The wall thickness of a section of pipe on the 20-inch diameter Columbia Gas Transmission system that ruptured last Tuesday in West Virginia was significantly deteriorated, said National Transportation Safety Board (NTSB) investigators Thursday.
There also was a pressure drop on the line, but the magnitude of the decrease was unknown as was whether the drop in pressure was the result of the rupture or its cause.
"In parts of [the] area, pipe wall thickness was measured to be less than a 10th of an inch thick," said NTSB board member Robert Sumwalt following two days of inspecting the rupture site near the pipeline's Lanham Compressor Station in the rural community of Sissonville, WV, which is about 15 miles north of Charleston.
He said the pipe wall was only 0.078 inch thick in certain areas, which amounts to about a 70% loss in wall thickness. The agency estimated that the wall was thinner along the bottom of the pipeline for about six feet.
The explosion on the Columbia Gas system Dec. 11 created a crater of 15 to 17 feet deep, according to Sumwalt. "When you look down into the crater, there's a 20-foot, seven-inch gap in the pipe, and...that part was ejected out of the crater about 40 feet. That pipe is about pretty much flattened out," he said.
Columbia CEO Jimmy Staton on Friday issued an "open letter" to the affected families of Kanawha County, WV -- "something went terribly wrong with our natural gas pipeline near Sissonville [Tuesday], and we are working tirelessly -- in full cooperation with state and federal authorities -- to find out why."
While the company is "thankful" that there were no serious injuries, it said it recognized that members of the community are going through significant hardship, particularly those whose homes were lost or damaged, he said. "Along with community partners and support groups, we are working to help those in need, providing temporary houses and other essentials."
On Friday, the NTSB said it would continue to interview control center personnel; prepare the damaged section of the pipeline for shipment to Washington, DC; and begin the process of extracting parts of the pipeline that were not ejected from the explosion crater. Sumwalt said the agency planned to excavate about six to 10 feet of undamaged pipeline to "try to get an idea of [what] the undamaged pipeline" looks like.
"There are many things that can cause pipe wall thickness to deteriorate, and that is exactly what we will be looking at...and then what finally led to the actual rupture and explosion of the pipeline," Sumwalt said. The NTSB did not say when the Columbia Gas pipeline was last inspected or how old it is.
Sumwalt declined to say that the pipe wall deterioration and drop in pressure contributed to the explosion, which occurred at 12:41 EST last Tuesday under Interstate 77. However these factors, especially thinning wall thickness, have been cited as causes in previous pipeline accidents. There were no major injuries in West Virginia. According to Sumwalt, there were isolation valves both upstream and downstream of the rupture, which were "manually shut off" at about 1:45 p.m. EST.
"We are very fortunate for the time of the explosion. There were no vehicles on the interstate," and no one was at home at the residences that were destroyed, said West Virginia Go. Early Ray Tomblin.
Sumwalt said officials had not determined whether the the drop in pressure was to such a low level that it should have sounded alarms at the Columbia Gas control center in Charleston. The pressure drop occurred at the upstream Lanham Compressor Station. "We understand that there were no alarms generated at the time of the accident" in the control center.
"As we speak...investigators are interviewing control center personnel to find out what indications the pipeline controller may have had associated with the pressure drop," he said last week.
NTSB investigators have been onsite at Sissonville since last Tuesday, just hours after the explosion. The 10-member investigation team is being lead by Ravi Chhatre, an expert on pipeline operations, fire and explosions and emergency-response efforts. Chhatre was the NTSB's investigator in charge of the four-member team that investigated the fatal San Bruno, CA, pipeline explosion in September 2010.
"We have not spoken in detail to Columbia Gas at this point, but certainly that is something that we will be doing, and we will have their representatives here working with us for the next several days," Sumwalt said last Wednesday.
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