Abstract:
Ultrasonic transducers are imbedded into sacrificial metal coupons which are located in the vicinity of underground or aboveground structures, such as a pipe or tank, which allow for the measurement of the effectiveness of impressed current cathodic protection systems and can be used to determine the corrosion rate of the structure that is being protected. When excited by a pulser-receiver excitation pulse, the ultrasonic transducers can be used to determine the thickness of the coupon and its rate of change over time. The sacrificial metal coupon ultrasonic transducer assembly can be located in the vicinity of underground piping, under or inside of a tank, underground or underwater, or inserted into structures where absolute material loss values or material loss rate of change is being monitored.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 62/213,813, filed Sep. 3, 2015, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    This application relates to the use of ultrasound transducers imbedded into a sacrificial anode that is located in the vicinity of an underground structure, such as a pipe or tank, for measuring the effectiveness of impressed current cathodic protection systems and determining the corrosion rate of the structure that is being protected. 
       BACKGROUND 
       [0003]    Buried or immersed metal structures, such as pipes and tanks, are exposed to an electrochemical corrosion process in the underground environment. The metal structure becomes an electrode and the soil an electrolyte so that an electrolytic cell is formed causing the corrosion of the buried structure. Some corrosion arises from naturally occurring processes at specific locations on the underground structure involving electrical current flow into the ambient soil electrolyte from sites acting as anodes via the corrosion reaction. Current will flow to specific locations on underground structures acting as cathodes where reduction reactions occur. Corrosion can also be caused or accelerated by voltages applied to a local region of the pipe by manmade structures, including local transit systems, overhead sub-surface power distribution systems, and industrial plants. 
         [0004]    There are generally two methods to protect the underground structure from corroding. These methods are referred to as “cathodic protection.” The first method is to attach sacrificial anodes onto or near the underground structure being protected, and the second is to install an impressed current system that generates a DC voltage and a low constant current in the specific vicinity of the structure being protected. 
         [0005]    Sacrificial anodes are pieces of metal more electrically active than the underground structure that can be attached to the underground structure for corrosion protection. Because these anodes are more active than the underground structure, the corrosive current will exit from the sacrificial anodes rather than from the underground structure. Thus, the underground structure is protected while the attached anode is sacrificed. Depleted anodes must be replaced for continued corrosion protection of the underground structure. 
         [0006]    An impressed current system uses a rectifier that converts alternating current to direct current. This current is sent through an insulated wire to the anodes, which are metal bars buried in the soil near the underground structure being protected. The current flows through the soil to the underground structure and returns to the rectifier through an insulated wire attached to the underground structure. The underground structure is protected because the current going to the underground structure overcomes the corrosion-causing current normally flowing away from it. 
         [0007]    With a cathodic protection system, industry accepted criteria involve the measurement of the electrochemical potential of the structure to establish the level of cathodic protection sufficient to mitigate corrosion of the buried metal structure. The ordinary practice to determine the necessary level of cathodic protection is to measure the potential difference between the buried structure, which is an electrode, and a reference electrode placed, at grade, in contact with the soil, which is an electrolyte. However, when this measurement is taken while the cathodic protection system is operating, a voltage drop through the soil due to the cathodic protection current, referred to as the IR (voltage) drop, causes an error in the potential measurement. 
         [0008]    In order to measure a potential that is free of IR drop, it is common to measure the potential immediately following interruption of the cathodic protection current. The instantaneous voltage drop which occurs immediately after the cathodic protection is turned off is equal to the IR drop caused by the interrupted cathodic protection current. Because the electrochemical interface of the protected structure has a capacitive component, the potential of that interface does not change immediately following interruption as does the IR drop. Therefore, the potential measured immediately following interruption of the cathodic protection current, when current, I, is zero, is the potential of the protected structure free of IR drop. This potential is referred to as off-potential. 
         [0009]    Problems arise in interrupting the cathodic protection. Extremely long buried pipelines have multiple cathodic protection stations, all of which must be interrupted simultaneously, or interrupted using a non-synchronous method in which all of the IR drops are summed. Galvanic cathodic protection systems are not designed to be interrupted because the anodes are typically directly connected to the protected structure. Additionally, second-party cathodic protection systems that are either unknown or cannot be interrupted may be present in the area. Other problems exist, also, such as stray current effects, e.g., from power distribution systems, dc transit systems, etc., that are not interruptable, and rapid IR transients, which immediately follow interruption. For instance, AC current magnetic fields created in the vicinity of high voltage power lines can propagate into the earth and induce corrosion. This is known as AC-induced corrosion. Such corrosion on cathodically protected underground pipelines is commonly the result of a combined action of the induced AC voltage, the cathodic protection conditions, a piping coating defect and the chemical and physical conditions of the soil. As a result, both DC and AC current fields can influence corrosion of underground structures. 
