{"operation":"document","citation":"PI-76-077","title":"Memo: Internal — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"1976-12-15","effective_on":null,"summary":"PI-76-077 response to Memo: Internal concerning 192.161.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-077.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-077.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-077","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/1976/PI76077.pdf","body":"<<<PAGE 1>>>\n\nDecember 15, 1976\nChief, Southern Region, MTP-50-SO\nActing Director, Office of Pipeline\nSafety Operations\nInterpretation of 192.161(d)(1)\nYour memorandum of August 20, 1976, asks, \"Are pipe stacks installed for the purpose of\ncontrolling relieved gas, under overpressure conditions, subject to rule 192.161(d)(1)?\"\nSection 192.161(d)(1) requires:\n(d) Each support on an exposed pipeline operated at a stress level of 50 percent or\nmore of SMYS must comply with the following:\n(1) A structural support must not be welded directly to the pipe.\nSection 192.3 defines the word \"pipeline\" as \"all parts of those physical facilities through which\ngas moves in transportation including pipe, valves, and other appurtenances attached to pipe,\ncompressor units, metering stations, regulator stations, delivery stations, holders and fabricated\nassemblies.\"\nThese pipe stacks do not contain gas in transportation but are only used to safely vent gas to\natmosphere that has been removed from the transportation system by the operation of an\nemergency relief valve. Thus, the vent pipe for a relief valve is not subject to these restrictions.\nWhen designing these pipe stacks, consideration must be given to the extreme forces and\nvibrations that often result from the discharge of a high pressure jet of gas. Stresses developed as\na result of this jet can cause failure of the stacks and may also be transferred to the relief valves\nand other pipeline facilities with a resulting possibility of failure. Considering the usual industry\npractice of designing discharge stacks for relief valves using pipe of equal or larger diameter than\nthe relief valve size and the fact that relief valves in a full open condition are operating at critical\nflow rates, it is doubtful that stress level due to internal gas pressure would reach 50 percent of\nSMYS. On a high pressure relief, the combined forces of valve vibration, gas stream thrust, and\nbending moments are very severe and must be considered in the design of the relief stack to\nprevent the failure of such piping.\nCesar DeLeon, MTP-1\ndal/192.161\n76-12-15\n1\n\n<<<PAGE 2>>>\n\nMEMORANDUM\nDATE: 8/20/76\nTO: Acting Director, MTP-1\nOffice of Pipeline Safety Operations\nFROM: Chief, Southern Region\nSUBJ: Interpretation of 192.161(d)(1)\nAre pipe stacks installed for the purpose of controlling relieved gas, under\noverpressure conditions, subject to rule 192.161(d)(1)?\nDuring normal operating conditions, these stacks would be under atmospheric\npressure.\nIf the answer is affirmative, I would also like a technical opinion as to whether,\nunder relieving conditions, it is reasonable to expect stack pressures similar to line\npressures when the stacks are essentially open ended.\nJames C. Thomas\ndal/192.161\n76-12-15\n2","truncated":false,"body_characters":2762}