Seal Failure Analysis Evaluation of Seal Components
Seal Failure Analysis Evaluation of Seal Components
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This Fluid Sealing Association Knowledge Series training provides examples of physical characteristics of failed seal components and the failure mode indicated by their condition. Included are evaluations of:
▪ Seal Face wear patterns
▪ Seal Face Examinations
▪ Elastomer Degradation
▪ Drive Mechanism Failures
▪ Seal Face Wear Patterns
▪ Seal Face Wear Examinations
▪ Elastomer Degradation
▪ Drive Mechanism Failures
Seal Face Wear Patterns
Normal wear
Wear track is even, centered, and not much wider than the narrow face (seal is running smoothly and true about the shaft)
Seal Face Wear Patterns
Narrow wear pattern
▪ Wear track is narrower than the narrow face
▪ Indicates face deflection resulting in reduced contact/sealing face area
▪ Possible causes:
➢ Effects of heat & pressure on face material & geometry
▪ Possible remedies:
➢ Reduce the pressure in the seal chamber
➢ select a seal design with adequate pressure limits.
Seal Face Wear Patterns
Wide wear pattern
▪ Wear track is wider than the narrow face
▪ Indicates shaft/sleeve runout
▪ Possible causes:
➢ Worn bearings
➢ Mis-centered sleeve
➢ Equipment misalignment
➢ Bad bearings
➢ Shaft deflection
➢ Bent shaft
➢ Pump cavitation
▪ Possible remedies:
➢ Address equipment repairs
➢ Select a seal designed for excessive motion and conditions
Seal Face Wear Patterns
No wear pattern
▪ No wear track indicates seal faces are not contacting, therefore there is likely high leakage & no sealing interface
▪ Possible causes:
➢ Mating face is hung up and not tracking the seat possibly due to improper installation dimension (component seal)
➢ Rotary component is not rotating with shaft
▪ Possible remedies:
➢ Correct the installation
➢ Eliminate slipping of the rotary drive
➢ Correct interference of the rotary with the seal chamber or gland
➢ Tighten gland bolts evenly, and make sure, that the stationary face is not cocked
➢ Consider a seal design with a flexibly mounted stationary face
Seal Face Wear Patterns
Uneven wear pattern
▪ This example shows a non-concentric wear track, where the narrow face is rotating off-centered from the wider stationary face. Because contact is even, seal was likely performing adequately.
▪ Possible causes:
➢ Mis-centered gland
➢ Mis-centered seal chamber
▪ Possible remedies:
➢ Realign the equipment
➢ Check the seal and gland centering
➢ Inspect for buildup around the seal
Seal Face Wear Patterns
Deep wear pattern on the hard face
▪ Indicates narrow face wore into wide face
▪ Possible causes:
➢ Narrow face material too hard, relative to wide face material
➢ Heavy abrasives from process tracked between faces or embedded into soft face
➢ Inadequate lubrication
▪ Possible remedies:
➢ Provide adequate flush to exclude abrasives from the seal chamber
➢ Change seal design (such as, dual versus single)
➢ Use hard faces
➢ Prevent crystallization of the sealing fluid
Seal Face Examination
Heat checking
▪ Indicates poor lubrication at sealing interface
▪ Possible causes:
➢ Dry-running possibly due to:
▪ Vertical installation where sealing fluid is not getting to seal chamber
▪ Loss of flush
▪ Air trapped in seal chamber
➢ Poor lubrication of seal interface possibly due to:
▪ Vaporization of the sealing fluid
▪ Excessive pressures or velocities
▪ Inadequate cooling
Seal Face Examination
Heat checking
➢ Possible remedies:
▪ Reduce the temperature by flushing or cooling the chamber
▪ Increasing the seal chamber pressure to obtain a minimum vapor pressure margin of 175 kPa (25 psi)
▪ Change seal face materials
▪ Change seal design
▪ Eliminate dry-running by venting vertical installations to remove trapped air and assuring that fluid is present in seal chamber prior to start-up
Seal Face Examination
Cracked hard face
▪ Indicates thermal or mechanical shock/failure
▪ Possible causes:
➢ Thermal shock: dry-running seal heats up and cracks, or perhaps quenched quickly with cold process or flush
➢ Mechanical shock: face overloaded possibly due to:
▪ Sleeve slipping on shaft
▪ Sleeve/housing change in relative position possibly due to:
▪ Bearing failure/motion
▪ Excessive thermal growth
▪ Equipment clog/clearing
