Most major offshore developments benefit from the presence of work-class and/or inspection-class Remote Operated Vehicles (ROVs) to carry out daily inspections, maintenance and other practical subsea operations.

One main goal in designing retrofittable strain monitoring instrumentation was to ensure its suitability for ROV handling and installation. This allows for smooth installation on facilities for which no structural health monitoring was originally planned and facilitates ease of maintenance and upgrading.

Schlumberger recently installed a system where the client had to monitor changing internal pressures caused by flow restriction issues in a subsea jumper for an existing Gulf of Mexico field. It was determined a retrofittable device capable of monitoring hoop strain changes resulting from internal pressure and temperature variances was required. It would also have to be a stand-alone device with no external power or communications hardware, and be ROV deployable.

A system was designed comprising hoop strain and temperature sensors, a single-atmosphere pressure housing (containing an opto-electronic interrogator, a battery pack, a data storage card, an LED output system), and a clamping system.

More detailed information can be found in the "Offshore" magazine, Volume 69  Issue 4   April 2009, or vist: http://www.offshore-mag.com/display_article/359640/120/ARTCL/none/none/1/Using-optical-fibers-for-integrity-monitoring-in-risers,-flowlines/