Case StudiesUrea melt pumps had been a reliability concern since commissioning (1992).
Majority of the concerns were related to the failure of mechanical seal.
Unexpected failures of seal were encountered during plant startups or during
pump changeover. It resulted in a major reliability concern as the continuity of
operation of plant had been at stake. Also huge expenses were incurred as
damaged seal caused other parts to fail. A typical overhaul costs around USD
10,000.
This Case Study highlights the identification of Failure Modes and steps taken to
resolve the issues pertaining to seal reliability on this service

Moin, Danish

English

Texas A&M University

Molten Urea Transfer Pump 
Seal Failures – Case Study
Author bio
Danish Moin
Danish is currently a Mechanical Maintenance Engineer at Engro Fertilizers' Urea Plant. His 
responsibilities include planning and execution of maintenance activities on centrifugal and PD 
machines of Urea plant along with investigation of reliability issues in rotary and static 
equipment of the aging plant. Previously he was working as Inspection Engineer at Engro 
Fertilizers and amassed valuable experience of FMEA studies pertaining to material failures.
Danish received B.E degree in Mechanical Engineering from National University of Sciences and 
Technology Pakistan, in 2013.
Danish Moin
Maintenance Engineer
Engro Fertilizers Ltd. Pakistan
dmoin@engro.com 
Abstract
Urea melt pumps had been a reliability concern since commissioning  (1992). 
Majority of the concerns were related to the failure of mechanical seal.
Unexpected failures of seal were encountered during plant startups or during 
pump changeover. It resulted in a major reliability concern as the continuity of 
operation of plant had been at stake. Also huge expenses were incurred as 
damaged seal caused other parts to fail. A typical overhaul costs around USD 
10,000.
This Case Study highlights the identification of Failure Modes and steps taken to 
resolve the issues pertaining to seal reliability on this service.
• Synopsis of the issue
• Teardown observations
• Benchmarking study
• FMEA Summary
• Post Improvement Results
• Lessons Learnt
Contents
• Single Stage OH1 type centrifugal pump conforming to API-610, operating
with the following conditions:
• Pump casing and mechanical seal housing are provided with 
Steam Jacketing
Synopsis
Urea Holdup Tank
Pressure = 0.89kg/cm2
Vol. = 0.8m3
Tk-241
P-
254s
Urea Melt Pump
Discharge Pressure = 13 kg/cm2
Discharge Flow = 40m3/hr
Parameter Value
Operating temperature 138 oC
Suction pressure 0.89 kg/cm2
Discharge pressure 13 kg/cm2
Discharge Flow 40 m3/hr
RPM 2950
Steam Jacketing 145 – 150 oC
• The mechanical seal being used is Single Mechanical Seal with the following details
• Type: Balanced Mechanical Seal, multi-spring design 
• Face Material Combination:  SiC + WC
• Flushing Plan: API 01 + 62 (Internal circulation through Pump Body + Steam Quenched)
• All seal failures related to this pump were reported during Plant Startup or Changeovers with standby pump. 
Such transient conditions provided a narrow window of opportunity and made it difficult to gather evidence of 
failure
• The multiple failure schemes made it necessary to conduct an FMEA study to finalize the potential causes 
failure mechanisms
Synopsis
• Inspection of failed seal components was conducted of a recent failure to help in narrowing down the cause of failure. Mentioned
below are the salient findings:
• Pump bearings found in okay condition, excessive axial or radial movement not observed
• All secondary sealing elements found okay
• Runout on Seal area of shaft found within acceptable limits
