Using Distributed Acoustic Sensing to Detect Structural Damage in Gas Pipelines

Abstract This study investigates the feasibility of using Distributed Acoustic Sensing (DAS) to monitor gas pipeline integrity, focusing on mechanical defects such as dents and deformations along the pipeline, as well as infrastructure issues such as loose supports. These defects can worsen over time and potentially lead to failures. This research highlights the use of internally installed fiber-optic cables for structural damage detection, using spectrum analysis and tracking resonant frequency shifts to detect such damages. Additionally, it examines how pipeline installation methods (supported and buried) affect the detection capabilities of the different optical cables deployed. Experiments were conducted on a 21-meter-long, industry-standard pipeline with a 4-inch diameter, featuring a 1-meter central segment specifically modified to introduce controlled damage scenarios. To assess deformation, the pipeline was tested with both minor and severe center dents. Infrastructure damage was simulated by selectively loosening supports in various configurations along the pipeline. The experimental testing matrix included five gas flow velocities (2, 6, 10, 14, and 18 m/s), four fiber-optic cable deployment methods (one external and three internal), and two types of pipeline installation: one configuration fully supported above ground and another buried to replicate in situ field conditions. Spectrum analysis of resonant vibration modes captured by the DAS system was performed to identify and locate structural changes by comparing the damaged conditions to the undamaged pipeline baseline. Results demonstrated that introducing a dent at the center of the pipeline selectively produced clear frequency shifts in the odd-indexed harmonic vibration modes, which have a maximum amplitude at that location and are therefore sensitive to structural changes there, while the even-indexed harmonic vibration modes remained unaffected because their amplitude at the center is minimal, rendering them insensitive to structural damage at that location. Loosening the central support produced a similar selective shift in even-indexed modes, with odd-indexed modes remaining unaffected. In contrast, loosening the second support from the inlet produced a different pattern, including merged peaks around 700 Hz and noticeable shifts near 500 Hz, indicating that the location of structural damage determines which vibration modes are altered. Additionally, pipeline installation influenced detection sensitivity. In the supported configuration, frequency shifts were clearly observed. However, in the buried setup, no significant frequency shifts were detected, suggesting that vibration damping in buried conditions reduces the detectability of the fiber cables. These findings highlight the feasibility of using DAS-based spectrum analysis to identify and locate structural changes in gas pipelines. This study presents a practical, field-deployable approach using internally installed fiber-optic cables for pipeline integrity monitoring. Additionally, it introduces resonant frequency shift analysis as a novel method for detecting and locating structural damage, an approach not widely adopted in the pipeline industry. By demonstrating how different structural modifications affect vibration modes, this work enhances the application of DAS-based spectral analysis for pipeline monitoring.