Centrifugal Pump Set Failure Modes and Causes

Pump Set Pump Setfailure modes failure mechanism

No Liquid Delivered Pump not primedLiquid returned backwardSuction valve shutDischarge valve shutSuction piping blockedDischarge piping blockedInsufficient NPSH availableMotor failureImpeller jammed by foreign bodyImpeller seizedSupply tank / vessel emptyNo liquid supply in pipeMotor wired wronglySpecific gravity higher than specifiedViscosity higher than specifiedVolute shatteredDrive coupling brokenDrive shaft brokenBearings in housing seizedBearings in motor seizedMotor power supply loss

Insufficient Flow Speed tuned downDischarge valve partially closedCavitationGas / vapour entrainment (poor suction piping design)Turbulence (fittings / valves too close to pump suction)Turbulence (restriction in line prior pump suction)Broken impellerBent vanes

Magnetic Field Motor Rotor Shaft Coupling Pump Shaft Pump Impeller

Incorrect impellerIncorrect impeller diameterSystem head too highInstrumentation errorSuction valve blockedSuction valve partially closedDischarge valve blockedDischarge valve partially closedSuction piping blockedDischarge piping blockedMotor wired wronglyMotor rotating backwardsRotational speed too lowExcessive air / vapour trapped in liquidInsufficient NPSH availableImpeller cloggedSpecific gravity higher than specifiedViscosity higher than specified

Intermittent Flow Air leak in suction lineExcessive air / vapour trapped in liquidLoss of prime e.g. liquid rans back through check / foot valve

Insufficient Pressure Instrumentation errorBroken impellerBent vanesIncorrect impellerIncorrect impeller diameterCavitationRotating backwardsRotational speed too lowInsufficient NPSH availableAssembled incorrectly

Pump Leaking Mechanical seal passesStuffing box packing excessively worn (for packed gland)Stuffing box bore damaged (for packed gland)Pump shaft surface damaged (for packed gland)Packing installed incorrectly (for packed gland)Flange leaks (flange not sealing)Flange leaks (gasket not sealing)Assembled incorrectlyVolute crackedVolute corrodedVolute erodedInadequate foundation size and design

5 72

Sources of Information:

http://www.vibanalysis.co.uk/technical

http://www.elongo.com/pdfs/BearingFailures990519.pdfThe McNally Institute CD http://www.delzer.com/Rexnord/falk/108010.pdf

Pump Impeller Liquid Flow

Impeller Impellerfailure modes failure mechanism

Chamber / Vane Wear Erosion (high flow rate)Erosion (internal flow recirculation)Erosion (suspended material on fluid)Pump-out vanes worn (if part of impeller design)Blocked balance holes between inlet and back of impeller (if part of impeller design)Cavitation

Corrosion Chemical corrosionGalvanic corrosion

Cavitation Damage Long suction pipeSmall diameter suction pipeBlocked suction pipePartially closed valve in suction lineNPSH available is to littleLiquid temperature rise

Loose on Shaft Assembled incorrectlyTaper seat damagedNut corrodedNut under torquedIncorrect impeller bore

Wear Ring Damage RecirculationSolids suspended in productErosion (high flow rate)Cavitation (pressure falls across cut water, like in a labyrinth)Incorrect impeller bore alignment

5 24

Blocked balance holes between inlet and back of impeller (if part of impeller design)

Volute Volutefailure modes failure mechanism

Wear Ring Damage RecirculationSolids suspended in productErosion (high flow rate)Cavitation

Cut Water Wear Erosion (high flow rate)Erosion (internal flow recirculation)Cavitation

Corrosion Chemical corrosionGalvanic corrosion

Cracked Pipe stressSoft foot dsitortion

3 11

Shaft Shaftfailure modes failure mechanism

Snapped Shaft Bending fatigue (surface crack initiated)Bending fatigue (surface corrosion initiated)Bending fatigue (surface damage initiated)Tortional fatigue (surface crack initiated)Tortional fatigue (surface corrosion initiated)Tortional fatigue (surface damage initiated)Shaft diameter too small for applicationShaft material tensile strength too low for applicationShaft rotating while bent by service loadEquipment jammed by productEquipment bearing seizedOverloaded during operationChemical attackGalvanic corrosionTemperature changes metallurgical propertiesStress raiser, scratches, mechanical damage (e.g. Pipe wrench used to turn seized shaft)Stress raiser, excessive interference fit with mating componentStress raiser, welding heat affected zone Fillet radius too smallFretting and pitting corrosionSurface defects such as welding inclusionsDeep machining marks or scratchesPoor blending of fillet radius into journalWear grooves at or close to fillet radius

Keyway Broken Keyway fatigueImproper keyway designInadequate shoulder fillet radiusMachining defects (residual stresses induced)Machining dimension /tolerance errorOverloaded during operation

