1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for calibrating an acoustic monitoring structure that may be mounted on a piping system.
2. Discussion of the Background
Third-party damage is the leading cause of pipeline failure in the world and accounts for 35-50% of pipeline incidents in the United States and Europe between 1970 and 2001. The damage is especially dangerous because it often goes unreported at the time of occurrence, allowing defects to deteriorate with devastating consequences months or years later, causing safety, environmental and public concern. There is, on average, one delayed failure every 33 days in the US and every 34 days in Europe, resulting from previously unreported third-party damage.
Every impact, large or small, on a pipewall creates acoustic waves that travel upstream and downstream in the pipeline product. Systems are available to provide fully managed, acoustic monitoring for accurate location and immediate risk assessment of impact events to aboveground and underground pipelines.
Such a system (as disclosed by U.S. Patent Application Publication no. 2009/0000381 by Allison et al., known as ThreatScan system from General Electric, 7105 Business Park Road, Houston, Tex., USA) measures the timing and relative magnitude of these waves to determine the impact location and severity. Data is transmitted via satellite to a monitoring center, where the situation is assessed in real time. The system provides fully managed, acoustic monitoring for accurate location and immediate risk assessment of impact events to aboveground and underground pipelines. The owner/operator of the pipeline that has the acoustic monitoring system installed receives notification about potential impact and damage events. Further, the system is capable of assessing the damage and sending results via internet and GSM mobile device to ensure timely notice.
More specifically, as shown in FIG. 1, the ThreatScan system 10 is capable to monitor impacts (shocks) 12 occurring to a pipe 14, that may be mounted above or underground. System 10 uses plural sensors 16 spaced apart along pipe 14 for detecting a sound source. Sensors 16 may be spaced between 3 to 21 km apart from each other. A sound source may be the impact 12, which may be produced by the accidental perforation of pipe 14, or other events that may break or not the integrity of pipe 14. Impact 12 generates a sound wave 18 that propagates inside pipe 14. Sound wave 18 propagates in opposite directions to sensors 16a and 16b through a fluid 20 that passes through pipe 14, for example, as shown in FIG. 1. Sensors 16a and 16b are configured to record a time of arrival of wave 18, and/or an intensity of the received wave. In an ideal model and geometry, knowing a distance D between two consecutive sensors 16a and 16b, and a sound speed v in the fluid passing pipe 14, a distance d1 from sensor 16a to impact 12 location may be determined based on formula:d1=[D(c−u)−Δt(c2−u2)]/2c, where c is the sound velocity through the fluid inside the pipe 14, u is the bulk flow velocity of the pipeline fluid, and Δt is a transit time difference for the shock to reach sensors 16a and 16b. The transit time difference is equal to T1−T2, where T1 is an arrival time at sensor 16a of a wave generated by the shock and T2 is an arrival time at sensor 16b of the wave generated by the shock. As also shown in FIG. 1, data from sensors 16 are provided to corresponding sensor stations 22 that may include, among other things, a signal processing unit and a power supply (not shown). The sensor stations 22 may communicate through an appropriate modem 24 or other appropriate device with a corresponding base station 26, which in turn may communicate with a satellite 28. Satellite 28 is also configured to communicate with a base station 30, which is in communication with a monitoring centre 32. The monitoring centre receives the data from sensors 16 or the processed data from sensor stations 22 and informs the operator of the centre about a potential damage that occurred in pipe 14 and the location of the damage. More details about the system set up and the procedure used for determining the distance d1 are disclosed in U.S. Patent Application Publication no. 2009/0000381 by Allison et al., the entire content of which is incorporated herein by reference.
However, a problem that can affect the system performance is the accurate determination of the sound path and behavior within the pipeline given the fact that various sections of the pipeline have different characteristics. More specifically, the path and behavior of the sound in the pipe is not known but assumed within current practices. Thus, these assumptions may impact the measured times of arrivals of the sounds at two adjacent sensors and their intensities, thus determining an inaccurate location of the shock impact.
Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks.