Centrifugal Pump Set Failure Modes

Centrifugal Pump Set Failure Modes and Causes

Pump Set Pump Setfailure modes failure mechanism

No Liquid Delivered Pump not primed

Liquid returned backwardSuction valve shut

Discharge valve shut

Suction piping blocked

Discharge piping blocked

Insufficient NPSH available

Motor failure

Impeller jammed by foreign body

Impeller seized

Supply tank / vessel empty

No liquid supply in pipe

Motor wired wronglySpecific gravity higher than specified

Viscosity higher than specified

Volute shattered

Drive coupling broken

Drive shaft broken

Bearings in housing seized

Bearings in motor seized

Motor power supply loss

Insufficient Flow Speed tuned down

Discharge valve partially closed

CavitationGas / vapour entrainment (poor suction piping design)

Turbulence (fittings / valves too close to pump suction)

Turbulence (restriction in line prior pump suction)

Broken impeller

Bent vanes

Incorrect impeller

Incorrect impeller diameter

System head too high

Instrumentation error

Suction valve blocked

Suction valve partially closed

Discharge valve blocked

Discharge valve partially closed

Suction piping blocked

Discharge piping blocked

Motor wired wronglyMotor rotating backwards

Rotational speed too low

Excessive air / vapour trapped in liquid


Impeller clogged

Specific gravity higher than specified

Viscosity higher than specified

Intermittent Flow Air leak in suction line

Excessive air / vapour trapped in liquid

Loss of prime e.g. liquid rans back through check / foot valve

Insufficient Pressure Instrumentation error

Broken impeller

Bent vanes

Incorrect impeller

Incorrect impeller diameter

Cavitation

Rotating backwards

Rotational speed too low


Assembled incorrectly

Pump Leaking Mechanical seal passes

Stuffing 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 incorrectly

Volute cracked

Volute corroded

Volute eroded

Inadequate foundation size and design

5 72

Sources of Information:

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

http://www.elongo.com/pdfs/BearingFailures990519.pdf

The McNally Institute CD

http://www.delzer.com/Rexnord/falk/108010.pdf

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 corrosion

Galvanic corrosion

Cavitation Damage Long suction pipe

Small diameter suction pipe

Blocked suction pipe

Partially closed valve in suction line

NPSH available is to little

Liquid temperature rise

Loose on Shaft Assembled incorrectly

Taper seat damaged

Nut corroded

Nut under torqued

Incorrect impeller bore

Wear Ring Damage Recirculation

Solids suspended in product

Erosion (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 Recirculation

Solids suspended in product

Erosion (high flow rate)

Cavitation

Cut Water Wear Erosion (high flow rate)

Erosion (internal flow recirculation)

Cavitation

Corrosion Chemical corrosion

Galvanic corrosion

Cracked Pipe stress

Soft 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 application

Shaft material tensile strength too low for application

Shaft rotating while bent by service load

Equipment jammed by product

Equipment bearing seized

Overloaded during operation

Chemical attack

Galvanic corrosion

Temperature changes metallurgical properties

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

Stress raiser, excessive interference fit with mating component

Stress raiser, welding heat affected zone

Fillet radius too small

Fretting and pitting corrosion

Surface defects such as welding inclusions

Deep machining marks or scratches

Poor blending of fillet radius into journal

Wear grooves at or close to fillet radius

Keyway Broken Keyway fatigue

Improper keyway design

Inadequate shoulder fillet radius

Machining defects (residual stresses induced)

Machining dimension /tolerance error


2 30


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 fluid

Abrasives in solution in the process fluid (crystallisation)

Abrasives from the environment such as sand and dirt

Abrasives from the environment such as product

Adhesive 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 separate

Blistered carbon face from air trapped in carbon expanding and blowing out

Surface finish deterioration

Pump shaft out-of-roundness

Blistering (seal face sub-surface vaporisation)

Excessive start-up torque

Excessive shaft end play

Seal installation misalignment

Pump shaft misalignment to driver

Pump shaft bent

Shaft bent due to overhang because impeller is located too far away from the bearing

Selective leaching is picking up elements from the piping system and depositing them on the seal face

