Failure Analysis of Compressed Natural Gas Containers for Automotive Use Session: Advanced Fuels Crash Safety

In 2009, the National Highway Traffic Safety Administration’s (NHTSA’s) Office of Defects Investigation made site visits to two different companies that utilized compressed natural gas (CNG) to fuel their vehicle fleets. The purpose of these site visits was to obtain information concerning two independent incidents where high pressure CNG fuel containers on fleet vehicles ruptured during or shortly after refueling. These containers were represented as conforming to industry standard ANSI/NGV2 [1], and were still within their 15 year manufacturer recommended service life (although they had experienced several years of on-road use). Further, the newer model containers were self-certified by the manufacturer as compliant with Federal Motor Vehicle Safety Standard (FMVSS) 304 [2]. After the container ruptures occurred, each of the companies, for reasons of safety, retired the sister vehicles in their fleets. The decommissioning of these fleets offered an opportunity to NHTSA to obtain some of the retired CNG containers, which experienced similar service conditions to those that ruptured during refueling, and to subject them to both nondestructive (NDE) and destructive evaluation (DE) to document in-service wear, damage and residual life. To this end, NHTSA entered into an Interagency Agreement with the National Aeronautics and Space Administration (NASA) White Sands Test Facility (WSTF), to conduct the evaluation of the used containers and compare them to unused containers of similar design. NASA has been performing test and evaluation of composite pressure vessels, similar to those designed for automotive use, since 1978. The objective of the evaluation is to gain valuable insight into the construction and deterioration elements that could suggest potential improvements in the existing standards. Destructive and nondestructive evaluation of the aged and new containers is on-going. This paper presents the results of the evaluation to date and potential future steps in the program.