NGVConnection Newsletter - June 2017

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Handling Challenges with Today’s CNG Fuel System Inspections

By Gordon Larsen, Senior Technical Instructor, NGVi

CNG fuel systems, especially for heavy-duty natural gas vehicles, have evolved greatly over the past decade. In today’s heavy-duty trucks and buses, CNG storage cylinders are combined into modules and installed on vehicles as a unit. The systems are engineered and installed according to NFPA 52, the installation code. One advantage of the modular concept is a clean, neat design that is easier to install.

Both engineering and installation of CNG fuel systems affect the ability of inspectors to perform required inspections. That’s why CNG fuel system inspectors must be thoroughly familiar with NFPA 52, the installation code for CNG fuel systems. Designed to ensure safety, NFPA 52 dictates everything from minimum clearances to proper installation locations to the design and construction of CNG cylinder packages, and is the guiding document not only for the initial installation of CNG fuel system components, but also for inspection. Besides assessing any damage or disrepair, it is the CNG fuel system inspector’s job to ensure that each component of the system is installed according to code.

Component Access is the Key
In addition to all the other high-pressure components, CNG fuel system inspectors MUST be able to visualize 360 degrees around every cylinder. This can be complicated by the configuration of the cylinders and the ability to access them.

The most common cylinder configuration for heavy-duty trucks is back-of-cab and/or saddle mounted cylinders. Back-of-cab cylinders are installed inside a protective cabinet which may or may not have inspection access panels. Older models of heavy-duty trucks may not have access panels or, if they do, the panels don’t provide adequate access. It is generally accepted that cabinets and shields do not have to be completely removed unless there is no other way to visualize the entire surface of every cylinder.

Saddle mounted cylinders are located on the side of the truck and also feature a protective shield that may be combined into a single module with the fuel management module. Inspection of these cylinders may not be possible without removing the entire shield. The ease with which shields can be removed varies from vehicle to vehicle.

Refuse trucks and transit buses often feature roof mounted cylinders with a clam shell type cover that hinges or in some cases, is completely removable. Cylinders on these vehicles can be easier to visualize, but require harnessing of the inspector to protect against falls. CNG fuel system inspectors must know that standing on the cylinders to perform inspections is prohibited by NFPA 52 because it could cause unintentional damage.

So What Are the Challenges?
A long-standing myth in the industry is that no visible damage to the shields automatically means there is no damage to cylinders. That is not the case. More frequently than not, when we deliver CNG fuel system inspector training, we see shields that are installed too close to cylinders, where the shields themselves rub on the cylinders and cause damage. This is because the minimum clearance was not obtained during installation, or even may have been altered during an accident.

Also, because of the challenges associated with visualizing 360 degrees around every CNG cylinder on some vehicles, some inspectors just don’t perform the complete inspection because of the time required to remove shields when necessary. While it saves time, this practice puts the company that owns the vehicle and/or that performs the inspection at huge risk in the event of an incident.

We also see problems with bolts and rivets. Bolts that are too long and do not adhere to the minimum clearance requirements can quickly damage cylinders. One of our recent refuse customer training classes revealed a vehicle with less than 1,000 miles that presented with Level 3 cylinder damage because of inadequate clearance for bolts. This damage was detected during the class, and the vehicle was red-tagged until the cylinder could be replaced.

Improper drainage is another challenge that can cause unnecessary cylinder damage. NFPA 52 requires that the shields be able to drain solids and liquids away from cylinders. This usually means that holes are drilled at appropriate intervals. At a recent class for a large freight delivery customer of NGVi, it was discovered that there was no allowance for drainage provided with the original CNG fuel system installation.

Another frequently encountered challenge is improper protection from exhaust and other heat-producing components. NFPA 52 2013 and prior versions require that any cylinder within eight inches of exhaust must be insulated or protected from heat in another acceptable manner. We also frequently encounter fuel systems where other components like hydraulic pumps have created damage.

Large-Diameter Cylinders Present Special Challenges
Development of large diameter cylinders has allowed NGV manufacturers to produce vehicles that feature range comparable to diesel vehicles. However, large diameter belly-mounted cylinders present special challenges that CNG fuel system inspectors must be aware of.

