Process allowing to increase the cracking corrosion resistance of a wire under stress

#The present invention relates to a method and to a system allowing to increase the cracking corrosion resistance of a wire under stress used for manufacturing armoured flexible pipes intended for petroleum reservoirs development.

#It is well-known that certain metals are sensitive to cracking corrosion when they are exposed to certain aqueous corrosive environments, notably aqueous environments containing hydrogen sulfide, and simultaneously subjected to tensile stresses, their sensitivity to cracking corrosion being all the higher as the plastic deformation under tensile stress is high. Stress cracking in a corrosive environment generally develops from the surface.

#Stress cracking resistance in an environment containing hydrogen sulfide (SSC: Sulfide Stress Cracking) is a determining property for steels intended for flexible oil pipes reinforcement. In fact, it conditions the nature of the steels that can be used, both in terms of composition and of state of treatment.

#Other features and advantages of the present invention will be clear from reading the description hereafter, with reference to the accompanying drawings wherein:

#FIG. 1 diagrammatically shows an implementation of the invention,

#FIG. 2 diagrammatically shows the shot blasting device according to the prior art,

#Brushing of the surfaces is carried out mechanically by means of brushes. FIG. 1 shows an equipment allowing the invention to be implemented. A flexible pipe core 1 consists of one or more polymer sheaths on which wire layers have already been wound. The wires wound at an angle close to 90° in relation to axis 4 form an armour, commonly referred to as pressure layer, taking part in the internal and/or external pressure resistance of the flexible pipe. The wires wound at an angle of about 45° in relation to axis 4 form an armour taking part in the tensile strength of the flexible pipe. The surface treatment by brushing according to the invention can be applied indiscriminately to all the metallic armours of the flexible pipe.

#The flexible pipe core is translated forward in relation to axis 4. One or more wire reels 7 mounted on a mobile conveyor 3 rotating in relation to axis 4 allow continuous delivery of wire 2. Thus, the core of a helically wound wire layer 8 is armoured by combining the rotating motion of conveyor 3 and the translation motion of core 1. During this operation, wire 2 undergoes a plastic deformation, and the face of the armouring situated outside the flexible pipe core undergoes a permanent tensile strain that can exceed 5% considering the typical dimensions of the flexible pipes and of the reinforcing wires.

#After being wound around the flexible pipe core, the wire is subjected to the brushing operation. A brush 5 actuated in rotation by a motor 6 brushes wire layer 8 that is already wound on the flexible pipe core. The translation and rotation mobilities, in relation to axis 4, of the assembly consisting of brush 5 and of motor 6 allow the whole external face of the wire layer apparent on the outside of the flexible pipe core to be treated.