Grease Sampling for Heavy-Industry Rotating Equipment

A practical field article for bearings, housings, rolling mills, auxiliaries, and grease-lubricated process machinery

Grease sampling is the controlled removal of a small, representative quantity of in-service grease from a machine so that the condition of the grease, the bearing, and the surrounding environment can be assessed. It is not simply “taking some old grease.” In heavy industry, the value of grease sampling depends almost entirely on where the sample is taken, when it is taken, how cleanly it is taken, and whether the same method is repeated over time.

The heavy-industry situation: a large bearing or roll housing with direct access to grease. For formal condition monitoring, that same concept should be converted into a controlled procedure: clean access point, clean disposable tool, clean sample container, defined sample zone, and full documentation. Avoid bare-hand sampling for laboratory trending; skin, sweat, dirt, fibers, and old shop contamination can distort results.

ASTM D7718 is the main reference practice for obtaining trendable in-service grease samples, and it explicitly addresses applications such as pillow-block bearings, electric motors, gearboxes, exposed bearings, open gears, failed grease-lubricated components, and cases where large or poorly mixed bearings require more than one sample location. (ASTM Store) ASTM D7918 addresses evaluation of in-service grease for properties such as flow, wear, contamination, oxidation, and consistency, including NLGI grades 00 to 3. (astm.org)

1. The purpose of grease sampling

The purpose of grease sampling is to obtain evidence from the grease that is actually participating in lubrication, sealing, contamination transport, and wear-debris transport.

A good grease sample can reveal:

Whether the grease is still soft enough, firm enough, and mobile enough for the bearing or gear cavity.
Whether the grease has hardened, bled oil excessively, dried, oxidized, washed out, or mechanically sheared.
Whether water, mill scale, dust, coal dust, cement dust, ore fines, pulp, process fluid, coolant, or cleaning chemicals are entering the housing.
Whether metallic wear particles are being generated by rolling elements, races, cages, seals, spacers, gears, shafts, or housings.
Whether the wrong grease, mixed grease, or incompatible thickener system has entered the component.
Whether automatic lubrication systems are actually delivering grease to the bearing, not merely to a pipe or a blocked distributor.
Whether relubrication quantity and frequency are purging contaminants or merely overfilling the housing.
Whether the sealing arrangement is working.
Whether a bearing problem detected by vibration, ultrasound, infrared thermography, temperature, or current signature analysis has a lubrication or contamination cause.

Grease sampling is especially valuable on critical equipment where the bearing is expensive, inaccessible, difficult to replace, or capable of causing major production loss: rolling mill stands, continuous caster segments, main fans, crushers, kilns, large electric motors, large conveyors, pelletizers, stackers, reclaimers, slew bearings, crane wheels, paper machine rolls, mining shovels, large pump motors, gear couplings, and process agitators.

2. Why grease sampling is harder than oil sampling

Oil circulates. Grease usually does not.

That single difference changes everything. In an oil system, a properly located live-zone sample valve can often provide a well-mixed sample from circulating lubricant. In a grease-lubricated bearing, the grease may exist in several different conditions inside the same housing:

Grease zone	Description	What it can tell you
Active grease	Grease near rolling elements, raceways, cage pockets, gear mesh, or sliding contact	Best indicator of lubrication condition, wear debris, heat, shear, and contact distress
Purge grease	Grease displaced out of the bearing through relief ports, seals, drains, or labyrinths	Useful for trending if collected consistently, but may be older, mixed, or from a dead zone
Seal-zone grease	Grease near outer seals, flingers, labyrinths, covers, and ingress points	Best indicator of water, dust, scale, cleaning-fluid, or process contamination ingress
Dead-zone grease	Grease trapped in corners, covers, cavities, unused pipe sections, or housing pockets	Can be very old, oxidized, dry, or contaminated but may not represent active lubrication
Freshly injected grease	New grease from nipple, grease gun, automatic line, or centralized system	Useful as a reference sample, but not representative of in-service grease
Failed-component grease	Grease collected during disassembly from raceways, rollers, cages, seals, and housing pockets	Highest forensic value if sampled by location before cleaning

A bearing can contain clean-looking new grease near the grease fitting, contaminated wet grease near the seal, dry hardened grease in a cover pocket, and metallic active grease near the loaded raceway. Mixing all of that into one bottle may produce a laboratory result that is mathematically average but diagnostically weak.

The rule is simple: sample by zone, label by zone, trend by zone.

3. The three most important principles

3.1 Sample the grease that matters

The best sample is usually the grease closest to the working contact: rolling element/raceway, loaded zone, cage pocket, gear tooth flank, spline, coupling tooth, or slew-bearing raceway. When that is not accessible, the next best option is grease that has just been displaced from that active zone through a known purge path.

Avoid taking a sample only because it is easy to reach. The easiest grease is often from a cover pocket, relief cavity, old drain channel, or external seal, and may not represent the bearing.

3.2 Be repeatable

A sample from the same machine but a different location is often not comparable. For trending, repeatability matters as much as laboratory accuracy.

Document:

Exact bearing position.
Exact housing side.
Exact sample point.
Whether sample was active, purge, seal-zone, dead-zone, or failure sample.
Whether sample was taken before or after relubrication.
How long the machine had operated since the last relube.
Whether machine was running, stopped hot, stopped cold, or opened during maintenance.
Sample tool used.
Amount of grease removed.
Any abnormal condition observed.

A single sample can help diagnose a problem. A repeatable sample can build a condition-monitoring program.

3.3 Do not contaminate the sample

Grease sampling often fails because the sample is contaminated during collection. Field contamination can come from dirty hands, cotton rags, wire brushes, old grease on the housing exterior, open containers, solvent residue, rust flakes, paint chips, scale, rainwater, dust, and reused tools.

Use clean disposable spatulas, syringes, grease-thief samplers, clean plastic tubes, clean stainless tools, or clean nitrile-gloved fingers only when necessary. Never place sample grease in a used bottle, food container, open grease cartridge cap, dirty plastic bag, or on a rag.

4. Sample types used in heavy industry

4.1 Fresh grease reference sample

Every grease analysis program needs a fresh reference sample. Without it, the laboratory may not know whether the in-service grease is degraded or whether it simply looks different because of its original formulation.

Collect fresh reference samples from:

New grease drum.
Grease pail.
Grease cartridge.
Bulk grease delivery.
Automatic lubrication reservoir.
Pump outlet.
Grease line endpoint, if line contamination is suspected.
Grease gun nozzle after purging a small amount.

For critical assets, retain a reference from every new batch or lot. If a mill changes from lithium complex to calcium sulfonate complex, polyurea, aluminum complex, clay, or synthetic-base grease, create a new baseline before comparing in-service samples.

