EPA/600/A-96/107
LEAK DETECTION/LEAK LOCATION IN
UNDERGROUND PIPELINES
Anthony N. Tafuri, James J. Yezzi, Jr.
U.S. Environmental Protection Agency
2890 Woodbridge Avenue
Edison, NJ 08837
Daniel J. Watts, John M. Carlyle
New Jersey Institute of Technology
323 Martin Luther King Blvd.
Newark, NJ 07102
For Presentation at
15th Biennial International Conference on the
Prevention, Behavior, Control and Cleanup of Oil Spills
Fort Lauderdale, FL
April 7-10, 1997

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Paper ID # 432, 1997 International Oil Spill Conference
LEAK DETECTION/LEAK LOCATION
IN UNDERGROUND PIPELINES1
Anthony N. Tafuri, James J. Yezzi, Jr.
U.S. Environmental Protection Agency
2890 Woodbridge Avenue
Edison, NJ 08837
Daniel J. Watts, John M. Carlyle
New Jersey Institute of Technology
323 Martin Luther King Blvd.
Newark, NJ 07102
ABSTRACT : The utilization of passive acoustic techniques to detect and locate leaks in
underground pipelines that carry pressurized liquids is being investigated in a joint research
program between the Department of Defense (DoD), the Department of Energy (DOE), and the
U.S. Environmental Protection Agency (EPA). Acoustic techniques offer more cost effective,
timely and accurate leak detection/location than currently established techniques; e.g.,
methodologies based on volumetric changes and others based on pressure loss. An experimental
facility for determining the capabilities and limitations of improved leak detection/leak location
methods based on advanced acoustic principles is being developed at EPA's Urban Watershed
Research Facility in Edison, NJ. Four representative pipeline systems will be installed and
evaluated: one typical of the petro- chemical industry, one typical of a Navy/Air Force hydrant
Opinions or assertions expressed in this paper are solely those of the individual authors and do
not necessarily represent the views and policies of the U.S. Environmental Protection Agency
(EPA). Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.

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refueling system, one typical of an Army central heating system, and a fourth typical of pipelines
associated with low level liquid wastes at DOE facilities. Results of acoustic experiments on an
existing 2 inch diameter test line have indicated that the fundamental theory behind passive
acoustic leak detection/location is solid Several different acoustic leak detection and location
methods have been explored to date; data have been produced by all of the techniques, proving
their usefulness.
INTRODUCTION
During the last ten years, the nation has become increasingly aware of the potential, and in many
cases the reality, of environmental damage from leaks in underground storage tanks and related
pipelines. Federal and state regulations have been developed that mandate inspections and regular
testing and encourage specific designs and materials of construction for underground storage
systems. More specifically, existing federal regulations (40 CFR Parts 280 and 281, September
1988) require that underground tanks and pipelines containing petroleum products and other
hazardous substances be tested for leaks on a regular basis and that once a leak has been detected,
it be corrected. While this requirement appears to be relatively simple, it, in fact, presents
substantial difficulty in implementation.
Over 300,000 releases from underground storage tanks and pipelines have been confirmed to date
and the EPA estimates that as many as 15 to 20% of the approximately 1.8 million regulated
underground storage systems in the country either are leaking or are expected to leak in the near
future. In addition, there are over 750,00 regulated aboveground storage facilities with similar

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problems. Most of these releases are caused by pipeline failure. There is an enormous number of
miles of pipeline associated with retail gasoline service stations; airport fueling facilities; Army,
Air Force, and Navy fueling depots; low level liquid waste management systems; nuclear power
plants; chemical manufacturing facilities; and similar installations throughout the country.
Undetected leaks pose a significant threat to environmental quality and public health. For
example, approximately half of the water supply in the United States comes from ground water.
Small quantities of gasoline released underground can contaminate millions of gallons of potable
water with contaminants such as benzene, a suspected carcinogen. Inland/overland pipeline
releases can also contaminate surface waters. The problem is not limited to water contamination,
leaking petroleum products can release vapors that seep into sewage systems and vaporize into
the air. These threats and the estimated $30 billion cost to remediate the results of pipeline leaks
clearly quantifies the national need for an effective and reliable leak detection and location
system.
The EPA, DoD, represented by the Army, Navy and the Air Force, and the DOE recognized this
problem and have developed a joint research program to develop equipment and protocols to
detect and locate leaks in these types of conveyance systems. This joint research program is
sponsored by DoD's Strategic Environmental Research and Development Program (SERDP), and
is being conducted by the New Jersey Institute of Technology's Emission Reduction Research
Center under a grant from the National Science Foundation.