         [0010]    In order to avoid the problems associated with interruption of the entire cathodic protection system, “coupons” are used to monitor the level of cathodic protection on buried metal structures such as pipes. The coupon is a bare metal sample having substantially the same metallurgical attributes as the pipe or other structure being monitored. The coupon is placed in the soil near the pipe and connected to the pipe. Therefore, the coupon is exposed to the same cathodic protection current source as the pipe. The connection between the pipe and the coupon is interrupted for a time period, during which time the potential difference between the coupon and a reference electrode is measured. The pipe&#39;s cathodic protection is never interrupted, since only the pipe-to-coupon connection is interrupted. The coupon&#39;s potential simulates the potential of a pipe coating defect of a similar surface area as the coupon. The coupon&#39;s potential can be measured without interrupting the cathodic protection to the pipe, and therefore without some of the problems inherent in interrupting the entire cathodic protection system. In addition, once the coupon is interrupted, it is an isolated, small piece of metal in the soil and stray currents are eliminated from its surface. In contrast, stray currents are generally not eliminated from a pipeline upon interruption of the entire cathodic protection system. 
         [0011]    Despite the existence of a significant number of devices for determining the effectiveness of cathodic protection, the need exists for a simple, inexpensive and accurate measuring device. In the description provided above, the coupon serves as a simulation of the behavior of the underground structure that is being protected. The coupon is used for measuring changes in electrical potential near and in the vicinity of the underground structure that is being protected. The changes in electrical potential are characteristically “noisy.” That is, the changes in the electrical potentials or the resistance of a coupon are not always consistent and are affected by temperature variations, the presence of stray currents themselves, instrumentation calibration challenges and operator error. There is a need for coupons that are not impacted by environmental or operator data-acquisition variables; coupons that can be measured with more precision and accuracy. 
       SUMMARY 
       [0012]    The present invention solves the foregoing problems by providing a coupon imbedded with one or more ultrasonic transducers that can determine the thickness of the coupon and can be energized and read from the surface by an operator with a suitable ultrasound pulse/receiver instrument. The piezoelectric ultrasound transducer converts the pulse of electrical energy into an acoustic pressure wave (sound). The pressure wave is coupled to the surface of a plate via fluid in a reservoir, or by an equivalent acoustic coupler. Most of the energy (sound) is reflected from the front surface of the plate due to the acoustic impedance discontinuity. Some energy enters the plate and travels through the plate and is reflected from the back surface of the plate back towards the front surface. Some of the reflected energy leaves the front of the plate and some is reflected towards the back surface of the plate. This reflection process continues. Energy is lost from the plate boundary surfaces for each reflection. Energy lost at the front of the plate travels back towards the ultrasound transducer where it is received and converted back to electrical energy. The electrical pulses received represent the two way acoustic front-to-back acoustic travel times. The thickness of the plate can be estimated by measuring the pulse to pulse travel time and knowing the velocity of sound in the plate under test. By searching for a reduction in the plate thickness, plate corrosion or pitting can be located. 
         [0013]    The transducers can be positioned directly underneath the coupon&#39;s surface and can, on operator demand, measure the thickness of the coupon. The coupon&#39;s thickness will change as the metallurgy of the underground structure changes in a way that alters the thickness of the coupon material as well. This information provides a direct rather than an inferred measure of rate of material loss due to any corrosion activity that may be occurring with the underground structure under protection. 
         [0014]    In one of many possible embodiments of the invention, the system includes two “smart ultrasonic coupons” or for simplicity “probes.” Each ultrasonic transducer has 2 wires. Each probe has 2 to 3 transducers; therefore, there are 4 to 6 transducer wires that allow each transducer to be activated from the surface by an operator. There is an additional ground wire available to the operator for each probe. Additionally, one probe has a reference electrode with a wire connected to it and available at the surface for operator access. A wire also is connected to the underground structure and is also available to the operator at the surface. This arrangement provides the operator with all the functionality associated with traditional cathodic protection test stations. However, the addition of the ultrasonic coupons located within each probe provides the operator with the added ability to directly monitor metal loss, a more accurate assessment of underground structural integrity. 
         [0015]    Coupons with imbedded ultrasonic transducers optionally but preferably can include one or more of the following features:
       1. Frequencies of the probe can be selected based on the required thickness of the coupon.   2. The metallic, sacrificial material within each probe can be changed to match that of the structure being monitored.   3. The area of the exposed surface of the coupon can be modified to accommodate increased sensitivity to DC current (10 cm 2 ) or AC current (1 cm 2 ).   4. The distance of the transducer from the coupon can be changed to improve the quality of the ultrasonic return and better decipher the echo-to-echo pulses needed to determine coupon thickness and change of thickness sensitivity.   5. Each transducer within the probe can generate a bulk wave that can be received by any adjacent transducer. Such a bulk wave can be used to evaluate local changes in the coupon surface that might not be detected if not present directly above an individual transducer.   6. Signal processing techniques can be applied to the activation and signal reception of each ultrasonic transducer such that “chirp” signals can be generated, received and analyzed in addition to traditional pulse-echo signals.       
 
