Due to the harsh conditions sub-sea flow lines are exposed, they are subject to clogging by hydrates. Up to now, sub-sea pipeline heating was mainly used for purpose of preservation in case of production shutdown to prevent this pipe clogging. Access to more complex fields with lower quality of oil or longer distances of transfer to process plant requires to permanently heat the oil to maintain good viscosity and high flow rate. With a requirement of 20 to 50 kW/km and length in excess of 50km, this heating process represents a significant amount of energy per year.