All CNG cylinders expand during the fueling process and contract as fuel is depleted. This has historically presented challenges for belly-mounted cylinders because it can be difficult to keep mounting brackets tight enough to prevent cylinders from moving but not so tight that they damage the gaskets or even the cylinders.

However, because of their size, the amount of expansion and contraction with large-diameter cylinders is greater, which in turn creates greater and more frequent problems with mounting brackets and gaskets. CNG fuel system inspectors must be able to identify and diagnose the common problems associated with these components: overtightened brackets that cause gaskets to split or be cut or “squeeze out” from under the brackets and allow brackets to damage cylinders.

The use of neck-mounted CNG cylinders helps mitigate this challenge, but
belly-mounted cylinders are still very prevalent in existing vehicles and will continue to need attention.

Meeting the Challenges
Several actions can help CNG fuel system inspectors meet the CNG fuel system inspection challenges identified in this article.

  1. A pre-in-service (detailed visual) inspection of every vehicle is essential. This allows technicians to establish a baseline condition for every new vehicle before it is placed into service and to detect any problems (like inadequate bolt clearances) BEFORE the problems become severe.

  2. Every CNG fuel system inspector must be thoroughly trained on NFPA 52 installation requirements for CNG fuel systems, in addition to how to identify and assess damaged components, including cylinders. The time invested in this training does not compare to the risk a company would take by not adequately preparing its technicians to perform the inspections.

  3. Establish a policy that EVERY CNG cylinder must be inspected and ensure technicians have the right tools to inspect cylinders that are located in tight spaces. These include a flashlight, a long-handled inspection mirror and a camera with an extension device. (At NGVi, we use a Go-Pro camera with an extension rod.)

  4. Make sure EVERY vehicle that is involved in an accident—no matter how minor it seems—receives a detailed CNG fuel system inspection. Impact of even five miles per hour can have an adverse impact on CNG fuel systems.

Today’s CNG vehicles are a great improvement over those available a decade ago, thanks not only to engine technology development but also to advances in CNG fuel system engineering and installation. Handling challenges with CNG fuel system inspections is yet another way fleets and dealerships can help extend that improvement and ensure that customers have a safe and reliable experience with NGVs.

To learn more about challenges with CNG fuel system inspections, check out NGVi's
ASE Accredited CNG Fuel System Inspector Training and our CNG Fuel System Inspector Certification Program.

NFPA 52 Now Requires Your CNG Station to Have a Maintenance Plan
By Leo Thomason, Executive Director, NGVi

Because of the unique physical properties of natural gas, the distinctive design and construction requirements of CNG fueling stations, and unique CNG station components like dryers, compressors, high-pressure storage, control systems and dispensers  designed specifically to handle pressurized gas, the operation and maintenance practices for CNG stations are very different from those used for liquid fuel stations. To ensure safety at CNG stations, sustain optimum performance, enhance reliability, control operating costs, and ensure environmental and regulatory compliance--performing routine and proactive maintenance on CNG stations is essential.


According to the 2016 version of NFPA 52, CNG fueling stations are now required to have an active, documented maintenance plan. The goals of such a plan include managing maintenance activities, monitoring system operation, providing emergency fueling support when required, enhancing equipment reliability and consistently delivering clean fuel to vehicles. The plan should address every CNG fueling station component and specify the maintenance intervals and  procedures required to keep the equipment safe and operable.

It is important to note that because the code requirements are retroactive, every CNG station--
currently operating or yet to be constructed--will now be mandated to have a maintenance plan implemented. Moreover, regardless of whether station maintenance is  conducted by in-house personnel, third party outside contractors, or some combination of both, the code still requires each station  to have a written maintenance plan in place.


Join Us for a Live One-Hour
Tech Talk Training Session

Required by Code: The CNG Fueling Station Maintenance Plan

Date: Thursday, September 14
Time: 11:30 a.m. PT/2:30 p.m. ET

Recent changes to CNG fueling station codes and standards require that every CNG fueling station have a written Maintenance Plan. Every Maintenance Plan should have standard content, including component manufacturer maintenance and repair guidelines, testing and recertification frequency, diagnostic information and more.