4.2 Routine trend sample

This is the standard periodic sample taken from the same point at the same operating condition. It is used for trend analysis.

Examples:

Quarterly sample from a fan bearing relief port.
Monthly sample from crusher bearing purge.
Sample every roll change from a rolling mill chock.
Sample every shutdown from a conveyor pulley plummer block.
Sample every outage from a large motor DE and NDE bearing.
Sample from a slew bearing at fixed clock positions.

Routine samples should be taken before relubrication, unless the established method is specifically based on controlled purge sampling during relubrication.

4.3 Investigative sample

This is taken because another condition-monitoring method or field symptom indicates a possible fault.

Triggers include:

Temperature rise.
Abnormal vibration.
High ultrasound.
Metallic particles in purge grease.
Grease leakage.
Water washing from seals.
Sudden grease color change.
Hard grease at relief.
Blocked grease line.
Unusual motor bearing noise.
Coupling overheating.
High bearing envelope acceleration.
Rolling mill bearing failure recurrence.
Frequent seal failure.
Excessive lubricant consumption.

Investigative sampling should usually include more than one zone: active grease if accessible, purge grease, seal-zone grease, and fresh grease reference.

4.4 Forensic failure sample

This is taken during teardown after bearing distress, seizure, cage failure, spalling, corrosion, overheating, or abnormal wear. It must be collected before cleaning the component.

Forensic grease sampling should be mapped:

Inner raceway grease.
Outer raceway grease.
Rolling element grease.
Cage pocket grease.
Loaded-zone grease.
Unloaded-zone grease.
Seal-side grease.
Drive-side and non-drive-side grease.
Top, bottom, entry side, exit side, operator side, drive side, or clock-position samples.
Grease from cracks, flakes, spalls, blue areas, rusted areas, or metal-debris accumulations.
Grease from housing pockets and drains separately.

Do not mix these unless instructed. The location may matter more than the chemistry.

5. Sampling locations: where to take grease

5.1 Active bearing zone

This is the preferred sample location when accessible. In a rolling bearing, active grease is close to the rollers, balls, raceways, cage, and loaded zone. In large bearings, this may be accessible only during shutdown, cover removal, bearing inspection, roll change, or overhaul.

Use active-zone sampling for:

Rolling mill stand bearings.
Large spherical roller bearings.
Four-row tapered roller bearings.
Crusher bearings.
Kiln support roller bearings.
Paper machine roll bearings.
Continuous caster roll bearings.
Slow-speed slew bearings.
Grease-lubricated trunnions.
Large fan pedestals.
Exposed bearings.

Best practice:

Clean the exterior before opening.
Open the access cover carefully without dropping debris.
Identify the loaded zone and grease path.
Remove only enough grease for analysis.
Avoid scraping steel surfaces unless wear-debris mapping is intended.
Place sample directly into clean container or sampler.
Label the exact location.

5.2 Purge or relief point

Many grease-lubricated bearings have a relief plug, drain plug, purge port, labyrinth drain, or vent. Grease from this point is often easier and safer to collect.

Purge sampling is useful when:

The purge path is known.
The sample is collected consistently.
The sample is taken before new grease reaches the relief.
The same amount of grease is displaced each time.
The sample is clearly labeled as purge grease.

Limitations:

It may be old grease.
It may come from the nearest easy flow path rather than the loaded zone.
Fresh grease may channel through the housing and bypass old grease.
It may exaggerate contamination if taken from an external seal.
It may dilute active wear debris if mixed with dead-zone grease.

5.3 Seal lip, labyrinth, or flinger zone

Seal-zone samples are excellent for diagnosing ingress but poor for judging the full bearing unless trended separately.

Use seal-zone sampling for:

Rolling mill water ingress.
Caster scale and water contamination.
Conveyor pulley dust ingress.
Cement plant dust ingress.
Coal handling dust ingress.
Paper machine water ingress.
Washdown areas.
Outdoor motors and fans.
Slurry pump support bearings.
Bearings near cooling sprays.

Label clearly: seal-zone sample, not active bearing sample.

5.4 Housing pocket or dead zone

Dead-zone samples are sometimes useful, but they should not be treated as normal in-service samples. They can reveal historical grease mixing, old hardened grease, or poor purge paths.

Use dead-zone sampling when investigating:

Hard grease blockage.
Grease not purging.
Incompatible grease mixing.
Oil bleed and thickener accumulation.
Overgreasing.
Long-term oxidation.
Housing design problems.
Automatic lubrication failures.

Label as dead-zone grease.

5.5 Automatic lubrication system sample points

For centralized lubrication systems, sample the grease system as well as the component.

Important sample locations:

Reservoir grease.
Pump suction area.
Pump outlet.
Main line.
Divider/progressive block inlet.
Divider/progressive block outlet.
Longest line endpoint.
Grease at component inlet.
Grease purged from component.
Grease at blocked or suspected line.

This is critical because a bearing failure may be caused by grease delivery failure, not grease formulation failure.

5.6 Failed bearing teardown locations

During teardown, sample before washing. Once solvent, steam cleaning, diesel, kerosene, degreaser, or compressed-air cleaning is used, the evidence is disturbed.

Teardown sample sequence:

Photograph as-found condition.
Mark bearing orientation.
Mark drive side, non-drive side, top, bottom, loaded zone, operator side, entry side, exit side.
Collect loose grease and debris separately.
Collect raceway grease.
Collect cage-pocket grease.
Collect seal-side grease.
Collect housing drain/pocket grease.
Collect any metallic debris separately.
Only then clean the bearing for visual failure analysis.

Bearing damage classification commonly separates modes such as fatigue, wear, corrosion, electrical erosion, plastic deformation, cracking, and fracture; grease samples are often used alongside visual bearing evidence to support root-cause analysis. (ISO)

6. Tools for grease sampling

6.1 Grease thief or dedicated grease sampler

A grease thief is a purpose-built sampler for obtaining small, repeatable in-service grease samples. It is particularly useful where the grease quantity is limited and the lab uses small-sample test methods.

Modern in-service grease analysis can be performed on very small samples when the correct sampler and test method are used; some standardized approaches can perform multiple tests from about 1 gram of grease, although required volume depends on the lab and test slate. (Plant Engineering)

Use for:

Pillow-block bearings.
Electric motors.
Gearboxes.
Valves.
Wind and slew bearings.
Limited-access housings.
Critical bearings where only a small amount can be removed.

Advantages:

Repeatable sample geometry.
Lower contamination risk.
Less grease removal.
Better suited to small-sample laboratory methods.
Can access through small ports.

