{"operation":"document","citation":"PI-14-0016","title":"Northern Utilities / Unitil Corporation — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2015-04-21","effective_on":null,"summary":"PI-14-0016 response to Northern Utilities / Unitil Corporation concerning 192.201, 192.621.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-14-0016.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-14-0016.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-14-0016","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/2015/Northern_Utilities_Inc_PI_14_0016_04_21_2015_Part_192.pdf","body":"<<<PAGE 1>>>\n\nU.S. Department of Transportation\nPipeline and Hazardous Materials\nSafety Administration\n1200 New Jersey Ave, S.E.\nWashington, D.C. 20590\nAPR 21 201S\nMr. Christopher J. LeBlanc\nDirector, Gas Operations\nUnitil Corporation\n325 West Road\nPortsmouth, NH 03 801\nDear Mr. LeBlanc:\nIn a letter to the Pipeline and Hazardous Materials Safety Administration (PHMSA) dated\nSeptember 5, 2014, on behalf ofNorthern Utilities, Inc. (Northern), Unitil requested an\ninterpretation on the applicability of the Federal gas pipeline safety regulations at 49 CFR\nPart 192. Specifically, you asked about the requirements for maximum allowable operating\npressure (MAOP) and system pressures during normal operation of a gas distribution system and\nduring a system emergency caused by the failure of pressure regulating equipment.\nYou explained your system as follows: Northern operates a pressure regulating station at the\npoint on its distribution system where it takes gas from Granite State Gas Interstate transmission\npipeline. 1 At the point of interconnection, the Granite State pipeline is operated at a MAOP of\n492 psig. The MAOP ofNorthern's downstream distribution system is 56 psig. Northern's\nfacilities at the station are configured as a dual-run. Run 1 is the primary run. Run 2 serves as a\nback-up if Run 1 were ever to fail in the closed position (diagram of the line was provided).\nEach Run is equipped with a \"worker\" regulator and a \"monitor\" regulator. On Run 1, the set\npoint on the \"worker\" regulator is 53 psig. The set point on the \"monitor\" regulator is 55 psig.\nA pressure gage is installed approximately six feet downstream of the pressure regulation\nequipment. The company's supervisory control and data acquisition (SCADA) system monitors\na pressure sensor that is at the end of the distribution system (at the furthest point downstream of\nthe regulator station). Recently, a failure of the worker regulator was simulated to assess the\noperation ofNorthern's over pressure protection. As the worker regulator failed the adjacent\ndownstream pressure gauge indicated a gradual increase in pressure to 57.2 psig for\napproximately one minute, after which the pressure returned to and remained at the 55 psig set\npoint ofthe monitor regulator. At no point during the simulation did the pressure rise above\n57.2 psig. Northern believes that the observed pressure increase to 57.2 psig for approximately\none minute resulted from the normal build-up pressure due to the mechanical operation of the\nmonitor regulator. This assessment has been confirmed by the manufacturer of the regulator.\n1 Northern and Granite State are wholly owned subsidiaries of Unitil Corporation.\nThe Pipeline and Hazardous Materials Safety Administration, Office of Pipeline Safety provides written\nclarifications of the Regulations ( 49 CFR Parts 190-199) in the form of interpretation letters. These letters reflect\nthe agency's current application of the regulations to the specific facts presented by the person requesting the\nclarification. Interpretations do not create legally-enforceable rights or obligations and are provided to help the\npublic understand how to comply with the regulations.\n\n<<<PAGE 2>>>\n\n2\nDuring this simulated failure, the SCADA pressure sensor at the end of the Northern system did\nnot register a pressure increase to 57.2 psig. The SCADA pressure sensor registered a pressure\nof 53 psig before the failure simulation, and a pressure of 55 psig after the failure simulation\nuntil the worker regulator was returned to service at 53 psig.\nBased on the above information, Northern requests interpretation on the following two issues:\n1. 