2 30

Stress raiser, scratches, mechanical damage (e.g. Pipe wrench used to turn seized shaft)

Shaft Seal (Mechanical)failure modes

Accelerated Seal Face Wear

Edge Chipping

Seal Face Cracked / Fractured

Open Seal Face - Axial

Open Seal Face - Radial

Static O-Ring Seal Failure

Dynamic O-Ring Seal Failure

Product Leakage

Seal Embrittlement

Fractured Spring

Clogged Spring

Axial Shear

Torsional Shear

Seal Face Distortion

Slow Mechanical Response

Bellows Cracked

16

Shaft Seal (Mechanical)failure mechanism

Abrasives suspended in the process fluidAbrasives in solution in the process fluid (crystallisation)Abrasives from the environment such as sand and dirtAbrasives from the environment such as productAdhesive wear at start-up (faces contacting)Carbonisation on faces (high temperature, high contact load)Stuck faces (film transfer of seal face material-of-construction)Scale build-up (filming)Vaporisation between faces (high temperature, high contact load)Vaporisation between faces (loss of lubrication film)Dirt dragged or blown across the faces when they separateBlistered carbon face from air trapped in carbon expanding and blowing outSurface finish deteriorationPump shaft out-of-roundnessBlistering (seal face sub-surface vaporisation)Excessive start-up torqueExcessive shaft end playSeal installation misalignmentPump shaft misalignment to driverPump shaft bentShaft bent due to overhang because impeller is located too far away from the bearingSelective leaching is picking up elements from the piping system and depositing them on the seal faceOne or both of the seal faces is not lapped flat to within three helium light bands (0,000033" or 1 micron)Mishandling damage to a lapped faceDamaged faces during deliveryUneven clamping not 'equal and opposite' across the stationary faceOne or both of the faces is being distorted by a temperature differentialWater hammer pressure surgeCarbon in metal holder under residual stress and not stress relieved remove residual stress in the lapped faceOxidizing agents and halogens attack all forms and grades of carbon-graphiteDe-ionized water can attack carbon sealChemicals attack carbon sealSilicon carbide seal attacked by acidic liquidSolvent flushed through pipes for cleaning attacked seal materialPoor / wrong carbon grade selectedCorrosion rate increased by temperature rise (10 degree Centigrade rise doubles corrosion rate in many fluids)The plating or hard coating is coming off from the hard faceRotating face is not centered in the stationary face and is running off the edge of the stationary faceDirt or solids are clogging the movable componentsForeign object has passed into the seal chamber and is interfering with the free movement of the sealSolids have packed up in front of the inner seal in a "back to back" dual seal design

Seal face rocks due to installation misalignmentVaporisation on seal facesPump shaft excess whipPump shaft excess deflectionVibration transferred to seal (pipe harmonics)

Vibration transferred to seal (out-of-balance)Vibration transferred to seal (loose mounting)Vibration transferred to seal (running at critical speed)Vibration transferred to seal (Cavitation)Vibration transferred to seal (Running well off BEP (for single volute))Water hammer pressure surge

Run dry (no product)Run dry (no barrier / quench fluid)Run dry (cavitation)Run dry (pump-out vanes create low pressure / vacuum)Thermal shock (distortion from sudden high temperature rise)High temperature differential across the ceramicExcessive fluid pressure on sealWater hammer pressure surgeExcessive pressure velocity (high pressure at slow rotational speed)Stress corrosion crackingBarrier / quench fluid failureThe elastomer is swelling up under a carbon face.The shaft is hitting the stationary face or the rotating seal face is hitting a stationary objectProduct is solidifying between the faces and they are breaking at start upExcessive vibration is causing the drive or anti-rotation pins to crack the faceCracked during assembly / disassembly. Inspect crack for tell-tale signs of discolouration deep inside seal indicating breakage prior installationShaft / sleeve is oversizeFretting corrosion between seal and shaftA gasket or fitting is protruding into the stuffing box and touching seal component

Pump shaft end playTrust movementWater hammer pressure surgeThermal growth differentialImpeller adjustment towards wet end of pump opens seal facesProduct is vaporizing and separating the faces allowing solid material to blow across the lapped faceDynamic elastomer not free to move due to oversize shaftDynamic elastomer not free to move due rough surface finishDynamic elastomer not free to move due to sticking to shaft from high surface temperatureDynamic elastomer not free to move due to contaminants locking it in placeChipper edges causing face separationSpiral failure where seal component stick and cause internal twistSprings stick and prevent dynamic movementSeal as mishandled during installationElastomer seals on a porous carbon surface rather than a hard metal surface. When the shaft rotation stops the elastomer relaxes and flows into the carbon surface irregularitiesSet screws have come looseSet screws corrodedInitial setting of seal incorrect and once experiencing a little wear the spring load has goneAxial temperature growth of the shaft has altered the original settingShaft sleeve moved when the impeller was tightened to the shaftSeal was set-screwed to a hardened shaft or sleeve and has slipped due to vibrationSpring has been painted and cannot compress fullyCartridge seal static seal has jammed and preventing proper location of facesInner seal of a dual seal application was not balanced in both directions and is opening up with reversing pressureSingle spring found in some seal designs was wound in the wrong direction for the shaft rotation

