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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #23-0041

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: United Testing Services

Individual Name: Anthony Roston

Location State: CA Country: US

View the Interpretation Document

Response text:

May 2. 2024

Anthony Roston
United Testing Services
Chabot Collision Building
20736 Lake Chabot Rd.
Castro Valley CA  94546-5406

Reference No. 23-0041

Dear Mr. Roston:

This letter is in response to your April 20, 2023, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to Department of Transportation (DOT) specification 39 (DOT 39) non-reusable (non-refillable) cylinders. You ask for additional clarification of the requirements in § 178.65 which state that "[b]razed seams must be assembled with proper fit to ensure complete penetration of the brazing material throughout the brazed joint." Specifically, you ask whether pictures that you submitted of a DOT 39 cylinder were representative of a weld with "complete penetration" and whether a cylinder weld with voids could still be in compliance with § 178.65.

As stated in an earlier letter of interpretation we issued and that you cited (Reference No. 21-0097), PHMSA cannot determine whether a violation of § 178.65 exists based solely on photographic evidence. While the criteria provided in the HMR are not specific to the presence of voids in welds, § 178.65(c)(2) specifies that for seams:

  • Brazing is not authorized on aluminum cylinders;
  • Brazing material must have a melting point of not lower than 1,000 °F;
  • Brazed seams must be assembled with proper fit to ensure complete penetration of the brazing material throughout the brazed joint;
  • Minimum width of brazed joints must be at least four (4) times the thickness of the shell wall; and
  • Brazed seams must have a design strength equal to or greater than 1.5 times the minimum strength of the shell wall.

I hope this information is helpful. Please contact us if we can be of further assistance.


Dirk Der Kinderen
Chief, Standards Development Branch
Standards and Rulemaking Division

178.65, 178.65(c)(2)

Regulation Sections

Section Subject
178.65 Specification 39 non-reusable (non-refillable) cylinders