NTSB Safety Recommendation P-22-005

NTSB safety recommendation P-22-005.

TO ENBRIDGE, INC.: Revise your integrity management program to include (a) data required to support the active or inactive status of each threat, including hard spots; (b) conditions and situations that require reassessment and re-evaluation of threat status, including flow reversal and other major projects; and (c) the interactions between hard spots and all types of corrosion.

Priority: CLASS II

Overall Status: Closed - Acceptable Action

Issued Date: 2022-09-14

Adopted Date: 2022-08-15

Overall Date Closed: 2023-03-30

Synopsis: On August 1, 2019, at 1:23 a.m. local time, an Enbridge Inc. (Enbridge) 30-inch natural gas transmission pipeline ruptured in Danville, Kentucky, releasing about 101.5 million cubic feet of natural gas that ignited. The accident resulted in 1 fatality, 6 injuries, and the evacuation of over 75 individuals in the Indian Camp Subdivision. Five residences were destroyed by resulting structure fires, and an additional fourteen were damaged. A nearby railroad track was also damaged, and over 30 acres of land were burned.

Probable Cause: The National Transportation Safety Board determines that the probable cause of the August 1, 2019, rupture of an Enbridge Inc. natural gas transmission pipeline and resulting fire was hydrogen-induced cracking at the surface of Line 15 in an area of damaged coal tar enamel coating resulting from a 2014 gas flow reversal project that increased corrosion rates and hydrogen generation. Contributing to this accident was Enbridge’s integrity management program, which did not accurately assess the integrity of the pipeline or estimate the risk from interacting threats.

Ntsbnumber: PLD19FR002

Report Number: PIR-22-02

Addressee Name: Enbridge, Inc.

