ADS Environmental Services Eureka2R QR 775019 A1 - Manual (Page 10)

ADS Eureka2R Leak Noise Correlator User Manual
6
Methods for Locating Leaks
Previous methods of leak location relied on an initial detection of a noise,
which was then traced along ground level to identify the location of the
maximum noise. The assumption was that this location was directly above the
location of the leak. The equipment used for this method included listening
sticks and stethoscopes, but these were difficult to use if the noise proved too
faint or loud for accurate location. Background noise was another problem;
therefore, electronically-filtered amplifiers were introduced in an attempt to
overcome such problems.
A correlator operates by comparing the noise detected at two different points
in the pipeline. Noise travels from the leak in both directions along the
pipeline at a constant velocity (depending on several factors). Therefore, if the
leak occurs at an equidistant location between the two sensors, these sensors
will detect the noise at the same time. Conversely, if the leak does not occur
at an equidistant location, then the sensors will detect the same noise at
different times. This correlator measures this difference (delay) in time.
The following diagram provides an illustration of this principle:
D
L L
Leak
X
Valve A Valve B
V * t
Assume the sensors are located on valves A and B (convenient access points
for underground pipes). However, the leak occurs closer to valve A.
By the time a particular noise from the leak has reached A, the same noise
heading towards B has travelled only as far as X. The distance from X to B
causes a delay (t) before the noise arrives at B. Therefore, the correlator
detects the delay (t) between the arrival of the noise at A and B. Assume the
velocity of sound is V and the distance between the sensors is D. As the
distance from X to B = V * t (velocity x time), then D = (2 * L) + (V * t).
This equation may be rearranged to provide L, the distance from the sensor
closer to the leak site:
L
D V t
=
− ( * )
2
The sound velocity can be calculated based on the pipe diameter and material,
and the distance between the sensors can be determined by careful
measurement. Therefore, the correlator can calculate and display the location