2. During normal operation (i.e., no system emergency) of a high pressure distribution\nsystem with a properly established MAOP of 56 psig, does the operator violate\n§ 192.621(a) ifthe system is operated above 56 psig?\nDuring a system emergency, such as a failed worker regulator, on a high pressure\ndistribution system with a properly established MAOP of 56 psig, does the operator\nviolate§ 192.201(a) if the system pressure does not exceed 62 psig?\nSection 192.621(a) states:\n(a) No person may operate a segment of a high pressure distribution system at a pressure\nthat exceeds the lowest of the following pressures, as applicable:\n(1) The design pressure of the weakest element in the segment, determined in accordance\nwith subparts C and D of this part.\n(2) 60 psi ( 414 kPa) gage, for a segment of a distribution system otherwise designed to\noperate at over 60 psi ( 414 kPa) gage, unless the service lines in the segment are\nequipped with service regulators or other pressure limiting devices in series that meet the\nrequirements of§ 192. i 97( c).\n(3) 25 psi (172 kPa) gage in segments of cast iron pipe in which there are unreinforced\nbell and spigot joints.\n( 4) The pressure limits to which a joint could be subjected without the possibility of its\nparting.\n(5) The pressure determined by the operator to be the maximum safe pressure after\nconsidering the history of the segment, particularly known corrosion and the actual\noperating pressures.\nResponse 1- Yes, the operator violates § 192.621 (a) if the MAOP is exceeded during normal\noperating conditions. Under the regulation, operators must use pipeline pressure\ncontrol equipment sized for pressure control with pressure sensors, actuators and\ncontrol or relief valves that react in a timely manner and have pressure settings\nthat do not exceed MAOP in accordance with Part 192.\nSection 192.201(a) states:\n(a) Each pressure relief station or pressure limiting station or group of those stations\ninstalled to protect a pipeline must have enough capacity, and must be set to operate, to\ninsure the following:\nThe Pipeline and Hazardous Materials Safety Administration, Office of Pipeline Safety provides written\nclarifications of the Regulations ( 49 CFR Parts 190-199) in the form of interpretation letters. These letters reflect\nthe agency's current application of the regulations to the specific facts presented by the person requesting the\nclarification. Interpretations do not create legally-enforceable rights or obligations and are provided to help the\npublic understand how to comply with the regulations.\n\n<<<PAGE 3>>>\n\n3\n(1) In a low pressure distribution system, the pressure may not cause the unsafe operation\nof any connected and properly adjusted gas utilization equipment.\n(2) In pipelines other than a low pressure distribution system:\n(i) If the maximum allowable operating pressure is 60 psi ( 414 kPa) gage or more, the\npressure may not exceed the maximum allowable operating pressure plus 1 0 percent, or\nthe pressure that produces a hoop stress of75 percent ofSMYS, whichever is lower;\n(ii) If the maximum allowable operating pressure is 12 psi (83 kPa) gage or more, but less\nthan 60 psi ( 414 kPa) gage, the pressure may not exceed the maximum allowable\noperating pressure plus 6 psi (41 kPa) gage; or\n(iii) If the maximum allowable operating pressure is less than 12 psi (83 kPa) gage, the\npressure may not exceed the maximum allowable operating pressure plus 50 percent.\nResponse 2-No, the operator does not violate§ 192.201(a) as long as the MAOP limits are met\nduring a system emergency and the pipeline meets the Subpart D - Design of\nPipeline Components requirements. In this case, the emergency operating limit is\n62 psi (56+ 6 psi). Emergency operating overpressure conditions are only allowed\nfor the time required to activate the overpressure protection device and are not\nmeant for long term or frequently occurring normal operating or periodic\nmaintenance conditions and, therefore, require immediate response by the operator\neither to shut down or reduce the operating pressure to the normal operating\nconditions.\nFinally, we would note that based upon your actions described in your letter, there may be some\nconfusion about appropriate testing and maintenance of a pressure limiting or regulator station\nfor buildup and set point. Conducting a simulated test on a pressure limiting or regulator station\nthat is not isolated from the system does not constitute a system emergency. It is a normal\noperation subject to the limitations described above. The pressure limiting or regulator station\nshould be isolated from the system prior to any testing of buildup and set points.