Rotating bellows seal has lost cooling and the anti-vibration lugs are engaging the shaft. Normal shaft movement or vibration will cause the faces to open

Pump shaft bent (excess run-out)Pump shaft excess whipPump shaft excess deflectionOut-of-balance impeller

Fretting corrosion under seal (by axial movement transmitted to the seal)Excessive elastomer temperatureExcessive fluid pressureInstallation error (elastomer damage)Corrosive attack (incompatible chemical)Water hammerCompression set (extreme temperature operation causes elastomer elasticity memory loss)Compression set (product is too hot)Elastomer swollen by incompatible chemical productElastomer has extruded because of high pressure or excessive clearance.Elastomer is cracked from too long on the shelf (particularly Buna-N (nitrile rubber))Elastomer is cracked (High heat hardens elastomer and cracks)Elastomer is cracked (cryogenic temperatures)The elastomer is twisted, cut or damaged on installationShaft is corroded, damaged, or fretted under the elastomerSeal body O-ring groove is damaged or coated with a solid materialWrong lubricant was used at installation to aid fitting the elesomer on the shaftOxidizers can attack the carbon black in O-rings and other elastomersDistorted sleeve or shaft

Fretting corrosion (axial movement transmitted to the seal)Excessive elastomer temperatureExcessive fluid pressureInstallation error (elastomer damage)Corrosive attack (incompatible chemical)Water hammer pressure surgeCompression set (extreme temperature operation causes elastomer elasticity memory loss)Compression set (product is too hot)Elastomer swollen by incompatible chemical productSolids attached at dynamic elastomerand preventing it from movingElastomer has extruded because of high pressure or excessive clearance.Elastomer is cracked from too long on the shelf (particularly Buna-N (nitrile rubber))Elastomer is cracked (High heat hardens elastomer and cracks)Elastomer is cracked (cryogenic temperatures)The elastomer is cut or damaged on installationOxidizers can attack the carbon black in O-rings and other elastomers

Insufficient seal face compressionInstallation error (wrongly located on shaft)Installation error (mounting screws loosen)Loss of spring tensionForeign material contamination on facesUinbalanced seals in dual seal applicationsApplication changes from vacuum to a positive pressure. O-rings are the only common elastomers that seal in both directions. Wedges, U cups, and chevrons do not have this ability

The glue between the carbon and its metal holder is not compatible with the productDifferential expansion between 'pressed-in' carbon and its metal holderOut-of-roundness of 'shrunk-in' carbon caused by the tolerace on the carbon outside diameter and the metal holder inside diameterGland gasket has failedCracked bellows Barrier / quench leck misdiagnosed as product leak

Contaminants in pumped fluidContaminants in barrier / flush fluidPumped fluid / seal material-of-construction chemical incompatibilityThermal degradation of material-of-constructionIdle periods between use

Material flawManufacturing flawStress corrosion due to tooling marksCorrosive attackSeal installation misalignment

Pumped fluid contaminated with solidsBarrier / flush fluid contaminated with solids

Excessive pressure loading

Improper lubrication causes excessive torqueExcessive fluid pressure surges

Excessive fluid pressure on sealForeign material trapped between facesExcessive pressure velocity (high pressure at slow rotational speed)Insufficient seal face lubrication film thickness

Excessive squeeze on seal facesExcessive seal swellSeal extrusionMetal-to-metal contact due to out of alignmentSeal rub (shaft deflection causes the mechanical seal to contact the bore of the stuffing box)Internal erosion (barrier / flush fluid contaminated with solids)The product interfers with the free movement of the components. The fluid is crystallising, solidifying, viscousA gasket or fitting is protruding into the stuffing box and touching seal componentForeign object has passed into the seal chamber and is interfering with the free movement of the seal

Stress corrosion cracking

178

This illustration describes a mechanical seal that can be classified into several different categories:

Carbon in metal holder under residual stress and not stress relieved remove residual stress in the lapped face

Corrosion rate increased by temperature rise (10 degree Centigrade rise doubles corrosion rate in many fluids)

Cracked during assembly / disassembly. Inspect crack for tell-tale signs of discolouration deep inside seal indicating breakage prior installation

Elastomer seals on a porous carbon surface rather than a hard metal surface. When the shaft rotation stops the elastomer relaxes and flows into the carbon surface irregularities