Addressee Status: Closed - Acceptable Action

Addressee Date Closed: 2023-03-30

Addressee Organization Type: P-Private Industry

Communication Date: 2022-09-14

Communication Type: Transmittal Letter

Communication Contents: This letter provides information about the National Transportation Safety Board’s (NTSB) August 15, 2022, report Enbridge Inc. Natural Gas Transmission Pipeline Rupture and Fire, Danville, Kentucky, August 1, 2019, NTSB/PIR-22/02. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Nonconservative assumptions used to calculate potential impact radius. • Incomplete evaluation of the risks caused by a change of gas flow direction. • Limitations in data analysis related to the 2011 in-line inspection. • Operators’ potential for incomplete assessment of threats and threat interactions. • Missed opportunities in training and requalification practices at Enbridge. Accordingly, the NTSB makes the following safety recommendations to the Pipeline and Hazardous Materials Safety Administration. Additional information regarding these recommendations can be found in the noted sections of the report. • Revise the calculation methodology used in your regulations to determine the potential impact radius of a pipeline rupture based on the accident data and human response data discussed in this report. (P-22-1) (See section 2.3) • Advise natural gas transmission pipeline operators on (a) the circumstances of this accident; (b) the need to evaluate the risks associated with flow reversal projects; and (c) the impacts of such projects on hydrogen-induced cracking. (P-22-2) (See section 2.4) • Advise natural gas transmission pipeline operators of the possible data limitations associated with hard spot magnetic flux leakage in-line inspection tools and analyses used in hard spot management programs and reinforce the need to follow industry best practices when conducting in-line inspection data analysis. (P-22-3) (See section 2.5) The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendations by number (Safety Recommendations P-22-1, -2 and -3). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the pipeline investigation report (PIR-22-02), "Enbridge Inc. Natural Gas Transmission Pipeline Rupture and Fire, Danville, Kentucky, August 1, 2019." Published on September 14, 2022. 2.6 Threat Assessment and Interactions To support threat deactivation, or the point at which threats can be considered stable, an operator must collect data to identify the potential threats. After excavating four hard spots in 2011, Spectra and later Enbridge considered the threat from hard spots eliminated on L15 VS4, thus deactivated. Although measurements from excavations showed conservative agreement with ILI predictions, the number of sites excavated (which were based on the number and severity of anomalies predicted) was statistically insignificant compared with the mileage inspected. After 2011, no further data on hard spots were collected, and Spectra and Enbridge performed no additional HSMFL ILI runs or analyses on Line 15 until after the 2019 accident, when the data were re-analyzed. In its 2019 audit, Dynamic Risk recommended Enbridge consider all threats possible and continually evaluate them, rather than eliminating certain threats entirely (Dynamic Risk 2019). The NTSB concludes that, although Enbridge had classified the threat of hard spots as inactive at the time of the accident on August 1, 2019, insufficient data were available to support this threat status on the ruptured pipeline segment because of the limitations in the HSMFL ILI tool and Enbridge’s analysis. On February 1, 2020, PHMSA published a guidance document on risk assessments and risk modeling, in part to address NTSB Safety RecommendationsP-15-10, P-15-12, and P-15-13 (PHMSA 2020). In 2015, the NTSB recommended that PHMSA update its guidance for gas transmission pipeline operators and inspectors on the evaluation of interactive threats (NTSB Safety Recommendation P-15-10); evaluate the safety benefits of risk assessment approaches allowed by IM regulations and disseminate the results of the evaluation (NTSB Safety Recommendation P-15-12); and update guidance for gas transmission pipeline operators and inspectors on critical components of risk assessment approaches (NTSB Safety Recommendation P-15-13). All three recommendations are classified “Closed—Acceptable Action.” This document recommended pipeline operators address all findings within a 2016 study by Kiefner & Associates, Inc. This study found that changes in operating conditions could intensify certain threats, including those posed by hard spots. Examples of operational changes included changes in temperature and cathodic protection loads, as well as reversal of flow direction (Muñoz and Rosenfeld 2016). Degradation of coating, increased rates of external corrosion, and decreased effectiveness of cathodic protection can also result from operational changes. The flow reversal significantly altered operating conditions on L15 VS4; however, Spectra and Enbridge did not assess L15 VS4 for how the change in operating conditions affected the hard spots between the 2014 flow reversal and the 2019 accident, missing an opportunity to identify threats to pipeline integrity, as discussed in section 2.4. The NTSB concludes that, had the status of threats on Line 15 been re-evaluated after the flow reversal project, Spectra or Enbridge would have had the opportunity to determine how the change in operating conditions affected the hard spots. When considering whether a threat is active or inactive, a pipeline operator must also account for interactions with other threats, according to 49 CFR 192.917. At the time of the 2019 accident, Enbridge’s IM program manual stated manufacturing threats did not interact with corrosion of any type. However, hard spots interact with external corrosion by destabilizing over time from the introduction of hydrogen by cathodic protection, as well as by interacting with internal corrosion. This has been shown in several industry standards and white papers, including API Recommended Practice 1160, Managing System Integrity for Hazardous Liquids Pipelines, and Kiefner & Associates, Inc.’s 2007 report, Evaluating the Stability of Manufacturing and Construction Defects in Natural Gas Pipelines (API 2001; Kiefner & Associates, Inc. 2007). Enbridge used data from the 2011 HSMFL ILI run to classify the threat of hard spots as inactive on the accident pipeline in the area of the rupture, but later analysis and external audits indicated that these data were not enough to substantiate that classification. Changes in pipeline operation—such as a major flow reversal project—can have significant impacts on threats such as hard spots, so Enbridge should have re-evaluated these threats after the project. Further, federal regulations require pipeline operators to account for interactions among threats in their pipelines, as certain threats can intensify others. The NTSB concludes that Enbridge’s processes and procedures were inconsistent with PHMSA guidance and industry knowledge of hard spot threat interactions, leading Enbridge to underestimate the risk posed by hard spots. Therefore, the NTSB recommends that Enbridge revise its integrity management program to include (a) data required to support the active or inactive status of each threat, including hard spots; (b) conditio