\nIf we can be of further assistance, please contact Tewabe Asebe of my staff at 202-366-5523.\nSincerely,\nDirector, Office of Standards\nand Rulemaking\nThe Pipeline and Hazardous Materials Safety Administration, Office of Pipeline Safety provides written\nclarifications of the Regulations ( 49 CFR Parts 190-199) in the form of interpretation letters. These letters reflect\nthe agency's current application ofthe regulations to the specific facts presented by the person requesting the\nclarification. Interpretations do not create legally-enforceable rights or obligations and are provided to help the\npublic understand how to comply with the regulations.\n\n<<<PAGE 4>>>\n\n0 Unitil\nSeptember 5, 2014\nMr. Jeff Wiese\nAssociate Administrator\nU.S. Department of Transportation\nPipeline and Hazardous Materials Safety Administration\nEast Building, 2nd Floor\n1200 New Jersey Ave., SE\nWashington, DC 20590\nDear Mr. Wiese:\nI am writing on behalf of Northern Utilities, Inc. d/ b/ a Unitil (\"Northern\") to request\nan interpretation from the Pipeline and Hazardous Materials Safety Administration\n(\"PHMSA\") on two questions regarding the requirements of 49 C.F.R. Part 192\nconcerning maximum allowable operating pressure (\"MAOP\"). Our questions relate to\nMAOP and system pressures during normal operation of a distribution system and\nduring a system emergency caused by the failure of pressure regulating equipment.\nWe believe some pertinent background on our distribution system configuration and\nthe results of a recent regulator station failure simulation would be helpful to you.\nSystem Configuration\nNorthern operates a pressure regulating station at the point on its distribution system\nwhere it takes gas from Granite State Gas Transmission, Inc.'s (\"Granite State\")\ninterstate transmission pipeline.\n1 Attachment A is a schematic of the station, which I\nam providing for your reference.\nGranite State's system at the point of interconnection is operated at an MAOP of 492\npsig. The MAOP of Northern's downstream distribution system is 56 psig.\nNorthern's facilities at the station are configured as a dual-run. Run 1 on Attachment\nA is the primary run. Run 2 serves as a back-up if Run 1 were ever to fail in the closed\nposition.\nEach Run is equipped with a \"worker\" regulator and a \"monitor\" regulator. On Run 1,\n1 Northern and Granite State are wholly owned subsidiaries of Unitil Corporation.\nChristopher J . LeBlanc\nDirector, Gas Operations\nleblanc@unitil.com\nT 603.294.5166 C 978.833.1225 www.unitil.com\n325 West Road\nPortsmouth, NH 03801\n\n<<<PAGE 5>>>\n\nMr. Jeff Wiese\nSeptember 5, 2014\nPage 2 of 7\nthe set point on the \"worker\" regulator is 53 psig, which is 3 psig below the Northern\nsystem MAOP. The set point on the \"monitor\" regulator is 55 psig, which is 1 psig\nbelow the Northern system MAOP.\nThis configuration is designed to provide over pressure protection as follows: if the\n\"worker\" regulator (set at 53 psig) were to ever fail to control downstream system\npressure, the \"monitor\" regulator would limit the downstream system pressure on\nNorthern's system to 55 psig (1 psig below MAOP).\nA pressure gage is installed approximately six feet downstream of the pressure\nregulation equipment. The Company's SCADA system monitors a pressure sensor that is\nat the end of the distribution system (in other words, at the furthest point\ndownstream of t he regulator station).\nFailure Simulation\nRecently, a failure of the worker regulator was simulated to assess the operation of\nNorthern's over pressure protection. As the worker regulator was failed the following\nwas observed: the adjacent downstream pressure gauge indicated a gradual increase\nin pressure to a high of 57.2 psig for approximately one minute, after which the\npressure returned to, and remained at, the 55 psig set point of the monitor regulator.\nAt no point during the simulation did the pressure rise above 57.2 psig. Northern\nbelieves that the observed pressure increase to 57.2 psig for approximately one\nminute resulted from the normal build-up pressure due to the mechanical operation of\nthe monitor regulator. Unitil's assessment has been confirmed by the manufacturer of\nthe regulator.