Regan Brown
CNG, or Compressed Natural Gas, is a popular alternative to gasoline for vehicles. CNG is stored in high-pressure tanks, also known as cylinders, which are typically located in the underbody of a vehicle. CNG tanks come in various sizes and types, with the most common size for trucks being a 21 x 60 cylinder that holds about 20 gallons of CNG. These tanks have a lifespan of 15 to 20 years and must be replaced once they reach their expiration date, as they cannot be safely requalified for extended use. The location of a CNG fuel tank in a vehicle is an important consideration, as it impacts the vehicle's performance, safety, and maintenance requirements.
| Characteristics | Values |
|---|---|
| Location | Mounted in the underbody of a vehicle or in the truck bed behind the cab |
| Useful Life | 15 to 20 years, depending on construction and certification |
| Expiration Date | Displayed on labels located on the tanks, as well as warning labels in the engine compartment |
| Replacement | Must be replaced by a qualified service facility; cannot be safely "requalified" for extended use |
| Inspection | Required every 36,000 miles or 3 years, whichever comes first |
| Pressure Rating | Industry standard is 3,600 psi; systems rated at 3,000 psi can withstand up to 125% of operating pressure |
| Temperature | Affected by ambient temperature; fuel expands and becomes less dense at higher temperatures |
| Filling | Slower "time-fill" method is more efficient than "fast-fill"; allows fuel to remain in a dense state |
| Types | Type 1, Type 2, Type 3, and Type 4 (lightest option with plastic liner) |
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What You'll Learn
CNG tanks are often located in the underbody of a vehicle
The underbody location is a popular choice for CNG tanks as it allows for easy access when refuelling. The tanks are designed to be refuelled at CNG stations, and the amount of refuelling will vary based on several factors, including the weather, temperature, station equipment, and storage vessel psi. The CNG cylinder will always have some fuel pressure remaining when the fuel gauge shows empty due to the fuel rail pressures needed to supply fuel to the engine.
CNG tanks are high-pressure fuel tanks, also known as cylinders, and they come in various sizes and types. The most common size for trucks is a 21" x 60" cylinder with a capacity of about 20 gallons of CNG. These tanks are typically mounted in the truck bed behind the cab. The Type 4 tank is a popular choice as it maximises CNG capacity while providing the best overall mileage, but it comes at a higher cost.
It is important to note that CNG tanks have expiration dates, typically ranging from 15 to 25 years, and they must be replaced once they reach the end of their useful life. The expiration date is indicated on a label on the tank, near the fueling connector, or under the hood. Visual inspections are also required every 36,000 miles or 3 years, whichever comes first.
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They are at risk of damage from road debris
CNG, or Compressed Natural Gas, is a popular alternative to petrol and gasoline. It is a cost-effective, efficient, and environmentally friendly fuel option for vehicles. CNG fuel tanks are typically located in the underbody of a vehicle, which exposes them to a higher risk of impact by road debris. This can cause damage to the tank, compromising its integrity and leading to potential safety hazards.
CNG tanks are pressurised to 3,600 pounds per square inch (psi), which means even minor damage from road debris can pose a significant danger due to tank quality degradation. For this reason, it is crucial to regularly inspect CNG tanks for any signs of damage or wear and tear. Qualified service facilities should perform these inspections, as they have the necessary training and equipment to safely vent and purge the tank of any residual CNG.
The location of CNG tanks in the underbody of vehicles makes them vulnerable to impact from road debris, curbs, and other obstacles. This can result in dents, scratches, or even punctures to the tank, compromising its structural integrity. Exposure to certain chemicals present in road debris can also cause corrosion and cracking of the tank over time. Therefore, it is essential for vehicle owners to be vigilant and proactive in inspecting and maintaining their CNG tanks to mitigate these risks.
To ensure the safety of CNG vehicles, owners should adhere to recommended maintenance schedules and inspections. Regular inspections by qualified professionals can help identify any damage caused by road debris and ensure the tank's integrity. Additionally, vehicle owners should be cautious when driving, especially on roads with debris or uneven surfaces, to minimise the risk of impact on the CNG tank. Minor impacts, such as driving over a curb, can still cause significant damage to the tank due to the pressurised nature of CNG systems.
Furthermore, CNG vehicle owners should be aware of the potential consequences of neglecting proper maintenance and inspections. A compromised CNG tank can pose a safety hazard, including the risk of explosion in the event of an accident. It is the responsibility of the vehicle owner to ensure their CNG tank is properly maintained and inspected to mitigate these risks. By prioritising regular maintenance and inspections, CNG vehicle owners can enhance the safety and longevity of their vehicles while utilising the benefits of this alternative fuel source.
