Method and system for direct electric heating of a double-walled pipe for transporting fluids

Abstract

A method and system for Direct Electrical Heating of a Pipe-In-Pipe pipeline for transporting fluids includes mechanically connecting the steel inner shell to the steel outer shell at different intervals of the pipeline, establishing an electrical and thermal insulation between the inner shell and the outer shell, applying an alternating electric current between an outer surface of the inner shell and an inner surface of the outer shell over the entire length of the pipeline so as to heat the inner shell of the pipeline by Joule effect, and placing on the outer surface of the inner shell at least one layer made of resistive and ferromagnetic material so as to increase the ratio of electric power transmitted to the inner shell.

1 . A method for Direct Electrical Heating of a Pipe-In-Pipe pipeline for transporting fluids, the pipeline comprising a steel inner shell intended to transport fluids and a steel outer shell positioned around the inner shell while being coaxial therewith in order to delimit an annular space therewith, the method comprising:
 mechanically connecting the inner shell to the outer shell at different intervals of the pipeline;   establishing an electrical and thermal insulation between the inner shell and the outer shell over an entire length of the pipeline; and   applying an alternating electric current between an outer surface of the inner shell and an inner surface of the outer shell over the entire length of the pipeline so as to heat the inner shell of the pipeline by Joule effect;   wherein it further comprises:   placing on the outer surface of the inner shell over the entire length of the pipeline at least one layer made of resistive and ferromagnetic material so as to increase a ratio of electric power transmitted to the inner shell.   
     
     
         2 . The method according to  claim 1 , further comprising placing on the inner surface of the outer shell over the entire length of the pipeline a jacket made of conductive and non-magnetic material. 
     
     
         3 . The method according to  claim 1 , wherein the alternating electric current which flows on the outer surface of the inner shell by skin effect and on the inner surface of the outer shell by proximity effect has a frequency of 50 Hz or 60 Hz. 
     
     
         4 . The method according to  claim 1 , wherein the alternating electric current is applied at several points of the pipeline each corresponding to at least one pipeline section, each pipeline section comprising an inner shell section and an outer shell section. 
     
     
         5 . The method according to  claim 2 , wherein placing the jacket made of conductive and non-magnetic material comprises inserting a tube made of conductive and non-magnetic material inside the outer shell, then expanding under pressure the tube against the inner surface of the outer shell. 
     
     
         6 . A Direct Electrical Heating system of a Pipe-In-Pipe pipeline for transporting fluids, the pipeline comprising a steel inner shell intended to transport fluids and a steel outer shell positioned around the inner shell while being coaxial therewith to delimit an annular space therewith, the system comprising:
 a plurality of mechanical links between the inner shell and the outer shell which are positioned at different intervals of the pipeline;   an electrical and thermal insulation between the inner shell and the outer shell which is positioned over an entire length of the pipeline; and   an alternating electric current generator applied between an outer surface of the inner shell and an inner surface of the outer shell over the entire length of the pipeline so as to heat the inner shell of the pipeline by Joule effect;   wherein it further comprises:   at least one layer made of resistive and ferromagnetic material positioned on the outer surface of the inner shell over the entire length of the pipeline so as to increase a ratio of electric power transmitted to the inner shell.   
     
     
         7 . The system according to  claim 6 , further comprising a jacket made of conductive and non-magnetic material positioned on the inner surface of the outer shell over the entire length of the pipeline. 
     
     
         8 . The system according to  claim 7 , wherein the jacket made of conductive and non-magnetic material is made of aluminum, copper, bronze, brass or zinc. 
     
     
         9 . The system according to  claim 7 , wherein the jacket made of conductive and non-magnetic material has a thickness comprised between 1 and 6 mm. 
     
     
         10 . The system according to  claim 6 , wherein the layer made of resistive and ferromagnetic material is made of electrical steel or amorphous metal. 
     
     
         11 . The system according to  claim 6 , wherein the layer made of resistive and ferromagnetic material has a thickness comprised between 1 and 3 mm. 
     
     
         12 . The system according to  claim 6 , wherein the mechanical links between the inner shell and the outer shell of the pipeline are annular shoulders evenly spaced over the entire length of the pipeline. 
     
     
         13 . The system according to  claim 7 , wherein the inner shell and the outer shell of the pipeline each comprise a plurality of shell sections connected end-to-end to each other by weld beads, the jacket made of conductive and non-magnetic material and the layer made of resistive and ferromagnetic material having discontinuities at the weld beads. 
     
     
         14 . The system according to  claim 13 , wherein an electrical continuity of the jacket made of conductive and non-magnetic material and of the layer made of resistive and ferromagnetic material is achieved directly through the inner and outer shells. 
     
     
         15 . The system according to  claim 13 , wherein the electrical continuity of the jacket made of conductive and non-magnetic material and of the layer made of resistive and ferromagnetic material is achieved indirectly through a conductive annular ring or a conductive sleeve which are positioned at the weld beads.