large image of a plain bearing shell

How To Diagnose Plain Bearing Failures

Diagnosing plain bearing failures is all about recognising the tell-tale signs of different wear out and other failure modes. Careful inspection of the failed bearing will usually reveal vital visual clues that can lead to a potential cause for the failure. However, do not stop at this stage. More than one mechanism of failure can lead to superficially similar bearing damage. Moreover, once failure has been initiated, the original mechanism may lead to other failure mechanisms and it is essential to identify the original cause.

A Picture is Worth A 1000 Words…

This page lists many typical plain bearing failure modes with images showing the associated failure pattern. The failure causes listed point towards a solution or areas for further investigation so that this type of failure can be prevented in the future. The information on this page is taken from our Tribology Handbook – a PDF version is available from our site here.

Need some more advice? – Get in touch and we’d be happy to help

Foreign Matter - With Fine Scoring

foreign-matter
Characteristics: Fine score marks or scratches in direction of motion, often with embedded particles and halos.

Causes: Dirt particles in the lubricant exceeding the minimum oil film thickness

Foreign Matter - With Severe Scoring

Wear signature showing ingress of foreign matter or debrisCharacteristics: Severe scoring and erosion of the bearing surface in the line of motion, or along lines of local oil flow.

Causes: Contamination of lubricant by excessive amounts of dirt particularly non-metallic particles which can roll between the surfaces

Wiping Wear Marks

Image shows the smearing of a journal bearing from a wiping failureCharacteristics: Surface melting and flow of the bearing material, especially when of low-melting point, e.g. whitemetals, overlays.

Causes: Inadequate bearing clearance, overheating, insufficient oil supply, excessive load, or operation with a non-cylindrical journal

Fatigue - Mosaic Cracking

Image shows a cracking pattern usually seen observed from excessive dynamic bearing overload
Characteristics: cracking, often in a mosaic pattern, and loss of areas of lining.

Causes: Excessive dynamic loading or overheating causing reduction of fatigue strength; over-speeding causing imposition of excessive centrifugal loading.

Fatigue Cracking - Resulting in Lining Loss

Image shows fatigue cracks in a journal bearing
Characteristics: Loss of areas of lining by propagation of cracks initially at right angles to the bearing surface, and then progressing parallel to the surface, leading to isolation of pieces of the bearing materials

Causes: Excessive dynamic loading which exceeds the fatigue strength at the operating temperature.

Fretting

Image shows an example of fretting wear
Characteristics: Welding, or pick-up of metal from the housing on the back of bearing. Can also occur on the joint faces. Production and oxidation of fine wear debris, which in severe cases can give red staining.

Causes: Inadequate interference fit; flimsy housing design; permitting small sliding movements between surfaces under operating loads.

Misalignment

Shows typical wear and failure characteristics for bearing mis-alignment
Characteristics: Uneven wear of bearing surface, or fatigue in diagonally opposed areas in top and bottom halves.

Causes: Misalignment of bearing housings on assembly, or journal deflection under load.

Dirty Assembly - Example 1

Shows localised overheating of bearing shell from poor assembly

Characteristics: Localised overheating of the bearing surface and fatigue in extreme cases, sometimes in nominally loaded areas.

Causes: Entrapment of large particles of dirt (e.g. swarf), between bearing and housing, causing distortion of the shell, impairment of heat transfer and reduction of clearance (see next column).

Dirty assembly - Example 2

Image shows poor bedding in of bearing shell - which leads to local over-heating

Characteristics: Local areas of poor bedding on the back of the bearing shell, often around a ‘hard’ spot.

Causes: Entrapment of dirt particles between bearing and housing. Bore of bearing is shown in previous column illustrating local overheating due to distortion of shell, causing reduction of clearance and impaired heat transfer.

Cavitation Erosion

Plain bearing image showing one typical form of cavitation erosion

Characteristics: Removal of bearing material, especially soft overlays or whitemetal in regions near joint faces or grooves, leaving a roughened bright surface.

Causes: Changes of pressure in oil film associated with interrupted flow.

Discharge Cavitation Erosion


Image showing discharge cavitation erosionCharacteristics:
Formation of pitting or grooving of the bearing material in a V-formation pointing in the direction of rotation.

Causes: Rapid advance and retreat of journal in clearance during cycle. It is usually associated with the operation of a centrally grooved bearing at an excessive operating clearance.

