Neglected and dirty pipes can result in several water quality issues. For example, iron and manganese sediments, which can accumulate due to poor filtering or pipe deterioration, can cause discoloration in drinking water supplies. Biofilms and biological growth can also occur in unchlorinated piping networks. This can lead to the formation of trihalomethanes (THMs) in water supplies, which can present several health risks. (Concerned about possible biofilms? Read Testing For Microbiologically Influenced Corrosion in Pipelines for more information.)
Conventional Pipe Cleaning Methods
Pipe cleaning is essential for maintaining the integrity and efficiency of a piping network. In the water treatment industry, where companies are under constant pressure to effectively manage their systems while ensuring potable water meets stringent quality requirements, pipe cleaning plays a crucial role.
In addition to water treatment, the outputs of other sectors, including the oil & gas, specialty chemical, and food and beverage industries, depend on the cleanliness of their piping networks. While several pipe cleaning methods such as water flushing, foam swabbing and air scouring are currently available, they possess several limitations.
To address the shortcomings of these other cleaning methods, Professor Joe Quarini of the University of Bristol’s engineering department, developed a relatively new concept for cleaning pipes known as ice pigging.
What is Ice Pigging?
Traditional pigging involves sending mechanical devices known as pipeline pigs or scrapers down a pipe to clean or inspect it. Ice pigging, on the other hand, uses an ice slurry to clean the inside of pipes. The semi-solid frozen medium essentially replaces the mechanical pigs used in conventional pigging.
During this innovative cleaning technique, the pipe section to be cleaned is isolated from the main's pressure by closing upstream and downstream valves. An ice delivery unit is then connected to a standard fitting, such as a fire hydrant, and the ice slurry is pumped into the pipe section to form an "ice pig."
Once the ice insertion is complete, the upstream valve is reopened to provide pressure, which pushes the ice pig through the pipe section. As the ice moves through the system, it scours the interior surface of the pipe, collecting sediments and wiping biofilm as it passes.
At the end of the pipe section, the sediment-laden ice is collected in a waste tanker, and the piping network is flushed before the network is reinstated.
Benefits of Ice Pigging
Ice pigging is considered to be a highly effective and low-risk method of removing sediments and other loose objects from pressurized piping networks. Some of the benefits of this cleaning technique include:
Lower Water Usage
One of the most popular methods of cleaning potable water networks is water flushing. This method, however, uses large volumes of water, and for large diameter pipes it may be challenging or impossible to achieve the required flow velocity for effective cleaning. Ice pigging, on the other hand, uses up to 50% less water because a constant stream of water is not required. This is a more sustainable cleaning method that puts less pressure on municipal potable water systems.
Minimal Disruption
Ice pigging is faster and more efficient than other pipe cleaning methods. Furthermore, once the ice slurry is removed from the pipe section and the system is flushed, the network can be immediately returned to service. Ice pigging, therefore, only results in an outage of a few hours as opposed to days with alternative cleaning techniques like foam swabbing.
Adaptable to Pipe Topology
One of the main benefits of ice pigging is the rheological properties of the ice slurry. The semi-solid ice used to clean the pipe is unique because it is pumpable like a liquid, yet acts like a solid pig when removing contaminants in the pipeline. This semi-solid property means that the ice can flow and change its shape, easily adjusting to the topology of the pipeline. Other methods such as swabbing, which work by forcing solid pigs through the pipeline, cannot be adjusted to adapt to changes in pipe diameter.
Additionally, because ice pigs cannot become permanently stuck (they eventually melt), there is no need for costly pig tracking and locating technology.
Less Internal Pipe Damage or Threat to the Environment
Some pipe cleaning methods, such as air scouring, are aggressive and can cause damage to the network as high-pressure air is forced through the pipe. Ice pigging, on the other hand, is considered to be non-aggressive because it does not apply undue stress on the piping network. Additionally, since ice pigging does not rely on toxic cleaning products or chemicals, they pose little to no threat to the environment.
Some Limitations of Ice Pigging
While ice pigging has numerous benefits, it is not without its flaws. According to an original study, ice pigging is currently limited to pipes up to 12-inches (30.5 cm) in diameter with lengths of up to 10,826 feet (3.3 km), and 18-inch (46 cm) diameter pipes up to 1,640 feet (0.5 km). External environmental temperatures can also affect the effectiveness of the ice pig. Warmer soils reduce the effective distance that the pig can travel before melting; therefore, this method may not be suitable for tropical climates.
Also, while ice pigging is more environmentally sustainable in terms of water usage and reduced toxic chemical usage, the process does require more energy because the ice slurry needs to be chilled and continuously agitated.
Furthermore, this method requires the use of specialty equipment, highly trained staff and third-party vendor support, making it more expensive per mile of pipe compared to unidirectional flushing (UDF). (Be sure to read The Tuberculation Battle: How to Effectively Use the Unidirectional Flushing Method for those instances when UDF is the method of choice.)
Conclusion
While pigging using mechanical devices has existed for decades, the use of ice slurries has revolutionized the pipe cleaning industry. This method uses significantly less water than unidirectional flushing, is less disruptive than foam swabbing, and is less detrimental to the pipe structure than air scouring. The semi-solid property of the ice also allows the ice pig to easily flow through different pipe diameters while effectively scraping contaminants as it passes through the network. While this method possesses some limitations, in many cases they are easily outweighed by the benefits.