Distributed fiber optic sensing has become a reliable method of preventative leak detection, ensuring pipeline integrity and delivering value added services such as pig detection/tracking and flow monitoring. A number of practical challenges such as the high risk and cost prohibitive nature of daylighting buried pipelines have resulted in the deployment of this technology being primarily limited to new pipeline projects. In this paper, we present internal deployment, among other potential retrofitting approaches, as a viable method of retrofitting existing pipelines, especially in high consequence areas.
Hifi’s high fidelity distributed sensing system (HDS) is capable of sensing acoustics, temperature, strain, and vibration. We present a case study for the deployment of this sensor system inside and outside a gas pipeline in Canada. We will discuss the practical design considerations for deploying this technology inside a pipeline, including the use of tow pigs for pulling the fiber optic cable inside the pipe, proper design of a pig launcher, selection of appropriate pressure levels during fiber injection, and choosing a reliable dislodgement mechanism to separate the fiber optic cable from the tow pig.
The paper will provide a comparison of the sensitivity levels of the internally and externally deployed fiber optic cables. Results from field verification and validation tests for the two sets of fiber optic sensors will be provided to showcase the effectiveness of internal deployment as a reliable pipeline monitoring solution. The field tests included tap tests, water and nitrogen based external leak simulations, and right-of-way ground disturbance testing.
Some challenges with internal deployment will be reviewed as well, including deployment length limitations and the potential need to retract the fiber optic cable prior to pipeline pigging or closing any block valves. Possible solutions such as piggable internal deployments and automatically retractable lines will be discussed.