An overview of fiber optic sensors for temperature, pressure, strain, and fatigue of subsea structures is provided. Current progress details efforts to ensure proper installation and bonding to existing risers, flow-lines, mooring lines, trees, and other structures in actual subsea environments. Developments include clamp prototypes, bonding techniques, long-term fatigue analysis, sensor calibration, and temperature compensation.
Fiber optic technology in subsea monitoring began over 20 years ago by migrating expertise from decommissioning of rocket motors. The first installations were on new installations of subsea pipelines, production risers, and drilling risers to measure strain and vibration for fatigue life monitoring. Of particular interest for these systems were detecting riser vortex induced vibration and strain throughout the touchdown zone. A prior limitation was that sensor installation was only performed top-side on new subsea equipment. This recent work demonstrates the capability to deploy on existing subsea equipment.
The novel contributions of this study are the developments that optimize the clamp design, bonding techniques, and factors that allow long-term service life. Button pull tests validate long term service life after the clamps are subjected to accelerated aging tests. Details on the subsea calibration also provide insight on the recent progress with post-installed sensors.
The purpose of reliable post-installed advanced sensors is not only to detect failures of subsea infrastructure but also to warn of signs of fatigue or hydrate formation that contribute to catastrophic failures. The calibration and testing mentioned in this paper are part of the Clear Gulf study, a collaboration formed in 2010 between the offshore energy industry and NASA. The study continues to make advances in highly sensitive monitoring systems that anticipate failures, catastrophic events, and flow assurance issues.