Failure Analysis John Crane

7/29/2019 Failure Analysis John Crane

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PerformanceAnalysis ofMechanical Seals

KRL 12/02


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Performance Analysis

Design

Seal Pump

Support System

Bearing

Coupling

Flush

Installation

Seal Pump

Operation

Pump Support System

Flush System

Mechanical Seal Life isAffected by:


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Undesirable passage or leakage of fluid past

sealing components causing:

Dilution of a process stream

Poisoning of the environment

An immediate safety hazard

The actual threshold for "failure" criteria is defined

by the user or a governmental agency.

A Definition of Seal Failure



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Mechanical 24%

Operation 40%

Poor Fluid Circuit Design 19%

Incorrect Seal Selection 9%

Miscellaneous 8%

Classification of Seal Failures



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Failure Mode:Criteria, volume, when

System Status: Changes, modifications, damage

History:Run length, symptoms, trends, systeminfluences

System and Equipment Checks

Disassembly and Visual Inspection

Comprehensive Examination

Diagnostic Path



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Noise: Continuous or periodic

Visual: Carbon dust, leak volume

Temperature changes: Process, support,environment

Leakage: Continually, startup, static, during excursions

When: Startup, seasonal,

Changes: procedure, human, conditions, fluid

Failure frequency: Immediate, variable, diminishing

Notable Indicators on Site



7/83Surfanalyzer

Stylus


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Part isHigh

Part isLow

Perfectly Flat

Reference Line


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John Crane Test Lab

Scanning Electron Microscope


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Contact

Pattern

Mating Ring Primary Ring

Full Contact Pattern


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Contact Wider Than Width

of Primary Ring Face

Drive NotchWear

Wide Contact Pattern


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Drive Notch Wear


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Off Center Wear Track


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Mating Ring Damage fromOff Center Shaft


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Sleeve Damaged byOff Center Shaft


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Sleeve Damaged byExcessive Shaft Runnout


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Sleeve Damage byExcessive Shaft Runout


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Heavy toModerate Contact

Light Contact

Possible

Edge Chipping

Rotation Due to

Pressure

Heavy Outside Diameter Contact


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LightContact

Heavy toModerate Contact

PossibleChipping

Rotation Due to

High Temperature

Heavy Inside Diameter Contact


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Mating ring misaligned, due to a high drive pin,or upset on support surface. Look for wear at

drive notches on the primary ring.

One High Spot on Mating Ring Face


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Full contact through approximately 270 as seen on seal ring face.

Pattern fades away at low spot. The primary ring may show "wire

drawing" in a position over the mating ring low spot.

Wear Track Through 270

The seal ring is being

distorted mechanically

or is not flat


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Wire Draw on Carbon Face


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Two large contact spots are noted while the pattern fadesaway between these areas.

Two High Spots on Mating Ring

The mating ring

is being distortedmechanically.

Pump casing split

line misalignment

is often the

cause.


26/83

Contact spots noted at gland stud locations on mating ring.Mating ring is being distorted mechanically by uneven gland surface.

Most often the gland nuts have been over tightened.

No Contact

Contact at

High Spots

Near Gland BoltsNo Unusual Wear

Gland Bolt Distortion


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Many small radial surface cracks through the entire wear track,normally visible to the eye. Squealing or popping sounds will often

be observed during operation.

Heat Checking of Entire Face

Caused by inadequate

fluid film at the seal

interface. This usually

results from inadequatevapor pressure margin

or flush rate.


28/83

Heat Checking and Pullouts


29/83

Thermally distressed area on seal face, located opposite ofthe flush port location.

Insufficient flush rate is most likely cause.

Undamaged Surface

at Flush Inlet

Heat Checked Area

Heat Checking 180 From Flush Port


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Patches of thermally distressed surface on face.

The sealed liquid, probably a light hydrocarbon, is

vaporizing at the seal interface.

Good Contact

Pattern

DistressedSurface

or Hot Spot

Patches of Heat Checked Surface


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High wear of seal face through 360 showing a phonographpattern appearance.

Abrasive Wear

Caused by

abrasiveparticles in the

process fluid or

from seal face

breakdown

resulting frominadequate flush

conditions.


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Abrasive Wear on Carbon Face


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Abrasive Wear; Dry Run of SiC Face


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Abrasive Wear; Dry Run of SiC Face

200 X

100 X


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Abrasive Wear on TC Mating Ring


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A seal face has one or more (several) uplifts or Blisters.Some may have been pulled out leaving a shallow crater.

Normally associated with carbon materials.

Blistering

Caused by highstresses in the

interface which

exceed the rupture

strength of the face

material. Viscousfluids, including lube

oils, are most often

the cause.


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Blistering


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A blistered or peeled surface layer on faces which have beencoated with a hard material.

Bond Failure of Coated Seal Ring

Coated partsshould be used

with caution.

Chemical activity

and mechanical

action can easilydisturb the

coating.


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One or more cracks extend all the way through the part.

Fractured Seal Ring

Often caused by

mishandling or

improper assembly. Canbe caused by excessive

torque, thermal shock,

mechanical (contact)

loading, or uneven

loading of brittle face

materials.


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Extensive erosion of a component at a location that is

exposed to process fluid.

Erosion of Seal Parts

An abrasive laden

seal flush which is

directed at the part(s)in question is a

common cause.

Trapped abrasives in

a seal chamber can

damage both pump

and seal

components.


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Erosion of Rotating Primary Ring


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Erosion of Stationary Mating Ring


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Material exhibits a rough matted appearance on surface

areas that are exposed to the process fluid.

