{"operation":"document","citation":"PHMSA FIR, Northern Natural Gas Co, 2008-05-23","title":"Failure Report- Northern Natural Gas Co 5/23/08","source_type":"incident","agency":"Pipeline and Hazardous Materials Safety Administration","status":"historical","official":true,"published_on":"2016-04-08","effective_on":"2008-05-23","summary":"Northern Natural Gas Co; Gas Transmission; MN; failure 2008-05-23; apparent cause: Natural Forces Damage.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-fir-failure-report-northern-natural-gas-co-52308.json","markdown":"https://regulus.evalyn.ai/document/phmsa-fir-failure-report-northern-natural-gas-co-52308.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-fir-failure-report-northern-natural-gas-co-52308","source_url":"https://www.phmsa.dot.gov/safety-reports/failure-report-northern-natural-gas-co-52308","body":"<<<PAGE 1>>>\n\nDOT US Department of Transportation\nPHMSA Pipelines and Hazardous Materials Safety Administration\nOPS Office of Pipeline Safety\nCentral Region\nPrincipal Investigator MNOPS/James Bunn/Karen Butler\nRegion Director Allan Beshore\nDate of Report 11/14/2014\nSubject Failure Investigation Report – Northern Natural Gas Co (NNG) –\nNatural Force Damage\nOperator, Location, & Consequences\nDate of Failure 05/23/2008\nCommodity Released Natural Gas\nCity/County & State Beaver Bay / Lake, Minnesota\nOpID & Operator Name 13750 Northern Natural Gas Co\nUnit # & Unit Name 903 Carlton [IA] (NNG) (NNG)\nSMART Activity # 124375\nMilepost / Location MP 59.5, Reserve Mining Branch Line MNB72701\nType of Failure Natural Force Damage, crack in a dent\nFatalities 0\nInjuries 0\nDescription of Area\nimpacted\nRural, Class 1, Non-HCA\nTotal Costs $530,000\n\n<<<PAGE 2>>>\n\nFailure Investigation Report – Northern Natural Gas Co – Natural Force Damage\nFailure Date 05/23/2008\nExecutive Summary\nOn May 23, 2008, an instrumented aerial leak survey was in progress by a contracted service for\nNorthern Natural Gas Company (NNG). During this leak survey, a leak was discovered in the Reserve\nMining Branch Line (MNB72701) at approximately 2:57 p.m. CDT. Local field personnel were notified\ndirectly from the contracted leak survey service. The NNG control center was contacted by field\npersonnel and began to reduce operating pressure (405 psig to approximately 275 psig). This pipeline\nserves the Reserve Mine and three additional towns in Minnesota. The leak was physically located at\napproximately 7:00 p.m. CDT by NNG field personnel at MP 59.5 in Lake County, Minnesota,\napproximately 1.1 miles northeast of the intersection of County Road 3 and County Road 4. The leak\nwas not located in an HCA. There were no reported evacuations, road closings, fires, injuries or fatalities\nas a result of the leak. The state partner, Minnesota Office of Pipeline Safety (MNOPS), investigated the\nrelease on-site. The leak originated at a 1-inch long crack that was located in a dent on the bottom of\nthe pipe. The pipe was found to be resting on a sharp piece of granite. The original construction of the\npipeline was in 1961. Ground subsidence was reported to have caused the dented pipe to fail. Weather\nand contract resource availability delayed the installation of a 16-inch Type B repair sleeve. The pipeline\nrepair work was completed on June 3, 2008. The operator has estimated the cost of this incident to be\n$530,000.\nAfter the incident, NNG ran High Resolution MFL and Caliber tools on the Reserve Mining Branch Line\nand discovered six dents with metal loss. MNOPS completed a follow-up inspection in 2009 and\nconfirmed that all six dents with metal loss were scheduled for repair by May of 2010. All repairs have\nbeen completed.