One 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 face

Damaged faces during delivery

Uneven clamping not 'equal and opposite' across the stationary face

One or both of the faces is being distorted by a temperature differential

Water hammer pressure surge

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

Oxidizing agents and halogens attack all forms and grades of carbon-graphite

De-ionized water can attack carbon seal

Chemicals attack carbon seal

Silicon carbide seal attacked by acidic liquid

Solvent flushed through pipes for cleaning attacked seal material

Poor / wrong carbon grade selected

Corrosion 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 face

Rotating face is not centered in the stationary face and is running off the edge of the stationary face

Dirt or solids are clogging the movable components

Foreign object has passed into the seal chamber and is interfering with the free movement of the seal

Solids have packed up in front of the inner seal in a "back to back" dual seal design

Seal face rocks due to installation misalignment

Vaporisation on seal faces

Pump shaft excess whip

Pump shaft excess deflection

Vibration 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))


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 ceramic

Excessive fluid pressure on seal


Excessive pressure velocity (high pressure at slow rotational speed)

Stress corrosion cracking

Barrier / quench fluid failure

The elastomer is swelling up under a carbon face.

The shaft is hitting the stationary face or the rotating seal face is hitting a stationary object

Product is solidifying between the faces and they are breaking at start up

Excessive vibration is causing the drive or anti-rotation pins to crack the face

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

Shaft / sleeve is oversize

Fretting corrosion between seal and shaft

A gasket or fitting is protruding into the stuffing box and touching seal component

Pump shaft end play

Trust movement


Thermal growth differential

Impeller adjustment towards wet end of pump opens seal faces

Product is vaporizing and separating the faces allowing solid material to blow across the lapped face

Dynamic elastomer not free to move due to oversize shaft

Dynamic elastomer not free to move due rough surface finish

Dynamic elastomer not free to move due to sticking to shaft from high surface temperature

Dynamic elastomer not free to move due to contaminants locking it in place

Chipper edges causing face separation

Spiral failure where seal component stick and cause internal twist

Springs stick and prevent dynamic movement

Seal as mishandled during 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

Set screws have come loose

Set screws corroded

Initial setting of seal incorrect and once experiencing a little wear the spring load has gone

Axial temperature growth of the shaft has altered the original setting

Shaft sleeve moved when the impeller was tightened to the shaft

Seal was set-screwed to a hardened shaft or sleeve and has slipped due to vibration

Spring has been painted and cannot compress fully

Cartridge seal static seal has jammed and preventing proper location of faces

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

Single 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 whip

Pump shaft excess deflection

Out-of-balance impeller

Fretting corrosion under seal (by axial movement transmitted to the seal)

Excessive elastomer temperature

Excessive fluid pressure

Installation error (elastomer damage)

Corrosive attack (incompatible chemical)

Water hammer

Compression set (extreme temperature operation causes elastomer elasticity memory loss)

Compression set (product is too hot)

Elastomer swollen by incompatible chemical product

Elastomer 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 installation

Shaft is corroded, damaged, or fretted under the elastomer

Seal body O-ring groove is damaged or coated with a solid material

Wrong lubricant was used at installation to aid fitting the elesomer on the shaft

Oxidizers can attack the carbon black in O-rings and other elastomers

Distorted sleeve or shaft

Fretting corrosion (axial movement transmitted to the seal)

Excessive elastomer temperature

Excessive fluid pressure

Installation error (elastomer damage)

Corrosive attack (incompatible chemical)


Compression set (extreme temperature operation causes elastomer elasticity memory loss)

Compression set (product is too hot)

Elastomer swollen by incompatible chemical product

Solids attached at dynamic elastomerand preventing it from moving

Elastomer 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 installation

Oxidizers can attack the carbon black in O-rings and other elastomers

Insufficient seal face compression

Installation error (wrongly located on shaft)

Installation error (mounting screws loosen)

Loss of spring tension

Foreign material contamination on faces

Uinbalanced seals in dual seal applications

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

The glue between the carbon and its metal holder is not compatible with the product

Differential expansion between 'pressed-in' carbon and its metal holder

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

Gland gasket has failed

Cracked bellows

Barrier / quench leck misdiagnosed as product leak

Contaminants in pumped fluid

Contaminants in barrier / flush fluid

Pumped fluid / seal material-of-construction chemical incompatibility

Thermal degradation of material-of-construction

Idle periods between use

Material flaw

Manufacturing flaw

Stress corrosion due to tooling marks

Corrosive attack

Seal installation misalignment

Pumped fluid contaminated with solids

Barrier / flush fluid contaminated with solids

Excessive pressure loading

Improper lubrication causes excessive torque

Excessive fluid pressure surges

Excessive fluid pressure on seal

Foreign material trapped between faces

Excessive pressure velocity (high pressure at slow rotational speed)

