Evidence-first editorial standard
This guide separates observed facts, engineering assumptions and data that still require confirmation. It does not promise a universal service life or replace the exact product data and project specification.
ASTM G75 rates the slurry, not only the material
The standard defines two results from the same apparatus: the Miller number, which expresses how abrasive a given slurry is against a reference material, and the SAR number, which expresses how a chosen material wears in that slurry. Together they separate two questions that are usually mixed up — is this slurry unusually abrasive, and is this material suited to it.
The test reproduces slurry wear far better than a dry sand test
A wear block is moved back and forth under load against a neoprene lap in a trough filled with the slurry, and its mass loss is measured over time. Because the particles are carried in the real liquid, at the real concentration, the result reflects the particle shape, size and hardness of the actual process stream — the variables a dry test such as ASTM G65 cannot capture.
Running a Miller test on the real slurry is worth it before an expensive lining decision
When a new ore body, a change of grind or a new tailings stream arrives, the Miller number shows whether the slurry is more abrasive than the one the plant knows, and the SAR numbers of candidate materials rank them in that slurry. For pipelines this informs the choice discussed in ceramic-lined, Ni-Hard or wearback pipe; for cyclones, the section-by-section choice in the hydrocyclone guide.
The test does not reproduce velocity, impact angle or geometry
The block moves slowly and at a shallow angle, so the result does not include the high-velocity impact at an elbow, the swirl at a cyclone inlet or the turbulence after a pump. A slurry with a high Miller number will wear a line fast, but where in the line it wears is still decided by the flow — as explained in the article on slurry velocity and pipe erosion.
How to read a Miller or SAR figure
Compare figures only from the same test and laboratory, on a sample that represents the stream at its worst rather than at its average, and record the solids concentration and particle size with the result. A Miller number quoted without the slurry it was measured on, or an SAR number for a material grade other than the one offered, gives no basis for a decision.
What to send with a slurry sample
Send enough representative slurry or dry solids with the target concentration, the particle size distribution, the mineralogy where known, the pH and temperature, and the materials to be ranked. Record the result in the line’s wear file alongside measured wear, so that test and field evidence can be compared at each shutdown.