By combination of elements like hydraulic tubes, electrical and optical signal cables and electrical power cables, umbilicals provide remote control of subsea oil and gas wells. Riser umbilical’s are terminated at offshore platforms or vessels, and will be exposed to tension and bending variations caused by waves and vessel motions.
Understanding how forces are transmitted between the elements in an umbilical is vital for correct calculation of the umbilical design life. When umbilicals are exposed to tension and bending, tension will be imposed in the individual elements. The magnitude of tension is governed by the overall tension and bending and also by the lay angles, placement in the cross section and the friction forces between the elements.
Some friction coefficients may be found in literature, but not all material combinations, and not for the conditions inside an umbilical.
A project was therefore initiated with the aim of developing a friction testing device capable of determining friction coefficients between all elements in environments that are representative for the conditions within an umbilical, i.e.: at various temperatures; in sinusoidal movements, like the bending movements in an umbilical; at representative contact pressures, speeds and temperatures; in various environments, like air and seawater; without crumpling soft elements like synthetic tapes.