Addressing the annulus of the flexible riser – control and predictions through data
Morten Strengelsrud, our Head of department for riser integrity has been working with monitoring of flexibles risers since 2012 – more specifically, he has been working with a vent gas monitoring (VGM) system.
“The first VGM system installed by FORCE Technology was installed on an FPSO in the Norwegian sector in 1999. Since then, the system has been perfected to provide data that allows us to monitor the current state of the riser annulus. With the history we can foresee possible scenarios under development in the near future.
A VGM system continuously monitors annulus gas flow and annulus free volume, and provides this data and the integrity status directly to the on-board control system. By observing trends of these, we are able to warn if something is abnormal and give warnings and alarms that actions must be taken to maintain the integrity. This is valuable information for the operator.
Incremental changes over time will paint a picture of the status quo and future status. Analysis of these changes will as an example, allow us to predict how much water accumulation you will have at a given time. Water ingress could create a highly corrosive environment together with CO2 or H2S, and should be addressed pre-emptively.
Gas sampling in bottles provides a basis for analysis at any given time. We are currently looking at a new feature that would allow the operators to receive an automated digital analyses of the data (stored in the cloud).
We see an ongoing trend of operators seeking continuous monitoring for increased control, but also for a solution that is more cost-effective in the long run. To ensure the optimum solution, we recommend to plan for this in the pre-FEED phase. This allows for a basic solution without customisation – tested and proven – quickly installed at the lowest cost.”