Posted on 25.09.2009 - 13:00 UTC in ROV NEWS by Rons_ROV_Links
A reduction in the capacity of its two intake pipes made it difficult for the Ohio American Water Co. in Ashtabula, Ohio, to meet customer demand, and the summer peak period was approaching. The plant maintenance supervisor called Pat Murphy, president of Lake Erie Diving Inc. in Painesville, Ohio, to determine the cause of the reduction. The commercial diving company specializes in long-distance pipe and tunnel inspections and cleaning.
Together, the 2,800-foot-long, 24-inch cast iron pipe and 3,000-foot-long, 30-inch reinforced concrete pipe draw 9 mgd from Lake Erie. Using divers to inspect such lengths of small-diameter pipes is not possible.
Murphy called Sean Newsome of SeaBotix Inc. in San Diego, Calif., for help. He recommended the LBV300XL MiniROV (remotely operated vehicle) underwater long-line penetration system, capable of 6,560-foot penetrations and 1,000-foot depths. Using the robot, Murphy inspected the lines and identified the problem. Removal of the blockage restored full capacity, enabling the utility to meet customer demand.
Water clarity in Lake Erie determined when Murphy could inspect the pipes. "The longer the lake stays calm, the clearer the water becomes," he says. "When conditions were right, we coordinated around the plant's morning and evening high water demands, and determined which pipe to inspect first."
How long a pipe is shut down depends on the plant's storage capacity, but Ohio American supplemented its four- to five-hour reserve by drawing water through the second pipe. Instead of discharging into a raw well, the utility's intake pipes couple to the pumps before coming to a common header in the plant. To access them, Murphy and his tender, the person who plays out the ROV's umbilical cord, excavated two 12-foot-deep pits, installed 8-foot diameter concrete vaults, and cut into the pipes.
The water in the vaults rose to the lake elevation, enabling Murphy to launch the robot without a confined-space entry. "We attached the 6,500-foot-long umbilical cord containing the fiber optic and power cables, lowered the robot into the water, and piloted it into the line," he says. Both pipes descend from 12 to 25 feet.
The umbilical cord weighs 400 pounds, and the 21- by 19- by 10-inch-high ROV weighs 36 pounds, but a special jacket on the former and syntactic foam on the latter made them both neutrally buoyant. Brushless direct-current thrusters on the vehicle - four forward, one vertical, and one lateral - enabled four-axis maneuverability. "I fly it down the pipe like a helicopter," says Murphy. "Due to previous ROV experience, it took 10 minutes to master the joystick and integrated control console."
A three-jaw grabber on the ROV retrieves large and small items, and the umbilical lifts 100 pounds. The robot has a 570-line 0.2 Lux color camera that tilts 180 degrees for a 270-degree field of view, and a 430-line 0.03 Lux black-and-white camera better suited to turbid water. Because the inspections required maximum lighting, Newsome mounted four 1,080-lumen LED lights on the crash frame, one per corner.
"They provide tremendous illumination and extremely broad coverage when mounted at opposing angles," says Newsome. "The single 700-lumen LED internal light also can track with the color camera as it tilts up or down." The LBV (little benthic vehicle) hand controller adjusted intensity and on/off functions.
"The robot fits inside 16-inch pipes, so it's a challenge for equipment that small to travel great lengths," says Murphy. "Long inspections are physically challenging to the pilot because they require intense, uninterrupted concentration. After four or more hours of watching the vehicle's progress in low visibility conditions, I'm suffering eyestrain and mental exhaustion."
Murphy took two 15-minute breaks per inspection, using the vertical thruster to lock the ROV to the crown of the pipe. The water in the pipe was static, but ROV speed depended on clarity. "The dirtier the water, the less you see, and the slower you go," says Murphy. The inspections averaged 15 fpm. Data was stored on tape and DVD.
At the pipe's deepest point, the camera revealed a 1/2- to 3/4-inch-thick layer of zebra mussels covering 100 percent of the wall, as well as sediment half-filling the line. "When the lake gets rough, it disturbs the silty mud on the bottom and it's drawn into the pipes," says Murphy.
The men retrieved the ROV by hand, but noticed areas where the umbilical cord might rub. The standard procedure is to thread the cord through a piece of rigid hose or send down a diver to guide it, but Murphy built an aluminum frame with plastic wheels. The unscrewing of two vertical bolts wedged the frame in position, and the umbilical cord rode over the wheels.
The device was ready for the four-and-a-half hour inspection of the 30-inch pipe. Besides sediment, Murphy found golf balls, two bowling balls, and a tire. No one knew how the large items got there, but the utility changed the style of its intake screen as a result.
Murphy rented a sewer-cleaning truck to jet the lines. "I supply the hoses and a head I modified to not remove tuberculation," he says. "I don't need piles of scale added to the sediment in the pipe."
Cleaning progressed 100 feet at a time. Workers pulled the material back to the vault, then pumped it to a lagoon. It took 50 hours to clean each pipe. The utility now has plenty of water for its customers, and a contract with Murphy to inspect and clean the pipes each spring.