\nSystem Details\nThe Northern Natural Gas Pipe Line system consists of approximately 15,000 miles of pipelines and\nstorage facilities. The system transports natural gas from the gathering fields in New Mexico, Texas,\nOklahoma and Kansas to market areas in the upper Midwest. The Reserve Mining Branch Line is part of\nthe Northern Branch System and provides natural gas to the mine as well as three towns including\nBeaver Bay and Silver Bay, Minnesota. The portion of the pipeline containing the failure was composed\nof 16-inch diameter by 0.219-inch wall thickness, API 5L X52, low frequency ERW line pipe manufactured\nby Republic Steel with coal tar enamel as the external coating and was cathodically protected. The\npipeline was installed in 1961.\nEvents leading up to the Failure\nThe maximum allowable operating pressure (MAOP) of the pipeline is 425 psig, which corresponds to a\nhoop stress level of 30 percent of the specified minimum yield strength (SMYS) of the pipe. The\npressure at the time and location of failure was 405 psig, which corresponds to a hoop stress of 29\npercent (95 percent of MAOP). The MAOP for the Reserve Mining pipeline was reported to be\nestablished in accordance with 192.619 (a) (4), the pressure determined by the operator to be the\nmaximum safe pressure after considering the history of the segment.\nPage 2 of 4\n\n<<<PAGE 3>>>\n\nFailure Investigation Report – Northern Natural Gas Co – Natural Force Damage\nFailure Date 05/23/2008\nEmergency Response\nThe pressure in the line at the time of detection of the leak was 405 psig. When the Control Center was\nnotified of the potential leak, actions to reduce line pressure were implemented. The pressure in the\npipeline was ultimately reduced to a pressure of approximately 275 psig. The area around the leak was\nsecured until repairs could be made. NNG reported the incident to the NRC at 6:27 p.m. CDT on May 23,\n2008.\nReturn to Service\nBetween May 23, 2008, and May 29, 2008, delays to repair activities occurred due to weather and\ncontract resource availability. On May 29, 2008, NNG began excavation activities in order to install\nstopple fittings. After the fittings were installed, a bypass was constructed around the leak area. The\nsection of the line that contained the leak was blown down and the line was excavated to expose the\nleak. The pipe was resting on a piece of granite at the leak location. A dent had formed in the pipe\nwhere it was resting on the rock. The dent was approximately 11 inches long, 7 inches wide and 0.903\ninches deep. The bottom of the dent contained a thru-wall crack that was approximately 1 inch long.\nThe repair to the failed section of pipe was made with a 16-inch Type B weld sleeve approximately 24\ninches long. On June 3, 2008, repair work was completed and the pipeline returned to normal service.\nInvestigation Details\nAngel Service ITT was conducting an aerial leak survey on the Reserve Mining Branch Pipeline on March\n23, 2008. The aerial leak survey contractor identified a potential leak site on the pipeline route and\nnotified NNG personnel at the NNG Carlton Compressor Station of the findings at approximately 2:57\np.m. CDT. Carlton personnel notified the NNG Control Center of the potential leak and the Control\nCenter began to reduce the pressure in the line. NNG dispatched a crew to the site of the potential leak\nwith a flame