Seal Face Examination
Cracked hard face
➢ Possible remedies:
▪ Use caution in handling seal rings
▪ Avoid overtightening clamped units
▪ Avoid dry running
▪ Provide cooling
▪ Change face materials
▪ Address any equipment causes
Seal Face Examination
Chipped edges
▪ Indicates mechanical material failure
▪ Possible causes:
➢ Flashing of sealing fluid, causing faces to open and close between bursts/flashing of sealed fluid
➢ Pump cavitation caused by improper pump or system adjustments for the pumped fluid
➢ Other system source of vibrational type mechanical shock
➢ In welded metal bellows designs, damage to the face can result from nutation or coning of the seal rings
➢ Shaft deflection
Seal Face Examination
Chipped edges
▪ Possible remedies:
➢ Restore equipment to manufacturer's specifications
➢ Avoid cavitation,
➢ Cool the seal chamber and provide adequate pressure in the seal chamber to avoid flashing
➢ Change face materials
➢ Improve face lubrication
➢ Use a seal design that includes a vibration dampener
➢ Change seal face materials
Seal Face Examination
Flaking or Peeling
▪ Indicates delamination of coating or plating from face
▪ Possible causes:
➢ Poor compatibility of plating to base face material (example: plating expands at different rate than base material)
➢ Chemical attack
➢ Thermal attack
➢ Poor adhesion of plating to base face material
▪ Possible remedies:
➢ Provide adequate cooling
➢ Change materials
➢ Change to a solid face material
Seal Face Examination
Blistering of Seal Face
▪ Indicates exceeding the seal material limits
▪ Pitting and blistering usually occur on the wearing face. Corrosion and spalling may occur on all exposed surfaces of the seal ring.
▪ Possible causes:
➢ Exceeding the PV limits (pressure, velocity, viscosity, and fluid type play roles in this type of failure)
➢ Poor material choice for fluid properties
➢ Sealing fluid being forced from a porous seal ring due to rapid temperature changes
Seal Face Examination
Blistering of Seal Face
▪ Possible remedies:
➢ Provide adequate cooling
➢ Change materials
➢ Avoid rapid temperature changes (dry-running) when using viscous sealing fluids
Seal Face Examination
Wire Drawing on seal face
▪ Indicates little or no face contact, allowing erosion due to high flow across faces and/or abrasives in flow.
▪ Often seen at low spots creating gaps between seal rings when left idle while under pressure
▪ Possible causes:
➢ Support surface of seal ring is uneven, causing distortion (damaged surface, contamination, excessive bolt torque in the case of a gland plate, or the split line of an axial split case pump being uneven)
Seal Face Examination
Wire Drawing on seal face
▪ Possible causes:
➢ Mating face is hung up (secondary seal friction, clogged springs, wedged debris, improper installation (component seal)
➢ Motion of shaft has exceeded seal capability
➢ Seal has exceeded its life, has worn, and no spring travel is left
▪ Possible remedies:
➢ Check the support surface of the seal ring seat for the cause of distortion
➢ Correct other potential causes for gaps between seal faces (see above)
Seal Face Examination
Abrasive wear
▪ Indicates abrasive process fluid is migrating between faces
▪ In split seals, could indicate mating face split misalignment
▪ Possible causes:
➢ Seal face breakdown resulting from inadequate flush conditions, or dryrunning of two hard faces
➢ Loss of flush
➢ Secondary seal friction
➢ Clogged springs
➢ Wedged debris
➢ Face materials too soft
Seal Face Examination
Abrasive wear
▪ Possible remedies:
➢ Eliminate the abrasives through the use of an abrasive separator, if applicable
➢ Use an external flush if dilution of the process is acceptable
➢ Use two hard faces
➢ If abrasive wear of two hard faces occurs eliminate the dry-running condition through a change in pump operation
➢ In a split seal, the face split alignment should also be checked and addressed, if needed
Seal Face Examination
Erosion of rotating primary ring
▪ Result of an abrasive laden seal flush, which is directed at the damaged part, or excessive velocity of the flush coming into the seal chamber. If the ring is rotating, then a groove will be generated around it. If the ring is stationary, then the damage will be limited to a single point around the circumference.
