In 2006, the city of Coronado, Calif., installed a 24-inch HDPE sewer force main parallel to a 24-inch ductile iron force main built in 1974. After switching the flow, city engineer Ed Walton wanted the condition of the old main assessed. The line, connecting Coronado and San Diego, lay 50 feet beneath San Diego Bay.
Contractors had failed to inspect all 3,600 feet of the pipe in 2004, so the city asked for another analysis. Elmer Alex, P.E., of Winzler & Kelly in San Diego, researched different camera inspection equipment.
“We needed a big, powerful system with visual and sonar options and full reverse capabilities,” he says. “Our engineers believed that lack of proper technology caused the previous inspection failures, and we weren’t about to duplicate them.”
Winzler & Kelly chose PIPE EYE International in Las Vegas, Nev., and Alex met with sales and marketing manager Simon Rideout to review as-built plans and logistics. The companies teamed on the proposal and won the bid. With the support of affiliate Affordable Pipeline Services (APS) in San Diego and the city’s cooperation, the Winzler & Kelly/PIPE EYE work force completed the inspection in two days.
Preparations
Risks involved confined-space entries and hazardous levels of hydrogen sulfide. “The outfall manhole was in the middle of San Diego’s Seaport Village, a shopping center and tourist attraction,” says Alex. “To reduce visual interest, and to avoid odor and gas issues and disturbing the merchants, we worked from 10 p.m. to 8 a.m. The city notified residents that we would be out there.”
Winzler & Kelly engineers advised using a camera to inspect the pipe, and sonar to record its interior profile and structural deformations, but sonar signals can illuminate a complete profile only if the pipe is full of liquid. Several weeks before the inspection, the city flushed and filled the main with clear water.
The initial plan was to enter the force main through a pump station on the Coronado side. “We anticipated that sludge and caked material in the pipe would block the camera, so we asked the APS crew under vice president Duane Johnson to clean the insertion point,” says Alex.
The structure had a 24-inch blind flange that blanked off the opening to the pipe. Following OSHA confined-space regulations, one of Johnson’s men entered the pump station and began removing the flange. He immediately encountered levels of hydrogen sulfide too high to mitigate and replaced the fitting.
“We decided to move the insertion point across the bay to the outfall manhole on the San Diego side,” says Alex. To prepare for the arrival of the inspection team the following night, APS determined where to set up the equipment, where to position the trucks, and what features around the site needed temporary relocation.
Second night
“The first thing APS did was tape off the area to keep out curious passersby,” says Alex. “We didn’t want them interfering with the inspection or getting too close in case hydrogen sulfide gas burped up.”
PIPE EYE technicians James Milward and Marty Duncan parked the truck close to the 8-foot-deep manhole, while Johnson’s crew checked the gas levels. Although the levels were safe for entry, they set up blowers and constantly monitored the atmosphere. “That was key,” says Alex. “APS had the works – standby rescue personnel, tripods, escape respirators, gas monitors, and air movers – enabling us to concentrate on the job.”
Duncan used an automated tripod crane to lower the unique, 300-pound pan-tilt-zoom camera and robotic crawler system nose first down the manhole. Then an APS employee entered and aligned the robot perfectly with the pipe. “Two reasons why we chose the equipment was because it was heavy enough not to float and it had the traction to climb steep slopes,” says Alex. The stagnant water in the pipe enabled Duncan to launch from the downstream outfall.
The 18- by 3-inch-square stainless steel tracks with welded rubber tank treads normally propel the robot at 30 fpm, but Milward reduced the speed to 10 fpm to enable precise sonar readings. Instead of 70 pounds per 1,000 feet on land, the 0.375-inch tether weighed 22 pounds per 1,000 feet underwater.
Eight 6-watt bulbs, four above and four below the nose of the camera, and four X50-watt quartz halogen variable-intensity bulbs illuminated the pipe. “We encountered small air pockets in some vertical curves where the slope changed,” says Milward. “Acoustic waves can’t pass through air, but the camera liked it and showed us the crown of the pipe.”
Pulling back
By the time Milward completed the 3,600-foot inspection, the robot was pulling 79 pounds of tether. A winch normally would retrieve the equipment, but Milward worried about the tether rubbing against the vertical curves. “The winch can pull 1,500 pounds and the tether’s break strength is 3,000 pounds,” he says. “Although the curves were large, we still considered them hazards in retrieving the camera.”
Using the system’s full reverse capabilities, Milward piloted the robot back to San Diego, while coordinating the winch to wind the tether onto the reel. The robot never faltered during its six-hour journey.
Preflushing had greatly increased visibility. The video inspection showed no structural defects. The sonar signal recorded the pipe’s average internal diameter at 22.8 inches. “We succeeded because this was a team effort between the City of Coronado, Winzler & Kelly, PIPE EYE and Affordable Pipeline Services,” says Alex, who is evaluating various rehabilitation methods with city engineer Ed Walton.
