{"operation":"document","citation":"PLD20LR001","title":"Enbridge Inc. Natural Gas Pipeline Rupture and Fire","source_type":"incident","agency":"National Transportation Safety Board","status":"current","official":true,"published_on":"2022-06-08","effective_on":"2020-05-04","summary":"Accident. in Hillsboro, KY, USA. on 2020-05-04. Enbridge Inc.. Rupture/fire","machine_formats":{"json":"https://regulus.evalyn.ai/document/ntsb-case-pld20lr001.json","markdown":"https://regulus.evalyn.ai/document/ntsb-case-pld20lr001.md"},"app_url":"https://regulus.evalyn.ai/document/ntsb-case-pld20lr001","source_url":"https://www.ntsb.gov/investigations/Pages/PLD20LR001.aspx","body":"NTSB investigation PLD20LR001.\n\nEvent Type: Accident\n\nEvent Date: 2020-05-04\n\nEvent City: Hillsboro\n\nEvent State Or Region: KY\n\nEvent Country: USA\n\nPipeline Operator: Enbridge Inc.\n\nPipeline Type: Gas Transmission - Regulated\n\nAccident Type: Rupture/fire\n\nCompletion Status: Completed\n\nReport Number: PIR2201\n\nReport Date: 2022-05-31\n\nProbable cause: The National Transportation Safety Board determines that the probable cause of the pipeline rupture was Enbridge Inc.’s analysis of an active landslide that did not fully address uncertainties associated with pipeline defects, landslide movement, and corresponding pipeline response.\n\nTier1Name: Emergency response\n\nTier2Name: Emergency shutoff\n\nTier1Name: System operating\n\nTier2Name: Fire (post-release)\n\nTier1Name: System operating\n\nTier2Name: Pipe structural malfunction/failure\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Support/oversight/monitoring\n\nFinding Tier3Name: Safety programs\n\nFinding Modifier Name: Pipeline operator\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Safety programs - Pipeline operator\n\nOfficial NTSB investigation data. NTSB findings determine probable cause and make safety recommendations; they do not adjudicate civil liability or regulatory violations.\n\nWhat Happened\nOn May 4, 2020, about 4:36 p.m. local time, a 30-inch diameter interstate natural gas transmission pipeline owned and operated by Enbridge Inc. (Enbridge) ruptured about 3 miles east–northeast of Hillsboro, Kentucky, resulting in a fire. [1] The rupture occurred on Line 10 at a hillside location that was previously identified by Enbridge for geotechnical monitoring because of an active landslide.[2]\n\nLine 10 was the northernmost of three parallel pipelines—Lines 10, 15, and 25—along the same right-of-way. At the time of the rupture, Line 10’s operating pressure was about 674 pounds per square inch, gauge.[3] The rupture occurred at a girth weld at an elevation of about 923 feet.[4] There were no fatalities or injuries, and Enbridge estimated the cost of property damage and emergency response at $11.7 million.\n\n(a) For more detailed information about this investigation, see the public docket and search for number PLD20LR001. Use the CAROL Query to search safety recommendations and investigations. (b) All times in this report are local time unless otherwise noted.\n\nThe rupture occurred on a Texas Eastern Transmission, Limited Partnership, pipeline. Texas Eastern Transmission is an indirect, 100-percent-owned subsidiary of Enbridge Inc.\n\nThe maximum allowable operating pressure of the pipeline was 936 pounds per square inch, gauge.\n\nA girth weld is used to join two pipes along their circumference. The girth weld that ruptured had been hydrostatically tested before the pipeline’s initial service in 1952 and retested in 1986; a hydrostatic test involves filling the pipeline with water at a predetermined pressure to test the pipeline’s integrity.\n\nWhat We Found\nWe determined that the probable cause of the pipeline rupture was Enbridge Inc.’s analysis of an active landslide that did not fully address uncertainties associated with pipeline defects, landslide movement, and corresponding pipeline response.\n\nPIR-22-01\n<<<PAGE 1>>>\n\nEnbridge Inc. Natural Gas Pipeline Rupture\nPIR-22/01\nIssued: May 31, 2022 Pipeline Investigation Report: PIR-22/01\nEnbridge Inc. Natural Gas Pipeline Rupture\nHillsboro, Kentucky\nMay 4, 2020\nFigure 1. Ruptured pipeline. (Source: BGC\nEngineering USA, Inc.)\n1. Factual Information\n1.1 Accident Summary\nOn May 4, 2020, about 4:36 p.m.\nlocal time, a 30-inch diameter interstate\nnatural gas transmission pipeline owned\nand operated by Enbridge Inc. (Enbridge)\nruptured about 3 miles east–northeast of\nHillsboro, Kentucky, resulting in a fire.\n1 (See\nfigure 1.) The rupture occurred on Line 10\nat a hillside location that was previously\nidentified by Enbridge for geotechnical\nmonitoring because of an active landslide.2\nLine 10 was the northernmost of\nthree parallel pipelines—Lines 10, 15 and\n25—along the same right-of-way. At the\ntime of the rupture, Line 10’s operating\npressure was about 674 pounds per\nsquare inch, gauge.