What are the actual loads from waves and current doing to a 14” production riser stress joint when installed at 1200m water depth?

FORCE Technology Norway and Kongsberg Maritime AS engineered and delivered an autonomous strain monitoring system to measure the actual loads seen by the stress joint during a four-month period. The system is based on FORCE Technology’s Hysens strain sensor, as well as experience and tools for accurate subsea strain measurement.

The system can be installed and retrieved by a work class ROV using a standard torque tool interface. Strain is measured at four evenly distributed locations around the circumference of the tapered stress joint, with a calibrated accuracy of better than ±5.6µstrain in the full range of ±2200µstrain.

The autonomous strain unit was fitted to the riser while the riser was onshore. The sensors were landed onto the stress joint and datalogging was activated before being launched and installed together with the riser. The system is logging data at a 10 Hz rate with a duty cycle to increase the battery life.

ROV retrieval of the unit from the riser, which is planned in spring of 2021, will provide our Client, a Major US O&G Operator, with valuable insight into what the stresses and bending moments really are on this particular production riser. Combined with the environmental loads for the period, the data can be used to establish more realistic fatigue estimates for this riser, and learnings for future references.

Once the data is downloaded, the system can be fitted with a new battery package and launched by ROV on the same or a different riser to harvest more information on how such systems are responding to the loads they are exposed to.

We are very excited for the day we can retrieve the unit and start analyzing the data later this year. Make sure to follow us on LinkedIn; we will return with more information when we have the results.