Inner seal of a dual seal application was not balanced in both directions and is opening up with reversing pressure

Rotating bellows seal has lost cooling and the anti-vibration lugs are engaging the shaft. Normal shaft movement or vibration will cause the faces to open

Application changes from vacuum to a positive pressure. O-rings are the only common elastomers that seal in both directions. Wedges, U cups, and chevrons do not have this ability

Out-of-roundness of 'shrunk-in' carbon caused by the tolerace on the carbon outside diameter and the metal holder inside diameter

The product interfers with the free movement of the components. The fluid is crystallising, solidifying, viscous

This illustration describes a mechanical seal that can be classified into several different categories:

Roller Bearings Roller Bearingsfailure modes failure mechanism

Bearing Wear Abrasive particles, such as grit or swarf that have entered the bearingLack of cleanliness before and during mounting operationIneffective sealsLubricant contaminated by worn particles from brass cageLubrication contamination (wear particles)Lubricant additives gradually been used upLubricant has lost its chemical lubricating propertiesLubricant loss through sealLubricant has leaked awayLubrication contamination (external liquid ingress)Lubrication contamination (liquid product ingress)Lubrication contamination (dust and dirt ingress)Lubrication contamination (solid product ingress)Lubrication contamination (sand and material from within castings, flaking protective coatings, rust from inside casBent shaftsSkewed ring from burrs or dirt on bearing mounting surfaces and bearing abutment surfacesShaft shoulders which are not perpendicular to the bearing abutment surfaceLocking nut faces which are not perpendicular to the bearing seating faceNon-concentric bores on which the bearings are mounted leading to an angular axis of rotation of the shaft and thReverse Loading Failure is one such failure which occurs due to the bearing getting loaded in the opposite directioBad bearing supplied (especially cheap bearings made of inferior material)Solids were introduced into the system during the assembly process because of a lack of cleanlinessShaft coupling bore machined off-center / skewed

Bearing Overheated Clearance looseness (shaft shrinkage)Clearance looseness (housing expansion)Clearance looseness (loose fit shaft)Clearance looseness (loose fit housing)Spalling of race waysInadequate or improper lubricationExcessive preload on account of fits being too tightInsufficient heat transmission from housing due to build-up of material and product over casingRapid cooling of housing causes shrinkage and reduction in clearanceIncorrect viscosity of the lubricantIncorrect lubricant chemistryForm 'varnish' residue and 'coke' at elevated temperature that destroys the ability of the grease or oil to lubricateOil level too lowOil level too highPlugged oil return holesOver greased bearingUnder greasing bearingSuction pressure too high and causing axial thrustOut-of-balance rotating elementHydrogen embrittlement or blistering by water within microscopic cracks on raceways and rolling elementsInsufficient clearance in labyrinth sealsBase frame distortedProcess temperature conducted along shaftNormal aspiration as the pump cooled down, and the moisture laden atmosphere entered the bearing caseAxially mislocated shaft couplingGrease or lip seals too tight

Brinell and False Brinell Hit during mounting / installationDented by self-weight load when standing-stillDented by vibration impact loads when standing-still e.g. machinery transported on rough roadsSituated close to machinery producing vibrationsMounting pressure applied to the wrong ring during installationExcessively hard drive-up on tapered seating during installationOverloading while not runningExcessive preload on account of fits being too tightSmearing on installation produces microscopic surface cracksStuffing box packing overtightened

Creeping Slippage Ring fit is oversizeRing fit is wornFretting corrosion

Smearing rollers and raceways Smeared roller ends from sliding under heavy axial loading and with inadequate lubricationRoller acceleration on entry into the loaded zone due to too much clearanceLoad is too light for the speedAs bearings are being mounted, the ring with the roller and cage assembly is entered askew, without being rotateBlows applied to the wrong ring or heavy preloading without rotating the bearingExternal surfaces of heavily loaded bearings from movement of the bearing ring relative to its shaft or housingSlip fit is too loose on sliding ringSmearing Thrust Ball Bearings due to rotational speed is too high in relation to the loading. The centrifugal force t

Surface Distress Cracks Inadequate lubricationImproper lubrication

Corrosion - Deep seated rust Presence of water, moisture over a long period of timePresence of corrosive substances

Corrosion - Fretting Fit too looseShaft seating with errors of formHousing seating with errors of form

Electrical Erosion Electrical fluting due to passage of electric current through rotating ringElectrical fluting due to passage of electric current through non-rotating ringEarthing problem in equipment

