Tech Tips: NGV On-Board Fuel Storage Cylinder Requirements and Standards

Natural gas vehicles are among the safest vehicles in the country. Compressed natural gas (CNG) is stored onboard vehicles at pressures from 3000 to 3600 psi in cylinders manufactured to stringent standards that help insure safety. Routine inspection of cylinders is a practice NGV fleet managers must perform. Here are some of the facts about CNG cylinder inspection and safety.

What's Actually Required?

It is required* that each vehicular CNG cylinder have a notice that states: "This container should be visually inspected after a motor vehicle accident or fire and at least every 36 months or 36,000 miles, whichever comes first, for damage or deterioration."

Although this statement uses the word "should" and not "must," AFVi and other industry partners strongly encourage fleets to consider the inspection of their tanks a firm requirement and incorporate it as part of their standard operation and maintenance practices.

What Does an Inspection Include?

A qualified inspector will recommend actions to ensure safety following an inspection and notation of problems, to include:

• Cuts
• Cracks
• Gouges
• Abrasions
• Discoloration
• Broken Fibers
• Loose Brackets
• Damaged Gaskets or Isolators
• Heat Damage

How Do I Know the Inspector Is Qualified?

The industry standard for being deemed a qualified inspector include that he or she must meet at least one of the following:

• Have a minimum of two years experience conducting container inspections
• Be supervised by someone with two years experience
• Be approved by the container manufacturer
• Be certified as an inspector by an organization with NGV training centers, an ‘authority having jurisdiction,' or a nationally recognized certification testing organization.

In addition, a qualified inspector must have knowledge of the various types of containers used, as well as damage allowances for each type. Manufacturers have inspection guidelines for each type of cylinder they produce and the inspector should have these readily available. And, of course, the inspector must have an understanding of inspection requirements, tests, and other procedures.

Where Are These Qualified Inspectors?

Many fleets have one or more employees that are qualified to do these inspections. Training classes are available through many agencies, including AFVi, which offers a two-day course many times throughout the year. Additionally, CSA America offers certification to those who pass their exam, which is proctored by AFVi at the end of the two-day session. Upon passing this optional exam, inspectors are that much more qualified to perform the inspection. The good news is that the U.S. Department of Energy has scholarship monies available to pay for both the training and, for those want to pursue CSA certification, for the exam fee. To receive this scholarship, you must apply before attending the training and must complete the training and pass the certification exam. For more information, go to the Clean Vehicle Education Foundation (the administrator of this program) at www.cleanvehicle.org.

Should a fleet not have their own qualified inspector, inspection services are offered by some NGV or cylinder manufacturers and some natural gas utilities. The CSA America website (www.csa-america.org) also lists inspectors they have certified by geographic area, some of whom may also offer inspection services.

What's the Life of These Cylinders?

Each cylinder has a "Do Not Use After" date printed on the cylinder label by the manufacturer. Following the recommended inspection guidelines and abiding by the recommended "Do Not Use After" date will go a very long way to ensuring the safety and integrity of your fleet's on-board fuel storage cylinders.

*U.S. Department of Transportation, National Highway Transportation Safety Administration (NHTSA) Federal Motor Vehicle Safety Standard 304 (49 CFR 571.304)