         [0022]    Non-limiting examples of applications for which a cathodic protection test station of the present invention can be used include:
       1. Aboveground or belowground tanks   2. Aboveground or belowground pipes and piping   3. Submerged structures such as those for bridges and buildings   4. Underground pilings, tunnels, and related infrastructure       
 
         [0027]    The ultrasonic cathodic protection test station of the present invention solves many of the monitoring accuracy and handling problems through the use of one or more piezoelectric ultrasonic testing (UT) transducers integrated into a sacrificial coupon. UT transducers are known to the non-destructive testing industry as one of the most accurate, repeatable and precise methods of determining material degradation and material loss. UT transducers have not been used in connection with sacrificial coupons, at least in part, because of the inability to effectively secure an ultrasonic transducer to a coupon for long periods of time. The connection interface between the UT transducer and the coupon changes over time, e.g., by evaporation or other chemical or physical changes, and as a result the ability of the transducer to transfer acoustic energy to the coupon is affected. The present invention solves this problem, and as a result UT transducers can be used to measure and monitor changes over time in a sacrificial coupon. 
         [0028]    The present invention further solves the foregoing problems by providing a coupon-ultrasonic measurement system combined with one or more transducers for determining material loss. The system includes a sacrificial coupon; one or more transducers supported under the sacrificial coupon and responsive to electrical energy from a pulser/receiver; remotely-located drive circuitry for energizing and receiving energy from the transducers; an attachment mechanism for use in above ground storage tanks for positioning the sacrificial coupon and transducer assembly under the tank; an a cabling mechanism for use adjacent to an underground pipe or underground tank; and processing and memory means for producing the excitation pulse, receiving the transmitted pulse, processing the signal to determine material thickness, and storing the resultant material thickness values for display and tracking. 
         [0029]    A sacrificial metal coupon is provided with one or more ultrasonic transducers which, when excited by a pulser-receiver excitation pulse, determines the thickness of the coupon and its rate of change over time. The sacrificial metal coupon ultrasonic transducer assembly can be placed adjacent to a pipe, under or inside of a tank, underground or underwater, or inserted adjacent to structures where absolute material loss values or material loss rate of change is being monitored. In order to characterize the type of metal loss due to corrosion or erosion, the excitation pulse can be a pulse-echo or chirp pulse and one transducer can insonify the coupon and the second transducer can receive the transmission a fixed distance away for further analysis. The use of ultrasound to measure metal loss in a sacrificial coupon minimizes the inaccuracy of traditional sacrificial coupon metal loss measurements and provides for a more convenient and safe method for determining coupon integrity. 
         [0030]    The test station&#39;s coupon-ultrasonic material measurement system can also be used to evaluate the effectiveness of chemical inhibitors which are used to mitigate the impact of localized electrical interference by changing the resistance characteristics of the surrounding earth electrolyte conditions. The UT test station, in its standard configuration, consists of a reference electrode, e.g., CuCuSo4 material, used to simultaneously measure the effectiveness of neighboring electromagnetic fields generated by cathodic protection impressed current systems. 
         [0031]    One aspect of the invention is a corrosion coupon probe including: two or more coupon bodies adapted for receiving sensors, receivers, transmitters, electrical components, and cabling for altering the distance of the corrosion coupons from the primary aboveground test station; cabling connected to the coupon body and adapted for receiving an ultrasonic testing (UT) transducer; one or more UT transducers secured to the coupon holder member; an acoustic couplant positioned adjacent the one or more UT transducers; a sacrificial coupon connected to the coupon holder member such that the sacrificial coupon is adjacent the acoustic couplant; an attachment body for inserting the sacrificial coupon into a liquid or underground, dry environment; and a reference electrode either attached to or positioned adjacent to the coupon body for simultaneously measuring corrosion rate of the sacrificial coupon and an electromagnetic field created by an impressed current cathodic protection system. 
         [0032]    A second aspect of the invention is a corrosion coupon probe including: a sacrificial coupon; one or more UT transducers; and an acoustic couplant, wherein the one or more transducers are connected to the sacrificial coupon and the acoustic couplant is positioned between the sacrificial coupon and the one or more UT transducers. 
         [0033]    A third aspect of the invention is a corrosion monitoring system including: a corrosion coupon probe having (i) a sacrificial coupon, (ii) one or more UT transducers, and (iii) an acoustic couplant, wherein the one or more transducers are connected to the sacrificial coupon and the acoustic couplant is positioned between the sacrificial coupon and the one or more UT transducers; processing means for producing an excitation pulse, for receiving a transmitted pulse from the sacrificial coupon, and for processing signals to determine sacrificial coupon material thickness; and memory means for storing material thickness values determined by the processing means. 
         [0034]    A fourth aspect of the invention is a separate wire that is welded to an aboveground or underground structure that is being protected and terminated at the at-grade, remote, test station for acquiring data for tracking and reporting. 
         [0035]    A fifth aspect of the invention is the presence of a ground reference wire fastened to each of the underground, or under tank, coupons and terminated at the at-grade test station. 
         [0036]    A sixth aspect of the invention is the presence of an above ground test station where all of the above-cited wires are terminated on separate test points along with the multi-pin connector containing the corrosion coupon probe UT transducer wires for receiving a transmitted pulse from the sacrificial coupon, and for processing signals to determine sacrificial coupon material thickness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
           [0038]      FIG. 1  is an exploded view of one of many possible embodiments of an ultrasonic cathodic protection test station; 
           [0039]      FIG. 2  is an exploded view of one of many possible embodiments of an ultrasonic corrosion coupon; 
           [0040]      FIG. 3  illustrates two potential operating locations of the test station; 
           [0041]      FIGS. 4A-4E  illustrate five modes of electrical to mechanical energy conversion used to characterize the amount of and type of material loss; 
           [0042]      FIG. 5  is a block diagram of the total coupon probe inspection system showing the relationship between the data logger and the test station probe assembly; and 
           [0043]      FIG. 6  illustrates the electrical terminals and connector for pulsing the UT transducers and receiving the UT data from the UT sacrificial coupons. 
       