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BACKGROUND
Presently only two methodologies are used to detect leaks in underground pipelines, one based
upon volumetric changes and the other on pressure loss. Both of these methods are time
consuming, costly and disruptive to operation of the pipeline; neither method can locate leaks.
A proposed new method for locating leaks in underground pipelines involves the application of
passive acoustic principles. EPA's National Risk Management Research Laboratory has
conducted applied research on acoustic technology for rapid, near-real-time leak detection and
location in pressurized pipelines typical of those found at retail service stations. The results of
these early activities suggest that acoustic measurements combined with advanced signal
processing can provide a means to detect and locate small leaks over long distances in pressurized
pipelines (Eckert, et al, 1992). The methodology locates leaks literally by the sound that is made
when the liquid escapes into the soil. This technique offers a more cost effective, timely and
accurate location than both of the other currently employed methodologies since pipelines can be
tested in minutes rather than days; leaks can be located without the use of costly, invasive
techniques; and remediation costs and product loss are reduced by timely and accurate leak
location. Further, the potential on-line monitoring capabilities of passive acoustics should allow
better control over product transfer systems. The major benefit of this capability will be the early
detection and location of leaks and the timely shutdown of leaking pipelines, thus helping to
prevent the release of contaminants into the environment.

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In order to obtain general industry acceptance of acoustic leak location, it is necessary to first
prove the claimed capabilities of the technique, and also define its limitations. Accordingly, the
applied research program discussed in this paper has been undertaken to develop passive acoustic
principles for improved leak detection/location in pipelines of varying sizes and configurations.
EXPERIMENTAL FACILITY
The task of the SERDP research program is to design, develop and demonstrate a passive
acoustic leak detection and location system that can be used on existing and newly installed
pipelines; pipeline systems that cannot be breached; and pipeline systems of various sizes,
compositions and configurations. Because this is an applied research program, emphasis is being
placed upon pipelines of interest to the constituent members of SERDP(/.e., Army, Navy, Air
Force, DOE). Accordingly, the following pipelines were chosen for acoustic experimentation:
(1) a 2 inch diameter pipeline typical of those found in the petro chemical industry; (2) a 12 inch
diameter pipeline typical of aircraft refueling hydrant systems used by the Navy and Air Force; (3)
a double-walled insulated pipeline, consisting of a 12 inch outer conduit and a 4 inch insulated
central carrier, typical of that used in Army central heating installations; and (4) a double-walled
pipeline, consisting of a 2 inch diameter carrier and a 4 inch diameter annulus containing a
pressurized gas.
These experimental pipelines are being installed at the EPA Urban Watershed Research Facility
located in Edison, NJ. The 12 inch diameter Navy/Air Force hydrant system will be 1000 feet
long and will have a dedicated test bed leak area, in which special pipeline spool pieces

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(containing artificial and natural leaks) can be bolted into the pipeline via flanges. The test bed
will measure 30 feet long by 9 feet wide and will contain a sloping entrance ramp to allow for
manipulation of the spool pieces and removal, replacement and compaction of the soil. Three
flanged sections along the pipeline will enable the evaluation of the acoustic effects of tees, valves
and flow diversion upon the leak signal.
The Army heating system will feature 500 feet of double-walled Ricwil® piping (consisting of a 4
inch diameter central carrier surrounded by 4 inches of calcium silicate insulation, all contained
within a 12 inch outer conduit) followed by 500 feet of 4 inch diameter return pipe. The Ricwil®
piping will be welded since the annulus between the central carrier and the outer conduit must
maintain 15 psi of pressure. The test line will contain a horizontal expansion loop and a teed-in
stub of 2 inch central carrier Ricwil piping, intended to permit investigation into their acoustic
effects on leak signals.
Ancillary equipment will include appropriate pumps, heaters and storage tanks. Flow through the
Navy/Air Force hydrant system will range up to 2,800 gpm, at 100 psi to 150 psi of pressure, at
ambient temperature. Flow through the Army system will range up to 1,000 gpm, at 50 psi of
pressure, at 200 degrees Fahrenheit.
Leaks will be generated with leak flow rates as small as 0.1 gph under operating conditions. This
will be accomplished using both natural and artificial leak sources. The artificial leak sources will
be comprised of plug inserts containing precision drilled holes, while the natural leak sources will
consist of actual pipe defects found in service by the Navy and the Army. The manner in which

