On May 1 and 2, the two-day rain total in some areas was greater than 19 in. In Nashville, the Cumberland River crested at nearly 52 ft, the highest level since 1937. The resulting floods caused damage to landmarks like the Grand Ole Opry House and Schermerhorn Symphony Center, and that damage got most of the media attention in the aftermath. But critical infrastructure was also damaged, and Nashville’s extensive sewer system needed to be inspected, cleaned and repaired as soon as possible.
Compliance Envirosystems LLC (CES) began work soon after floods receded. “It’s a big contract,” says CES project manager Damian Hardwick, “I’m in charge of the large diameter pipe inspection. We were already scheduled to inspect 98,000 ft of large diameter this year, and the floods doubled that to about 200,000 lf — so, we need to move fast. Cleaning and repair crews are depending on us to tell them what to do.”
Large diameter sewer pipe, in Nashville, ranges from 2 ft all the way up to 18-ft brick pipes that were built in 1876. “We’re always working in ‘live’ pipe,” explains Hardwick. “And all the flooding left a lot of debris — that’s why we’re here.”
Pipes this big, with active flow, present serious challenges to inspection contractors. Just lighting the area for video cameras is difficult, and since much of the debris is submerged, sonar is needed to inspect sewer bottoms. Given the amount of work to be done, CES crews couldn’t afford the time needed for separate video and sonar passes, and instead relied on “Totally Integrated Sonar and CCTV Inspection Technique” (TISCIT).
But TISCIT presents its own challenges, especially with the lighting requirements of large diameter pipe.
Powering and controlling CCTV, sonar, lights, steerable tractor and remote elevator (which lifts the video camera to the approximate center of pipe remotely, and saves crew trips down into pipes) has traditionally required at least two cables on separate drums, with cable lengths of 1,500 ft or less. Two cable drums equal approximately twice the hassle of one drum: transporting and managing two drums slows down work significantly. And a run length of 1,500 ft is not that great either — a 2,000-ft run length would add up to a lot more lineal feet of pipe inspected each week.
When it comes to large diameter pipe, Hardwick is one of the world’s most experienced field men. His background, mostly in the United Kingdom, includes work on 30-ft diameter storm water tunnels in Bristol and 130-year-old brick sewers in the Guernsey Channel Islands. He’s managed the inspection of millions of feet of large diameter sewer and, while working with CES, has been one of the pioneers of sonar sewer inspection in the United States.
“I knew getting the system down to one cable would be a challenge,” he says, “especially in sewer lines, going from two cables to one has tremendous advantages, and I hoped it could be done. And even though it’s unusual to go 2,000 ft with sonar, I hoped we could do that too.”
Fortunately, CES has been working with Cobra Technologies for a number of years, developing an innovative TISCIT inspection system. Four years ago, Cobra built a single-cable TISCIT system for CES — the first of its kind. “When we told CES we could do what they wanted with one cable, they didn’t believe us,” says Cobra president Alan Grant. “I’m glad we were able to prove it was possible. We’re still the only firm building a one-cable TISCIT system.”
Now, CES wondered if Cobra could build a similar system with enough light to illuminate the huge Nashville pipes, power a remote elevator and a steerable crawler.
Building an Extraordinary System
“The technical issues of getting everything working on a single cable were complex, to say the least,” Grant says. Several engineering innovations were used to make everything work on the single cable. For example, Cobra’s pan, tilt, zoom camera uses the camera power supply for lighting — this eliminates the need for a separate line controlling lights, since the lights could be at constant 100 percent brightness, with video level controlled by camera’s auto iris.
Still, it was a challenging task. “The steerable crawler needed four wires, the sonar needed four wires and the video needed three wires,” Grant explains. “We had already used 11 of the 12 wires available, and we hadn’t yet provided the additional lighting needed for large diameter pipe and we weren’t yet able to control the remote elevator.”
Cobra designed a system that would send high voltage to the crawler on the camera voltage line and used electronic components at the crawler to convert the high voltage to the required voltages for individual components, including the sonar, the camera, the elevator and the two additional sets of lights needed in 200-in. pipe. “In fact,” Grant says, “we had sufficient power to run a third set of lights, if needed.”
Lighting was based on Luxeon illuminators, which offered huge advantages for sewer work. Luxeon illuminators are low amperage and low voltage, in addition they are cool, which means they are safer to work with in confined spaces. Cobra fitted the lighting system with collimators, so that the light beam can be adjusted in width to suit the diameter of the pipe being inspected. “And the ‘bulbs’ should last indefinitely,” says Grant. “We’ve been using Luxeon illuminators for five years and they’ve never needed replacement.”
All of the above, including the cable drum and control systems, were built onto an enclosed Polaris ATV, with an electronics rack to handle all the required equipment. CES provided a 28-ft gooseneck trailer, with a generator. And Cobra Technologies had a few additional suggestions for Hardwick.
“For example, we insisted on a 17-in. sunlight readable monitor, capable of VGA and video functionality,” says Grant, “We knew from past experience that putting one’s head under a tarp to view a monitor in sunlight gets old all too fast.”
So How’s the New System Working Out?
“We had a break-in period, figuring out operational issues,” Hardwick admits. “But since then, it’s all been working great.”
Using the new system, Hardwick and his crew have been able to perform video and sonar inspection of up to 4,000 ft of pipe a day. That’s a significant increase. “It’s made my life so much easier,” says Hardwick, “Compared to two cable drums and a limit of 1,500 ft, the Cobra system is much more efficient. If all we had saved was pulling the extra drum into the woods, it would have been worth it. With the extra cable, better lighting, steerable crawler and the remote elevator it’s a dream system.”
Cobra designed and built a float box to manage the camera, lights and sonar when used on floats.
For large diameter pipe, CES usually deploys four-person crews, and they work hard. In Nashville, manhole depths range from 50 to 95 ft, and they sometimes work at night to avoid traffic. Because of enclosed space safety issues, they’re usually using respirators and other blowers, and because the pipes are ‘live’ the work is dirty and cold. So it’s never going to be easy work, but for Nashville to recover from some of the worst flooding in its storied history, it’s work that has to be done.
Angus W. Stocking is a freelance writer, based in Beaver Dam, Wis.