to be taken. 
     Pipelines are also inspected to monitor possible corrosion of them. In particular, test points are placed along the pipeline to allow for pipe-to-soil potential measurement for determining whether the protected metal pipe is corroding or not. These measurements are usually taken at physical locations along the pipeline. As an example, radio systems use UHF and require a surface antenna and a battery to take measurements along the pipeline. These radio systems are more expensive than the users would desire, and hence such systems only cover a small niche of the market where corrosion can be extreme. Also since pipelines are often in harsh and remote environments, obtaining physical access to locations along the pipeline can be challenging and difficult. Accordingly, a need exits for an improved system and method to take measurements along a pipeline or other metallic pipe. 
     SUMMARY 
     A remote terminal unit for use in monitoring a metallic pipe, consistent with the present invention, includes a measurement unit configured to take an electrical measurement between a reference electrode electrically coupled to the pipe and a coupon composed of a sacrificial corrosion material. A control unit is electrically coupled to the measurement unit and configured to receive the electrical measurement from the measurement unit. A communication unit is electrically coupled to the control unit and configured to receive the electrical measurement from the control unit, modulate the electrical measurement with a carrier signal to generate a modulated signal, and transmit the modulated signal on the pipe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, explain the advantages and principles of the invention. In the drawings, 
         FIG. 1  is a diagram of a system for remote powering and communication of sensors for monitoring pipelines; 
         FIG. 2  is a block diagram of a main measurement unit for the system; and 
         FIG. 3  is a block diagram of a remote terminal unit for the system. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention include a remote system for cathodic protection monitoring of protected metallic pipelines, using the pipe itself for communication from a main measurement unit to multiple ultra-low power remote test points with sensors. The measurement data from the remote test points can be used for assessing the corrosive conditions around a pipeline section. The test points can be completely buried and thus away from accidental damage or vandalism. The test points can optionally be equipped with an RFID marker for above ground location and survey at locations along the pipeline. 
       FIG. 1  is a diagram of a system for remote powering and communication of sensors for monitoring a pipe  10  used within a pipeline. The pipeline is typically used to carry oil, natural gas, or water. The monitoring of the pipeline can be used, for example, to detect corrosion, cracks, or defects in the pipeline. 
     The system includes a main measurement unit  12  electrically coupled to pipe  10  and remote terminal units  14 ,  16 , and  18  electrically coupled to pipe  10  and located remote from each other and main measurement unit  12 . Only three remote terminal units are shown for illustrative purposes, and the system can include many remote terminal units depending upon, for example, a length of pipe  10 . Remote terminal units  14 ,  16 , and  18  are spaced apart from one another by at least one mile and more typically by at least three to five miles. Remote terminal unit  14  is likewise located at least one mile and more typically at least three to five miles from main measurement unit  12 . These distances for the spacing of the remote terminal units are based upon measurements along pipe  10 . Remote terminal units  14 ,  16 , and  18  periodically take electrical measurements from pipe  10  and transmit those measurement along pipe  10  along with identifying information such as the physical locations of the corresponding remote terminal unit and a date and time stamp of when the measurements were taken. By transmitting the electrical measurements along the pipe, the system can eliminate the need to access the pipe at the corresponding physical locations for measurements, although the remote terminal units can optionally be accessed at their physical locations in order to obtain the electrical measurements from them. 
       FIG. 2  is a block diagram of main measurement unit  12  for the system. Main measurement unit  12  includes a control unit  32 , such as a processor, for controlling operation of main measurement unit  12 . Control unit  32  is electrically coupled to a measurement unit  30 , a communication unit  26 , a logger  38 , and an optional radio frequency identification (RFID) tag or marker  34 . An auxiliary power source  28 , such as a battery, can provide power to control unit  32  and the other components in main measurement unit  12  via control unit  32 . Main measurement unit  12  can optionally include a connection to a power source, such as an electrical utility grid, with auxiliary power source  28  providing back-up power. 
     Measurement unit  30  is electrically coupled to a protection and interface unit  24  to take an electrical measurement between a reference electrode  22  electrically coupled to pipe  10  and a coupon  20  composed of a sacrificial corrosion material, for example a piece of metal similar to the material for pipe  10  and possibly with a corrosion protection coating. Reference electrode  22  can be located on pipe  10  in physical and electrical contact with the pipe. Communication unit  26  can modulate the electrical measurement with a carrier signal and transmit the modulated signal over pipe  10  via a power amplifier. Communication unit  26  can also receive, via a low noise amplifier, electrical measurements in modulated signals transmitted over pipe  10  from the remote terminal units. These received modulated signals are demodulated by communication unit  26  to obtain the electrical measurements. 
