This article evaluates flow assurance by heat trace cables for wet insulated flowlines as an alternative to direct electrical heating or chemicals. Heat trace cables are attractive for their simple and flexible design and that they can be retrofitted. Case studies of a 14" flowline, where trace heat cables are placed outside the coating, indicate that fluid temperatures can be maintained at 25-55 °C. Heating capability depend on flowline geometry, heating cable type and burial depth. Commercial heat trace cables are available for flowline lengths including at least 50 km. Heat trace cables with conventional electrical insulation can deliver power in the 100 kW/km range.
Electrical heating is used to maintain the mixture of oil, gas and other substances in onshore and subsea flowlines at elevated temperatures to prevent wax and hydrates from causing blockage in the flowline. By heating the flowline electrically, the need for chemical injection is reduced considerably.
Electrical heating has proved to be suitable for short, as well as for long flowlines since heat can be generated evenly along the whole length. Electrical heating is expected to be increasingly deployed as an elegant technical solution to optimize flow assurance management during the service life of production flowline. The electrical heating may be used continuously, at production stops and/or during tail production.
Electrical heating has been used for several decades on onshore facility pipes, probably starting with the simple design of an insulated wire (Burpee, 1977). Later, other techniques emerged, such as induction heating, impedance heating and skin effect heating, (Rafferty, 2002). The latter has been installed on a 600 km line (Hamill, 2016), but it has also been tested on a submerged flowline (Wan, 2020). For subsea pipe-in-pipe installations, heat trace cables exist in a few installations and are described in several publications, e.g., in (Gooris 2016; Verdeil, 2019).
