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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 #21-0038

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

Interpretation Response Details

Response Publish Date:

Company Name: Momentive Performance Materials

Individual Name: Ms. Kirsten Pink

Location State: NY Country: US

View the Interpretation Document

Response text:

August 26, 2021

Ms. Kirsten Pink
Momentive Performance Materials
260 Hudson River Road
Waterford, NY  12188

Reference No. 21-0038

Dear Ms. Pink:

This letter is in response to your April 9, 2021, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to pressure relief devices for MC 331 cargo tanks. Specifically, you ask for clarification of the requirements for pressure relief devices when a MC 331 cargo tank is used to transport "UN2988, Chlorosilanes, water-reactive, flammable, corrosive, n.o.s., 4.3, Packing Group (PG) I."

We have paraphrased and answered your questions as follows:

Q1. You ask whether § 178.337-9(a)(1)—which reads "See § 173.315(i) of this subchapter."—would apply to a MC 331 cargo tank transporting "UN2988, Chlorosilanes, water-reactive, flammable, corrosive, n.o.s., 4.3, PG I."

A1. The answer is yes. ection 178.337-9 is part of the design specification requirements for MC 331 cargo tanks. Therefore, to be in compliance with the design specification requirements for a MC 331 cargo tank, the requirements of § 178.337-9(a)(1) must be met, which include the requirements of § 173.315(i).

Q2. You ask what the set-to-discharge pressure is for a pressure relief valve installed in a MC 331 cargo tank with a maximum allowable working pressure (MAWP) of 250 psi, and used in “UN2988, Chlorosilanes, water-reactive, flammable, corrosive, n.o.s., 4.3, PG I" service.

A2. As explained in PHMSA's response to a previous request for Letter of Interpretation (LOI) 16-0090, § 173.315(i)(3) was amended in 2001 to add new requirements for UN portable tanks. In doing so, the term "tank" was modified to "portable tank, other than a UN portable tank," thereby omitting cargo tanks from the specifications of the paragraph.

However, pressure relief setting requirements for cargo tanks are found in § 180.407(j). Section 180.407(j)(1)(iv) specifies that pressure relief valves for MC 330 and MC 331 cargo tanks must open at not less than the required set pressure and not more than 110% of the required set pressure. The valves must also reseat to a leak-tight condition at no less than 90% of the required set pressure. Therefore, the allowable start-to-discharge pressure range for a pressure relief device installed in a MC 331 cargo tank with an MAWP of 250 psi is from 250 psi to 275 psi.

I hope this information is helpful. Please contact us if we can be of further assistance.

Sincerely,

T. Glenn Foster
Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division

173.315(i), 173.315(i)(3), 178.337-9, 178.337-9(a)(1), 180.407(j)(1)(iv)

Regulation Sections

Section Subject
173.315 Compressed gases in cargo tanks and portable tanks
178.337-9 Pressure relief devices, piping, valves, hoses, and fittings
180.407 Requirements for test and inspection of specification cargo tanks