NTSB Safety Recommendation P-22-003

NTSB safety recommendation P-22-003.

TO THE PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION: 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.

Priority: CLASS II

Overall Status: Closed - Acceptable Action

Issued Date: 2022-09-14

Adopted Date: 2022-08-15

Overall Date Closed: 2025-06-16

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: PHMSA

Addressee Status: Closed - Acceptable Action

Addressee Date Closed: 2025-06-16

Addressee Acronym: PHMSA

Addressee Organization Type: G-Federal Government

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. 2.5 In-Line Inspection Tool and Data Analyses The 2011 hard spot in-line inspection data discussed in sections 1.8.4.1 and 1.8.5 were analyzed twice by ILI vendors: the first analysis in 2011 predicted 16 potential hard spots, while the second analysis in 2019 (requested by the NTSB after the rupture) predicted 441 hard spots. Although hard spots occur during manufacturing and would have been present at the time of the 2011 HSMFL ILI run, the closest hard spot reported by NDT Systems & Services in 2011 following their analysis was located about 2.2 miles from the rupture site. After the 2019 accident, the NTSB performed hardness and microhardness testing in the area of the fracture origin. The NTSB found that two hard spots identified in the 2019 NDT Global analysis near the fracture origin were significantly harder than ILI predictions; in fact, these two hard spots were one hard spot. Further, at an additional location where the 2019 NDT Global analysis predicted a hard spot, the NTSB found that no hard spot was present. Including the four verification digs in 2011 and the NTSB measurements, only seven points were available for comparison between predicted and actual hard spots. A sample size of 7 out of 441 is statistically insignificant, and no trends can be determined from these limited data. Insufficient data are currently available to determine the accuracy of NDT Systems & Services’ hard spot tool, NDT Systems & Services’ 2011 analysis report, or NDT Global’s 2019 analysis report. The NTSB recognizes that the 2019 analysis conducted by NDT Global identified more hard spots than the 2011 analysis. However, the presence of the hard spot found by the NTSB during postaccident testing that exceeded the size and hardness specified by current API 5L standards suggests limitation in either the hard spot tool, the HSMFL ILI inspection method, or of the analysis of the collected data. NDT Systems & Services’ performance specification for its hard spot tool did not clearly state if the probability of detection, location accuracy, and sizing accuracy applied to hard spots, metal loss anomalies, or both. To be consistent with the 2005 edition of API STD 1163, all these specifications should have been included, as well as the limitations of the tool when detecting hard spots. For example, NDT Systems & Services should have listed the upper and lower detection limits for hard spots. At the time of the 2011 HSMFL ILI run, API STD 1163 had been an industry best practice for almost 6 years. The analysis of ILI data further complicates the issue of tool limitations, as some ILI tools, including hard spot tools, rely heavily on analyst interpretation when processing the raw data. Different software settings selected by the analyst, such as gain, and equipment specifications, including monitor resolution, can result in large differences in findings, which in turn impact ILI predictions. NDT Systems & Services’ 2011 analysis did not discuss any specifics on the analysis methods or settings. In addition to running its HSMFL ILI tool on Line 15 and other TET pipelines, NDT Systems & Services ran its tool on at least 1,320.8 miles of pipelines owned by other operators. As stated above, the tool’s performance specifications were incomplete, field verifications consistent with current regulations were insufficient to validate ILI tool performance, and insufficient data were available on the accuracy of the hard spot tool. Even if an operator were to conduct data analyses according to industry standards, because of the deficiencies noted with the tool, the NTSB is concerned that pipelines inspected with NDT Systems & Services’ HSMFL ILI tool may have similar unidentified issues. Therefore, the NTSB concludes that the extent of hard spots on other pipelines evaluated using NDT Systems & Services’ HSMFL ILI tool is likely unknown because of the limitations of the tool and analysis techniques found during this investigation; thus, operators who have relied on this tool for hard spot detection may be unable to effectively manage pipeline integrity. The NDT Systems and Services HSMFL ILI tool was not the only tool of this type on the market in 2011. However, starting in 2013, the number of available HSMFL ILI tool vendors diminished, including NDT Systems and Services, which discontinued the use of their tool the year before. Since 2013, new HSMFL ILI tools have been developed, and the availability and maturity of these tools and the analysis of their data has advanced. The advancement in the analysis of the data was demonstrated by the increase of potential hard spots identified in the 2019 analysis conducted by NDT Global; even using data from the old tool, additional hard spots were identified. However, the NTSB also found that the identification did not represent real world findings following the 2019 analysis; thus, a more advanced tool may help improve hard spot identification. Hard spots are often considered inactive threats, and pipeline operators can consider inactive threats stable. If operating conditions are stable and hard

Addressee Acronym: PHMSA

Addressee Organization Type: G-Federal Government

Communication Date: 2023-01-11

Communication Type: Official Correspondence

Communication Contents: You responded that PHMSA will review accident data and advise pipeline operators on the appropriate in-line inspection technologies for different anomalies, including possible data limitations associated with hard spot detection. We are aware that you discussed this recommendation with pipeline operators during your December 13–15, 2022, public meeting in Houston. Pending the completion of this action, Safety Recommendation P-22-3 is classified OPEN-- ACCEPTABLE RESPONSE.

