CGA’s C-6 Publication Series Guides the Inspection of Compressed Gas Cylinders for Safe Filling, Transport, and End Use

Do you fill or ship high- or low-pressure steel, aluminum, or composite cylinders? Are you aware of the U.S. Department of Transportation (DOT) and Transport Canada (TC) regulations that must be followed before shipping these cylinders? If the answer to either question is “Yes,” then you need the CGA C-6 series of standards (all updated in 2019), which include:

• CGA C-6, Standard for Visual Inspection of Steel Compressed Gas Cylinders
• CGA C-6.1, Standard for Visual Inspection of High Pressure Aluminum Alloy Compressed Gas Cylinders
• CGA C-6.2, Standard for Visual Inspection and Requalification of Fiber Reinforced High Pressure Cylinders
• CGA C-6.3, Standard for Visual Inspection of Low Pressure Aluminum Alloy Compressed Gas Cylinders

CGA C-6 Publication Series Overview

Millions of compressed gas cylinders that conform to U.S. DOT and Transport Canada specifications are used every day. These cylinders may be of high- or low-pressure steel construction, high- or low-pressure aluminum construction, or carbon fiber construction. All these cylinders must first be inspected to be sure they can be safely filled, shipped, and used at customer sites.

The regulations of both the United States and Canada require that a cylinder not be filled but  condemned when it leaks, when there is internal or external corrosion, denting, bulging, or when evidence of rough usage exists to the extent that the cylinder is likely to be weakened appreciably.

To ensure that these and other pertinent regulations are complied with, the Compressed Gas Association (CGA) provides a series of four standards with criteria that cylinder requalifiers, owners, fillers, operators, etc. may use to accept, reject, and condemn compressed gas cylinders for continued use.

Each of these four CGA safety standards has been Incorporated by Reference by U.S. DOT.

These standards are updated on a 5 to 7 year revision cycle by CGA’s Cylinder Specifications Committee, in order to provide users with the most up to date and current information to ensure safety at the filling plant, while in transportation, and at the use site.

When each standard is revised, a copy is sent to the U.S. DOT for consideration to update the Incorporation by Reference to the most recent edition.

We provide a brief description of each of these standards below, highlighting important new information found in the most recent revisions.

CGA C-6, Standard for Visual Inspection of Steel Compressed Gas Cylinders

12th Edition, published in August 2019

Reviews inspection procedures, including preparation of cylinders for inspection, exterior inspection, interior inspection (if required), nature and extent of damage to be looked for, and some tests that indicate the conditions of the cylinder, etc. A sample inspection report is shown in Appendix A that may be revised to suit the user’s requirements.

Major changes in the 12th Edition from previous editions include:

• Provides expanded list of definitions.
• Adds new inspection methods for low pressure (< 900 psi) cylinders.
• Identifies specific methods of sidewall leaks in low pressure cylinders.
• Lists inspection criteria for footrings and shrouds on low pressure cylinders.

The 1993, 7th Edition is currently referenced at 49CFR171.7.

CGA C-6.1, Standard for Visual Inspection of High Pressure Aluminum Alloy Compressed Gas Cylinders

7th Edition, published in August 2019

Provides a standard for the visual inspection and hydrostatic testing of aluminum alloy cylinders with a service pressure of 1800 psig (12 410 kPa) and above. This standard covers preparation for inspection and hydrostatic testing as well as inspection criteria such as corrosion limits, dents, arc burns, fire damage, neck defects, etc.

The 7th Edition includes the following important updated information:

• Provides expanded list of definitions.
• Adds new section reflecting the requirements for ultrasonic examination inspection of these cylinders.
• Includes Transport Canada requirements, to make the publication harmonized for both the U.S. and Canada.
• Incorporates information from the discontinued CGA Safety Bulletin SB-22, Aluminum Cylinders-Guidelines for Heat Exposure Indicating Systems (2013).
• Updates text to eliminate non-enforceable “should and could” verbiage. The publication text is now enforceable.

The 2002, 4th Edition is currently referenced at 49CFR171.7.

CGA C-6.2, Standard for Visual Inspection and Requalification of Fiber Reinforced High Pressure Cylinders

8th Edition, published in October 2019

This standard includes expanded considerations and requirements for new carbon fiber cylinder types.

The most recent two editions include the following important updated information:

• Incorporates UN Pressure Receptacle information and multiple-element gas containers.
• Includes typical marking identification for DOT and TC cylinders.
• Adds list of CGA and government publications required for testing and inspection.
• Provides descriptions, instructions and details, including applicable special permit numbers for fiber reinforced high pressure cylinders.
• Expands descriptions, including the exposure to corrosive materials and elevated heat environments.
• Contains tables listing allowable defect types and sizes, as well as color photograph samples.
• Includes various nonstructural cosmetic conditions that do not affect the safe use of a cylinder.

This publication is required for use by approved requalification facilities in both the United States (49 CFR) and Canada (CAN/CSA B339) for the visual examination and hydrostatic retesting of composite cylinders. It provides a valuable guideline for end users or owners for the continued assessment of the physical condition of these types of cylinders.

The 1996, 3rd Edition is currently referenced at 49CFR171.7.

CGA C-6.3, Standard for Visual Inspection of Low Pressure Aluminum Alloy Compressed Gas Cylinders

4th Edition, published in July 2019

This standard provides data and details for the periodic inspection of aluminum cylinders with a service pressure of 500 psi (3447 kPa) or less. The publication also contains color photos of defects.

The 4th Edition includes the following informational updates:

• Provides an expanded list of definitions.
• Lists inspection criteria for footrings and shrouds.
• Incorporates expanded information on requalification methods for low pressure aluminum cylinders.

The 1991, 1st Edition is currently referenced at 49CFR171.7.

In conclusion, the CGA C-6 series of safety standards provides the compressed gas cylinder community with valuable direction to ensure compliance with the cylinder inspection regulations of the U.S. DOT and Transport Canada.