Limitations:

Requires training.
Requires correct adapter/access point.
May not work well with extremely hard, dry, stringy, fibrous, or heavily contaminated grease.
Not always suitable for large open cavities unless used with location discipline.

6.2 Disposable spatula or scoop

Use a clean disposable plastic spatula or scoop for open housings, chocks, covers, and large bearings.

Best for:

Rolling mill chocks during roll change.
Split plummer block housings.
Open bearing inspections.
Couplings opened for inspection.
Open gear tooth samples.
Seal-zone samples.
Failed bearing teardown.

Avoid wooden sticks, dirty screwdrivers, rusty scrapers, or anything that sheds fibers.

6.3 Syringe and tube

A syringe with clean tube can collect semi-fluid grease, soft grease, or grease from ports.

Best for:

NLGI 000, 00, 0, or soft NLGI 1 grease.
Gear couplings.
Centralized lubrication points.
Small ports.
Grease pockets.
Long narrow cavities.

Do not reuse syringe tips unless cleaned to laboratory-level cleanliness.

6.4 Stainless-steel spatula or scraper

Useful when grease is hard, dry, or crusted, but it carries risk of introducing metallic particles if the tool scrapes the housing or bearing.

Use carefully for:

Hardened grease in covers.
Dead-zone sampling.
Open gear lubricant.
Forensic sampling.
Coupling teeth.

If wear metal analysis is important, avoid aggressive scraping of steel surfaces.

6.5 Tube, straw, or cannula

A clean tube or cannula can reach deeper into a housing through an inspection port. This is useful where surface grease differs from internal grease.

Use for:

Large plummer blocks.
Bearing caps.
Gear-coupling cavities.
Slew bearing ports.
Chock housings.
Open covers with deep grease pockets.

6.6 Purge collection cup or bottle

A clean cup can collect grease expelled from relief ports during controlled relubrication.

Use for:

Motors.
Fan bearings.
Conveyor bearings.
Pump bearings.
Crusher bearings.
Autolube components.
Bearings where direct access is unsafe.

Do not let purged grease touch dirty housing surfaces before collection.

6.7 Magnetic plug or debris collector

Magnetic plugs are not grease samples by themselves, but they are valuable companion evidence. If ferrous paste or flakes collect on a magnetic plug, collect both the grease sample and the debris.

Keep magnetic debris separate from grease if the lab will perform particle morphology.

7. Sample quantity

The correct quantity depends on the laboratory and the required test package.

As a practical guide:

Purpose	Typical minimum
Visual inspection only	pea-sized amount may be enough
Small-sample screening	about 1 g may be enough with the correct sampler and method
Wear debris, FTIR, consistency screening	commonly 1–5 g, depending on lab
Full grease analysis package	often 5–20 g
Traditional basic testing without a dedicated small sampler	may require much more
Forensic failure investigation	collect multiple samples, each separately labeled

Some laboratories require much larger sample volumes when samples are not submitted in a small-sample device; one lab brochure, for example, states that samples submitted without a grease-thief device may require 1 ounce, or 28 grams, for basic analysis. (SGSCorp) Therefore, confirm sample quantity with the laboratory before building the field procedure.

Never remove so much grease that the bearing is starved after sampling. For critical bearings, replace only according to the established relubrication procedure, and document any grease added after sampling.

8. Timing of grease sampling

8.1 Before relubrication

This is usually the best time for routine condition monitoring. The grease has experienced its full service interval and is more likely to show degradation, contamination, or wear debris.

Use this timing for:

Motors.
Fans.
Pumps.
Conveyors.
Crushers.
Mill stands.
Caster bearings.
Gear couplings.
Kiln bearings.
Paper machine rolls.

8.2 During controlled relubrication

This is useful when the sample is collected from a relief port as grease is slowly added.

Procedure:

Clean relief area.
Remove relief plug or open purge path.
Collect any existing purge grease separately if present.
Add grease slowly using the normal grease type.
Collect the first old grease displaced from the relief.
Stop before new grease dominates the sample.
Label as controlled purge sample.
Record amount of grease added.

This method is common on electric motors and housed bearings, but the sample is a purge-path sample, not necessarily an active-zone sample.

8.3 During shutdown inspection

This is preferred for direct active-zone sampling.

Use during:

Planned outage.
Bearing inspection.
Roll change.
Chock maintenance.
Crusher inspection.
Coupling inspection.
Open gear inspection.
Seal replacement.
Motor overhaul.
Bearing replacement.

8.4 Immediately after abnormal event

Take an investigative sample after:

Water ingress event.
Seal failure.
overheating.
vibration alarm.
bearing noise.
abnormal purge.
blocked lube line.
process upset.
contamination event.
grease changeover mistake.

Do not wait until the housing is cleaned or regreased.

8.5 At removal or failure

If a bearing is removed, sample grease before cleaning. Mark orientation and collect mapped samples. This is often the last chance to preserve evidence.

9. General field procedure for grease sampling

Step 1: Prepare the sampling plan

Before going to the machine, know:

Equipment ID.
Component ID.
Bearing type.
Lubrication point number.
Grease type and NLGI grade.
Last relube date.
Relube quantity.
Operating hours since last relube.
Sampling location.
Sampling method.
Required sample quantity.
Lab test package.
Safety requirements.

Step 2: Prepare clean tools

Bring:

Clean sample bottles or grease-thief samplers.
Disposable spatulas.
Syringes or tubes if needed.
Nitrile gloves.
Lint-free wipes.
Clean solvent for exterior cleaning, if allowed.
Labels.
Marker.
Sample forms.
Zip bags.
Camera or phone for photos.
Small brush for exterior cleaning only.
Plug wrench or cover tools.
Lockout/tagout equipment if required.

Step 3: Make the job safe

Follow plant safety rules.

Typical precautions:

Lockout/tagout for exposed rotating parts.
Guarding and permit requirements.
Hot surface protection.
Pinch-point control.
Fall protection for elevated equipment.
Confined-space rules where applicable.
Stored-energy control.
No loose clothing near rotating equipment.
No sampling from live exposed shafts unless the machine design has a safe remote sample point.

Step 4: Clean the exterior

Clean around the fitting, cover, purge plug, drain, or inspection port before opening. Do not push external dirt into the housing.

Use caution with solvents. Solvent residue can affect grease analysis. Allow cleaned areas to dry.

Step 5: Open the access point

Open carefully. Keep loose paint, rust, gasket pieces, or dust from falling into the housing or sample.

If opening a large cover, photograph the as-found condition before touching the grease.

Step 6: Remove non-representative surface contamination if required

If the exterior surface has obvious dirt, do not include that dirt unless the purpose is seal-zone contamination investigation. For active-zone samples, remove superficial dirt without disturbing the deeper grease.

