ABSTRACT

Filament-wound composite cylinders are used in the marine and transportation industries for storing breathing gases (SCUBA, firefighting) and gaseous fuels (vehicles). These cylinders offer light weight, corrosion resistance, dimensional stability, and the ability to store more air than equivalent metal tanks. The design methodology currently used for composite tanks, however, cannot yet guarantee their safe operation. Accordingly, the U.S. Department of Transportation (DOT) is unable to issue full certification of filamentwound tanks. Rather, some types of composite pressure tanks currently are manufactured under DOT Exemption, TC Regulation 3FCM. The composite tank industry desires to improve their safe use and to obtain full certification. To this end, a new tank design has been proposed that uses an inexpensive, embedded fiber optic sensor system (FOSS). Three versions of an embedded microbend sensor have been built and tested. A description of the design is presented.

INTRODUCTION

Although microbending of optical fibers [Udd, 1995a; 1995b) generally is regarded as a poor sensor for measuring strain accurately, with the proposed designs it functions well as a sensor for tank volume change. By monitoring any changes in the tank volume of a used tank relative to a newly manufactured tank, structural degradation can be calibrated. Thus, while marginally adding to the cost of manufacturing filament-wound tanks, the microbend FOSS could add substantially to the useful life of the tank by monitoring its structural integrity each time the tank is filled with gas [Knapp, et al., 1999; 2000; 2001].

SENSOR DESIGN

Conventional metal SCUBA (self-contained underwater breathing apparatus) and LNG (liquid natural gas) tanks are checked periodically for structural integrity by immersing the tank in water and measuring the displaced volume of water as the tank is pressurized. Excessive displaced water indicates a faulty tank that must be removed from service.

This content is only available via PDF.
You can access this article if you purchase or spend a download.