Bearing Failure Modes: 6 Types per ISO 15243, Causes & Solutions

Bearing failure is the degradation or complete loss of a rolling bearing's function caused by one or more damage mechanisms acting on the raceway surfaces, rolling elements, cage, or structural integrity of the inner/outer rings — classified into 6 primary modes by ISO 15243:2017.

According to SKF Bearing Damage and Failure Analysis, only about 0.34% of industrial bearings reach their calculated L₁₀ life — the vast majority fail prematurely due to preventable causes: improper lubrication (43%), contamination (27%), incorrect mounting (16%), and overloading (10%). Systematic root cause analysis after each bearing failure eliminates recurring problems, reduces unplanned downtime, and optimizes bearing maintenance costs. This article provides a detailed technical analysis of all 6 failure modes per ISO 15243:2017 — visual identification, root causes, and prevention strategies — along with a 4-stage failure progression timeline, a failure analysis checklist, and real factory case studies from Vietnamese manufacturing plants. Primary references: SKF, FAG/Schaeffler — Failure Analysis Guide WL 82 102, NSK Technical Report — Bearing Damage Analysis, and ISO 15243:2017.

Overview of 6 Failure Modes per ISO 15243:2017

ISO 15243:2017 classifies bearing damage into 6 primary categories. Each category has distinct damage mechanisms, surface appearance, and specific prevention methods. The summary table below helps maintenance engineers quickly identify the failure type observed in the field.

Bearing Failure Progression — 4 Stages

Bearing failure is not instantaneous. Degradation progresses through 4 detectable stages using vibration monitoring and signal analysis techniques.

At a cement plant in Hai Phong, the maintenance team detected a 22320 E C3 bearing on an ID fan at Stage 2 through clear BPFO peaks in the envelope spectrum. They scheduled replacement during a planned kiln shutdown 2 weeks later — preventing an unplanned outage estimated to cost 500 million VND per day.

Mode 1 — Rolling Contact Fatigue / Spalling

Visual Appearance

Rolling contact fatigue produces spall craters on the inner or outer ring raceway. Spalling characteristics: bright metallic crater bottom (freshly exposed metal), sharp edges, irregular shape, starting at 1–2 mm and propagating rapidly. Rolling element surfaces may also exhibit pitting — smaller craters distributed randomly. As spalling progresses, detached metal fragments cause secondary damage to the cage and adjacent rolling elements.

Root Causes

Rolling contact fatigue is the "natural" failure mode — occurring when a bearing reaches its fatigue life limit under normal loading. However, most spalling occurs well before calculated L₁₀ life due to:

• Actual load exceeding design — shaft misalignment (see shaft alignment), impact loads, excessive belt tension
• Insufficient lubrication — kappa ratio (κ) < 1 causing metal-to-metal contact, increasing surface stress
• Contamination — hard particles in grease creating surface indents → stress concentration → crack initiation
• Incorrect mounting — excessive interference fit reducing operating clearance, increasing contact stress

Prevention

• Calculate adjusted L₁₀a life with modification factors (a₁, aISO) to select adequately rated bearings
• Maintain kappa ratio κ ≥ 1 through proper lubrication type and relubrication interval
• Use appropriate bearing seals to prevent contamination ingress
• Achieve shaft alignment within ≤ 0.05 mm offset and ≤ 0.05 mm/100 mm angular tolerance

Factory case — Steel mill in Ba Ria: A cooling water pump for the EAF (electric arc furnace) used 6316 C3 bearings (d = 80 mm). Bearings failed at 8,000 hours — only 40% of calculated L₁₀ life of 20,000 hours. Analysis revealed spalling concentrated on the inner ring with indent marks from hard particles at spall origins. Root cause: worn labyrinth seal allowing iron oxide dust into the grease. Corrective action: added supplementary V-ring seal outside the labyrinth, shortened relubrication interval from 3,000 to 1,500 hours. Result: bearing life increased to 22,000+ hours.