Step 7: Collect from the defined zone

Take grease from the planned location. Do not wander around the housing collecting random grease. If several areas look different, collect them as separate samples.

Examples:

“Fan 2, DE bearing, relief purge sample.”
“Mill stand 4, work roll top chock, drive side, seal-zone grease.”
“Crusher 1, outboard spherical roller bearing, active grease from lower loaded zone.”
“Motor M-204, NDE bearing, purge during controlled relube.”
“Slew ring, 6 o’clock purge point, after 90° rotation.”

Step 8: Fill and seal container

Place grease directly into the container. Avoid entraining large amounts of air or dropping debris from the exterior.

Cap immediately.

Step 9: Label immediately

Label before leaving the machine.

Minimum label fields:

Plant.
Area.
Equipment ID.
Component.
Bearing position.
Sample point.
Sample zone.
Date and time.
Grease type.
Sampler name.
Operating condition.
Last relube date/time.
Relube quantity since last sample.
Abnormal observations.

Step 10: Restore machine condition

Reinstall plugs, caps, covers, relief vents, guards, and fittings. Clean excess grease. Ensure relief paths are not blocked.

Step 11: Ship and record

Submit samples promptly. Avoid leaving samples in hot vehicles, dusty shops, or direct sunlight. Record the sample in the CMMS, lubrication database, or reliability system.

10. Housing-specific grease sampling guidance

10.1 Pillow-block and plummer-block bearings

These are common on fans, conveyors, crushers, screens, pumps, roll tables, and material-handling equipment. They may contain spherical roller bearings, self-aligning ball bearings, tapered roller bearings, or split bearings.

Best sample locations:

Relief port purge.
Lower housing grease near rolling element path.
Seal-side grease near labyrinth or contact seal.
Cap pocket grease if investigating dead zones.
Active grease during cap removal.

Recommended method:

For routine trending, use a fixed purge port or dedicated sample port.
For inspections, remove the cap and collect active grease from the lower loaded zone.
On split housings, sample drive side and non-drive side separately if contamination is directional.
On outdoor conveyors, sample both seal-zone and active-zone grease when water or dust ingress is suspected.

Common mistakes:

Sampling grease nipple residue.
Sampling only fresh grease from the grease gun.
Sampling old grease from the housing cap and comparing it with active-zone samples.
Mixing seal grease and bearing grease.
Collecting after pumping new grease until fresh grease appears.

10.2 Split bearing housings

Split housings allow excellent access, but they also introduce contamination risk when opened.

Use a mapped approach:

Top cap grease.
Lower loaded-zone grease.
Inboard seal side.
Outboard seal side.
Rolling element/cage area.
Drain pocket.

For a routine program, choose one primary trend point and keep forensic/mapped sampling for outages or abnormalities.

10.3 Cartridge and flanged bearing units

These are common on conveyors, packaged equipment, fans, food/process equipment, and smaller auxiliary machines.

Sampling options:

Relief port purge.
Seal edge.
Fitting-adjacent cavity if a sampler can reach.
Teardown sample if sealed or inaccessible.

Because access is limited, the best strategy is often to install a controlled relief/sampling point during rebuild or replacement.

10.4 Take-up bearings

Take-up bearings on belt conveyors often operate in dusty, wet, misaligned, and shock-loaded environments.

Sample separately:

Head pulley drive side.
Head pulley non-drive side.
Tail pulley bearings.
Bend pulley bearings.
Take-up pulley bearings.
Gravity take-up bearings.
Screw take-up bearings.

For conveyors, the environment often differs between sides. A bearing facing spillage, washdown, rain, or belt carryback may show contamination earlier than the opposite bearing.

10.5 Electric motor bearings

Large electric motors commonly have drive-end and non-drive-end bearings with grease inlet and relief. Sampling must not damage shields, seals, windings, or internal passages.

Best sample locations:

DE relief port.
NDE relief port.
Purged grease collected during controlled relubrication.
Bearing cavity during overhaul.
Seal area if contamination ingress is suspected.

Recommended routine method:

Sample before relubrication where possible.
If using purge sampling, remove relief plug and collect grease displaced by slow greasing.
Keep DE and NDE samples separate.
Record motor running/stopped condition.
Record grease quantity added.
Avoid overpressurizing the bearing cavity.

Common mistakes:

Sampling after pumping large quantities of fresh grease.
Mixing DE and NDE grease.
Ignoring relief path blockage.
Pushing grease into windings.
Treating relief grease as fully representative of active bearing grease without trending history.

10.6 Pump bearing housings

Many process pumps are oil-lubricated, but auxiliary motors, small pumps, vertical pump motors, and some bearing arrangements are grease-lubricated.

Sample by position:

Pump inboard bearing.
Pump outboard bearing.
Motor DE.
Motor NDE.
Coupling-end bearing.
Thrust bearing, if grease-lubricated.

For vertical pumps and vertical motors, identify whether grease migrates downward, accumulates above the bearing, or purges through a lower drain. Sample according to actual grease path.

10.7 Fan and blower bearing pedestals

Fans are excellent candidates for grease sampling because bearings are often large, accessible, and critical.

Applications:

ID fans.
FD fans.
PA fans.
Cooling tower fans.
Baghouse fans.
Sinter plant fans.
Process exhaust fans.
Mine ventilation fans.

Best sample locations:

DE and NDE bearing reliefs.
Plummer block lower loaded zone.
Seal-zone grease for outdoor fans or dirty gas fans.
Purge grease before relubrication.

Record:

Fan speed.
Bearing temperature.
Vibration condition.
Recent washdown or rain exposure.
Grease interval.
Damper/load condition if abnormal.

10.8 Gearboxes with grease-lubricated bearings or grease pockets

Many industrial gearboxes are oil-lubricated, but some have grease-lubricated auxiliary bearings, seals, couplings, or slow-speed stages.

Sampling locations:

Bearing grease cavity.
Seal grease cavity.
Purged grease from bearing labyrinth.
Gear coupling between gearbox and driven machine.
Grease line feeding auxiliary bearing.
Dead-zone grease near covers.

Keep gearbox oil samples and grease samples separate. Do not let oil-contaminated grease be misinterpreted unless the grease cavity is designed to share lubricant.

10.9 Gear couplings

Gear couplings can contain semi-fluid grease or coupling grease that experiences sliding, centrifugal separation, oil bleed, oxidation, and wear debris generation.

Best sample locations:

Coupling half near gear teeth.
Bottom of coupling casing.
Grease from both hubs separately.
Grease from spacer section.
Purged grease from inspection plug.
Failed coupling tooth area.

