Many utility companies have begun instituting asset management plans to maintain and improve their distribution and collections systems. In order to conserve resources and money the goal of water systems should be to lose less than 15 percent of their treated water through holes in their distribution systems. Wastewater plants can save money by reducing infiltration of water through leaks therefore treating only the water that their customers send into their collections systems and reducing pumping costs by having clean lines. Pigging distribution and collections lines is an accepted practice in the industry as a means of cleaning and maintaining lines. Some issues have arisen over time when systems have used solid pigs to scrape the inside of pipeline walls.
Ice pigging is a fairly new technology that eliminates many of the problems associated with solid pigging. Utility Service Co. , based in Atlanta, Ga., is the exclusive service provider and license holder for water and wastewater ice pigging applications in the U.S. and Canada. Ice pigging is a slurry of ice and low concentration salt water. Using a saltwater brine instead of pure freshwater helps to maintain the integrity of the ice pig by depressing the freezing point. The ice pigging method involves pumping an ice slurry into a pipe through a hydrant or a 2-inch fitting. System pressure pushes the ice pig downstream to exit through a hydrant or other fitting. The ice pig works much the same way a glacier does. Instead of bulldozing sediment and biofilm, the ice pig incorporates them into the ice. Specialized launch and retrieval stations are not required, and customer service isolation usually is not necessary, either.
Traditional pigging or swabbing methods can lead to open trench construction if the pig or swab becomes stuck. Ice pigs do not typically get stuck like solid pigs or soft swabs. If the ice pig were to become stuck, simply waiting for the pig to melt and then flushing the line is all that is necessary. Ice pigs can negotiate pipe bends, diameter changes, broken gates valves and inline butterfly vales without affecting the cleaning process. Because of the significantly reduced likelihood of getting an ice pig stuck, this process is very advantageous for pipes that are under railroad crossings, river crossings or high-traffic downtown areas. Ice pigging can be used to clean pipes with diameters varying from ¼ inches to 24 inches.
Ice pigging also uses considerably less water than unidirectional flushing or swabbing. Ice pigging usually uses less than two pipe volumes, while unidirectional flushing typically uses at least four to seven pipe volumes. Swabbing can use even more than unidirectional flushing. Ice pigging can also deliver better cleaning effectiveness, up to 1,000 times more than using water alone. During an ice pigging project in North Carolina, an 18,000-foot PVC pipe with a 6-inch diameter was cleaned of more than 350 pounds of sediment, for an average of 87 pounds/mile. A sewer system in Pennsylvania used ice pigging to clean about 1,200 feet of a 4-inch cast iron force main at a pump station. Pump operation improved, with an average discharge rate increasing by 29 percent. Removal of debris inside the pipe reduced friction losses and improved operating efficiency.
Ice pigging has many applications in drinking water and wastewater. It has the potential to become a sustainable best practice for potable water distribution main and sewer force main cleaning in the United States.
The following link shows an ice pig being used to clean biofilms from the inside of a 3-inch hose. http://www.youtube.com/watch?v=uYZXiktse4c
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