Integrity detection of mooring chains by the approach of thermography

Abstract

Reliability and safety issues of mooring chains are causing concern in recent years. Accordingly, some efforts have been made for detecting the structural integrity of mooring chains. However, a fully successful mooring chain condition monitoring technique has not been achieved today. This is largely due to the fact that mooring chains are submerged in water and the currently available nondestructive testing technologies are difficult to apply in wet environment. To overcome this issue, a new mooring chain condition monitoring method is studied in this paper with the aid of thermography technique. The research is conducted based on two philosophies, i.e. (1) the mooring chain material has much higher thermal conductivity than that of water. Therefore, when the mooring chain is heated, the thermal energy will transmit mostly inside the chain, rather than dispersing in water; (2) the defects occurring in the mooring chain will disturb the transmission of thermal flow inside the mooring chain and consequently change the distribution of the temperature in the adjacent area. To demonstrate the effectiveness of the proposed method, both numerical and experimental researches are conducted in this paper. The research results have shown that thermography is indeed valid in detecting the integrity of mooring chains. ring in it. In reality, a defective mooring chain may but is not necessary lead to broken of the mooring line when it is subject to extreme loads. For example, Remotely Operated Vehicle (ROV) inspection has been popularly adopted for inspecting typical damage and loss of integrity of marine structures. It can be equally applied to the inspection of mooring chains. However, ROV inspection only provides snapshot of the surface of mooring chains, which could be covered by thick layer of marine lives. Therefore, visual inspection via ROV is unable to provide the operator with reliable information about the actual structural health condition of mooring chains. Moreover, the application of ROV inspection is limited by weather windows and access, it is unlikely to realize the continuous monitoring of the mooring chain. In order to obtain continuous monitoring data from mooring chains, AVT Reliability attempted to use strain gauge to monitor the integrity of mooring chains and applied the devised strain gauge based measurement system to assessing the integrity of the 9 mooring chains installed on a 870,000 barrel oil storage tanker (AVT Reliability 2017). The novelty of such a system is that it does not