Failure Report- Northern Natural Gas Co 5/23/08

Page 1Official PDFDOT US Department of Transportation PHMSA Pipelines and Hazardous Materials Safety Administration OPS Office of Pipeline Safety Central Region Principal Investigator MNOPS/James Bunn/Karen Butler Region Director Allan Beshore Date of Report 11/14/2014 Subject Failure Investigation Report – Northern Natural Gas Co (NNG) – Natural Force Damage Operator, Location, & Consequences Date of Failure 05/23/2008 Commodity Released Natural Gas City/County & State Beaver Bay / Lake, Minnesota OpID & Operator Name 13750 Northern Natural Gas Co Unit # & Unit Name 903 Carlton [IA] (NNG) (NNG) SMART Activity # 124375 Milepost / Location MP 59.5, Reserve Mining Branch Line MNB72701 Type of Failure Natural Force Damage, crack in a dent Fatalities 0 Injuries 0 Description of Area impacted Rural, Class 1, Non-HCA Total Costs $530,000#

Page 2Failure Investigation Report – Northern Natural Gas Co – Natural Force Damage Failure Date 05/23/2008 Executive Summary On May 23, 2008, an instrumented aerial leak survey was in progress by a contracted service for Northern Natural Gas Company (NNG). During this leak survey, a leak was discovered in the Reserve Mining Branch Line (MNB72701) at approximately 2:57 p.m. CDT. Local field personnel were notified directly from the contracted leak survey service. The NNG control center was contacted by field personnel and began to reduce operating pressure (405 psig to approximately 275 psig). This pipeline serves the Reserve Mine and three additional towns in Minnesota. The leak was physically located at approximately 7:00 p.m. CDT by NNG field personnel at MP 59.5 in Lake County, Minnesota, approximately 1.1 miles northeast of the intersection of County Road 3 and County Road 4. The leak was not located in an HCA. There were no reported evacuations, road closings, fires, injuries or fatalities as a result of the leak. The state partner, Minnesota Office of Pipeline Safety (MNOPS), investigated the release on-site. The leak originated at a 1-inch long crack that was located in a dent on the bottom of the pipe. The pipe was found to be resting on a sharp piece of granite. The original construction of the pipeline was in 1961. Ground subsidence was reported to have caused the dented pipe to fail. Weather and contract resource availability delayed the installation of a 16-inch Type B repair sleeve. The pipeline repair work was completed on June 3, 2008. The operator has estimated the cost of this incident to be $530,000. After the incident, NNG ran High Resolution MFL and Caliber tools on the Reserve Mining Branch Line and discovered six dents with metal loss. MNOPS completed a follow-up inspection in 2009 and confirmed that all six dents with metal loss were scheduled for repair by May of 2010. All repairs have been completed. System Details The Northern Natural Gas Pipe Line system consists of approximately 15,000 miles of pipelines and storage facilities. The system transports natural gas from the gathering fields in New Mexico, Texas, Oklahoma and Kansas to market areas in the upper Midwest. The Reserve Mining Branch Line is part of the Northern Branch System and provides natural gas to the mine as well as three towns including Beaver Bay and Silver Bay, Minnesota. The portion of the pipeline containing the failure was composed of 16-inch diameter by 0.219-inch wall thickness, API 5L X52, low frequency ERW line pipe manufactured by Republic Steel with coal tar enamel as the external coating and was cathodically protected. The pipeline was installed in 1961. Events leading up to the Failure The maximum allowable operating pressure (MAOP) of the pipeline is 425 psig, which corresponds to a hoop stress level of 30 percent of the specified minimum yield strength (SMYS) of the pipe. The pressure at the time and location of failure was 405 psig, which corresponds to a hoop stress of 29 percent (95 percent of MAOP). The MAOP for the Reserve Mining pipeline was reported to be established in accordance with 192.619 (a) (4), the pressure determined by the operator to be the maximum safe pressure after considering the history of the segment. Page 2 of 4#

