🚧 Under construction — VoTechWorks is being built. A free tech program — complimentary, as our commitment to get America working.
voTechWorksGrade 13 · a vocational technology learning center, by urbanicity
newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › Industrial Maintenance › Bearings: Selection, Installation, Lubrication, and Failure Analysis › Lesson 9
MFG-INDU16-03 · Lesson 9 · 15 clock hours · theory

Bearing Failure Analysis: Modes, Root Causes, and Reporting

Objective. Students will identify at least six bearing failure modes from physical samples and photographs and state a probable root cause and corrective action for each using a standard failure analysis framework.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed engineer or certified journey-level tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Bearing Failure Analysis Matters

Bearings are among the most common points of mechanical failure in industrial and marine equipment. When a bearing fails unexpectedly, the result can be costly downtime, damaged machinery, and serious safety hazards. Failure analysis is the disciplined process of examining a failed bearing, identifying what went wrong, tracing it to a root cause, and recommending a corrective action so the failure does not repeat. Mastering this process is a core skill for any industrial maintenance technician.

The Failure Analysis Framework

A reliable failure analysis follows a consistent sequence:

1. Gather information — document the equipment ID, bearing designation, operating conditions (load, speed, temperature), lubricant type and interval, and installation history.

2. Examine the bearing — inspect raceways, rolling elements, cage, and seals visually and, when available, under magnification.

3. Identify the failure mode — match the physical evidence to a recognized pattern.

4. Determine the root cause — ask why the damage pattern occurred, using tools such as a fishbone (cause-and-effect) diagram.

5. Write a corrective action — state the specific change to prevent recurrence.

6. Document and report — record findings on a structured condition report so the organization learns from the event.

The Eight Major Failure Modes

Fatigue spalling (surface fatigue): Appears as pitting or flaking of the raceway or rolling-element surface. Material breaks away in irregular chips, leaving a rough, cratered surface. Root cause is cyclic stress that has exceeded the bearing's rated life — often because the load is higher than specified, the bearing is undersized, or service has exceeded calculated L10 life. Corrective action: verify load calculations, select a bearing with adequate dynamic load rating, and review service intervals.

True brinelling: Permanent indentations in the raceway spaced exactly at the rolling-element pitch. Caused by a static overload — such as a heavy impact during installation or transport with a press-fit applied through the rolling elements. Corrective action: always apply installation force to the ring being press-fitted, never through the rolling elements; use proper tooling.

False brinelling: Shallow, polished or reddish-brown elliptical indentations at rolling-element spacing. Caused by vibration while the bearing is stationary (for example, a motor stored on a vibrating floor, or a vessel riding at anchor). There is no true plastic deformation — the damage is fretting wear and oxidation. Corrective action: rotate stored equipment periodically, use anti-fretting grease, isolate equipment from vibration during storage.

Corrosion: Red or brown staining, pitting, or etching on raceways and rolling elements. Moisture enters through failed seals, condensation, or improper lubricant. Saltwater environments in the marine sector make this mode especially common. Corrective action: inspect and replace seals, switch to a corrosion-inhibiting lubricant, and ensure bearing housings are sealed against the environment.

Contamination wear: Scratching, scoring, or embedded particles visible on raceways and rolling elements. Fine particles — dirt, weld spatter, metal chips — act as abrasives. Root cause is contaminated lubricant or poor cleanliness during installation. Corrective action: filter lubricant, follow clean-room practices during installation, upgrade sealing arrangements.

Misalignment wear: Non-uniform wear patterns across the width of the raceway — heavier on one side or in a diagonal band. Caused by angular or parallel shaft misalignment, or a distorted housing bore. Corrective action: realign shafts to specification, check housing bore geometry, and use a self-aligning bearing if slight angular error is unavoidable.

Lubrication failure (over- and under-lubrication): Under-lubrication produces heat discoloration (gold, blue, or black temper colors on raceways) and adhesive wear. Over-lubrication generates excess heat from churning, can force grease past seals, and may cause the same discoloration. Corrective action: follow the bearing manufacturer's relubrication schedule and quantity specifications exactly.

Electric current damage (fluting): A washboard pattern of evenly spaced grooves or pitting across the raceway circumference, often with a frosted appearance. Stray electrical current (from variable-frequency drives, welding ground paths, or static) arcs through the bearing. Corrective action: install insulated bearings or shaft grounding rings, verify proper grounding of VFD-driven motors.

Reading Physical Evidence Systematically

When you examine a failed bearing, work from the outside in: check the housing fit marks, then the outer ring, then the inner ring, then the rolling elements, and finally the cage. Note the location of damage relative to the load zone. Photograph or sketch before you disturb the bearing. Record what you see, not what you expect to see.

