How to Identify and Prevent Both Failure Modes
A failed bearing comes off the machine showing evenly spaced depressions at rolling element intervals. The maintenance team writes it up as brinelling, orders a replacement, and moves on. In six months, the new bearing fails the same way.
The problem is that brinelling is not one failure mode. It is two, true brinelling and false brinelling, that look nearly identical on the failed bearing but arise from completely different mechanisms, have different root causes, and require different corrective actions. Installing a replacement without identifying which type caused the failure guarantees a repeat. ISO 15243:2017 classifies them under separate failure categories for exactly this reason. For the full ISO 15243 framework covering all six primary bearing failure categories, see our article on bearing failure modes: what they look like and what actually causes them.
True brinelling is a plastic deformation failure; false brinelling is a corrosion/fretting failure. The distinction is diagnostic, preventive, and operational. This article explains both mechanisms, how to tell them apart in the field, and what programs eliminate each.
The Origin of the Term — and Why It Creates Confusion
The word brinelling comes from Johan August Brinell, the Swedish engineer who developed the Brinell hardness test in 1900. The Brinell test works by pressing a hardened ball into a material surface under a known load and measuring the resulting indentation. Bearing damage that left similar-looking indentations in bearing raceways became known as brinelling by analogy.
The confusion entered when engineers discovered that some indentations in bearing raceways weren’t caused by overload at all, they were caused by vibration on stationary bearings during shipping. J.O. Almen of General Motors first described this phenomenon in 1937, observing that new automobile wheel bearings arrived damaged after long-distance shipping, and that the damage increased with shipping distance and seasonal road conditions. Because the damage pattern looked like brinelling but wasn’t caused by the same mechanism, he called it false brinelling.
The visual similarity that confused Almen still confuses maintenance teams today. Both patterns show evenly spaced depressions at rolling element pitch spacing on the raceway. The distinction requires examining the character of the marks, not just their location.
True Brinelling: The Physics of Plastic Deformation
True brinelling is defined by one specific mechanical event: the contact stress between a rolling element and the raceway exceeds the material’s elastic limit. When the Hertzian contact pressure at the rolling element-raceway interface exceeds the yield strength of the bearing steel, the steel permanently deforms. The rolling element sinks into the raceway surface, leaving an indentation that will never recover. This is permanent plastic deformation, the same physical phenomenon the Brinell hardness test intentionally creates, occurring unintentionally in the bearing.
The Static Load Rating and When It Matters
The relevant engineering parameter for true brinelling is C0, the basic static load rating (ISO 76). ISO standards define C0 as the load that produces a maximum contact pressure of 4,200 MPa at the most heavily loaded rolling element contact, resulting in a total permanent deformation of approximately 0.0001 times the rolling element diameter. In practical terms: exceed C0, and the rolling elements will indent the raceway. For the complete framework on how C, C0, and S0 interact, and how to calculate S0 for your application, see our guide on bearing load ratings (C vs. C0) and how they impact real equipment life.
A bearing that is correctly sized for its running dynamic load (C) can still experience true brinelling if its static rating (C0) is insufficient for the shock loads, startup loads, or static dead-weight conditions the application imposes.
Sizing only for dynamic life without checking S0 is one of the most common paths to true brinelling in practice.
Common Causes of True Brinelling in Industrial Practice
What True Brinelling Looks Like
False Brinelling: The Physics of Fretting Wear
False brinelling is classified under fretting corrosion (ISO 15243 Section 5.3.3.3), a fundamentally different failure category from plastic deformation. No yield point is exceeded. No metal is permanently deformed. Instead, the damage is caused by progressive material removal through the fretting mechanism. It is, at its core, a lubrication starvation failure mode, the contact zone is deprived of film not by inadequate grease volume but by micro-oscillations that prevent replenishment. Our article on under-lubrication and starvation in bearings covers the full starvation family and how false brinelling fits within it.
The mechanism: when a stationary bearing experiences vibration, the rolling elements undergo micro-oscillations, extremely small back-and-forth movements, against the raceways. These oscillations are too short to allow the bearing to rotate far enough to redistribute lubricant. The lubricant film is squeezed out of the contact zone and cannot replenish between cycles. Without lubricant film, the metal asperities of the rolling element and raceway make direct contact. Each micro-oscillation abrades a small amount of surface material. The wear debris oxidizes into reddish-brown iron oxide particles. Those particles accumulate at the contact zone, become abrasive, and accelerate further wear.
The ASTM D4170 test standard, Standard Test Method for Fretting Wear Protection by Lubricating Greases, was developed specifically because of false brinelling. The test evaluates grease formulations’ ability to protect oscillating bearings from fretting wear and was originally developed to predict the fretting performance of greases in automobile wheel bearings shipped long distances. That origin, damage observed in vehicles before they reached their first owner, underscores the central industrial risk: bearings failing before they are ever put into service.
