Abstract:
A nondestructive evaluation method for determining the material used in a below ground service line includes inserting a probe with a wave measurement device therein into an area corresponding to a location of a service line; inciting a service line wave through an exposed portion of the service using a vibratory shaker; measuring, by the wave measurement device, a substrate wave created by the service line wave passing thought the service line and into the substrate; identifying, by a data acquisition system, the service line wave velocity; comparing the service line wave velocity to a known set of wave velocities in service line according to a service line material; and identifying the service line material in the service line by comparing the wave velocity in the service line with the known set of wave velocities.

Description:
BACKGROUND 
       [0001]    In 1991, the US EPA published the ‘Lead and Copper Rule’ (LCR) regulation to address the widespread legacy use of lead pipes for potable water delivery and service lines. While well-intended, the regulation received immediate push-back from municipal water utility companies that cited compliance with the regulation was too difficult to implement in the LCR&#39;s time-line and owner-utility responsibility was ill-defined. As a result, the American Water Works Association (AWWA) sued the EPA in 1993 and a Federal Appeals Court partially sided with the AWWA. After several years of back and forth, the LCR was amended in 2000 to allow for utility companies to perform partial replacements of water delivery lines. This made the problem worse, as it allowed for the utility companies to replace main water lines, but leave the lead service lines intact and the responsibility of the landowner to complete the replacement. This has left many homeowners unsure or falsely sure of whether their service lines are made of lead. 
         [0002]    This issue has come to the forefront of the Nation&#39;s attention due to the recent problems found in Flint, Michigan. Flint is not alone in their plight in dealing with this issue, nearly all urban areas have used and continue to have lead service and distribution lines. This problem is particularly worse in older and larger cities including Washington, DC, Boston and Philadelphia due to scarce records of the original pipe installations. 
         [0003]    Considering this history, there is a current need to rapidly and cost effectively identify the service line material supplying water to homeowners and residents in urban areas. Since visual line inspection or water sampling are the current methods for line material testing—the former is time and effort consuming, and the latter is costly and unreliable. 
       SUMMARY OF THE INVENTION 
       [0004]    A nondestructive evaluation method for determining the material used in a below ground service line includes inserting a probe with a wave measurement device therein into an area corresponding to a location of a service line; generating a service line wave through an exposed portion of the service using a vibratory shaker; measuring, by the wave measurement device, a substrate wave created by the service line wave passing thought the service line and into the substrate; identifying, by a data acquisition system, the service line wave velocity; comparing the service line wave velocity to a known set of wave velocities in service line according to a service line material; and identifying the service line material in the service line by comparing the wave velocity in the service line with the known set of wave velocities. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  shows a graph of sound wave velocities in various materials. 
           [0006]      FIG. 2  shows a schematic of the proposed method. 
           [0007]      FIG. 3  shows a detailed view of an accelerometer probe. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0008]    1.0 Review of NDE Techniques for the Detection and Location of Pipelines 
         [0009]    Common nondestructive evaluation (NDE) methods have different advantages and limitations when applied to the detection, location and material characterization of buried pipelines. Some of these methods are briefly reviewed in the following. 
         [0010]    1.1 Closed Circuit Television (CCTV) 
         [0011]    Originally introduced in the 1960s for the detection of leaks in pipes and sewers, this system used of a television camera inserted in the pipe and remotely controlled by an operator. Visual observation includes the collection and inspection of CCTV images for material recognition, which is usually a slow process. Moreover, these methods may require a pipe to be drained before inspection, resulting in high operative costs. 
         [0012]    1.2 Electromagnetic Induction (EMI) Methods 
         [0013]    Current state-of-the-art electromagnetic induction (EMI) metal detectors can detect small metal objects at shallow depths and large metal objects at greater depths under a wide range of environmental and soil conditions. The method introduces an electromotive force in the pipe, which in turn causes eddy currents to flow in the metal. The method compares the measured decay in time of such currents, which depends on the size, shape, and magnetic properties (conductivity and permeability) of the metal, to a signature library of conductive objects, thus enabling the detection and classification of the pipe. 
