Method and device for induction heating of an inner pipe of an assembly of coaxial pipes

A device for induction heating an inner pipe of coaxial pipes, the device comprising:

• induction heater means comprising at least one electromagnetic induction coil coaxially surrounding the outer pipe of the coaxial pipes;
• and
• raising means for raising a portion of coaxial pipes above a sea bed together with said induction coil(s) surrounding it.

A method of heating an inner pipe of a set of coaxial steel pipes comprising an inner pipe and an outer pipe, wherein the inner pipe is heated by induction using an electromagnetic induction coil surrounding the outer pipe coaxially to 40° C., the coil passing electrical power at a frequency lower than 100 Hz optimized for maximum energy efficiency of Joule effect heating of the inner pipe, the inner and outer steel pipes presenting the thermal capacity characteristics of pipe steels and the thermal insulation of the annular space between the inner and outer pipes being such that the time required for cooling from 40° C. to 20° C. is at least 24 h.

A method of heating an inner pipe of a set of coaxial steel pipes comprising an inner pipe and an outer pipe, wherein the inner pipe is heated by a movable induction heater which includes at least one electromagnetic induction coil surrounding the outer pipe coaxially, the heater movable along the set of coaxial pipes, the coil passing electrical power at a frequency lower than 100 Hz optimized for maximum energy efficiency of Joule effect heating of the inner pipe, wherein the inner pipe is heated to a temperature T2 with the movable induction heater device, said movable heater device being moved at a speed of at least n km/day so that the temperature of the inner pipe for a given length of pipe remains greater than T1 less than T2, where T2-T1 is greater than the temperature drop of the inner pipe over one day.