Feasibility evaluation for non-contact ultrasonic inspection of mooring chains through marine growth

Abstract

Mooring chains are subject to dynamic loads and corrosion. A challenging aspect in assessing the integrity of mooring chains is the presence of marine growth. Marine growth removal is expensive, environmentally damaging, and includes the risk of restarting corrosion process. The focus of this research is on the feasibility of mooring chains assessment in the presence of marine growth using active and passive ultrasound techniques. The approach includes experimental and numerical investigations for fatigue and corrosion damage. In the experimental part, specimens with and without marine growth have been designed, manufactured, and subjected to a series of experiments to determine the transmission characteristics of ultrasound waves through marine growth and its interaction with damage. Fatigue crack signals were simulated on the specimens using Hus-Nelson source. For the investigated compositions, the signal amplitude drop due to the presence of marine growth. Accelerated corrosion experiments were conducted to reproduce corrosion-induced acoustic emissions. Corrosion-induced signals were successfully detected and localized. Active ultrasound experiments were conducted using guided waves. These waves were successfully excited and measured in the test sample with naturally-cultured marine growth. The investigation suggests that guided waves can have a high potential for identification of fatigue cracks in the mooring chains. These experiments were complemented with numerical simulation of the setup. For the sake of computational efficiency and accuracy, a higher-order spectral finite element method was used. Simulations were further extended to investigate and confirm the possibility of detection of surfacebreaking cracks in the test sample.