Quantity and quality benefits of in-service invasive cleaning of trunk mains

Abstract

Abstract. Trunk mains are high risk critical infrastructure where poor performance can impact on large numbers of customers. Both quantity (e.g. hydraulic capacity) and quality (e.g. discolouration) of trunk main performance are affected by asset deterioration in the form of particle accumulation at the pipe wall. Trunk main cleaning techniques are therefore desirable to remove such material. However, little is quantified regarding the efficacy of different maintenance interventions or longer-term changes following such cleaning. This paper presents an assessment of quantity and quality performance of a trunk main system pre, post and for 12 months following cleaning using pigging with ice slurry. Hydraulic calibration showed a 7 times roughness height reduction after ice slurry pigging, evidencing substantially improved hydraulic capacity and reduced headloss. Turbidity response due to carefully imposed shear stress increase remained significant after the cleaning intervention, showing that relatively loose material had not been fully removed from the pipe wall. Overall the results demonstrate that cleaning by pigging with ice slurry can be beneficial for quantity performance, but care and further assessment may be necessary to realise the full quality benefits.

Review of Ice Slurry Pigging Techniques for the Water Supply Industry: Engineering Design and Application

“…Within a specific range, the higher flow velocity is associated with more possibility of plug flow and higher pressure drops, as well as longer survivability of ice pigs. ,, While the ice pig is pushed through the pipe by primary pressure, the ice pig velocity corresponds to the water velocities in pipelines. Consequently, an infinite flow velocity is impossible . In contrast, the velocity can be quite low, and even interval flow (pipes are not filled with water under pressure continuously) may occur in intermittent water distribution systems …”

“…Finally, the TSS per unit length, volume, and area of a specific cleaned pipe section can be obtained (Figure ). From the turbidity response accounting for controlled excess imposed shear, a reduction in discoloration risk after ice pigging can be observed, while long-term water quality improvements still require detailed exploration …”

“…The results showed that the roughness of a cleaned pipe decreases by seven times after ice pigging, which is associated with improved hydraulic capacity. An increased effective pipe diameter also indicates that a mass of loose deposits has been removed …”

“…Consequently, an infinite flow velocity is impossible. 103 In contrast, the velocity can be quite low, and even interval flow (pipes are not filled with water under pressure continuously) may occur in intermittent water distribution systems. 104 When the water velocity is relatively high within pipelines in DWDS, plug flow, ideal pressure drop, and longevity of ice pigs can be more accessible.…”

Data-Driven Study of Discolouration Material Mobilisation in Trunk Mains

“…In particular, significant research has been carried out on developing methods to intermittently clean trunk mains with minimal cost and required downtime [16][17][18].…”