ionization unit. When the crew reached the area of the leak, the leak was confirmed when\nan area of dead vegetation was observed and a reading of 5 percent Lower Explosive Limit was\nmeasured. NNG secured the site and continued to monitor the atmosphere until a stopple bypass could\nbe installed and the leak site could be excavated. After the line was excavated it was found to be resting\non a sharp piece of granite at the leak location. A dent had been formed in the pipe body where the\npipe was resting on the granite. A 1-inch long thru-wall crack was found in the bottom of the dent. The\nrepair to the failed section of pipe was made with a 16-inch Type B weld sleeve approximately 24 inches\nlong. On June 3, 2008, repair work was completed and the pipeline returned to normal service.\nIn February of 2009, NNG completed High Resolution MFL and Caliber tools on the Reserve Mining\nBranch pipeline. MNOPS reviewed the information associated with the Inline inspection (ILI) during an\ninspection in May of 2009 (inspection was called the Welcome audit). The ILI run determined that there\nwere no immediate repairs required, 28 scheduled repairs, and six dents with metal loss (wall loss less\nthan or equal to 5 percent). All six dents were reported by the operator as occurring outside of a High\nConsequence Area and were repaired by May of 2010.\nFindings & Contributing Factors\nThe failure origin was a 1-inch crack located in a dent in the pipe body. The crack was located in the\nPage 3 of 4\n\n<<<PAGE 4>>>\n\nFailure Investigation Report – Northern Natural Gas Co – Natural Force Damage\nFailure Date 05/23/2008\nbottom of a dent that measured approximately 11 inches in length, 7 inches circumferentially and 0.903\ninches deep. A rock that was impinging on the pipeline at the 6 o’clock position caused the dent.\nGround subsidence, combined with the impinging rock, caused the dented pipe to fail.\nAppendix Description\nA Maps and Photographs\nB NRC Report\nC Operator’s Incident Report\nPage 4 of 4\n\n<<<PAGE 5>>>\n\nAppendix A\nMap Removed\nFile Available at PHMSA\n\n<<<PAGE 6>>>\n\nAppendix A - Maps and Photographs\nWide-angle image showing impinging rock\nCloseup of impinging rock\nPage 2 of 8\n\n<<<PAGE 7>>>\n\nAppendix A - Maps and Photographs\nHilly area leading up to failure site\nAdditional broad view of site\nPage 3 of 8\n\n<<<PAGE 8>>>\n\nAppendix A - Maps and Photographs\nExcavation site\nAlternate angle\nPage 4 of 8\n\n<<<PAGE 9>>>\n\nAppendix A - Maps and Photographs\nConstructing bypass\nPage 5 of 8\n\n<<<PAGE 10>>>\n\nAppendix A - Maps and Photographs\nBypass from alternate angle\nArea after rain\nPage 6 of 8\n\n<<<PAGE 11>>>\n\nAppendix A - Maps and Photographs\nCloseup of damage to pipe wall\nHand excavation\nPage 7 of 8\n\n<<<PAGE 12>>>\n\nAppendix A - Maps and Photographs\nCompleted repair\nPage 8 of 8\n\n<<<PAGE 13>>>\n\nAppendix B - NRC Report\nNAT FOR PUBLIC US ENTER 1-800-421-8302\npocatie ediator third party hat commith a Privacy lans\nIncident Report # 871912\nINCIDENT DESCRIPTION\nRepoet Type: $ 12i27 On 23-MAX-08\nThe sheddent vas discovered on 23-MAY -08 at 17:30 Local time.\nIncident Cause: UNKNOWN\nAffected Medium: AIR / ATMOPSHERE\nSUSPECTED RESPONSIBLE PARTY\nOrganization:\nNORTHERN NATURAL GAS COMPANY\nOMAHA, NE 68124\nType of Organization: PRIVATE ENTERPRISE\nCounty: LAKE\nINCIDENT LOCATION\nCity: SILVER BAY State: MI\n*** CALLER HAD VERY LITTLE INFORMATION***\nRELEASED MATERIAL (S)\nAlso Known As:\nCHRIS Code: ONG\nOfficial Material Name: NATURAL GAS\nQty Released: 0 UNKNOWN AMOUNT\nCALLER IS REPORTING THAT NATURAL GAS RONASED FROM AN UNDERGROUND PIPELINE DUE TO\nUNKNOWN CAUSES.