When It’s Time To Consider Ice Pigging

In 2013, the City of Reidsville began a unidirectional flushing program for water mains 12" and smaller.

After heavy manganese buildup was noticed in 16" pipe during recent construction, the City decided to explore options to clean the larger diameter pipes.

In ice pigging, ice slurry is injected into the water main and used to scour the inside of the pipe. It can be pumped in like a liquid, but forms into a semi-solid pig once in the pipe.

The ice is produced on location, with food grade salt used to control consistency. Additional chlorine may be added as disinfectant.

An estimated 121lbs of sediment were removed from 1,050’ of 16” pipe using ice pigging. Further lab analysis showed that significant amounts of iron and manganese were removed.

In 2001, Professor Joe Quarini of the University of Bristol’s engineering department developed a concept for cleaning pipes. After some development of this idea alongside the local water utility, a process was discovered and bestowed with a unique moniker. The process of ice pigging was born.

Pipe pigging was already a well-established practice for cleaning pipes before Professor Quarini introduced his tweak on the process. It involves sending a metal or plastic device known as a “pig” — so-called because of the squeal emitted as it squeezes its way along a line — through a dirty pipe. Ice pigging is much the same concept, but the cleaning apparatus is made of ice, making it a more flexible agent for traveling through pipes.

In the first step of ice pigging, the main is isolated by closing the valves on either side. Then operators pump ice slurry — a semiliquid made of many small ice crystals — into the pipe while monitoring and managing the downstream pressure. By opening the upstream valve, the natural pressure in the system pushes the ice slurry along the pipe and passes it over every surface, collecting sediment and biofilm as it goes. When it reaches the end of the section, the now-dirty ice can be collected separately or discharged along with the water. The pipe is flushed and returned to service.

Traditional pigging, or “swabbing,” requires a launching and retrieval station and carries the risk of the material pig getting stuck in blockage, complex layouts, or diameter changes. If an ice pig were to get stuck, it would eventually melt. Ice pigging is more effective than flushing and has more of an impact in larger pipes than air scouring does.

“Ice pigging is a good solution for cleaning critical sections of pipe that cannot be taken out of service for long periods of time because of the lower risks involved with ice pigging versus using a traditional pig,” said John Collett, PE with Hazen and Sawyer. Collett gave a presentation on the practice and how it was deployed to help Reidsville, NC, at a 2015 AWWA Conference.

Ice pigging is ideal for pipes between 50mm and 600mm and is capable of removing soft deposits and buildup.

Excerpted from Water Online

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