Wear contamination in stationary and mobile equipment fluids and oils is the bane of most maintenance managers responsibilities. Given advances in equipment manufacturing, most components in an engine, hydraulic, fuel or coolant system have close-tolerances for particles.
What does this mean?
Most equipment failures are caused by contamination under 4 microns (the sub-micron particles that can squeeze between bearings and damage seals).
So, how do you find out what particles are in your systems, wearing on components and causing catastrophic failures?
Here is your official guide to fluid analysis – which ones are critical to your fluid management program, what each one does, and the ones you need to do together to achieve real results.
Particle Counting / Particle Quantification Index (PQI)
(Ferrous Density Test)
OEI Recommendation: Necessary for consistent condition monitoring.
What it analyzes: On-site wear particle concentration (Wear particles are primarily iron. This test is often considered a ferrous density test).
Why it matters: PQI detects the total concentration of wear particles in a sample. By monitoring the level of ferrous (iron) wear particles over a period of time, you can predict accelerated component wear.
How it works: Each sample is passed over a sensor which measures the bulk magnetic content of the oil.
Limitations: Does not differentiate particle sizes or element types.
Needs to be done with: Patch Test or Analytical Ferrography to cover all bases.
Patch Test
Our thoughts: Necessary / best for on-site condition monitoring.
What it analyzes: On-site visual analysis of particle concentration, type, and size.
Why it matters: Comparing the patch to reference slides provides an ISO code. The types of wear particles can be examined on-site for immediate understanding of fluid conditions.
How it works: Pass the oil through a filter membrane, and with the aid of microscope, count the deposited wear particles or compare the patch to reference slides to determine an ISO Rating.
Limitations: This method is insensitive to air bubbles and water droplets, which can interfere with the readings of the instrumental particle counters.
Needs to be done with: PQI or Analytical Ferrography to cover all bases.
Analytical Ferrography
Our thoughts? Best in class, covers all bases analysis.
What it analyzes: Particle size, concentration, and shape.
Why it matters: The detail in this best-in-class, off-site analysis pinpoints component wear, how (and how often) it was generated, and its root cause.
How it works: The solid debris suspended in a lubricant is separated and systematically deposited onto a glass slide for microscopic examination. The microscope uses both reflected (top) and transmitted (bottom) light to distinguish the size, shape, composition, and surface condition of ferrous and non-ferrous wear particles.
Limitations: This method is costly but effective in identifying all aspects of wear particles down to 4 microns and below.
Needs to be done with: Patch Test or PQI for consistent monitoring
Spectroscopy: Scanning Electron Microscope (SEM)
Our Thoughts: Spectroscopy is great so long as you’re getting all three tests, and a patch test to get the full story of your equipment’s & fluid’s condition.
SEM tells you particle size.
What it analyzes: Identifies the sizes and structures of wear particles in a fluid sample that are under 10 microns.
Why it matters: When the particles’ metallurgy, size, and shape are known with high accuracy, it’s easier to determine their type, origin, and root cause.
How it works: The SEM scans the sample with an electron beam to produce a magnified image for analysis. Electron microscopy is performed at high magnifications to generate high resolution images that precisely measure particles under 10 microns.
Limitations: This analysis must be done with other tests because it is blind to particles in excess of 10 microns and does not identify particle concentrations.
Needs to be done with: Spectroscopy EDS & XRD tests… as well as the patch test for consistent onsite monitoring.
Spectroscopy: Energy-dispersive X-ray (EDS)
Our Thoughts: Spectroscopy is great so long as you’re getting all three tests, and a patch test to get the full story of your equipment’s & fluid’s condition.
EDS tells you element concentrations.
What it analyzes: Identifies the concentrations of each element in a sample.
Why it matters: Understanding the elements in a fluid sample will identify the fluid condition and sources of wear.
How it works: The sample is stimulated by electrons or high-energy photons. Each atom absorbs, then emits, that energy in varying spectrums of light. The varying light energy is measured to determine concentrations of each element.
Limitations: This test is blind to particles larger than 10 microns and must be done with additional tests that identify the particle density, size, and element.
Needs to be done with: Spectroscopy SEM & XRD tests… as well as the patch test for consistent onsite monitoring.
Spectroscopy: X-ray Diffractometer (XRD)
Our Thoughts: Spectroscopy is great so long as you’re getting all three tests, and a patch test to get the full story of your equipment’s & fluid’s condition.
XRD tells you particle characteristics.
What it analyzes: Once particle composition has been determined, XRD will show it’s phase, grain size, texture, crystallinity, and stress.
Why it matters: Data about wear particle structure gives insight into which conditions are causing component stress.
How it works: XRD uses diffraction patterns to detect crystalline structure.
Limitations: SEM or EDS is required to determine the elemental composition. Ap-proaching an unknown sample with XRD alone may be confusing.
Needs to be done with: Spectroscopy SEM & EDS tests… as well as the patch test for consistent onsite monitoring.