Method and system for the remote detection of the position of a pig device inside a pressurized pipeline
A method and a system remotely detect the position of a pig device inside a pipeline for transporting pressurized fluids, like for example long distance oil and gas pipelines having a strategic international value. The method foresees equipping the pipeline with pressure sensors in contact with the fluid, located at at least one of the two terminals of the pipeline, and the sending and processing of signals by a control unit. The operation of the system is that of identifying and locating, in real time and continuously, a pig device that moves intermittently inside the pipeline, for example during cleaning, monitoring, measurement and non-destructive control operations.
1. A method for remote detection of a position of a pig device inside a pipeline configured for transporting a pressurized fluid, wherein the pig device advances in the pipeline with an intermittent movement, with alternating advance and stoppage phases, the method comprising:
detecting continuously, by a measurement station located in at least one terminal of the pipeline, sound waves generated inside the pipeline by pressure variations in the pressurized fluid which arise at a front side and/or a rear side of the pig device during the alternating advance and stoppage phases;
analyzing and processing, using a controller, stationary waves caused by reverberations inside the pipeline of the sound waves generated in time periods of the stoppage phase of the pig device;
identifying a family of resonance harmonics connected with presence of the stationary waves, a reverberation period and/or a resonance frequency of each said stationary wave, a propagation speed of the sound waves in the pressurized fluid inside the pipeline being known, being univocally connected to a length of a section of the pipeline being tested; and
determining based on the reverberation period and/or the resonance frequency of each said stationary wave, a distance of the pig device with respect to the measurement station allowing calculation of the position of the pig device along the pipeline.
2. The method according to claim 1 , wherein the detection phase of the sound waves generated inside the pipeline is performed by two measurement stations respectively located at a first terminal end and at a second terminal end of the pipeline.
3. The method according to claim 2 , wherein the controller performs measurements of the arrival times of signals deriving from the sound waves detected by the two measurement stations.
4. The method according to claim 1 , wherein the propagation speed of the sound waves in the pressurized fluid inside the pipeline is obtained using mathematical sound propagation models which take into consideration physical and geometrical characteristics of a system consisting of the pipeline, the pressurized fluid transported, and a surrounding environment of the pipeline.
5. The method according to claim 1 , wherein the controller is configured to record and analyze a posteriori a track of a last signal deriving from the sound waves generated by the pig device, thus checking the position of the pig device inside the pipeline even if the pig device is blocked definitively and can no longer be restarted.
6. The method according to claim 1 , wherein the pressurized fluid is transported in the pipeline with an absolute pressure ranging from about 3 bar to about 10 bar.
7. The method according to claim 1 , wherein a differential pressure between the front and rear sides of the pig device ranges from about 1 bar to about 3 bar.
8. The method according to claim 1 , wherein the pressurized fluid consists of natural gas.
9. A system for remote detection of a position of a pig device inside a pipeline configured for transporting a pressurized fluid, wherein the pig device advances in the pipeline with an intermittent movement, with alternating advance and stoppage phases, the system comprising:
at least one measurement station, situated in at least one terminal of the pipeline, said measurement station comprising one or more sensors configured to continuously detect sound waves generated inside the pipeline by pressure variations in the pressurized fluid which arise at a front side and a rear side of the pig device during the alternating advance and stoppage phases; and
a controller operatively connected to said one or more sensors, said controller being configured to
analyze and process stationary waves caused by reverberations inside the pipeline of the sound waves generated in time periods of the stoppage phase of the pig device, said controller also being configured to identify a family of resonance harmonics connected with presence of stationary waves, wherein a reverberation period and/or resonance frequency of each said stationary wave, a propagation rate of the sound waves in the pressurized fluid inside the pipeline being known, are univocally connected to a length of a section of the pipeline being tested, and
determine, based on the reverberation period and/or the resonance frequency of each said stationary wave, a distance of the pig device with respect to the measurement station allowing calculation of the position of the pig device along the pipeline.
10. The system according to claim 9 , further comprising two measurement stations respectively located at a first terminal end and at a second terminal end of the pipeline.
11. The system according to claim 9 , wherein said one or more sensors consist of hydrophones or vibroacoustic sensors.
12. The system according to claim 11 , wherein said hydrophones or vibroacoustic sensors are configured to detect a frequency range from 0.01 Hz to 10 Hz.
13. The system according to claim 9 , wherein said controller is operatively connected to said one or more sensors by a wired communication system.
14. The system according to claim 9 , wherein said controller is operatively connected to said one or more sensors by a wireless-type communication system.