The rupture that knocked out full-service on a part of Williams' Leidy Line in Northeast Pennsylvania in June 2015 was caused by corrosion, according to a report from the U.S. Pipeline and Hazardous Materials Safety Administration (PHMSA).
The report, released over the summer, said the cause of the failure on Leidy line B near Unityville, PA, was "near-neutral stress corrosion cracking of the pipe." Shielding and coating failure, in addition to "cyclic pressures during bidirectional flow" were also identified as leading causes, PHMSA said.
Leidy delivers Marcellus Shale natural gas from Northeast Pennsylvania to the Transcontinental Gas Pipe Line. A bidirectional system consisting of multiple pipes, the Leidy Line is capable of moving 3.5 Bcf/d. The failure occurred on a 24-inch diameter section of the line where it runs parallel to two others on June 9, 2015 (see Daily GPI, June 23, 2015; June 11, 2015). At the time, residents in the area reported hearing a loud roaring sound when the pipeline failed. About 150 people were evacuated by first responders as a precaution.
PHMSA said 96.4 MMcf of natural gas was released in the rupture. No injuries were reported and the incident caused "minimal environmental damage," the report said. Volumes on the system were not significantly affected. The company was able to reroute gas and make deliveries through the A and C lines, which were returned to normal operating pressures just a few days later.
PHMSA's investigation revealed that on the morning of the incident, Williams personnel repositioned valves on line B to allow gas to flow west to Leidy Storage. A review of records showed pressure slowly increased throughout the day. But the agency said operating pressure at the time of failure was 1,141 psi, which was below the 1,200 psi maximum allowable operating pressure.
The line was installed in 1963 and had no history of corrosion. A portion of the Texas Eastern pipeline, known as the Penn-Jersey system, exploded and caught fire in April in Westmoreland County, PA, causing significant property damage and severely burning one resident (see Daily GPI, April 29). In a preliminary investigation of that incident, PHMSA said corrosion was the likely cause (see Daily GPI, May 4). Spectra Energy later said that a failed tape coating likely contributed to the corrosion (see Daily GPI, Sept. 14).