Advantages of Type II-S Hydrogen Storage

The question we get asked the most about here at WireTough is, “What’s the big advantage of using a Type II-S cylinder instead of a Type I cylinder?”

To help answer that question, it’s important to remember that weight savings isn’t necessarily a big advantage when you’re taking about ground storage. Up to this point, Type I cylinders have been listed as costing less per cylinder than our Type II-S cylinders. However, when you begin comparing capacity coupled with cost per kilogram of hydrogen stored, the real advantages begin to shine. In Figure 1, you can begin see the advantage of Type II-S cylinders even at low storage quantities. One Type II-S cylinder will cost about 50 percent less than four typical Type I cylinders.

Figure 1

When you begin getting into larger storage needs, our design really shows its advantages above others in the market. As you can see in Figure 2, there is a cost savings based upon kilograms of hydrogen stored, and there is also a cost savings within the infrastructure of the storage facility. That additional savings means a smaller footprint is required to store the same amount of hydrogen compared to Type I cylinders. Less cylinders required also means less plumbing, valves, racks and regulators. The cost savings begins to add up, and that savings goes beyond simply the cylinder price.

Figure 2

We can help you discover even more additional savings advantages with Type II-S cylinders, such as fatigue life, overcoming hydrogen embrittlement, safety and overall durability. Our team at WireTough would love to tell you more about this product and how it can help your business. To learn more, contact [email protected].


PRESS RELEASE: ASME certification obtained for new hydrogen storage cylinder



Cylinder to be tested in Mojave Desert

Pictured is WireTough’s 350 bar cylinder designed under a DOE program being prepared for testing.

Dateline: [Bristol, VA.]: WireTough Cylinders, LLC has obtained the U3 Certification stamp under The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section VIII-Div 3 for its Type II-S cylinder design for bulk storage of gaseous hydrogen at a pressure of 350 bar. WireTough Cylinders is at the forefront of a technological revolution that is set to transform the world of energy storage using its Type II-S cylinders. It pioneered the design and advanced manufacturing techniques for its patented steel wire-wrapped pressure vessels. These vessels are cost-effective and exhibit high durability and fatigue resistance under service conditions of deep pressure cycles. They are engineered to securely store 40.7 kilograms of hydrogen at a maximum operating pressure of 350 bar. In an era where clean energy, energy efficiency, and cost-effectiveness are paramount, WireTough’s mission is to lead the charge in providing cutting-edge solutions for on-ground, long-duration energy storage enabling the following critical applications:

  • Storage of excess energy generated during peak generation periods in renewable, fossil fuel, and nuclear energy power plants, paving the way for a more efficient and reliable energy grid.
  • Bulk storage of hydrogen for refueling trucks, passenger cars, off-road vehicles, ships, trains, and forklifts, propelling the green transportation revolution forward.

These vessels are 50% lighter, expected to be significantly more cost-effective, and require considerably less space on the basis of per KG of hydrogen stored. Below is a more detailed look at the design specifications for WireTough’s new hydrogen cylinder.




Max Operating Pressure Design Pressure  







Cylinder Weight


Water Capacity


Weight of H2 stored at 350 bar
bar psi bar psi mm in mm ft KG Lbs. Liters Cu ft KG Lbs.
350 5075 500 7250 647 25.5 7600 25 3675 8095 1715 59 40.7 90

The U.S. DOE has recently announced plans for creating seven regional hubs within the US for generating three million metric tons of hydrogen annually by the year 2030. If only 0.1% percent of this capacity is saved onsite in storage facilities, it will require thousands of such tanks over five years. WireTough has been selected to submit a full proposal for the award of the MAKE IT Prize of $5M to manufacture these cylinders. WireTough invites partners to commercialize this technology on a large scale and can be contacted via email or its website.

WireTough can be contacted via email at [email protected] or [email protected]. Learn more about WireTough Cylinders at

WireTough’s High Pressure Hydrogen Storage Solution

WireTough Cylinders, LLC produces pressure vessels for hydrogen storage at pressures ranging from 50 to 87.5 MPa (500 to 875 bar).  At these higher pressures, WireTough’s wire-wrapped technology has a distinct advantage because it can offer far longer service life and durability at a very competitive price. We have designated our cylinders as Type II-S to differentiate them from Type II cylinders wrapped with fiberglass or carbon fiber. The potential uses for these pressure vessels are:

