Konferensartikel

Direct electrical heating (DEH) is a technology for preventing hydrate formation and wax deposit inside oil and gas pipelines. Nexans Norway AS is researching and developing DEH solutions for deep waters. The company has produced a deep-water DEH piggyback cable that can carry its own weight at 1 070 m water depth. When this DEH system is installed outside the coast of Africa, it will be the world’s deepest DEH system. For deep-water cables, including umbilicals, the maximum allowable tension (MAT) is an important parameter that limits the water depth which the cable can be installed at. As MAT by definition is calculated for straight (non-bent) cables, it can be argued from a theoretical point of view that friction should be disregarded. However, from a practical point of view, one can argue that the cable is rarely perfectly straight, which justifies inclusion of friction. This paper derives the relation between the cable’s axial tension, the axial tensions of the individual cable elements, and friction, with emphasize on how friction influences MAT. Four different approaches for calculating friction’s influence on MAT are presented. These approaches range from fully neglecting friction to including the maximum possible friction. Two approaches include friction up to a certain curvature limit, which corresponds to an "almost straight" cable, and neglect the friction for higher curvatures. The most conservative approach gives 19% lower MAT than the least conservative approach for the deep-water DEH piggyback cable.

Axisymmetric Analysis; Cable Capacity; Capacity Curve; Cross Section Analysis; Maximum Allowable Tension; Maximum Handling Tension; Offshore Technology; Riser; Subsea Cable; Umbilical