{"operation":"document","citation":"PI-82-002","title":"Wisconsin Public Service Commission — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"1982-02-01","effective_on":null,"summary":"PI-82-002 response to Wisconsin Public Service Commission concerning 192.201.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-82-002.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-82-002.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-82-002","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/1982/PI82002.pdf","body":"<<<PAGE 1>>>\n\nFebruary 1, 1982\nMr. William A. Slagg, P.E., Director\nGas Bureau, Engineering Division\nWisconsin Public Service Commission\nHill Farms State Office Building\nMadison, WI 53702\nDear Mr. Slagg:\nWe regret the delay in responding to your request for an interpretation of §192.201(a)(2)(i), and\nit is our conclusion that an interpretation, as such, is not necessary.\nYou are correct in stating that §192.201(a)(2)(i), when it states \"may not exceed,\" means \"may\nnever exceed.\"\nThe allowable override of 10 percent of the MAOP is included in the regulation which, for your\nexample, amounts to 6 psig. The MAOP plus the 6 psig equals 66 psig and not the 105 psig\nwhich the calculations, submitted by the operator, showed that the system could be subjected to\nfor 21 seconds.\nAccording to the relief regulator's manufacturer (see copy of Bulletin P-13F enclosed), the 2-inch\nmodel 63F back pressure regulator is undersized for this application.\nIf you have any further questions, please contact me.\nSincerely,\nMelvin A. Judah\nActing Associate Director\nfor Pipeline Safety Regulation\nMaterials Transportation Bureau\nEnclosure\ndal\\192\\201\\82-02-01\n1\n\n<<<PAGE 2>>>\n\nSeptember 29, 1980\nMr. Frank Fulton, Chief of Pipeline Safety\nEnforcement Division\nRoom 8430 NASSIF Building\n400 7th Street, South West\nWashington, DC 20590\nDear Mr. Fulton:\nThe Gas Bureau of the Public Service Commission of Wisconsin encountered a field problem\ninvolving the sizing of relief valves which we believe requires an interpretation of the gas safety\ncode by your office. The situation is not a particularly compli-\ncated one, per se, but neither is it an obvious one and the interpretation can have a considerable\neffect on both our inspec-\ntion procedures and the design criteria of the gas utilities in Wisconsin.\nSection 192.201 is entitled \"Required capacity of pressure relieving and limiting stations\" and\nstates in subsection 192.201(a)(2)(i) that \"If the maximum allowable operating pressure is 60 psig\nor more, the pressure may not exceed the maximum allowable operating pressure plus 10 percent\nor the pressure which produces a hoop stress of 75 percent of SMYS, whichever is lower.\"\nThe Wisconsin Gas Bureau has been interpreting the above usage of the term \"may not exceed\" as\n\"may never exceed\", (at least as far as overpressure relief design criteria are concerned) even for a\nperiod as short as a few seconds. Gas industry design criteria would appear to more generally\nbase its calculations on the hourly considerations. It is this variance in interpretations which we\nare asking to be resolved by your office.\nThe problem which illustrates the differences in interpretations resulted from the Gas Bureau\ninspection of the Browntown town border and district regulator stations. The first district\nregulator station in Browntown in 10,900 feet of 2-inch pipe (equivalent) downstream from the\ndal\\192\\201\\82-02-01\n2\n\n<<<PAGE 3>>>\n\ntown border station. The town border station supplies gas at 270 psig, which is assumed to be\nthe maximum pressure available at the first regulator station inlet. The outlet of this single, 2 inch\nbody, Fisher 57 \"S\" regulator supplies a distribution system with an MAOP of 60 psig which is\nprotected against overpressuring by a 2-inch Fisher 63F relief valve set at 66 psig with a rated\ncapacity of 186,000 cubic feet per hour. Calculations and flow chart data agree that the critical\nflow to this regulator station is 50,000 cubic feet per hour. Interpretation of the situation on an\nhourly basis\n2\nwould indicate that the overpressure relief capacity is more than adequate. Gas Bureau\ninterpretation of the attached data (supplied to us by the utility) would indicate that failure of the\nsingle regulator in a wide open position would subject the downstream distribution system to\npressures in excess of MAOP + 10% (up to 105 psig.) for up to 21 seconds and therefore, the\nrelief valve capacity is inadequate under subsection 192.201(a)(2)(i).\nOur analysis of the situation is that the single Fisher 57 \"S\" regulator in wide open position with\nany pressure at its inlet in excess of approximately 173 psig can supply more gas to the relief\nvalve than it can vent without increasing its inlet pressure (and thus the downstream system\npressure) above the MAOP plus 10% figure. In the \"worst case\" condition, the drawdown of the\nlinepack is a significant factor for some 21 seconds in the overpressuring situation. The data on\nthe attached lateral analysis sheets are from standard computations, flow chart review and\nmanufacturer's data.\nWe will be awaiting your interpretation.\nSincerely,\nWilliam A. Slagg, P.E., Director\nGas Bureau\nEngineering Division\ndal\\192\\201\\82-02-01\n3","truncated":false,"body_characters":4703}