Insufficient seal face lubrication film thickness

Excessive squeeze on seal faces

Excessive seal swell

Seal extrusion

Metal-to-metal contact due to out of alignment

Seal 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, viscous

A gasket or fitting is protruding into the stuffing box and touching seal component

Foreign 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:

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

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 bearing

Lack of cleanliness before and during mounting operation

Ineffective seals

Lubricant contaminated by worn particles from brass cage

Lubrication contamination (wear particles)

Lubricant additives gradually been used up

Lubricant has lost its chemical lubricating properties

Lubricant loss through seal

Lubricant has leaked away

Lubrication 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 castings, etc)

Bent shafts

Skewed ring from burrs or dirt on bearing mounting surfaces and bearing abutment surfaces

Shaft shoulders which are not perpendicular to the bearing abutment surface

Locking nut faces which are not perpendicular to the bearing seating face

Non-concentric bores on which the bearings are mounted leading to an angular axis of rotation of the shaft and thus misaligning the rotating axis of the bearings

Reverse Loading Failure is one such failure which occurs due to the bearing getting loaded in the opposite direction in which it is intended to bear the load. This type of failure is quite common in angular contact and thrust bearings

Bad 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 ways

Inadequate or improper lubrication

Excessive preload on account of fits being too tight

Insufficient heat transmission from housing due to build-up of material and product over casing

Rapid cooling of housing causes shrinkage and reduction in clearance

Incorrect viscosity of the lubricant

Incorrect lubricant chemistry

Form 'varnish' residue and 'coke' at elevated temperature that destroys the ability of the grease or oil to lubricate the bearing

Oil level too low

Oil level too high

Plugged oil return holes

Over greased bearing

Under greasing bearing

Suction pressure too high and causing axial thrust

Out-of-balance rotating element

Hydrogen embrittlement or blistering by water within microscopic cracks on raceways and rolling elements

Insufficient clearance in labyrinth seals

Base frame distorted

Process temperature conducted along shaft

Normal aspiration as the pump cooled down, and the moisture laden atmosphere entered the bearing case

Axially mislocated shaft coupling

Grease or lip seals too tight

Brinell and False Brinell Hit during mounting / installation

Dented by self-weight load when standing-still

Dented by vibration impact loads when standing-still e.g. machinery transported on rough roads

Situated close to machinery producing vibrations

Mounting pressure applied to the wrong ring during installation

Excessively hard drive-up on tapered seating during installation

Overloading while not running

Excessive preload on account of fits being too tight

Smearing on installation produces microscopic surface cracks

Stuffing box packing overtightened

Creeping Slippage Ring fit is oversize

Ring fit is worn

Fretting corrosion

Smearing rollers and raceways Smeared roller ends from sliding under heavy axial loading and with inadequate lubrication

Roller acceleration on entry into the loaded zone due to too much clearance

Load is too light for the speed

As bearings are being mounted, the ring with the roller and cage assembly is entered askew, without being rotated during insertion

Blows applied to the wrong ring or heavy preloading without rotating the bearing

External surfaces of heavily loaded bearings from movement of the bearing ring relative to its shaft or housing

Slip fit is too loose on sliding ring

Smearing Thrust Ball Bearings due to rotational speed is too high in relation to the loading. The centrifugal force then impels the balls to the outer part of the shallow raceways. There the balls do not roll satisfactorily and a great deal of sliding occurs at the ball-to-raceway contacts

Surface Distress Cracks Inadequate lubrication

Improper lubrication

Corrosion - Deep seated rust Presence of water, moisture over a long period of time

Presence of corrosive substances

Corrosion - Fretting Fit too loose

Shaft seating with errors of form

Housing seating with errors of form

Electrical Erosion Electrical fluting due to passage of electric current through rotating ring

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

Earthing problem in equipment

Raceway Spalling Excessive preload on account of fits being too tight

Excessive drive-up on a tapered seating

Excessive preload adjustment e.g. Single row angular contact ball bearings or taper roller bearings

Temperature differential between inner and outer rings too great

Foreign particles in the lubricant, metal particles from within the system, etc allow wear particles to be jammed between roller and race causing impact stress

Cavitation induced stress overload

Vibration induced stress from running off BEP

Clearance 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 tightened

Incorrect mounting, which results in axial loading, e.g. excessive preloading of angular contact ball bearings and taper roller bearings.

