The paperreports the experimental part of a development project on the design and fatigue perfonnance of composite umbilicals. A series of tests have been carried out, both full scale tests on complete umbilicals and more fundamental tests, to improve the understanding of the internal behaviour of an umbilical, to verify the theoretical analysis and to gather physical data necessary for the development of an analytical theory for calculating internal stresses in an umbilical being bent over a sheave.
Over recent years, umbilicals have been increasingly used in many offshore applications worldwide for subsea control, chemical injection etc. The failure of these components in a remote subsea installation can be extremely expensive both in lost production and rectification. Unfortunately, insufficient knowledge of the complex behaviour of umbilicals has often led to defective design, manufacture, installation and operation. A UK Dep. of Energy report, dated July 1990 state a high percentage of failures for umbilicals (Knight et.a!. 1990). Following the failures, fault analyses were of course carried out. However, it became obvious that some form of planned R&D was necessary. Since 1985 BP, ABB Norsk Kabel and EFI, which is a part of the SINTEF Group, Norway, have run a project with the objective of acquiring a better understanding of the behaviour of umbilicals and to identify factors having a significant influence on the life of umbilicals. It was decided, as a start, to concentrate on electrical umbilicals, both unarmoured and armoured, and to try to determine the stresses and the fatigue life of an axially loaded umbilical running back and forth over a sheave. If this problem is amenable to analysis, it is expected that more complex umbilicals and other types of bending problems can be included in later phases.
