Operation dynamic tests are usually performed to check the behavior of the umbilical and their accessories, when they are submitted to operation loading conditions. In this case, the test loading should be applied in order to lead the sample to its theoretical failure. Because the umbilical steel armors are assembled helically, then, part of the applied loads will be transformed into pressure on the intermediate sheath, which, in turn, will tend to squeeze the internal components of the umbilical (electrical cables, hydraulic hoses, etc.). At the end of the tests, the umbilical is then dissected and its internal components are submitted to complementary tests, in order to check whether they are still able to maintain their integrity and functionality. Hydraulic hoses, particularly, are manufactured in polyamide 11 reinforced with aramid layers and are usually submitted to dimensional, leakage, burst and volumetric expansion tests, all standardized by API 17 E [1].
For a specific application, an umbilical, composed by four electrical cables and five hydraulic hoses, has been developed and, following, tested. One has observed that its hydraulic hoses have failed the leakage and burst tests. Analyzing the umbilical cross section design by using numerical analyses tools, one has noticed that the hoses were the most stressed components during the dynamic tests, what could have damaged them before their complementary tests. In order to take the hoses to a safer stress level, a modification of the umbilical cross section design has been proposed, based on studies also performed with the aid of numerical analysis tools. In order to assess the performance of the hoses with the new cross section design, new dynamic and complementary tests have been performed. One has observed a good improvement in the hydraulic hoses performance. Thus, based on the numerical and experimental data, the objective of this work is to demonstrate the applicability of general numerical analysis tools on the performance improvement of umbilicals and their components by means of a case study.
According to standard API 17 E [1], umbilical cables must be designed to incorporate the functional requirements and meet the mechanical properties required to withstand harsh environmental conditions in both static and dynamic applications during its whole lifetime. The utilization of an umbilical cable defines the shape of its cross section arrangement, i.e., the number of hydraulic hoses, cables for transmission of electrical signals/power, chemical injection lines and optical cables. The diameter necessary to accommodate all components, the final weight of the umbilical and the constraints on their allowable loads and deformations are factors that determine the number, arrangement and strength and stiffness of the steel armour wires and plastic sheaths, used to protect the central components from the harmful environment [2].
In order to verify if the umbilical and its components will fulfill their design requirements during their whole lifetime, a test program for qualifying the umbilical itself and its functional components (electrical cables, hydraulic hoses and tubes, optical cables, etc.) must be defined. As a general directive, the qualification tests will subject the umbilical sample to pressure, tension, bending and compressive loads, simulating the product manufacturing, handling, installation, operation and recovery loading [3]. Additionally, complementary tests must be performed to demonstrate that the functional components of the umbilical will keep their characteristics after the installation and operation loads are applied [3].
