Offshore Riser Tension Monitoring

Offshore Riser Tension Monitoring

Late 2018, Cementys engineering team finalized its first deepwater riser real-time monitoring project.

The instrumentation operation took place in the Gulf of Mexico, on an existing Tendon Leg Platform (TLP), exposed to frequent Loop Current events.

Vortex Induced Vibrations (VIV) of a riser in severe loop currents can decrease the riser fatigue life and thus may have significant cost impacts.

VIV suppression devices are essential to minimize those events, eventhough VIV behavior presents one of the biggest simulation uncertainties facing the riser engineers.

This shows that full scale monitoring is essential to improve our understanding of VIV response of risers equipped with VIV suppression devices.

Cementys designed and set up a system to measure the strain variation of Top Tension Risers (TTRs), focusing on one of the regions where fatigue damage is expected to be greatest : the top of the riser, around 20 meters above sea level. The objective is to compare efficiency of the different currently installed VIV suppression devices and estimate the induced fatigue damage during a single Loop Current event.

The system is based on the ExtensoVib vibrating wire strain sensors, allowing for accurate strain measurements, with a resolution below 0.1 microstrain.

Each riser is equipped with six ExtensoVib extensometers with a 60° separation: 3 sensors for one monitoring system, 3 others for redundancy.

Sensors are connected to two dynamic data loggers, making a high frequency measurement (20Hz) for high frequency riser oscillations.

 

ExtensoVib risers are bonded directly on the riser metal surface, without the coating, to measure directly the surface strain, without drift or recalibration for a period of several years.

Cementys has a remote access to check the incoming data. The real-time axial loads and bending moments are analyzed in correlation with loop current conditions to follow the fatigue damage accumulation.

ExtensoVib sensors represent a cost-effective solution for riser monitoring projects.

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