\nDuring this simulated failure, the SCADA pressure sensor at the end of the Northern\nsystem did not register a pressure increase to 57.2 psig. The SCADA pressure sensor\nregistered a pressure of 53 psig before the failure simulation, and a pressure of 55 psig\nafter the failure simulation until the worker regulator was returned to service at 53\npsi g.\nQuestions for Interpretation\nNorthern requests interpretation from PHMSA on two issues:\n( 1) During normal operation (i.e., no system emergency) of a high pressure\ndistribution system with a properly established MAOP of 56 psig, does the\noperator violate 49 C. F.R. § 192.621 (a) if the system is operated above 56 psig?\n(2) During a system emergency, such as a failed worker regulator, on a high\npressure distribution system with a properly established MAOP of 56 psig, does\nthe operator violate 49 C. F. R. § 192.201 (a) if the system pressure does not\nChristopher J. LeBlanc\nDirector, Gas Operations\nleblanc@unitil.com\nT 603.294.5166 C 978.833.1225 www.unitil.com\n325 West Road\nPortsmouth, NH 03801\n\n<<<PAGE 6>>>\n\nMr. Jeff Wiese\nSeptember 5, 2014\nPage 3 of 7\nexceed 62 psig?\nA. Northern's Position.\nNorthern believes that the answer to Question 1 is \"yes,\" an operator violates the code\nif during normal operations it purposefully operates the system above its property\ndetermined MAOP. Although Part 192 does not permit a system to be operated above\nMAOP, the code does allow system pressures that are slightly above MAOP caused by a\nfailure of pressure regulating equipment. For a high pressure distribution system with\nan MAOP of 56 psig, Section 192.201 (a)(2) allows the maximum system pressure during\na system emergency to be no greater than 6 psig over MAOP, or 62 psig. Therefore,\nNorthern believes that the answer to Question 2 is \"no,\" there is not a code violation if\nthe system pressure is 62 psig or lower during a system emergency. The rest of this\nletter explains Northern's position in greater detail.\nB. Code Analysis.\nMAOP is defined in 49 C.F.R. § 192.3 (Definitions) as \"the maximum pressure at which a\npipeline or segment of a pipeline may be operated under this part.\" Section 192.619\nprovides the means for determining MAOP for plastic and steel pipelines, Section\n192.621 provides the means for determining MAOP for high pressure distribution\nsystems and Section 192.623 provides the means for determining MAOP for low\npressure distribution systems. Specifically, Section 192.621 (a) begins as follows:\n(a) No person may operate a segment of a high pressure distribution\nsystem at a pressure that exceeds the lowest of the following pressures,\nas applicable ....\nSection 192.621 (a), therefore, prohibits the \"operation\" of a distribution system at a\npressure that exceeds the lowest of several pressures stated in Section 192.621 (a).\nAlthough \"operate\" is not defined in Part 192, based on the context in which it is used\nin Part 192 we believe \"operate\" refers to the normal day-to-day operation of the\nsystem, and is not intended to include a system emergency caused by the failure of a\nworker regulator. See 49 C.F.R. § 192.605(a) (requiring operators to prepare and\nfollow \"a manual of written procedures for conducting operations and maintenance\nactivities and for emergency response); 49 C.F.R. § 192.605(b) (listing procedures that\nmust be included in the O&M manual for \"maintenance and normal operations\" of\nsystem).\nAccordingly, we believe that maximum allowablr operating pressure is exactly what it\nsays it is: the maximum pressure at which a system can be operated under normal\noperating conditions. Therefore, Northern believes that the answer to Question 1 is\nyes, an operator violates the code if during normal operations it purposefully operates\nthe system above its properly determined MAOP (which is 56 psig in the Northern\nChristopher J. LeBlanc\nDirector, Gas Operations\nleblanc@unitil.com\nT 603.294.5166 C 978.833.1225 www.unitil.com\n325 West Road\nPortsmouth, NH 03801\n\n<<<PAGE 7>>>\n\nMr. Jeff Wiese\nSeptember 5, 2014\nPage 4 of 7\nexample we have given).