Page 3Failure Investigation Report – Northern Natural Gas Co – Natural Force Damage Failure Date 05/23/2008 Emergency Response The pressure in the line at the time of detection of the leak was 405 psig. When the Control Center was notified of the potential leak, actions to reduce line pressure were implemented. The pressure in the pipeline was ultimately reduced to a pressure of approximately 275 psig. The area around the leak was secured until repairs could be made. NNG reported the incident to the NRC at 6:27 p.m. CDT on May 23, 2008. Return to Service Between May 23, 2008, and May 29, 2008, delays to repair activities occurred due to weather and contract resource availability. On May 29, 2008, NNG began excavation activities in order to install stopple fittings. After the fittings were installed, a bypass was constructed around the leak area. The section of the line that contained the leak was blown down and the line was excavated to expose the leak. The pipe was resting on a piece of granite at the leak location. A dent had formed in the pipe where it was resting on the rock. The dent was approximately 11 inches long, 7 inches wide and 0.903 inches deep. The bottom of the dent contained a thru-wall crack that was approximately 1 inch long. The repair to the failed section of pipe was made with a 16-inch Type B weld sleeve approximately 24 inches long. On June 3, 2008, repair work was completed and the pipeline returned to normal service. Investigation Details Angel Service ITT was conducting an aerial leak survey on the Reserve Mining Branch Pipeline on March 23, 2008. The aerial leak survey contractor identified a potential leak site on the pipeline route and notified NNG personnel at the NNG Carlton Compressor Station of the findings at approximately 2:57 p.m. CDT. Carlton personnel notified the NNG Control Center of the potential leak and the Control Center began to reduce the pressure in the line. NNG dispatched a crew to the site of the potential leak with a flame ionization unit. When the crew reached the area of the leak, the leak was confirmed when an area of dead vegetation was observed and a reading of 5 percent Lower Explosive Limit was measured. NNG secured the site and continued to monitor the atmosphere until a stopple bypass could be installed and the leak site could be excavated. After the line was excavated it was found to be resting on a sharp piece of granite at the leak location. A dent had been formed in the pipe body where the pipe was resting on the granite. A 1-inch long thru-wall crack was found in the bottom of the dent. The repair to the failed section of pipe was made with a 16-inch Type B weld sleeve approximately 24 inches long. On June 3, 2008, repair work was completed and the pipeline returned to normal service. In February of 2009, NNG completed High Resolution MFL and Caliber tools on the Reserve Mining Branch pipeline. MNOPS reviewed the information associated with the Inline inspection (ILI) during an inspection in May of 2009 (inspection was called the Welcome audit). The ILI run determined that there were no immediate repairs required, 28 scheduled repairs, and six dents with metal loss (wall loss less than or equal to 5 percent). All six dents were reported by the operator as occurring outside of a High Consequence Area and were repaired by May of 2010. Findings & Contributing Factors The failure origin was a 1-inch crack located in a dent in the pipe body. The crack was located in the Page 3 of 4#

Page 4Failure Investigation Report – Northern Natural Gas Co – Natural Force Damage Failure Date 05/23/2008 bottom of a dent that measured approximately 11 inches in length, 7 inches circumferentially and 0.903 inches deep. A rock that was impinging on the pipeline at the 6 o’clock position caused the dent. Ground subsidence, combined with the impinging rock, caused the dented pipe to fail. Appendix Description A Maps and Photographs B NRC Report C Operator’s Incident Report Page 4 of 4#

Page 5Appendix A Map Removed File Available at PHMSA#

Page 6Appendix A - Maps and Photographs Wide-angle image showing impinging rock Closeup of impinging rock Page 2 of 8#

Page 7Appendix A - Maps and Photographs Hilly area leading up to failure site Additional broad view of site Page 3 of 8#

Page 8Appendix A - Maps and Photographs Excavation site Alternate angle Page 4 of 8#

Page 9Appendix A - Maps and Photographs Constructing bypass Page 5 of 8#

Page 10Appendix A - Maps and Photographs Bypass from alternate angle Area after rain Page 6 of 8#

Page 11Appendix A - Maps and Photographs Closeup of damage to pipe wall Hand excavation Page 7 of 8#