\nINCIDENT DETAILS\nDo Regulated: TRAITON\nPipeline Above/Below Ground: BELOW\nDAMAGES\nINJURIES:\nFire Involved: No\nFATALITIES:\nNO\nNO\nFire Extinguished: UNKNOWN\nHospitalized:\nEVACUATIONS:\nNO\nEmp1/Crew:\nEmp1/Crew:\nDamages:\nNO\nWho Evacuated:\nPassenger:\nPassenger:\nOccupant:\nRadius/Area:\nClosure Type\nLength of\nDirection of\nAir:\nN\nDescription of Closure\nClosure\nClosure\nRoad:\nN\nArtery: N\nMajor\nWaterway:\nN\nTrack:\nN\nPassengers Iransferred: NO\nPage 1 of 2\n\n<<<PAGE 14>>>\n\nAppendix B - NRC Report\nEnvironmental Impact: NO\nMedia Interest: NONE Community Impact due to Material:\n____________________________________________________________________________\nREMEDIAL ACTIONS\nLOWERING PRESSURE ON THE LINE\nRelease Secured: YES\nRelease Rate:\nEstimated Release Duration:\n____________________________________________________________________________\nWEATHER\nWeather: OVERCAST, ºF\n____________________________________________________________________________\nADDITIONAL AGENCIES NOTIFIED\nFederal: NONE\nState/Local: NONE\nState/Local On Scene: NONE\nState Agency Number: NO REPORT #\n____________________________________________________________________________\nNOTIFICATIONS BY NRC\nATLANTIC STRIKE TEAM (MAIN OFFICE)\n23-MAY-08 19:33\nUSCG ICC (ICC ONI)\n23-MAY-08 19:33\nDOT CRISIS MANAGEMENT CENTER (MAIN OFFICE)\n23-MAY-08 19:33\nU.S. EPA V (MAIN OFFICE)\n23-MAY-08 19:37\nFLD INTEL SUPPORT TEAM DETROIT (COMMAND CENTER)\n23-MAY-08 19:33\nMN BUREAU OF CRIMINAL APPREHENSION (OPERATIONS CENTER)\n23-MAY-08 19:33\nMN DEPT OF HEALTH (MAIN OFFICE)\n23-MAY-08 19:33\nMN U.S. ATTORNEY'S OFFICE (ATTN: CARL WAHL)\n23-MAY-08 19:33\nNTL ENVMTL EMERG CENTRE CANADA (MAIN OFFICE)\n23-MAY-08 19:33\nNATIONAL INFRASTRUCTURE COORD CTR (MAIN OFFICE)\n23-MAY-08 19:33\nNOAA RPTS FOR MN (MAIN OFFICE)\n23-MAY-08 19:33\nSECTOR SAULT ST MARIE (MSO DULUTH)\n23-MAY-08 19:36\nMSD ST. PAUL (CGIS)\n23-MAY-08 19:33\nSURFACE TRANS SECURITY INSPECT PROG (COMMAND CENTER)\n23-MAY-08 19:33\nUSCG DISTRICT 9 (COMMAND CENTER)\n23-MAY-08 19:33\n____________________________________________________________________________\nADDITIONAL INFORMATION\nCALLER HAD NO ADDITIONAL INFORMATION.\n___________________________________________________________________________\n***\nEND INCIDENT REPORT # 871912 ***\nPage 2 of 2\n\n<<<PAGE 15>>>\n\nAppendix C - Operator's Incident Report\nNOTICE: This report is required by 49 CFR Part 191. Failure to report can result in a civil penalty not to exceed $25,000 for each violation Form Approved\nfor each day that such violation persists except that the maximum civil penalty shall not exceed $500,000 as provided in 49 USC 1678. OMB No. 2137-0522\nU.S. Department of Transportation\nResearch and Special Programs\nAdministration\nINCIDENT REPORT - GAS TRANSMISSION AND\nGATHERING SYSTEMS\nReport Date\nJun 05, 2008\nNo.\n20080058 -- 4441\n(DOT Use Only)\nINSTRUCTIONS\nImportant: Please read the separate instructions for completing this form before you begin. They clarify the\ninformation requested and provide specific examples. If you do not have a copy of the instructions, you\ncan obtain one from the Office Of Pipeline Safety Web Page at http://ops.dot.gov .