\nAlthough MAOP addresses normal operating conditions, Part 192 recognizes that events\ncan happen through component failures that the system must be designed to\nwithstand. For example, Subpart D of Part 192 (Design of Pipeline Components) states\nthat it:\nPrescribes minimum requirements for the design and installation of\npipeline components and facilities . . . In addition, it prescribes\nrequirements relating to protection against accidental over pressuring.\n49 C.F.R. § 192.141 (Scope of Subpart D).\nOne of the provisions in Subpart D that relates to protection against \"accidental over\npressuring\" is Section 192.195:\n§ 192.195 Protection against accidental over pressuring.\n(a) General requirements. Except as provided in §192.197, each\npipeline that is connected to a gas source so that the maximum\nallowable operating pressure could be exceeded as the result of\npressure control failure or of some other type of failure, must have\npressure relieving or pressure limiting devices that meet the\nrequirements of §§192.199 and 192.201 . . ..\nUnder Section 192.195, when pressure on a pipeline could exceed MAOP due to failure\nof a pressure control device, the pipeline must have pressure relieving or pressure\nlimiting devices that meet the requirements of Section 192.201 . Section 192.201\nstates:\n§192.201 stations.\nRequired capacity of pressure relieving and limiting\n(a) Each pressure relief station or pressure limiting station or group of\nthose stations installed to protect a pipeline must have enough\ncapacity, and must be set to operate, to insure the following:\n* * It *\n(2) In pipelines other than a low pressure distribution system:\n(i) If the maximum allowable operating pressure is 60\np.s.i. (414 kPa) gage or more, the pressure may not\nChristopher J. LeBlanc\nDirector, Gas Operations\nleblanc@unitil.com\nT 603.294.5166 C 978.833. 1225 www.unitil.com\n325 West Road\nPortsmouth, NH 03801\n\n<<<PAGE 8>>>\n\nMr. Jeff Wiese\nSeptember 5, 2014\nPage 5 of 7\nexceed the maximum allowable operating pressure plus\n10 percent, or the pressure that produces a hoop stress of\n75 percent of SMYS, whichever is lower;\n(ii) If the maximum allowable operating pressure is 12\np.s. i. (83 kPa) gage or more, but less than 60 p.s. i. (414\nkPa) gage, the pressure may not exceed the maximum\nallowable operating pressure plus 6 p.s.i. (41 kPa) gage;\nor\n(iii) If the maximum allowable operating pressure is less\nthan 12 p.s. i. (83 kPa) gage, the pressure may not exceed\nthe maximum allowable operating pressure plus 50\npercent.\nUnder Section 192.201 (a)(2), pressure relief and pressure limiting stations for the\nprotection of high pressure systems must be set to operate at no more than a specified\npressure in excess of MAOP. This pressure difference between MAOP and the\nmaximum pressure is determined based on the system's MAOP. For systems with an\nMAOP between 11 and 59 psig, the pressure regulator used for pipeline protection can\nbe set to achieve a system pressure that is no more than 6 psig above the system\nMAOP. For a 56 psig high pressure system, the overpressure protection monitor\npressure regulator must be set to a set point no greater than 61 psig.\nThis 6 psig pressure difference is necessary to allow the system to be operated at its\nMAOP, while also allowing overpressure protection devices to operate properly without\ninterfering with system pressure regulation. In a worker-monitor configuration such as\nNorthern's, there must be enough separation between the set points of the worker\nregulator and monitor regulator so they do not \"fight\" for control of system pressure.\nThis \"fighting\" results from the typical operation of a pressure regulator, including the\nnormal pressure build-up when a regulator takes control of system pressure.\n2 When\nthe regulators \"fight,\" the result is unstable system operation, pressure surges, and\npremature wear of the regulator components (such as diaphragms and springs). When\n2 If the set points for the worker regulator and the monitor regulator are too close, they will\nfight to control the system pressure due to the normal operating characteristics of pressure\nregulators. Consider, for example, a system where the set point for the monitor regulator is\nset only 1 psig higher than the set point for the worker regulator. During normal operation of\nthe worker regulator, it will open and close to maintain pressure at its set point. When the\nmonitor regulator senses the system pressure at its set point, it will begin to close, causing\nsystem pressure to decrease and then reopen as it senses the system pressure decrease. The\nworker, in response to decreasing pressure caused by the monitor closing, will re-open, and the\nmonitor will again begin to close, setting up a cycle where the two regulators alternate back\nand forth or \"fight\" for control.