Vibroacoustic monitoring of pigging operationsin subsea gas transportation pipelines

Pig tracking, especially in long subsea pipelines, is still a challenging problem. We have carried out a long term vibroacoustic monitoring field test, by measuring pressure variations within the fluid and vibrations on the pipe shell at the terminal station of an offshore gas pipeline. During the field test, several pigging operations have been observed, in different scenarios, comprising gas pumping restart (low pressure), smart pig inspection, and standard maintenance (high pressure). A travelling pig generates fluid transients, related to the compression of the fluid ahead of it, and to the sounds produced by the interaction with the inner pipe wall. These transients propagate along the pipeline and can be recorded at distances up to tenths of kilometers. Their identification and classification can be crucial for real time pig tracking and detection of anomalies. In this paper we describe the test campaign results. Then, we analyze the acoustic signals recorded for some pigging scenarios, we show original ways of displaying the results, also with audio rendering, and we compare the experimental measurements using mathematical models of sound propagation within the pipes. This study is a step towards the development of a remote monitoring system for pigging operation and inspection.