• Even wear marks observed on the seal faces without deep scratches
• Both seal faces found shattered
• Hold tank level drops observed in Level monitoring 
record
Teardown Observations
Shattered Stationary Seal FaceShattered Rotary Seal Face
Teardown Observations
Hold up vessel level monitoring during 02 separate startups with reported seal failure
• A benchmarking study was carried out with 03 neighboring Urea Manufacturing industries. Following are the 
main learnings of the study:
• Urea Melt service is a challenging service to handle irrespective of the Plant Process designer 
• All neighboring industries face similar issues with mechanical seal reliability, irrespective of seal 
manufacturer, model
• Hardware modifications (changing seal make and model) provided little relief
• All benchmarked industries showed similar failure mechanism; shattering of seal faces
• All benchmarked industries were using the same hard-hard faces material combination
Benchmarking Study
FMEA Summary
Criticality Analysis Remarks
Function 
requirement
Failure Mode Failure Cause Probability Consequence Detectability
Mechanical 
Seal/Sealing
Secondary 
sealing elements 
failing
1. Aging of elastomer
2. Improper Installation
Low Med Low
Ruled out due to no history of 
secondary elements failing
Inadequacy of 
seal face 
materials
Wrong Face material 
combination for the 
service
Low High Med
Literature(1) suggests for abrasive
services,  Hard-Hard face 
combination is preferred
Urea solution 
crystallization 
b/w seal faces
1. Failure of Quenching 
steam
Med High Low
There were steam leakages in the 
steam circuit but were addressed 
alongside as well
Seal faces 
cocking
1. Clogging of multi-
spring seal
Med High Low
Ruled out as even monospring seals 
did not  prove effective
Cavitation
1. Low NPSH
2. Chocking in suction 
line
3. Urea sol. Flashing
High High Med.
All  collected Evidence suggested
strong possibility of cavitation 
Poor Lubrication 
between Seal 
Faces
1.Dry/ Poor lubrication 
due to pump cavitation High High Low
Root cause of shattered seal faces is 
heat shock by pump cavitation. (2)
• The biggest contributor of Mechanical Seal failure was finalized as Cavitation and variation in 
Concentration of Urea solution as:
• Neighboring industries also confirmed failure mode to be shattering of seal faces
• Failure instances corresponded with Low liquid levels in hold up tanks
• Following is the breakup of the improvements made so far:
Post Improvement Results
Mode of Failure Measure Combined Effect
Cavitation
Alarm Level increased from 10% to 20% 
level of Holdup Tank Zero seal failures in the last 6 startups 
and changeoversVariation in Conc. Of Urea solution Urea melt pumps are now lined up post 
confirmation of high concentration
• Urea melt is a challenging service to deal with. High number of seal failures are common in Urea Fertilizer 
Manufacturing sites
• A different face material combination (other than hard-hard) is not recommended for use on abrasive services 
like molten urea
• A multispring seal ideally should not be used for services that can crystallize. However, with adequate steam 
quenching and heating of seal chamber prior to startup, the need of a monospring seal can be avoided
• Prior heating of pumps on similar applications is mandatory before taking in service. For the equipment 
discussed in this case study, a heating time of ~3 hours is necessary before the pump temperature reaches the 
product temperature
Lessons Learnt
• (1) Michael Huebner, 2005, “Material Selection for Mechanical Seals”, Texas A&M Turbolab
Symposium
• (2) The Japan Society of Industrial Machinery Manufacturers, 2008, “Mechanical Seal Hand Book 
Trouble shooting” P.80
References


