Analytical Ferrography Reporting
What is a WPA flag?
The WPA on your report stands for “Wear Particle Analysis”. This field exists to show whether the Ferrography results are flagged or not. Results that we rate as normal or marginal do not get a flag, but for samples more abnormal than these, our standard Reportable/Unacceptable/Severe flag levels apply.
Ferrography rating?
The scale is 0 to 10. Generally speaking, a 0-2 rating classifies as normal or marginal. A “3” rating may either be normal or reportable, depending on the component type and the level of wear particles expected. Furthermore a “3” or “4” would be considered Reportable, a “5” or “6” would be Unacceptable, and a “7” or higher would be severe.
Something to keep in mind is that the test is designed primarily to examine the wear particles themselves rather than contaminants or oxidative breakdown products. It is possible that a relatively high level of contaminants may not cause the overall Ferrography test to be flagged if they do not appear to be causing any abnormal wear patterns.
Is the rating more reflective of quantity or particle size?
The rating addresses both. In most cases, the rating will be primarily based upon the quantity of particles observed. However, the size of the wear particles does play an important part. A small number of abnormally large wear particles will cause us to rate the sample higher than we would for a the same number of normal-sized wear particles.
Types of particles
Normal wear vs. severe wear
Normal wear particles appear as small, flat platelets smaller than approximately 20 microns in size. These are generated from normal patterns of wear in your equipment. Severe wear particles exhibit a wear mode known as “Severe Sliding Wear”, and appear as elongated, mostly flat particles with deep grooves cut into them. This abnormal wear mode is not commonly seen.
Dark Metal Oxides / Oxidation / Red Oxides / Corrosive Wear
Dark metallo-oxides are iron wear particles that have been partially oxidized, to give their outer surface a black appearance. This process requires high-heat conditions, so a large number of them may indicate that they were formed during an instance of lubricant starvation. The Oxidation category looks at oxidative breakdown by-products of the oil itself, and is not directly related to any wear particle.
Red oxides are rust particles. They can appear in a couple of different crystal forms, but they are Iron oxide rust particles. Corrosive wear particles are very small, and are not usually of critical concern. They are formed by a chemical or electrochemical process, perhaps relating to oil additive depletion. Dark metallo-oxides and red oxides line up in the magnetic field lines, as they are still ferromagnetic.
Organic or Inorganic
“Inorganic” is where we rate inorganic contaminants such as dust/dirt/sand/flyash. These, in practical experience, are the majority of the contaminants. The “Organic” category refers to contaminants that are more life-based, such as leaves/grass/pollen, etc. We don’t typically flag your ferrography based on these categories, but it gives some broad classification of what kind of contamination we are seeing.
Friction Polymers
Friction polymers are not particles per se, but rather a translucent, amorphous “goo” that we observe. They are not usually of critical concern. They form when the oil is exposed to high load or stress conditions. They may or may not have small metal or contaminant particles embedded in them.
Friction polymers won’t show up on the particle count test, as they aren’t really a physical particle, but more of a “goo”.
Does the OPC typically classify chunks/laminar wear/spheres as fatigue or sliding particles?
Chunks are formed through Fatigue Wear, and that’s how they would show up in the OPC. Laminar wear particles are flat and correspond to Sliding Wear in the OPC. Spheres would be a more tricky particle to predict in terms of the OPC, as it would depend on the silhouette that the sphere would produce.
Additional Resources
What is Analytical Ferrography?