BMT Scientific Marine Services has launched a fully-qualified ROV-Serviceable Subsea Strain Sensor Assembly (SSSA) for monitoring the structural integrity of subsea structures (tendons, production risers, steel catenary risers, platform legs and braces, etc).
Until now, sensors were limited to diver serviceability due to the finesse needed to handle them and the inability of an ROV to manipulate the standard nuts and bolts that hold sensors to the pipe. Due to the large cost and risk associated with mobilizing a diver spread to change-out a failed sensor, these systems have had to rely on redundancy, with multiple sensors deployed to achieve the system design life.
With the ROV-serviceable SSSA, Floating production storage and offloading (FPSO) and platform operators have the opportunity to benefit from an increased degree of system reliability and quicker, simpler replacement operations.
BMT Scientific Marine Services (BMT) has developed its existing diver serviceable strain sensor into one that is serviceable by ROV. This has been achieved by designing a special ROV tool and alignment cage for sensor removal or installation. The tool for handling the sensor mates with this cage, which is bolted to the riser or subsea structure and provides the precise alignment needed to attach the sensor repeatedly and accurately. The design is purely mechanical and is compatible with an ROV equipped with one 5-function and one 7-function manipulator. As long as the failed sensor is replaced in the presence of at least three functioning sensors, the absolute tension or bending moment measurement is preserved during and after the change-out operation.
Because significant changes had been made to the mounting and attachment architecture, BMT thoroughly tested the new design to make sure these alterations did not degrade the sensor's measurement accuracy. Laboratory testing demonstrated the full-scale accuracy of the sensor to be equal to that of the diver-serviceable designs. In addition, full-scale ROV tank testing has proved the ability of a typical work-class ROV to completely remove and replace a sensor repeatedly. The first 10 deliverable sensors have passed extensive factory acceptance testing at BMT's facility in California and are now ready for deployment