Designing Tank Cars for Normal Service and Accident Forces

A better understanding of the in-service loads tank cars are subjected to is needed for several reasons. Severe loads seen in normal service are responsible for numerous incidents of tank car structural damage or complete failure. A few incidents of tank car structural damage or failures have recently occurred without any prior warning to the train crew, i.e., under completely “normal” operating conditions. Identification of what is causing undue, high forces on the tank cars is needed. Additionally, since the tank car industry is preparing to implement damage tolerance fatigue analysis, this load spectrum must be further investigated. Yard impacts and forces seen by the tank car during in-train an accidents and are also not presently documented in terms of stresses throughout the load carrying members of the tank car.

Recent advances in microprocessor technology and methods of collecting data to build an accurate load spectrum will be used to combine existing Freight Equipment and Environmental Sample Test (FEEST) data with selective data collection and analysis to provide a better understanding of the actual load spectrum seen by tank cars. This information will be used to improve tank car structural integrity. Gathering and analysis of such data will be the aim of this project.

Similar research is needed for load spectrum forces and impacts in accident conditions. This type data, if it exists, has not been compiled for ready reference. This data is important for use by designers in determining the likely sites of damage and action required. This project will gather this data from literature, industry database, and application of engineering principles. This data will need to be updated periodically; therefore this will be an on-going project.

Railroad Transportation of Spent Nuclear Fuel 

With the renewed interest in finding a repository for long-term storage of radioactive materials (RAM) and spent nuclear fuel, there is a need to revisit issues related to railroad transportation of these materials. Research will focus on the safe transportation by railroad using available accident environment analyses to determine potential forces that may be encountered by the railroad spent nuclear fuel casks if involved in an accident. Current research is focusing on a risk assessment of the safety of transporting spent nuclear fuel in regular freight service versus dedicated train service. This is an on-going project.

Gross Weight Railcars Greater than 263,000 pounds

The current regulations forbid transportation of hazardous materials in tank cars with a gross weight more than 263,000 pounds. However, the railroad industry is moving rapidly in the construction and operation of railcars with gross rail loads of greater than 263,000 pounds. Tank car builders and owners are presently submitting applications to the Department of Transportation for the use of these increased gross-weight cars. Fatigue analysis is performed on these cars using the FEEST-1 or FEEST-2 loading spectrums, as industry’s rationale. The scaling up method used to account for the increased gross weight is a linear method. A peer consensus is that longitudinal and vertical coupler loads must be scaled up or changed to account for the increased gross weight of the cars. Before such a requirement may be considered or put in place, a study of appropriate scaling factors must be made. A more thorough understanding of changes in in-train forces with changes in gross weight may be developed by a review of past FRA research involving the train operation and energy simulator (TOES), and the ‘ADAMS’ computer models and translating those studies to the study of increased gross weight tank cars. The issue of buckling of adjacent light, normal and heavy tank cars will also be investigated. The study results will be used as a guide in evaluating future requests for the use of increased gross weight tank cars and railcars or as a minimum will direct R&D efforts for the safe transportation of such loads. This research is expected to continue through FY 2004.

Assessment and Validation of the Methodologies for Engineering Reliability 

Accidents, tank car structural failures, and the existence of defects in structural components of railroad tank cars lead the FRA to believe that measures of reliability for tank car components must be defined and detailed reliability assessments on a variety of components should be performed. This type of assessment should be performed for each unique component design to define and document boundaries for the reliable use of each tank car. This project will continue through FY 2003.

The reliability of the tank car may be defined as the probability that, when operating under stated environmental conditions, the tank car will perform its intended function adequately for a specified interval of time. In assessing the tank car reliability, it is necessary to define and categorize different modes of tank car failure. Although complete and catastrophic failure is easily recognized, tank car performance as a safe packaging of hazardous materials can deteriorate and elements contributing to this deterioration (e.g., corrosion, cracks, pitting, fatigue, changes in material properties) need to be documented. Reliability functions, expected life, hazard functions, and failure rates must to be defined for tank cars. Since the reliability of the tank car will be a function of several design variables and parameters, developing a methodology for combining these random variables into a tank car “strength” function is necessary. The results of this assessment can quantitatively provide the tank car owner with information that may be used to define and document boundaries for the reliable use for each tank car, allowing the tank car owner to implement guidelines for the maintenance and use of tank cars based on the assessment performed.