Page 12Appendix A - Maps and Photographs Completed repair Page 8 of 8#

Page 13Appendix B - NRC Report NAT FOR PUBLIC US ENTER 1-800-421-8302 pocatie ediator third party hat commith a Privacy lans Incident Report # 871912 INCIDENT DESCRIPTION Repoet Type: $ 12i27 On 23-MAX-08 The sheddent vas discovered on 23-MAY -08 at 17:30 Local time. Incident Cause: UNKNOWN Affected Medium: AIR / ATMOPSHERE SUSPECTED RESPONSIBLE PARTY Organization: NORTHERN NATURAL GAS COMPANY OMAHA, NE 68124 Type of Organization: PRIVATE ENTERPRISE County: LAKE INCIDENT LOCATION City: SILVER BAY State: MI *** CALLER HAD VERY LITTLE INFORMATION*** RELEASED MATERIAL (S) Also Known As: CHRIS Code: ONG Official Material Name: NATURAL GAS Qty Released: 0 UNKNOWN AMOUNT CALLER IS REPORTING THAT NATURAL GAS RONASED FROM AN UNDERGROUND PIPELINE DUE TO UNKNOWN CAUSES. INCIDENT DETAILS Do Regulated: TRAITON Pipeline Above/Below Ground: BELOW DAMAGES INJURIES: Fire Involved: No FATALITIES: NO NO Fire Extinguished: UNKNOWN Hospitalized: EVACUATIONS: NO Emp1/Crew: Emp1/Crew: Damages: NO Who Evacuated: Passenger: Passenger: Occupant: Radius/Area: Closure Type Length of Direction of Air: N Description of Closure Closure Closure Road: N Artery: N Major Waterway: N Track: N Passengers Iransferred: NO Page 1 of 2#

Page 14Appendix B - NRC Report Environmental Impact: NO Media Interest: NONE Community Impact due to Material: ____________________________________________________________________________ REMEDIAL ACTIONS LOWERING PRESSURE ON THE LINE Release Secured: YES Release Rate: Estimated Release Duration: ____________________________________________________________________________ WEATHER Weather: OVERCAST, ºF ____________________________________________________________________________ ADDITIONAL AGENCIES NOTIFIED Federal: NONE State/Local: NONE State/Local On Scene: NONE State Agency Number: NO REPORT # ____________________________________________________________________________ NOTIFICATIONS BY NRC ATLANTIC STRIKE TEAM (MAIN OFFICE) 23-MAY-08 19:33 USCG ICC (ICC ONI) 23-MAY-08 19:33 DOT CRISIS MANAGEMENT CENTER (MAIN OFFICE) 23-MAY-08 19:33 U.S. EPA V (MAIN OFFICE) 23-MAY-08 19:37 FLD INTEL SUPPORT TEAM DETROIT (COMMAND CENTER) 23-MAY-08 19:33 MN BUREAU OF CRIMINAL APPREHENSION (OPERATIONS CENTER) 23-MAY-08 19:33 MN DEPT OF HEALTH (MAIN OFFICE) 23-MAY-08 19:33 MN U.S. ATTORNEY'S OFFICE (ATTN: CARL WAHL) 23-MAY-08 19:33 NTL ENVMTL EMERG CENTRE CANADA (MAIN OFFICE) 23-MAY-08 19:33 NATIONAL INFRASTRUCTURE COORD CTR (MAIN OFFICE) 23-MAY-08 19:33 NOAA RPTS FOR MN (MAIN OFFICE) 23-MAY-08 19:33 SECTOR SAULT ST MARIE (MSO DULUTH) 23-MAY-08 19:36 MSD ST. PAUL (CGIS) 23-MAY-08 19:33 SURFACE TRANS SECURITY INSPECT PROG (COMMAND CENTER) 23-MAY-08 19:33 USCG DISTRICT 9 (COMMAND CENTER) 23-MAY-08 19:33 ____________________________________________________________________________ ADDITIONAL INFORMATION CALLER HAD NO ADDITIONAL INFORMATION. ___________________________________________________________________________ *** END INCIDENT REPORT # 871912 *** Page 2 of 2#