Sampling notes:

Mark motor side and driven side.
Sample before cleaning.
Inspect for oil separation, dry soap, metallic paste, bronze/copper particles, seal fragments, and hardened grease.
Do not mix grease from both coupling halves if one side shows abnormal wear.

10.10 Open gears and girth gears

Open gear lubricants may be grease-like, asphaltic, high-viscosity, or tacky compounds. Sampling is useful for contamination, wear, and lubricant condition.

Applications:

Kiln girth gears.
Ball mill gears.
SAG mill gears.
Rotary dryers.
Crushers.
Dragline gearing.
Large slew drives.

Best locations:

Loaded tooth flank.
Tooth root.
Pinion tooth.
Gear tooth.
Spray pattern area.
Accumulated lubricant at guard bottom.
Edge of gear face if alignment issue suspected.

Important:

Do not sample only fallen material from the guard bottom unless investigating waste and contamination.
Active tooth-flank lubricant is more representative.
Map samples across face width if edge loading is suspected.

10.11 Slewing rings and large slow-speed bearings

Large slew bearings do not mix grease uniformly because motion may be oscillatory, partial rotation, or very slow. ASTM D7718 notes that large bearings with limited rotation or insufficient mixing may require more than one sample to obtain trendable results. (ASTM Store)

Applications:

Stackers.
Reclaimers.
Ship unloaders.
Cranes.
Excavators.
Wind turbine blade/yaw bearings.
Ladle turrets.
Furnace roof rotation bearings.
Rotary tables.

Best practice:

Sample at multiple clock positions.
Record angular position.
Sample loaded and unloaded zones separately.
Rotate the bearing if safe and collect purge from several points.
Keep gear-tooth lubricant separate from raceway grease.
Use the same clock positions for trend samples.

Example mapping:

12 o’clock.
3 o’clock.
6 o’clock.
9 o’clock.
High-load zone.
Water-ingress side.
Grease inlet nearest pump.
Farthest point from pump.

10.12 Rolling mill stand bearings

Rolling mill bearings are among the most important grease sampling applications in heavy industry. Roll-neck bearings and chock bearings face water, scale, shock load, high load, vibration, misalignment, rolling coolant, and frequent roll changes.

Bearing types may include:

Four-row tapered roller bearings.
Four-row cylindrical roller bearings.
Spherical roller bearings.
Thrust bearings.
Work roll bearings.
Backup roll bearings.
Intermediate roll bearings.
Edger roll bearings.
Guide roll bearings.
Pinch roll bearings.
Looper roll bearings.
Roller table bearings.

Key sampling zones:

Zone	Why it matters
Drive side chock	Different load, heat, and contamination exposure than operator side
Operator side chock	Often different water/scale exposure
Top roll bearing	May differ from bottom roll due to water drainage and heat
Bottom roll bearing	Often more exposed to water pooling, scale, and debris
Entry side	May see coolant, scale, or strip debris differently
Exit side	May show heat and product-process contamination
Seal-side grease	Best for water/scale ingress detection
Inner bearing rows	Best for active lubrication and wear evidence
Outer bearing rows	Good for seal and edge-loading evidence
Chock drain/purge	Useful if collected consistently
Roll shop grease after dismantling	Excellent forensic evidence if sampled before washing

Routine sampling strategy for rolling mills:

Define sample points by mill stand, roll type, side, and chock.
Sample during roll change before washing or regreasing.
Keep DS and OS separate.
Keep top and bottom chocks separate.
Keep seal-zone grease separate from bearing-row grease.
Collect active grease from near rollers/raceway if accessible.
Collect purge/drain grease separately.
Record campaign length, tonnage, rolling hours, product mix, water events, and bearing temperature if available.
Compare against fresh grease from the roll shop lubrication system.
Preserve debris particles separately if visible.

For rolling mills, a single mixed sample from “the chock” is often not enough. The bearing may have a clean side and a water-damaged side. If the sample is mixed, the failure mechanism may be diluted.

10.13 Continuous caster and roller-table bearings

Caster and roller-table bearings see water, steam, scale, high temperature, shock loads, misalignment, and slow/oscillatory rotation.

Applications:

Caster segment rolls.
Withdrawal and straightener rolls.
Runout table rolls.
Hot strip roller table bearings.
Billet caster rolls.
Slab caster rolls.
Pinch rolls.

Sampling options:

Purged grease from auto-lube points.
Seal-zone grease.
Bearing grease during segment overhaul.
Grease from failed roll bearing before cleaning.
Grease from distributor block outlet.
Grease from farthest lube line.

Important documentation:

Segment number.
Roll number.
Bearing side.
Strand position.
Water leak history.
Auto-lube divider point.
Operating hours or cast tonnage.
Grease consumption.

For autolubed caster bearings, sample the lubrication system as well as the bearing. A clean reservoir sample does not prove that grease reached the bearing.

10.14 Crushers, screens, and mining equipment bearings

Mining and aggregate bearings often contain large quantities of grease and face heavy shock, dust, water, vibration, and contamination.

Applications:

Jaw crusher bearings.
Cone crusher bearings.
Gyratory crusher spider bushings and bearings where greased.
Vibrating screen bearings.
Apron feeder bearings.
Conveyor pulley bearings.
Dragline and shovel bearings.
Stacker/reclaimer bearings.
Mill trunnion auxiliary grease points.

Sampling focus:

Active bearing zone during outage.
Purge grease from each bearing.
Seal-side grease facing dust or slurry.
Grease from auto-lube line endpoints.
Hardened grease from reliefs.
Metallic paste from seals or drains.

Do not compare a crusher bearing active sample to a conveyor bearing purge sample. Each asset class needs its own baseline and alarm logic.

10.15 Cement, lime, and mineral processing equipment

Cement and mineral plants expose grease to abrasive dust, heat, vibration, and sometimes water.

Applications:

Kiln support rollers.
Kiln thrust rollers.
Cooler fans.
Separator bearings.
Bucket elevator bearings.
Conveyor bearings.
Crusher bearings.
Mill auxiliary bearings.
Open gears.
Drag chain bearings.

Sampling focus:

Dust ingress at seals.
Hardening due to heat and dust.
Oil bleed from high temperature.
Abrasive wear debris.
Purge path effectiveness.
Automatic lubrication system delivery.

Seal-zone samples are especially useful in cement service, but they should not be confused with active-zone bearing samples.

10.16 Paper machine and pulp industry bearings

Paper machines often combine high speed, water, steam, heat, chemical exposure, and difficult access.

