asme seal

8/4/2019 asme seal

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©John Crane Inc. 2005

Mechan ical Seals

Frank HuntingtonSenior Regional EngineerJohn Crane Inc.Norcross, [email protected]


Agenda

How seals function

Dual seals

• Pressurized (Double seals)

• Non-pressurized (Tandem seals)

• Dual seal support systems

Seal system troubleshooting

Seal installation

Common seal failure examples

Questions


A narrow gap must bemaintained in order to allow alubricating film to exist, whileminimizing the rate of leakage

A typical seal face film thicknessis 10-50 μ-in (micro-inches).

A typical piece of paper is5,000 μ-in thick.

Minimizing Leakage

Most seal faces are producedwith a finished flatness of 2helium light bands. Thiscorresponds to 23.2 μ-in.

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Maintaining Flatness

Heat

Heat that is generated byfriction at the faces can resultin distortions that will affect

face flatness

A part that is hotter at one endwill expand more at that end

The result is a larger gap at theface outer diameter


Maintaining Flatness

Pressure

Depending on design,pressure can result in thedeflection of a part, having anaffect on face flatness

The most common distortion isshown here

The result is a closed OD,which starves the face oflubricant


FlushMaximizes performance and extends seal life.Removes heat generated at faces.Provides cool clean lubricating liquid.

Removing Heat

Flush Injection

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Common Single-seal flush plans


Process

Buffer Atmosphere P r e s s u r e

Unpressurized(Tandem)

Dual Unpressurized Seal


Dual Unpressurized: P1 > P2

P2

Buffer Fluid

P1

Process Buffer Atmosphere

Dual Unpressurized Seal

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Process Barrier

Atmosphere P r e s s u r e

Pressurized(Double)

Dual Pressurized Seal


Dual Pressurized P2 > P1

Process Barrier Atmosphere

P2

Barrier Fluid

P1

Dual Pressurized Seal


Common Dual-seal support systems

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Barrier/ Buffer Fluids

Provides all cooling and lubrication for outer seal

May provide some cooling of inner seal

If pressurized (barrier), provides lubrication of inner

seal


Trouble Shooting

Identifying conditions that mayadversely affect seal performance

Process system

Primary equipment

Auxiliary equipment

Seal support system(s)

Operation


Trouble Shooting

Classification of seal failures

Operation

40%

Mechanical

24%

Fluid circuit

19%

Selection

9%

Other

8%

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Centrifugal Pump Operation

Operating at high flow

Capacity (GPM)

Efficiency

H - Q

N P S H

R

H e a d

( F e e t )

RisksCavitation (lack of NPSHA)

Hydraulically induced shaftdeflection

Accelerated bearing wear


Centrifugal Pump Operation

Operating at low flow

Capacity (GPM)

Efficiency

H - Q

N P S H

R

H e a d

( F e e t )

RisksIncreasing temperature rise

Suction recirculation (vibration)

Hydraulically induced shaftdeflection

Accelerated bearing wear

In GeneralNever operate below 15% of

BEP

Be aware of designs requiring

higher minimum flow (somemay be 80% of BEP)

POSSIBLE CAUSES CORRECTIVE ACTION

Worn bearings

Excessive shaft runnout

Bent shaft

Excessive vibration

Restore equipment tomanufacturer’s standards

Operate equipment understable conditions

.140”. 095”

Wide Wear Trackon Mating Ring

WIDE WEAR TRACKON MATING RING

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DEEP GROOVEON SEAL FACE

Inadequate lubrication

Abrasives in process fluid

Flush seal with a fluid with goodlubricating qualities at an adequate

flow rate

Consider face materials that canwithstand abrasive particles

Prevent crystallization of

process fluid


FACE BLISTERINGand PULLOUTS

Process fluid too viscous forthe face material

Adhesive condition causedby fluid physical property

change in the interface

Provide adequate cooling

Change face materials


FRACTURED orCRACKED SEALFACE

Thermal shock

Mechanical shock or impact

Avoid uneven or overtightening of fasteners

Maintain consistent flush toseal

Determine cause of mechanicalshock or impact

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METAL BELLOWSWELD FAILURE

Torsional fatigue resultingfrom inadequate facelubrication

Excessive vibration

Apply adequate, continuouslubricating flush to seal

Maintain equipment vibrationat acceptable level


CHIPS, CRACKSin SEAL RING

Mishandling of parts

Excessive breakaway friction

Follow proper installation

procedure

Change drive system design


O-RING SWELL

NormalSize

Swelled

Chemical attack Change elastomer to one

appropriate for the fluid beingsealed

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ELASTOMER withCUTS and NICKS

Improper installationtechnique

Sharp steps/surface breakson mounting surface

Use chamfers on shaftand sleeve steps

Remove sharp edges atkeyways, threads, etc.



Sealing Solutions

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