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Interpretation Response #98-0604 ([National Propane Gas Association] [Mr. W.H. Butterbaugh, CAE])

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

Interpretation Response Details

Response Publish Date:

Company Name: National Propane Gas Association

Individual Name: Mr. W.H. Butterbaugh, CAE

Location State: DC Country: US

View the Interpretation Document

Response text:

OCT 5, 1998


Mr. W.H. Butterbaugh, CAE                Ref. No. 88-0022

Director, Regulatory Affairs

National Propane Gas Association

Suite 1004

1101 17th Street, NW

Washington, D.C. 20036

Dear Mr. Butterbaugh:

This is in response to your letter requesting clarification of the annual leakage test requirements specified in 49 CFR Part 180.407(c). Your questions are paraphrased and answered below:

Q1. Is the purpose of the leakage test to determine whether there is a release of lading to the atmosphere?

A1. The purpose of the leakage test is to determine whether a cargo tank, including its piping, can retain the lading, as proved by its ability to maintain the test pressure. The use of leak detector solutions is considered an efficient means for detecting where a leak exists in a cargo tank that fails to maintain the test pressure.

Q2. Must we test individual valves in the piping system during the leakage test?

A2. In order to satisfy requirements of § 180.407(h)(I), the leakage test must include not only the cargo tank itself, but also "product piping with all valves and accessories in place and operative". On most propane cargo tank motor vehicles (bobtails) this would include the internal self-closing stop valve, if used instead of an excess flow valve, all other valves including excess flow valves, pumps, meters, swivel joints, hose, filling connector, and piping, including any "flexible" sections and it would include the vapor transfer piping system, if installed. Because cargo tanks in liquefied petroleum gas service may be leakage tested at 60 psig, well below 80 percent of the tank's design pressure, pressure relief valves also must be leakage tested. The intent is to prove the leakage integrity of the cargo tank wall and the entire piping system. Valves fitted with the by-pass feature recognized in § 178.337-11(a)(1)(vi), of course, could not pass a closed-valve test were this type of test required.

As with other requirements of the Hazardous Materials Regulations, these tests and inspections are considered to be the minimum. More rigid test conditions and/or more frequent testing might be called for under some conditions, for example, if an owner suspected that the internal stop valve was not seating properly.

I apologize for the delay in preparing this response and hope that it has not caused you any inconvenience. If you need further assistance, please contact us.



Thomas G. Allan

Senior Transportation Regulations Specialist

Office of Hazardous Materials Standards


Regulation Sections

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