1. Field of the invention:
This invention relates in general to flexible pipes for conveying fluids at high pressure, and in particular to those used for subsea oil and gas drilling and production.
2. Description of the Prior Art:
In subsea well production and drilling operations, flexible pipes are used for various purposes such as underwater flowlines. A flexible pipe is herein considered to be a pipe having, at least during installation, sufficient flexibility along its longitudinal axis to accept a minimum radius of curvature in the order of five to twenty times the diameter of the pipe, without weakening the structure.
These pipes must resist combined hoop and longitudinal end loads from the high pressure conveyed fluids as well tensile loading during installation and operation. These pipes must also withstand crushing due to external pressures with or without internal pressure inside. Once in place, the internal pressure makes the pipe stiffer, and flexibility is no longer needed. A flexible pipe is easier to transport and install than a rigid pipe.
A typical flexible pipe structure comprises at least one fluid containing tube made of polymer material. A reinforcing armor of metal wires is wound spirally around the fluid containing tube. In some instances, a third structure consisting of a helical winding of interlocking strips is located inside the containing tube. This last structure prevents the fluid containing tube from collapsing under flexible pipe annular pressure and provides radial support to the reinforcing armor while the flexible pipe is under tensile loads without internal pressure. Improvements in strength, manufacturing ease, and cost are desirable.