\nChristopher J. LeBlanc\nDirector, Gas Operations\nleblanc@unitil.com\nT 603.294.5166 C 978.833.1225 www.unitil.com\n325 West Road\nPortsmouth, NH 03801\n\n<<<PAGE 9>>>\n\nMr. JeffWiese\nSeptember 5, 2014\nPage 6 of 7\nthere is sufficient separation between the set points for the worker and monitor, there\nis no \"fighting\" between the two regulators. The worker can do its job maintaining\nsystem pressure, and the monitor can stand by ready to regulate system pressure if\nthe worker malfunctions such that it fails to regulate downstream pressure.\nSection 192.201 (a)(2) allows overpressure protection to be effective and avoids\n\"fighting\" regulators. The 6 psig difference for 12-59 psig MAOP systems allows the\ntwo regulators to each serve their respective function without interference by the\nother regulator. If the worker regulator fails to regulate downstream system pressure,\nthe monitor regulator will take control and regulate system pressure at a pressure that\ncould exceed MAOP, but not so much greater than MAOP that it would compromise the\nsafety or integrity of the system while the worker regulator is repaired or replaced.\nFinally, it is important to understand that the code recognizes that pressure regulators\nare mechanical devices that naturally experience \"build-up\" pressure situations.\nSection 192.605(b) lists the requirements of an operator's O&M manual. Section\n192.605(b)(5) requires the O&M manual to include procedures for:\n(5) Starting up and shutting down any part of the pipeline in a manner\ndesigned to assure operation within the MAOP limits prescribed by this\npart, plus the build-up allowed for operation of pressure-limiting and\ncontrol devices.\nSection 192.605(b)(5) takes into consideration that pressure limiting and\ncontrol devices have \"allowed\" build-up pressures, and during start up and shut\ndown these pressure build-ups may temporarily result in a system pressure that\nexceeds MAOP. These build-up pressures are exactly what Northern\nexperienced when the failure of the worker regulator was simulated and the\nmonitor regulator set at 55 psig allowed the system pressure to rise to 57.2 psig\nfor about a minute during pressure build-up before returning the system\npressure to t he monitor regulator's 55 psig set point (which was still below the\n56 psig system MAOP). What Northern experienced was simply the acceptable\nbuild-up pressure that is normal for a monitor regulator used to prevent system\nover pressuring. And, in any event, the pressure on the system never exceeded\nthe allowed 62 psig, even at the pressure gauge that is adjacent to the point of\nregulation.\nFor these reasons, Northern believes that the answer to Question 2 is \"no,\"\nthere is no violation of the Code if during a system emergency (such as the\nfailure of a worker regulator) the pressure on a 56 psig MAOP high-pressure\nsystem rises above MAOP but does not exceed 62 psig.\nChristopher J. LeBlanc\nDirector, Gas Operations\nleblanc@unitil.com\nT 603.294.5166 C 978.833.1225 www.unitil.com\n325 West Road\nPortsmouth, NH 03801\n\n<<<PAGE 10>>>\n\nMr. JeffWiese\nSeptember 5, 2014\nPage 7 of7\nWe look forward to your response to the questions we have presented. If you\nneed any further background information, or if anything in this letter needs\nclarification, I hope you will not hesitate to call me.\nSincerely\nChristopher J . LeBlanc\nDirector, Gas Operations\nChristopher J. LeBlanc\nDirector, Gas Operations\nleblanc@unitil.com\nT 603.294.5166 C 978.833.1225 www.unitil.com\n325 West Road\nPortsmouth, NH 03801\n\n<<<PAGE 11>>>\n\n= Granite state bes\n(mAop 492)\nGRANITE STATES GAS\nM&R STATION\nPEASE AFB\nROCKINGHAM, NH\nAdig\n) FIL TER\n6'Pv\n4 Pr\n2'BV METER 4'BV\n* set point\nHOOT\n•BV\n20\nREGÚLATOR REGULATOR\nset point. 55\n28V\nGS\nRun 1\n2°BV\nNORTHERN\nmaop 56psig\nTO UTILITIES\nREGULATOR REGULATOR\nlocation\nsure\nPressure\nGage","truncated":false,"body_characters":25160}