In this Tech Talk, NGVi’s co-founder and CNG fueling station expert Leo Thomason will describe the code requirements for a Maintenance Plan, as well as detail the Maintenance Plan content, who should be accountable for the plan and how to keep it up to date.





Since CNG stations vary based on design, size and performance specifications, their maintenance plans cannot be generically applied and must be designed based on each station’s unique equipment  and operating conditions. Additionally, because CNG station components have to be maintained in accordance with manufacturer instructions, the plan must be in compliance with each specific manufacturer’s equipment.

Before a maintenance plan can be established, it is critical that the station owner understands what the station was designed to deliver and what performance levels are required of the equipment. They should evaluate station performance standards for:

  • Fuel  Delivery  –  usually expressed as the quantity of fuel to be dispensed over a  specified time period, or number of  vehicles to be fueled over a particular time period, or the fueling pressure at a specified temperature. This information helps evaluate whether the station is performing as specified.

  • Gas Quality – specifications for oil content, water content, and odorant level. Since gas quality can significantly affect the performance of the station and fueled vehicles, this information is vital.

  • Operation  and  Maintenance – the amount of time that the station is expected to be operational and when maintenance can be performed.

  • Overall  Operation  and  Maintenance  Costs – total  operating costs for the station, including fuel, maintenance and energy costs. This specification helps determine whether the station is operating within the projected cost limits.  

  • Local Service – regardless of whether the station uses a third party maintenance contractor or in-house  personnel, this specification helps determine whether the minimum specifications for service expectations are met.

  • Noise Level –  the minimum specification for noise level, measured in decibels.

  • Liquid and vapor fugitive emissions – a specification which establishes the minimum liquid or vapor fugitive emissions coming from the station’s equipment.

A complete maintenance plan should include manufacturer maintenance and repair guidelines, testing and recertification frequency, diagnostic information and much more. It should clearly define what is to be done, who will do it and when it is to be performed.


Effective CNG station maintenance plays an important role in ensuring the operational health safety and reliability  of the equipment. Since every CNG fueling station, even if maintained by a third-party, is now required by code to have a written  maintenance plan, station owners and everyone involved in implementation and execution of this plan must be fully familiar with the station components and their function. They must understand performance levels of the equipment, and know the maintenance and operating principles of their CNG fueling station(s). Having a full understanding of the station’s functions, specifications and applicable maintenance practices will not only help station owners  more effectively manage in-house and/or third party maintenance personnel, but also assures that the station maintenance plan is fully and properly executed.


To learn more about how to develop the NFPA-52 required plan, sign up for our September Tech Talk entitled Required by Code: The CNG Fueling Station Maintenance Plan or register for our comprehensive CNG Fueling Station Operation and Maintenance Training, available as either an e-learning or instructor-led course.

NGVi Sponsor Spotlight:
CP Industries, Inc. – More Than a Century of Innovation

By CP Industries, Inc.


When Christy Park Plant was built in 1897 on the old Penney Farm, in McKeesport, Pennsylvania, it consisted of a single main working building and one small office building. It was designed to manufacture seamless steel tubing and small compressed gas cylinders. Christy Park’s new equipment could make larger and stronger cylinders by hot forging—either cupping and drawing a round steel plate or by hydraulic piercing of a solid steel billet to form a seamless cylinder. Within a year, about 125 employees were producing 50-pound carbon dioxide cylinders, the first seamless steel pressure vessels.


Military Partnership 

Within that first year, however, fate, in the form of the Spanish American War intervened. The company was found to be ideally suited to manufacture munitions. Beginning with the manufacturing of armaments for Teddy Roosevelt’s Rough Riders, in Cuba, the company continued to arm our nation’s military until the close of the Vietnam War in 1975. Overall, the contributions from a little mill in a little town were truly amazing. During World War II alone, the company contributed over 22.6 million shells, 3.7 million bombs, 1.3 million rocket tubes and motors, and a million cylinders and air flasks.

