Prevention and Monitoring of Fatigue-Corrosion of Flexible Risers’ Steel Reinforcements

Flexible pipelines used for oil production on floating platforms are subject to dynamic loads and are designed to ensure no fatigue failure over their service life. Their reinforcing layers are located in a very confined environment called the annular space and are made out of high strength steel wires. If these steel wires are subjected to a wet corrosive environment, corrosion fatigue can become an issue, especially for sour service applications with the presence of H₂S and CO₂. Over the past years, Flexi France has dedicated a lot of effort not only to predict the composition of the environment in the annular space and the steel wires’ fatigue-corrosion behaviour, but also towards the prevention of corrosion and the monitoring of this annular space. Several innovative solutions recently developed and tested in Flexi France are presented in this paper concerning prevention of annular space flooding by seawater ingress or by diffused water. The paper also presents new designs for integrating monitoring sensors into the pipe structure and corrosion fatigue mitigation methods. Inspection and monitoring methods by integration of sensors or conduits within the pipe structure during its manufacture are now commercially available. These technologies, some of which are already applied on offshore fields, extend the usage limits of high strength steels and increase the fatigue life of dynamic risers. This is of primary importance for demanding applications such as deepwater, high pressure and/or sour service production.