analytical ferrography the forensic science of oil analysis

The Forensic Scienceof Oil Analysis

Utilizing Analytical Ferrography To Diagnose Wear Conditions and Prevent Machine Failure

Analytical Ferrography

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Analytical Ferrography: A Powerful Diagnostic Tool

There are many tests available for used fluids

analysis. Some tests are qualitative while others

are quantitative in scope. One test often

overlooked is Analytical Ferrography.

Analytical Ferrography is among the most

powerful diagnostic tools in oil analysis today.

When implemented correctly it is an excellent

tool when attempting to diagnose an active

wear problem, yet it too has its limitations. It is

frequently excluded from oil analysis programs

because of its comparatively high price and a

general misunderstanding of its value.

The test is qualitative, which means it relies on

the skill and knowledge of the ferrographic

analyst. While this can have definite

advantages, the interpretation is somewhat

subjective and requires detailed knowledge of

wear debris failure modes.

The test procedure is also lengthy and requires

the skill of a trained ferrographic analyst. As

such, there are significant costs in performing

Analytical Ferrography not present in other oil

analysis tests.

Nevertheless, if time is taken to fully

understand what Analytical Ferrography

uncovers, most agree that the benefits

significantly outweigh the costs and elect to

automatically incorporate it when abnormal

wear is encountered.

The Facts About


Analytical Ferrography is the best

method for determining severity and

type of wear present.

There are no particle size or metallurgy

limitations.

Wear can be documented by digital

photography.

The test procedure is lengthy and

requires the skill of a trained analyst

The test is a qualitative test, which

means the interpretation is somewhat

subjective and relies on the skill and

knowledge of the ferrographic analyst.

TESTOIL20338 Progress DriveStrongsville, OH 44149216-251-2510www.testoil.com

Free Analytical Ferrography

At TestOil, Analytical Ferrography is automatically

performed on all

Machine Condition anomalies triggered by the ba

sic testing. If we

see a Marginal or Critical machine condition, an A

nalytical Ferrography

is added to the sample at no additional charge. A

fter viewing the

ferrogram under the microscope the analysts are

then capable of

making a much more informed assessment and

recommendation of

making a much more informed assessment and

recommendation of

the health of the equipment.


Inside The Lab

To perform Analytical Ferrography the solid

debris suspended in a lubricant is separated and

systematically deposited onto a glass slide. The

slide is examined under a microscope to

distinguish particle size, concentration,

composition, morphology and surface condition

of the ferrous and non‐ferrous wear particles.

This detailed examination, in effect, uncovers

the mystery behind an abnormal wear condition

by pinpointing component wear, how it was

generated and often, the root cause.

The Ferrogram

Analytical Ferrography begins with the magnetic

separation of machine wear debris from the

lubricating oil in which it is suspended using a

ferrogram slide maker. The lubricating oil

sample is diluted for improved particle

precipitation and adhesion. The diluted sample

flows down a specially designed glass slide

called a ferrogram. The ferrogram rests on a

magnetic cylinder, which attracts ferrous

particles out of the oil (Figure 1).

Due to the magnetic fluid, the ferrous particles

align themselves in chains along the width of

the slide with the largest particles being

deposited at the entry point. Nonferrous

particles and contaminants, unaffected by the

magnetic field, travel downstream and are

randomly deposited across the length of the

slide. The deposited ferrous particles serve as a

dyke in the removal of nonferrous particles. The

absence of ferrous particles substantially

reduces the effectiveness with which

nonferrous particles are removed.

After the particles are deposited on the

ferrogram, a wash is used to remove any

remaining lubricant. The wash quickly

evaporates and the particles are permanently

attached to the slide. The ferrogram is now

ready for optical examination using a

bichromatic microscope.

Figure 1. The Metal Alloy of the Particles Determines Whether They Line up On or Adjacent to the Magnetic Field


Particle Identification

The ferrogram is examined under a polarized bichromatic microscope equipped with a digital camera.

