USA Banner

Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

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

Interpretation Response #13-0042 ([City Machine and Welding, Inc.] [Mr. Kent Carroll])

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

Interpretation Response Details

Response Publish Date:

Company Name: City Machine and Welding, Inc.

Individual Name: Mr. Kent Carroll

Location State: TX Country: US

View the Interpretation Document

Response text:

May 22, 2013

Mr. Kent Carroll
City Machine and Welding, Inc.
P.O. Box 51018
Amarillo, TX 79159

Ref. No.: 13-0042

Dear Mr. Carroll:

This is in response to your February 7, 2013 email requesting clarification of the requirements for the marking of a plus (+) sign on DOT 3A, 3AX, 3AA, 3AAX, and 3T cylinders as specified in § 173.302a(b) of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180).  Specifically, you ask if a cylinder that passed the permanent expansion requirement, but exceeded the elastic expansion rejection limit (REE) may be returned to service (1) at the same or a lower service pressure or (2) 10 % in excess of its marked service pressure.  

The + sign is added following the test date marking on a cylinder to indicate that a cylinder complies with § 173.302a(b) and is permitted to be filled to a pressure 10%  in excess of its marked service pressure.  All of the conditions in § 173.302a(b) must be met, including compliance with either the average wall stress or the maximum wall stress limitations shown in    § 173.302a(b)(3).  

If a cylinder has less than 10 % permanent expansion as demonstrated by the volumetric expansion test (§ 180.205(i)(1)(iv)), but fails the REE examination, the + sign may not be marked on the cylinder after the requalification test date marking since the cylinder did not comply with the average wall stress requirement.  In this case, the cylinder may be returned to service at its marked service pressure. As specified in § 180.205(c)(3), for DOT specification cylinders, the marked service pressure may only be changed upon approval from the Associate Administrator for Hazardous Materials Safety and in accordance with written procedures specified in that approval.

I hope this information is helpful.  If you have further questions, please do not hesitate to contact this office.


Delmer Billings
Senior Regulatory Advisor
Standards and Rulemaking Division

173.302, 180.205





Regulation Sections

Section Subject
173.302a Additional requirements for shipment of nonliquefied (permanent) compressed gases in specification cylinders
180.205 General requirements for requalification of specification cylinders