\n0\nPART A – GENERAL REPORT INFORMATION\nCheck one or more boxes as appropriate:\nOperator Name and Address\nOriginal Report Supplemental Report Final Report\n13750\na. Operator's 5-digit Identification Number (when known) / /\nb. If Operator does not own the pipeline, enter Owner’s 5-digit Identification Number (when known) / /\nNORTHERN NATURAL GAS CO\nc. Name of Operator ______________________________ _______________________________________________________\n1111 SOUTH 103RD STREET\nd. Operator street address ________________________________________________________________________________________\nOMAHA, DOUGLAS, NE, 68124\ne. Operator address _______________________\nCity, County or Parrish, State and Zip Code\n2. Time and date of the incident\n5. Consequences (check and complete all that apply)\n05 1457 23\n2008\n/ / / / / / / /\n0\nhr. month day year\n0\n3. Location of incident\nNon-employee Contractors: / /\na.\nAPPROXIMATELY 1 MILE WEST OF LA\nb. Injury requiring inpatient\nNearest street or road\nb.\nBEAVER BAY LAKE\n0\nCity and County or Parrish\n0\nNon-employee Contractors: / /\nc.\nMN 55601\nState and Zip Code\nd. Mile Post/Valve Station\nAPPROX 59.5\ne. Survey Station No.\nf. Latitude: Longitude:\n(if not available, see instructions for how to provide specific location)\ng. Class location description\nOnshore: Class 1 Class 2 Class 3 Class 4\n47.27101 -91.34526\nc. Property damage/loss (estimated) Total $\nGas loss $ Operator damage $\nPublic/private property damage $\nd. Release Occurred in a ‘High Consequence Area’\ne. Gas ignited – No explosion f. Explosion\nOffshore: Class 1 (complete rest of this item)\nArea ___________________ Block # ___________\nState / / or Outer Continental Shelf\nh. Incident on Federal Land other than Outer Continental Shelf\nYes No\ni. Is pipeline Interstate Yes No\n4. Type of leak or rupture\n0\nLeak: Pinhole Connection Failure (complete sec. F5)\nPuncture, diameter (inches)\nRupture: Circumferential – Separation\nLongitudinal – Tear/Crack, length (inches)\nPropagation Length, total, both sides (feet)\nN/A\nOther:\nPART B – PREPARER AND AUTHORIZED SIGNATURE\nBYRON H. WOOD\n(type or print) Preparer's Name and Title\n(402) 398-7606\n0\na. Fatality Total number of people: / /\n0\nEmployees: / / General Public: / /\n0\nhospitalization Total number of people: / /\n0\nEmployees: / / General Public: / /\n530000\n15800 514200\ng. Evacuation (general public only) / / people\nReason for Evacuation:\nEmergency worker or public official ordered, precautionary\nThreat to the public Company policy\n6. Elapsed time until area was made safe:\n1\n/ / hr. / / min.\n7. Telephone Report\n871912 05 23 2008\n/ / / / / / / /\nNRC Report Number month day year\n8. a. Estimated pressure at point and time of incident:\n1 405\nPSIG\nb. Max. allowable operating pressure (MAOP): PSIG\nc. MAOP established by 49 CFR section:\n192.619 (a)(1) 192. 619 (a)(2) 192. 619 (a)(3)\n192.619 (a)(4) 192. 619 (c)\n425\nd. Did an overpressurization occur relating to the incident? Yes No\n(402) 398-7396\nArea Code and Telephone Number\nBYRON.WOOD@NNGCO.COM\nPreparer's E-mail Address Area Code and Facsimile Number\nDate Area Code and Telephone Number\nAuthorized Signature (type or print) Name and Title\nForm RSPA F 7100.2 ( 01-2002 ) OPS Data Facsimile Page 1 of 3\nPage 1 of 3\n\n<<<PAGE 16>>>\n\nAppendix C - Operator's Incident Report\nPART C - ORIGIN OF THE INCIDENT\n1. Incident occurred on\nTransmission System\nGathering System\nTransmission Line of Distribution System\n2. Failure occurred on\nBody of pipe Pipe Seam\nJoint\nComponent\nOther:\nPlastic (If plastic, complete all items that apply in a-c)\nPART D – MATERIAL SPECIFICATION (if applicable) PART E – ENVIRONMENT\n3. Material involved (pipe, fitting, or other component)\nSteel\nPlastic failure was: a.ductile b.brittle c.joint failure\nMaterial other than plastic or steel: _________\n4. Part of system involved in incident\nPipeline Regulator/Metering System\nCompressor Station Other:\n1961\n5. Year the pipe or component which failed was installed: / /\n16\n1. Nominal pipe size (NPS) / / in.