Where False Brinelling Occurs in Industrial Facilities
What False Brinelling Looks Like
Side-by-Side: True vs. False Brinelling at a Glance
| Characteristic | True Brinelling | False Brinelling |
|---|---|---|
| Definition | Plastic deformation — permanent indentation from a force exceeding the material’s yield strength | Fretting wear — progressive material removal from micro-oscillation of a stationary or lightly loaded bearing |
| ISO 15243 class | Plastic deformation — Section 5.5.2 | Corrosion / fretting corrosion — Section 5.3.3.3 |
| Primary cause | Single overload event: impact, static overload, installation shock, dropped equipment | Continuous vibration on stationary bearing: transport, standby adjacent to running equipment, oscillating applications |
| Timing | Instantaneous — one event causes full damage | Progressive — worsens over time with continued vibration |
| Spacing of marks | Exactly matches rolling element pitch spacing | Exactly matches rolling element pitch spacing — the key visual confusion |
| Surface inside mark | Original machining marks often visible — metal deformed, not worn away | Original finish worn away completely — surface looks polished or matte |
| Material at edges | Raised edges / burrs of displaced metal | No raised edges — material is worn away, not pushed aside |
| Color / debris | Clean metallic color — no rust debris | Reddish-brown or black debris — oxidized iron wear particles (the rust sign) |
| Grease condition | Grease may appear normal | Grease discolored dark brown/black with fine metallic powder |
| Primary prevention | Adequate static safety factor S0; proper installation tools; shaft locking during transport | Periodic rotation of standby equipment; vibration isolation; grease with anti-fretting additives |
Sources: ISO 15243:2017; TFL Bearing True vs. False Brinelling Guide; ScienceInsights Brinelling Explained; ONYX Insight Failure Atlas
Field Diagnosis: A Step-by-Step Decision Process
When a failed bearing shows evenly spaced depressions at rolling element intervals, the following five-step examination distinguishes true from false brinelling. Steps 1 and 2 are often sufficient; steps 3–5 confirm ambiguous cases.
True Brinelling is a Force problem (impact / overload). The correction addresses what produced that force.
False Brinelling is a Motion problem (vibration / oscillation without lubrication). The correction addresses what produced that motion and why the lubricant couldn’t protect the contact.
Getting the classification wrong means implementing the wrong prevention, and guaranteeing the next bearing fails the same way.
Preventing True Brinelling
Use the Correct Installation Method — Every Time
The most common cause of true brinelling is improper installation, specifically force applied through the rolling elements rather than directly to the bearing ring. The correct rule is absolute: force must be applied only to the ring being pressed, never transmitted through the rolling element assembly.
- Never drive a bearing ring with a hammer and drift. Use a bearing press with a proper adapter that contacts only the ring face being mounted. For the correct interference fit specifications that govern how much force is required, and why the fit itself must be verified before installation, see our guide on bearing fits and tolerances (ISO 286 interference-fit framework).
- For inner ring mounting onto a shaft, induction heating or oil bath heating to achieve a controlled interference fit is the preferred method. The ring expands uniformly, slides onto the shaft with minimal force, and shrinks to grip when cooled, no impact required.
- For simultaneous fitting of both rings, use a tool that contacts both rings at the same time with equal force distribution.
- Never use a standard bearing as a pressing tool to install another bearing.
Verify the Static Safety Factor S0 Before Commissioning
Every bearing application subject to shock loads, heavy static loads, or significant startup inertia should have its static safety factor verified: S0 = C0 / P0 where P0 is the maximum equivalent static load, including the worst-case shock or startup condition.
The complete S0 calculation methodology, including how to account for startup inertia and worst-case shock loading in the equivalent static load P0, is in our bearing load rating guide.
Secure the Shaft During Transport and Storage
Any assembled equipment being shipped or stored should have the shaft locked against rotation and translation. Equipment left with a free-rotating shaft in a vehicle transfers every road vibration through the rolling element contacts, and depending on amplitude, may exceed C0 at the contact zone.
Preventing False Brinelling
This is the most universally applicable and most immediately implementable prevention measure. Manual rotation of the shaft, even a few turns, redistributes the grease and changes the contact point of the rolling elements on the raceway. Recommended weekly for backup pumps and fans. Note: the PM action for standby equipment is periodic shaft rotation, not more frequent regreasing. For the distinction between idle-equipment management and calculated running intervals, see our guide on how to calculate bearing relubrication intervals.
Anti-vibration mounts, rubber isolation pads between the baseplate and floor, and flexible pipe connections that decouple the standby machine from the running machine’s structural vibration are all effective. When new equipment is laid out, standby machines should be positioned on isolated foundations or equipped with isolation mounts.