Raceway Spalling Excessive preload on account of fits being too tightExcessive drive-up on a tapered seatingExcessive preload adjustment e.g. Single row angular contact ball bearings or taper roller bearingsTemperature differential between inner and outer rings too greatForeign particles in the lubricant, metal particles from within the system, etc allow wear particles to be jammed Cavitation induced stress overloadVibration induced stress from running off BEPClearance tightness (shaft expansion)Clearance tightness (housing shrinkage)Clearance tightness (tight shaft fit)Clearance tightness (tight housing fit)Pinched bearing (shaft ovality excessive)Pinched bearing (housing ovality excessive)Pinched bearing (pipe stress distortion)Pinched bearing (Soft foot causing frame distortion)Distorted bore of Plummer blocks from mounting on an uneven base becoming oval when the base bolts are tighIncorrect mounting, which results in axial loading, e.g. excessive preloading of angular contact ball bearings and tThe non-locating bearing has jammed.Axial freedom of movement has not been sufficient to accommodate the thermal expansion.

Cracked Rings Blows, with a hammer or hardened chisel, have been directed against the ring when the bearing was being mounFatigue cracks (installation misalignment cyclic overloading)Fatigue cracks (differential frame growth misalignment cyclic overloading)Fatigue cracks (bent shaft cyclic overloading)Fatigue cracks (shaft deflection from running off BEP)Fatigue cracks (Smearing during installation causes surface crack initiation)Fatigue cracks (Fretting corrosion caused crack initiation)Clearance tightness (shaft expansion)Clearance tightness (housing shrinkage)Clearance tightness (tight shaft fit)Clearance tightness (tight housing fit)Sliding under heavy axial loading and with inadequate lubrication

Cage Damage Fatigue cracks (vibration forces of inertia are so great as to cause fatigue cracks to form in the cage material, aftFatigue cracks (run at speeds in excess of cage design subjecting it to heavy forces of inertia that may lead to fraFatigue cracks (bearing rings are fitted out of alignment with each other, the path of the rollers take an oval configSevere acceleration and retardation, in conjunction with fluctuations in speed cause forces of inertia. These givInadequate lubrication Abrasive particlesFragments of flaked material or other hard particles may become wedged between the cage and a rolling element, Bearing is severely misaligned

Seized Bearing Metal to metal contact cause micro-weldingClearance tightness causes lack of rolling element rotationInadequate lubrication (viscosity too low)Inadequate lubrication (moisture in lubricant)Excessive mechanical overload (bearing too small in surface area)Excessive mechanical overload (high operating load)Rolling element jammed and not rolling due to solid contaminantRolling element jammed and not rolling due mechanical stressGrease or lip seal contact on the shaft, right next to the bearings. These seals can add as much as 38°C (100°F) Lock nut came loose

13 129

Category

Lube contamination by inclusionLube contamination by inclusionLube contamination by ingressLube contamination by ingressLube contamination by ingressLube chemical degradationLube chemical degradationLubricant lossLubricant lossLube contamination by ingressLube contamination by ingressLube contamination by ingressLube contamination by ingress

Lubrication contamination (sand and material from within castings, flaking protective coatings, rust from inside casLube contamination by ingressInstallation error

Skewed ring from burrs or dirt on bearing mounting surfaces and bearing abutment surfaces Installation errorShaft shoulders which are not perpendicular to the bearing abutment surface Installation errorLocking nut faces which are not perpendicular to the bearing seating face Installation errorNon-concentric bores on which the bearings are mounted leading to an angular axis of rotation of the shaft and thInstallation errorReverse Loading Failure is one such failure which occurs due to the bearing getting loaded in the opposite directioInstallation errorBad bearing supplied (especially cheap bearings made of inferior material) Material strength failureSolids were introduced into the system during the assembly process because of a lack of cleanliness Lube contamination by inclusion

Installation error

Incorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceLube contamination by inclusionLube contamination by inclusionLube chemical degradation

Insufficient heat transmission from housing due to build-up of material and product over casing Temperature changeTemperature changeLube chemical degradationLube chemical degradation

Form 'varnish' residue and 'coke' at elevated temperature that destroys the ability of the grease or oil to lubricate Lube chemical degradationLubricant lossLubricant excessiveLubricant excessiveLubricant excessiveLubricant insufficientOperational induced stressUnbalance

Hydrogen embrittlement or blistering by water within microscopic cracks on raceways and rolling elements Lube contamination by ingressIncorrect fits and toleranceIncorrect fits and toleranceTemperature change

Normal aspiration as the pump cooled down, and the moisture laden atmosphere entered the bearing case Lube contamination by ingressInstallation errorInstallation error

Installation errorOperational induced stress

Dented by vibration impact loads when standing-still e.g. machinery transported on rough roads Operational induced stressOperational induced stressInstallation errorInstallation errorOperational induced stressIncorrect fits and toleranceInstallation errorInstallation error

Incorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and tolerance

Smeared roller ends from sliding under heavy axial loading and with inadequate lubrication Incorrect fits and toleranceRoller acceleration on entry into the loaded zone due to too much clearance Incorrect fits and tolerance

Incorrect fits and toleranceAs bearings are being mounted, the ring with the roller and cage assembly is entered askew, without being rotateInstallation errorBlows applied to the wrong ring or heavy preloading without rotating the bearing Installation errorExternal surfaces of heavily loaded bearings from movement of the bearing ring relative to its shaft or housing Incorrect fits and tolerance

Incorrect fits and toleranceSmearing Thrust Ball Bearings due to rotational speed is too high in relation to the loading. The centrifugal force tOperational induced stress

Lubricant insufficientLube chemical degradation

Lube contamination by ingressLube contamination by ingress

Incorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and tolerance

Electrical induced damageElectrical fluting due to passage of electric current through non-rotating ring Electrical induced damage

Electrical induced damage

Incorrect fits and toleranceIncorrect fits and tolerance

Excessive preload adjustment e.g. Single row angular contact ball bearings or taper roller bearings Incorrect fits and toleranceIncorrect fits and tolerance

Foreign particles in the lubricant, metal particles from within the system, etc allow wear particles to be jammed Lube contamination by ingressOperational induced stressOperational induced stressIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and tolerance

Distorted bore of Plummer blocks from mounting on an uneven base becoming oval when the base bolts are tigh Installation errorIncorrect mounting, which results in axial loading, e.g. excessive preloading of angular contact ball bearings and tInstallation error

Incorrect fits and toleranceAxial freedom of movement has not been sufficient to accommodate the thermal expansion. Installation error

Blows, with a hammer or hardened chisel, have been directed against the ring when the bearing was being mounInstallation errorInstallation error

Fatigue cracks (differential frame growth misalignment cyclic overloading) Incorrect fits and toleranceInstallation errorOperational induced stress

Fatigue cracks (Smearing during installation causes surface crack initiation) Installation errorIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceIncorrect fits and toleranceInstallation error

Fatigue cracks (vibration forces of inertia are so great as to cause fatigue cracks to form in the cage material, aft UnbalanceFatigue cracks (run at speeds in excess of cage design subjecting it to heavy forces of inertia that may lead to fraOperational induced stressFatigue cracks (bearing rings are fitted out of alignment with each other, the path of the rollers take an oval configInstallation errorSevere acceleration and retardation, in conjunction with fluctuations in speed cause forces of inertia. These giv Operational induced stress

Lubricant insufficientLube contamination by inclusion

Fragments of flaked material or other hard particles may become wedged between the cage and a rolling element, Lube contamination by ingressInstallation error

Lube chemical degradationIncorrect fits and toleranceLube chemical degradationLube chemical degradationDesign errorOperational induced stressLube contamination by ingressIncorrect fits and tolerance

Grease or lip seal contact on the shaft, right next to the bearings. These seals can add as much as 38°C (100°F) Design errorInstallation error

SKF List of bearing failure causes - Bearing failures and their causes - Product information 401WearWear caused by abrasive particlesWear caused by inadequate lubricationWear caused by vibrationIndentationsIndentations caused by faulty mounting or overloadingIndentations caused by foreign particlesSmearingSmearing of roller ends and guide flangesSmearing of rollers and racewaysRaceway smearing at intervals corresponding to the roller spacingSmearing of external surfacesSmearing in thrust ball bearingsSurface distressCorrosionDeep seated rustFretting corrosionDamage caused by the passage of electric currentFlaking (spalling)Flaking caused by preloadingFlaking caused by oval compressionFlaking caused by axial compressionFlaking caused by misalignmentFlaking caused by indentationsFlaking caused by smearingFlaking caused by deep seated rustFlaking caused by fretting corrosionFlaking caused by fluting or cratersCracksCracks caused by rough treatmentCracks caused by excessive drive-upCracks caused by smearingCracks caused by fretting corrisonCage damageVibrationExcessive speedWearBlockageOther causes of cage damage

SKF List of bearing failure causes - Bearing failures and their causes - Product information 401

Wear caused by abrasive particlesWear caused by inadequate lubrication

Indentations caused by faulty mounting or overloadingIndentations caused by foreign particles

Smearing of roller ends and guide flangesSmearing of rollers and racewaysRaceway smearing at intervals corresponding to the roller spacing

Damage caused by the passage of electric current

Flaking caused by oval compressionFlaking caused by axial compressionFlaking caused by misalignment

Flaking caused by deep seated rustFlaking caused by fretting corrosionFlaking caused by fluting or craters

Cracks caused by rough treatmentCracks caused by excessive drive-up

Cracks caused by fretting corrison

Flexible Drive Coupling Flexible Drive Couplingfailure modes failure mechanism (Tyre Coupling)