Addressee Organization Type: P-Private Industry

Communication Date: 2023-03-31

Communication Type: Official Correspondence

Communication Contents: -From Garrett Wilkie, Director Operational Excellence Enbridge GTM- Engineering and Asset Management, Enbridge, Inc.: Enbridge Inc. (Enbridge or the Company) appreciates the National Transportation Safety Board’s (NTSB or the Board) March 30, 2023 letter classifying Enbridge’s actions performed in response to the above-referenced recommendations issued by the NTSB. Footnote: On September 14, 2022 the NTSB issued recommendations P-22-4, P-22-5, and P-22-6 to Enbridge, concerning the NTSB’s August 15, 2022 Pipeline Investigation Report on the rupture of natural gas pipeline, Line 15 on Enbridge’s TETLP pipeline system that occurred in Danville, Kentucky on August 1, 2019. The recommendations are associated with the NTSB’s investigation of the rupture of natural gas pipeline, Line 15 on Enbridge’s Texas Eastern Transmission, L.P. (TETLP) pipeline system that occurred in Danville, Kentucky on August 1, 2019. The NTSB determined that Enbridge’s actions performed in response to recommendations P-22-5 and P-22-6 satisfy the Board’s recommendations and classified them as “Closed-Acceptable Action.” With respect to recommendation P-22-4, the NTSB determined that the actions outlined by Enbridge may satisfy the recommendation, once completed, and classified it as “Open Acceptable Response.” Enbridge submits this update to its December 13, 2022 letter to confirm completion of outstanding actions associated with P-22-4. At the time of its December 13, 2022 letter, Enbridge was finalizing (1) a third party review of historical operating data on TETLP Line 15 and (2) implementing changes associated with Enbridge’s internal management of change process (MOC), a part of Enbridge’s integrated management system (IMS) consistent with the American Petroleum Institute’s Recommended Practice (RP) 1173, Pipeline Safety Management Systems. Below is a summary of the reviews that have now been completed and procedural revisions that have been implemented. 1. Third Party Review of Historical Operating Data: Enbridge engaged third party experts to conduct a review of historical operating data on TETLP Line 15 since before the flow reversal projects began in 2014 to the present for any impacts on corrosion control effectiveness. The historical review integrated data from 2010 to 2022 on Line 15 to review cathodic protection (CP) levels and pipeline coating effectiveness through evaluation of annual survey data, CP ground bed and rectifier current output history, supplemental CP ground bed installations, compressor discharge temperatures in both flow direction, and corrosion in-line inspection data. Other than what the NTSB identified in its Pipeline Investigation Report (PIR-22/02), there has not been any indication that the flow reversal project adversely impacted corrosion control equipment effectiveness. Enbridge concluded that revisions to the Gas Transmission and Midstream (GTM) integrity management plan (IMP) are not warranted as a result of this historical data review. Footnote: Enbridge GTM includes pipeline transmission systems located in the U.S. and Canada where operated by Enbridge or its subsidiaries. See https://www.enbridge.com/about-us/natural-gas-transmission-and-midstream 2. MOC Process: Enbridge completed a review and revision of its program level processes in alignment with the IMS MOC process requirements and incorporated consideration of the NTSB’s recommendation. Specifically, Enbridge identified certain areas of improvement within the MOC process and implemented associated revisions to account for adequate MOC reviews for potential impacts to integrity performance and integration into ongoing integrity assessment planning of major projects, including gas flow reversals. Consistent with its goal of continuous improvement, Enbridge also regularly incorporates appropriate updates to these processes based on lessons learned and when implementing new rulemakings. With this update, Enbridge’s entire Gas Transmission and Midstream business unit, including TETLP, has fully implemented all of the NTSB recommendations. The initiatives that Enbridge has undertaken in response to the Danville, Kentucky incident and the relevant NTSB recommendations have enhanced Enbridge’s programs and efforts. Enbridge believes they will lead to significant advancement of the industry’s management of the hard spot threat. Enbridge is determined to continually improve its safety culture, performance, and to lead industry in safety best practices. Please do not hesitate to contact me if you have any questions or concerns regarding this update.