The microscope uses both reflected (top) and transmitted (bottom) light to distinguish the size, shape,

composition and surface condition of ferrous and nonferrous particles (Figure 2). The particles are

classified to determine the type of wear and its source.

Green Light Source Below Slide, Causing Light to be Transmitted Up Through the Side

Figure 2. Red Light Source Above Slide,

Causing Light to be Reflect Off Top of Particles


Examining The Evidence ‐ Wear Particles

The particles contained in a lubricating fluid

carry detailed and important information about

the condition of the machine components.

Analytical Ferrography requires extensive

analyst training to properly interpret the

results. Evaluation of a ferrogram can differ

between analysts due to the subjectivity of the

analysis. The level of training and experience

will also impact the accuracy of the ferrographic

evaluation.

A trained oil analyst can visually determine the

severity of wear on the unit using a microscope

to classify the particles according to size, shape,

and metallurgy. The analyst can evaluate the

concentration, size, shape, composition, and

condition of the particles, which indicates

where and how they were generated.

Solid contaminants can also be visually

identified provided they’re commonly found.

Sand and dirt, fibers, oxidation products, rust,

and metal oxides are examples of

contamination debris that can be identified.

Analytical Ferrography is the best method for

determining severity and type of wear present

with no particle size or metallurgy limitations.

Analytical Ferrography reports typically include

a photomicrograph of the debris found, along

with specific descriptions of the particles in

their suspected cause. The following pages are

the photomicrographs and classifications of

wear that are detected using Analytical

Ferrography.

Size Does Matter...So Does Shape and Metallurgy!

Particles are categorized based on size, shape, and metallurgy. Conclusions can be drawn regarding the wear rate and health of the component that the sample was drawn from. The analyst relies on the following to determine the following characteristics of the particles:

✓ Composition: Color can identify the composition of the particles. Heat treating the slide causes specific color changes to occur in various types of metals and alloys. The particle’s composition indicates its source.

✓ Shape: The particle’s shape reveals how it was generated. Abrasion, adhesion, fatigue, sliding, and rolling contact wear modes each generate a characteristic particle type in terms of its shape and surface condition.


Case Closed: Photomicrographs & Wear Classifications

Rubbing Wear Description. Ferrous particles, less than 30 microns in size. Some Sources: Rubbing wear is typically found in both reciprocating and non‐reciprocating units. Comments. On a ferrogram the particles tend to align in chains. Normal ferrous wear can be categorized as low alloy, cast iron and high alloy steel.

Severe Wear Description. Metallic particles greater than 30 microns. Fatigue or component overload that cause larger pieces of wear to detach creates severe wear. Comments. Severe wear is a definite sign of abnormal running conditions.

Sliding Wear Description. Metallic particles, both normal and severe, with sliding striations along one or more surfaces. Sliding wear can be created when two parts of a machine scrape together. Comments. Sliding striations are often a good clue as to what part of a machine is causing wear.

Laminar Description. Thin, smooth particles which appear to have been rolled flat. Roller bearings, areas where high‐pressure angled or lateral contact occurs. Comments. Wear created by extraneous particle if the laminar has small holes or indents.

Cutting Wear Description. Shaved metal particles that look like wood shavings from a lathe. Seen in sleeve bearings and shaft couples. Abrasives embedded in soft bearing or burrs on hardened metals create these wear particles. Comments. Worm drives have a tendency to create this type of particle. When seen it indicates abnormal wear.


Dark Metal Oxide Wear Description. Grey to black chunks with a semi‐metallic appearance and mottled edges. Some Sources: Breakdown of boundary film, excessive operating temperatures, lubricant oxidation. Comments. The darker the color, the more severe the oxidation of the particle.

Sphere Description. A relatively smooth spherical particle. Spheres are created in bearing fatigue cracks, typically roller bearings. Comments. Spheres are often precursors of bearing spalls. A large increase in quantity is indicative of imminent spalling.