         [0014]    A method based on eddy currents, the Remote Field Eddy Current (RFEC) method, has been also developed for the inspection of both ferromagnetic and non-ferromagnetic conducting tubular from the inside. 
         [0015]    Based upon this method, a hydroscope may enable non-destructive evaluation of buried cast or ductile iron and steel pipes. This technique assesses the condition of water pipelines by sensing the changes in an electromagnetic signal as it passes through the pipe wall, which helps characterize the material. 
         [0016]    1.3 Ground Penetrating Radar (GPR) 
         [0017]    Ground Penetrating Radar (GPR) constitutes a well-established technology that uses electromagnetic waves to identify buried objects by detecting their reflections. Whenever a radar pulse strikes a boundary interface of contrasting dielectrics, a portion of the radar wave reflects back to the surface and a receiving antenna records it. The typical feature used to locate the pipes are hyperbolic patterns of the time of flight generated by a linear scan of the antenna above the surface (reflected signal traces). 
         [0018]    Although different algorithms that use GPR data have been successfully developed for detection and geometric characterization purposes (including the effect of fluid interface), the material characterization of the buried pipe remains a challenging task. Moreover, the depth of penetration is greatly reduced in presence of conductive soils such as clay and saturated soils, which induce high signal attenuation. 
         [0019]    1.4 Broadband Electromagnetics/Wave Impedance Probe (WIP) 
         [0020]    The broadband EM technique is a hybrid of Ground Penetrating Radar and electromagnetic techniques, able to detect differences in the electromagnetic impedance of the tested material. Although the system is suited for pipelines of relatively small diameter (&gt;200 mm) and shallow surveys at the 0.5-10.0 m scale, it may not be useful for other pipelines as well. 
         [0021]    1.5 Infrared Thermography (IR) 
         [0022]    This method relies on the use of an infrared scanner, sensitive to short- or medium-wave infrared radiation, to measure variations in temperature produced by the effect of the pipeline, which it converts into thermographic images in which objects are represented by their thermal rather than their optical values. However, as with the GPR, the location using infrared thermography is affected by the properties of the surrounding ground, and in particular moisture content. Similarly, ground cover and wind speed may influence results. The greatest drawback however is its inability to measure depth. 
         [0023]    2.0 Alternate Method of Detecting Pipe Material 
         [0024]    While these methods provide some vision of buried infrastructure, most face challenges in quickly and accurately characterizing the service line material. A non-destructive evaluation may measure the velocity of a propagating stress wave through a length of line. Because stress waves travel at significantly different velocities within various materials as illustrated by  FIG. 1 , a measurement of the velocity of a stress wave will give an indication to the presence of lead. This may be seen in  FIG. 1  that shows a set of service line wave velocities according to material where the wave speed in lead is ½ to ⅓ to that in other common pipe materials. 
         [0025]      FIG. 2  shows an implementation of a nondestructive evaluation apparatus that may use this wave measurement technology. As shown, a vibratory shaker  230  attached to an accessible/exposed service line  220  located within or outside a building  240 , generates a vibration and service line wave  232  in the service line  220 . The service line wave  232  propagates along the service line  220  and into the substrate as substrate waves  235 . Accelerometers within accelerometer probes  200  detect the substrate waves  235  and transmit data regarding the substrate waves  235  to a data acquisition unit DAQ  260  that analyzes the data and issues projections about the service line  220  material. 
         [0026]    The below subsections give more detail about each of these components and their application. 