Applications:

Felt rolls.
Press rolls.
Dryer section bearings.
Calendar rolls.
Yankee auxiliary equipment.
Conveyor and fan bearings.
Vacuum pump motors.
Agitators.

Sampling focus:

Water ingress.
Grease washout.
High-temperature oxidation.
Softening or hardening.
Seal performance.
Bearing side exposed to showers or steam.

Sample drive side and tending side separately where exposure differs.

10.17 Power plant auxiliary rotating equipment

Power plants have many grease-lubricated auxiliaries.

Applications:

ID, FD, and PA fan bearings.
Coal conveyor bearings.
Pulverizer auxiliary bearings.
Cooling tower fan motors.
Pump motors.
Ash-handling equipment.
Dampers and actuators.
Motor-operated valves.

Sampling focus:

Motor DE/NDE grease.
Fan bearing purge.
Outdoor water ingress.
Coal dust ingress.
High-temperature oxidation.
Overgreasing and relief blockage.
Grease line delivery in remote systems.

Motor-operated valves and other grease-lubricated components are within the type of configurations addressed by ASTM D7718. (ASTM Store)

10.18 Process mixers, agitators, and vertical shafts

Agitators and mixers often have upper and lower bearings, seals, and sometimes slow-speed grease-lubricated supports.

Sampling focus:

Upper bearing grease.
Lower bearing grease.
Seal contamination.
Product ingress.
Water or chemical ingress.
Grease hardening near heated vessels.
Grease softening due to process fluid.

Record whether the machine was washed, steamed, cleaned-in-place, or exposed to chemical fumes.

10.19 Cranes, hoists, and material-handling machinery

Applications:

Crane wheel bearings.
Rope sheaves.
Drum bearings.
Slew bearings.
Hoist gearbox couplings.
Ladle crane auxiliary bearings.
Ship unloader bearings.

Sampling focus:

Slow-speed bearing zones.
Edge loading.
Water ingress outdoors.
Grease drying from long intervals.
Shock-load wear debris.
Seal-zone contamination.
Multi-point slew bearing mapping.

11. Sampling large bearings

Large bearings require special discipline because grease is not uniformly distributed.

Examples:

Rolling mill chock bearings.
Slew bearings.
Crusher bearings.
Large fan bearings.
Kiln support roller bearings.
Paper machine roll bearings.
Large electric motor bearings.
Mine shovel bearings.
Stacker/reclaimer slew bearings.
Large conveyor pulley bearings.

For large bearings, use a mapped sampling plan.

11.1 Clock-position mapping

Record the sample position as clock orientation:

12 o’clock.
3 o’clock.
6 o’clock.
9 o’clock.
Loaded zone.
Unloaded zone.
Seal side.
Opposite seal side.

For a rotating outer ring or unusual load path, define the map relative to the housing and load direction, not just gravity.

11.2 Side mapping

Record:

Drive side.
Non-drive side.
Operator side.
Work side.
Inboard.
Outboard.
Entry side.
Exit side.
Top.
Bottom.

11.3 Row mapping

For multi-row bearings:

Row 1.
Row 2.
Row 3.
Row 4.
Thrust row.
Radial row.
Seal-side row.
Inner row.
Outer row.

This is essential for four-row rolling mill bearings, where water or load damage may concentrate in one row.

11.4 Do not mix unless the purpose is average condition

For large bearings, a composite sample may be useful for general grease condition, but it can hide localized failure. If a bearing is expensive or critical, submit separate samples first. The lab or reliability engineer can decide later whether to composite data.

12. Sampling from automatic lubrication systems

Automatic lubrication can create a false sense of security. Grease may be present in the reservoir but not reach the bearing. A divider block may cycle while one line is blocked downstream. Grease may separate, harden, or become contaminated in long lines.

Sampling points:

System location	Purpose
Reservoir top	Detect contamination introduced during filling
Reservoir bottom	Detect settled water, dirt, separated oil, sludge
Pump outlet	Confirm grease leaving pump
Main line	Check line contamination or hardening
Divider block inlet	Confirm supply condition
Divider block outlet	Confirm delivered grease condition
End of longest line	Detect hardening, separation, starvation risk
Component inlet	Confirm grease arriving at bearing
Component purge	Confirm grease passing through bearing

Common errors:

Sampling only the reservoir and assuming all bearings receive good grease.
Ignoring blocked lines.
Ignoring wrong grease added to reservoir.
Failing to sample grease after long idle periods.
Not labeling which divider outlet feeds which bearing.

13. Sampling before and after grease changeover

When changing grease type, the sampling program should be tightened.

Collect:

Old in-service grease before change.
Fresh old grease reference, if still available.
Fresh new grease reference.
Mixed purge during transition.
In-service grease after one relube cycle.
In-service grease after stabilization.

Do not trend new grease against old grease without marking the changeover. Many abnormal lab results are simply the result of mixed thickener chemistry, changed base oil, changed additive system, or different color.

14. What to record on every grease sample

A grease sample without context is weak evidence. The label and sample form are part of the sample.

Record:

Plant and area.
Equipment name.
Equipment tag.
Component tag.
Bearing number.
Bearing type, if known.
Housing type.
Sample point ID.
Sample zone: active, purge, seal, dead-zone, fresh, failure.
Grease brand and product.
NLGI grade.
Thickener type, if known.
Base oil type, if known.
Last relubrication date.
Grease quantity added last time.
Method of relubrication.
Automatic system setting, if applicable.
Operating hours since last relube.
Operating hours on bearing.
Operating temperature.
Speed.
Load or production rate.
Abnormal vibration/temperature/noise.
Environment: dust, water, steam, scale, chemicals.
Machine state during sampling.
Sample date and time.
Sampler name.
Photos taken.
Any visible grease condition: color, odor, water, metal, hardening, oil bleed, dryness, lumps, fibers, grit.

For rolling mills, also record:

Mill stand.
Roll type.
Roll position.
Chock number.
Campaign tonnage.
Rolling hours.
Product type.
Cooling water condition.
Seal condition.
Roll shop wash status.
DS/OS.
Top/bottom.
Entry/exit side.

15. Visual observations during sampling

Visual inspection is not a substitute for lab analysis, but it gives immediate field clues.

Look for:

Observation	Possible meaning
Milky grease	Water emulsification
Free water droplets	Severe water ingress
Rust-colored grease	Corrosion or iron oxide contamination
Black grease	oxidation, heat, carbon, wear debris, process contamination
Silver/metallic sheen	metallic wear debris
Bronze/gold particles	cage, bushing, thrust washer, or bronze component wear
Hard dry crust	oxidation, heat, oil loss, long interval, wrong grease
Oil puddling	oil separation, overheating, overgreasing, incompatibility
Lumps or graininess	thickener breakdown, contamination, incompatible mixing
Stringy/tacky change	polymeric/open gear lubricant behavior or contamination
Gritty feel	dust, scale, ore fines, cement dust, sand
Chemical odor	process contamination or solvent ingress
Fresh grease only at purge	possible channeling or overgreasing

Do not rely on color alone. Grease color can change because of dye, graphite, molybdenum disulfide, thickener type, base oil, contamination, oxidation, or mixing.