\n.22\n2. Wall thickness / / in.\n5LX\n52000\n3. Specification SMYS / /\n4. Seam type\nERW\n5. Valve type\nREPUBLIC\n1. Area of incident In open ditch\nUnder pavement Above ground\nUnder ground Under water\nInside/under building Other:\nPART F – APPARENT CAUSE\ncause you indicate. See the instructions for this form for guidance.\na. Pipe Coating\nb. Visual Examination\nBare\nLocalized Pitting\n1. External Corrosion\nCoated\nGeneral Corrosion\nOther: ____________________\nNo Yes, Year Protection Started: / /\n2. Internal Corrosion\ne. Was pipe previously damaged in the area of corrosion?\nF2 – NATURAL FORCES\n3. Earth Movement => Earthquake Subsidence Landslide Other:\n4. Lightning\n5. Heavy Rains/Floods => Washouts Flotation Mudslide Scouring Other:\n38\n2. Depth of cover: inches\n6. Pipe or valve manufactured by in year / /\nImportant: There are 25 numbered causes in this section. Check the box to the left of the primary\ncause of the incident. Check one circle in each of the supplemental items to the right of or below the\nF1 – CORROSION If either F1 (1) External Corrosion, or F1 (2) Internal Corrosion is checked, complete all subparts a – e.\nc. Cause of Corrosion\nGalvanic Stray Current\nImproper Cathodic Protection\nMicrobiological\nStress Corrosion Cracking\nOther: ____________________\nd. Was corroded part of pipeline considered to be under cathodic protection prior to discovering incident?\nNo Yes, How long prior to incident: / / years / / months\n6. Temperature => Thermal stress Frost heave Frozen components Other:\n7. High Winds\nF3 - EXCAVATION\n8. Operator Excavation Damage (including their contractors) / Not Third Party\n9. Third Party Excavation Damage (complete a-d)\na. Excavator group\nGeneral Public Government Excavator other than Operator/subcontractor\nb. Type: Road Work Pipeline Water Electric Sewer Phone/Cable Landowner Railroad\nOther:\nc. Did operator get prior notification of excavation activity?\nNo Yes: Date received: / / mo. / / day / / yr.\nNotification received from: One Call System Excavator Contractor Landowner\nd. Was pipeline marked?\nNo Yes (If Yes, check applicable items i – iv)\ni. Temporary markings: Flags Stakes Paint\nii. Permanent markings: Yes No\niii. Marks were (check one) Accurate Not Accurate\niv. Were marks made within required time? Yes No\nF4 – OTHER OUTSIDE FORCE DAMAGE\n10. Fire/Explosion as primary cause of failure => Fire/Explosion cause: Man made Natural\n11. Car, truck or other vehicle not relating to excavation activity damaging pipe\n12. Rupture of Previously Damaged Pipe\n13. Vandalism\nForm RSPA F 7100.2 ( 01-2002 ) Page 2 of 3\nPage 2 of 3\n\n<<<PAGE 17>>>\n\nAppendix C - Operator's Incident Report\nF5 – MATERIAL AND WELDS\nMaterial\n14. Body of Pipe => Dent Gouge Wrinkle Bend Arc Burn Other:\n15. Component => Valve Fitting Vessel Extruded Outlet Other:\n16. Joint => Gasket O-Ring Threads Other:\nWeld\n17. Butt => Pipe Fabrication Other:\n18. Fillet => Branch Hot Tap Fitting Repair Sleeve Other:\n19. Pipe Seam => LF ERW DSAW Seamless Flash Weld\nHF ERW SAW Spiral Other:\nComplete a-g if you indicate any cause in part F5.