Installability of Umbilicals

Abstract Offshore umbilical systems are essential for transmitting power and signals required to operate subsea facilities. In particular, umbilicals are made of a large number of elements with different engineering materials to accommodate constantly increasing requirements from oil and gas industry for production in deep waters and subsea processing. Often offshore umbilicals are installed using a reel lay or a carousel method and hence they are subject to large bending, axial and crush loadings during the installation process. In order to guarantee the structural integrity and installability of umbilicals during the installation process, umbilical manufacturers have to carry out a detailed structural analysis of the umbilicals. Such an analysis requires a deeper understanding in the structural mechanics of complicated cross sections subjected to various loadings. This increases the cost and manufacturing time of the umbilicals. This paper will present a simple method to carry out a detailed three dimensional finite element analysis of the umbilicals which will help to define safe installation limits such as the minimum reel/carousel/sheave(s) radiuses, maximum installation tension and tensioner crush operating loads. A 3 Dimensional Umbilical Simulation Tool, known as 3DUST has originally been developed by DeepSea (Dixon and Zhao, 2008), now a McDermott subsidiary. 3DUST is capable of three dimensional modelling of umbilicals and consists of pre-processing and post-processing features. Using the pre-processing feature, a modelling input deck with different materials, geometries, boundary conditions of any umbilical can be generated. This input deck is compatible with Abaqus finite element analysis software. Once the input deck is analysed, the post-processing feature can generate results with the installation capacity such as bending, axial load, crush load and ovality of the umbilical analysed, which can in turn be used to determine the adequacy of the reel lay or carousel system of the installation vessel. The paper will demonstrate the use of 3DUST for the installability analysis of an example umbilical with original analysis carried out for providing solution to an installation challenge of the umbilical. The paper will also present the results of the example umbilical obtained from 3DUST. A particular significance of the paper is not to demonstrate the computational mechanics involved in the analysis of umbilicals, but to address key challenges in the structural mechanics of the umbilicals and to simplify the umbilicals' analysis method by using 3DUST, a knowledge based system with capabilities including suitable finite element meshing of geometries, material assignments, defining boundary conditions and presenting relevant results. It is noted that this method has been applied to many deepwater umbilicals in West Africa, Golf of Mexico and Brazil.