     Control unit  32  stores these electrical measurements in logger  38 , such as a non-volatile memory, for access and retrieval. For example, an external communication link  40  is electrically coupled to logger  38  to provide above ground wired or wireless access  42  to the information stored within logger  38 . The wired access can include, for example, an above ground electrical connection, such as a universal serial bus (USB), to access logger  38  via a wired connection. The wireless access can include, for example, a short-range wireless connection to logger  38  such as the BUETOOTH technology. In addition, an above ground RFID reader  36  can optionally be used to access the information stored within logger  38  via RFID tag  34  and control unit  32 . 
       FIG. 3  is a block diagram of a remote terminal unit, such as remote terminal units  14 ,  16 , and  18 , for the system. The remote terminal unit includes a control unit  62 , such as a processor, for controlling operation of the remote terminal unit. Control unit  62  is electrically coupled to a measurement unit  60 , a communication unit  56 , and an optional RFID tag or marker  64 . A power source  58 , such as a battery, provides power to control unit  62  and the other components in the remote terminal unit via control unit  62 . 
     Measurement unit  60  is electrically coupled to a protection and interface unit  54  to take an electrical measurement between a reference electrode  52  electrically coupled to pipe  10  and a coupon  50  composed of a sacrificial corrosion material, for example a piece of metal similar to the material for pipe  10  and possibly with a corrosion protection coating. Reference electrode  52  can be located on pipe  10  in physical and electrical contact with the pipe. Communication unit  56  can modulate the electrical measurement with a carrier signal and transmit the modulated signal over pipe  10 . An above ground RFID reader  66  can optionally be used to initiate and obtain the electrical measurement via RFID tag  64  and control unit  62 . 
     For both the main measurement unit and remote terminal units, the corresponding control units  32  and  62  can be programmed to take the electrical measurements at periodic time intervals, for example every three months or every six months. The control units  32  and  62  can also be programmed to initiate the electrical measurement upon receiving a signal from the corresponding RFID readers  36  and  66  via tags  34  and  64 , and transmit the measurement to the corresponding RFID reader  36  and  66  via tags  34  and  64 . Control units  32  and  62  are preferably implemented with a very low power microcontroller that runs at low voltage. Alternately, the control units can be implemented with programmable logic cells. 
     The communication units  26  and  56  can be implemented with, for example, circuitry to modulate the electrical measurement with the carrier signal and, in the case of the main measurement unit, also demodulate the received modulated signals. In particular, the communication units preferably comprise an inductor L (1 H) and a capacitor C (5 uF) connected in series to form a resonant LC tank circuit. The remote terminal units obtain their operating voltage and power from this tank circuit but can also modulate the discharge cycle of the tank circuit to communicate back to the main measurement unit. 
     The electrical measurements are modulated by the corresponding communication units  26  and  56  with a low frequency carrier signal for transmission, for example a 1 KHz signal having an 80% duty cycle. Lower frequencies, less than 1 KHz, can be used and would travel further but would also require larger LC tank circuit components. However, the carrier frequency used should avoid ambient noise caused by the 50/60 Hz power and its low order harmonics, because they may limit the usable dynamic range which reduces the usable distance. For shorter distances, higher frequencies, greater than 1 KHz, can be used. Modulation techniques known for use with RFID systems, for example, can be used to modulate and transmit the electrical measurements. 
     The remote terminal units transmit the electrical measurements to the main measurement unit when those measurements are taken, as the remote terminal units may not have a logger to store them. The main measurement unit can optionally transmit the electrical measurements taken by it to other main measurement units, if the system has more than one main measurement unit. These low frequency modulated signals can be transmitted along the pipe at least one mile and more typically at least three to five miles along the pipe to a main measurement unit located at those distances from the remote terminal units as measured along the pipe. 
     Also for both the main measurement unit and remote terminal units, the electrical measurements are taken as an electrical potential difference between the reference electrode and coupon, effectively comparing corrosion between the pipe and the coupon in order to provide an indication of possible corrosion of the pipe. The corresponding measurement units  30  and  60  can be implemented with, for example, circuitry for detecting such a potential difference and outputting a signal relating to the potential difference. The measurement units are preferably implemented with a low power low voltage analog-to-digital (A/D) converter with an interface between the measurement units and the control units. 
     The corresponding protection and interface units  24  and  54  can be implemented with, for example, circuitry to electrically interface the measurement units with the reference electrodes and coupons and to provide electrical protection for the measurement units. The electrical measurement are typically transmitted with identifying information, also modulated with the carrier signal. The identifying information can include, for example, the following for the corresponding remote terminal unit transmitting the electrical measurement: an identifier for the remote terminal unit; a physical location of the remote terminal unit such as latitude and longitude coordinates or a particular location along the pipe; and a date and time stamp of when the electrical measurement was taken. 
     Both the main measurement unit and the remote terminal units can be contained within housings for environmental protection. Furthermore, pipelines with cathodic protection already have stations in place for transmitting the power for such protection, and those stations can provide convenient locations for placing the main measurement unit and remote terminal units, although the units can be placed elsewhere along the pipeline as well.