         [0027]    2.1 Accelerometers 
         [0028]    The accelerometer probes  200  first would be inserted into the ground/substrate  250 . The accelerometer probes  200  may be placed in a line, grid, or other pattern corresponding to an area where a user believes a service line  220  to be. A grid pattern helps attain reliable readings of a wave  235  traveling through the substrate  250  because a grid patterns gives more readings, which minimize the effects of voids and varying substrate  250  conditions. A minimum of 2 accelerometer probes  200  in theory and 4 accelerometer probes in practice give baseline acceptable results. And even more give even better results. 
         [0029]    Within the grid, line, or other pattern, the distance between accelerometer probes  200  may ideally be between 15 cm to 5 m to a depth from the surface to just below the pavement and/or backfill line. The closer the accelerator probe  200  tip gets to the line  220 , the more accurate the data received. 
         [0030]      FIG. 3  shows a detailed view of an accelerometer probe  200 . The probe  200  includes a protective sheath  210  that is inserted or follows a drilled hole into the substrate  250 . The sheath  210  includes a hollow portion with a cavity  212  and protective or hardened tip  214 . The tip  214  may be made from stainless steel or other corrosion resistant and hardened material and may be integral with, or detachable from, a main body  211  of the sheath  210 . 
         [0031]    The sheath  210  may be 0.5 inches wide and as long as necessary to place the sheath tip  214  in close proximity to the service line  220 . Within the hollow portion  212  and resting on a platform  213  provided by the tip  214  is the accelerometer  216 . The accelerometer  216  may include an electrical connector  217  engaged to an electrical wire  218  that transmits data to the DAQ  260 . Although a wire  218  is shown, the accelerometer  216  may communicate with the DAQ  260  wirelessly. 
         [0032]    The accelerometer  216  may rest on a protective mounting  215  to minimize the effect of any damaging impacts to the tip  214 . 
         [0033]    Although this application describes accelerometers  216 , other wave/vibration measurement devices may also be used such as geophone sensors, impact echo sensors, or acoustic emission sensors. 
         [0034]    2.2 Excitation 
         [0035]    Once the accelerometer probes  200  are in place, a user begins to send various service line waves  232  through the line  220  via a hammer (not shown) or the vibratory shaker  230 . This shaker  230  imparts a frequency varying excitation to the water line  220  in the building  240  that propagates out through the service line  220 . In use, a user may send a broad range of amplitudes and frequencies through the line  220  from 0.01 kHz to 1,000 kHz. The lower frequency waves will not react to corrosion and other defects in the line  220  in the same way that higher frequency waves will, but the variety of waves traveling through the line  220  will give the DAQ  260  more data points. 
         [0036]    As the waves  235  travel through the service line  220 , some of the energy of the wave may be lost to the substrate  250 . This loss may travel to the embedded probes  200  and be identified via the DAQ  260 . 
         [0037]    2.3 Measurement and Data Acquisition 
         [0038]    Referring again to  FIG. 2 , as the service line wave  232  travels through the line  220 , it excites substrate waves  235  that are detected by the accelerometer probes  200 . To measure the velocity that the service line wave  232  is traveling through the line  220 , the DAQ  260  may record the distance “d” between a first and second probe  200   a,    200   b  and the time elapsed between receipt of the substrate wave  235  detection at each probe  200   a ,  200   b.  The velocity of the shaker wave  232  may be measured by dividing the distance d by this time. 
         [0039]    The DAQ  260  or other processor may then compare this velocity to known velocities in various material service lines  220  to determine the material used in the line  220 , as shown in  FIG. 1 , for example. 
         [0040]    In use, the DAQ  260  collects many data points from the various waves and frequencies and performs statistical analysis to discard outlier data that may be caused by tree roots, pipe irregularities, substrate changes, etc. to arrive at a projected line wave speed and material. 
         [0041]    The above method and apparatus may yield rapid testing times of approximately 1 hour and result in minimal disturbance to the pavement/sidewalk/ground. 
         [0042]    While the invention has been described with reference to the embodiments above, a person of ordinary skill in the art would understand that various changes or modifications may be made thereto without departing from the scope of the claims.