Page 15Appendix C - Operator's Incident Report NOTICE: 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 for 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 U.S. Department of Transportation Research and Special Programs Administration INCIDENT REPORT - GAS TRANSMISSION AND GATHERING SYSTEMS Report Date Jun 05, 2008 No. 20080058 -- 4441 (DOT Use Only) INSTRUCTIONS Important: Please read the separate instructions for completing this form before you begin. They clarify the information requested and provide specific examples. If you do not have a copy of the instructions, you can obtain one from the Office Of Pipeline Safety Web Page at http://ops.dot.gov . 0 PART A – GENERAL REPORT INFORMATION Check one or more boxes as appropriate: Operator Name and Address Original Report Supplemental Report Final Report 13750 a. Operator's 5-digit Identification Number (when known) / / b. If Operator does not own the pipeline, enter Owner’s 5-digit Identification Number (when known) / / NORTHERN NATURAL GAS CO c. Name of Operator ______________________________ _______________________________________________________ 1111 SOUTH 103RD STREET d. Operator street address ________________________________________________________________________________________ OMAHA, DOUGLAS, NE, 68124 e. Operator address _______________________ City, County or Parrish, State and Zip Code 2. Time and date of the incident 5. Consequences (check and complete all that apply) 05 1457 23 2008 / / / / / / / / 0 hr. month day year 0 3. Location of incident Non-employee Contractors: / / a. APPROXIMATELY 1 MILE WEST OF LA b. Injury requiring inpatient Nearest street or road b. BEAVER BAY LAKE 0 City and County or Parrish 0 Non-employee Contractors: / / c. MN 55601 State and Zip Code d. Mile Post/Valve Station APPROX 59.5 e. Survey Station No. f. Latitude: Longitude: (if not available, see instructions for how to provide specific location) g. Class location description Onshore: Class 1 Class 2 Class 3 Class 4 47.27101 -91.34526 c. Property damage/loss (estimated) Total $ Gas loss $ Operator damage $ Public/private property damage $ d. Release Occurred in a ‘High Consequence Area’ e. Gas ignited – No explosion f. Explosion Offshore: Class 1 (complete rest of this item) Area ___________________ Block # ___________ State / / or Outer Continental Shelf h. Incident on Federal Land other than Outer Continental Shelf Yes No i. Is pipeline Interstate Yes No 4. Type of leak or rupture 0 Leak: Pinhole Connection Failure (complete sec. F5) Puncture, diameter (inches) Rupture: Circumferential – Separation Longitudinal – Tear/Crack, length (inches) Propagation Length, total, both sides (feet) N/A Other: PART B – PREPARER AND AUTHORIZED SIGNATURE BYRON H. WOOD (type or print) Preparer's Name and Title (402) 398-7606 0 a. Fatality Total number of people: / / 0 Employees: / / General Public: / / 0 hospitalization Total number of people: / / 0 Employees: / / General Public: / / 530000 15800 514200 g. Evacuation (general public only) / / people Reason for Evacuation: Emergency worker or public official ordered, precautionary Threat to the public Company policy 6. Elapsed time until area was made safe: 1 / / hr. / / min. 7. Telephone Report 871912 05 23 2008 / / / / / / / / NRC Report Number month day year 8. a. Estimated pressure at point and time of incident: 1 405 PSIG b. Max. allowable operating pressure (MAOP): PSIG c. MAOP established by 49 CFR section: 192.619 (a)(1) 192. 619 (a)(2) 192. 619 (a)(3) 192.619 (a)(4) 192. 619 (c) 425 d. Did an overpressurization occur relating to the incident? Yes No (402) 398-7396 Area Code and Telephone Number BYRON.WOOD@NNGCO.COM Preparer's E-mail Address Area Code and Facsimile Number Date Area Code and Telephone Number Authorized Signature (type or print) Name and Title Form RSPA F 7100.2 ( 01-2002 ) OPS Data Facsimile Page 1 of 3 Page 1 of 3#

