|Thesis abstract: |
This thesis deals with monitoring of pipelines through acoustic measurements. Acoustic monitoring is a technique that exploits the fact that any disturbance occurring in the pipe infrastructure or in the conveyed fluid produces or influences acoustic transients which propagate as waves within the fluid at distances of many kilometers, carrying information on the originating event and on the propagation channel. I first analyze the theory of elastic wave propagation in pipelines and present a suitable matrix method to compute propagation parameters in fluid-filled pipelines possibly buried or submerged, taking into account several propagation effects among which fluid thermo-viscosity, pipe elasticity, external load and radiation. The propagation parameters can be found at any frequency and for any axisymmetric propagation mode. The theoretical study was functional to the design and development of a registered technology (e-vpms®) for pipeline monitoring which I contributed to. This system in fact employs a discrete network of vibro-acoustic monitoring stations mounted along gas or liquid pipelines which measure synchronized physical signals. Thanks to measurements performed on a buried in-service oil pipeline, I have experimentally validated the propagation method presented in the whole range of frequency of interest. Propagation parameters of acoustic waves were also measured in many in-service gas pipelines and found in agreement with theory. An important application of the monitoring system is the leak detection system that was tuned and validated on an in¿service oil pipeline. In gas pipelines instead I describe some methods of pig (pipeline inspection gauge) tracking and a successful application of acoustic reflectometry on a pipeline to find and characterize anomalous pipe sections. Moreover I propose, through real examples, further advanced processing to measured and stored data such as the long term monitoring which allows to identify the standard operational conditions in a pipeline and therefore detect possible anomalous situations. A last type of application concerns the use of theoretical models of wave propagation and of fluid properties to interpret the measurements and obtain further information on the conveyed fluid and the flow regime.