RIN and DOT Marking Requirements for Cylinder Requalifiers

A Requalifier Identification Number (RIN) is a four-character code that the Pipeline and Hazardous Materials Safety Administration (PHMSA) assigns to a facility authorized to inspect, test, and requalify high-pressure cylinders used in hazardous materials transportation. Under 49 CFR Part 107, Subpart I, no facility may stamp a requalification date on a cylinder, or otherwise represent that a cylinder has been requalified, without holding a current RIN.¹ The RIN and DOT marking requirements for cylinder requalifiers cover two connected things: how a facility earns and keeps that four-character code, and exactly how it must stamp each passing cylinder so the marking survives inspection.

Getting a RIN From PHMSA

The application is not the first step. Before PHMSA will review anything, the facility must hire an independent inspection agency that PHMSA has already approved. That agency conducts an on-site review of equipment, procedures, and personnel, and the applicant pays for the visit. PHMSA does not cover the cost.² Only after the agency issues a satisfactory report and a letter of recommendation can the facility file with PHMSA.

The submission itself has two layers. Under 49 CFR 107.705(a), every applicant provides the name, street address, mailing address, and telephone number of the person on whose behalf the application is made, identifies the regulatory section, and describes the activity for which approval is sought. Filings go by mail to the Associate Administrator for Hazardous Materials Safety (PHH-32), by fax, or by email to approvals@dot.gov.³

On top of those general items, 49 CFR 107.805(c) requires facility-specific details: the facility manager’s name; the specific DOT specification or special permit cylinders the facility intends to inspect, test, repair, or rebuild (DOT 3AA and DOT 3HT are common examples); a signed and dated statement that the facility will operate in accordance with Subchapter C of Title 49; and, for mobile units, the equipment and vehicles used, the geographic area of operations, and any differences from a fixed-facility operation. The independent inspection agency’s letter of recommendation and inspection report must be included in the package.² Vague or incomplete submissions, especially ones missing equipment details or cylinder specifications, risk rejection or a request for more documentation.

PHMSA reviews the full package against federal safety standards. A successful applicant receives a RIN certificate valid for five years from the date of issuance, provided the facility maintains its qualifications at or above the level observed during the independent inspection. Renewal requires a written request to approvals@dot.gov at least 60 days before the approval expires, and the facility should expect a fresh independent inspection as part of that renewal.⁴

What the DOT Requalification Marking Must Show

Every cylinder that passes requalification is marked in the format set by 49 CFR 180.213. The mark has three core components arranged in a row: the month of the test, the four-character RIN, and the year of the test. The RIN sits between the month and year in a square pattern: first character upper left, second upper right, third lower right, fourth lower left. That square layout is what distinguishes the requalification stamp from the cylinder’s original manufacturing codes.⁵

Read from left to right, a mark showing “05,” the RIN square, and “24” tells anyone handling the cylinder that it was last tested in May 2024. That date is the starting point for calculating when the next requalification is due.

The Star and Plus Symbols

Two symbols can replace the standard “X” in the marking and change what the cylinder is authorized to do.

A five-point star indicates the cylinder qualifies for a ten-year requalification interval instead of the standard five. This applies to certain DOT 3A and 3AA cylinders that meet specific conditions, including being manufactured after December 31, 1945, being used exclusively for non-corrosive gases, and being dried immediately after hydrostatic testing.⁶
A plus sign (+) indicates the cylinder is authorized for filling up to 10 percent above its marked service pressure, provided it meets the elastic expansion criteria in 49 CFR 173.302a(b).⁵

Requalification Intervals by Cylinder Type

There is no single interval that applies across the board. DOT 3HT cylinders must be retested every three years. DOT 3A and 3AA cylinders are generally tested every five years but can qualify for ten- or twelve-year intervals depending on their use and condition. DOT 8 and 8AL cylinders have a baseline interval of ten years. Some cylinders, including DOT 3E and 4L, do not require periodic testing at all. The full table appears in Table 1 to 49 CFR 180.209(a).⁶

Size, Placement, and Method

The general requalification markings, meaning the month, year, and any special symbols, must be at least 6.35 mm (1/4 inch) high. The RIN characters within the square have a smaller minimum of 3.18 mm (1/8 inch).⁵ Undersized characters are an easy way to trigger a marking violation.

