PHMSA proposes hazmat revisions for certain cargo tanks
Apr 12, 2007 2:07 PM
The Pipeline and Hazardous Materials Safety Administration (PHMSA) is proposing hazmat regulations revisions that address issues submitted by petitions from certain members of the industry that address structural integrity requirements for the design and construction of DOT406, DOT407, and DOT412 cargo tank vehicles; requirements for manhole assemblies; and pressure relief valves.
Among those submitting petitions were the Tank Trailer Manufacturers Association (TTMA), Keehn Service Corp, and Compressed Gas Association, according to the proposal published in the Federal Register April 12. Comments on the proposal must be submitted by June 11, 2007.
The proposal (49 CFR Parts 107, 171, 172, 173, 176, 178, and 180) also addresses DOT specification cylinders and UN pressure receptacles.
PHMSA stated that Section 178.345-3 prescribes structural integrity requirements for the design and construction of DOT 406, DOT 407, and DOT 412 cargo tank motor vehicles. Paragraph (a) specifies the general requirements and acceptance criteria for structural integrity. TTMA requested the revision of paragraph (a) to reference TTMA Recommended Practice (RP) No. 96-97, Structural Integrity of DOT 406, DOT 407, and DOT 412 Cylindrical Cargo Tanks, December 1, 1997 Edition. This standard contains methods for calculating the structural integrity of DOT 406, DOT 407, and DOT 412 cylindrical cargo tanks in conformance with Sec. 178.345-3 and 178.345-8(e).
"Based on the Federal Motor Carrier Safety Administration's review of TTMA RP No 96-97, we agree with the petitioner that using the methods outlined in the publication for calculating the structural integrity of cargo tanks will be beneficial to manufacturers in reducing time to perform the calculations," PHMSA stated. "Therefore, we propose to revise Sec. 178.345-3(a)(3) to reference the updated TTMA RP 96-01, 2001 Edition, as suitable guidance for performing the structural integrity calculations."
Section 178.345-5 prescribes requirements for manhole assemblies used on DOT 406, DOT 407, and DOT 412 cargo tank motor vehicles. Paragraph (f) specifies that all fittings and devices mounted on a manhole cover, coming in contact with the lading, must withstand the same static internal fluid pressure and contain the same permanent compliance markings as those prescribed in paragraph (e) for the manhole cover. Because paragraph (e) already requires the manhole cover to be marked with a statement certifying that the manhole cover meets the requirements in Sec. 178.345-5, TTMA (P-1372) , PHMSA agreed that to mark the manhole's fittings is duplicative of the manhole cover marking requirement in paragraph (e). Therefore, we propose to remove the redundant wording in paragraph (f).
Keehn Service Corp noted that Section 180.407 prescribes requirements for the periodic testing and inspection of specification cargo tanks. Paragraph (d)(3) of Sec. 180.407 requires each reclosing pressure relief valve that is required to be removed and tested to be able to open at the required set pressure and reseat to a leak-tight condition at 90 percent of the set-to-discharge pressure or the pressure for the applicable cargo tank specification. Paragraph (g)(1)(ii)(A) of Sec. 180.407 requires each self-closing pressure relief valve that is an emergency relief vent to open at the required set pressure and seat to a leak-tight condition at 90 percent of the set-to-discharge pressure or the pressure for the applicable cargo tank specification.
Keehn stated that the majority of pressure relief valves installed on MC-330 and MC-331 cargo tank motor vehicles transporting liquefied petroleum gas have a start-to-discharge set pressure of 250 psi. Keehn said it is difficult for existing or rebuilt valves to open at this exact pressure. In fact, a margin of error of as much as 4 psig could occur when using a typical 0-400 psig pressure gauge. Keehn requested PHMSA specify a start-to-discharge tolerance for pressure relief valves.
"We agree with the petitioner that it may be difficult for a pressure relief valve to function exactly at the specified set pressure and that we should allow a margin of error," PHMSA stated. "Therefore, we propose to revise paragraphs (d)(3) and (g)(1)(ii)(A), of Sec. 180.407, to specify that reclosing and self-closing pressure relief valves must be set-to-discharge at a pressure no more than 110 percent of the required set pressure. Providing for a tolerance is consistent with the set-to-discharge tolerance allowed for certain other DOT specification pressure vessels."
Click here to see the published proposal.
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