    
    
     DETAILED DESCRIPTION 
       [0044]    Referring generally to  FIG. 1 , there is shown an embodiment of an ultrasonic cathodic protection test station (“test station”)  100  of the present invention. The test station  100  includes a mounting tube (:tube”)  102  that is adapted for receiving sensor wires and/or transmitters, electrical components, and various connectors for configuring the tube  102  depending on the intended use of the test station  100 . The tube  102  optionally but preferably includes a data I/O terminal  106 , which optionally but preferably is detachably fastened to the tube  102 . 
         [0045]    Two or more ultrasonic coupons can be located via a cabling assembly at any distance from the test station tube  102 . The shape of the coupon can be altered to fit the requirements of the environment that it is monitoring. In  FIG. 1 , two types of coupon bodies are shown. A round body  103  coupon preferably is used adjacent to, for instance, an underground pipeline. An elongated body  104  coupon can be used for use in aboveground storage tanks. A wire  105  is provided for attachment to an underground structure, in the case of a pipe, for instance, or for attachment to an above or below ground tank. The wire  105  is terminated at the I/O terminal  106 . A reference electrode assembly  107  is connected to a cable assembly of any length that is terminated at the I/O terminal  106 . Ground wires  108  and  109  are connected to each of the UT sacrificial coupons, e.g.,  103 , and terminated at the I/O terminal  106 . 
         [0046]    The test station  100  can include a data logger  110 , which optionally but preferably contains software to pulse and acquire the UT information, prepare the data for subsequent analysis within the data logger, or transmit the data wirelessly to a remotely located receiver. The data logger  110  further can be used to organize the data within a database for future analysis. The data logger  110  can interface to any computer  112  via an input/output cable such as a USB cable. 
         [0047]    The test station  100  can include an umbilical  111  in communication with the data logger  110 , which optionally but preferably is interfaced with a general purpose computer or has independent processing means, and further includes a pulser/receiver unit. The umbilical  111  can transmit electrical energy, or pulses, created by the pulser/receiver in the data logger  110  to the test station coupons  103  or  104 . The umbilical  111  also can transmit an electrical representation of the return signal from one more transducers in the test station  100  coupon  103  or  104  back to the data logger  110 . 
         [0048]    Referring generally to  FIG. 2 , there is shown one of many possible embodiments of an ultrasonic corrosion coupon transducer assembly (“transducer assembly”)  200 . The transducer assembly optionally but preferably has a body with one or more openings. A piezoelectric chip  201  can be positioned in each of the openings in the transducer assembly  200 . For purposes of this invention, “piezoelectric chip” and “transducer” can be used interchangeably. In one of many possible alternative embodiments of the invention, the transducers  201  can be connected to a bottom surface of a coupon  203  by machine screws or other fastening means. An acoustic couplant  202  can be positioned within the transducer assembly  200  adjacent to the sacrificial coupon  203  and couplant  202 . The acoustic couplants  202  are placed between the face of the piezoelectric chips  201  in the transducer assemblies  200  and the bottom surface of the coupon  203 . As the machine screws or other fastening means are tightened, the couplants  202  are compressed to a fixed point that will not alter the quality of the UT transducer A-scan. The transducer assemblies  200  optionally but preferably are sealed and are waterproof so the assembly  200  can be positioned anywhere to monitor metal loss remotely using ultrasound as long as the wiring is properly sealed. 