Premature Component Wear Shaft misalignment axialShaft misalignment parallelShaft misalignment angularShaft thermal expansionSevere distortion under maximum instantaneous torque (wind-up)Erratic/pulsating/high-inertia loadsExcessive back-lash within coupling for shock loadsRotational speed is beyond design RPMLoosening of the coupling's fastener to the shaftChanged assembly gap between hubs of the couplingDamaged or broken componentsBore machined askewBore machined non-concentricExcessive shaft end floatBent shafts, excessive run-outExcess back-lash between coupling parts / componentsMaterial-of-Construction incorrect for duty loads / torque

Hub Damage Shaft out-of-round or incorrect formSplit / cracked due to improper interference fitMovement of the hub on the shaftShaft surface finish too rough and offers insufficient surface area for supportShaft not straightShaft under bore nicked, hammer-rash or damagedAxial misalignmentConcentrated heat on the hubs cause distortion

Keyway Failure Excessive shaft interference fitHigh torque load transmitted through the keyExcessively loose fitting key allows high impact on start / reverse

Key Failure Excessively loose fitting key allows high impact on start / reverseImproper key material selectedCorrosionChemical attackHigh torque load transmitted through the key

Elastometric Element Failure Excessive torque loadingAtmospheric contamination / deteriorationChemical attackOverloadTorsional vibrations (look for liquefaction of the material internal of the insert)Coupling out-of-balanceCracked due to rubber hardening from chemical contaminationElastomer material has limited service lifeExcessive high temperature

Flange Fastener Failure High starting or impact loads occur in combination with reversing service or severe load fluctuations exist, fasteners have failed in reverse bending fatigueBending fatigue loading may also be characterized by: fretting corrosion on the bolt body diameter, imbedding of the bolt washer face diameter into the sleeve, wallowing out of the sleeve flange holes and/or offset of the bolt body diameter.Insufficient fastener tightening torqueSystem torsional vibration

Reversing loads which exceed the flange joint capacitySystem was subjected to unexpected overloadsElongated bolt holes due to fastener impact (fastener loosened off)Elongated bolt holes due to fastener impact (fastened insufficiently tight)Cyclic fatigue life exceededShaft passes through natural frequncy and large vibrations / movements cause micro-motion of coupling flanges

6 52

Sources of Information:http://pt.rexnord.com/products/e-catalog/catalog/CachedImages/0000001/t004_r00171_v0.pdfhttp://motionsystemdesign.com/mag/couplings_shafts/

Flexible Drive Couplingfailure mechanism (Gear Coupling)

Gear couplings, frictional movment on teeth due to misalignmeGear couplings, loss of lubricant filmGear couplings, not relubricated as maintenanceGear couplings, contaminated lubricant

Severe distortion under maximum instantaneous torque (wind-up) Gear couplings, sleeve seal cage end ring failures may result fGear couplings, teeth lock-up due to excessive misalignmentGear couplings, teeth lock-up due to excessive misalignment

Shaft surface finish too rough and offers insufficient surface area for support

Excessively loose fitting key allows high impact on start / reverse

Excessively loose fitting key allows high impact on start / reverse

Torsional vibrations (look for liquefaction of the material internal of the insert)

Cracked due to rubber hardening from chemical contamination

High starting or impact loads occur in combination with reversing service or severe load fluctuations exist, fasteners have failed in reverse bending fatigueBending fatigue loading may also be characterized by: fretting corrosion on the bolt body diameter, imbedding of the bolt washer face diameter into the sleeve, wallowing out of the sleeve flange holes and/or offset of the bolt body diameter.

Elongated bolt holes due to fastener impact (fastener loosened off)Elongated bolt holes due to fastener impact (fastened insufficiently tight)

Shaft passes through natural frequncy and large vibrations / movements cause micro-motion of coupling flanges

Flexible Drive Couplingfailure mechanism (Jaw Coupling)

Jaw Coupling, elastomer compression set from over-torqueJaw Coupling, elastomer compression set from normal useJaw Coupling, excessive hub spider leg wearJaw Coupling, shaft radial misalignmentJaw Coupling, shaft angular misalignmentJaw Coupling, shaft axial misalignmentJaw Coupling, hub spider jaws sheared

High starting or impact loads occur in combination with reversing service or severe load fluctuations exist, fasteners have failed in reverse bending fatigueBending fatigue loading may also be characterized by: fretting corrosion on the bolt body diameter, imbedding of the bolt washer face diameter into the sleeve, wallowing out of the sleeve flange holes and/or offset of the bolt body diameter.