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the leak sources are inserted into the pipeline is critical since acoustic impedance mismatches
could invalidate experimental results. Ideally, what is required are acoustically transparent joints
between the pipeline and the leak source; in practice, consistency of acoustic coupling is the key .
to experimental success. Other experimental details are the type, compaction value and water
content of the soil around the pipeline. These factors affect the acoustic impedance of the soil,
which in turn governs the attenuation of the sound as it propagates down the pipeline.
ACOUSTIC EXPERIMENTS
Experiments were conducted to guide the final design of the pipeline systems (e.g., configuration,
length, leak rates, backfill material and conditions) using the existing 2 inch diameter, 200 foot
long pipeline (subsequently extended to 500 feet) filled with pressurized water at the EPA Test
Facility (Pollock, 1996). The experiments were conducted using a variety of commercial-offrthe-
shelf instruments, that employed several location techniques, sensor types and leak sources.
Signal detection is the most important part of passive acoustic leak detection. The leak generates
a quasi-steady-state signal, which is superimposed on background noise (caused by pumps, flow
through the pipe, vehicles, etc.). To locate the leak in this environment it is necessary to find a
signal characteristic that belongs only to the leak itself, and cannot be a part of the background.
This was accomplished in the experiments by bracketing a suspected leak site with two sensors
and then searching for similarities in the signals produced by both sensors (Figure 1).
When such similarities were found, the time difference of their arrival at each sensor was
determined. Using this time difference and the sensor spacing, it was possible to determine the
location of the leaks.1

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Acoustic Leak Detection/Location
Approach for Pressurized Pipelines
Wall


A/D

Computer
Acoustic
Transducers





A/D

A/D



Leak
Acoustic
Signal
Acoustic
Transducer
I Figure 1 Acoustic Leak Detection/I-ocation: i

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One of the similarities that was searched for was the intermittent pulses in the quasi-steady-state
signal. Such pulses could be caused by the flow through the leak being periodically blocked, for
example, by dirt falling onto the exterior of the pipe, or bubbles being forced through the leak
orifice. These pulses were detected using a threshold detection circuit on each sensor's output,
and then measuring the time difference between a pulse arriving at sensor 1 and its counterpart
arriving at sensor 2. When statistically sufficient samples of the pulses were collected, the leak
location was clearly revealed as a peak in a histogram chart showing the numbers of times pulses
were detected with specific time differences of arrival between the sensors.
Another similarity that was searched for was precise replication of signal variations at both
sensors. Normally, signal variations between two sensors are totally random, but when a single
source is located between two sensors there is a pattern to the variation. This pattern can be
detected through the use of mathematical functions, such as cross-correlation and coherence. The
cross-correlation function yields the time difference of arrival of similar signals between two
sensors directly, thus giving information that can be used for leak location directly. The
coherence function, on the other hand, measures the linear dependence between two signals as a
function of frequency. To calculate the leak location using coherence it is necessary to sweep
through the range of all possible delay values between the two sensors, noting the delay value
when the coherence is the highest, and using this delay to calculate leak location.
The detection frequency of the sensor that is used to detect the sound from underground pipeline
leaks is another major consideration. Environmental noise, such as that from pumps, vehicles,
etc., tends to have most of its energy at low frequencies, e.g., below 30 kHz. Attenuation of

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sound, however, increases with the frequency of the sound. Thus, although the leak might stand
out more from environmental noise at higher frequencies (have a better signal-to-noise ratio), the
sensor spacing needed to reliably detect the leak could be so small as to be impractical. To obtain
information on this effect, sensors resonant at 15 kHz, 30 kHz and 150 kHz were used.
Results of experiments on the 2 inch pipeline indicated that 15 kHz sensors (bracketing the leak
source and using threshold detection circuitry to detect the time difference of arrival of pulses)
produced the most reliable leak location across the variety of leak sources. However, for specific
leak sources even 150 kHz sensors produced useful results. Cross-correlation and coherence
detection did not work very well in this pipeline because the presence of tee joints every 10 feet
introduced echoes and other anomalies in the waveforms that destroyed the similarities in the
waveforms arriving at the bracketing sensors. Another interesting result was how variations in
pressure, as well as the introduction of nitrogen gas into the fluid in the pipeline, helped to
enhance leak location.
CONCLUSIONS
1.	A new leak location method, based upon passive acoustic techniques, is being investigated
under an applied research program sponsored by SERDP. This method offers significant
speed and cost advantages over established techniques that are based upon volumetric
changes and on pressure loss.
2.	Acoustic experiments have proven that the fundamental theory behind passive acoustic

