MechanicalSealTroubleShootingGuide

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Bell & Gossett Centrifugal Pumps

Mechanical Seal Failure

Troubleshooting Guide

Table of Contents

Section I – Mechanical Seal Failure Diagnostic Flow Chart

Section II - Mechanical Seal Failure Troubleshooting Check List

Section III - Mechanical Seal Failure - Typical Modes of Failure

September 8, 2003

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Normal Seal Service LifeVaries per application.

1Abnormally Short

Term Seal Life.Identify seal

installed in pumpVia serial number

Premature Seal Failure?Identify seal service life

2Identify fulloperating

conditions.

3Investigate pump

service/maintenance

history

4System water

quality & test onglycol

applications

Abnormal?

Normal?

Continued

Section IMechanical Seal Failure Diagnostic Flow Chart

Procedure

Seal life normal or abnormal? Identify how many operating hours the seal has runtrouble free. Seal life can vary dramatically with operating conditions andapplication. A major seal vendor has advised that normal seal life on elastomerbellows seals can reach up to 26,000 operating hours under ideal conditions. Thoseconditions require a properly installed seal operating consistently in fresh cleanwater at ambient temperatures, and correct pressure / velocity limitations. Anyvariance from these conditions will greatly reduce seal life.

(1) Identify the part number of the seal currently installed via pump serial number ororder number. Determine if the correct seal was supplied with the pump for theapplication. Refer to B&G Sales Bulletin 4976 “Mechanical Seal SelectionGuidelines” published 11/2000.

(2) Identify pump operating conditions, application type, fluid type, chemicaltreatment, temperature, and pressures. Are there any other pumps in the system (inparallel, other loops etc) that are also having problems? Gather information on theapplication to check if the pump and seal are matched to the application. UseBulletin # 4976 dated 11/00 "Mechanical Seal Selection Guidelines" as a reference.

(3) Investigate the pumps service/maintenance history. Is this the original seal suppliedwith the pump? Were the seals installed correctly? What lubricant was used forinstallation? Refer to the pumps IOM for correct installation instructions.

(4) System water quality is often taken for granted. The quality of water mixed withglycol concentrate can have an enormous impact on seal life. Marginal qualitywater can lead to the development of scale, sediment, deposits or the creation ofsludge. Poor water quality can damage the system by depleting the corrosioninhibitor. Refer to Service Bulletin 4941 update issued with" Mechanical SealGuidelines" as stated above for minimum water quality. A simple test used by DowChemical Company to ensure water quality meets less than 100ppm of hardness canbe conducted in the field. Use a small sample bottle with 50% glycol and 50%water from the same source used to fill the system. Let the solution stand for 8-12hours shaking occasionally. If any whitish sediment forms, the water is to hard andshould not be used to fill the system.

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Mechanical Seal Failure Diagnostic Flow Chart Procedure Continued

Continued From Page 1

(5)

Perform a through visual inspection of all seal components. Using simplemagnification (5x – 10x magnifying glass or jeweler’s loupe) and an adequate lightsource, inspect all seal components. Use the attached checklist and typical seal failureillustrations to locate and document any suspicious component damage.Contact the B&G Service Department. Return suspected failed seal components forinspection and analysis if instructed.

(6)Request return of a system fluid sample to the B&G Service Department for analysis.Occasionally, the B&G Service Department requests that a fluid sample be returned sothat it can be sent out for a lab analysis. This process is costly and not always accurate.Problems include rapidly changing system fluid conditions that can lead to inaccurateresults. Chemical injection/slug feeding methods may cause varying chemicalconcentrations at the pump over time. Because of the inherent problems and costs of alab fluid analysis, we avoid this process if at all possible. We consider the condition ofthe mechanical seal faces and other components to be the only accurate measure tocause of failure.If a system fluid sample is required, use the following procedure to obtain the sample:

1. Fluid Samples should be taken from a valve located in the lowest point in thesystem piping.

2. The valve, the sample is taken from should be purged prior to collecting thesample.

3. The system fluid should be in circulation at the time the sample is taken, so thatany solids within the system stay in suspension.

4. The sample should be placed in a lab-approved sample-bottle and always labeled.

(7)Recommend alternate seal type and or fluid conditions. The B&G Service Departmenttypically writes a report where system fluid maintenance is recommended, and thecondition of the seal components are reviewed for cause of failure. If the standard(B&G) seal was first used, the Service Department may recommend the use of acarbon Vs tungsten carbide or silicon Vs silicon carbide face seals.

(8)Follow up with the B& G Service Department with the status of any changes made tothe system and how the pumps are performing.

5Request return ofparts to B&G for

inspection

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Recommendalternate sealtype and or FluidConditions

8 Follow up

With Status

6

Request return ofsystem fluid sample

for analysis

5Request return ofparts to B&G for

inspection

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Section IIMechanical Seal Failure Troubleshooting Check List

Date: Representative:Report completed by: Contact Name:

Phone Number: Fax Number:E-mail Address:__________________________________________

Basic InformationHow many operating hours has the existing seal been in service?