Mode 2 — Wear / Abrasion

Visual Appearance

Wear causes the raceway surface to lose its original polish — becoming dull, micro-scratched, or scored. The raceway widens and radial clearance increases. Rolling elements decrease in diameter with uniformly scratched surfaces. Steel cages wear at guide surfaces; polyamide cages wear at pocket edges. Grease inside turns black from suspended metallic wear particles.

Root Causes

• Abrasive wear — dust, sand, scale particles entering through seals or present in contaminated grease
• Adhesive wear — grease depleted or degraded → metal-to-metal contact → micro-welding and surface tearing
• False brinelling — vibration while bearing is stationary (standby equipment, transport) → oscillating micro-friction at contact points
• Sliding wear — cylindrical/tapered rollers sliding at ends under excessive axial load

Prevention

• Upgrade bearing seal system — contact seals for heavy dust environments
• Maintain lubrication at correct intervals and quantities (G = 0.005 × D × B grams)
• Filter lubricating oil to ISO 4406 level 17/14 or better
• For standby equipment: manually rotate shaft 10 revolutions weekly or install slow-speed automatic turning device

Factory case — Cement plant in Ninh Binh: A ball mill used 23052 CC/W33 bearings (d = 260 mm, D = 400 mm) on the pinion shaft. Grease turned dark black within 500 hours — normal service life should maintain light color for at least 2,000 hours. Grease analysis found iron particle content at 850 ppm (limit: < 100 ppm). Root cause: labyrinth seal installed incorrectly — radial gap 3 mm instead of designed 0.5 mm, allowing clinker dust ingress. Corrective action: reinstalled labyrinth seal with correct clearance, added purge grease supply line at seal. Bearing life increased from 4,000 hours to 14,000 hours.

Mode 3 — Corrosion

Visual Appearance

Corrosion produces red-brown (rust) or black (black oxide) deposits on raceway surfaces, rolling elements, and ring end faces. Two common patterns:

• Moisture corrosion: Red-brown rust at contact points between rolling elements and raceway — forming evenly spaced etching patterns matching rolling element pitch. Caused by condensation from temperature cycling or equipment washdown.
• Fretting corrosion: Red-brown oxide powder at fit surfaces (bore/shaft interface, OD/housing interface). Caused by micro-motion between mating metal surfaces when the fit is too loose.

Root Causes

• Water ingress — high-pressure washdown, condensation during equipment cool-down cycles, cooling system leaks
• Incorrect storage — new bearings stored in humid warehouses (> 80% RH) without rust-preventive oil, or original packaging opened prematurely
• Degraded grease — aged grease losing rust-inhibiting properties, water accumulation in grease > 500 ppm
• Loose fit — bore tolerance too loose (j5 instead of k5/m5) causing micro-motion → fretting

Prevention

• Use sealed bearings (2RS/2RZ) for wet or washdown environments
• Apply dual bearing seal arrangement: contact seal + labyrinth seal
• Correct storage practices: stable temperature, RH < 60%, keep original packaging sealed until mounting
• Verify fit tolerances per manufacturer recommendations — deep groove ball bearings on rotating shaft: k5/m6; housing bore: H7

Factory case — Seafood processing plant in Ca Mau: A ventilation fan motor in the processing area used 6310-2RS C3 bearings (d = 50 mm). Bearings failed at 3,000 hours — designed life was 25,000 hours. Disassembly revealed red rust on the raceway; grease contained water (crackle test indicated > 2,000 ppm water content). Root cause: daily floor washing with high-pressure hose spraying directly onto bearing housings. The original 2RS seals could not withstand water pressure. Corrective action: added external V-ring seal, reoriented housing to avoid direct water spray, switched to calcium sulfonate complex grease (superior rust protection). Bearing life increased to 20,000+ hours.

