A January 4th United States Pipeline and Hazardous Materials Safety Administration (“PHMSA”) letter addresses a question asking for clarification of the Hazardous Materials Regulations (“HMR”) applicable to thickness testing and repair of a DOT Specification MC 331 cargo tank.

The PHMSA letter is responding to a July 20, 2016 letter from One CIS Insurance Company (“CIS”) requesting that the agency provide a scenario in which an MC 331 cargo tank shows corroded, gouged, or abraded areas and asks to what minimum thickness the tank should be tested and repaired.

PHMSA responded stating:

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.

The agency also notes 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.

PHMSA states that the issue will be addressed in a future rulemaking.

A copy of the January 4th letter can be downloaded here.