\n3 The rupture occurred\nat a girth weld at an elevation of about 923\n1 (a) For more detailed information about this investigation, see the public docket and search for\nnumber PLD20LR001. Use the CAROL Query to search safety recommendations and investigations. (b) All\ntimes in this report are local time unless otherwise noted.\n2 The rupture occurred on a Texas Eastern Transmission, Limited Partnership, pipeline. Texas\nEastern Transmission is an indirect, 100-percent-owned subsidiary of Enbridge Inc.\n3 The maximum allowable operating pressure of the pipeline was 936 pounds per square inch, gauge.\n1\n\n<<<PAGE 2>>>\n\nEnbridge Inc. Natural Gas Pipeline Rupture\nPIR-22/01\nfeet.4 There were no fatalities or injuries, and Enbridge estimated the cost of property\ndamage and emergency response at $11.7 million.\n1.2 Integrity Management\nIn the years before the rupture, several indications were available to Enbridge that\nLine 10 was exposed to external loads (loads transmitted to a pipeline from an external\nsource):\n• Results of an April 17, 2018, in-line inspection (ILI) indicated pipeline\nmovement of about 4.2 feet.5\n• On October 9, 2018, Enbridge identified the rupture location as a potential\ngeohazard.\n• On April 16, 2019, an aerial patrol observed erosion on the right-of-way near\nthe rupture location.\n• Results of a June 7, 2019, ILI indicated pipeline movement of about 5.2 feet.\n• A July 8, 2019, ground inspection identified scarps.\n6\nIn 2019 and 2020, Enbridge evaluated Line 10 for geohazard threats. After a site\nassessment in October 2019 and analysis comparing the strain exerted on the pipeline\n(tensile strain demand) to the strain capacity of the pipeline (tensile strain capacity),\nEnbridge determined that urgent action was not required but recommended monitoring\nand mitigation of the identified threats.\n7\nIn February 2020, Enbridge held a multidisciplinary review meeting to determine\nthe monitoring and mitigation plan for this location. Based on estimated tensile strain\ndemand and other geotechnical considerations, Enbridge planned to install strain\ngauges and improve drainage. According to Enbridge, they also planned to complete\n4 A girth weld is used to join two pipes along their circumference. The girth weld that ruptured had\nbeen hydrostatically tested before the pipeline’s initial service in 1952 and retested in 1986; a hydrostatic\ntest involves filling the pipeline with water at a predetermined pressure to test the pipeline’s integrity.\n5 In-line inspection is an internal pipeline inspection technique that uses magnetic flux leakage,\nultrasound, eddy current or other sensing technology to locate and characterize indications of defects, such\nas metal loss or deformation in the pipeline.\n6 A scarp is a steep surface of exposed material produced by differential, or non-uniform, ground\nsurface movement.\n7 (a) The tensile strain demand is the amount of strain that is being exerted on the system or material,\nwhereas the tensile strain capacity is the amount of strain that the system or material can withstand; strain\ncan be expressed as a ratio or percentage. (b) Enbridge estimated a tensile strain demand of 0.6 percent\nby adding the maximum bending strain at a girth weld to the estimated axial strain. (c) The tensile strain\ncapacity analysis assumed a flaw 2 inches in length and 0.0394 inches in depth. (d) After applying a safety\nfactor, Enbridge determined that the tensile strain capacity threshold was 1 percent for the girth welds.\n2\n\n<<<PAGE 3>>>\n\nEnbridge Inc. Natural Gas Pipeline Rupture\nPIR-22/01\nadditional monitoring, mitigation and stress relief in summer 2020. The rupture occurred\nbefore the monitoring and mitigation activities were completed.\n1.3 Postaccident\n1.3.1 Postaccident Geotechnical Assessment\nFollowing the rupture, a contractor directed by the National Transportation Safety\nBoard (NTSB) found that the area around the incident site was highly susceptible to\nlandslides and determined that Line 10 was situated in past landslide deposits at the\nrupture location. The contractor concluded that Line 10 was installed within a landslide\nfeature that was accelerating, causing a rapid increase in strain on the pipeline before\nthe rupture. The contractor indicated that landslide acceleration in the 6 months before\nthe rupture was likely driven by high levels of precipitation, pre-existing cracks in the soil,\nground water movement along the pipeline trenches, and loading from grading\nactivities.