The Electric Trace Heating System uses an array of insulated electric heating elements in thermal contact with the pipeline or flowline being heated. The applied electrical power is dissipated as heat by Joule effect resistive heating. The system can be applied to either flexible pipe or rigid pipe-in-pipe. Trace heated flexible pipe is suitable for risers and manifold, well, or sled jumpers. Trace heated rigid pipe-in-pipe is suitable for longer applications such as flowlines.
The trace heating system is composed of a number of components. A dedicated power supply, topsides furnishes electrical power. The power supply is connected to a power control unit which regulates electrical power supplied subsea. An umbilical conducts electricity from the topsides to a subsea umbilical termination that is connected to the near end of the electrically heated flowline using standard ROV wet-mateable power connectors and flying leads. The flowline end termination may include an ROV panel with ports for the electrical connectors. A flanged bulkhead arrangement serves as the interface between the flowline and other subsea equipment.
The trace heated flowline, either flexible or rigid, contains an array of low electrical resistance copper core cables, grouped by three’s, to form 3-phase star connection circuits. At the near end of each circuit, each of the three electrical cables is fed with one phase of alternating current. At the far end of each circuit, the three cables are connected to each other to form a star connection. Where the cables meet, the sum of the three current phases is nil, thus the advantage of the 3-phase circuit is that a return cable is unnecessary. Depending on the heating requirements of the system, the number of sets of 3-phase circuits can typically range between 2 and 4, and may include one spare circuit if required.
Trace Heating Electric Heat System
The rigid pipe version of the trace heating system typically utilizes reelable pipe-in-pipe. The pipe-in-pipe flowline is insulated with high performance passive insulation such as mineral wool, microporous silica, or proprietary compounds like Aerogel or IzoFlex. The insulation is used to achieve the necessary degree of passive thermal performance. For all the insulation schemes except IzoFlex, some type of centralizer is required and are typically spaced at a pitch of approximately two meters in order to protect the lightweight insulation materials from crushing during reel installation. IzoFlex insulation has sufficient rigidity and structural strength to resist crushing thus centralizers are not required. The trace heating cables are fitted snugly between the inner flowline and the insulation, and may also include optical fibers as a means of flowline temperature profile monitoring if heating requirements are pushing the temperature capabilities of the electrical insulation of the trace heat cabling.
Two competing suppliers of electric trace heating systems for subsea flowlines in the industry:
- InTerPipe - Izoflex insulated pipe-in-pipe flowlines with electric trace heating
- Technip / Coflexip - Flexible risers and flowlines with electric trace heating