During the last 20 years, one of the main industry problems of floating units is the failures of chains along the mooring line. In long term waves induced axial loads in the mooring line with a frequency from 0.01 Hz to 1 Hz, which produce a tension-tension fatigue in the mooring chains. The tension-tension fatigue is due to cyclic range of tension variation loading in the chains, where a crack can initiate and grow until a fracture is produced. Therefore, Lloyd’s Register and TWI are interested to establish a better understanding of failure generated by tension-tension fatigue, including crack initiation and crack growth in mooring chains using Acoustic Emission Technique (AET). AET is a potential structural health monitoring tool which can serve as an early warning system for the offshore industry. Acoustic emissions are the elastic energy waves that are spontaneously released by a material undergoing deformation.
There is a need for good data on current conditions, to establish a better understanding of failure, including crack initiation/propagation, and use of best technology to determine safety margins and the development of new techniques. In addition to answer some questions that the industry has in this moment, for example: Is AET a way to detect a crack initiation before crack growth or chain fails?, How long time has the offshore industry available yet to change a mooring line, from crack initiation to failure?.
The purpose of the project is to develop a methodology for monitoring the integrity of mooring chains based on Acoustic Emission Technique, where a signal processing methodology will be implemented to monitor crack initiation and crack growth generated by Tension-Tension fatigue in studless chains. Implementing Acoustic Emission Technique in a test rig to monitor crack initiation and crack growth in studless chains of big diameter, to know the life of the chains before failure.