\n1.3.2 Postaccident Metallurgical Testing and Tensile Strain Analysis\nOther contractors directed by the NTSB evaluated the ruptured girth weld,\nremoved and evaluated exemplar girth welds, and estimated the tensile strain demand\nand capacity. Two incomplete penetration and lack of root fusion defects were identified\non the fracture face of the ruptured girth weld.8 One defect was about 7 inches long and\n0.13 inches deep. The other defect was about 4.9 inches long and 0.10 inches deep.\nThe objective of the tensile strain demand analysis was to estimate the strain on\nthe pipeline caused by land movement at the failure location. The results of the pre- and\npost-rupture tensile strain demand analyses are shown in Table 1. The analyses assessed\noverall performance and did not account for known defects.\n8 (a) Incomplete penetration defects occur when the weld root is not completely filled. (b) Lack of root\nfusion defects occur when the weld fails to fuse one side of the joint in the root. (c) The root is the point at\nwhich the weld metal intersects the base metal and extends furthest into the weld joint.\n3\n\n<<<PAGE 4>>>\n\nEnbridge Inc. Natural Gas Pipeline Rupture\nPIR-22/01\nTable 1. Estimated tensile strain demand\nPipeline\nConfiguration\nPre-Rupture Analyses\n(Enbridge)\nPost-Rupture\nAnalyses\n(NTSB Investigation)\nApril 2018 N/A 1.8%\nJuly 2019 0.6% N/A\nMay 2020 N/A 3.0%\nFurther, tensile strain capacity analysis was performed to determine the amount of\nstrain that a pipe section with a representative girth weld could withstand. The tensile\nstrain capacity was estimated by evaluating exemplar girth welds, fabricating and testing\nmaterial property samples, and developing a finite element model. The model used to\nestimate tensile strain capacity explicitly included flaws found in the exemplar girth welds\nthat were up to 4 inches in length. The estimated tensile strain capacity was between 1.3\npercent and 2 percent.\n1.3.3 Postaccident Actions\n1.3.3.1 Enbridge\nEnbridge issued several new procedures for managing geohazards, including for\nestimating tensile strain capacity, conducting multidisciplinary reviews, and determining\nappropriate response actions. Enbridge reported that the new procedures would result\nin a reduced tensile strain capacity threshold (0.5 percent) on Line 10 in the area where\nthe rupture occurred, which, given the information available before the incident, would\ntrigger a high-priority response action.9 Additionally, Enbridge acknowledged that the\npre-rupture strain demand methodology may have underestimated the actual strain\ndemand. Enbridge indicated that it would continue to work with its contractors to\ndetermine whether a different method with an appropriate level of conservatism should\nbe applied.\n1.3.3.2 Pipeline and Hazardous Materials Safety Administration\nOn June 1, 2020, the Pipeline and Hazardous Materials Safety Administration\n(PHMSA) issued an amended Corrective Action Order to Enbridge that required\ncorrective actions be taken with respect to Lines 10, 15 and 25 for failures on August 1,\n9 The high-priority response action requires a site visit within 48 hours, site-specific monitoring plan\nwithin 30 days, immediate pressure reduction or shutdown, and drainage installation, if appropriate, for\nsite-specific conditions.\n4\n\n<<<PAGE 5>>>\n\nEnbridge Inc. Natural Gas Pipeline Rupture\nPIR-22/01\n2019, near Danville, Kentucky, and May 4, 2020, near Hillsboro, Kentucky.10 The order\nrequired Enbridge to reduce the operating pressure of the affected segment, review\nprior ILI results, and review and assess its emergency response plans, operations, and\npublic awareness program. Further, on December 21, 2021, PHMSA issued a Notice of\nProbable Violation, Proposed Civil Penalty, and Proposed Compliance Order to\nEnbridge alleging probable violations related to the Hillsboro accident.\nOn May 26, 2022, PHMSA issued an advisory bulletin, citing the Hillsboro\naccident among others, that reminds owners and operators of gas and hazardous liquid\npipelines of the potential for damage to pipeline facilities caused by earth movement in\nvariable, steep, and rugged terrain and for varied, changing subsurface geological\nconditions. The bulletin states that changing weather patterns, including increased\nrainfall and higher temperatures, can result in flooding, soil saturation, and erosion\nimpacting soil stability surrounding pipeline facilities. PHMSA’s advisory bulletin further\nlists pipeline safety actions operators should consider to ensure pipeline safety.\n11\n2. Analysis\nIn 2018, Enbridge identified the rupture location as a potential geohazard. They\ntook action to analyze the active landslide and started taking steps to mitigate the hazard\nbefore the rupture. However, Enbridge’s pre-rupture analysis estimated a girth weld\ntensile strain demand that was at least three times lower than post-rupture analysis later\nindicated. The post-rupture analysis demonstrated that in April 2018 or earlier Enbridge\ncould have foreseen the likelihood that the tensile strain demand would exceed the\nstrain capacity due to documented land movement at the site.