         [0049]    The coupon  202  material can be of one or more types of metal or non-metal that are subject to loss of integrity due to corrosion or erosion and where the loss and rate of loss can be precisely measured with the use of ultrasound transducers attached to the coupon material. In an alternative embodiment, the coupon material can be of one or more types of metal or non-metal that are subject to loss of integrity due to chemical attack and where the chemical attack can be associated with change in the exposed liquid product quality or a change in process conditions. In yet another alternative embodiment, the coupon material can be of one or more types of metal or non-metal that are subject to loss of integrity due to corrosion, erosion or chemical attack and where the electrical pulses of one or more transducers can be used to induce one or more different mechanical wave patterns which can be used to characterize the amount and type of material loss on the surface of the coupon material. 
         [0050]    The ultrasonic corrosion coupon assembly  200  can be placed near or offset from a surface it is designed to monitor. The ultrasonic corrosion coupon  203  is used as a surrogate to extrapolate the corrosion, pitting, metal loss, etc. of the pipe or other structure being monitored. The changes to the coupon  203  are representative of the changes to the pipe or other structure being monitored, and the condition of the structure being monitored can be determined indirectly by monitoring the status of the coupon  203  from the I/O terminal  106 . 
         [0051]      FIG. 3  shows two of the many possible locations for the placement of an ultrasonic cathodic protection test station  100 . The test station  100  can be placed adjacent to a mechanical structure, such as an aboveground storage tank. The coupon  113  located on the elongated embodiment of a ultrasonic test station probe  114  can be used as a surrogate to extrapolate the corrosion, pitting, metal loss, etc. of the storage tank or other structure being monitored. The changes to the coupon  113  are representative of the changes to the underside of the tank, e.g., the condition of the tank floor or other structure being monitored can be determined indirectly by monitoring the status of the coupon  113 . The probe  114  also can include a reference electrode  115 , which can be used to measure potential difference of the impressed current impinging on the pipe or tank bottom, for instance, and ground. The data logger  116  contains software to pulse and acquire the UT information, prepare the data for subsequent analysis within the data logger, or transmit the data wirelessly to a remotely located receiver, and organize the data within a database for future analysis. 
         [0052]    As shown in  FIGS. 4A-4E , there are at least five modes of mechanical energy signal processing that may be applicable to the present invention. The first mode, shown in  FIG. 4A , is created by the compression of the material directly under the UT transducer that reverberates from the front surface of the coupon to the back surface. The thickness of the coupon material can be determined by dividing the signal travel time from surface-to-surface in the coupon material by the speed of sound of the material. 
         [0053]    The second mode, shown in  FIG. 4B , of mechanical energy created by the UT transducer is referred to as a bulk wave. The bulk wave is created by one UT transducer, Transducer(i), that is received by the adjacent UT transducer, Transducer(ii), located a fixed distance from the transmitting UT transducer. The energy transmitted into the coupon material will change as a function of any change in the mechanical integrity of the coupon. Changes in mechanical integrity can be in the form of overall reduction in thickness, the appearance of localized pitting or the appearance of cracks. The total energy created by the bulk wave can be referred to as the root mean squared (RMS). The RMS value of a set of continuous-time waveforms is the square root of the arithmetic mean of the squares of the values, or the square of the function that defines the continuous waveform. The formula for a continuous function (or waveform) f(t) defined over the interval T 1 &lt;t&lt;T 2  is: 
         [0000]    
       
