Automated Application of Full Matrix Capture to Assess the Structural Integrity of Mooring Chains

Abstract

In-service mooring chains are subjected to harsh environmental conditions on a daily basis, which increases the necessity of integrity assessment of chain links. Periodic structural health monitoring of mooring chains is mandatory and vital in order to maintain the safety of floating platforms. Application of ultrasound for in-service mooring chain inspection is still in its infancy due to the lack of accessibility, in field operational complexity and the geometrical features of mooring systems. With the advancement of robotic/ automated systems (i.e. chain climbing robotic mechanisms), interest in in-situ ultrasound inspection has increased. Presently, ultrasound inspection has been confined to the weld area of the chain links. However, according to recent studies on fatigue and residual stresses, ultrasound inspection of the chain crown should be further investigated. A new application of ultrasonic phased array full matrix capture is discussed in this paper for investigation of the chain crown. Due to the complex geometry (i.e. curved and limited access) of the chain crown, a surface mapping technique has been added to the presented full matrix capture technique. The inspection method presented in this study is suitable for chain links both in air and underwater. A continuous water supply wedge was developed in order to supply couplant for in air inspection. Development of a technique which can be adapted for robotic inspection was considered, and an automated manipulator was used to carry out inspections. The design of the inspection method and the robotic manipulator is discussed in this article. The technique is validated with laboratory experiments.