Addressee Acronym: PHMSA

Addressee Organization Type: G-Federal Government

Communication Date: 2025-06-16

Communication Type: Official Correspondence

Communication Contents: We commend PHMSA for hosting the December 13–15, 2022, public meeting in Houston, Texas, focusing on these recommendations. National Transportation Safety Board (NTSB) staff presented at this meeting, and other NTSB staff attended to listen to public input on these recommendations. On November 18, 2024, PHMSA published Advisory Bulletin ADB-2024-011, “Evaluation of Potential Hard Spots – In-line Inspection Tools and Analysis,” which was issued due to advancements in knowledge of hard spot susceptibility—most notably that what was once considered to be an issue confined to a single manufacturer of specific, limited manufacturing years is now understood to include potentially other manufacturers and manufacturing years. Additionally, the presence of hydrogen may result in hydrogen-induced cracking due to accumulation of stress on the steel. The bulletin encourages owners and operators to expand their hard spot threat evaluation to all pipe manufactured before 1970, regardless of manufacturer. The bulletin also advises operators to follow industry best practices when using in-line inspection tools. This action meets the intent of this recommendation. Accordingly, the Board has classified Safety Recommendation P-22-3 CLOSED-- ACCEPTABLE ACTION. Thank you for your commitment to pipeline safety.