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leak location in pipelines is solid. Several different acoustic location methods have been
explored to date, leak location data have been produced by all of them. Techniques for
enhancing the detectability of leak sources are also being developed under the program.
3. The test pipelines at the EPA Facility in Edison, NJ, (typical of those commonly found in
the petrochemical industry, at aircraft refueling facilities, and in Army central heating
systems) enable the controlled-condition examination of the capabilities and limitations of
acoustic emission leak location methodologies. These pipeline systems mimic actual field
operating conditions, yet bring a necessary ease of access for experimental investigation.
BIOGRAPHY
Anthony Tafuri is the Principal Investigator for the SERDP Acoustic Leak Location project. He
has over 25 years of experience with EPA as an environmental engineer, and holds a Master of
Science degree in Sanitary Engineering from New York University and a Master of Science
degree in Civil Engineering from Columbia University. His current interests include research in
the prevention, detection and cleanup of releases from aboveground and underground storage
systems.

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REFERENCES
1.	E.G. Eckert, J.W. Maresca, Jr., R.W.Hillger, and J.J. Yezzi, Location of Leaks in
Pressurized Pipelines bv Means of Passive-Acoustic Sensing Methods. Leak Detection
Monitoring for Underground Storage Tanks, ASTM STP 1161, Philip B. Derringer and
Thomas M. Young, Eds. Philadelphia, American Society for Testing and Materials, 1992
2.	Pollock, A. A., Leak Location Using Acoustic Techniques at the EPA Test Facility.
Edison, NJ, Report R96-472, Physical Acoustics Corporation, Princeton, NJ, July 1996.

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TECHNICAL REPORT DATA
(Please read instructions on the reverse before completing)
1.REPORT NO. 2.
EPA/600/A-96/107
3. REC
4.TITLE AND SUBTITLE
Leak Detection/Leak Location in Underground Pipelines
5. REPORT DATE
10/15/96
6 PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
A.N. Tafuri, J.J. Yezzi, Jr., US EPA, UWMB, Edison, NJ 08837
D.J. Watts, J.M. Carlyle, NJIT, Newark, NJ 07102
8.. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
New Jersey Institute of Technology
323 Martin Luther King Drive
Newark, New Jersey 07102
10. PROGRAM ELEMENT NO.
NA
11. CONTRACT/GRANT NO.
NA
12. SPONSORING AGENCY NAME AND ADDRESS
National Risk Management Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Peer Reviewed Conference Paper - Proceedings
14. SPONSORING AGENCY CODE
EPA 600/14
15. SUPPLEMENTARY NOTES
Project Officers: Anthony N. Tafuri (908) 321-6604 / James J. Yezzi, Jr. (908)321-6703
r- 16. ABSTRACT
""^-The utilization of passive acoustic techniques to detect and locate leaks in underground pipelines that carry
pressurized liquids is being investigated in a joint research program between the Department of Defense
(DoD), the Department of Energy (DOE), and the U.S. Environmental Protection Agency (EPA)^Acoustic
techniques offer more cost effective, timely and accurate leak detection/location than currentlyestablished
techniques, e.g., methodologies based on volumetric changes and-others'baseH on pressure loss. An
experimental facility for determining the capabilities and limitations of improved leak detection/leak location
methods based on advanced acoustic principles is being developed at EPA's Urban Watershed Research
Facility in Edison, NJ^Four representative pipeline systems will be installed and evaluated: one typical of the
petro-chemical industry, one typical of a Navy/Air Force hydrant refueling system, one typical of an Army
central heating system, and a fourth typical of pipelines associated with low level liquid wastes at DOE
facilitieSix^Results of experiments on an existing 2 inch diameter test line have indicated that the fundamental
theory behind-passive acoustic leak detection/location is solid. Several different acoustic leak detection and
location methods have been explored to date, data have been produced by all the techniques, proving their
usefulness, v/
17.
KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
pipelines
USTs/ASTs
acoustic
b. IDENTIFIERS/OPEN ENDED TERMS
leak detection
leak location
leak prevention
c. COSATI Field/Group
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
20 . SECURITY CLASS (This page)
Unclassified
22. PRICE

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