(1) Pump and Seal Information

Pump Series Serial Number Pump SizeBell & Gossett Order Number Config. NumberFor Inline Pump installations, what is the pump orientation? Vertical Motor Horizontal Motor

(2) Operating ConditionsPump ApplicationFluid DescriptionOperating Temperature Maximum Working PressureChemical Treatment TypeSystem pH*% Concentration Abrasive particulate in fluid based on PPM

(3) Service/Maintenance History

Is the failed seal the factory installed original?

If the failed seal is not the original fitted from the factory, did a B&G representative install the replacement, if so whatrepresentative?

Identify the lubricant used for installation of the replacement seal

(4) System Water Quality

If the system fluid contains water, what was the source? (I.e.: well, city, distilled, deionized)Results of the Simple Water Quality Test as described in procedure notes

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(5) Inspection of Failed Seal

Complete a full visual inspection using 5-10x magnification and good illumination. Document the following:Faces (I.E. Scoring, “Record Grooving” Heat Tracing)Elastomers (I.E. Heat Degradation, Hardening, Chemical Attack)Metallurgy (I.E. Pitting, Mechanical Failure)Additional Remarks

* System pH should be checked using accurate instrumentation. It is suggested to use a Hanna Pocket pHmeter, Model HI 98107 pHep or equivalent. The meter should have a range of at least 0.0 to 14.0 pH.

(6) System Fluid Sample

Retain the system fluid lab report, with this file.

(7) Recommendation of Alternate Seal Type

What alternate seal type or materials of construction were recommended?

What system maintenance was recommended?

Retain a copy of the recommendation made to the Representative with this file.

(8) Follow Up

Date of Follow-up:Status:

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Section IIIMechanical Seal Failure Troubleshooting - Modes of Failure

Components of a Typical Mechanical Seal

Possible Leak Paths of a Typical Mechanical Seal

Spring(Stainless Steel)

Elastomeric Bellows or O-Ring (EPR, Buna N, or Viton)

Rotating Primary Ringwith Matte Finished

Face(Usually Carbon)

Retainer(Brass or Stainless Steel)

Stationary Seat InsertWith Super Polished Face

Usually Ceramic, TungstenCarbide, or Silicon Carbide w/EPR,

Buna N orViton cup/o-ring

Spring Holder(Brass or

Stainless Steel)

Between ElastomericBellows and back sideof Primary Ring

Between StationarySeat insert and cupor O-Ring and SeatBoreBetween Primary Ring and

Stationary Insert FacesBetween Bellows or O-Ringand Shaft or Sleeve

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Mechanical Seal Failure Troubleshooting

Mode of Failure: Excessive Iron Oxide Deposits

Iron Oxide (Rust) Deposits

The above illustration is a water/glycol sample (red) in the bottom of a white pail. Note the sedimenton the bottom.

The above is iron oxide sediment circulating within a system. Iron oxide can be detrimental to seal life.Use a magnet to determine if iron oxide is present within a fluid sample.

Iron oxide limitations for seals used in B&G pumps with carbon/ceramic seal faces should not exceed 6% @1 micron particle diameter.

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Mode of Failure: Scored or “Record Grooved” Primary Ringor Seat Inserts

Standard material Buna, or EPT/Carbon/Ceramicseals are suitable for glycol type fluid applicationsprovided the quality of the water utilized as wellas maintaining a proper concentration level ofglycol to water. The carbon face to the right is“record grooved” a sign of a dirty system whichcaused seal failure.An indication of heavy concentrations of abrasiveparticulate within the system fluid, passedbetween the seal faces. A scored face provides adirect leak path across the seal faces.

Possible Cause Corrective Action(In order of recommendation)

• Solids or abrasive damage (1) Eliminate solids or abrasives from process fluid if possible.(2) Install a Sediment Separator or Cuno Filter

Kit if the pump is stuffing box equipped and operating conditions are met. (See B&G Sales Bulletin 4976).(3) Change seal selection to a hard face type. (Consult factory for recommendation details)

Magnified Image

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Mode of Failure: Face Failure - Carbon Blistering

A pitted or blistered carbonface indicates the system fluidhad flashed to steam,damaging the carbon face andcreating a direct leak path.

Possible Cause Corrective Action

• Overheating of the seal face, either by lack of Check the operating temperature of theflush fluid or dry running. Process fluid could pump. Ensure temperature does notalso be exceeding temperature limits of the seal. exceed the maximum temperature rating

of the pump/seal. Refer to Bulletin 4976(11/2000) for seal material temperaturelimitations. Install Brazed Plate HeatExchanger Kit if required (-S

Configured pumps.)