\nLike all analyses, tensile strain demand and capacity calculations include certain\nmodeling assumptions and associated uncertainties that must be considered in any\ndecision-making that relies on the results. Notably, Enbridge’s pre-rupture analyses did\nnot appropriately consider uncertainties such as weld defects, changes in the slope and\ndirection of the landslide that could increase the susceptibility of the girth welds to\nfracture, acceleration of the landslide, or the response of the pipeline to these factors. As\n10 The August 1, 2019, rupture that occurred near Danville, Kentucky, is currently under investigation by\nthe NTSB. Additional information can be found in the public docket for NTSB investigations (number\nPLD19FR002) by accessing the NTSB Dockets Link at www.ntsb.gov.\n11 The suggested actions include, but are not limited to, monitoring geological and environmental\nconditions near facilities, including changing weather patterns; identifying areas surrounding pipelines that\nmay be prone to large earth movement; developing design, construction, and monitoring plans and\nprocedures and developing mitigation measures to remediate identified locations; and tracking changes in\nground conditions. For more information, see PHMSA Advisory Bulletin: Potential for Damage to Pipeline\nFacilities Caused by Earth Movement and Other Geological Hazards,\nhttps://www.phmsa.dot.gov/news/phmsa-advisory-bulletin-potential-damage-pipeline-facilities-caused-\nearth-movement-and-other.\n5\n\n<<<PAGE 6>>>\n\nEnbridge Inc. Natural Gas Pipeline Rupture\nPIR-22/01\na result, Enbridge determined that no immediate action was needed to mitigate the\nidentified geohazard threat and therefore did not take necessary actions before the\nrupture.\nAs a result of this accident, Enbridge issued new procedures for estimating tensile\nstrain capacity, conducting multidisciplinary reviews, and determining appropriate\nresponse actions, reporting the new procedures would result in a reduced tensile strain\ncapacity threshold. Further, PHMSA took enforcement action against Enbridge. PHMSA\nalso issued an advisory bulletin on damage to pipeline facilities from earth movement in\nrugged, steep terrain, citing the Hillsboro accident among recent land movement\nevents.\n3. Probable Cause\nThe National Transportation Safety Board determines that the probable cause of\nthe pipeline rupture was Enbridge Inc.’s analysis of an active landslide that did not fully\naddress uncertainties associated with pipeline defects, landslide movement, and\ncorresponding pipeline response.\nThe National Transportation Safety Board (NTSB) is an independent federal agency dedicated to\npromoting aviation, railroad, highway, marine, and pipeline safety. Established in 1967, the agency is\nmandated by Congress through the Independent Safety Board Act of 1974, to investigate transportation\naccidents, determine the probable causes of the accidents, issue safety recommendations, study\ntransportation safety issues, and evaluate the safety effectiveness of government agencies involved in\ntransportation. The NTSB makes public its actions and decisions through accident reports, safety studies,\nspecial investigation reports, safety recommendations, and statistical reviews.\nThe NTSB does not assign fault or blame for an accident or incident; rather, as specified by NTSB\nregulation, “accident/incident investigations are fact-finding proceedings with no formal issues and no\nadverse parties … and are not conducted for the purpose of determining the rights or liabilities of any\nperson” (Title 49 Code of Federal Regulations section 831.4). Assignment of fault or legal liability is not\nrelevant to the NTSB’s statutory mission to improve transportation safety by investigating accidents and\nincidents and issuing safety recommendations. In addition, statutory language prohibits the admission into\nevidence or use of any part of an NTSB report related to an accident in a civil action for damages resulting\nfrom a matter mentioned in the report (Title 49 United States Code section 1154(b)).\nFor more detailed background information on this report, visit the NTSB investigations website and\nsearch for NTSB accident ID PLD20LR001. Recent publications are available in their entirety on the NTSB\nwebsite. Other information about available publications also may be obtained from the website or by\ncontacting—\nNational Transportation Safety Board\nRecords Management Division, CIO-40\n490 L’Enfant Plaza, SW\nWashington, DC 20594\n(800) 877-6799 or (202) 314-6551\n6","truncated":false,"body_characters":18296}