Molten Urea Transfer Pump Seal Failures

Texas A&amp;M Repository

Molten Urea Transfer Pump Seal Failures – Case StudyAuthor bioDanish MoinDanish is currently a Mechanical Maintenance Engineer at Engro Fertilizers' Urea Plant. His responsibilities include planning and execution of maintenance activities on centrifugal and PD machines of Urea plant along with investigation of reliability issues in rotary and static equipment of the aging plant. Previously he was working as Inspection Engineer at Engro Fertilizers and amassed valuable experience of FMEA studies pertaining to material failures.Danish received B.E degree in Mechanical Engineering from National University of Sciences and Technology Pakistan, in 2013.Danish MoinMaintenance EngineerEngro Fertilizers Ltd. Pakistandmoin@engro.com AbstractUrea melt pumps had been a reliability concern since commissioning  (1992). Majority of the concerns were related to the failure of mechanical seal.Unexpected failures of seal were encountered during plant startups or during pump changeover. It resulted in a major reliability concern as the continuity of operation of plant had been at stake. Also huge expenses were incurred as damaged seal caused other parts to fail. A typical overhaul costs around USD 10,000.This Case Study highlights the identification of Failure Modes and steps taken to resolve the issues pertaining to seal reliability on this service.• Synopsis of the issue• Teardown observations• Benchmarking study• FMEA Summary• Post Improvement Results• Lessons LearntContents• Single Stage OH1 type centrifugal pump conforming to API-610, operatingwith the following conditions:• Pump casing and mechanical seal housing are provided with Steam JacketingSynopsisUrea Holdup TankPressure = 0.89kg/cm2Vol. = 0.8m3Tk-241P-254sUrea Melt PumpDischarge Pressure = 13 kg/cm2Discharge Flow = 40m3/hrParameter ValueOperating temperature 138 oCSuction pressure 0.89 kg/cm2Discharge pressure 13 kg/cm2Discharge Flow 40 m3/hrRPM 2950Steam Jacketing 145 – 150 oC• The mechanical seal being used is Single Mechanical Seal with the following details• Type: Balanced Mechanical Seal, multi-spring design • Face Material Combination:  SiC + WC• Flushing Plan: API 01 + 62 (Internal circulation through Pump Body + Steam Quenched)• All seal failures related to this pump were reported during Plant Startup or Changeovers with standby pump. Such transient conditions provided a narrow window of opportunity and made it difficult to gather evidence of failure• The multiple failure schemes made it necessary to conduct an FMEA study to finalize the potential causes failure mechanismsSynopsis• Inspection of failed seal components was conducted of a recent failure to help in narrowing down the cause of failure. Mentionedbelow are the salient findings:• Pump bearings found in okay condition, excessive axial or radial movement not observed• All secondary sealing elements found okay• Runout on Seal area of shaft found within acceptable limits• Even wear marks observed on the seal faces without deep scratches• Both seal faces found shattered• Hold tank level drops observed in Level monitoring recordTeardown ObservationsShattered Stationary Seal FaceShattered Rotary Seal FaceTeardown ObservationsHold up vessel level monitoring during 02 separate startups with reported seal failure• A benchmarking study was carried out with 03 neighboring Urea Manufacturing industries. Following are the main learnings of the study:• Urea Melt service is a challenging service to handle irrespective of the Plant Process designer • All neighboring industries face similar issues with mechanical seal reliability, irrespective of seal manufacturer, model• Hardware modifications (changing seal make and model) provided little relief• All benchmarked industries showed similar failure mechanism; shattering of seal faces• All benchmarked industries were using the same hard-hard faces material combinationBenchmarking StudyFMEA SummaryCriticality Analysis RemarksFunction requirementFailure Mode Failure Cause Probability Consequence DetectabilityMechanical Seal/SealingSecondary sealing elements failing1. Aging of elastomer2. Improper InstallationLow Med LowRuled out due to no history of secondary elements failingInadequacy of seal face materialsWrong Face material combination for the serviceLow High MedLiterature(1) suggests for abrasiveservices,  Hard-Hard face combination is preferredUrea solution crystallization b/w seal faces1. Failure of Quenching steamMed High LowThere were steam leakages in the steam circuit but were addressed alongside as wellSeal faces cocking1. Clogging of multi-spring sealMed High LowRuled out as even monospring seals did not  prove effectiveCavitation1. Low NPSH2. Chocking in suction line3. Urea sol. FlashingHigh High Med.All  collected Evidence suggestedstrong possibility of cavitation Poor Lubrication between Seal Faces1.Dry/ Poor lubrication due to pump cavitation High High LowRoot cause of shattered seal faces is heat shock by pump cavitation. (2)• The biggest contributor of Mechanical Seal failure was finalized as Cavitation and variation in Concentration of Urea solution as:• Neighboring industries also confirmed failure mode to be shattering of seal faces• Failure instances corresponded with Low liquid levels in hold up tanks• Following is the breakup of the improvements made so far:Post Improvement ResultsMode of Failure Measure Combined EffectCavitationAlarm Level increased from 10% to 20% level of Holdup Tank Zero seal failures in the last 6 startups and changeoversVariation in Conc. Of Urea solution Urea melt pumps are now lined up post confirmation of high concentration• Urea melt is a challenging service to deal with. High number of seal failures are common in Urea Fertilizer Manufacturing sites• A different face material combination (other than hard-hard) is not recommended for use on abrasive services like molten urea• A multispring seal ideally should not be used for services that can crystallize. However, with adequate steam quenching and heating of seal chamber prior to startup, the need of a monospring seal can be avoided• Prior heating of pumps on similar applications is mandatory before taking in service. For the equipment discussed in this case study, a heating time of ~3 hours is necessary before the pump temperature reaches the product temperatureLessons Learnt• (1) Michael Huebner, 2005, “Material Selection for Mechanical Seals”, Texas A&M TurbolabSymposium• (2) The Japan Society of Industrial Machinery Manufacturers, 2008, “Mechanical Seal Hand Book Trouble shooting” P.80References

https://oaktrust.library.tamu.edu/bitstream/1969.1/172444/1/01_Moin.pdf

Molten Urea Transfer Pump Seal Failures

Abstract

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Texas A&M University

Texas A&M Repository

Molten Urea Transfer Pump Seal Failures

Abstract

Similar works

Full text

Available Versions

Texas A&M University

Texas A&amp;M Repository

Texas A&M Repository