Under the FRA regulations, tank car owners are required to employ periodic structural integrity inspections including tank shell thickness tests and inspections of tank car welds. By limiting the required inspection to known areas of crack initiation, RSPA and FRA expect an increase in the probability of defect detection, as well as an improvement in the reliability of the inspection results and a reduction in the inspection costs. As part of this rule, five NDE methods are presently authorized: dye penetrant; radiography; magnetic particle; ultrasonic; and, aided visual inspection. Other nondestructive evaluation methods may be used by US DOT exemption, such as acoustic emission and direct visual inspection.
This rule also requires tank car repair facilities to document the sensitivity and reliability of the nondestructive evaluation methods used for the structural integrity inspections. With the large number of welds to be inspected on tank cars to meet the structural integrity requirements of this rule, development of improved global NDE will significantly improve the probability of finding defects. Presently, acoustic emission evaluation of tank cars is providing not only information about the welds that must be inspected under the new requirements, but also any defects on any part of the tank shell. Further evaluations of acoustic emission technologies as well as the development of other highly sensitive global NDE methods will increase the number of defects detected.
In its report on Ensuring Tank Car Safety, the TRB recommended that US DOT should continue to work closely with industry to identify methods for verifying the structural integrity of in-service tank cars, including nondestructive test methods to supplement or replace existing test requirements. Further, the TRB recommended that results from the inspections and tests should be routinely collected to monitor tank car condition, improve test and inspection methods, and enhance tank car design, maintenance, and repair standards. The following projects address these issues.
The Damage Assessment Program needs augmentation to relieve emergency responders’ concerns when responding to hazardous materials accidents. Emergency responders, due to lack of information, sometimes let nature take its course, where it may have been possible to avert catastrophic conditions. These guidelines will be periodically updated when new technologies become available. The current effort is scheduled for completion in FY 2001.
A tank car accident in Waverly, TN in the 1970's resulted in the death of a number of emergency responders when a tank car ruptured unexpectedly. The tank car had an undetected crack that grew over several days and resulted in the disaster. As a result, the AAR’s Bureau of Explosives developed a set of guidelines for use by emergency responders. These guidelines were visual and were based on the opinions of technical experts. The emergency response guidelines being used will be reviewed for adequacy, timeliness and accuracy.
Because the FRA found that the continued use of stub sill tank cars poses an imminent and unacceptable threat to public safety, the FRA issued Emergency Order No. 17, in September 1992, requiring owners of stub sill tank cars to comply with the AAR Tank Car Stub Sill Inspection Program, and the AAR Tank Car Stub Sill Inspection Procedure.
Under EO17 and the AAR circular, owners must inspect the stub sill area on such cars and may not return the cars to service until all defects have been repaired and the cars are in full compliance with the Federal railroad safety regulations and the AAR Tank Car Manual. Inspection priorities were established based on characteristics discovered in other inspections and based on accumulated mileage. After an evaluation of inspection data, the railroad and tank car industries, along with FRA, NTSB recommended DTA for tank shells and structural elements, have agreed that performing DTA of each stub sill design will give tank car owners the information they require to make sound decisions on inspection and maintenance of their tank cars. The FRA is participating with the industry to develop a DTA program for use by the tank car owners, builders and users for the assurance of continued tank car structural integrity. Model validation and verification testing will also be conducted. This effort will continue through FY 2003.
Research conducted in the 1970s and early 1980s led to regulations for head shields for certain hazardous material tank cars. Scale model and full-scale tests were conducted. Further work was conducted in the mid-1980s on tank cars for transporting chlorine and for aluminum tank cars resulting in the development of a puncture model. Puncture models for other type tank cars need to be developed and validated. This research will evaluate the current models for puncture resistance of tank car heads and determine the correlation between the empirical equations to estimate puncture velocity and actual puncture. Finite element analysis to predict the puncture velocity of tank car shells will also be conducted. This research will continue through FY 2003.
The presently required periodic hydrostatic testing has to be phased out and replaced with acceptable nondestructive evaluation methods. Of importance is the comparability of the methods especially documented reliability and sensitivity of detection of the defect/flaw in the test specimen. This is an industry/regulators project that will continue through at least 2002.
Acoustic emission tank car inspection techniques will continue to be investigated, both for periodic inspection and inspection after damage or after involvement in accidents. Present focus will be on the source location and improved detection interpretation capability of the procedure, and this effort will continue through FY 2002.
HAZMAT tank cars involved in an accident need to be immediately identified and located. More often than not, tank cars are derailed and are not easily identified and located within the derailment. Remote inspection is necessary for emergency response persons. The FRA will pursue R&D in this field. Advances in nanotechnology will be evaluated for application to tank car identification and this project will take several years to complete after it is started in FY 2003.