Constantly Innovating

In between periods of gearing up to supply our military, Christy Park invested in its cylinder manufacturing processes with pioneering developments in engineering, in equipment, new buildings, and new machinery. Through the infancy of cylinder production, much of the manufacturing technology that became standard within the industry was developed by the plant’s own engineers, and much of the necessary machinery and equipment was built in their own shops. In 1910, for example, the company built a machine to spin the necks of compressed gas cylinders—a technology that is still in use today.


Christy Park’s versatility and resourcefulness helped the company prosper, as it installed equipment for welding and assembly operations in the manufacture of low-pressure gas tanks. Commercial demand for cylinders was based on industry’s expanding need for on-site ground storage of an ever wider variety of compressed gases. This growing industrial market required cylinders for transporting those gases from source to consumer, and Christy Park worked with manufacturers of gas carrying equipment such as truck trailers and railroad cars to develop safe and efficient methods. In fact, Christy Park designed and built the first trailer unit using large OD “jumbo” tubes, proving their viability. As ASME, ICC and DOT created and revised their regulations and specifications, Christy Park played a major role, providing the basis for many of those agency’s specifications and regulations.


For NASA, Christy Park’s strong and dependable cylinders were the perfect solution to storing critical gases at high pressures at launching sites. The plant supplied a host of cylinders for ground support storage and energy systems for the Atlas, Titan and Jupiter launching facilities. Christy Park was a very big part of Alan Shepard’s sub-orbital space flight, John Glenn’s orbiting of the earth, and Neil Armstrong’s trip to the moon. Today, every NASA launch site depends on Christy Park pressure vessels for the storage and supply of critical gases.


Along with Navy flasks and NASA vessels, the plant’s cylinder markets continued to manufacture ASME storage units for industrial gases, DOT cylinders for gas transportation truck trailers, and aerospace, petro-chemical processing, construction, food production, industrial controls, medicine, power generation, undersea exploration, and oil and gas production.


The Change to CPI

In the early 1980s, as the domestic steel industry fell into a period of retrenchment, Christy Park’s parent company U.S. Steel began a restructuring, eliminat­ing some of its smaller operations. Christy Park was purchased on July 31, 1986 by Stanwich Partners of Stamford, Connecticut, and renamed CP Industries, Inc. Because all of the plant’s experienced management and production people remained with the company, a successful re-birth of the company was possible. That re-birth resulted in a dramatic increase in productivity, and two years later CPI became a part of Chatwins Group, comprised of independent divisions that offer a broad range of fabricated and machined industrial parts and products.


A Commitment to the Future

In domestic markets, CP Industries has a large stake in the development of alternate fuels for vehicles.  Today, CP Industries is a global supplier of pressure vessels for a safe and reliable way to transport and store an ever growing variety of pressurized gases and fuels.  From ground storage for refueling stations, to on-board cylinders for vehicles or tube trailers for transporting fuels and gases, the company can deliver top quality, highly engineered storage solutions for an array of applications. 


The growing interest and market demand for light-weight, cost effective storage solutions has created opportunity for new ideas and solutions. The company has designed a line of Type IV all-carbon cylinders for passenger and commercial vehicles, public transit, refuse trucks and other on-board vehicle storage applications. These cylinders are tested and qualified in accordance with ANSI/NGV2 (2007) and are FMVSS 304 compliant.  Available in a variety of diameters and lengths, these cylinders are manufactured with a seamless non-metallic strap or neck mount liner, full carbon fiber wrap and PU end caps for added drop protection. When weight and cost savings with increased payload and vehicle range are essential, these fully-composite cylinders are an ideal solution. The company’s Type IV all-carbon cylinders provide a high volume to weight ratio, while maintaining high durability with safe operation of utmost concern.


Today, there is an emerging need for various Hydrogen storage applications at pressures up to 15,000 psi (1034 bar) in the industry. Designs that address the demands of lowering $$/kg of hydrogen stored, and that incorporate life cycle requirements of industry standards are vital. CP Industries stands ready to meet the challenge. Type 1 (all steel) vessels designed for the required higher pressures of Hydrogen are manufactured to ASME, Section VIII, Division 3 standards. The company’s skilled engineering team can work in conjunction with end users in determining pressure cycles and design a compatible solution.