The 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 mounted

Fatigue 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, after a time leading to cage fracture)

Fatigue cracks (run at speeds in excess of cage design subjecting it to heavy forces of inertia that may lead to fractures)

Fatigue cracks (bearing rings are fitted out of alignment with each other, the path of the rollers take an oval configuration. If the cage is centred on the rollers, it has to change shape for every revolution it performs)

Severe acceleration and retardation, in conjunction with fluctuations in speed cause forces of inertia. These give rise to considerable pressure on cage contacting surfaces, with consequent heavy wear

Inadequate lubrication

Abrasive particles

Fragments of flaked material or other hard particles may become wedged between the cage and a rolling element, preventing the latter from rotating round its own axis

Bearing is severely misaligned

Seized Bearing Metal to metal contact cause micro-welding

Clearance tightness causes lack of rolling element rotation

Inadequate 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 contaminant

Rolling element jammed and not rolling due mechanical stress

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

Lock nut came loose

13 129

Category

Lube contamination by inclusion


Lube contamination by ingress



Lube chemical degradation


Lubricant loss

Lubricant loss





Lubrication contamination (sand and material from within castings, flaking protective coatings, rust from inside castings, etc)Lube contamination by ingress

Installation error

Skewed ring from burrs or dirt on bearing mounting surfaces and bearing abutment surfaces Installation error

Shaft shoulders which are not perpendicular to the bearing abutment surface Installation error

Installation error

Non-concentric bores on which the bearings are mounted leading to an angular axis of rotation of the shaft and thus misaligning the rotating axis of the bearingsInstallation error

Reverse Loading Failure is one such failure which occurs due to the bearing getting loaded in the opposite direction in which it is intended to bear the load. This type of failure is quite common in angular contact and thrust bearingsInstallation error

Material strength failure

Solids were introduced into the system during the assembly process because of a lack of cleanliness Lube contamination by inclusion

Installation error

Incorrect fits and tolerance







Insufficient heat transmission from housing due to build-up of material and product over casing Temperature change

Temperature change



Form 'varnish' residue and 'coke' at elevated temperature that destroys the ability of the grease or oil to lubricate the bearingLube chemical degradation

Lubricant loss

Lubricant excessive

Lubricant excessive

Lubricant excessive

Lubricant insufficient

Operational induced stress

Unbalance

Hydrogen embrittlement or blistering by water within microscopic cracks on raceways and rolling elements Lube contamination by ingress



Temperature change

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

Installation error

Installation error

Installation error


Dented by vibration impact loads when standing-still e.g. machinery transported on rough roads Operational induced stress


Installation error

Installation error



Installation error

Installation error




Smeared roller ends from sliding under heavy axial loading and with inadequate lubrication Incorrect fits and tolerance

Roller acceleration on entry into the loaded zone due to too much clearance Incorrect fits and tolerance


As bearings are being mounted, the ring with the roller and cage assembly is entered askew, without being rotated during insertionInstallation error

Blows applied to the wrong ring or heavy preloading without rotating the bearing Installation error

External surfaces of heavily loaded bearings from movement of the bearing ring relative to its shaft or housing Incorrect fits and tolerance


Smearing Thrust Ball Bearings due to rotational speed is too high in relation to the loading. The centrifugal force then impels the balls to the outer part of the shallow raceways. There the balls do not roll satisfactorily and a great deal of sliding occurs at the ball-to-raceway contactsOperational induced stress








Electrical induced damage





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


Foreign particles in the lubricant, metal particles from within the system, etc allow wear particles to be jammed between roller and race causing impact stressLube contamination by ingress











Distorted bore of Plummer blocks from mounting on an uneven base becoming oval when the base bolts are tightenedInstallation error

Incorrect mounting, which results in axial loading, e.g. excessive preloading of angular contact ball bearings and taper roller bearings.Installation error


Axial 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 mountedInstallation error

Installation error


Installation error


Fatigue cracks (Smearing during installation causes surface crack initiation) Installation error






Installation error

Fatigue cracks (vibration forces of inertia are so great as to cause fatigue cracks to form in the cage material, after a time leading to cage fracture)Unbalance

Fatigue cracks (run at speeds in excess of cage design subjecting it to heavy forces of inertia that may lead to fractures)Operational induced stress

