Research On The Topology Of The Logic Based Methodologies And The Applications Of The Reliability Analysis For Subsea Pipeline Engineering

Subsea pipeline is a structure constantly operated under the complicated environmental stresses, such as waves, vortex, current. It also has to survive from the extreme cases like earthquake, floating ice, seabed shift, etc. Meanwhile, certain properties of the structure creep corrode and wear out over the long term serving period. Once leaking, the oceanic and biological damage can be substantial and catastrophic. It is very important to maintain a good reliability and safety throughout the designed lifetime. The reliability of a structure is predetermined by reliability design. Based on this subject, the thesis develops a new theory and methodologies to improve the current reliability design scheme. The researched starts with analyzing a real case of subsea pipeline reliability risk assessment. By summarizing the existing methods and results, the shortages of subjectivity in Logic Trees are pointed out. A new series of model, "Failure Expansion Tree" (FET) are hence built based on the new (five) principles proposed to overcome the each shortage of the conventional logic trees. The reliability risk factor identification of the subsea pipeline case is therefore re-evaluated using the new models, qualitatively, quantitatively and sensitively. The comparison of the two results are shown and discussed. Next, following the same principles, a model specifically designed for the energy coverage for the reliability test, "Energy Expansion Tree" (EET) is built. Also, the classical "Function Flow Model" (FFM) is extended by first introducing the energy aspect into it. Instead of the traditional reliability test which focuses on the lifetime estimation only, the total energy outcome of the modeling is put into a new reliability testing method, "Multi Environmental Over Stress Test" (MEOST), to discover the weak links in the design as well. Finally, to complete the research theory, an extra study is conducted to analyze the reliability design of the high energy, complex system against’black swan" events. A "Generic Energy Expansion Tree" (GEET) is built to provide a general guide for such systems. By discussing various historical disasters, the interruption strategy of each case is suggested. Therefore an all scale reliability design strategy is completed in this thesis.The more detailed description is as following:1. A five principle series for the more logical split strategy is established based on the current Fault Tree Analysis (FTA) and the MECE principles in Pyramid Theory. An innovative logic tree, Failure Expansion Tree, is proposed which improves the traditional logic trees.. It describes a different thinking approach for risk factor identification and reliability risk assessment. By providing a more comprehensive and objective methodology, the rather subjective nature of FTA node discovery is significantly reduced and the resulting mathematical calculations for quantitative analysis are greatly simplified. Applied to the Infant Mortality and Useful Life phase of a subsea pipeline engineering project, the approach provides a more structured analysis by constructing a tree following the laws of physics and geometry. Resulting improvements are summarized in comparison table form.2. For reliability testing an EET and a companion EFM are proposed and. Different from conventional approaches, the EET provides a more comprehensive and objective way to systematically identify external energy factors affecting reliability. The EFM introduces energy loss into a traditional Function Model to identify internal energy sources affecting reliability. The combination creates a sound way to enumerate the energies to which a system may be exposed during its lifetime.3. The energies produced in "2" are into planning an accelerated life test, the MEOST. The test objective is to discover weak links and interactions among the system and the energies to which it is exposed, and design them out. As an example, the methods are applied to the pipe in subsea pipeline. However, they can be widely used in other civil engineering industries as well. The proposed method is compared with current methods.4. This thesis takes the position that no matter how well a system, especially a complex system, containing high energy storage, has been designed, the potential of the failure is always is inevitable. By thinking in terms of energy and process physics, two new tools to assist in this analysis are employed, the GEET and the EFM. The purpose is to find the opportunities to short circuit the chain of events in such a way as to achieve relatively fail-safe behavior. Till now, a complete reliability design method’s development to cover all-scale systems is provided.