  • Fueling stations for light vehicles, such as cars and light trucks. This market is projected to grow rapidly.
  • Fueling stations for heavy duty vehicles. The market for 18-wheel trucks and buses is emerging; Nikola’s goals in that regard will be transformative. They plan to begin producing trucks in 2022 and build 100 hydrogen fueling stations per year from 2022 through 2028.
  • There are companies that manufacture fuel cells for standby power generation such as GenCell and Hydrogenics. This market has been historically growing.
  • Hydrogen is being used to power a wide range of other vehicles. For example,  Plug Power has 13,000 forklifts running on fuel cells in a market that is also expanding.
  • Excess power produced during peak periods from renewable energy sources and during lean demand periods can be stored by generating hydrogen for use during high demand periods.
  • Shell Oil has committed to build 50 new fueling stations in Southern California in the next 5 years. Each station will require a ground storage capacity of 600 KG of hydrogen.
  • European companies such as H2B2, Haskell, and FTI have ambitious plans to expand in the US.

WireTough’s Type II-S cylinder design uses a commercially available steel liner that is wrapped with several layers of off-the-shelf, very high strength steel wire filaments, held together by epoxy. WireTough’s technology is patented and proprietary. The high ductility of steel wires (>15%) in the wrap allows the cylinders to be pressurized to greater than two-times their  maximum allowable pressure during the manufacturing process. This over-pressurization process is called “autofrettage” and it causes plastic flow in the liner and locks high compressive stresses in the entire cross-section of the liner that enhances the tank’s fatigue cyclic life during service. This is a key issue in storing corrosive gases like hydrogen.

The primary competing technology, steel liners wrapped with carbon fiber, is limited in its’ ability to sustain high autofrettage pressures because the carbon fiber filaments have low ductility (≤ 0.5%).  Because carbon fiber wrapped cylinders cannot be pressurized as much during the manufacturing process, they do not bring the benefits of long cycle life that WireTough’s tanks do.

The manufacturing processes and design feasibility of steel wire-wrapped cylinders has been demonstrated as part of a Department of Energy (DOE) sponsored project executed by WireTough for cylinders with a maximum operating pressure of 875 bar. WireTough has obtained certification under ASME Boiler and Pressure vessel Code (BPVC) Section VIII-Division 3 for its design.

Type II-S wire-wound steel cylinders, first introduced in 2011 for onboard CNG storage tanks in vehicles, have superior resistance to impacts and ballistics and fire. The cylinders tested were made from 0.25” thick wall liners and contained only 8 layers of wire. The hydrogen cylinders utilize liners > 1.0” thick wall and  20  layers of steel wire and will therefore have much higher impact and ballistic resistance. Extensive testing was conducted to demonstrate WireTough’s superior resistance to impact, ballistics, salt water corrosion resistance and fire.

Environment Assisted Cracking (EAC) is a major design concern when working with high strength, quenched and tempered ferritic steels used in pressure vessels for storing hydrogen. The Type II-S cylinders have been designed with EAC as the main design criterion. ASME Boiler and Pressure Vessel Code Committee has recognized this and has proposed rules under its Division 3 that are based on fracture mechanics, an approach ideally suited for considering EAC as an integral part of the design process. WireTough’s Type II-S pressure vessel has been designed in accordance with this ASME Code.

WireTough’s bullet test cylinder proved to be very robust, deflecting .30 cal. bullet fire and only being penetrated when hit with a .50 cal. BMG round and even that penetration could not continue through the other side.

The exterior surface condition of the Type II-S cylinder after a bonfire test showing that the steel wrap was still intact.

Exterior surface of the Type II-S tank after exposure to salt water for 28 days while being cycled for 3,200 cycles.










The Table below provides comparisons of design lives estimated using the ASME Section VIII-Division 3 recommended procedures for service in hydrogen. Life and storage capacities of Type I cylinders rated for 45 MPa pressure and WireTough’s Type II-S cylinders of comparable weights are compared.


Design Lives and Capacity of Type I and Type II-S Cylinders

Autofrettage plays an important role in boosting the design life of hydrogen storage vessels during deep pressure cycling. Some cylinders in a cascade will experience deep cycles in which the pressures will fluctuate between the maximum operating pressure, Pmax, and a minimum pressure that can be as low as 5 to 10% of Pmax. For Pmax of 90 MPa, the life of autofrettaged cylinders  are estimated to be several times higher than cylinders that are not autofrettaged. 


WTC of Bristol, Virginia, Awarded $2 Million Dollar Department of Energy Grant.