Mode 4 — Electrical Erosion / Fluting

Visual Appearance

Electrical erosion creates two distinctive surface patterns:

• Craters (arc damage): Small pits (5–100 μm) scattered or clustered on the raceway. Crater bottoms show resolidified metal with dark discoloration. Occurs when large currents pass through the bearing (e.g., grounding fault events).
• Fluting (washboard pattern): Parallel grooves evenly spaced across the raceway, perpendicular to the rolling direction. Groove spacing 0.3–1.5 mm. This is the signature pattern of VFD (Variable Frequency Drive) stray currents — caused by electrical discharge machining (EDM) effect through the oil film millions of times per second.

Root Causes

• VFD/inverter stray currents: PWM inverters generate common-mode voltage on the motor shaft. When shaft voltage exceeds the oil film breakdown threshold (~1–15 V), current pulses discharge through the bearing — each pulse lasts only nanoseconds but repeats millions of times per second, causing micro-melting of the raceway surface → gradual accumulation into fluting. According to ABB Technical Note, inverters with 4–16 kHz switching frequency generate millions of discharge events per second.
• Welding stray currents: Welding equipment grounded through machine frame; welding current passes through bearing instead of ground cable.
• Static electricity: Conveyor belts generating static charge, discharging through bearing on roller shaft.

Prevention

• Install insulated bearings (ceramic coating on outer ring — SKF INSOCOAT, FAG J20AA) for VFD-driven motors
• Install shaft grounding rings (Aegis, Electro Static Technology) to provide a low-impedance discharge path away from the bearing
• Use symmetrically shielded motor cables with 360° shield termination at both ends
• Reduce PWM switching frequency where permissible (from 8 kHz to 4 kHz reduces pulse amplitude)

Factory case — Textile plant in Binh Duong: A 55 kW motor controlled by a Danfoss VFD driving a fabric tentering machine. The 6312 C3 bearing on the DE (Drive End) failed after 6 months — disassembly revealed pronounced fluting on the outer ring raceway with parallel grooves spaced 0.5–0.8 mm apart. The NDE (Non-Drive End) bearing was unaffected. Grease had a characteristic burnt smell. Root cause: VFD-driven motor without any shaft current mitigation. Corrective action: installed shaft grounding ring on DE, replaced NDE bearing with insulated bearing (ceramic coated). After 2 years of operation, no recurrence of fluting.

Mode 5 — Plastic Deformation / Brinelling

Visual Appearance

Plastic deformation creates indentations (dents) on the raceway surface — two distinct patterns:

• True brinelling: Evenly spaced indentations on the raceway, spacing matching the rolling element pitch. Each dent mirrors the shape of the rolling element (circular for balls, rectangular for cylindrical rollers). Caused by impact loads or static loads exceeding the C₀ rating.
• False brinelling: Shallower depressions with polished or slightly rusted bottoms, located in the load zone under static load. Caused by external vibration when the bearing is stationary (e.g., equipment transported over rough roads, or a standby motor positioned beside a running motor).

Root Causes

• Impact loads during mounting — using a hammer directly on the outer ring during shaft mounting (force transmitted through rolling elements) — see bearing mounting guide
• Excessive static load — bearing subjected to standing load exceeding static load rating C₀ (e.g., jacking equipment through bearing housing)
• Vibration while stationary — standby motor vibrating sympathetically with adjacent running motor → false brinelling
• Transport without shock absorption — heavy equipment transported long distances over rough roads

Prevention

• Mount bearings using proper tools — pressing sleeves, induction heaters, or hydraulic nuts. Never use a hammer.
• Design bearing housings to accommodate lifting loads — provide dedicated jack points that bypass the bearing
• Standby equipment: install vibration isolation pads or manually rotate shafts periodically
• Transport: lock rotating shafts, install shock-absorbing pads, choose smoother transport routes

Factory case — Paper mill in Bac Ninh: A 90 kW motor driving a vacuum pump used 6316 C3 bearings (d = 80 mm, C₀ = 36 kN). After installing the new motor, the bearing produced a clicking noise from the very first start. Inspection revealed true brinelling — 9 evenly spaced dents on the inner ring raceway (matching the 9 balls). Root cause: the fitter used a hammer on the 80 mm shaft end, transmitting impact force through the balls into the raceway. Corrective action: replaced bearing, mounted using an SKF TIH 030m induction heater — heating the inner ring uniformly to 80°C before sliding it onto the shaft. Additionally provided mounting procedure training for the maintenance team.