Flexible Drive Couplingfailure mechanism (Disc Coupling)

Disk couplings, cracking or breaks in the individual disk packs or boltsDisk couplings, check for loose disk pack bolts and/or nutsDisk couplings, disk cyclic fatigue due to excessive misalignment

Bending fatigue loading may also be characterized by: fretting corrosion on the bolt body diameter, imbedding of the bolt washer face diameter into the sleeve, wallowing out of the sleeve flange holes and/or offset of the bolt body diameter.

Electric Motor Electric Motorfailure modes failure mechanism

Over-Current Draw Mechanical overloadPoor power conditioningExcessive effective service factorOver-voltageVoltage unbalanceBrushes fail openVoltage surgesDrop a phase due to winding failure

Fail to Start Power provider interruptionUnder-voltageCable mechanically damagedCable burnt-out from overloadCable connection overheatedMotor starter failure

Rotor Damage Winding is saturated with water (ingress of water)Aspirated moisture (ingress of humidity)High operating temperatureHigh ambient temperatureVariable frequency drives are employed, insulation life expectancy will be reducedChemical ingress degrades internalsDirt build-up on cooling finsFrequent stops and startsStarting method cause high starting loadsRotor faults, casting voidsRotor faults, broken rotor barsInsulation-to-ground faultsAir gap faults, including eccentric rotorsOverloading (load demands exceeding the rating of the motor)Improper matching of motor to load (inertia matching)Loose internal wiring connectionsVibration / mechanical loosenessExcessive starts and reversals Unequal voltage between phases Voltage surges, switching power circuits ,lightning strikes, capacitor discharges and solid-state power devices Nuisance trippingTransient voltage peaks

Stator Damage Very high currents in the stator winding due to a locked rotor condition Dirt build-up on cooling finsBalance weight came loose and struck the windingWinding is saturated with water (ingress of water)Aspirated moisture (ingress of humidity)Moisture over motor allows short-circuit current to earthTerminal bolting to wrong connectionTerminal bolting loose connectionLoose internal wiring connections

Insulation-to-ground faultsOverloading (load demands exceeding the rating of the motor)Excessive starts and reversals Voltage surges, switching power circuits ,lightning strikes, capacitor discharges and solid-state power devices Nuisance trippingTransient voltage peaksShorts between conductors or coils

Rotor Bar Failure Poor welded connectionVibration due to misalignmentVibration transmitted by nearby equipmentVibration due to loose mountingsVibration from out-of-balanceFrame distortion from softfoot

Bearing Failure Excessive radial or axial loadingElectric current flowing through bearings from inverters (Variable Frequency Drive waveforms)Insufficient bearing lubricationExcess bearing lubricationLubricant is contaminatedIncorrect lubricantOut-of-balance, rotor unbalancedOut-of-balance, balance weight lostInduced vibrationShaft misalignmentWrong coupling type or installationBelt misalignmentIncorrect belt tensionDefective bearing housingsDefective shaft mountingBad mechanical fitsHigh static loading when stoppedFrame warpageBroken mountsBase plate distortionMissing or deteriorated groutingFoundation deteriorationInadequate foundation size and designBad or worn shaftShaft, bent and run-out excessiveShaft, axial float excessiveinduced mechanical vibrationOverhung loadsMechanical resonanceRotor deflection

Shaft Broken Stress raiser, corrosionStress raiser, chemical attackStress raiser, scratches, mechanical damage (e.g. Pipe wrench used to turn seized shaft)Locked rotorBending/ torsional fatigue from misalignmentMassive imposed overloadKeyway fatigueImproper keyway designInadequate shoulder fillet radius

Manufacturing defects (residual stresses induced)Overloaded during operationFretting and pitting corrosion

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Variable frequency drives are employed, insulation life expectancy will be reduced

Overloading (load demands exceeding the rating of the motor)

Voltage surges, switching power circuits ,lightning strikes, capacitor discharges and solid-state power devices

Very high currents in the stator winding due to a locked rotor condition

Overloading (load demands exceeding the rating of the motor)

Voltage surges, switching power circuits ,lightning strikes, capacitor discharges and solid-state power devices

Electric current flowing through bearings from inverters (Variable Frequency Drive waveforms)

Stress raiser, scratches, mechanical damage (e.g. Pipe wrench used to turn seized shaft)

Pump Set Base Frame Pump Set Base Framefailure modes failure mechanism

Loose on Foundation Hold-down bolt nuts looseHold-down bolts corrodedHold-down bolts pulled out of concreteExcessive machine vibration

Warped Frame Foundation not levelPulled-down unequally on hold-down boltsImpact by object

Corroded Frame Chemical attackWater sitting in contact with frame

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Pump Set Foundationfailure modes

Broken Foundation

Corroded Foundation

Foundation Moves

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Pump Set Foundationfailure mechanism

Impact by objectConcrete shrink cracksFoundation support flexsGround conditions unsuitable

Chemical attack

Ground strength weakUndersize foundation

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