Page 16Appendix C - Operator's Incident Report PART C - ORIGIN OF THE INCIDENT 1. Incident occurred on Transmission System Gathering System Transmission Line of Distribution System 2. Failure occurred on Body of pipe Pipe Seam Joint Component Other: Plastic (If plastic, complete all items that apply in a-c) PART D – MATERIAL SPECIFICATION (if applicable) PART E – ENVIRONMENT 3. Material involved (pipe, fitting, or other component) Steel Plastic failure was: a.ductile b.brittle c.joint failure Material other than plastic or steel: _________ 4. Part of system involved in incident Pipeline Regulator/Metering System Compressor Station Other: 1961 5. Year the pipe or component which failed was installed: / / 16 1. Nominal pipe size (NPS) / / in. .22 2. Wall thickness / / in. 5LX 52000 3. Specification SMYS / / 4. Seam type ERW 5. Valve type REPUBLIC 1. Area of incident In open ditch Under pavement Above ground Under ground Under water Inside/under building Other: PART F – APPARENT CAUSE cause you indicate. See the instructions for this form for guidance. a. Pipe Coating b. Visual Examination Bare Localized Pitting 1. External Corrosion Coated General Corrosion Other: ____________________ No Yes, Year Protection Started: / / 2. Internal Corrosion e. Was pipe previously damaged in the area of corrosion? F2 – NATURAL FORCES 3. Earth Movement => Earthquake Subsidence Landslide Other: 4. Lightning 5. Heavy Rains/Floods => Washouts Flotation Mudslide Scouring Other: 38 2. Depth of cover: inches 6. Pipe or valve manufactured by in year / / Important: There are 25 numbered causes in this section. Check the box to the left of the primary cause of the incident. Check one circle in each of the supplemental items to the right of or below the F1 – CORROSION If either F1 (1) External Corrosion, or F1 (2) Internal Corrosion is checked, complete all subparts a – e. c. Cause of Corrosion Galvanic Stray Current Improper Cathodic Protection Microbiological Stress Corrosion Cracking Other: ____________________ d. Was corroded part of pipeline considered to be under cathodic protection prior to discovering incident? No Yes, How long prior to incident: / / years / / months 6. Temperature => Thermal stress Frost heave Frozen components Other: 7. High Winds F3 - EXCAVATION 8. Operator Excavation Damage (including their contractors) / Not Third Party 9. Third Party Excavation Damage (complete a-d) a. Excavator group General Public Government Excavator other than Operator/subcontractor b. Type: Road Work Pipeline Water Electric Sewer Phone/Cable Landowner Railroad Other: c. Did operator get prior notification of excavation activity? No Yes: Date received: / / mo. / / day / / yr. Notification received from: One Call System Excavator Contractor Landowner d. Was pipeline marked? No Yes (If Yes, check applicable items i – iv) i. Temporary markings: Flags Stakes Paint ii. Permanent markings: Yes No iii. Marks were (check one) Accurate Not Accurate iv. Were marks made within required time? Yes No F4 – OTHER OUTSIDE FORCE DAMAGE 10. Fire/Explosion as primary cause of failure => Fire/Explosion cause: Man made Natural 11. Car, truck or other vehicle not relating to excavation activity damaging pipe 12. Rupture of Previously Damaged Pipe 13. Vandalism Form RSPA F 7100.2 ( 01-2002 ) Page 2 of 3 Page 2 of 3#

