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What You Need to Know About DOT Hydrostatic Testing

by Feb 14, 2017Weld Testing

The Department of Transportation employs strict guidelines for any business which transports low-pressure stainless steel cylinders containing compressed gas and other chemical materials. These guidelines are set forth by DOT Pipeline and Hazardous Materials Safety Administration (PHMSA), and in accordance with the Compressed Gas Association (CGA).

About DOT Specifications

DOT specifications are designed to regulate the strength and quality of stainless steel cylinders, and therefore requires that stainless steel cylinders are tested every 3, 5, 10, or in exceptional cases, 12 years. The frequency with which a cylinder must be tested depends upon the age of a cylinder, the type of gas or chemicals it contains, the particular material of the cylinder, and its OEM rating. See the following chart for the requirements specific to cylinder type: Recertification Chart.

If a cylinder is designated for a specific pressure limit, and it is determined that the cylinder is not equipped to handle that pressure, then the cylinder cannot be certified for use. These guidelines are designed to help prevent unnecessary disasters that may occur due to the transporting of faulty cylinders, and therefore it is crucial to understand and comply with these regulations at times. According to PHMSA, “Through PHMSA oversight programs, serious pipeline incidents have decreased by 39% since 2009.”

Markings and Pressure Limits

DOT cylinders are required to be marked with a specific rating, and each required marking must be maintained so that it is clearly legible at all times. When a cylinder is retested or rebuilt, the marking must be updated as necessary to continue to meet this requirement.

Cylinders that are certified to transport higher pressure limits can be used, if necessary, to transport what would otherwise be placed in a lower pressure canister. For example, cylinders certified for DOT-4B500 use are authorized for use where DOT-4B300 certification is indicated.

DOT Testing Certification

In order to maintain DOT compliance, the cylinders must be periodically tested by a certified DOT testing facility. The testing facility should be equipped to test, inspect, certify, repair and/or rebuild low-pressure stainless-steel cylinders according to the appropriate methods for hydrostatic testing.

According to PHMSA, “A [facility] must meet the requirements of 49 CFR Sections 107.805, 180.211, and 180.212 to be approved to inspect, test, certify, repair, or rebuild a cylinder in accordance with a DOT specification or a UN pressure receptacle under subpart C of part 178 or subpart C of part 180, or under the terms of a special permit issued under this part.”

A facility may be certified for testing one or more ratings of cylinders. Therefore, it’s important to research any businesses offering DOT cylinder testing services, to ensure that they are certified to test to the particular cylinders that are being transported.

Benefits of Hydrostatic Testing

Hydrostatic testing is one of the most effective ways to test the structural integrity of stainless steel cylinders. It can also help businesses to effectively prevent potential disasters that may occur due to use of structurally weak cylinders. In addition, companies can avoid penalties from DOT for not complying with cylinder testing certifications.

Axenics Hydrostatic Testing capabilities

Axenics is qualified to test, inspect, certify, repair and/or rebuild low-pressure stainless-steel cylinders. We hold the following DOT Stainless Steel Cylinder Approval:

  • RIN#: 1550, expires 6/19/2020
  • K#: KI33, expires 6/19/2020
  • M#: M6329, expires 3/9/2020
  • Cylinder Type: 4B260 + 4B300

We use a state of the art hydrostatic tester to perform requalification testing. Cylinders are inspected for leaks, and the integrity of each unit is confirmed.

If you have low-pressure canisters that require certification or recertification, please contact us to discuss your specific needs.

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