Placement is where a small mistake becomes an expensive one. Markings must go on the upper end of the cylinder: the shoulder, top head, or neck. Stamping on the sidewall is prohibited for most cylinders, and a cylinder that has been stamped on the sidewall must be condemned. One misplaced stamp turns a functioning cylinder into scrap.⁷ Previous requalification markings must remain legible and cannot be obliterated. When the marking space fills up, older dates may be removed by peening, but only with the owner’s permission, only while maintaining minimum wall thickness, and never by removing the original manufacturing test date.⁵

Acceptable methods include stamping, engraving, scribing, or applying a label embedded in epoxy that stays legible and durable throughout the cylinder’s life. Composite cylinders cannot be stamped at all. Instead, a pressure-sensitive label carrying the requalification data must be affixed and overcoated with epoxy near the original manufacturer’s label. Fire extinguisher cylinders may also use pressure-sensitive labels. DOT 3HT cylinders require low-stress steel stamps at a depth no greater than the original manufacturing specification.⁵

Records Behind the Mark

A facility holding a RIN must maintain requalification records at every location where it inspects, tests, or marks cylinders.¹ Under 49 CFR 180.215, pressure test and visual inspection records must capture, for each cylinder:

Date of requalification, serial number, and DOT specification or special permit number
Marked pressure and actual dimensions
Manufacturer’s name or symbol (if present) and year of manufacture
Owner’s name or symbol (if present) and gas service
Results of the visual inspection
Actual test pressure, total expansion, elastic expansion, permanent expansion, and percent permanent expansion
Disposition of the cylinder, including the reason for any repeated test, rejection, or condemnation
Identification of the test operator

Calibration test records have their own list: date, serial number of the calibrated cylinder, calibration test pressure, expansion values, and test operator identification. Records for welding repairs, rebuilding, or reheat treatment must be kept for a minimum of 15 years. Records of unsuccessful tests must also be retained; documentation for cylinders that failed cannot be discarded.⁸

Reporting Facility Changes and Ownership Transfers

Any change in the facility’s name, address, ownership, testing equipment, or the management and personnel performing requalification work must be reported in writing to the Associate Administrator (PHH-32) within 20 days of the change.² Ownership transitions are where this deadline most often gets missed.

The RIN does not transfer with the facility. PHMSA treats certificates of registration as non-transferable in mergers, acquisitions, and asset sales. A company buying an existing requalification facility must file its own application before performing any regulated activity. If a company acquires another and runs it as a subsidiary without changing the subsidiary’s corporate structure, the subsidiary may continue under its existing approval, but it cannot operate under the parent company’s certificate. A change in Federal Tax ID number or legal suffix, such as “ABC” becoming “ABC LLC,” generally signals a new entity that needs its own registration.⁹

Penalties for Marking and Authority Violations

Operating without a valid RIN carries a baseline civil penalty of $5,000. Letting authority lapse by failing to renew costs $2,500 plus $600 for each additional year of lapsed status. Marking a RIN on a cylinder before successfully completing the hydrostatic test draws a $1,000 penalty, and improperly marking the RIN or retest date adds another $1,000.¹⁰

Baseline numbers can climb quickly. A knowing violation of federal hazardous material transportation law can reach up to $102,348 per violation. If the violation causes death, serious injury, or substantial property destruction, the maximum jumps to $238,809. Each day a continuing violation persists counts as a separate offense, and multiple occurrences of the same violation are assessed individually.¹¹ Criminal penalties are also available: a knowing or willfully reckless violation can result in fines under Title 18 of the U.S. Code and up to five years in prison, doubling to ten years where the violation involves a hazardous material release that causes death or bodily injury.¹⁰

1
eCFR. 49 CFR 180.205 – General Requirements for Requalification of Specification Cylinders
2
eCFR. 49 CFR 107.805 – Approval of Cylinder and Pressure Receptacle Requalifiers
3
eCFR. 49 CFR 107.705 – Filing of Registration Statements, Reports, and Applications
4
Pipeline and Hazardous Materials Safety Administration. Cylinder Requalifiers
5
eCFR. 49 CFR 180.213 – Requalification Markings
6
eCFR. 49 CFR 180.209 – Requirements for Requalification of Specification Cylinders
7
eCFR. 49 CFR 180.205 – General Requirements for Requalification of Specification Cylinders
8
eCFR. 49 CFR 180.215 – Reporting and Record Retention Requirements
9
Pipeline and Hazardous Materials Safety Administration. Hazmat Registration – Mergers, Acquisitions, and Legal Status Changes
10
eCFR. 49 CFR Part 107 Subpart D – Enforcement
11
eCFR. 49 CFR 107.329 – Maximum Penalties