Page 17Appendix C - Operator's Incident Report F5 – MATERIAL AND WELDS Material 14. Body of Pipe => Dent Gouge Wrinkle Bend Arc Burn Other: 15. Component => Valve Fitting Vessel Extruded Outlet Other: 16. Joint => Gasket O-Ring Threads Other: Weld 17. Butt => Pipe Fabrication Other: 18. Fillet => Branch Hot Tap Fitting Repair Sleeve Other: 19. Pipe Seam => LF ERW DSAW Seamless Flash Weld HF ERW SAW Spiral Other: Complete a-g if you indicate any cause in part F5. a. Type of failure: Construction Defect => Poor Workmanship Procedure not followed Poor Construction Procedures Material Defect b. Was failure due to pipe damage sustained in transportation to the construction or fabrication site? Yes No c. Was part which leaked pressure tested before incident occurred? Yes, complete d-g No d. Date of test: / / mo. / / day / / yr. e. Test medium: Water Natural Gas Inert Gas Other: f. Time held at test pressure: / / hr. g. Estimated test pressure at point of incident: PSIG F6 – EQUIPMENT AND OPERATIONS 20. Malfunction of Control/Relief Equipment => Valve Instrumentation Pressure Regulator Other: 21. Threads Stripped, Broken Pipe Coupling => Nipples Valve Threads Mechanical Couplings Other: Form RSPA F 7100.2 ( 01-2002 ) OPS Data Facsimile Page 3 of 3 22. Ruptured or Leaking Seal/Pump Packing 23. Incorrect Operation a. Type: Inadequate Procedures Inadequate Safety Practices Failure to Follow Procedures Other: b. Number of employees involved who failed post-incident drug test: / / Alcohol test: / / c. Were most senior employee(s) involved qualified? Yes No d. Hours on duty: / / F7 – OTHER 24. Miscellaneous, describe: 25. Unknown Investigation Complete Still Under Investigation (submit a supplemental report when investigation is complete) PART G – NARRATIVE DESCRIPTION OF FACTORS CONTRIBUTING TO THE EVENT (Attach additional sheets as necessary) ON MAY 23, AT APPROXIATELY 14:57 THE CARLTON LOCATION WAS NOTIFIED BY ANGEL SERVICE ITT CORP, THAT THEY HAD COMPLETED THEIR AERIAL LEAK SURVEYING. UPON REVIEW OF THE INFORMATION IT APPEARED THAT THERE WAS A DETECTION OF A SINGLE METHANE INDICATION IN LAKE COUNTY, MN ON THE 16-INCH RESERVE (MNB69801) BRANCH LINE ON THE PIPELINE RIGHT OF WAY APPROXIMATELY 1.1 MILES WEST OF LAX LAKE ROAD @ APPROXIMATE MILEPOST 59.5. NORTHERN PERSONNEL PROCEEDED TO REDUCE THE PRESSURE FROM 405 TO 300 PSIG AND SENT PERSONNEL TO THE SITE TO UTILIZE PORTABLE LEAK DETECTION EQUIPMENT TO VERIFY IF THERE WAS A LEAK. A LEAK WAS DETECTED @ THE APPROXIMATE LOCATION INDICATED. A STRONG HYDRO CARBON SMELL WAS DETECTED, A READING OF 5% LEL WAS INDICATED AND A PATCH OF DEAD VEGETATION APPROXIMATELY 15 FT IN DIAMETER WAS NOTED. ACTIONS WERE TAKEN TO ACQUIRE THE SERVICES OF A CONTRACTOR AND ARRANGE FOR NORTHERN'S STOPPLE CREW TO PROCEED TO THE SITE. AN 8-INCH STOPPLE AND BYPASS WAS INSTALLED AROUND THE LEAK AREA, THEN THE SECTION OF LINE WAS BLOWN DOWN AND EXCAVATED. A ROCK WAS FOUND TO HAVE IMPINGED ON THE PIPELINE AT THE 6 O'CLOCK POSITION. THE IMPINGMENT RESULTED IN A DENT MEASURING APPROXIMATELY 11 INCHES LONGITUDINALLY, SEVEN INCHES CIRCUFERENTIALLY AND 0.903 INCHES DEEP. THERE WAS A CRACK LOCATED AT THE BOTTOM OF THE DENT MEASURING APPROXIMATELY 1-INCH LONG. IT WAS DETERMINED THAT THE LEAK COULD BE REPAIRED BY INSTALLATION OF A 2-FOOT BY 16-INCH TYPE B PRESSURIZED CONTAINING SLEEVE. INSTALLATION OF THE SLEEVE WAS COMPLETED ON JUNE 3. ALL WELDS WERE INSPECTED USING MAGNETIC PARTICLE AND ULTRASONIC THICKNESS METHODS. THE PIPELINE BETWEEN THE STOPPLE FITTINGS WAS PURGED, PRESSURE TESTED AND RETURNED TO NORMAL 405 PSIG SERVICE. THERE WAS NO FIRE, NO INJURIES AND NO LOSS OF SERVICE TO ANY CUSTOMERS. THE ROOT CAUSE OF THE LEAK WAS A ROCK IMPINING ON THE LINE AND GROUND SUBSIDENCE. A FINAL REPORT WILL BE COMPLETED UPON DETERMINATION OF THE TOTAL COST OF REPAIRS. SUPPLEMENTAL REPORT: IN THE NARRATIVE IT WAS INDICATED THAT THE LINE NUMBER WAS MNB69801, WHICH IS INCORRECT AND SHOULD INSTEAD BE MNB72701. SUPPLEMENTAL/FINAL REPORT TOTAL COST OF REPAIRS ESTIMATES INCLUDING GAS LOSS HAVE BEEN UPDATED THE ROOT Page 3 of 3#