The blast of high-pressure natural gas that led to dozens of home explosions last week in Massachusetts very likely damaged the system’s antiquated pipeline network and could lead to a long period of testing and repairs before full service is restored to thousands of customers.
The pipeline system received 12 times its normal pressure before the blasts last Thursday evening, perhaps more in places, according to data released by lawmakers and investigators. Much of the system is made of cast iron, which is brittle and can crack under pressure, said Richard Kuprewicz, a consultant who specializes in pipelines.
As a result, NiSource Inc.’s Columbia Gas of Massachusetts must test the scores of supply lines to at least the 8,600 customers before gas can be switched back on, a painstaking process, Kuprewicz said. That means people may be waiting weeks or months for household basics like hot water, heat and cooking.
“It takes a while to do this,” Kuprewicz said. “Meanwhile, the winter is coming.”
While people living in the region were allowed to return home on Sunday and electrical power was restored, NiSource hasn’t said when it expects to get its gas supply system working again.
8,600 Customers Affected
Of the 8,600 customers affected, some won’t see service returned until pipes in their neighborhoods are replaced, Ken Stammen, a NiSource spokesman said in a telephone interview. Gas could be restored for others before a full replacement, Stammen added. It’s “impossible” to know how many customers fall into each category and the timetable for restoration hasn’t been determined, he said.
Though replacing gas pipelines typically takes years and is done in small segments to reduce disruption, the company said it’s accelerating its plans to replace the pipelines as rapidly as possible.
“We are not currently turning gas service back on for customers on the affected system in the area,” Columbia said on a website for customers. “Our first priority is to ensure the safety of the public and the community. We do expect this to be an extended restoration process.”
In addition to the core of customers in the most affected areas, an additional 5,800 customers live outside those areas but had their gas shut off as a precaution, Stammen said. Service has been restored to most of them.
The U.S. National Transportation Safety Board confirmed that the failures, which triggered explosions across three towns and killed one person struck by a falling chimney, were triggered by “an over-pressure situation,” Robert Sumwalt, the agency’s chairman, said in a briefing on Sunday.
Major supply lines are pressured to 75 pounds per square inch, Sumwalt said. The pressure is supposed to be reduced to 0.5 pounds in the smaller pipes that transmit gas onto streets and into homes, he said.
While Sumwalt stopped short of saying what caused the pressure spike, a device designed to regulate pressure appears to have tried to add gas because it was hooked up to a pipe that was taken out of service, he said. If a sensor to the out-of-service pipe registered no pressure, the system would be programmed to boost gas in the lines, Sumwalt said.
Readings within the system indicated that pressure reached at least 6 pounds, which is 12 times the recommended level, according to a letter Monday from Massachusetts’ two senators, Ed Markey and Elizabeth Warren.
The lawmakers, both Democrats, said that they hoped to hold hearings on the failure and demanded that the utility provide records on how it responded. The pressure figures were reported by the U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration, they said.
As many as 80 homes and buildings were destroyed or damaged in the explosions and fires that followed. At least 25 people were injured, the senators said.
Some homes have been without hot water or gas for cooking since then, and autumn arrives in just a few days. The demand for overnight heating typically begins in that part of New England in the first week of October, according to Matt Rogers, president of Commodity Weather Group LLC, a forecaster in the natural gas industry.
“We are looking at all options that are out there to meet our customer needs,” Stammen said. “We don’t want anybody” to get cold, he added. “All options mean all options.”
Vast sections of U.S. natural gas utilities are made up of outdated cast iron pipes that could be as old as 100 years and unprotected steel that is also subject to corrosion and wear.
The 48-mile sector involved in Thursday’s explosions is cast iron and bare steel, according to the company. The exact age of the pipes wasn’t available, Stammen said. They pre-date the 1970s, when regulations required plastic or protected steel.
Such older pipes are prone to failures and tests with sensors show that they frequently leak, said Rob Jackson, the chairman of the department of Earth System Science at Stanford University.
Yet the explosions in the Massachusetts communities of Lawrence, North Andover and Andover, don’t appear to be typical of leaks seen in older systems, Jackson said. While it’s not uncommon to find multiple leaks along a single pipeline, they tend to be confined to small areas, he said.
“I’ve been working on this issue for a decade and I haven’t seen this kind of disaster,” he said.
Kuprewicz, who is president of Accufacts Inc. in Redmond, Washington, said natural gas utilities are required by U.S. law to have fail-safe systems to prevent such a failure.
“These over-pressure events are really rare,” he said. “You have to be really messed up.”
Once a system is over-pressurized, it can take hours to undo and the forces on the pipes can be massive, he said.
The explosions in homes may have been caused by failures of interior pipes and appliances, but outside pipes could also have cracked, allowing gas to enter houses, he said. Additionally, leaks could also have occurred in the distribution system that haven’t been detected yet.
“If they’ve over-pressurized it, you can bet there are other leaks out there,” he said.
Utilities have a variety of methods of checking whether distribution pipelines are damaged. One way, for example, is to pump a harmless gas like nitrogen into individual pipe sections to see if they hold the pressure, he said. If they don’t, then crews have to locate the leak and repair it.
It could take several weeks to repair the existing system. Replacing the pipes – which often occurs by slipping narrower plastic pipe inside existing pipe to minimize the amount of digging – will take months, Kuprewicz said.
In April, Columbia filed a petition with the Massachusetts Department of Public Utilities to increase annual revenues by $24.1 million in part to help replace aging infrastructure. All three towns were listed as areas where neighborhood lines would be replaced, the utility said on its website Thursday.
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