Leaching

Caused bychemical attack of

one or more

phases of a multi-

phase material.


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Leaching of RBSiC Mating Ring


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Metallic materials exhibit a cracked, rough, or irregular

surfaces. Carbon materials may become soft.

Acids, caustics, chlorides, de-ionized water to name a few.

Look at weld zones, crevices, friction areas, springs, etc.

Corrosive Chemical Attack


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Chemical Attack


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Chemical Attack


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A formation of hard, brittle material between seal and shaftsleeve that may impede free movement of the seal.

Caused by oxidation or stripping of hot hydrocarbon fluids

in the presence of seal face generated heat.

Application of a steam quench often cures this problem.

Hydrocarbon Coking

Solid Deposits Coking


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Hydrocarbon Coking


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Hydrocarbon Coking


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Grainy, often abrasive substance that may form on either sideof the seal; though typically on seal faces or the atmospheric

side. Abrasive wear on the seal faces or hang-up are the most

common observations.

Application of a liquid quench and possibly the use of hardseal ring materials are typical remedies.

Face Grooving

Dissolved Solids Deposits

Deposits


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Caustic Deposits


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Process borne polymers, solids, or contaminants that imbedin or adhere to areas on either side of a seal. Polymers may

form in the presence of seal face or pump generated heat.

An exclusionary flush plan or slurry style seal design may be

required.

Deposits

Suspended Solids Fouling


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Polymer Deposits (Reactor Application)


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Iron Oxide Deposits (Pipeline Application)


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Solids Fouling of Metal Bellows


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Fouling of Seal Face


58/83

Physical damage on O-rings, U-cups, V-rings or soft packing.

Normally caused by mishandling during assembly or a defect.

Cuts or Tears on Secondary Seal

Always inspect partsfor visible defects and

inclusions before

installation. Mounting

surfaces should not

have sharp edges orburrs that could cause

damage.


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A thin lip has formed on the entire ID or OD of the O-ring.Some materials may exhibit a shredded appearance.

Normally caused by application of pressure beyond the

limits of the design. Elastomer swell or expansion in a

confined space will often result in the same damage.

NormalRing

Lip

Shredding

O-Ring Extrusion


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O-Ring Extrusion


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Extrusion of Perfluoroelastomer


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Extrusion of Perfluoroelastomer


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O-ring Blowout (Reverse Pressure)


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One surface will be flat from material being abraded orchaffed. The ring may adhere to, or discolor the adjoining

surface.

Caused by sliding contact at a point where static contact

was intended.

FlatNormalRing

Worn Surface on O-Ring


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Worn ID Surface on Dynamic O-Ring


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Worn ID Surface on Dynamic O-Ring


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The part is hard and has several cracks, it is easily broken when

bent by hand. Damage may be on process side, atmospheric

side, or only in areas in contact with a specific part.

Temperature too high for material in use. Possible chemical

attack if the damage is evident only on its wetted side.

Hard, Cracked Elastomer


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Hard, Cracked Elastomer


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The part is permanently deformed with flat sides on its

sealing surfaces. The most common cause of O-ring failure.

Caused by designs that over compress the material,

resulting in a permanent set. Some elastomers are more

susceptible than others to compression set.

Flat

Surfaces

NormalRing

Elastomer Compression Set


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The part has become either softer or harder than normal. It may

have swelled, formed blisters, or portions have been severely

deteriorated.

Chemical Attack on Elastomer

When in doubt,

elastomers

should be

compared to an

experience

database or

subjected to an

immersion test.

Original

Size


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Fluoroelastomer Swell in Methanol


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Fluoroelastomer Decay in Ammonia


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Process Side Attack from HF Acid


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Atmospheric Side in HF Acid Service


75/83

Many small blisters and ruptures throughout the part caused

by explosive decompression.

A fluid which is a gas at atmospheric pressure, is being

sealed under high pressure and over time is absorbed into

the elastomeric material. When the pressure is released too

quickly the fluid which is trapped in the elastomer expands

rapidly resulting in damage to the part.

Blister Rupture

Blistered and Ruptured Elastomer


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Metal surface which has been in contact with the secondary

seal has a rough and worn appearance.

Fretting

Fretting occurs

when continuous

small movementsinherent to a

dynamic

secondary seal

occur while in

contact with ametal shaft sleeve

or shaft.


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Drive mechanisms are damaged; worn, distorted, or chipped.

Caused by excessive loads or relative movement between

drive components and the driven part.

Drive Dent Wear Sheared Drive Pin

Worn or Distorted Drive Components


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Springs are distorted, cracked, broken, or corroded.

Stress corrosion cracking, general corrosion, fatigue,

excessive shaft speed, and over extension or compression of

the spring.

Broken or Distorted Coil Springs


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Excessive vibration of the metal bellows.

Metal Bellows Separation at One End

Torsional fatigue;

usually at 1st or 2nd ID

weld from either end.

Normally caused by

inadequate face film

(stick-slip)


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Metal Bellows Fatigue (Magnified)


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Applied pressure greater than rating for the metal bellows.

Caused by pressure excursions or expansion of contained fluid.

Metal Bellows Over Pressurization


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Metal Bellows Over Pressurization

From ID

Normal

From OD


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The bellows has cracks in one or more locations at any point

on the bellows, normally at or near a weld. May only bedetectable in a leak testing device.

Stress corrosion cracking is a common cause.

Cracks in Metal Bellows

Documents

Failure Analysis John Crane