Bristol, Va. — August 18, 2014 — On August 13, 2014, the U.S. Department of Energy (DOE) formally announced two grants for hydrogen storage technology development; WireTough Cylinders LLC of Bristol, Virginia was selected by DOE as the primary investigator for a $2 million project grant to build low cost, high pressure hydrogen storage vessels using its patent pending steel wire over-wrap process. The second project grant for hydrogen storage was awarded to the Oak Ridge National Laboratory, which incorporated WireTough’s technology into its proposal. These two projects were part of the Energy Department’s $20 million, grant program designed to find companies to research and develop affordable, efficient fuel cell and hydrogen technologies. “We knew we were a perfect fit to produce these tanks and we’re proud the federal government recognizes this as well,” stated Amit Prakash, the President of WireTough., “It is a huge endorsement of our technology. It’s not just a big deal for us, but for our region.”

The Energy Department was seeking cutting edge technologies to provide better storage for future uses of hydrogen as a fuel. WireTough’s goal is to develop a 30 foot tank with a large storage volume of 700 gallons (2,600 liters) at high pressures (12,700 psi). The project result will be a cost-effective solution to store hydrogen, allowing the hydrogen vehicle fuel to ultimately be sold at a target cost of $4 per gasoline gallon equivalents (GGE, 1 GGE=2.6 Kg of CNG or 1 Kg of Hydrogen).

Additionally, WireTough will be introducing their latest technology advancement: a line of ground storage solutions for compressed natural gas (CNG) filling stations with a capacity of 100 to 300 gasoline gallon equivalents (GGE). CNG fill stations of this size allow owners of fleet vehicles (delivery trucks, buses, garbage trucks, etc.) to quickly refuel when they return to their terminal nightly. These ground storage units will use the company’s patent pending wire reinforcement technology to create storage tanks approved by the American Society of Mechanical Engineers (ASME) that will store CNG at 5000 psi. WireTough’s ground storage solutions are expected to cost 30% to 50% less than currently available storage tanks and the technology used will provide extremely strong tanks, using far less steel.

Currently, WireTough Cylinders makes a line of CNG vehicle tanks that are stronger and lighter in weight than solid steel (Type I) tanks and priced competitively. WireTough currently produces tanks that range in size from 57 liter water volume(5 gge) to 260 liter (22 gge). WireTough’s tank technology combines the high strength and ductility of the ultra-tensile wire in combination with a ductile steel liner produce a safe, damage tolerant vessel at a competitive price.

About WireTough Cylinders LLC
WireTough began as Polywire Tough Composites, Ltd., established in 2003, from a team of four engineers, who as a group were responsible for over 40 US patents. In 2010, Wiretough Cylinders was officially incorporated. Their extensive knowledge in pressure vessels, high strength steel, machine design, composites, engineering mechanics and physics, has made their products superior in both cost and function. WireTough is known for its light weight, economical, wire reinforced pressure vessels for gas storage. In 2011 the company successfully received US DOT FMVSS-304 and ANSI-NGV-2-2007 for its Type II CNG cylinders. The company is the only producer of steel body CNG cylinders in the USA. ###

If you would like more information or to schedule an interview, please contact Doug Deeken at (330) 687-8674 or (330) 658-9045, or e-mail at [email protected].

Hydrogen and CNG Systems. WireTough Cylinders LLC


Welcome to WireTough Cylinders LLC website! Producers of CNG and hydrogen fuel containers, we strive to bring quality products and services to our customers at a very affordable value! Our facility is located in Bristol, VA. Nestled within the Blue Ridge Mountains, along highway 81. The region is known for a fairly temperate climate and a full richness of cultural diversity. Many venues, including sports, entertainment and industry come together in a warm cornucopia beautiful scenery and rustic charm!

Dr. Amit Prakash, PHD has led the WireTough team in CNG production and recently, we’ve moved into hydrogen ground storage as this fuel source is proving to be much more attractive as a viable alternative to fossil fuels. We’re breaking new ground in cylinder technology, which will help to ensure hydrogen availability now and potentially, well into the future as it has also proven to be a much cleaner, environmentally stable source of fuel!

With a growing line of products available, WireTough Cylinders is a dependable source for gas and air storage, providing both DOT certified mobile fuel containers for use in many applications such as fleet services like regional shipping and waste management, to ASME certified ground storage, which aids greatly in the development of a much larger alternative fuel source footprint. We’re developing technologies in the areas of air supply as well! Projects like mine safety and mobile solutions for use in modern firefighting and as technologies advance, it’s hard to say where our innovations will take us!

WireTough Cylinders is dedicated to moving forward with our respective industry by continuing to grow with industry needs. Our dedication to the continued development of products and innovative solutions is paramount to our goal of breaking new ground and setting new trends in pressure vessel technology, time and time again! We’ve dedicated our entire business to bringing quality products and services to our customers in the industry by staying on the cutting edge of research and development!