16. Common grease sampling mistakes

Mistake 1: Sampling after greasing

Fresh grease can dilute or hide the evidence. Unless the procedure is controlled purge sampling, take routine samples before relubrication.

Mistake 2: Sampling from the grease nipple

The grease fitting usually contains fresh grease, old dirt, or fitting residue. It does not represent the bearing.

Mistake 3: Mixing zones

Active bearing grease, seal grease, purge grease, and dead-zone grease should not be mixed unless a composite sample is intentionally required.

Mistake 4: Using dirty tools

Dirty screwdrivers, rags, knives, and reused containers can destroy sample validity.

Mistake 5: No fresh reference

Without fresh grease baseline, it is harder to identify oxidation, additive depletion, mixing, thickener changes, and abnormal contamination.

Mistake 6: No sample-point consistency

A purge sample this month and an active-zone sample next month are not a valid trend.

Mistake 7: Ignoring relube history

A sample taken 10 hours after relube cannot be compared directly with one taken 1,000 hours after relube unless the program accounts for it.

Mistake 8: Taking only one sample from a large bearing

Large bearings may have localized water ingress, localized wear, or poor grease distribution. One random sample may miss the problem.

Mistake 9: Cleaning before forensic sampling

Washing the bearing before collecting grease removes evidence.

Mistake 10: Over-interpreting a non-representative sample

If the sample came from a dead pocket, say so. If it came from a dirty seal, say so. The lab needs to know.

17. Grease sampling matrix by application

Application	Preferred sample	Secondary sample	Special note
Rolling mill chock bearing	Active grease near bearing rows during roll change	Seal-zone grease, drain/purge grease	Keep stand, roll, chock, side, row, and campaign data separate
Work roll bearing	Seal-side and active-zone samples	Purge sample	Water and scale ingress are major concerns
Backup roll bearing	Active row samples	Chock pocket sample	Map multi-row bearings
Continuous caster roll bearing	Purged grease from autolube and overhaul active grease	Seal-zone sample	Verify grease delivery from divider block
Conveyor pulley plummer block	Relief purge before relube	Seal-zone sample	Dust and water vary by pulley location
Crusher bearing	Active-zone sample during outage	Purge sample	Shock-load wear debris and contamination are key
Vibrating screen bearing	Purge sample, active if opened	Seal-zone sample	Sampling must account for high vibration and grease shear
Large fan bearing	DE/NDE purge or active plummer block sample	Seal-zone sample	Pair with vibration and temperature data
Electric motor bearing	DE/NDE relief purge	Overhaul active sample	Avoid overgreasing and winding contamination
Gear coupling	Tooth-zone grease	Bottom casing grease	Keep driver and driven sides separate
Open gear	Loaded tooth flank	Guard-bottom accumulation	Guard-bottom sample is not always representative
Slew bearing	Multiple clock-position purge samples	Loaded-zone sample	Do not rely on one sample
Kiln support roller bearing	Active bearing or purge sample	Seal-zone sample	Heat and dust contamination are common
Paper machine roll bearing	Active or purge sample	Water-exposed seal sample	Record steam/water exposure
Pump motor bearing	Motor DE/NDE purge	Overhaul active sample	Separate pump and motor samples
Autolube-fed bearing	Bearing purge sample	Reservoir, pump outlet, divider outlet	Confirm delivery, not only reservoir condition
Sealed-for-life bearing	Teardown active grease	Seal grease	Usually forensic, not routine
Crane wheel bearing	Seal-zone and purge sample	Teardown active grease	Shock load and water ingress may be localized
Agitator bearing	Active or purge sample	Seal contamination sample	Product ingress may be the main issue

18. Rolling mill grease sampling: detailed field model

For a steel plant, use a structured grease-sampling hierarchy.

18.1 Routine roll-shop sampling

During roll change or chock service:

Identify stand and roll.
Confirm chock number.
Photograph as-found grease and seals.
Sample before washing.
Collect DS and OS separately.
Collect top and bottom separately.
Collect seal-zone grease separately.
Collect active bearing-row grease separately if accessible.
Collect visible water, rust, or metallic grease separately.
Record campaign tonnage and hours.

18.2 Example labels

“HSM Stand F3 Work Roll Top Chock DS Seal Zone.”
“HSM Stand F3 Work Roll Top Chock DS Row 1 Active Grease.”
“HSM Stand F3 Work Roll Bottom Chock OS Drain Purge.”
“Plate Mill Backup Roll Chock DS Inner Row Active.”
“Caster Segment 7 Roll 14 OS Autolube Purge.”

18.3 What not to do

Do not scoop random grease from the chock exterior.
Do not sample after pressure washing.
Do not mix drive side and operator side.
Do not mix top and bottom chocks.
Do not mix seal grease and bearing grease.
Do not compare roll-shop wash-contaminated samples with in-service samples.
Do not sample only the fresh grease near the inlet.

18.4 When a mill bearing fails

Collect:

Grease from damaged row.
Grease from undamaged row.
Grease from water-entry side.
Grease from opposite side.
Grease from seal cavity.
Grease from drain.
Any metal flakes.
Fresh grease from the roll shop system.
Grease from the automatic line or manual gun used on that chock.

The comparison between damaged and undamaged zones is often more valuable than a single absolute lab number.

19. Purge sampling: correct method and interpretation

Purge sampling is common because it is practical. It must be controlled.

19.1 Correct purge sampling method

Clean the purge/relief area.
Remove cap or plug.
Discard external contaminated grease.
Collect existing purge if it is already present and label it.
If no grease is present, slowly add grease using the normal relube method.
Collect the first displaced in-service grease.
Stop once fresh grease color/texture appears.
Record quantity added.
Reinstall relief plug only if required by design.
Clean area.

19.2 How to interpret purge samples

Purge samples are excellent for trending if the purge path is consistent. They are weaker for pinpointing localized bearing damage unless supported by active-zone samples.

A purge sample can be strongly influenced by:

Grease channeling.
Overgreasing.
Relief-port location.
Housing fill level.
Hard grease blockage.
Seal design.
Bearing rotation direction.
Grease inlet location.
Grease viscosity and NLGI grade.
Temperature.
Last relubrication time.

