Louisiana Gas Service Company — Pipeline Safety Interpretation

Page 1Aug 12, 1976 Mr. D. L. Meriwether Director of Technical Standards Louisiana Gas Service Company P.O. Box 433 Harvey, Louisiana 70058 Dear Mr. Meriwether: This responds to your letter dated May 10, 1976, requesting an interpretation of Title 49 CFR Part 192.179(c). Question: Where valves are installed at a closer interval than those as specified in 192.179(a), must a blowdown be installed between each set of valves? Answer: Yes, Section 192.179(c) states: "Each section of a transmission line, other than offshore segments, between main line valves must have a blowdown valve with enough capacity to allow the transmission line to be blown down as rapidly as practicable. Each blowdown discharge must be located so the gas can be blown to the atmosphere without hazard and, if the transmission line is adjacent to an overhead electric line, so that the gas is directed away from the electrical conductors." The purpose of the pipeline blowdown valves are for exhausting gas from the line when required by repairs, emergencies, or other conditions. Question: Is there a guideline that determines the blowdown capacity for a certain size and length of pipeline? Answer: Guidelines to determine blowdown capacity are not a function of this Office. Because the issuing gas jet from a blowdown valve produces a violent reaction thrust, proper blowdown design is of major importance and is the responsibility of the operator. Blowdown valve sizes may be selected by using various applicable formula and/or charts that are provided in handbooks such as the Gas Engineer's Handbook, or from valve manufacturers' literature. We trust that this adequately responds to your inquiry. Sincerely, Cesar DeLeon Acting Director dal\192\179\76-08-12 1#

Page 2Office of Pipeline Safety Operations May 10, 1976 Department of Transportation Materials Transportation Bureau Office of Pipeline Safety Operations 400 7th Street S.W. Washington, D.C. 20590 Gentlemen: We would like to have an interpretation regarding Part 192.179(c) of Title 49 of the Code of Federal Regulations. Where valves are installed at a closer interval than those as specified in 192.179(a), must a blowdown be installed between each set of valves? Rule 192.179(c) also states that the blowdown valve must have a capacity to allow the transmission line to be blown down as rapidly as practicable. Is there a guideline that determines the blowdown capacity for a certain size and length of pipeline? At your convenience, we would appreciate an interpretation of this regulation. Yours very truly, LOUISIANA GAS SERVICE COMPANY D. L. Meriwether Director of Technical Standards dal\192\179\76-08-12 2#

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