The century-old cast-iron pipe runs beneath one of the city’s busiest streets, and like thousands of other service lines across Massachusetts, it’s leaking potentially explosive and environmentally damaging natural gas.
Until recently, National Grid would have had to dig nearly 200 holes to plug the leaks beneath Berkeley Street in the Back Bay, months of tedious work that would have forced road closures, detours, and repeated service interruptions for residents living nearby.
Now, the utility company, which is repairing or replacing some 3,400 miles of mains and gas lines, has a new tool in its arsenal: a robot that can do the job about three times faster, without any need to turn off the gas.
Even better, the repairs require only a single hole in the ground, one small enough to keep the traffic flowing beside it.
“We don’t need to do a major construction project that bothers a lot of people,” said Walter Fromm, director of gas construction in New England for National Grid, one of the state’s largest utilities.
The squat robotic machine uses lasers, cameras, and drills to seal joints. In one day, it can seal six leaky joints — the area where two pipes come together.
A traditional crew, which has to dig a hole by every joint, needs an average of three days to repair just one.
On Berkeley Street, a team of contractors has spent the past few weeks using the robot to methodically seal joints on a project that would have otherwise taken as long as six months.
When they began last month, the team parked their specially equipped van between Newbury Street and Commonwealth Avenue, then dug several feet down to the 122-year-old main.
Without the robot, National Grid would have had to dig a trench every 12 feet along the main, about 133 holes in all.
Next, they cut into the main, creating a valve to prevent gas from releasing, and fitted the opening with what is known as a launch tube.
Gently loading the wheeled robot into the tube, the crew fed it into the gas main with a long, Kevlar-coated tether that allowed them to control it.
Using joysticks, video cameras, and an array of computers, the crew guided the robot through the 24-inch main, spending about an hour on each joint and injecting a special sealant that should allow the line to remain in service without leaking for another 50 years, they said.
“It’s very safe,” said Eric Even, the team’s leader, as he monitored the robot’s progress. “You could put a match down there, and it would go right out.”
One of the main benefits for utilities is that the robot lets them allocate their crews and resources elsewhere, said Nathan King, a spokesman at ULC Robotics, in Hauppauge, N.Y., which built and operates the 3-foot aluminum robot, known as CISBOT.
National Grid began testing the robot in 2010 and now uses it as much as it can to repair its aging network of lines, many of which have been leaking for decades.
Natural gas is mainly composed of methane, a greenhouse gas that’s about 25 times more potent than carbon dioxide.
Repairing the lines also reduces safety risks — some leaks have caused explosions, including one that injured about a dozen people in Dorchester in 2014 — and saves ratepayers money. A 2013 federal study found that in Massachusetts, residents paid as much as $1.5 billion from 2000 to 2011 for gas that was lost to leaks.
Utilities are legally required to immediately repair leaks that pose a risk of explosion, and a 2014 state law requires them to repair minor leaks on streets that are under construction, near school zones, or around trees that appear to be dying.
The utilities had allowed those leaks to linger indefinitely, because they didn’t see them as imminent threats.
In March, utility companies reported to the state that they had 16,596 gas line leaks as of December 2015, down from more than 20,000 leaks two years before.
National Grid, which owns pipes that account for more than half of the state’s gas leaks, has committed $3 billion over the next five years to repair its mains and service lines, with the goal of replacing all of its leak-prone pipes in 20 years.
Since 2010, the company has replaced more than 650 miles of pipes, and it plans to replace another 845 miles over the next five years.
National Grid has the robot scheduled for jobs throughout the region this summer. Company officials said using it costs about three times less than sealing the leaks conventionally.
But ULC Robotics, which says it makes the only robots that repair leaks in gas mains, has only four of the machines, and the crews require extensive training.
The company plans to deploy more robots in the coming years.
As the Back Bay crew sat in their van on a recent afternoon, using the robot’s drill to bore holes into the cast iron, traffic flowed along without a problem.
The project is scheduled to be completed sometime in early June, according to the company.