A water infrastructure corrosion expert reviews a paper by researchers at the University of Bristol on an innovative technique called ice pigging for the water supply industry.
Fine particles in drinking water distribution systems, such as sand and corrosion by-products, are the main cause for water discoloration, resulting in customer complaints.
Current Water Main Cleaning Technologies
Current industry standard procedures include unidirectional water flushing, air scouring, and conventional pigging. Flushing involves pumping water at high velocities through the pipes to displace and carry away particulates (sometimes measured in units known as grains.) Conventional pigging consists of pushing a cleaning pig through the pipe to push or wipe away loose particulates. (For more on related techniques, see Understanding a New Trend: In Situ Cleaning and Coating.)
Both systems have drawbacks. The first tends to use very large volumes of water, and it may be impossible to get the required velocities in large diameter pipes. The second requires system improvements (launch and receiving stations), and may run the risk of damaging the pipe walls.
Ice Pigging Has Certain Advantages
Ice pigging on the other hand, is an alternative to water flushing and conventional pigging. It uses a phase change material (ice-water slurry), which can be introduced into and removed from existing pipe networks with minimal modifications to the infrastructure.
This new technology uses significantly less water. Another advantage is that the ice pig changes shape to fit the containing topology and is able to navigate bends and restrictions. The ice pig is guaranteed to never get stuck, because it will simply melt away.
The viability of these concepts has been taken to the next stage by demonstrating the potential of the technology on live mains. The initial field evaluations performed by Bristol Water (BW) and the results to date are very encouraging, and BW invested resources to initiate the commercialization of the technology. The ice pigging technology has since been commercialized and brought to the United States.
Ice Pigging Limitations
Based on the original study, there appears to be some current limitations to the application of this technology, including:
- Current limits to pipes of up to 12-inch (30.5 cm) diameter, and of lengths up to 10,826 feet (3.3 km), and 18-inch (46 cm) diameter up to 1,640 feet (500 m).
- The length in which the ice pigged can effectively travel depends on:
- Initial ice fraction of the pig (the higher the ice fraction, the further it can travel).
- Velocity it can be propelled (the higher the speed, the further the distance).
- Environmental temperature (warmer potable water in pipes in warmer soil tends to reduce the distance that the pig can travel).
Does Ice Pigging Have Application for Pipe Corrosion Control?
This technology appears to offer another means of cleaning pipes that are experiencing sand buildup or internal pipeline corrosion by-products that are impacting water quality. (Learn more about microbiologically influenced corrosion(MIC) in the article Testing For Microbiologically Influenced Corrosion in Pipelines.) However, in its current state of development, the technology is a pipeline cleaning methodology, and not a corrosion control mitigation process. Its ability to remove particulates does not provide a continued means of corrosion control.
To effectively provide corrosion control, modifications in the water chemistry is required. Those adjustments normally occur at the water treatment plant to adjust the chemistry to meet regulatory water quality standards, and to minimize the corrosion of metallic infrastructure components throughout the distribution system.
As a particulate removal technology, the technique appears safe, can remove loose particulates, and is guaranteed to never get stuck in the system. Additionally, it appears that the technology may reduce water waste and downtime when compared with existing methodologies.
Based on the information available, ice pigging is in the early stages of testing and validation in the potable water supply industry. As field applications and related data become available, then further implementation of this technology could be easily accelerated.