Ensure flush tubing is not kinked, orblocked HSC-S, HSCS,-S or –D configured pumps.

Magnified Image

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Mode of Failure: Face Failure -Dry Run


• Solids or abrasive damage (1) Eliminate solids or abrasives from process fluid if possible.(2) Install a Sediment Separator or Cuno Filter Kit if thepump is stuffing box equipped and operating conditions aremet. (See B&G Sales Bulletin 4976).(3) Change seal selection to a hard face type. (Consult factory for recommendation details)

• Dry run damage. Ensure the system, and pump is bled of air on start-up and(Air entrapment in seal chamber) air never enters the seal chamber during the operation of

the pump.

This silicon carbide seat insert has a deep wear trackworn into the super polished face. A wear track willcreate a direct leak path. This seal was “Dry Run”and failed after only a few operating hours.

Magnified Image

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This ceramic stationary insert’s face was destroyed when metalfragments suspended in the system fluid attempted to pass between

the faces creating a direct leak path.

Magnified Image


Mode of Failure: Face Failure - Metal Fragments in System Fluid


Metal fragments or filings circulating within Identify fragment material and locate sourcesystem fluid. The fragment attempted to escape of the stray material. If copper, check systemto the atmospheric side (Low-pressure, and inside diameter) tube bundles, fittings and tubing.of the ceramic stationary insert. Flush system & refill.In this case history, the fragments were copper.

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Magnified Image

This silicon carbide seat insert wasinstalled backwards in the seat bore.Note the rough, partially worn awaygrind marks on the backside of the seatface. The opposite, polished face isalways installed towards the primaryring.


Mode of Failure: Face Failures - Incorrect Installation

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Mode of Failure: Face Failure - Cracked or Fractured Seat Inserts

Possible Cause

• Cracked during installation

• Thermal Shock due to wet/dry running.

• Thermal shock caused by extreme system fluidtemperature differentials during static or dynamicpump operation.

Corrective Action

Install seat insert in accordance to the sealinstallation instructions contained within theappropriate IOM.

Ensure the system, and pump is bled of airon start-up, and air never enters the sealchamber during the life of the pump.

Upgrade seal to EPT/Tungsten Carbide materials.

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Possible Causes Corrective Action• A high concentration of solids collected between the carbon I.D. and the pump shaft or sleeve.

• Mechanical misalignment, either on seal installation, or within the pump itself. Check alignment and correct if required.

• The pump is operating beyond the recommend- Resize pump & or impeller trim. ed 25% of BEP range limitations causing shaft defection..


Mode of Failure: Face Failure - Chips on the I.D. of the Seal Faces

The I.D. of this carbon primary ring waschipped after solids circulating in theprocess fluid collected between the I.D. ofthe ring and pump shaft. Broken chunksof carbon were driven between the facescausing catastrophic seal failure.

Magnified Image

(1) Eliminate solids or abrasives from process fluid if possible.

(2) Install a Sediment Separator or Cuno Filter Kit if thepump is stuffing box equipped and operating conditionsare met. (See B&G Sales Bulletin 4976).

(3) Change seal selection to a hard face type (Consult factory for recommendation details)

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Mode of Failure: Dry Run Damage

Carbon Face is blisteredIndicating abnormal

heat and friction.

The carbon drive notches have spun, and aremisaligned with the retainer notches. An

indication of abnormally high torque loadsbetween the carbon face and the seat insert.

Abnormal wear in the drive system

Shredded NeopreneTreat.

Magnified Image

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Mode of Failure: Elastomer Heat Damage

Catastrophic failure of this seal’s elastomer bellowsoccurred due to the temperature of the process fluidexceeding the temperature limit of the seal.

Possible Cause Corrective ActionProcess fluid temperature to high for therating of the pump/seal. (1) Upgrade the seal with a temperature limit

above the maximum application temperature.

(2) Install Brazed Plate Exchanger Kit if required(-S configured pumps.)

(3) Ensure flush tubing is not kinked, blockedHSC-S, HSCS, -S or –D configured pumps.

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Mode of Failure: Chemically Attacked Seal Elastomers

Normal Size

Swollen

Cause

• Locate and identify all chemicals that mayMay have come in contact with the elastomer.Include lubricants used for seal installation,system fluid compatibility, and any chemicalsUsed to flush the system.

Corrective Action

(1) Check the pump’s IOM for recommended seal Installation lubricants.

(2) Refer to Bulletin 4976 (11/2000), 4941 (3/24), and4566 (attached) for chemical compatibility. If the

chemical is not listed, consult factory for an alternate elastomer recommendation if available.

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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -References:

For further technical information regarding mechanical seals, see the following web sites and technical bulletins:• B&G Bulletin 4976 “Mechanical Seal Selection Guidelines” published 11/17/2000• McNally Institute See “Links” on the B&G web site at www.bellgossett.com• The Burgmann Dictionary at www.burgmann.com

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