Umbilicals are composite cables responsible for communication, control and power supply of offshore systems for oil exploitation. They can be composed of elements such as power and signal cables, hoses, tubes and fiber optics. Due to their critical role of providing control and power, umbilicals properties and operational limits must be correctly calculated in order to prevent failures, which can be costly and harmful to the environment.
In order to address these needs, the main goal of this paper is to study the viability of using a finite element analysis tool for calculating the allowable bending radius (ABR) and the crush resistance of these cables. Using this tool, the engineer can have a sound basis for choosing the best cross section design at early stages of the project.
The ABR is particularly important at the point where the umbilical touches the seabed, named touchdown point (TDP). This parameter limits the possible operational configurations for the cable and has a significant influence in its fatigue lifespan. Currently, the methods used to predict the ABR of thermoplastic umbilicals are mostly empirical and/or based on samples, but, as we go to deeper areas — as the recent ultra-deep water field discoveries in Brazil, Angola and others — more accurate ways of estimating this parameter are needed.
Another effect of the higher water depths is the increase of tension on umbilicals during installation. Therefore, tensioners with higher load capacity are needed, requiring umbilicals with higher crush resistance. Sample testing during a qualification program is the main method to obtain the value of this parameter, but is costly.
Due to its reliability and relative low costs compared to sample testing, the use of a finite element tool is an attractive alternative for obtaining these limits. In this paper, crush resistance and ABR will be calculated for thermoplastic umbilicals — the most common type of umbilical used in Brazilian offshore oil exploitation — and the results will be compared with the ones achieved by traditional methods. This comparison shows the applicability of using finite element analysis for determining these parameters.