Analysis of a composite fiber wrapped gas cylinder for deep diving submersibles

Light weight gas storage bottles developed for the
aerospace industry are evaluated for deep ocean
submergence service. Each JOHNSON-SEA-LINK classed
submersible carries 18 filament-wound aluminum
cylinders for storage of breathing and ballast gas. A
standard industrial aluminum cylinder is reinforced
with a circumfrentially-wrapped fiberglass/epoxy
matrix. Upon curing of the composite matrix, the
cylinders undergo an auto-frettage process which
increases the internal service pressure 1.8 times
above that of the bare liner. The resulting pressure
vessel is attractive for use on manned submersibles.
The cylinders are nearly 60% lighter in air than the
steel T-bottles they replace, and actually provide in
excess of 15 lbs. of buoyancy in sea water when empty.
In order to determine the performance and safety
aspects of these vessels when subjected to the extreme
external pressure of the submersibles' operating
depth, Harbor Branch Foundation has completed an
extensive program including fatigue testing,
destructive external-pressure crush tests,
metalographic analysis, classical structural analysis,
and the formulation of a computer model using Finite
Element Method (FEM) techniques. The computer model
was verified by destructive tests performed both on
cylinders which were either "virgin" or had been
cyclically loaded with external pressure to simulate
the effects of extended submersible service life.
Substantiation of numerical and FEM analysis with
experimental results enabled determination of the safe
working depth for this type of cylinder.