The present invention relates to a method for connecting a rigid submarine pipe and a flexible submarine pipe, and to an installation suitable for using this connection method.
These submarine pipes are designed to transport hydrocarbons in a marine environment and in particular to carry the hydrocarbons between a submarine installation installed on the seabed and a surface marine installation, for example a platform situated on the surface of the marine environment.
The rigid submarine pipe is extended over the seabed from a submarine installation, and it terminates in a free connection end. The flexible submarine pipe has a flow-line portion that lies on the seabed and has a suspended portion that is designed to join the surface installation. The flow-line portion terminates in an input end that is connected at the free connection end of the rigid pipe so that the suspended portion lies in a catenary overhanging the free connection end. In addition, the installation comprises anchoring means to hold the flow-line portion anchored in the seabed at an anchor point of the flow-line portion so as to allow this flow-line portion to form an undulation separated from the seabed, between the anchor point and the suspended portion, and thereby to prevent this flow-line portion from impacting on the seabed when the vertical position of the surface installation fluctuates.
Reference may in particular be made to document FR 2 746 977, which describes such an installation.
However, in certain operating circumstances, the temperature variations of the extracted hydrocarbon cause longitudinal deformations of the rigid pipe and as a result the movement of the free connection end.
Consequently, the flow-line portion of the flexible pipe that lies between the free connection end of the rigid pipe and the anchor point is likely to be moved in translation on the seabed, which on the one hand causes its intrinsic longitudinal deformation and, on the other hand its abrasion. The aging of this flow-line portion is then accelerated.
In addition, the suspended portion of flexible pipe that lies as a catenary exerts a longitudinal pull on the rigid pipe at its free connection end. Now, when the rigid pipe retracts, particularly when the flow of hydrocarbon is stopped and the pipe cools, the retraction forces oppose the pulling forces exerted by the flexible pipe, so that the rigid pipe risks being damaged. Although it was feasible before, for shallow and medium-depth submarine installations, to work easily on the damaged rigid pipe, this work is no longer feasible for submarine installations at very great depths.