NTSB Releases KY Pipeline Rupture Report


Earlier this week, the National Transportation Safety Board announced that a manufacturing defect and ineffective cathodic protection led to the 2019 natural gas pipeline explosion in Danville, Kentucky.

The explosion of the 30-inch pipeline, owned and operated by Enbridge Inc., caused the death of one person, destroyed five homes, damaged fourteen other residences and burned about 30 acres of land.

What Happened

Around 1:23 a.m. on Aug. 1, 2019, regional gas pipeline Line 15 ruptured, resulting in flames reaching bout 300 feet in the air that could be seen throughout the county. A local meteorologist reported that the explosion was so huge it showed up on the radar.

At the time, Kentucky State Police spokesman Robert Purdy said at least five homes were destroyed and structures within 500 yards were damaged. A handful of people who were missing after the blast had also been accounted for.

About 75 people were evacuated, with authorities urging people to stay away as crews worked to contain the damage. One woman appeared to have left her home due to the fire and had been overtaken by the heat, leading to her death. She was taken to the medical examiner’s office to determine cause of death.

Purdy said the fire burned so hot that it left the landscape barren, burning trees and grass and leaving only red dirt, rocks and gravel. It took firefighters hours to douse the flames, having to refill trucks repeatedly to return to the scene.

Nearby railroad tracks owned by Norfolk Southern Corporation were also damaged by the blast, forcing 31 trains to back up overnight, authorities said. Crews worked to repair the tracks and were reopened later in the day.

Emergency managers had determined that the rupture involved the Texas Eastern Transmission pipeline, which is owned and operated by Enbridge. The pipeline reportedly stretches several thousand miles from the Mexican border in Texas to New York City.

Enbridge spokesman Jim McGuffey said at the time that the two other nearby gas lines didn’t appear to be affected but would be inspected. He also said there was no indication of what might have caused the explosion.

In an update on Aug. 8, Enbridge stated that they had completed preliminary air, soil and water sampling from the incident site, with results indicating no risk to human health. The company also said that they had taken two adjacent natural gas pipelines out of service as a precautionary measure.

That same day, Enbridge received a corrective action order from the Pipeline and Hazardous Materials Safety Administration. “We are working diligently to comply with the requirements identified by the PHMSA, and to return to service two adjacent natural gas pipelines near the incident site that were taken out of service as a precautionary safety measure,” the company said.

One pipeline, the Texas Eastern Line 25, was returned to service on Aug. 26, with Line 10 returning to service on Sept. 1. This was reportedly done after a thorough evaluation to validate the integrity of the pipeline in compliance with regulatory requirements.

The NTSB had sent three investigators to the site the day of the incident. In its preliminary report, the board said that a 33.2-foot-long section of the pipeline was ejected and landed about 481 feet southwest of the rupture site.

Initial data provided by Enbridge from its gas control center showed that a rate-of-change gas pressure alarm was received for Line 15 at the time of the rupture, with the Danville compressor station operator also receiving the alarm. The operator told investigators he could see the fire from his station.

According to the report, the ruptured pipeline was produced by A.O. Smith Corporation and placed into service in 1957. The pipe had an electric flash-welded seam and was coated with coal tar enamel. The portion of Line 15 at the rupture site consisted of 0.375-inch wall thickness steel pipe, with a maximum allowable operating pressure of 936 pounds per square inch.

At the time of the rupture, gas was flowing and operating at 925 pounds per square inch. The area had not been designated by Enbridge as a High Consequence Area. Inspections had been performed to evaluate the pipeline material properties in 2011, along with pipeline geometry evaluation in 2018 and 2019.

The NTSB also found that Line 15 had previously ruptured on Nov. 2, 2003, in Moorhead, Kentucky. 167,100 million cubic feet of natural gas had been ignited, but no fatalities or injuries occurred in that incident. The NTSB did not investigate this rupture.

Investigation Results

On Wednesday (Sept. 14), the NTSB released a new report regarding the accident, stating that a pre-existing manufacturing defect, known as a hard spot, combined with a degraded pipeline coating and ineffective cathodic protection led to hydrogen-induced cracking at the outer surface of the pipe.

The NTSB reports that Enbridge’s integrity management program did not accurately assess the condition of the pipeline or estimate the risk from interacting threats. The report said that Enbridge underestimated the risk posed by hard spots because its processes and procedures were inconsistent with PHMSA’s guidance and industry knowledge of hard spot threat interaction.

Investigators reportedly noted that Enbridge and its predecessors increased cathodic protection voltages on the affected pipeline segment to compensate for the increased external corrosion. 

According to the release, the NTSB issued three safety recommendations to the PHMSA and three recommendations to Enbridge, addressing the following:

  • Incomplete evaluation of the risks caused by a change of gas flow direction;
  • Limitations in data analysis related to in-line inspection tool usage;
  • Incomplete assessment of threats and threat interactions; and
  • Missed opportunities in training and requalification practices.

In an emailed statement to The Associated Press, Enbridge spokesman Michael Barnes said the company was “deeply sorry for the impact to the community and to the family who lost a loved one,” adding that the findings are a “stark reminder” of the importance of safely maintaining and operating the company’s pipelines.

Barnes said in the statement that the company takes the NTSB recommendations “very seriously” and has “worked diligently to understand the contributing factors to this incident and (has) made tremendous strides to change our procedures, processes and conducted extensive inspections in an effort to make our pipes safer than ever.”

The full pipeline accident report can be viewed here. The accident docket, which contains photos, interviews and other factual material, can be found here.


Tagged categories: Accidents; Cathodic disbondment; Cathodic protection; Coating failure; Explosions; Fatalities; Fire; Health & Safety; Health and safety; NA; North America; NTSB (National Transportation Safety Board); Oil and Gas; Pipeline; Pipelines; Program/Project Management

Join the Conversation:

Sign in to our community to add your comments.