Non‐Ferrous Metal Wear Description. Any metallic particle that is not ferrous. Most common include aluminum, copper alloy, chrome, and babbitt. Non‐ferrous wear can be created by the machines or as additive packages in the lubricant. Comments. Non‐ferrous metallic wear can be across the entire length of a ferrogram. These particles will not be aligned with the ferrous wear chains.

Contaminants Description. Dirt, sand and other silica particulate. Contaminants can enter into a system by a variety of ways: poor seals, incorrectly installed breather, during oil change, etc. Comments. Some can appear like crystals. Contaminants are easily identified by using only the transmitted light source on the microscope.

Fiber Description. Fibers are thread like material made of asbestos, paper, glass or a synthetic material. Most common source is filter material. Could be from machine housing, cleaning rages, or air contaminants. Comments. A small amount of fibrous material in oil is common.

Red Oxide Description. Iron oxides or rust. It appears as orange/red in color. Red oxides are produced when moisture enters into a system. Water does not have to be present when red oxides are seen, as they are often difficult to filter out of oil. Comments. Red oxides are not necessarily magnetic like ferrous wear. Alpha hematite is paramagnetic and will be found on all regions of a ferrogram.


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Points To Remember

Only a skilled analyst can determine the nature, severity and root cause of abnormal wear by analyzing

the size, shape, color, magnetism light effects and surface detail of wear particles. This information

enables maintenance to implement effective corrective action, but don't forget these 4 important

points:

It is proven that Analytical

Ferrography is an excellent tool

when attempting to diagnose an

active wear problem. However,

remember that the test is a qualitative test,

which relies on the skill and knowledge of the

ferrographic analyst. Be sure you enlist the

services of an experienced analyst because the

interpretation is somewhat subjective and

requires detailed knowledge, not just of

analytical chemistry, but also machine and

tribological failures.

The test procedure is lengthy and

requires the skill of a well‐trained

analyst. As such, there are

significant costs in performing

Analytical Ferrography not present in other

fluids analysis tests. But, if time is taken to fully

understand what Analytical Ferrography can

uncover, most agree that the benefits

significantly outweigh the costs and elect to

automatically incorporate it when an abnormal

wear condition is encountered.

As with all fluids analysis samples, it

is extremely importance to properly

take samples of the fluid. Samples

should be taken that are

representative of the conditions that are going

on inside the equipment. Representative

samples are dependent on the way the sample

is taken and the location where the sample is

taken from. This is especially important when

using Analytical Ferrography.

Another critical factor in fluids

analysis, and Analytical Ferrography

in particular, is the need of the

customer to provide as detailed as

possible the specific information about the

machine/component the sample was taken

from. This includes lubricant information,

component manufacturer, model and type of

component. The more detailed the

machine/component information, the better

the diagnosis of the test results.

Case Study I Equipment: Ingersoll Rand single‐stage centrifugal pump

Application: A steel mill uses this pump to boost the water pressure it supplies to the hot mill for descaling. Thin scale forms rapidly on the hot slab and must be removed before entering the mill stands. The high pressure descaling water breaks it loose from the slab and removes it. The pump has babbitt sleeve bearings with a Kingsbury thrust bearing on the outboard bearings. This is a 12,000 gpm, single inlet pump driven by a 2000 hp motor at 1780 rpm.

History: Oil samples from this pump are routinely sent for analysis and historically have exhibited normal machine and lubricant conditions. Spectroscopic analysis and direct reading ferrography are routinely performed in order to trend the wear of the lubricated bearings. Analytical Ferrography is automatically performed when there is a machine abnormality.

Problem Sample: The sample drawn on 7/3/12 exhibited excess iron wear, abnormal silicon and excessive total ferrous wear. The machine was given a critical condition and Analytical Ferrography was automatically initiated to pinpoint the source of the problem.

