Finite Element Analysis of Crack Growth for Structural Health Monitoring of Mooring Chains using Ultrasonic Guided Waves and Acoustic Emission

Abstract

As offshore oil and gas exploration and production goes further afield and into deeper waters, more offshore operations, are conducted from floating platforms, which are moored to the seabed by chains, polyester tether lines, or combinations of both. Moreover, the forecasted large scale deployment of offshore renewable energy systems in deep water will rely upon similar mooring systems. Mooring lines are safety-critical systems on offshore floating and semi-submersible platforms. The lines are usually subject to immense environmental and structural forces such as currents, oceans waves, and hurricanes. Other forces include impact with the seabed, abrasion, increased drag due to accumulation of marine organisms and salt water corrosion. Failure of one or more of mooring lines can result in disastrous consequences for safety, the environment and production.Mooring chain life can be significantly reduced, leading to unacceptable risk of catastrophic failure, if early damage is not detected. Chain mounted equipment is available to monitor chain tension and bending, but detection of damage caused by stress concentrations, fatigue, corrosion and fretting or combinations of these is not currently possible. The Ultrasonic Guided Waves (UGW) and Acoustic Emission (AE) techniques are capable of detecting cracks in mooring chains and fatigue damage. This paper describes a methodology of Finite Element Analysis (FEA) for crack initiation and crack growth simulation for Structural Health Monitoring (SHM) applying UGW and AE.