\na. Type of failure:\nConstruction Defect => Poor Workmanship Procedure not followed Poor Construction Procedures\nMaterial Defect\nb. Was failure due to pipe damage sustained in transportation to the construction or fabrication site? Yes No\nc. Was part which leaked pressure tested before incident occurred? Yes, complete d-g No\nd. Date of test: / / mo. / / day / / yr.\ne. Test medium: Water Natural Gas Inert Gas Other:\nf. Time held at test pressure: / / hr.\ng. Estimated test pressure at point of incident: PSIG\nF6 – EQUIPMENT AND OPERATIONS\n20. Malfunction of Control/Relief Equipment => Valve Instrumentation Pressure Regulator Other:\n21. Threads Stripped, Broken Pipe Coupling => Nipples Valve Threads Mechanical Couplings Other:\nForm RSPA F 7100.2 ( 01-2002 ) OPS Data Facsimile Page 3 of 3\n22. Ruptured or Leaking Seal/Pump Packing\n23. Incorrect Operation\na. Type: Inadequate Procedures Inadequate Safety Practices Failure to Follow Procedures Other:\nb. Number of employees involved who failed post-incident drug test: / / Alcohol test: / /\nc. Were most senior employee(s) involved qualified? Yes No d. Hours on duty: / /\nF7 – OTHER\n24. Miscellaneous, describe:\n25. Unknown\nInvestigation Complete Still Under Investigation (submit a supplemental report when investigation is complete)\nPART G – NARRATIVE DESCRIPTION OF FACTORS CONTRIBUTING TO THE EVENT (Attach additional sheets as necessary)\nON MAY 23, AT APPROXIATELY 14:57 THE CARLTON LOCATION WAS NOTIFIED BY ANGEL SERVICE ITT CORP, THAT THEY HAD\nCOMPLETED THEIR AERIAL LEAK SURVEYING. UPON REVIEW OF THE INFORMATION IT APPEARED THAT THERE WAS A DETECTION\nOF A SINGLE METHANE INDICATION IN LAKE COUNTY, MN ON THE 16-INCH RESERVE (MNB69801) BRANCH LINE ON THE\nPIPELINE RIGHT OF WAY APPROXIMATELY 1.1 MILES WEST OF LAX LAKE ROAD @ APPROXIMATE MILEPOST 59.5. NORTHERN\nPERSONNEL PROCEEDED TO REDUCE THE PRESSURE FROM 405 TO 300 PSIG AND SENT PERSONNEL TO THE SITE TO UTILIZE\nPORTABLE LEAK DETECTION EQUIPMENT TO VERIFY IF THERE WAS A LEAK. A LEAK WAS DETECTED @ THE APPROXIMATE\nLOCATION INDICATED. A STRONG HYDRO CARBON SMELL WAS DETECTED, A READING OF 5% LEL WAS INDICATED AND A PATCH\nOF DEAD VEGETATION APPROXIMATELY 15 FT IN DIAMETER WAS NOTED. ACTIONS WERE TAKEN TO ACQUIRE THE SERVICES OF A\nCONTRACTOR AND ARRANGE FOR NORTHERN'S STOPPLE CREW TO PROCEED TO THE SITE. AN 8-INCH STOPPLE AND BYPASS WAS\nINSTALLED AROUND THE LEAK AREA, THEN THE SECTION OF LINE WAS BLOWN DOWN AND EXCAVATED. A ROCK WAS FOUND TO\nHAVE IMPINGED ON THE PIPELINE AT THE 6 O'CLOCK POSITION. THE IMPINGMENT RESULTED IN A DENT MEASURING\nAPPROXIMATELY 11 INCHES LONGITUDINALLY, SEVEN INCHES CIRCUFERENTIALLY AND 0.903 INCHES DEEP. THERE WAS A\nCRACK LOCATED AT THE BOTTOM OF THE DENT MEASURING APPROXIMATELY 1-INCH LONG. IT WAS DETERMINED THAT THE LEAK\nCOULD BE REPAIRED BY INSTALLATION OF A 2-FOOT BY 16-INCH TYPE B PRESSURIZED CONTAINING SLEEVE. INSTALLATION\nOF THE SLEEVE WAS COMPLETED ON JUNE 3. ALL WELDS WERE INSPECTED USING MAGNETIC PARTICLE AND ULTRASONIC\nTHICKNESS METHODS. THE PIPELINE BETWEEN THE STOPPLE FITTINGS WAS PURGED, PRESSURE TESTED AND RETURNED TO\nNORMAL 405 PSIG SERVICE. THERE WAS NO FIRE, NO INJURIES AND NO LOSS OF SERVICE TO ANY CUSTOMERS. THE ROOT\nCAUSE OF THE LEAK WAS A ROCK IMPINING ON THE LINE AND GROUND SUBSIDENCE. A FINAL REPORT WILL BE COMPLETED\nUPON DETERMINATION OF THE TOTAL COST OF REPAIRS.\nSUPPLEMENTAL REPORT: IN THE NARRATIVE IT WAS INDICATED THAT THE LINE NUMBER WAS MNB69801, WHICH IS INCORRECT\nAND SHOULD INSTEAD BE MNB72701.\nSUPPLEMENTAL/FINAL REPORT TOTAL COST OF REPAIRS ESTIMATES INCLUDING GAS LOSS HAVE BEEN UPDATED THE ROOT\nPage 3 of 3","truncated":false,"body_characters":23476}