Spectroscopic Analysis (ppm)DATE 7/3/12 6/23/12 3/20/12 12/23/11 9/28/11 6/15/11

Iron 171.03 5.45 1.84 3.71 10.43 5.57

Copper 5.71 2.84 3.25 2.08 2.93 4.59

Lead 2.53 ‐ ‐ ‐ ‐ ‐

Aluminum ‐ ‐ ‐ ‐ ‐ ‐

Silicon 31.23 8.0 7.78 4.94 4.84 3.51

Calcium 56.27 39.44 25.71 136.89 114.34 41.6

Phosphorus 303.4 310.36 318.15 535.85 507.0 258.4

Zinc 405.75 114.47 115.07 403.22 388.0 117.8

Ferrous Wear Concentration (ppm)DATE 7/3/12 6/23/12 3/20/12 12/23/11 9/28/11 6/15/11

Total Ferrous 2118.0 22.2 33.6 24.2 33.4 13.4


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Analytical Ferrography showed high amounts of dark metallic oxides and low alloy. This correlated with the data from the spectrometer and the direct read ferrography.

Conclusions: The maintenance department issued a work ticket to change the oil and inspect the pump bearings. Upon inspection it was found that the thrust bearing was severely damaged. The thrust shoes were deeply scored and the thrust assembly was badly damaged. The pump was pulled from operation. The routine oil analysis uncovered a problem that was easy to repair. The inspection occurred on a planned basis, thus preventing possible downtime. If the pump were left in service, it would have catastrophically failed. This pump costs more than $50,000!

Case Study II Equipment: Westinghouse 5,000 HP Motor

Application: A steel mill uses this motor to drive a double reduction gearbox on a roughing mill at an input speed of 450 rpm. The motor has babbitt sleeve bearings and is coupled to the gearbox with a #11 Kop‐Flex gear coupling.

History: Oil samples from this motor are routinely sent for analysis and historically have exhibited normal machine and lubricant conditions. Spectroscopic analysis and direct reading ferrography are routinely performed in order to trend the wear of the lubricated bearings. Analytical Ferrography is automatically performed when there is a machine abnormality.

Problem Sample: The sample drawn on 5/18/12 exhibited excess lead wear, excess tin wear and a high total ferrous wear count. The customer was called and submitted another sample. The sample drawn on 5/24/12 exhibited the same abnormalities and the machine was given a marginal condition and Analytical Ferrography was automatically initiated to pinpoint the source of the problem.

Spectroscopic Analysis (ppm)DATE 5/24/12 5/18/12 2/7/12 11/16/11 8/24/11 5/4/11

Iron 38.17 37.98 4.91 3.41 3.72 3.65

Copper 15.15 16.37 14.15 13.58 14.27 13.53

Lead 139.34 134.33 25.27 22.11 23.26 23.33

Tin 28.30 22.61 ‐ ‐ ‐ ‐

Silicon 7.39 8.83 ‐ ‐ ‐ ‐

Phosphorus 99.48 93.16 88.4 87.1 98.42 93.15

Zinc 61.44 51.63 50.19 45.79 48.49 50.85

Ferrous Wear Concentration (ppm)DATE 5/24/12 5/18/12 2/7/12 11/16/11 8/24/11 5/4/11

Total Ferrous 169.8 58.5 46.4 21.8 23.3 32.0

Analytical Ferrography showed high amounts of low alloy steel and dark metallic oxides. The colored particles on the top slide are low alloy steel that changed color after heat treatment.

Conclusions: The results of the oil analysis initiated a visual inspection, which revealed that the coupling appeared to be locked. The maintenance department issued a work order to inspect the motor bearing and coupling. Upon removal of the bearing cap, it was found that the faces of the bearing were wiped. The bearing surface that the shaft rode on was also starting to wipe. The bearing was changed.

Maintenance completed the repairs on a planned basis with no delay to the mill. If left unrepaired, the motor bearing would have failed catastrophically. Such a failure while the mill was running would have caused a four‐hour delay to the mill with a cost in excess of $60,000!


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analytical ferrography the forensic science of oil analysis

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