Mode 6 — Fracture / Cracking

Visual Appearance

Fracture is the most dangerous failure mode — the bearing completely loses load-carrying capacity. Types of fracture:

• Inner ring cracking from excessive interference fit: Axial crack along the inner ring, typically initiating from the bore edge. The inner ring expands under hoop stress exceeding the material's tensile strength.
• Outer ring fatigue cracking: Circumferential crack originating from a spall crater, propagating under cyclic loading.
• Cage fracture: Cage fragments break loose, jam between rolling elements → catastrophic cascade failure.
• Rolling element fracture: Balls or rollers crack — typically from localized thermal damage (severe lubrication starvation) or overloading.

Root Causes

• Excessive interference fit — bore tolerance tighter than k5 for heavy rotating shafts causing hoop stress exceeding the tensile limit of the inner ring
• Localized heating — lubrication starvation → friction → heat → microstructural transformation (hardness drop) → reduced strength → cracking
• Misalignment — deep groove ball bearings subjected to angular misalignment > 0.05° causing concentrated loading → accelerated fatigue → rapid cracking
• Incorrect heat treatment — substandard bearings with improper through-hardening → brittle ring
• Outer ring creep — outer ring rotating within housing due to loose fit → wear → cross-section reduction → cracking

Prevention

• Follow manufacturer fit tolerance specifications — refer to bearing mounting guide
• Maintain continuous lubrication — never allow bearings to run dry, even for minutes
• Achieve shaft alignment using laser alignment tools — target ≤ 0.05 mm offset
• Use genuine bearings only — ZVL Slovakia, SKF, FAG, NSK, NTN — with certified heat treatment and material documentation

Factory case — Sugar mill in Long An: A cane press shaft used 23228 CC/W33 C3 bearings (d = 140 mm). The inner ring developed an axial crack after 3 months of operation. Analysis revealed the shaft was machined to incorrect tolerances — shaft diameter Ø140.08 mm (exceeding the m6 upper limit of Ø140.068 mm). The excessive interference fit generated ~300 MPa hoop stress on the inner ring — approaching the tensile strength of 100Cr6 bearing steel. Combined with impact loads from sugarcane, total stress exceeded the limit → cracking. Corrective action: remachined shaft to m6 tolerance (Ø140.018–140.068 mm), verified with outside micrometer before mounting. After 2 crushing seasons (18 months), the bearing remains operational.

Failure Analysis Checklist

When removing a failed bearing, follow this systematic analysis procedure to identify the root cause and prevent recurrence.

Step 1 — Gather Information Before Removal

• [ ] Record bearing code, manufacturer, installation date, operating hours
• [ ] Document symptoms: vibration, temperature, noise, when first detected
• [ ] Save vibration monitoring data: velocity trend, FFT spectrum, envelope spectrum
• [ ] Measure shaft diameter with outside micrometer (at 3 positions: both ends + center)
• [ ] Measure housing bore with bore gauge
• [ ] Check shaft alignment — record offset and angular values

Step 2 — Remove and Preserve Sample

• [ ] Remove bearing using proper tools — avoid causing additional damage
• [ ] Collect grease sample before cleaning — seal in clean container, label with date and location
• [ ] Photograph bearing in as-found condition (before cleaning) — 4 orientations + close-ups of damaged areas
• [ ] Clean bearing with pure solvent (n-heptane or proprietary bearing cleaner)
• [ ] Photograph after cleaning — close-ups of damaged areas under good lighting

