Case study - Successful trunk main correlations in Australia, the land of long pipes

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Courtesy of Gutermann AG

The Aquasscan TM Successfully locates leaks at distances over 1KM in Sydney.

The Gutermann Aquascan TM (Trunk Main) correlator provided a series of high performance correlations in trials performed in Sydney, Australia.  Sydney Water provided a 1.2 KM of 600mm OD Steel trunk main for a series of tests to be performed to evaluate the performance.  The testing was administered by Veolia Water & Sydney Water with on-site assistance provided by ADS Environmental.

The performance of both accelerometers and hydrophones was tested during this trial.  The installation of Accelerometers is far easier and always the preferred option when tappings are not available.  To deploy an accelerometer sensor, you need access to the pipeline, so a magnetic connection can be made.  To use hydraphones, a tapping must be made in the main so that the sensor can make contact with the water column.

You can see on the map on the previous page that when a sensor is deployed at position “A”, it will be right next to one of Sydney’s busiest highway’s generating a large amount of low frequency background noise.  There is a strong possibility that this background noise can drown out the sound of the leak and make correlating impossible during busy traffic periods.  If this is the case the trials may have to be performed at night.

The pin hole leak was simulated at point “B” by placing a cap over the valve with a small hole approx 1mm diameter drilled into the cap.  The scour valve was used as a leak simulation at point “D”, to create a 1 L/S leak it was opened about 2 turns and to create 0.3 L/S it was opened half a turn.  

Measurement 1 is a simulated leak on a 600mm OD steel pipe over a distance of 746m and the leak is simulated by activating a scour valve to generate a 1L/S leak. Hydraphones were used in this correlation and the high quality correlation peak instantly identifi ed the position of the leak to be 428.3m from sensor A and 317.7m from Sensor B. The correlator latched to this peak after about 15 seconds, providing an almost instant result. The actual scour position is 426m from sensor A and 310 from sensor B. The exact distance measurement is yet to be confi rmed, the sketch indicates a distance of 736m, however the distance entered into the correlator was 746m, an error of 10m.

Measurement 2 is a simulated leak on a 600mm OD steel pipe over a distance of 746m and the leak is simulated by activating a scour valve to generate a 1L/S leak. Accelerometer sensors were used in this correlation and the high quality correlation peak instantly identifi ed the position of the leak to be 428.3m from sensor A and 317.7m from Sensor B. The actual scour position is 426m from sensor A and 310 from sensor B. The difference between the correlations in Measurement 1 and Measurement 2 is that measurement 1 uses Hydraphone sensors and Measurement 2 uses accelerometer sensors.

A tapping on the main is required to use hydraphones as they actually measure the sound and pressure wave in the water column, where as the accelerometer sensors make a magnetic connection to the pipe wall to detect the leak noise travelling along the pipe wall. With the resounding success of measurement 1 and measurement 2, the distance was extended to 1226m and the size of the leak was reduced to 0.3L/S.

Measurement 3 shows the correlation with hydraphones and Measurement 4 with accelerometers. The leak was instantly found with the hydraphones in measurement 3 and a very high quality leak peak accurately plotted the position of the leak. This leak is simulated with a sluice valve at 0.3L/S.

Measurement 4 shows the leak position correlated using the accelerometer sensors. Filters had to be applied to improve the shape of the peak indicating the leak position and the peak is far less dominant than the correlation with the hydraphones. The accelerometers picked up a signifi cantly wider range of noises and these background noises are drowning out the sound of the leak.
The fact that sensor A was right next to “Liverpool Road”, one of Sydney’s busiest roads, would have increased the amount of background noise. If this correlation was performed at night with less traffi c noise, I would expect a much higher quality peak.

To test the equipment to extreme limits a new leak simulation was trialled which had a tapping on the 600mm OD steel main with a plastic hose leaking 5L/S. This was not detected by the hydraphones or accelerometer sensors over the 1226m length. Measurement 5 shows the poor quality correlation about 50m from the actual leak position, this measurement was performed with hydraphones.

Sensor B was then relocated to make the total distance 220m with a pin hole leak about 1mm diameter releasing about 8ltrs/min. The successful result to this correlation is shown in Measurement 6, a little fi ltering was performed during the correlation to fi nd the leak within about 30 seconds. The leak position indicated of 100.1m from sensor A and 113.9m from sensor B is believed to be accurate to 100mm.

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