A practical approach to the prediction of lifetime of large diameter multi-layer wire ropes for use in deepwater deployment systems
Torque neutral or low torque wire rope constructions of large diameter are used to satisfy the increasing demands of installing large structures in great water depths. For these types of wire rope it becomes very important to monitor the integrity of the rope throughout its lifetime via an integrated rope monitoring system. This process can be based on monitoring of the usage of each rope section in terms of load and accumulated bending cycles in combination with a rope inspection programme covering non-destructive inspection techniques and visual inspection. The prediction of the rope lifetime based on its usage is an integral part of such a rope monitoring system. A benchmark has been set by a series of laboratory bending fatigue tests with frequent magneto-inductive inspections and visual examinations. This test series acts as the basis for the prediction of the rope lifetime for the tested wire rope constructions. Throughout its service life the usage of the ropes in terms of bending cycles and loads is monitored constantly and accompanied by magnetic and visual inspections to determine the rope damage per section due to bending fatigue, wear and tear and internal corrosion. This article covers the requirements for a successful integration of a rope monitoring system in subsea deployment systems; elaborated conclusions on the advantages of the application of such a system are made. This paper is part of a series of publications of this research work. Further information on the conducted tests can be found in the OTC 2008 paper , temperature measurements are published at ISOPE2008 , magnetic flux NDT tests were published at the OMAE2008  and implications for offshore installation tasks were published at the DOT2008 .
Author(s): O. Vennemann and B. Ernst