Investigation and development of an innovative pigging technique for the water-supply industry

Water-supply companies monitor the state of their pipe networks and ensure that the pipes are clean and free of inert loose deposits by flushing and pigging. Flushing involves forcing high speed water through the pipes so as to carry away particulates, pigging consists of forcing an object (the pig) through the pipe so as to push or wipe away the loose material. 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 purpose built launch and receive stations and may run the risk of damaging the pipe walls. This paper presents an innovative alternative to water flushing or conventional pigging for the potable-water-supply industry. This alternative uses a phase change material (ice—water slurry), which can be introduced into and removed from existing pipe networks with minimal alterations. The underlying concept is that when an ice slurry is propelled through pipes at modest speeds, the wall shear is two to four orders of magnitude higher than that which would have been achieved had water (only) been travelling in the pipe at the same speed. Thus, even with relatively low speeds, the ‘ice pig’ is able to achieve efficient cleaning and removal of loose materials. This technology has the advantage that the ice pig changes its shape to fit the containing topology, hence it is able to navigate bends, contraction/expansions and partly open vales, while cleaning the containment walls and transporting particulates. Lastly, the ice pig is guaranteed never to get stuck, as it will simply melt away, if left for sufficient time. The paper presents laboratory experimental data, qualitatively demonstrating the capability of the technique and quantitative data enabling engineers to scale and size the ice pig for full scale trials. Finally, preliminary work from full scale trails on live water trunk mains is briefly presented and discussed.