Casing and Impeller Wear Rings

Impeller and casing wear rings are subjected to two different forms of wear. Even in the absence of any solid particles in the process fluid, the wear rings can be damaged by sliding wear (also called metal-to-metal wear) due to unintentional contact between the rotating (e.g. impeller wear ring) and stationary (e.g. casing wear ring) surfaces resulting in wear ring rub.

This is especially problematic with most corrosion resistant alloys which have a propensity for metal-to-metal wear and/or galling, and the severe seizure of a pump fitted with austenitic stainless steel wear rings.

To reduce the risk of seizure it is prudent to use dissimilar metals for casing and impeller wear rings, ensure a minimum 50HB hardness difference between the rings or coat the wearing surfaces with a suitable anti-galling coating.

If there are any solid particles present in the process medium the particles can move through the wear ring interface if they are small enough, due to the pressure differential across the wear ring, and depending on the size of the particle this can result in abrasion (e.g. when particles are approximately the same size as wear ring clearance) or erosion (e.g. when particles are much smaller than wear ring clearance).