         
           
             
               
                 f 
                 rms 
               
               = 
               
                 
                   
                     1 
                     
                       
                         T 
                         2 
                       
                       - 
                       
                         T 
                         1 
                       
                     
                   
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                       ∫ 
                       
                         T 
                         1 
                       
                       
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                               ( 
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                         2 
                       
                        
                       
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             , 
           
         
       
     
         [0054]    and the RMS for a function over all time is 
         [0000]    
       
         
           
             
               f 
               rms 
             
             = 
             
               
                 lim 
                 
                   T 
                   → 
                   ∞ 
                 
               
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                 . 
               
             
           
         
       
     
         [0055]    The effective RMS voltage (or power) of one or more sinusoids can be obtained without the use of calculus and can be calculated by squaring a waveform, taking the mean of the squared waveform and then computing the square root, as given by: 
         [0000]    
       
         
           
             
               V 
               rms 
             
             = 
             
               
                 
                   mean 
                    
                   
                     [ 
                     
                       
                         v 
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                           ( 
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               = 
               
                 
                   
                     area 
                      
                     
                         
                     
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                     under 
                      
                     
                         
                     
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                     the 
                      
                     
                         
                     
                      
                     curve 
                      
                     
                         
                     
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                       of 
                        
                       
                           
                       
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                     observation 
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                     length 
                   
                 
               
             
           
         
       
     
         [0000]    where the observation length is the period, or integer multiple of the period, for as long as possible for the aperiodic signals generated by the piezoelectric-induced mechanical waves in the coupon. The total RMS value for any bulk wave can be measured and the resultant RMS return can be displayed as depicted in  FIG. 4C . 
         [0056]    An additional way to provide greater information about the current condition of the coupon and any change due to external factors is through the frequency response of the coupon. The total frequency response associated with the mechanical vibrations produced by the coupon as a result of the piezoelectric transducer, shown in  FIG. 4D , can provide information about changes in the coupon&#39;s integrity. A fast Fourier transform (FFT) algorithm can be used to convert components of a signal, in this case mechanical vibrations, from its time domain to a representation in the frequency domain. There are a number of different types of FFT formulas but the most common one used for discrete Fourier analysis is noted below and is used in the current embodiment of the coupon-ultrasonic material measurement system: 
         [0000]    
       
         
           
             
               
                 X 
                 k 
               
               = 
               
                 
                   
                     ∑ 
                     
                       n 
                       = 
                       0 
                     
                     
                       N 
                       - 
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         [0057]    Finally, another method of detecting change in the integrity of the coupon is through the use of a spectrographic analysis as shown in  FIG. 4E . In the this case, the mechanical energy resulting from the vibrations produced by the coupon as a result of the piezoelectric transducer can be displayed in terms of the coupons frequency response distributed over time. 
         [0058]      FIG. 5  depicts the relationship of the components of a UT testing station  100 . One or more coupons, e.g., a round coupon  103  or an elongated coupon  104 , depending on the structure to be monitored and its location, is communicably connected with an I/O terminal. The I/O terminal can be connected to a data logger, which optionally but preferably contains software to pulse and acquire the UT information, prepared the data for subsequent analysis within the data logger, or transmits the data wirelessly to a remotely located receiver. The data logger further can be used to organize the data within a database for future analysis. The data logger can interface to any computer via an input/output cable such as a USB cable. 
         [0059]      FIG. 6  shows one of many possible embodiments of an I/O terminal  600  with terminal connections: a reference electrode  601 ; a connection  602  to a wire connected to an underground structure; a connection  603  to an UT coupon located adjacent to the underground structure; a connection  604  to an UT coupon located further away from the underground structure; and one or more external electronic connectors  605  can be included and adapted for receiving an electronic connector extension cable  606  or an umbilical. An umbilical can be used as a conduit that houses wires necessary for providing electrical pulses to and from a pulser/receiver, which can be either attached to or located remotely from, a coupon-ultrasonic material measurement system of the present invention. A Radio Frequency Identification Device (RFID)  607  can be located onto the terminal I/O block  600 . 
       CONCLUSION 
       [0060]    While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the invention should not be limited by any of the above-described exemplary embodiments.