PREDICTION of OFFSHORE MOORING ROPES

Round Table Application of Wire Rope Endurance Research – Delft 1993

ABSTRACT

The paper discusses the results of an extensive programme of investigation modelling the fatigue behaviour of large diameter ropes of the types used for mooring buoyant offshore structures. The test programme has included tension-tension fatigue testing and combined, in phase, bending-tension testing. Constant amplitude tests have been complemented by block loading tests to simulate more closely the offshore conditions. This new body of fatigue test data is discussed in the context of comparable results obtained by other investigators. Procedures are described which have been developed for establishing a safe service life. Design incorporating endurance prediction, is found to depend on two significant issues: the accuracy of the predicted load spectrum, and the differences between ropes. The scatter in fatigue performance for any given rope is not considered to be a dominant variable, which has a significant implication on potential length effects. The long term effects of the seawater environment remain an area of some uncertainty.

Author: Chaplin, C.R.