Addressee Acronym: PHMSA

Addressee Organization Type: G-Federal Government

Communication Date: 2025-01-17

Communication Type: Official Correspondence

Communication Contents: -From Tristan H. Brown, Deputy Administrator: PHMSA’s Actions to Address Safety Recommendations P-22-002 and P-22-003: Following the NTSB investigation into the Danville incident and recommendations, PHMSA responded to the NTSB in correspondence dated November 25, 2022, for Recommendations P-22-002 and P-22-003. PHMSA reviewed incident and accident data and available information regarding hard spots and the appropriate methodologies and technologies for detecting them. PHMSA met with industry and technology companies to gather information regarding hard spot management programs and appropriate in-line inspection (ILI) technologies for detection and evaluation of different anomalies, including hard spots. PHMSA hosted a three-day public meeting in Houston, Texas, in December 2022. The Agency provided an overview of the Danville incident and the NTSB’s findings and recommendations in PIR-22-02, and invited stakeholders to present information related to hard spot detection methodologies. Subsequently, PHMSA identified more pipe manufacturers and pipe vintages that could have issues with hard spots. As a result, on November 18, 2024, PHMSA published Advisory Bulletin ADB-2024-011 (ADB) titled, Identification and Evaluation of Potential Hard Spots – In-line Inspection Tools and Analysis. In this ADB, PHMSA alerted operators of advancements in knowledge of hard spot susceptibility to include multiple pipe manufacturers and manufacturing years; hydrogen-induced cracking; new developments in ILI technologies to better identify features associated with hard spots; significant improvements in data analytic methods to enable older data to be re-analyzed to identify previously unknown features; and information stating that data verification should not be limited in scope and should include a thorough review of all relevant data. PHMSA also detailed actions pipeline operators should consider taking to ensure pipeline safety, including review of pipeline design and construction records to determine hard-spot susceptibility; review of known integrity issues; development and implementation of enhanced assessment approaches to material hardness anomaly validations; re-evaluation of existing ILI data; and publicly sharing findings. The scope of the ADB included owners and operators of gas, hazardous liquid, and carbon dioxide pipeline systems—beyond the original scope of the NTSB’s recommendations. PHMSA’s Actions to Address Safety Recommendation P-22-002: By correspondence dated January 11, 2023, the NTSB classified this Safety Recommendation as “Open – Acceptable Response” pending PHMSA’s update of the advisory bulletin for flow reversal (ADB-2014-04). While PHMSA initially considered an update of ADB-2014-04, the safety objectives of P-22-002 were achieved through multiple complementary actions to ADB 2014-04 and the requirements of existing regulations. These actions include direct engagement with pipeline operators at our December 2022 public meeting where we discussed the Danville incident findings, the need for the recently issued ADB-2024-01, and our past and on-going research & development (R&D) in this and related area. The pipeline safety regulationsi in Title 49 Code of Federal Regulations (CFR) Parts 190–199 require natural gas transmission pipeline operators to assess and manage hard spots both within and outside of high consequence areas (§ 192.710, § 192.921(a), and § 192.937(c)). These regulations also require notification of flow reversals expected to last more than 30 days (§ 191.22(c)(1)(v)); require integrity assessment methods capable of detecting susceptible hard spots with cracking (§ 192.710, § 192.921(a), and § 192.937(c)); and specify evaluation and remediation of crack or crack-like defects (§ 192.917(e)(6)). The regulations also require controlling the amount of cathodic protection to prevent coating or pipe damage (§ 192.463(c)) and prescribe requirements for threat identification risk analysis (§ 192.917). Operators must integrate pertinent information including from operations and maintenance activities; manufacturer and manufacture dates; the existence of disbonded coatings or other conditions that compromise the effectiveness of corrosion protection; and industry experience for incident, leak, and failure history (§ 192.917(b)). Additionally, operators subject to integrity management requirements must implement measures beyond those specifically prescribed in the regulations to prevent and mitigate the consequence of pipeline failure in high consequence areas. As preventative and mitigative measures, operators must consider, among others, establishing and implementing adequate operation and maintenance processes that could enhance safety; re-coating damaged/disbonded coating; and testing to determine unknown material mechanical properties to ensure or substantiate maximum allowable operating pressure (§ 192.935). ADB 2014-04 and its corresponding supplementary guidance document specifically address reviewing past integrity assessments, noting that threat locations may change and previously stable threats may become unstable due to operational changes. The ADB stated that it may not be advisable to perform flow reversals on pipelines with history of failures, leaks, or manufacturing defects. PHMSA’s recent ADB 2024-01 expands on ADB 2014-04 by alerting operators of advancements in knowledge of hard spot susceptibility across multiple pipe manufacturers and manufacture years; hydrogen-induced cracking; new developments in ILI technologies and data analytics; and specific actions operators should take to ensure pipeline safety. In a December 2022 public meeting, PHMSA also highlighted the January 2017 amendments to the pipeline safety regulations requiring notifications of flow reversals, conversions to service, and changes in commodity. Meeting materials may be found on PHMSA’s website. PHMSA’s review of incident and accident reports from August 15, 2022—the date P-22-002 was issued—through December 2024 did not identify any incidents or accidents where flow reversal or hydrogen-induced cracking was causal or the apparent cause to the incident or accident. REQUEST FOR CLOSURE OF RECOMMENDATIONS P-22-002 AND P-22-003: PHMSA takes its responsibility to fully address all NTSB recommendations seriously and works hard to continuously improve its pipeline safety program. Based on the actions PHMSA has taken, I am requesting that Safety Recommendations P-22-002 and P-22-003 be classified as “Closed-Acceptable Action.” PHMSA looks forward to working with your office as it continues to strive to ensure the safe, reliable, and environmentally sound operation of the nation’s pipeline transportation system. If you have any questions or require additional information, please do not hesitate to contact me, or have your staff contact Damon Hill, Deputy Director of Governmental, International, and Public Affairs.

Addressee Acronym: PHMSA

Addressee Organization Type: G-Federal Government

Communication Date: 2022-11-25

Communication Type: Official Correspondence

Communication Contents: -From Tristan H. Brown, Deputy Administrator, PHMSA: Concur. PHMSA will review accident data and information regarding hard spots and the appropriate methodologies/technologies for detecting hard spots and communicate to operators the results of the data analysis and discuss appropriate in-line inspection technologies for different anomalies including hard spot detection. PHMSA continually seeks to use and evolve its oversight program, including changes to pipeline safety policies and inspection and enforcement approaches. A major tenet of PHMSA’s oversight program is that pipeline operators must know and understand their pipeline systems and use appropriate technologies and procedures to address risk to prevent pipeline failures while considering the inherent limitations of technology. PHMSA prescribes factors that must be addressed to mitigate risk and conducts inspections to ensure adequate measures are carried out effectively. PHMSA also invests in research and development that advances the best expertise in the world to help improve technology, especially detection methods relevant to pipeline failures. PHMSA is fully committed to carrying out its pipeline safety oversight authority to improve safety and protect Americans while addressing all of the NTSB safety recommendations. PHMSA also values the role of the NTSB and our collective pipeline safety partnership. We believe the planned actions described above will adequately address the safety recommendations and we look forward to working with you and the dedicated staff at the NTSB as we continue our important work to help ensure the safe, reliable, and environmentally sound operation of the nation’s pipeline transportation system.