Pipelines require inspection for integrity to regulatory reasons. Pipeline operators put significant effort into planning and conducting inspections, with the pre-inspection cleaning campaign often being lengthy and costly because of the need to minimize the risk of a failed inspection due to cleanliness issues. Current methods for monitoring a pipeline's cleanliness rely on theoretical modelling and human interpretation of factors, such as debris removed from pipelines, rather than measurement of actual pipe cleanliness. This paper details a solution to this challenge using transient dynamics analysis.

The method is based on analyzing the signal response generated by a pressure wave transiting the pipeline as it is affected by geometrical changes in the system. By capturing high-resolution pressure measurement on an ultra-high-speed logger, the generated pressure wave can be recorded for analysis. Applying acoustic velocity gradient modeling to the measured data in conjunction with effect of the system and the fluid parameters, the profile of the internal bore of the system can be found, and the deposit on the pipe wall can, therefore, be accurately determined.

This paper details how the theory behind the method is confirmed by results observed when used during a controlled, full-scale field-trial environment in addition to subsequent activities to survey system profiles. A case study is presented demonstrating that the method enables operators to make decisive asset-performance decisions and review deposit buildup in a safe and cost-effective manner without having to stop production. The theoretical method for the calculation of acoustic velocity for a known system and fluid parameters is shown to be accurate within tolerances compared to the acoustic velocity gained in the field by recording the time of flight between two known points. It is demonstrated that restrictions can be detected to a level of accuracy of ±3 mm of thickness, as verified by comparison with other debris detection methods.

The described analysis is a unique method for determining the cleanliness of pipelines which can offer significant advantages from traditional methods. It can provide information in a repeatable and verified level of accuracy without the requirement for expensive and time-consuming intrusive intervention, which enables operators to execute and verify pre-inspection cleaning in the most efficient and cost-effective manner, thus maximizing the likelihood of a successful inline inspection run.

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