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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 #16-0130

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

Interpretation Response Details

Response Publish Date:

Company Name: One CIS Insurance Company

Individual Name: Edgar A. Whittle

Country: US

View the Interpretation Document

Response text:

January 04, 2017

Mr. Edgar A. Whittle
Director, Codes & Standards
One CIS Insurance Company

Reference No. 16-0130

Dear Mr. Whittle:

This letter is in response to your July 20, 2016, letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR parts 171-180) applicable to thickness testing and repair of a DOT Specification MC 331 cargo tank. Specifically, you provide a scenario in which an MC 331 cargo tank shows corroded, gouged, or abraded areas and ask to what minimum thickness the tank should be tested and repaired.

Section 180.407(i)(4)(ix) requires that thickness testing be performed on known thin areas of the tank shell, which could include those that are corroded, gouged, or abraded. As specified in § 180.407(i)(9), an MC 331 cargo tank built before October 1, 2003, must be thickness tested to a minimum thickness based on the U1A form, minus any corrosion allowance.  For an MC 331 cargo tank built on or after October 1, 2003, the minimum thickness is the value indicated on the specification plate. In accordance with the acceptable results of tests and inspections in § 180.411(a) and (b)(2), corroded or abraded areas—as well as dents, cuts, digs, and gouges-should have a minimum thickness no less than the prescribed specification, which in this case is an MC 331 cargo tank.

Please note that § 180.407(b)(1), (d)(5), and (e)(3) specify that corroded or abraded areas must be thickness tested in accordance with § 180.407(i)(2), (i)(3), (i)(5), and (i)(6). For consistency, paragraphs (b)(1), (d)(5), and (e)(3) should also reference paragraph (i)(9) as it provides thickness specifications for MC 331 cargo tanks.  This issue will be addressed in a future rulemaking.

I trust 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

180.407(i)(4)(ix), 180.407(i)(9), 180.411(a) and (b)(2), 180.407(b)(1), (d)(5), and (e)(3), 180.407(i)(2), (i)(3), (i)(5), and (i)(6)

Regulation Sections

Section Subject
180.407 Requirements for test and inspection of specification cargo tanks
180.411 Acceptable results of tests and inspections