Step 3 — Classify the Damage

• [ ] Compare visual appearance against 6 ISO 15243:2017 failure modes (see Overview table)
• [ ] Identify affected components: inner ring, outer ring, rolling elements, cage, seals
• [ ] Determine distribution pattern: full circumference or localized? Load zone or non-load zone?
• [ ] Analyze grease: color, odor, consistency, water content (crackle test), metal particles (patch test)

Step 4 — Determine Root Cause and Corrective Action

• [ ] Cross-reference failure mode + distribution pattern + operating conditions → identify root cause
• [ ] Define corrective actions: change bearing specification, fit tolerance, lubrication, sealing, or operating conditions
• [ ] Update bearing maintenance schedule based on findings
• [ ] Archive in maintenance database — each record includes: photos, bearing code, operating hours, root cause, corrective action

Detailed Comparison of 6 Failure Modes

Grease Analysis — Rapid Diagnostic Tool

Bearing grease analysis is the first diagnostic tool a maintenance engineer should use when examining a failed bearing. Grease carries the "memory" of every operating condition the bearing has experienced.

Impact of VFDs on Electric Motor Bearings

Variable Frequency Drives (VFDs) are increasingly common in Vietnamese industry — from pumps and fans to compressors. However, VFDs are the leading cause of electrical erosion damage to electric motor bearings, particularly in motors rated above 30 kW.

Mechanism: PWM inverters generate high-frequency common-mode voltage (shaft voltage) oscillating at 2–20 kHz. When shaft voltage exceeds the oil film breakdown threshold (~1–15 V), current pulses discharge through the bearing — each pulse lasts only nanoseconds but repeats millions of times per second, causing micro-melting of the raceway surface → gradual accumulation into fluting patterns.

Protection measures in order of priority:

1. Shaft grounding ring — simplest retrofit solution, mounted externally on the motor. Reduces shaft voltage by > 90%.
2. Insulated bearings — ceramic coating on the outer ring (or inner ring). Completely blocks current through the coated bearing, but current may still pass through the unprotected bearing at the opposite end.
3. Hybrid bearings (Si₃N₄ ceramic rolling elements) — silicon nitride ceramic rolling elements provide complete electrical insulation. Highest cost but greatest durability, with added benefits of reduced friction and higher permissible speeds.
4. dV/dt filter or sinewave filter — filters PWM pulses into near-sinusoidal waveform. Protects both bearings and motor winding insulation.

Key Takeaways

• ISO 15243:2017 classifies 6 bearing failure modes: rolling contact fatigue, wear, corrosion, electrical erosion, plastic deformation, and fracture — each with distinct surface patterns and root causes
• Bearing degradation progresses through 4 stages — vibration monitoring detection at Stage 1–2 enables planned replacement, avoiding unplanned downtime
• 43% of premature failures stem from improper lubrication — maintaining correct lubricant type, quantity, and interval is the single most effective preventive measure
• VFDs cause fluting damage on motor bearings — shaft grounding rings or insulated bearings are mandatory for VFD-driven motors
• Mounting with proper tools (pressing sleeves, induction heaters) prevents brinelling — never use a hammer on bearings
• Grease analysis after bearing removal is the fastest diagnostic step — grease color, smell, and particle content reveal the damage mechanism
• The 4-step failure analysis checklist (gather info → remove sample → classify → root cause) enables accurate diagnosis and prevents recurrence
• ZVL Slovakia supplies deep groove ball bearings and spherical roller bearings manufactured to EU quality standards — suitable replacements for demanding industrial applications in Vietnam

Related articles:

• Bearing Maintenance — Full Technical Guide
• Bearing Lubrication — Grease, Oil, Formulas
• Bearing Vibration Monitoring
• Bearing Mounting Best Practices
• Electric Motor Bearings