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Long-Range Nonintrusive Integrity Testing
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Concept
Digital Correlation is a computerized acoustic technique developed by Flow Metrix, Inc.1 that can accurately pinpoint pipeline leaks of all sizes. Vibration sensors are mounted nonintrusively on a pipe at long range up to a mile apart. Synchronized vibration recordings are analyzed in a 15-minute process using advanced signal processing techniques. Any leaks present are detected and pinpointed with a typical error of less than 3 feet.
Principle of Operation:
Turbulence from leaks in pressurized pipelines creates traveling pressure waves which propagate through the fluid of a buried pipeline. The velocity of propagation depends both on the fluid and on the dimensions and material of the pipe. Digital Correlation measures the difference in propagation time of the pressure wave from the leak to each sensor.
The exact location of the leak source is then pinpointed using the measured time and known velocity.X = distance of the point of leak from the reference sensor
D = distance between two sensors
V = velocity of wave propagation
Δt = difference in propagation time
The location of leaking point in the pipe: X = ( D - V*Δt ) / 2
Deployment
Two Field Sensor Units (FSUs) are deployed at remote locations on the pipeline. The FSUs have precision time-keeping, processing, and data storage capabilities, together with digital radio links to a rugged portable PC. The FSUs are synchronized by radio from the PC and then make 90-second recordings. During the recording the FSU processors independently assess the vibration signals, encode the leak sound component, and save the recorded data in memory.
Two Field Sensor Units (FSUs) are deployed at remote locations on the pipeline. The FSUs have precision time-keeping, processing, and data storage capabilities, together with digital radio links to a rugged portable PC. The FSUs are synchronized by radio from the PC and then make 90-second recordings. During the recording the FSU processors independently assess the vibration signals, encode the leak sound component, and save the recorded data in memory.
Retrieve + Analysis
After recording the FSUs are brought into radio range of the PC for data transfer. Leak sources appear as peaks in the Correlation Display (see right). Flow Metrix’s patented Advanced Leak Frequency Analysis (ALFA) accurately and individually pinpoints any leak(s) present in a few seconds following data transfer. If a leak is present outside the span of the sensors the DigiCorr can detect the direction of the leak. One or both sensors can then be moved and a new recording made to pinpoint the leak. A significant length of pipe can be quickly and effectively scanned to detect and pinpoint the location of leaks.
Applications
Failed Hydrostatic Test: If the pipe loses pressure during hydrostatic pressure testing, the DigiCorr provides fast, nonintrusive pinpointing to locate the leak at a fraction of the cost and time of traditional tracer methods.
 New, 18-inch, ductile iron pipe which failed during hydrostatic testing at less than 200 psi. This small pinhole leak was accurately pinpointed with sensors approximately 500 feet apart. Direct Assessment: The DigiCorr can be used to survey a section of pipe directly without taking the pipeline off-line and without exposing large sections of the pipeline. The DigiCorr process is completely nonintrusive and can assess up to one mile of pipeline in about 15 minutes |
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Emergency Location / Flow Assessment: The DigiCorr can quickly locate leaks or other pipeline anomalies that may develop in pipelines during normal operations. The Correlation Display (see right) shows an example where the DigiCorr pinpointed the exact location of a pig lodged in a 4" carbon steel pipeline transporting liquid propane. The pig was instantly detected from over half a mile away.
Benefits
- Works on all sizes of pipe carrying any liquid or gas under pressure
- No disruption to normal operations
- Assesses up to one mile at a time
- Detects extremely small leak
DigiCorr: Long-Range Nonintrusive Integrity Testing
1 DigiCorr technology has been developed by Flow Metrix since 1997 and is protected by U.S. and international patents (U.S. patent No. 5,974,862).