Always label purge samples as purge samples.

20. Active-zone sampling: correct method and interpretation

Active-zone samples are diagnostically stronger but usually require access.

20.1 Correct active-zone method

Lock out equipment.
Open housing or inspection cover.
Photograph as-found condition.
Identify rolling elements, cage, raceway, or gear mesh.
Collect a small amount from the active contact area.
Avoid scraping metal unless intentionally collecting debris.
Keep different zones separate.
Seal and label immediately.
Close housing with correct cleanliness controls.

20.2 Interpretation

Active-zone grease is best for:

Wear debris.
surface distress evidence.
oxidation from contact heat.
mechanical shear.
grease starvation.
wrong grease.
contamination that reached the bearing.

It may not be best for identifying the original ingress path. For ingress path, collect seal-zone grease too.

21. Seal-zone sampling

Seal-zone grease is often the first grease to show water, dust, scale, process fluid, or cleaning chemical ingress.

Use when investigating:

Bearing corrosion.
Water washout.
Mill scale ingress.
Cement dust ingress.
Coal dust ingress.
Ore dust ingress.
Outdoor rain exposure.
Steam exposure.
Process fluid leakage.
Seal failure.

Procedure:

Clean only exterior loose dirt that is not part of the seal interface.
Collect grease from immediately inside the seal or labyrinth.
Do not mix with bearing active grease.
Label as seal-zone sample.
Photograph seal condition.
Record seal damage, missing flinger, blocked drain, or water marks.

22. Failed bearing grease sampling

When a bearing fails, grease is evidence. Treat the housing like a failure-analysis scene.

22.1 Before removing bearing

Collect:

Purged grease.
Leakage grease.
Grease around seals.
Grease near heat-discolored areas.
Grease containing visible metal.
Grease from the drain or bottom pocket.

22.2 During disassembly

Collect:

Grease from each bearing row.
Grease from loaded zone.
Grease from unloaded zone.
Grease from cage pockets.
Grease from rolling elements.
Grease from inner and outer raceway.
Grease from cracked or spalled areas.
Grease from seal cavity.
Grease from housing pockets.

22.3 After bearing removal

Collect:

Remaining housing grease.
Debris from housing bottom.
Magnetic debris.
Filtered debris if grease was washed through a screen.
Fresh grease reference.
Grease from delivery system.

Do not wash first.

23. Chain of custody and sample integrity

For routine plant trending, chain of custody may be simple. For warranty, failure analysis, insurance, or OEM dispute, it must be more formal.

Include:

Sample ID.
Date/time.
Person collecting.
Witness, if required.
Asset ID.
Exact location.
Photos.
Container seal.
Storage condition.
Transfer record.
Lab submission form.
Requested analysis.
Notes on representativeness.

For high-value bearings, photograph the sample location with the sample bottle visible in the frame.

24. Building a grease sampling program

24.1 Select assets

Prioritize:

High downtime cost.
High bearing replacement cost.
High safety risk.
History of bearing failures.
Severe contamination.
Harsh environment.
Remote or inaccessible equipment.
Critical production bottlenecks.
Equipment already monitored by vibration.

24.2 Define sample points

Each point needs a unique ID.

Example:

FAN-101-DE-PURGE.
FAN-101-NDE-PURGE.
MILL-F3-WR-TOP-DS-SEAL.
MILL-F3-WR-TOP-DS-ACTIVE.
CRUSHER-2-OB-ACTIVE.
CASTER-S7-R14-OS-PURGE.
SLEW-01-6OCLOCK-PURGE.

24.3 Define sample frequency

Frequency depends on criticality, environment, failure history, and access.

Typical logic:

Critical main process bearings: every outage, roll change, campaign, or monthly/quarterly.
Severe contamination bearings: more frequent until stable.
Electric motors and fan bearings: quarterly, semiannual, or during relube events depending on criticality.
Autolube systems: sample reservoir and endpoints during planned PMs.
Sealed bearings: sample at overhaul or failure.
Slew bearings: periodic multi-point sample, often aligned with inspection schedule.
Gear couplings: during coupling inspection or shutdown.

24.4 Create baselines

Baseline types:

Fresh grease baseline.
New bearing commissioning sample after run-in.
Stable normal in-service trend.
Known good purge sample.
Known contaminated sample for comparison.
Post-corrective-action sample.

24.5 Integrate with other technologies

Grease sampling works best with:

Vibration analysis.
Ultrasound.
Infrared thermography.
Motor current analysis.
Operator inspections.
Temperature trending.
Seal inspections.
Relube records.
Bearing failure analysis.

ASTM’s overview of D7718 notes that grease analysis and inspection can be combined with technologies such as infrared imaging, vibration analysis, and ultrasonic vibration analysis to support predictive maintenance decisions. (ASTM Store)

25. Field checklist

Use this checklist before every sample.

Before sampling

Correct asset identified.
Correct sample point identified.
Correct sample container available.
Fresh reference sample available or planned.
Machine state recorded.
Last relube known.
PPE and safety controls complete.
Exterior cleaned.
Camera ready.

During sampling

Sample taken before relube, unless controlled purge method is used.
Correct zone sampled.
Different zones kept separate.
Clean tool used.
Enough grease collected.
Container capped immediately.
Visual observations recorded.
Photos taken.

After sampling

Label complete.
Access point restored.
Relief path restored.
Excess grease cleaned.
Sample form complete.
Sample stored properly.
Lab instructions clear.
CMMS or reliability record updated.

26. Recommended sample label format

A strong label format is:

Plant-Area-Equipment-Component-Position-Zone-Date

Examples:

Steel-HSM-F3-WR-Top-DS-Active-2026-06-17
Cement-Kiln2-SupportRoller-OB-Purge-2026-06-17
Power-FDfan1-DE-Purge-2026-06-17
Mine-Crusher2-IB-SealZone-2026-06-17
Caster-Seg7-Roll14-OS-AutolubePurge-2026-06-17

On the sample form, expand abbreviations so the laboratory understands the context.

27. Summary

Grease sampling is a precision maintenance task. In heavy industry, the best grease sample is not necessarily the easiest grease to reach. The sample must represent a defined zone: active bearing grease, purge grease, seal-zone grease, dead-zone grease, fresh grease, or failure grease.

For small auxiliary machines, a consistent purge sample may be enough. For large main process bearings such as rolling mill stand bearings, caster bearings, slew bearings, crusher bearings, kiln bearings, and large fan bearings, mapped multi-point sampling is often necessary. Keep sides, rows, seals, loaded zones, and purge paths separate.

The highest-value rule is:

Do not ask “Did we get grease?” Ask “What exact machine condition does this grease represent?”