Analysis of Direct Electrical Heating

Sandwich pipes consisting of two concentric metal pipes with insulation material in annulus have been developed to meet challenging mechanical and thermal requirements of deep and ultra-deepwater oil and gas production. Passive thermal insulation is designed to meet flow assurance requirements under steady-state production conditions, but is unlikely to meet more severe conditions during transient events such as warm-up and cool-down. In this chapter, we present a sandwich pipe system with active electrical heating, provided by a number of electrical resistance strips stuck longitudinally over the outer surface of the inner metal pipe. A steady-state heat transfer analysis is carried out to determine the temperature distribution in a cross section of the sandwich pipe, the power requirement of electrical heating, and the overall heat transfer coefficient. It is shown that the sandwich pipe with active heating is a viable solution to meet severe flow assurance requirements of ultra-deepwater oil production.