The global shift to use of vehicles powered by fuels other than gasoline, like natural gas and hydrogen, has spurred substantial growth in the manufacture of pressure vessels. Pressure vessels are used to store fuel in a car or truck (15 to 150 liters in volume), akin to a gas tank for a combustion-type engine, or for bulk storage applications. The largest market is for smaller on-vehicle tanks, which are classified into types:
CNG Type I: All-metal construction, generally steel.
CNG Type II: Mostly metal with some fiber overwrap in the hoop direction, mostly steel or aluminum with a glass fiber composite; the metal vessel and composite materials share approximately equal structural loading.
CNG Type III: Metal liner with full composite overwrap, generally aluminum, with a carbon fiber composite; the composite materials carry the structural loads.
CNG Type IV: An all-composite polymer liner — typically high-density polyethylene (HDPE) — with carbon fiber or hybrid carbon/glass fiber composite; the composite materials carry all the structural loads.
Each vessel type has its benefits and liabilities. Type I vessels are the least expensive, with estimated production costs of roughly $5 per liter of volume. The metalworking skills and equipment needed to produce them are widely available internationally. To their detriment, Type I vessels also are the heaviest, weighing approximately 3.0 lb/liter (1.4 kg/liter). By comparison, Type II vessels cost about 50 percent more to manufacture but can reduce the weight of the storage containers by 30 to 40 percent. Type III and Type IV vessels take the weight savings even further, weighing between 0.75 and 1.0 lb/liter (0.3 and 0.45 kg/liter). The cost of Type III and Type IV vessels, however, is roughly two times greater than Type II vessels and 3.5 times greater than the all-metal Type I tanks.
According to a recent report, Growth Opportunities in Global Composites Cylinder Market 2011- 2016: Trends, Forecast and Market Share Analysis (Lucintel, Las Colinas, Texas), the composites cylinder market is expected to grow at a compounded annual growth rate (CAGR) of 13.8 percent, and the end product market is expected to surpass $1 billion (USD) by 2016.
Most composite pressure vessels are manufactured via filament winding, which can be relatively time consuming. As a result, research has focused on production methods with shorter cycle times. One such application is a 40-liter pressure vessel manufactured by Profile Composites (Sidney, British Columbia, Canada) using Baydur polyurethane from Bayer MaterialScience (Pittsburgh, Pa.) and braided carbon fiber from A&P Technology Inc. (Cincinnati, Ohio). The tank is produced in 20-minute cycles using specialized RTM equipment developed by MAG IAS (Hebron, Ky.). Profile is receiving U.S. Department of Transportation funding for the tank’s development and is currently near the end of the license/standards phase. The MAG RTM cell developed for manufacturing the tank is highly automated, repeatable and consistent, and it requires very little manual intervention. One cell will produce about 10,000 tanks annually. Larger tanks are under development, ranging from 60 to 160 liters.
The largest pressure vessel is the 40-ft/12.2m long, 4,600-lb/2,087-kg all-composite Titan,manufactured by Lincoln Composites (Lincoln, Neb.), a sister company to Raufoss Fuel Systems (Raufoss, Norway) and a subsidiary of Hexagon Composites (Ålesund, Norway). Dynetek Industries (Calgary, Alberta, Canada) has received U.S. Department of Transportation approval for two Type III products rated at 3,000 psi and 6,500 psi (206 bar and 450 bar), which are arranged into modules of 39 vessels each on truck trailers that carry either three or six modules. These bulk-transport applications are still seeking commercial and/or regulatory acceptance, but they have the potential to contribute an additional 1.6 million to 1.8 million lb (726 to 816 metric tonnes) of composite pressure vessels annually, worth about $50 million, by 2013.