Addressee Organization Type: P-Private Industry

Communication Date: 2022-12-13

Communication Type: Official Correspondence

Communication Contents: -From Al Monaco, President and Chief Executive Officer, Enbridge Inc.: Incorporating lessons learned and reassessing the condition of its pipelines has been a foundational component of the Enbridge GTM’s IMP since its inception, including consideration and analysis of interacting threats. Since the Danville, Kentucky incident, Enbridge has committed extensive resources to improving management of all threats for improved safety and reliability, resulting in a shift in the approach of its Asset Integrity Program for its GTM assets, including: (1) consolidation of all previous asset specific IMPs into the Enbridge GTM IMP that is applied across the entire GTM system; (2) a threefold increase in ILI and anomaly excavations; (3) development of the safety case program to validate program results; and (4) quantitative risk assessments based on facts and data. As set forth below, Enbridge GTM agrees with NTSB recommendation P-22-5. Toward that end, Enbridge has implemented the recommendation to further enhance its GTM IMP with respect to threat interaction, aspects of which have been incorporated in updates to IMP standard operating procedures (SOPs) since the incident and through the development of a new process detailing management of interacting threats as part of Enbridge GTM’s IMP. (a) IMP revisions to address “data required to support the active or inactive status of each threat, including hard spots.” The Enbridge GTM IMP requires data specific to each pipeline to be collected, including those elements listed within ASME B.31.8S Table 4.2.1, as well as construction and pipe attribute records, incident history, corrosion control records, continuing surveillance records, patrolling records, maintenance history, internal inspection records, applicable industry data, and operator qualification records. Each pipeline is assessed in the context of level of susceptibility, likelihood of occurrence, and risk against all threats listed within ASME B31.8S, including hard spots. Factors informing threat susceptibility are established in accordance with industry guidelines and documented within threat specific IMP guidance documents which specify the conditions and data required to evaluate threat susceptibility. Threat susceptibility is determined based on the unique factors for each threat and assessment plans are prioritized accordingly. Susceptibility and assessment planning for all threats are reviewed annually and updated as new data such as inspection results, research, or incident failure analysis requires changes to the threat assessment plan. Similarly, through the Enbridge GTM Risk Algorithm Document (RAD), threat susceptibility and likelihood are calculated and used to determine the overall risk of a threat on each line segment and thereby informing assessment planning on each pipeline. In addition, likelihood and risk are reviewed at least annually and updated when new data is available. In response to the Danville, Kentucky incident, Enbridge performed the following specific to data and threat susceptibility for hard spots and which has been incorporated into relevant Enbridge GTM IMP SOPs and which Enbridge believes addresses NTSB recommendation P-22-5(a): 1. Consideration of Manufacturing Threats under IMP: IMP documents that specify data informing threat susceptibility and assessment guidance of the manufacturing threat have been updated to include additional guidance for hard spots based on findings from the 2019 incident. Additionally, a safety case analysis was performed in 2021 to further establish parameters of hard spot susceptibility on the Enbridge GTM system. See Pipeline Integrity – Integrity Management Plan, version 2.2 (2022-06-13); GTM Risk Algorithm Document (2021-11-18) (see p. 68); Threat Response Guidance Document (TRGD) – Manufacturing, version 3.0 (2022-05-11); Safety Case: Manufacturing Defect System-wide Assessment (July 6, 2021). 2. Hard Spot Tool Qualification: Based on RWP Increments 1 and 2, qualification of ILI tools and work with ILI vendors to develop, test, evaluate, and qualify ILI tools capable of detecting, identifying and characterizing hard spots, thereby providing additional quantitative data informing the status of the hard spot threat. See PI-04.509 In-Line Inspection Response for Hard Spot Anomalies, version 1.2 (2022-07-15); PI-04.104 Comprehensive Assessment Method Selection, version 1.2 (2022-08-08). 