▪ Possible causes:
➢ Face selection is too soft
➢ Loss of flush
➢ Ineffective flush
Seal Face Examination
Erosion of rotating primary ring
▪ Potential Remedies:
➢ If the damaged ring is made of carbon, then replace it with a hard face material if appropriate
➢ Redirect the flush away from the ring.
➢ If the cause is excessive velocity, then add an orifice to restrict the flow rate of the flush, or use a distributed flush
Elastomers
▪ Elastomers can be used as O-rings, boots, bellows, gaskets and other secondary seals.
Look for:
➢ Swelling
➢ Cuts and abrasion
➢ Hard and cracked
➢ Extrusion
Elastomers
Swelling
▪ Possible causes:
➢ Chemical incompatibility
▪ Possible remedies:
➢ Select an elastomer that is suitable for the pumped product
Elastomers
O-ring cuts and nicks
▪ Possible causes:
➢ Sharp edges on equipment or seal components
▪ Possible remedies:
➢ Rework contact surfaces to meet seal manufacturer's specifications for smoothness
➢ Remove sharp edges and raised material from previously used set screws
➢ If practical, temporarily place tape over threaded sections of equipment shafts and provide chamfers on the shaft or sleeve
Elastomers
Hard or cracked elastomer bellows
▪ Possible causes:
➢ Chemical incompatibility
➢ Excessive heat
▪ Possible remedies:
➢ Cool the seal chamber
➢ Select an elastomer with a higher temperature rating
➢ Select an elastomer that is chemically compatible with the pumped product
Elastomers
Extruded O-ring
▪ Possible causes:
➢ Excessive pressure
➢ Excessive temperature
➢ Extrusion gaps too large or out of specification
➢ Chemical incompatibility
➢ Excessive vibration
▪ Possible remedies:
➢ Reduce pressure
➢ Cool the seal chamber
➢ Use a backup ring
➢ Change seal design or dimensions
Elastomers
Extruded
O-ring ▪ Possible remedies:
➢ Change O-ring material to a higher durometer (hardness) after consulting with the seal manufacturer
➢ Select an elastomer that is chemically compatible with the pumped product
➢ Eliminate sources of excessive vibration
Elastomers
Compression set
▪ Possible causes:
➢ Excessive heat
➢ Chemical incompatibility
➢ Over compression
▪ Possible remedies:
➢ Cool the seal chamber
➢ Change the elastomer
➢ Reduce pressure
Elastomers
Mechanical damage and wear
▪ Possible causes:
➢ Excessive motion
➢ Poor finish on mating surface
▪ Possible remedies:
➢ Eliminate the runout condition
➢ Check the surface condition of the shaft or sleeve
Elastomers
Blistered and/or ruptured
▪ Possible causes:
➢ Explosive decompression (After a period of service under high pressure, if pressure is reduced too rapidly, entrained gasses expand and blow out and rupture the elastomer)
▪ Possible remedies:
➢ lower the rate of decompression
➢ Change the elastomer to a more resistant compound
Drive Mechanisms
Bellows fracture
▪ Examined for fracture, thermal discoloration, and chemical corrosion.
▪ Check equipment alignment and condition, installation, pump cavitation, vibration levels, and seal operating limits.
Drive Mechanisms
Contact of rotary parts with stationary components
▪ Examine for rubbing on their outside diameters for thermal discoloration, and chemical corrosion and pitting.
▪ Check equipment alignment, seal and chamber dimensions, seal design, installation, set screw settings, temperature limits, product buildup, and vibration levels.
Corrosion of metal parts
▪ Source of corrosion could be chemical or galvanic
▪ Change seal metallurgy if necessary
Wear on springs from undue axial motion or chemical attack
▪ Check equipment alignment
▪ Change metallurgy, spring design, or seal design
Drive Mechanisms
Wear on pins and drive lugs
▪ Wear or shearing may be evident on the parts, the body of drive casing, shaft or sleeve
▪ Check equipment alignment, runout of shaft, vibration, and torque limitations of seal design
Drive Mechanisms
Coking is a buildup of varnish or product sludge on the atmospheric side
▪ Result of chemical or thermal breakdown of a hydrocarbon sealing fluid as it crosses the seal face
▪ Coke can clog the seal and wear carbon seal faces and can be deposited on the rotary casing body and inside of the gland.
▪ Use a steam purge on the atmospheric side of the seal, flush from a clean cool source, cool the seal chamber, change face materials, or change to a heat transfer fluid with higher temperature limits
