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Ice Pigging: New Water, Sewer Pigging Method Offers Unique Benefits
“The utilization of ice pigging in water distribution lines has been slow to expand because the equipment necessary to generate and deliver the quantities of ice at the quality needed for successful operations is all custom made,” Ervin said. “The equipment is not currently available on the open market in the U.S. We are working with several U.S. manufacturers to determine whether we can use their equipment with the ice pigging technology.”
[inline:=A series of sample bottles collecting the waste. The samples are collected from left to right during the operation showing the clean water before the pig, the waste removed by the pig, and the clean water after the pig has been removed from the water main.]
Utility Service Co. has two ice pigging rigs in the U.S. and has performed demonstration projects in seven states -- most along the east coast -- and completed full scale projects in New Hampshire and North Carolina.
Ice pigging technology requires an ice-making facility, storage tank, flow analysis unit and delivery pump, Ervin continued. The ice is generated on-site using local potable water and a freezing point depressant, typically National Sanitation Foundation International (NSF) certified table salt. Other freezing point depressants are available depending upon the situation. Ice-making equipment must be mobile, but large enough to generate more than 10 tons of ice.
Ice pigging usually is performed with a two-person crew. The only support needed is for traffic control, personnel to operate valves to isolate the main and a tanker truck, if the waste cannot be sent to the sanitary sewer.
Comparing ice pigging to other pipe-cleaning procedures, Ervin said unidirectional flushing typically uses between four to seven pipe volumes of water, swabbing often even more.
“Ice pigging usually uses less than two pipe volumes during the process,” he said. “Because the ice pig is a slurry and not a solid pig, it virtually cannot get stuck. If the pig would get stuck, we allow the ice to melt and flush from the system. This prevents the utility service provider from having to take the main out of service to extract a lost or stuck pig.
“Ice pigs can negotiate bends, changes in diameters, broken gate valves and in-line butterfly valves while still providing an effective cleaning effort. Therefore, this technology would be very advantageous for highly-sensitive areas or critical pipes that may be located under railroad crossings, river crossings or high traffic downtown areas where the risk of getting a pig stuck would be extremely costly or dangerous to operations.”