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They have a useful life of 15 to 20 years
CNG fuel tanks have a useful life of 15 to 20 years, depending on their construction and how they were certified by the manufacturer. CNG cylinders are expensive, with a Type 4 carbon fibre tank costing around $4,000. They are, however, built to last, with a lifespan of up to 20 years. CNG tanks are high-pressure systems, typically rated at 3,600 psi in the US, and they are designed to withstand up to 125% of their operating pressure.
The lifespan of a CNG tank is determined by the manufacturer and set at the time of construction. The original 1992 cylinder standard set a service life of 15 years, which was extended to 20 years in 1998. A further revision in 2007 increased the potential lifespan to 25 years. Most countries have adopted these standards.
CNG tanks cannot be recertified or reused once they reach their expiration date. This is because there is no safe way to requalify the tanks for extended use. The expiration date is displayed on a label on the tank, and owners should make a habit of noting this date at routine service intervals. When a tank expires, it must be replaced by a qualified service facility, which will safely vent and purge the tank of any remaining natural gas.
It is important to be aware of the expiration date of a CNG tank, as there is no national system to notify owners when their tanks reach the end of their useful life. Visual inspections are required every 36,000 miles or 3 years, whichever comes first. Tanks mounted to the underbody of a vehicle are at a higher risk of damage from road debris and impacts, so regular safety inspections are critical to ensure the integrity of the tank.
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They are labelled with expiration dates
CNG fuel tanks have a lifespan of 15 to 20 years, depending on their construction and how they were certified by the original manufacturer. They are labelled with expiration dates, which can be found on the tank itself, near the fueling connector, or under the hood in the engine compartment. These labels typically read "DO NOT USE AFTER (EXPIRATION DATE)", for example, "DO NOT USE AFTER 01/2027".
There is no national system in place to notify owners when their CNG tanks reach their expiration date. It is the responsibility of the vehicle owner or fleet manager to have the tank replaced at the end of its life. This replacement must be carried out by a qualified service facility, as it requires properly trained personnel and specialised equipment to safely vent the CNG from the tank and purge it with nitrogen to eliminate any pressure or fire danger.
The expiration date of a CNG tank is determined by its designed lifespan, which is based on the cyclical stress of filling and emptying, heating and cooling, and the components in safety devices. Over time, the high pressure in the tank can cause components to wear, leading to potential leakages or failures, which can be hazardous. Additionally, exposure to certain chemicals may cause corrosion and cracking. Therefore, it is crucial to adhere to the expiration dates and properly decommission expired CNG tanks to ensure safety.
While there is no official enforcement of these rules, using a tank past its expiration date comes with significant liability risks. The tank manufacturer, installer, and inspector are cleared of any liability, and the consequences of failure fall solely on the user. As such, it is imperative to be aware of the expiration date of your CNG tank and to plan accordingly, whether by retaining the vehicle and installing replacement tanks or opting for a different vehicle.
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They should be replaced by a qualified service facility
CNG fuel tanks are typically located under the body of a vehicle, which exposes them to a higher risk of impact by road debris or damage from driving over a curb. This makes regular safety inspections critical for CNG fuel systems. Inspections are required after any incident that could potentially cause damage to the tank, such as a fire or accident. Additionally, tanks on vehicles with a gross weight rating of over 10,000 lbs must be inspected annually by a qualified service facility, while light-duty vehicle tanks should be inspected every three years or 36,000 miles, whichever comes first.
CNG tanks have a useful life of approximately 15 to 20 years, depending on their construction and original certification. Once a tank reaches its expiration date, it must be replaced as there is no method to safely extend its use. The replacement process should be performed by a qualified service facility with the proper equipment and trained personnel. This ensures the safe venting and purging of residual CNG from the tank, eliminating any potential pressure or fire dangers.
It is important to note that there is no national system in place to notify owners when their CNG tanks reach their expiration date. Therefore, vehicle owners or fleet managers must take responsibility for staying informed about expiration dates and arranging for tank replacements as necessary. When a CNG tank expires, it must be rendered unusable and discarded, as reusing an old fuel tank can pose significant dangers.
To ensure safety and compliance with regulations, it is recommended to locate certified inspectors or qualified service facilities through reputable sources such as the CSA Group website or the Natural Gas Vehicle Institute Certified Inspector Lookup Tool. By following these guidelines and working with qualified professionals, vehicle owners can maintain the safety and proper functioning of their CNG fuel systems.
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Frequently asked questions
The CNG fuel tank is usually mounted in the truck bed behind the cab.
There are four types of CNG tanks, designated by their design and production method, including the liner material. Type 1 steel cylinders are the most common but very heavy. Type 2 cylinders are a compromise, with a metal liner and composite wrap. Type 4 is the lightest option, with a plastic liner, and will give you the best mileage.
CNG tanks have a lifespan of 15 to 20 years, depending on their construction and certification. They must be replaced when they reach their expiration date, as they cannot be recertified.
