HEATING SYSTEM FOR CRUDE OIL TRANSPORTING METALLIC TUBES

Heating system for crude oil or other viscous fluids transporting metallic tubes having a thermal insulation, wherein a defined length of the said metallic tube acts as a heating element, which is electrically insulated by the tube insulation itself and whereby the metallic tube has connections with respective feeder and return cables at the beginning and at the end of the length of the tube defining the length of the heating element.

In the FIGURE there is illustrated an insulated metallic tube 1 (pipeline) connecting the template 2 installed at the sea bottom 3 with the process unit 4 installed on the platform 5 . Because of the thermal insulation of the metallic tube 1 the crude oil coming from the template 2 can be transported with a sufficient viscosity to the platform 5 . If for any reason the crude oil transportation has to be stopped the formation of hydrate plugs or wax deposits may occur. When starting transportation again the plugs and remaining cold crude oil in the section 6 will block new oil transportation because of its higher viscosity inspite of the thermal insulation of the metallic tube 1 . To avoid such a problem the metal tube 1 in the section 6 will be heated by direct impedence heating. For this purpose a single phase power supply 7 installed on the platform 5 is connected with a riser cable 8 containing one or more insulated feeder and return conductors, maybe stranded with another and being protected in the normal way by an armouring and an outer sheathing. The feeder and return cables may have connectors. At the end of the riser cable 8 its armouring and sheathing has been cut back and one feeder and one return conductor is connected with a corresponding feeder cable 9 and a respective return cable 10 by connecting elements 11 and 12 . Insulated flanges 13 and 14 act as connecting devices for the feeder cable 9 and the return cable 10 with the metallic tube (pipeline) 1 . Although the design of the flanges 13 and 14 may be quite different it is necessary to have a dimension for current transport to the metallic tube 1 up to 12.000 A and the flanges must be insulated towards the sea water. The flow line section between the processing unit 4 and the electric insulating flange 14 may be of a flexible flowline design. Instead of using conncetors in having the riser cable 8 being connected with the feeder cable 9 and the return cable 10 both consisting only of a power core with an insulation but without an outer metallic screen and/or armouring sometimes it will be useful to cut back or remove the armouring and the sheath of the riser cable as before but to extend the feeder and the return conductor of the riser cable now as feeder cable 9 and return cable 10 to the connecting flanges 13 respectively 14 . The electrical flanges 13 and 14 electrically isolate the section 6 from the rest of the pipeline; i.e. there is no metallic (electric) path through these items. In the case of a stop of crude oil transportation in the metal tube 1 before and/or during and/or after oil stop section 6 of the metal tube 1 will be heated by direct impedance from the single phase power supply 7 with the service voltage. The section 6 heated by an AC current flow secures that at the time of oil transportation starting the remained crude oil will have sufficiently low viscosity. The present invention should not be restricted to the above example showing the principle. So the same heating system can be used in the case crude oil transportation has to be made between a template on the sea bottom and a ship or between two or more ships. The FIGURE shows the feeder cable 9 and the return cable 10 laid in parallel relationship to the section 6 of the metallic tube 1 . For handling and protection purposes the normal arrangement would be that at least the feeder cable 9 and the return cable 10 are attached to the insulated metal tube 1 , in section 6 during installation. A connector 15 will ease feeding cable repair after any damage.