Safe packaging and transport of hazardous materials is of vital importance to tank car builders, users, federal regulatory agencies, as well as the general public. Reliability-centered maintenance (RCM) can be used to effectively maintain the reliability of tank car systems in guarding against lading loss due to equipment failures. Adequate and cost-efficient maintenance decisions depend on the ability to understand tank carís characteristics and its responses under various service conditions, and the ability to analyze and predict tank carís performance and resistance deterioration as a function of usage.
To support the informed decision-making and planning for the RCM through quantitative risk analysis and prediction, the objective of this project is to develop a methodology that applies modern reliability methods to perform reliability analysis on tank car structures. Tank car failure with respect to lading loss under service conditions falls into two broad categories: (a) tank car structure failures (Structure-Related Non-Accident Release, or, SR-NAR), and (b) non-structural failures, such as loading/unloading devices, pressure release devices, and valves. Category (b) failures are often due to reasons such as loose fitting, venting, overloaded cargo, and missing parts, etc. Some of the characteristics of this category include high occurrences, mostly in small quantities, and often human error-related.
Category (a) failures (SR-NAR) occur infrequent but likely with high consequences. It is often age-related and due to structural deterioration often in terms of corrosion and metal fatigue. The Figure below shows the four possible causes for the SR-NAR. It is this category that is the focus of the project. In developing the reliability analysis methodologies, corrosion and fatigue, the two commonly encountered failure mechanisms for railroad tank car structures, have been considered for both component reliability problems and the system reliability problems.
In developing component (i.e. a single failure mode at a single location) reliability analysis methodologies , the following three scenarios have been considered: (i) general corrosion, (ii) fatigue crack growth, and (iii) corrosion-accelerated fatigue crack growth. In developing a system (i.e. multiple-site damage, and/or multiple failure modes) reliability analysis methodology, the following three scenarios have been considered: (a) corrosion damage at multiple locations, (b) fatigue damage at multiple locations, and (c) coexistence of fatigue and corrosion damage at multiple locations. These cases cover most of the commonly-encountered practical situations that occur in the tank car fleet.