Global Design and Analysis of Umbilical in Offshore Applications

Abstract

An umbilical is an assembly of fluid conduits (thermoplastic hoses and steel tubes), cables (electrical and fibre optic), and power cores, joined together for flexibility and over-sheathed, with or without armouring, for mechanical strength and stability. The emphasis of this paper is on the global configuration design and analysis of offshore umbilicals. The extreme and interference analysis methodologies are presented. One example is given for the application of very small OD electrical umbilical in shallow water in West Africa. The proposed global configurations are presented. Another example is presented for the application of a hydraulic umbilical in deep water in the Gulf of Mexico. The selection of the global umbilical configuration in deep water depends on the host vessel. In other words, the vessel motion characteristics may dominate the umbilical configuration selection for the deep water application. This paper also deals with the influence of the bottom current on the global design of the umbilical in deep water. It can be concluded that an optimized umbilical global configuration, which meets the strength and interference design criteria, can be achieved for the application of a small OD electrical umbilical in shallow water in West Africa as well as for a steel tube designed hydraulic umbilical in deep water in the Gulf of Mexico.

Ageing of thermoplastic umbilical hose materials used in a marine environment I – Polyethylene

“…[18][19][20] The gravimetric data suggest significant morphological changes are being induced by exposure to the fluids. Studies of the heat of fusion of the HDPE and melt temperature ( Figure 3) indicate that there is an initial increase in crystallinity on application of pressure to a value of 60%; exposure to water at 40 C produces a negligible change to the ÁH of fusion.…”

“…DSC analysis of the initial material before exposure to pressure gave a value for the ÁH of fusion of 139 J/g À1 and a melt temperature T m of 110 C. Assuming that the ÁH of fusion of pure polyethylene crystal is 290 J/g À1 , this implies that the material is 48% crystalline. [18][19][20] The gravimetric data suggest significant morphological changes are being induced by exposure to the fluids. Studies of the heat of fusion of the HDPE and melt temperature (Figure 3) indicate that there is an initial increase in crystallinity on application of pressure to a value of 60%; exposure to water at 40 C produces a negligible change to the ÁH of fusion.…”

“…[11][12][13] The primary concern in ageing studies has been the violation of the outer protective plastic layer and the consequent corrosion of the metal sheathing. Umbilical cables come in a variety of different forms [14][15][16][17][18][19] and each presents its own challenges. The main factor influencing the life of a cable is the continual cyclic stress created by waves.…”