{"operation":"document","citation":"PI-76-051","title":"Arizona Corporation Commission — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"1976-09-02","effective_on":null,"summary":"PI-76-051 response to Arizona Corporation Commission concerning 192.195.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-051.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-051.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-051","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/1976/PI76051.pdf","body":"<<<PAGE 1>>>\n\nSep 02 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\npetroleum gas systems, stating that the pressure in the storage tank exceeds 60 psig during\nsummer, and suggests a technical review and \"rule changes to eliminate the use of relief valves on\npiped LP gas systems except when used as a second overpressure device downstream of a\nmonitor 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\nis not readily apparent from the information presented. Further discussion, therefore, seems\nappropriate solely for clarification and to avoid any possibility of misinterpretation. Title 49 CFR\nSection 192.195 requires that pressure limiting or relieving devices must be provided so that the\nmaximum 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\nthe system must have properly designed pressure regulation devices which can be activated in the\nevent of some failure and will prevent overpressuring.\nThe criteria for determining whether a requirement exists for a monitor, relief, automatic shut off,\nor other arrangement for overpressure protection, thereby, is the MAOP of the pipeline and not\nnecessarily a system pressure in excess of 60 psig.\nA maximum actual operating pressure of 60 psig for a distribution system is applicable as criteria\nonly in connection with service regulator requirements. As set forth in 49 CFR Section 192.197,\npressure limiting or relief devices are required in addition to the service regulator if system\npressure exceeds 60 psig, but for distribution pressures below 60 psig, no pressure limiting device\nis 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\nthe MAOP of the referenced systems is 60 psig or that the services are not equipped with pressure\nlimiting or relief devices.\ndal\\192\\195\\76-09-02\n1\n\n<<<PAGE 2>>>\n\nRegarding your suggestion that Federal regulations be changed with respect to the use of relief\nvalves on petroleum gas systems, a review by this Office has concluded that the initiation of rule\nmaking procedures for such modification is unwarranted for the following reasons:\n1. 2. 3. 4. Current Federal regulations, prescribing requirements for the characteristics,\napplication and installations of pressure relief devices, provide adequate and\nappropriate levels of safety. Federal Standard, 49 CFR Section 192.11,\nincorporates NFPA Standards No. 58 and 59 by reference but significantly\nprescribes that Part 192 shall prevail in the event of conflict. Paragraph (b)(3) of\nSection 192.11 particularly provides that discharge vents from relief valves must\nbe located so as to prevent any accumulation of gas at or below ground, and 49\nCFR Section 192.199(e), reinforcing this requirement, specifies that a pressure\nrelief device must have discharge stacks, vents, or outlet ports located where gas\ncan be discharged into the atmosphere without undue hazard.\nNumerous other requirements of Part 192 and NFPA 58 provide extensive coverage of\nthe design, application, and installation of relief devices, and since relief devices may not\nbe installed where discharged gas will accumulate on the ground or cause undue hazard,\nthe expressed central concern is null.\nPressure relieving devices in most instances are the only practicable means of providing\noverpressure protection for vaporizers, containers, and hydrostatic relief between valves.\nNFPA 58 Section 314 requires that regulators used to control distribution or utilization\npressure be as close to the container as practicable. Since other required pressure\nrelieving 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.\nIn certain circumstances, such as a small closed distribution system, a pressure relief\ndevice may be the best means of assuring safety from overpressure.\nConstraints imposed by the Office of Pipeline Safety Operations (OPSO) on an operator's\ndesign flexibility are inappropriate where commensurate safety benefits are not evident.\nWe hope that this explains OPSO's position to your satisfaction and provides information which\nmay be of help in determining whether an installation is in compliance with Federal regulations.\nSincerely,\ndal\\192\\195\\76-09-02\n2\n\n<<<PAGE 3>>>\n\nCesar DeLeon\nActing Director\nOffice of Pipeline\nSafety Operations\ndal\\192\\195\\76-09-02\n3\n\n<<<PAGE 4>>>\n\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\nover 60 pounds. I have cited LP companies in the past for the lack of over-pressure protection of\ntheir distribution systems when fed with a single regulator set at 15 pounds. As a result, most\nhave installed monitor regulators. However, one company is planning on a relief valve. As I read\nthe 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\npressure in the system; and the system relight procedure must be implemented which is quite\ncostly and disturbing to customers.\nI cannot condone the use of a relief (apparently legal) as it spills LP gas which is heavier than air,\nthus causing a hazard due to the ground hugging characteristics. In this case the relief valve\ndischarge is in a somewhat remote area; but, for example, one can never be sure where kids will\nbe.\nTo protect the system with monitors would be better, but with the vaporizer and piping\narrangement at least three monitors would be required. Therefore, the operator is installing a\nrelief valve on the inlet to the system.\nI am suggesting that your technical section review the situation and make rule changes to\neliminate the use of relief valves on\ndal\\192\\195\\76-09-02\n4\n\n<<<PAGE 5>>>\n\npiped LP gas systems except when used as a second over-pressure device downstream of a\nmonitor and working regulator combination and as required on LP storage tanks.\nSincerely,\nARIZONA CORPORATION COMMISSION\nH.R. Garabrant, P.E.\nGas Utilities Safety Engineer\nUtilities Division\ndal\\192\\195\\76-09-02\n5","truncated":false,"body_characters":6829}