Pipelines are considered to be the safest and most economical way of transporting liquid and gas over a long distance. They are used for transporting crude oil and natural gas in process industries, for water transportation and distribution systems in urban and rural areas, for transporting aviation fuel and hydraulic piping as well as air pressure chambers in aircraft. Leaking pipelines can lead to spillage of hydrocarbon fluid into the surrounding environment, and consequently result in fire or outright explosion of the pipeline system as well as production loss, damage to the environment and potential loss of lives. Therefore, accurately identifying and predicting the location and growth of defects are essential and enable the operator to assess and actively manage the integrity of the pipelines. Current leakage detection methods use several non-destructive testing methods such as magnetic particle inspection, radiographic, ultrasonic, pressure transient and acoustic signal methods. This thesis presents acoustic wave propagation-based methods to identify leakage and blockage in pipe systems. In the study, the acoustic finite-element analysis (AFEA) method is employed to simulate acoustic wave propagation in fluid-filled pipes with leakage and blockage but without flow. Computational fluid dynamics (CFD) analysis was also employed to simulate acoustic wave propagation in fluid-filled pipes with leakage and blockage under flow conditions. In addition, experimental testing was conducted to validate some of the numerical results. The experiments consisted of the measurement of acoustic wave propagation in an air-filled pipe with leakage and blockage. The main investigations and contributions of the thesis are summarised as follows, 1) An efficient finite element analysis (FEA) procedure to simulate acoustic wave propagation in fluid-filled pipes is developed. The developed technique overcomes the large errors that occur in the numerical predictions of acoustic wave propagation. The use of different acoustic element types of 2D-like and 3D formulations, and of linear and quadratic interpolations, are investigated in order to deduce the most accurate acoustic FEA approach, and thereby, to minimise the errors. 2) The CFD technique is applied to simulate acoustic wave propagation and reflectometry in a fluid-filled pipe with flow. This is a novel approach of using CFD to predict the acoustic wave propagation in a pipeline in the presence of flow. 3) AFEA and CFD were employed to simulate acoustic wave propagation and reflectometry in a fluid-filled pipe with and without flow. The Time of Flight approach was used on the predicted acoustic waveforms for the pipes with leakage in order to identify the presence of leakage and to predict the size and location of the leakage in the fluid-filled pipe in the presence of flow. 4) Detection of blockage from the predicted data obtained from the CFD and FEA simulation of acoustic wave propagation/reflection in air-filled pipelines without mean flow. Also, the CFD technique was also used to simulate the acoustic wave propagation/reflection in air-filled pipelines with mean flow. Furthermore, the Time of Flight approach was used to identify size and locate the blockage from the simulated data. 5) The experimental measurements of acoustic wave propagation in a straight air-filled intact pipe and air-filled pipes with leakage. The Time of Flight approach was employed to identify size and locate the blockage from the simulated data. Furthermore, the measured and simulated results are compared to validate the simulated results.
