High-Performance DEH-PiPfor Subsea Tiebacks: Theoretical Electrical Model and Performance Measurements

Abstract

The High-Performance DEH-PiP is a new technology for electrical heating of subsea tieback flowlines, able to be used for long distances thanks to an enhanced electrical efficiency. This paper describes the theoretical electrical model of this technology and its experimental validation. DEH-PiP is a well-known and field-proven technique for subsea flowline heating, but it exhibits a relatively poor electrical efficiency compared to emerging heat-traced PiPs. The approach presented in this paper to solve this drawback has been first to analyze the heat losses within the conventional DEH-PiP, then to design a new outer pipe to decrease dramatically its impedance. A strong effort was spent on the building of an accurate electrical model for the High-Performance DEH-PiP, and finally full-scale electrical tests on a representative prototype were carried out to validate the theoretical model. On the basis of the conventional DEH-PiP technology, specific design modifications were undertaken to enhance the electrical efficiency and thus the flowline step-out in the High-Performance DEH-PiP solution. A specific electrical model was developed and is detailed progressively in this paper from the basic electromagnetics considerations to the complete Finite Element Analysis including the magnetization curves of the pipe steel and the impact of magnetic hysteresis on the heating performances. Dedicated experimental works were conducted to validate the electrical model, on a specific prototype and the test bench associated. The electrical measurement curves are discussed, showing a good correlation between the theory and the experiments, and demonstrating the relevance of the electrical model. The impact of the improved electrical performance on the tieback heated flowline configuration is then discussed. This paper introduces the detailed experimental and modeling work performed to allow for the electrical engineering of a new DEH-PiP design, reaching significantly higher electrical efficiency, in the range of 90%-95%. This new solution allows reduced Greenhouse Gases Emissions by enhanced performance, lower voltage supply level enabling for longer flowlines, and lighter power chains.