Greases with low base oil viscosities and high bleeding rates show less false brinelling damage because the bleed oil can reflow into the contact zone during micro-oscillations. Greases with anti-fretting or anti-wear additives (molybdenum disulfide, solid EP additives) provide additional protection when the film thickness becomes marginal. For how base oil viscosity, thickener type, and additive packages each contribute to bleed behavior and film maintenance, see our article on grease composition: what each component does and how to match it to the application. For what the NLGI grade measures and when to specify a softer grade for oscillating conditions, see our guide on NLGI grades and choosing the right grease consistency for real applications.
In wind turbines, the standard approach to false brinelling in pitch bearings involves service pitching, programming the pitch control system to perform periodic large-angle rotations that redistribute lubricant across the full raceway, even when operational conditions don’t require it. This principle applies to any oscillating application: if the motion amplitude is insufficient to redistribute lubricant during normal operation, supplementary lubrication or periodic larger-angle movements need to be built into the operating or maintenance procedure.
Pre-greasing bearings before transport, ensuring full lubricant fill, helps maintain a film in the contact zone during vibration-induced micro-oscillations. Wind turbine manufacturers pre-grease bearings before shipping to turbine assembly locations as a standard practice specifically to prevent false brinelling during transit. For any assembled equipment being shipped long distances, verifying that bearing positions are fully lubricated before departure reduces transport-induced fretting damage.
Condition Monitoring: Detecting Both Failure Modes Before Catastrophic Failure
Both true and false brinelling produce characteristic vibration signatures that worsen as the damage progresses. Neither failure mode is repairable, once detected, the bearing should be replaced, but condition monitoring extends the window between first detection and catastrophic failure, allowing planned rather than emergency replacement.
- Low-speed click or clunk: audible rhythmic clicking as each rolling element traverses a brinelling depression. The frequency is predictable: shaft speed × number of rolling elements × load zone fraction = click frequency.
- Vibration analysis: brinelling damage generates vibration at bearing defect frequencies (BPFO, BPFI). Brinelling marks are evenly spaced initially, which may produce a more regular harmonic structure in the vibration spectrum than the irregular signatures of progressive spalling. For the four-stage vibration progression model, the full BPFO/BPFI/BSF/FTF frequency framework, and how to distinguish brinelling-type signatures from spalling-type signatures, see our article on bearing spalling: how it starts, how it spreads, and the warning signs your team can catch early.
- Temperature rise: both damage types cause increased rolling element impacts as rolling elements traverse the damage, generating heat. A bearing running warmer than its baseline, even if vibration has not yet risen significantly, warrants inspection.
Routine vibration routes typically cover running equipment, not standby equipment. A standby pump developing false brinelling will not appear in vibration data until it is started.
The only way to detect false brinelling in standby equipment before startup is periodic inspection of the bearing housing and lubricant condition during the PM route, checking for the dark, iron-oxide-contaminated grease that indicates active fretting.
True brinelling and false brinelling have one thing in common: the failed bearing shows marks at rolling element spacing. Everything else is different, mechanism, root cause, corrective action, and prevention strategy. Treating them as the same problem because they look similar produces the same outcome as treating no problem: the next bearing fails for the same reason.
The diagnosis takes five minutes with a magnifying glass and the knowledge of what to look for. Rust-colored debris points to false brinelling. Clean, shiny indentations with the original surface finish inside point to true brinelling. That examination determines whether the corrective action is a bearing installation procedure change or a standby equipment rotation program.
Five minutes of inspection, grease color, surface texture inside the marks, presence or absence of raised edges, tells you which failure mode you’re dealing with, which root cause produced it, and what has to change to prevent the next failure. That information is worth more than the cost of the replacement bearing you’re about to install.
Related Articles — Bearing Failure Analysis and Prevention
C0, S0, ISO 76; the static load rating framework that prevents true brinelling by verifying margin against overload at the bearing selection stage.
The full ISO 15243 framework; where true brinelling (plastic deformation) and false brinelling (fretting corrosion) sit within the six primary failure categories.
The starvation family that false brinelling belongs to; seven root causes, damage patterns, and program-level fixes.
The four-stage vibration progression model and BPFO/BPFI frequency framework for distinguishing brinelling from spalling in the vibration spectrum.
ISO 286 interference-fit framework; the installation foundation that eliminates the most common cause of true brinelling.
Base oil viscosity, thickener bleed behavior, and additive packages; the grease-side fundamentals that govern false brinelling protection in oscillating and standby applications.
What the consistency number means, how it affects bleed rate, and when to specify a softer grade for oscillating contact conditions.
Calculated intervals for running equipment; and the distinction between running-hour-based intervals and the idle-time management that standby equipment actually requires.
