{"operation":"document","citation":"PI-76-0112","title":"Pipeline Safety Interpretation PI-76-0112","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"1976-09-02","effective_on":null,"summary":"PI-76-0112 concerning 192.11.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-0112.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-0112.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-0112","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/1976/g76-09-02_Garabrant_192.11-lmx.pdf","body":"<<<PAGE 1>>>\n\nPI-76-0112\nSeptember 2, 1976\nMr. H. R. Garabrant\nGas Utilities Safety Engineer\nUtilities Division\nArizona Corporation Commission\n2222 West Encanto Blvd., Suite 210\nPhoenix, Arizona 85009\nDear Mr. Garabrant:\nThis responds to your letter dated June 23, 1976, which discusses overpressure protection of petroleum gas systems,\nstating that the pressure in the storage tank exceeds 60 psig during summer, and suggests a technical review and “rule\nchanges to eliminate the use of relief valves on piped LP gas systems except when used as a second overpressure device\ndownstream of a monitor and working regulator combination and as required on LP storage, tanks.”\nThe significance of your comment that LP tank pressure will exceed the specific value of 60 psig is not readily apparent\nfrom the information presented. Further discussion, therefore, seems appropriate solely for clarification and to avoid\nany possibility of misinterpretation. Title 49 CFR Section 192.195 requires that pressure limiting or relieving devices must\nbe provided so that the maximum allowable operating pressure (MAOP) of a pipeline will not be exceeded, and that a\ndistribution system which is supplied from a source having a higher pressure than the MAOP of the system must have\nproperly designed pressure regulation devices which can be activated in the event of some failure and will prevent\noverpressuring.\nThe criteria for determining whether a requirement exists for a monitor, relief, automatic shut off, or other arrangement\nfor overpressure protection, thereby, is the MAOP of the pipeline and not necessarily a system pressure in excess of 60\npsig.\nA maximum actual operating pressure of 60 psig for a distribution system is applicable as criteria only in connection with\nservice regulator requirements. As set forth in 49 CFR Section 192.197, pressure limiting or relief devices are required in\naddition to the service regulator if system pressure exceeds 60 psig, but for distribution pressures below 60 psig, no\npressure limiting device is required other than a service regulator having certain characteristics.\nOn the basis of the described criteria, it must be assumed that 60 psig is significant either because the MAOP of the\nreferenced systems is 60 psig or that the services are not equipped with pressure limiting or relief devices.\nRegarding your suggestion that Federal regulations be changed with respect to the use of relief valves on petroleum gas\nsystems, a review by this office has concluded that the initiation of rule making procedures for such modification is\nunwarranted for the following reasons:\n1. Current Federal regulations, prescribing requirements for the characteristics, application and installation of\npressure relief devices, provide adequate and appropriate levels of safety. Federal Standard, 49 CFR Section\n192.11, incorporates NFPA Standards No. 58 and 59 by reference but significantly prescribes that Part 192 shall\nprevail in the event of conflict. Paragraph (b)(3) of Section 192.11 particularly provides that discharge vents from\nrelief valves must be located so as to prevent any accumulation of gas at or belowground, and 49 CFR Section\n192.199(e), reinforcing this requirement, specifies that a pressure relief device must have discharge stacks,\nvents, or outlet ports located where gas can be discharged into the atmosphere without undue hazard.\nNumerous other requirements of Part 192 and NFPA 58 provide extensive coverage of the design, application,\nand installation of relief devices, and since relief devices may not be installed where discharged gas will\naccumulate on the ground or cause undue hazard, the expressed central concern is null.\n\n<<<PAGE 2>>>\n\n2. Pressure relieving devices in most instances are the only practicable means of providing overpressure protection\nfor vaporizers, containers, and hydrostatic relief between valves. NFPA 58 Section 314 requires that regulators\nused to control distribution or utilization pressure be as close to the container as practicable. Since other\nrequired pressure relieving devices would be present, all in the same general area, little, if any, benefit would\nderive from the exclusion of the one relief device on the distribution system.\n3. In certain circumstances, such as a small closed distribution system, a pressure relief device may be the best\nmeans of assuring safety from overpressure.\n4. Constraints imposed by the Office of Pipeline Safety Operations (OPSO) on an operator's design flexibility are\ninappropriate where commensurate safety benefits are not evident.\nWe hope that this explains OPSO's position to your satisfaction and provides information which may be of help in deter-\nmining whether an installation is in compliance with Federal regulations.\nSincerely,\nSIGNED\nCesar DeLeon\nActing Director\nOffice of Pipeline\nSafety Operations\n\n<<<PAGE 3>>>\n\nArizona Corporation Commision\n222 West Encanto Blvd., Suite 210\nPhoenix, Arizona 85009\nJune 23, 1976\nMr. Cesar DeLeon\nOffice of Pipeline Safety Operations\nDepartment of Transportation\nWashington, D.C. 20590\nDear Cesar:\nIn a piped gas propane system during the summer time, the pressure on the LP storage tank is over 60 pounds. I have\ncited LP companies in the past for the lack of over-pressure protection of their distribution systems when fed with a\nsingle regulator set at 15 pounds. As a result, most have installed monitor regulators. However, one company is planning\non a relief valve. As I read the rules, there are three choices (condensed to simplify) that are legal to provide protection:\n(1) A monitor regulator\n(2) An automatic shutoff valve\n( 3 ) A relief valve\nFor a situation such as this a shutoff valve (2 above) is obviously undesirable as you lose the gas pressure in the system;\nand the system relight procedure must be implemented which is quite costly and disturbing to customers.\nI cannot condone the use of a relief (apparently legal) as it spills LP gas which is heavier than air, thus causing a hazard\ndue to the ground hugging characteristics. In this case the relief valve discharge is in a somewhat remote area; but, for\nexample, one can never be sure where kids will be.\nTo protect the system with monitors would be better, but with the vaporizer and piping arrangement at least three\nmonitors would be required. Therefore, the operator is installing a relief valve on the inlet to the system.\nI am suggesting that your technical section review the situation and make rule changes to eliminate the use of relief\nvalves on piped LP gas systems except when used as a second over-pressure device downstream of a monitor and\nworking regulator combination and as required on LP storage tanks.\nSincerely,\nARIZONA CORPORATION COMMISSION\nH. R. Garabrant, P.E.\nGas Utilities Safety Engineer\nUtilities Division","truncated":false,"body_characters":6799}