A Reliability and Failure Analysis Study of Critical Components

關鍵部件可靠性失效分析算例

Student thesis: Doctoral Thesis

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Award date2 Sep 2019

Abstract

Reliability engineering has two main objectives; prevent catastrophic failures of critical components and systems, and avoid deviation from tolerable performance standards that have serious consequences such as investment losses, human safety, loss of product quality, etcetera. However, no matter how effective and efficient a reliability program is, these events will always occur. It is therefore relevant to establish feasible processes to fully comprehend the root causes leading to events affecting a system’s performance. The significant consequences of any failure of a critical component in critical infrastructure have drawn continuing research related to reliability and resilience across many industries. Much of the research done has been on networked structures to identify the critical component. However, a gap still exists in investigating and predicting failures of identified critical components. The realization that one component, a critical component, in one system could affect many systems is the motivation of the current research.

Root cause analysis (RCA) is one of the most commonly used tools in the industry to analyze various failures by identifying the underlying causes. Treating symptoms of failures only offers a short term relief and the problem is likely to reoccur. This work begins by proposing a holistic root cause analysis method incorporating non-technical concerns to improve the competence of existing methods; the proposed method has been applied on Asbestos pipes failing in service. Additionally, A root cause risk analysis method has been proposed based of failure data using a three-layered Bayesian network by establishing the relationships of three events; cause, incident, and accident, risks can be identified; the technique has been applied to an atmospheric and vacuum distillation unit. As a significant root cause of many failures in metallic structures, corrosion has been actively researched from different perspectives. Corrosion-related failures are not only costly; they pose considerable safety and environmental issues. From the damage tolerance and Physics of Failure (PoF) perspectives, a knowledge gap of what happens before cracks resulting from corrosion defects still exists. This problem is addressed based on its physical and chemical properties founded on fracture mechanics principles. A time-dependent reliability method has been proposed using the stress intensity factor (SIF) to define a failure criterion using Finite Element Analysis to obtain the stress concentration factor (SCF).

Further, by considering the corrosion defects as a crack-like shaped with sharp fronts, the J-integral method has been employed to derive the solution of the SIFs for the corroded structure, a model for estimating the SIF for a corrosion pit with high aspect ratio has been proposed. The proposed methodology has been applied on Cast Iron pipe. This work concludes that the developed methods can assist asset manager to accurately analyze failures and predicting the cracks initiation from corrosion in structures for cost-effective maintenance, repair, and replacement.