Fatigue cracks (bearing rings are fitted out of alignment with each other, the path of the rollers take an oval configuration. If the cage is centred on the rollers, it has to change shape for every revolution it performs)Installation error

Severe acceleration and retardation, in conjunction with fluctuations in speed cause forces of inertia. These give rise to considerable pressure on cage contacting surfaces, with consequent heavy wearOperational induced stress



Fragments of flaked material or other hard particles may become wedged between the cage and a rolling element, preventing the latter from rotating round its own axisLube contamination by ingress

Installation error





Design error




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

Installation error

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

Wear

Wear caused by abrasive particles

Wear caused by inadequate lubrication

Wear caused by vibration

Indentations

Indentations caused by faulty mounting or overloading

Indentations caused by foreign particles

Smearing

Smearing of roller ends and guide flanges

Smearing of rollers and raceways

Raceway smearing at intervals corresponding to the roller spacing

Smearing of external surfaces

Smearing in thrust ball bearings

Surface distress

Corrosion

Deep seated rust

Fretting corrosion

Damage caused by the passage of electric current

Flaking (spalling)

Flaking caused by preloading

Flaking caused by oval compression

Flaking caused by axial compression

Flaking caused by misalignment

Flaking caused by indentations

Flaking caused by smearing

Flaking caused by deep seated rust

Flaking caused by fretting corrosion

Flaking caused by fluting or craters

Cracks

Cracks caused by rough treatment

Cracks caused by excessive drive-up

Cracks caused by smearing

Cracks caused by fretting corrison

Cage damage

Vibration

Excessive speed

Wear

Blockage

Other causes of cage damage

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

Wear caused by abrasive particles

Wear caused by inadequate lubrication

Indentations caused by faulty mounting or overloading

Indentations caused by foreign particles

Smearing of roller ends and guide flanges

Smearing of rollers and raceways

Raceway smearing at intervals corresponding to the roller spacing

Damage caused by the passage of electric current

Flaking caused by oval compression

Flaking caused by axial compression

Flaking caused by deep seated rust

Flaking caused by fretting corrosion

Flaking caused by fluting or craters

Cracks caused by rough treatment

Cracks 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 axial

Shaft misalignment parallel

Shaft misalignment angular

Shaft thermal expansion

Severe distortion under maximum instantaneous torque (wind-up)

Erratic/pulsating/high-inertia loads

Excessive back-lash within coupling for shock loads

Rotational speed is beyond design RPM

Loosening of the coupling's fastener to the shaft

Changed assembly gap between hubs of the coupling

Damaged or broken components

Bore machined askew

Bore machined non-concentric

Excessive shaft end float

Bent shafts, excessive run-out

Excess back-lash between coupling parts / components

Material-of-Construction incorrect for duty loads / torque

Hub Damage Shaft out-of-round or incorrect form

Split / cracked due to improper interference fit

Movement of the hub on the shaft

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

Shaft not straight

Shaft under bore nicked, hammer-rash or damaged

Axial misalignment

Concentrated heat on the hubs cause distortion

Keyway Failure Excessive shaft interference fit

High torque load transmitted through the key

Excessively loose fitting key allows high impact on start / reverse

Key Failure Excessively loose fitting key allows high impact on start / reverse

Improper key material selected

Corrosion

Chemical attack

High torque load transmitted through the key

Elastometric Element Failure Excessive torque loading

Atmospheric contamination / deterioration

Chemical attack

Overload

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

Coupling out-of-balance

Cracked due to rubber hardening from chemical contamination

Elastomer material has limited service life

Excessive 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 fatigue

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.

Insufficient fastener tightening torque

System torsional vibration

Reversing loads which exceed the flange joint capacity

System was subjected to unexpected overloads

Elongated bolt holes due to fastener impact (fastener loosened off)

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

Cyclic fatigue life exceeded

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

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Sources of Information:http://pt.rexnord.com/products/e-catalog/catalog/CachedImages/0000001/t004_r00171_v0.pdf

http://motionsystemdesign.com/mag/couplings_shafts/

Flexible Drive Couplingfailure mechanism (Gear Coupling)

Gear couplings, frictional movment on teeth due to misalignment

Gear couplings, loss of lubricant film

Gear couplings, not relubricated as maintenance

Gear couplings, contaminated lubricant

Severe distortion under maximum instantaneous torque (wind-up) Gear couplings, sleeve seal cage end ring failures may result from high misalignment, improper gap setting and/or hub axial float

