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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 #11-0121 ([Thompson Tank, Inc.] [Mr. David Thompson])

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

Interpretation Response Details

Response Publish Date:

Company Name: Thompson Tank, Inc.

Individual Name: Mr. David Thompson

Location State: CA Country: US

View the Interpretation Document

Response text:

March 15, 2012


Mr. David Thompson
Thompson Tank Inc.
8029 Phlox Street
Downey, CA 90241

Ref. No.:  11-0121

Dear Mr. Thompson:

This is in response to your May 26, 2011, letter requesting further clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) based on two letters issued by this office (Ref. No. 10-0219, 11-0002) regarding inspection and use of non-DOT specification cargo tank motor vehicles constructed from glass fiber reinforced plastics (GFRP) authorized by several Department of Transportation (DOT) special permits.  Your questions are restated and answered below:

Q1.  If the resin rich barrier is destroyed and replaced with a sprayed in lining, is the new liner still considered a corrosion barrier and not a lining?

A1.  In our May 11, 2011 letter (11-0002), we clarified that GFRP cargo tanks authorized by DOT special permits incorporate a corrosion barrier that is a thin resin rich area that is part of the cargo tank wall.  A spray lining used to repair the corrosion barrier would constitute a corrosion barrier and not a lining.

Q2.  Some GFRP cargo tanks authorized by DOT special permits have a carbon layer between the corrosion barrier or lining material and the cargo tank wall for the purpose of spark testing the liner.  Is this carbon layer also a corrosion barrier and not an interior lining?  Is the inspection facility required to perform a spark test?

A2.  Based on the information provided in your letter, the carbon appears to serve as a conductive layer and does not protect the cargo tank from attack from the lading.  The carbon layer would not be considered a corrosion barrier or a lining material.  However, linings on any cargo tanks that are manufactured with conductivity should be spark tested in accordance with the manufacturer's requirements.

Q3.  When will the DOT inform the original manufacturers of the GFRP cargo tanks authorized by DOT special permits of their responsibilities to furnish inspection facilities, when requested, the proper procedures to verify the minimum thickness and structural integrity of the cargo tank wall and enforce compliance?

A3.  The HMR require any person performing thickness testing to be trained in the proper use of the thickness testing device used in accordance with the manufacturer's instruction (§ 180.407(i)(2)).  Special permits that authorize the manufacture, marking, sale and use of GFRP cargo tanks (e.g. DOT SP-9166, 10878, 11565, 12516, 14275, 14277, 14779) include specific requirements for visual inspection in addition to those items required to be inspected by § 180.407.  These requirements include an inspection to detect cracks, gouges, debonding or delamination of any layers.  In accordance with these special permits, the manufacturer must be notified and authorize any repairs to the pressure vessel, including repairs to the corrosion barrier.

I hope this answers your inquiry.  If you need additional assistance, please contact the Standards and Rulemaking Division at (202) 366-8553.


Ben Supko
Acting Chief, Standards Development
Standards and Rulemaking Division


Regulation Sections

Section Subject
180.407 Requirements for test and inspection of specification cargo tanks