Method for pressurizing the inner flow space of a flexible pipe intended for transporting hydrocarbons

The present invention relates to a method for pressurising the inner flow space of an underwater flexible pipe intended for transporting hydrocarbons, which includes the following steps: a) providing a flexible pipe which includes a reinforcement layer made up of a short-pitch winding of at least one metal wire with non-contiguous turns around a thermoplastic polymer sheath defining an inner space; b) filling the inner space of the flexible pipe with an oil; c) increasing the inner pressure Pi of the flexible pipe to at least 10 MPa, the inner pressure being exerted by said oil; and then d) maintaining the inner pressure Pi of the flexible pipe at a pressure of at least 10 MPa for a time D of at least one minute, characterised in that said oil has a kinematic viscosity at 40°C, measured according to the ASTM D445 standard, of more than 10 mm2/s. Said method makes it possible to reduce or even to prevent the appearance of cavitations and cracks on the polymer sheath.