Gear couplings, teeth lock-up due to excessive misalignment

Gear couplings, teeth lock-up due to excessive misalignment

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



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 fatigue


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-torque

Jaw Coupling, elastomer compression set from normal use

Jaw Coupling, excessive hub spider leg wear

Jaw Coupling, shaft radial misalignment

Jaw Coupling, shaft angular misalignment

Jaw Coupling, shaft axial misalignment

Jaw 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 fatigue


Flexible Drive Couplingfailure mechanism (Disc Coupling)

Disk couplings, cracking or breaks in the individual disk packs or bolts

Disk couplings, check for loose disk pack bolts and/or nuts

Disk couplings, disk cyclic fatigue due to excessive misalignment


Electric Motor Electric Motorfailure modes failure mechanism

Over-Current Draw Mechanical overload

Poor power conditioning

Excessive effective service factor

Over-voltage

Voltage unbalance

Brushes fail open

Voltage surgesDrop a phase due to winding failure

Fail to Start Power provider interruption

Under-voltage

Cable mechanically damaged

Cable burnt-out from overload

Cable connection overheated

Motor starter failure

Rotor Damage Winding is saturated with water (ingress of water)

Aspirated moisture (ingress of humidity)

High operating temperature

High ambient temperatureVariable frequency drives are employed, insulation life expectancy will be reduced

Chemical ingress degrades internals

Dirt build-up on cooling fins

Frequent stops and starts

Starting method cause high starting loads

Rotor faults, casting voids

Rotor faults, broken rotor bars

Insulation-to-ground faults

Air gap faults, including eccentric rotors

Overloading (load demands exceeding the rating of the motor)

Improper matching of motor to load (inertia matching)

Loose internal wiring connections

Vibration / mechanical looseness

Excessive starts and reversals

Unequal voltage between phases

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

Nuisance tripping

Transient voltage peaks

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

Dirt build-up on cooling fins

Balance weight came loose and struck the winding

Winding is saturated with water (ingress of water)

Aspirated moisture (ingress of humidity)

Moisture over motor allows short-circuit current to earthTerminal bolting to wrong connection

Terminal bolting loose connection

Loose internal wiring connections

Insulation-to-ground faults


Excessive starts and reversals


Nuisance tripping

Transient voltage peaks

Shorts between conductors or coils

Rotor Bar Failure Poor welded connection

Vibration due to misalignment

Vibration transmitted by nearby equipment

Vibration due to loose mountings

Vibration from out-of-balance

Frame distortion from softfoot

Bearing Failure Excessive radial or axial loading

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

Insufficient bearing lubricationExcess bearing lubrication

Lubricant is contaminated

Incorrect lubricant

Out-of-balance, rotor unbalancedOut-of-balance, balance weight lost

Induced vibration

Shaft misalignment

Wrong coupling type or installationBelt misalignment

Incorrect belt tension

Defective bearing housings

Defective shaft mounting

Bad mechanical fitsHigh static loading when stopped

Frame warpage

Broken mounts

Base plate distortion

Missing or deteriorated grouting

Foundation deterioration

Inadequate foundation size and design

Bad or worn shaft

Shaft, bent and run-out excessive

Shaft, axial float excessive

induced mechanical vibration

Overhung loads

Mechanical resonance

Rotor deflection

Shaft Broken Stress raiser, corrosion

Stress raiser, chemical attack


Locked rotor

Bending/ torsional fatigue from misalignment

Massive imposed overload

Keyway fatigue

Improper keyway design

Inadequate shoulder fillet radius

Manufacturing defects (residual stresses induced)


Fretting and pitting corrosion

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5

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



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



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


Pump Set Base Frame Pump Set Base Framefailure modes failure mechanism

Loose on Foundation Hold-down bolt nuts loose

Hold-down bolts corroded

Hold-down bolts pulled out of concrete

Excessive machine vibration

Warped Frame Foundation not level

Pulled-down unequally on hold-down bolts

Impact by object

Corroded Frame Chemical attack

Water sitting in contact with frame

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1 2

Pump Set Foundation

failure modes

Broken Foundation

Corroded Foundation

Foundation Moves

3

1

Pump Set Foundation

failure mechanism

Impact by object

Concrete shrink cracks

Foundation support flexs

Ground conditions unsuitable

Chemical attack

Ground strength weak

Undersize foundation

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Documents

Centrifugal Pump Set Failure Modes