Distributed Fiber Optic Sensing (DFOS) for Continuous Pipeline Monitoring — The Next Step Beyond AE in Online NDT [2026 Update]

Following our previous article on Acoustic Emission (AE) monitoring of tank floor plates, this post focuses on another rapidly expanding online monitoring technology for process piping: Distributed Fiber Optic Sensing (DFOS). While AE excels at localized acoustic detection, DFOS turns a single optical fiber cable, spanning tens of kilometers, into a continuous chain of virtual sensors — eliminating the blind spots inherent to point sensors. Since 2025, DFOS deployments have accelerated across refineries and gas pipelines worldwide, positioning it as a cornerstone of the online-monitoring era.

What Is DFOS? DAS, DTS and DSS Explained

DFOS technologies are grouped by the physical quantity they measure. DAS (Distributed Acoustic Sensing) captures acoustic and vibration signals along the fiber, typically using Coherent OTDR (C-OTDR). DTS (Distributed Temperature Sensing) retrieves temperature profiles via Raman-scattering-based ROTDR. DSS (Distributed Strain Sensing) tracks strain and deformation. A single fiber can deliver tens of thousands of virtual sensing points and measure over distances of up to roughly 200 km.

Latest Research on Pipeline Leak Detection (2025)

A 2025 study published in MDPI Sensors evaluated DAS performance for gas pipeline leak detection using a 21 m steel pipeline with a 1 m test section. The experiment varied leak diameters (¼" to 1"), orientations (top, side, bottom), and flow velocities (2–18 m/s) under both supported and buried configurations. The results showed that leak detectability depends on a complex interplay of flow rate, leak size, orientation, pipeline installation method, and cable type. Notably, internally deployed flat and black cables showed superior sensitivity for high flow rates, larger leaks, and bottom-oriented defects — a breakthrough for inspecting unpiggable pipelines that conventional smart-PIG surveys cannot reach.

Deployment in Refineries and Petrochemical Plants

Germany-based AP Sensing offers an integrated pipeline monitoring platform that combines leak detection and localization, real-time PIG tracking, Third-Party Intrusion (TPI/PIDS), and surveillance of block valve stations, refineries, processing plants, and tank farms. Because fiber can be laid alongside the pipe or buried in the same trench, retrofits do not require large-scale sensor installation works — a key driver of rapid adoption in overseas facilities.

AI Integration and Market Outlook

A 2025 paper in Frontiers in Big Data demonstrated multimodal fusion of DTS and DAS vibration signals with machine learning for intelligent oil-pipeline leak monitoring. Combining thermal anomalies with acoustic anomalies significantly improves the detection of micro-leaks and early-stage precursors that single-sensor approaches tend to miss. On the market side, Fiber Market Insights projects the fiber-optic sensing market to grow at a CAGR of 10.4% through 2026, with oil and gas identified as the leading end-use segment.

Challenges for Adoption in Japan

In Japan, distributed fiber sensing is already established in bridge and tunnel infrastructure monitoring, but plant-piping applications are still in their early days. The hurdles are retrofit cable-routing costs, environmental tolerance under high temperature, steam, and chemical exposure, and the organizational capability for continuous data review. Combining AE-based local monitoring with DFOS-based full-length coverage offers a pragmatic path to eliminate blind spots in high-temperature, elevated, or buried lines that inspectors cannot easily access. At Urisol Inc., we aim to blend classical NDT methods such as VT and UT with these next-generation online-monitoring techniques to further improve the accuracy of asset-integrity assessments.

Summary

DFOS, whether DAS, DTS, or DSS, transforms a single fiber into a continuous "line sensor" that complements the inherent limits of point sensors and periodic inspection. Recent 2025 research highlights AI fusion gains and real deployments in overseas refineries. AE and DFOS are complementary rather than competing, and future articles will explore integrated multi-sensor online-monitoring case studies in greater depth.

References

• MDPI Sensors, "Leakage Detection Using Distributed Acoustic Sensing in Gas Pipelines" (2025). https://www.mdpi.com/1424-8220/25/16/4937
• Frontiers in Big Data, "Intelligent leak monitoring of oil pipeline based on distributed temperature and vibration fiber signals" (2025). https://www.frontiersin.org/journals/big-data/articles/10.3389/fdata.2025.1667284/full
• IEEE Xplore, "A Review of Distributed Fiber–Optic Sensing in the Oil and Gas Industry." https://ieeexplore.ieee.org/document/9652039/
• AP Sensing, "Pipeline Monitoring | Fiber Optic Leak Detection." https://www.apsensing.com/en/application/process-automation-and-pipeline-monitoring/pipeline-monitoring
• Lazoc Inc., "Distributed Acoustic Sensor (DAS) — Technology Overview." https://lazoc.jp/technical/das/
• KLV Co., Ltd., "Types and Deployment Examples of Fiber Optic Sensing." https://www.klv.co.jp/corner/fiber-optic-sensing.html
• ACS Omega, "Pipeline Polluted Gas Leakage Detection in Chemical Parks Based on the Distributed Fiber Optic Sensing Data Fusion Algorithm" (2025). https://pubs.acs.org/doi/10.1021/acsomega.5c03024