Besides the traditional Type 1 (all steel) vessels, CP Industries has the capability of utilizing its existing Type 4 (full composite) technology for Hydrogen storage. The vessels are designed and manufactured to the ASME, Section X, Class 3 specification. The company’s designs adhere to NFPA 2 requirements and incorporate high flow piping manifolds, valves, flanges, paint systems and seismic bracing as well as certifications for use in a variety of countries. Assemblies can be customized with any number of vessels of different pressures to meet end user cascade banking demands. CP Industries can assist with valuable technical assistance on installation techniques, and provide continuing support after the system is on line.


CP Industries continues to change, adapt and invest in its future by investing in new technologies, facilities and, most important, in people. The company is still the leading producer of large OD seamless pressure vessels and is one of only five companies in the world with the equipment and knowledge to produce them. Only CP Industries brings a history of 120 years of pioneering experience in pressure vessel production and compressed gas technology.

CNG Fuel Price Report
From Clean Cities Alternative Fuel Price Report published by National Renewable Energy Laboratory (NREL) for DOE's Clean Cities Program

Overall Average Fuel Prices (as of April 2017)


Nationwide Average Price for Fuel This Report

Nationwide Average Price for Fuel Last Report

Change in Price This Report vs. Last Report

Units of Measurement

Gasoline (Regular)




per gallon





per gallon





per GGE

NGVs and CNG in the News


PG&E Delivers $4 million in Rebates to Customers Using Compressed Natural Gas as a Clean Fuel -- Business WireThe Meadville Tribune

CNG Station Planned for Flanders by Fluxys and Mattheeuws
-- NGV Global

Los Angeles Transit Operator Expanding CNG Fleet Commitment-- Natural Gas Intelligence

Public CNG station opens in York, PA--CCJ Commercial Carrier JournalEnvironmental Leader

CP Industries, Inc. Welcomes New Sales Member to Their Team

Upcoming Training and Certification from NGVi

NGV Essentials and Safety Practices CNG Fuel System Inspector Training
August 15, 2017 Atlanta, GA
September 12, 2017 Chicago, IL

With a focus on safety, this one-day course teaches technicians the fundamentals of natural gas, CNG and LNG fuel systems and maintenance practices for NGVs.

August 16-17, 2017 Atlanta, GA
September 13-14, 2017 Chicago, IL

Two-day session that provides you with the proper techniques for inspecting CNG fuel systems, including on-board compressed natural gas fuel storage cylinders.

NGVi CNG Fuel System Inspector Certification Exam

August 18, 2017 Atlanta, GA
September 15, 2017 Chicago, IL

NGVi's CNG Fuel System Inspector Certification Exam delivers a rigorous, independent assessment of the knowledge, competency, and application of skills necessary for technicians to properly conduct CNG fuel system inspections, according to all applicable codes, standards, and industry best practices.

Register Now


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Essentials of CNG Station
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September 26-27, 2018
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and Safety Practices

October 2, 2018
Sacramento, CA

Level 2: CNG Fuel System
Inspector Training

October 3-4, 2018
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About NGVi

Natural Gas Vehicle Institute is North America’s leading provider of training and consulting on natural gas as a transportation fuel.

Our services address the full range of natural gas vehicle and fueling issues, including:

Technical consulting services – Sizing and designing compressed natural gas fueling stations, vehicle assessments and technical assistance for fleets, CNG fueling station troubleshooting, natural gas vehicle maintenance facilities upgrades, liquefied natural gas fleet and fueling management.

Technical training – NGV Essentials and Safety Practices, CNG Fuel System Inspector Training, Heavy-Duty NGV Maintenance and Diagnostics Training, Light-Duty NGV Maintenance and Diagnostics Training, CNG Fuel System Design and Installation Training, Essentials of CNG Station Operation and Maintenance Training, Essentials of CNG Station Planning, Design and Construction Training and CNG/LNG Codes and Standards Training for Fire Marshals and Code Officials.


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