Utilising Hydraulic Transient Excitations for SHM of pipeline with Distributed Optical Fibre Sensing

Distributed Optical Fibre Sensor (DOFS) have been applied in monitoring the structural health of water pipelines over the past decades. Most of these studies show that DOFS is very effective for static and quasi-static measurements and can be used for monitoring the condition of a pipeline. However, there is still lack of research being done using DOFS to monitor the dynamic response of the pipeline. As it is well known that pressure transients (water hammer) can occur in any pressurised pipeline system due to changes in the operating conditions. This thesis aims to show the ability of DOFS to exploit these transient hydraulic pressure along the pipeline for assessing its condition. In this regard, the main aims of this thesis is to demonstrate the concept of utilising this natural stimulus to enhance the pipeline structural health monitoring with the distributed sensing. This concept was demonstrated on two different type of pipe material (a) plastic (flexible) and (b) cast iron (rigid).
   
   The ability of distributed optical fibre sensors to monitor the dynamic response of the pipes was first demonstrated through an experimental program where fibre sensors were instrumented helically around a flexible plastic pipe. The pressure transient was induced by changing the operating conditions (valve closures and operating pump). The dynamic strain response measured along the fibre sensors was compared with the measured pressure profile. Moreover, three experimental case studies (single/multiple anomalies, material loss and leakage) conducted along the monitored plastic pipes will also be reported using a water hammer as a transient excitation for structural health monitoring applications using DOFS. The findings show that the response of the pipe is accentuated during transient events. Therefore, any additional features present along the pipe will be actuated during transient events.
   
   Then, the potential of distributed optical fibre sensors for monitoring fatigue damage growth was demonstrated in a laboratory-based study. Distributed fibre sensors were instrumented on a cast iron (rigid) pipe. An artificial damage was machined to the pipe to initiate crack due to fatigue cyclic loadings. It was observed that the distributed optical fibre sensors manage to detect the initiation of the crack, as well as, monitoring the fatigue crack growth along the pipe. The results confirmed that a distributed optical fibre sensors are able to enhance the detection of localised damage in a structure when subjected to transient excitation.   
   
   The overall findings of this thesis are expected to contribute towards the development of smart pipes capable of relaying information on its structural health to pipeline operators.