Safety During Failure Analysis

Apply lockout/tagout (LOTO) before removing any bearing from service — always follow your facility's written LOTO procedure. Wear cut-resistant gloves when handling failed bearings; spalled edges are extremely sharp. Wear safety glasses at all times in the lab. If the failure involved high heat, let the bearing cool before handling. Dispose of contaminated lubricant according to your facility's hazardous waste procedures.

Writing the Condition Report

A structured report must include: equipment ID and location, bearing designation and manufacturer, date of removal, operating conditions, failure mode with evidence, probable root cause, corrective action taken, and prevention recommendation. Clear, factual language matters — your report may drive a purchasing decision, a design change, or a maintenance schedule revision.

Key terms10

Fatigue spallingFlaking or pitting of raceway or rolling-element surfaces caused by cyclic stress exceeding the material's endurance limit.
True brinellingPermanent plastic indentations in the raceway at rolling-element pitch spacing, caused by a static overload or improper installation impact.
False brinellingShallow fretting-wear indentations that mimic true brinelling but are caused by vibration of a stationary bearing, not plastic deformation.
FlutingA washboard pattern of evenly spaced grooves across the raceway caused by electrical current arcing through the bearing.
Root causeThe fundamental reason a failure occurred — the condition or action that, if corrected, prevents recurrence.
Fishbone diagramA cause-and-effect diagram that organizes potential causes of a problem into categories (such as method, machine, material, environment) to identify root cause.
Fretting corrosionSurface damage and reddish oxide debris produced by small oscillatory motion between contacting surfaces under load, commonly seen in false brinelling.
Condition reportA structured document recording a bearing's identification, operating history, observed failure mode, root cause determination, and corrective action.
L10 lifeThe calculated number of operating hours or revolutions at which 10% of a group of identical bearings under identical conditions would be expected to develop fatigue failure.
Contamination wearAbrasive damage to raceways and rolling elements caused by hard particles — dirt, debris, or metal chips — in the lubricant or introduced during installation.
In class: Failure mode lecture and sample station tour: instructor presents the major failure modes (fatigue spalling, brinelling, false brinelling, corrosion, contamination wear, misalignment wear, overlubrication/underlubrication, electric current damage) using a bearing failure analysis wall chart and actual failed bearing samples labeled A–H; students sketch each sample and annotate the damage location. · Root cause mapping exercise: students receive eight condition report cards describing a bearing failure (operating conditions, lubricant used, installation method, run hours); working in pairs they map each description to a failure mode on a cause-and-effect (fishbone) diagram and write a corrective action recommendation. · Written failure report: each student selects one failed sample from the lab collection, photographs it (or sketches to scale), completes a structured failure analysis report (equipment ID, operating conditions, failure mode, probable cause, corrective action, prevention recommendation) using an industry-standard condition report template.
Materials: Failed bearing sample collection (minimum eight distinct failure modes); bearing failure analysis wall chart (SKF or equivalent); condition report template; cause-and-effect diagram worksheet; camera or smartphone for photos; student notebooks.
Check: Written failure analysis report graded against a rubric: correct failure mode identification, plausible root cause, and actionable corrective action — minimum score of 75% on rubric required; oral follow-up question by instructor to confirm student can defend findings.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Industrial Maintenance — Bearings
1. A technician removes a motor bearing and finds pitting and flaking of the inner raceway across the full load zone. The motor has run well beyond its calculated service interval at rated load. Which failure mode best describes this damage?
NCCER Industrial Maintenance — Bearings
2. A pump bearing is pulled for inspection and shows evenly spaced, shallow elliptical marks at rolling-element pitch on the outer raceway. The marks have a polished, reddish-brown appearance. The pump sat idle for three months next to a running compressor. What is the most probable failure mode?
MSSC CPT — Maintenance Awareness
3. A marine propulsion motor bearing displays a repeating washboard groove pattern evenly spaced around the entire raceway circumference. The motor is controlled by a variable-frequency drive. What corrective action is MOST appropriate?
MSSC CPT — Safety
4. Which safety precaution is MOST critical before removing a failed bearing from a machine for analysis?
NCCER Industrial Maintenance — Bearings
5. A technician's condition report notes that a bearing was removed with scratch marks and embedded metallic particles on the rolling elements. The lubrication interval was followed correctly. What is the most probable root cause?
NCCER Industrial Maintenance — Bearings
6. When completing a structured bearing failure analysis report, which piece of information is LEAST likely to help determine the root cause?
MSSC CPT — Problem Solving and Process Improvement
7. A fishbone (cause-and-effect) diagram is used in bearing failure analysis primarily to:
NCCER Industrial Maintenance — Bearings
8. A bearing is found with heavier wear on one side of the inner raceway and a diagonal wear band rather than a uniform load zone. Operating load is within specification. What failure mode and corrective action best match this evidence?
Record this lesson on my transcript. Sign in with your key and enrollment email to record lessons (enroll free if you have no key). This page stays open to read and practise.
← Previous lessonProgram planNext lesson →