3. Hard Spot Tool Validation: Validated the accuracy and conservatism of the ILI hard spot tools through testing and field assessments. See PI-04.509 In-Line Inspection Response for Hard Spot Anomalies, version 1.2 (2022-07-15); PI-01.304 Hard Spot Examination, version 1.2 (2022-07-07). As a process of continuous improvement, Enbridge GTM has scheduled additional hard spot ILI reassessments on TETLP Lines 15 and 25 in March and September of 2023 to further validate the 2020 inspection program findings, which Enbridge will complete by November 1, 2023. 4. Third Party Review of Historical Operating Data: As noted in Enbridge’s response to NTSB recommendation P-22-4, Enbridge engaged third party experts to conduct a review of historical operating data on TETLP Line 15 since the flow reversal projects began in 2014. Enbridge will incorporate any learnings informing data requirements for threat status into the threat assessment analysis by March 31, 2023. (b) IMP revisions to address “conditions and situations that require reassessment and re-evaluation of threat status, including flow reversal and other major projects.” As part of Enbridge GTM’s shift to a quantitative integrity management approach, Enbridge evaluated and consolidated best practices from all legacy GTM pipeline IMPs into one plan that is applied consistently across the entire system. The new GTM IMP, published in 2020 and updated in 2022, includes comprehensive threat susceptibility, inspection, assessment, mitigation, monitoring, and continuous improvement requirements that are designed to ensure safe and reliable performance of the system. Enbridge believes that with these changes, its existing GTM IMP addresses NTSB recommendation P-22-5(b) regarding conditions that trigger the need to reevaluate threat status, including flow reversal and major projects. Specific to conditions and situations that require reassessment and re-evaluation of threat status, including flow reversal and other major projects, the GTM IMP requires continuous evaluation of all threats, including integration of new information when available, and assessment plans are updated and MOC reviews are performed when changes in operating conditions, including major projects such as flow reversals, are planned. Assessment plans are updated when an existing asset has a change in service conditions, if new threats are identified, or upon the completion of an integrity assessment of the asset. See Pipeline Integrity – Integrity Management Plan, Sec. 1.2, Integrity Plans, version 2.2 (2022-06-13). Additionally, any changes to threat susceptibility conditions or likelihood of occurrence resulting from any change in operations, including major projects and flow reversals, are evaluated and mitigated prior to placing a project in service. Under the GTM IMP, threat susceptibility, status, likelihood, risk, assessment, and mitigation plans are evaluated on an ongoing basis to ensure all facilities are fit for service. As stated in the response to P-22-4, Enbridge is currently evaluating its IMS MOC processes in consideration of the conditions that may warrant reassessment of threat status and Enbridge will make revisions as needed by March 31, 2023. In addition, reviews are regularly conducted as a matter of course to incorporate lessons learned and when implementing new rulemakings. (c) IMP revisions to address “the interactions between hard spots and all types of corrosion.” Threat interactions are a critical element of the Enbridge GTM IMP. En

Addressee Organization Type: P-Private Industry

Communication Date: 2023-03-30

Communication Type: Official Correspondence

Communication Contents: We note that you have consolidated all previous asset-specific IMPs into a single gas transmission and midstream (GTM) IMP that is applied across your entire GTM system. Additionally, you enhanced your asset integrity program to include a threefold increase in in-line inspection (ILI) and anomaly excavations, a safety case program to validate program results, and quantitative risk assessments based on facts and data. You have also completed the following: • updated your IMP documents to include additional guidance on hard spots • performed a safety case analysis to further establish parameters of hard spot susceptibility on your GTM system • worked with ILI vendors to evaluate and qualify ILI tools that can detect and characterize hard spots • revised your GTM IMP to include guidance on conditions that trigger the need to reevaluate threat status, including flow reversal and major projects • revised your GTM IMP to address the interaction between hard spots and all types of corrosion • adopted this hard spot inspection and repair criteria into your standard operating procedures across your entire GTM pipeline system These actions satisfy Safety Recommendation P-22-5, which is classified CLOSED-- ACCEPTABLE ACTION.