One of the largest movers of the world economy is the oil and gas industry. The industry generates billions of barrels of oil to match more than half the world’s energy demands. Production of energy products at such a massive scale is supported by the equally massive oil and gas infrastructure sprawling around the globe. Especially characteristic of the industry are vast networks of pipelines that traverse tens of thousands of miles of land and sea to carry oil and gas from the deepest parts of the earth to faraway destinations. With such lengths come increased chances for damage, which can have disastrous consequences owing to the hazardous substances typically carried by pipelines. Subsea pipelines in particular face increased risk due to the typically harsher environments, the difficulty of accessing deepwater pipelines, and the possibility of sea currents spreading leaked oil across a wide area. The opportunity for research and engineering to overcome the challenge of subsea inspection and monitoring is tremendous and the progress in this area is continuously generating exciting new developments that may have far reaching benefits far outside of subsea pipeline inspection and monitoring. Thus, this review covers the most often used subsea inspection and monitoring technologies as well as their most recent developments and future trends.

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An impact event on a pipeline generates stress waves that travel along the pipeline, and the traveling stress waves can be easily detected by distributed piezoceramic transducers. To pinpoint impact location on a pipeline, the time of arrival (TOA) is commonly used and the envelope calculated by the Hilbert transform is an effective method to determine the TOA. However, the envelope used to extract the TOA depends on the manual selection of the trigger threshold. In fact, the instant phase, that changes regularly from -pi to pi as the stress wave travels, is an important characteristic parameter of the signal, and the TOA can be determined by the periodicity of the instant phase. However, this fact has been overlooked in calculating TOA in the literature. In this paper, a new method, time of arrival with instant phase (TOAIP), is developed to calculate the TOA without the need of manual selection of the threshold. Taking into account the non-stationarity of the signal and noise interference, short time window Fourier transform and band-pass filter are utilized to extract the useful signal, the TOA is then determined by using the instant phase which is based both the first zero-crossing point of signal and the periodicity of the phase. In general, most of the pipeline impact localization realize one-dimensional positioning along its length direction. Another novelty of this paper is the development of the two-dimensional impact location (TDIL) that can estimate the impact location information along both length and circumferential directions. Experimental studies based on pipeline with distributed lead zirconate titanate (PZT) transducers mounted on the surface of the pipeline are carried out in this research. Both of physical measurements and inversion results have verified the accuracy and reliability of TOAIP and TDIL on the pipeline.