Cavitation erosion - Example 2

Several bearings showing the typical hallmarks of cavitation corrosion

Characteristics: Attack of bearing material in isolated areas, in random pattern, sometimes associated with grooves.

Causes: Impact fatigue caused by collapse of vapour bubbles in oil film due to rapid pressure changes. Softer overlay (Nos. 1, 2 and 3 bearings) attacked. Harder aluminium – 20% tin (Nos 4 and 5 bearings) are usually not attacked under these particular conditions.

Corrosion

Plain bearing corrosion wear characteristic profile

Characteristics: Removal of lead phase from unplated copper-lead or lead-bronze, usually leading on to fatigue of the weakened material.

Causes: Formation of organic acids by oxidation of lubricating oil in service. Consult oil suppliers; investigate possible coolant leakage into oil.

Tin Dioxide Corrosion

Wear profile for tin dioxide corrosion of plain bearings

Characteristics: Formation of hard black deposit on surface of white-metal lining, especially in marine turbine bearings. Tin attacked, no tin-antimony and copper-tin constituents.

Causes: Electrolyte (sea water) in oil.

Sulphur Corrosion

Wear characteristics from Sulpur corrosion of plain bearings

Characteristics: Deep pitting and attack or copper-base alloys, especially phosphor-bronze, in high temperature zones such as small-end bushes. Black coloration due to the formation of copper sulphide.

 

Causes: Attack by Sulphur compounds from oil additives or fuel combustion products.

Wire Wool Damage - Example 1

Wire wool damage to plain bearings caused by large particle embedding

Characteristics: Formation of hard black scab on whitemetal bearing surface, and severe machining away of journal in way of scab, as shown on the right.

Causes: It is usually initiated by a large dirt particle embedded in the whitemetal, in contact with journal, especially chromium steel.

Wire Wool Damage - Example 2

Image showing the damage to a plain bearing from sever catastrophic machining of the journal - sometimes called wire wool damage
Characteristics: Severe catastrophic machining of journal by ‘black scab’ formed in whitemetal lining of bearing. The machining ‘debris’ looks like wire wool.

Causes: Self-propagation of scab, especially with ‘susceptible’ journals steels, e.g. some chromium steels.

Electrical discharge

Images showing the wear signature for bearing electrical discharge
Characteristics: Pitting of bearing surface and of journal; may cause rapid failure in extreme cases.

Causes: Electrical currents from rotor to stator through oil film. Often caused by faulty earthing.

Fretting Due To External Vibration

bearing fretting wear signature for external vibration
Characteristics: Pitting and pick-up on bearing surface.

Causes: Vibration transmitted from external sources, causing damage while journal is stationary

Overheating

Image showing the plain bearing overheating cracks
Characteristics: Extrusion and cracking, especially of whitemetal-lined bearings.

Causes: Operation at excessive temperatures.

Thermal Cycling Damage


Characteristics: Surface rumpling and grain-boundary cracking of tin-base whitemetal bearings.

Causes: Thermal cycling in service, causing plastic deformation, associated with the non-uniform thermal expansion of tin crystals.

Faulty Assembly - Example 1


Characteristics: Localised fatigue or wiping in nominally lightly loaded areas.

Causes: Stagger at joint faces during assembly, due to excessive bolt clearances, or incorrect bolt disposition (bolts too far out).

Faulty assembly - Example 2


Characteristics: Overheating and pick-up at the sides of the bearings.

Causes: Incorrect grinding of journal radii, causing fouling at fillets.

Incorrect Journal Grinding


Characteristics: Severe wiping and tearing-up of bearing surface.

Causes: Too coarse a surface finish, or in the case of SG iron shafts, the final grinding of journal in wrong direction relative to rotation in bearing

Inadequate Oil Film Thickness


Characteristics: Fatigue cracking in proximity of a groove.

Causes: Incorrect groove design, e.g. positioning a groove in the loaded area of the bearing.

Inadequate lubrication


Characteristics: Seizure of bearing.

Causes: Inadequate pump capacity or oil gallery or oilway dimensions. Blockage or cessation of oil supply.

Bad Bonding of Lining to Shells


Characteristics: Loss of lining, sometimes in large areas, even in lightly loaded regions, and showing full exposure of the backing material.

Causes: Poor tinning of shells; incorrect metallurgical control of lining technique