Design of a machine to test the strength of synthetic mooring ropes used in marine technology

The technology of platform anchorage systems has been developing quickly nowadays. Due to the oil extraction in deep waters, the traditional mooring types, such as anchor cable/wire rope/anchor cable in catenary shape, were replaced by a “Taut-Leg” geometry. This type, characterized by an anchor cable/synthetic cable/anchor cable, operates in a straight mode, reducing weight and modifying the mooring operation. Therefore, the synthetic ropes for offshore platform anchorage are long and robust, with large number of sub-ropes arranged in a parallel mode in order to increase mechanical strength. Petrobras has used this new form of technology with polyester cables since the beginning of this decade; despite this fact, there is a lack of knowledge of the behavior related to structural integrity (residual life, total life, etc.). Taking it into account, Petrobras and Policab (Stress Analysis Laboratory at the Federal University of Rio Grande, Brazil) have been interested in developing a test machine capable of executing static rupture tension tests (maximum value of 300 ton) and fatigue in tension tests (150 ton). Both tests have to be applied to sub-ropes, simulating environmental conditions (sea wave frequency and displacement under storm conditions). The main objective of this paper is to present the methodology used for analyzing alternatives in order to choose the machine that meets the requirements, from the creative process to its conception. The test machine, which is the final product of this study, is described.

Author(s): A. Goncalces, P.R.F. Teixeira and F.E.G. Chimisso