Coating failure is being blamed in part for pipeline corrosion that led to a massive natural-gas explosion in Alabama in December.
The blast at 3:07 p.m. Dec. 3 in Sweet Water could be heard for more than 30 miles, causing a 90-minute blaze that burned eight acres of pine forest. Reports said flames were nearly 100 feet high. The pipeline was shut down immediately, and no injuries were reported.
|More than 1,100 feet of smoking ground surrounds the site of a 2008 pipeline explosion in Appomattox, VA. That blast—like one in December in Alabama—was blamed on external corrosion.|
The U.S. Pipeline and Hazardous Materials Safety Administration is investigating the blast, along with pipeline owner Williams-Transco. Transco is one of three pipeline systems operated by Williams Gas Pipeline Company.
However, the company’s “analytical reports” have already blamed corrosion for the explosion.
“Extremely corrosive soil conditions, combined with failures in the pipeline’s protective coating and cathodic protection system ultimately weakened the pipe, causing it to rupture,” Williams spokesman Chris Stockton said in a statement.
Problem ‘Not Recognized’
The company did not say exactly why it had not spotted and addressed the corrosion earlier.
“Although we have systems and processes in place to prevent and identify corrosion, our investigation indicated there were multiple factors working in conjunction that led to this problem not being recognized,” Stockton said.
The line was smart-pigged in early October, but Transco had not yet received those data from the vendor when the rupture occurred, Cindy Ivey, manager of public outreach for Williams, said earlier.
Corrective Action Order
Stockton said Williams-Transco had made “significant changes to our corrosion control program” since the explosion to prevent a recurrence.
“These changes are designed to more closely monitor levels of pipeline protection from corrosion, assure a higher degree of protection equipment uptime, and provide higher standards for levels of corrosion protection,” he said. “We are also continuing our investigation into this failure to better enhance our corrosion control procedures in the future.”
|Flames rise over Sweet Water, AL, on Dec. 3 after a pipeline rupture. Coatings failure contributed to the explosion, the pipeline owner says.|
The company has been working under a PHMSA Corrective Action Order since the blast. That order details a list of actions required before the pipeline is returned to service. Stockton said Williams-Transco was also “taking steps above and beyond regulation to ensure our pipeline is safe.”
He said the pipeline had been smart-pigged again, to check for other areas of corrosion, metal loss and any other anomalies. After that, he said, the line will be hydrostatically tested at pressures above normal operating pressure.
Previous Corrosion Problems
The statement says Transco will “do our best to learn from this incident,” but the company has been in trouble over pipeline corrosion before.
In April 2010, a 24-inch-diameter Transco line built in 1949 leaked near Kingston, TX. The leak was not reported to PHMSA for four days, due to permissions required to excavate the line, which was on private property.
Ultimately, that leak was traced to Microbiologically-Influenced Corrosion (MIC), as well as degraded, damaged coal tar coating at the leak site. In the end, Transco had to replace 30 feet of pipeline to make the repair.
In September 2008, a Transco 30-inch diameter pipeline dating from 1955 ruptured in Appomattox, VA.
The blast ripped a 32-foot section of pipe from the ground and scorched more than 1,100 feet of surrounding ground.
Five people were injured, 23 families were evacuated, two homes were destroyed, and four others were damaged. The property damage exceeded $3 million.
That blast was also laid to external corrosion, which caused 40% pipe wall loss.
PHMSA eventually fined Transco $952,500 for corrosion control lapses that led to the accident—the first major fine the agency had issued in several years.
The notice of probable violation says Williams violated a provision for buried lines installed before Aug. 1, 1971, that requires cathodic protection of externally coated pipelines.
“Williams did not maintain cathodic protection sufficient to control corrosion along the entire coated pipeline as evidenced by its corrosion record showing low pipe-to-soil readings for Line B in the vicinity of the rupture site,” the notice reads.