**6. Pipe wear**

An unavoidable consequence of flows containing particles is wear. Enormous costs to industry are attributable to wear, but costs can be reduced by careful design. Since 2017, many advances have been made in the study of erosion-corrosion in experimental and *in-situ* monitoring of wear, condition monitoring, the monitoring of wall erosion and computational modeling to name but three.

Designers of slurry systems will often reach for answers from Computational Fluid Dynamics (CFD). There is certainly a promising future for CFD erosion modeling, but that advance is not yet with us. Despite improved particle impact modeling, dynamically deforming geometry and improved particle tracking, the accuracy of erosion predictions is poor. There is hope of improvement from two comparatively new approaches explored by authors in this volume. The Discrete Phase Model (DPM) plots the path of a group of dynamically similar particles through a continuous liquid, while the Discrete Element Model (DEM) tracks individual particles and

solves the equations of motion as they interact with each other. In theory, the accuracy of the DPM approach can therefore be improved by a coupling with DEM. A CFD-DPM-DEM combination has been used to model air-particle flows, but no attempt at extending the technique to solid-liquid flows has been reported to date. There is great potential for this combination but a disincentive to its development is the very large computational cost that would be incurred. One of the most significant improvements in the application of CFD is the Moving-Deforming-Mesh (MDM) approach. The computational mesh is updated at regular intervals based on local erosion rate and the geometry of the wall. In this way erosive deformations are integrated into the flow field and secondary erosion patterns can be predicted.

Very little research has been carried out on the influence of pipe layout. on the life of vulnerable components. Pipe geometry upstream of a vulnerable pipe section can have a significant effect on erosion rates. For example, the swirl pipe design described above can show significant wear reductions in adjacent downstream pipe components. Unsurprisingly internal surface finish (particularly in pipe elbows) has a disproportionate effect on the erosion pattern suffered in service. Comparatively minor melioration in this area could be influential in increasing component lifetimes.
