Fibers for Composite Pressure Vessels

Since 1970 pressure vessel manufacturers have been using continuous fibers filaments, also known as tows or roving, to improve the physical properties of pressure vessels. Starting with what the industry calls a type II vessel; high strength fibers, such as glass fiber, were wrapped around the cylindrical sections of steel and aluminum pressure vessels to add reinforcement allowing a roughly 30% reduction in overall vessel mass.

In 1973, a full glass or carbon fiber shell was filament wound on top of a metallic vessel, which was only designed to bear 10% of the overall hydrostatic load. This vessel known as a composite overwrapped pressure vessel (COPV) was considered a type III, and further reduced the mass versus type II vessels by approximately 50%. This was significant for the pressure vessel industry because it allowed for the pressure ratings to be increased without significantly increasing the vessels mass.

The type III vessels remained state of the art (SOTA) for more than 30 years until the first all-composite vessel was introduced in 1995. The all composite pressure vessel (type IV) used the fibers or tows to contain the entire force of the pressurized gas, while using only a heavy rigid plastic liner to serve as a permeation barrier. These all composite pressure vessels weighed only 1/10 of the mass of all metal vessels enabling the industry to use their products in applications where vessel mass is incredibly important. The vessels however came with some significant drawbacks, because of the porosity of the polymers used in the liners they have a tendency to permeate gas overtime, unlike the metal lined type II and type III designs.

As the fiber reinforcement became more and more significant in pressure vessel design, fiber manufacturers began refining their offerings and experimenting with new fiber types like carbon fiber, which is currently the most popular reinforcement in composite pressure vessels, because of its incredible stiffness and tensile strength. In addition to carbon and glass, new fibers were created such as Kevlar a type of aramid fiber and basalt fiber. These new fibers offered contrasting mechanical properties such as impact resistance, and low temperature resistance to the pressure vessel designer’s arsenal.  

As new composite pressure vessel applications emerged, the need for unique mechanical properties and increasing economic pressures create a need for hybrid vessels which could either use distinct and separate layers of fiber for different roles such as impact/ abrasion resistance, or different fibers in the same band to get the properties of both fibers throughout the laminate.