Chopra, Anurag

Kumar, Arun

Texas A&amp;M Repository

“Severe corrosion on rotor blades of back pressure type Steam Turbine due to unique reason”. What Went Wrong ?Arun Kumar Anurag ChopraHMEL, Guru Gobind Singh Refinery , INDIAPresenter/Author biosArun Kumar (Author)Arun Kumar is working with HPCL‐ Mittal Energy Ltd., India, as Head of Maintenance & Reliability of high complexity Refinery complex, Guru Gobind Singh Refinery at Bathinda, India. Has over 30 years of experience in the areas of erection, commissioning, maintenance, equipment reliability, turnaround planning and execution, troubleshooting and performance improvement of Rotating Equipment, in Process Plant/ World Class Oil Refinery. Arun is mechanical engineering graduate with post‐graduation in business management. He has presented number of technical papers at international venues and lectured at Turbomachinery and Pump Symposia, including tutorial and case studies. He is advisory committee member of Asian Turbomachinery Symposium , Turbomachinery Lab., Texas A&M University.Anurag Chopra (Co‐Author)“The co‐author is having more than 18 years of experience in field of Reliability & Maintenance of Rotating Equipment inthe top refineries of India and presently working as Lead‐ Rotating Equipment Reliability at HMEL Refinery in India. Hasbeen regular training faculty on rotating equipment for young engineers across refinery and has contributed informulating overall rotating equipment strategies mainly predictive, preventive maintenance and bringing abouttransformation in rotating asset management by adapting latest technologies/tools available. The Co‐author also haslong exposure of rotary equipment vibration analysis – both casing and shaft and has designed, started and led conditionmonitoring programs in no. of refineries and has won accolades for the same.”Summary of the Case StudyThe case study depicts an unique reason for corrosion on blades of a BackPressure Turbine (BPT) for Generator drive leading to huge maintenance costwithin 4 years of turbine installation and commissioning.Based on the observations collected during overhauling and analysisthereafter, it was concluded that reason for the corrosion on turbine bladingwas wet ambience inside the turbine casing during machine idle condition.Action plan was prepared and implemented to avoid reoccurrence and isdiscussed in detail in subsequent slides.The equipment overhauling was mainly planned due to higher vibration fromequipment along with other reasons like increased steam leakages fromturbine end seals leading to lube oil contamination.Brief DescriptionSTG-3 (Steam Turbine Generator) installed in Captive Power Plant ofRefinery is back pressure control machine and drives electric generatorwith reduction gear-box. The brief equipment specifications are:Description ValueSteam Inlet Conditions 105kg/cm2 g @ 505 degCSteam Exhaust Conditions 5 Kg/cm2g @ 400degCTurbine RPM 5000 Generator RPM 3000Rating 32 MWNo of Impulse Stages 1No of Reaction Stages 19Brief DescriptionSteam Turbine major overhauling revealed deterioration to steam pathcomponents in the form of corrosion, erosion, pitting and othercomponents in lube oil circuit like bearings.The present case study is limited to investigation on corrosion onthe steam path components, corrective actions taken and machineperformance after corrective actions.Brief HistoryMilestonesMechanical Completion of Equipment : 19-12-2011Ready For Commissioning : 06-04-2012Commissioning (First Synchronization) : 28-04-2012Hours From Date Of Commissioning : 30793 HrsRunning Hours : 27187 HrsNote• From April’12 to July’12, the no. of running hrs. 1121 against available 2280 hrs.due to intermittent running.• From July’14 to Sep’14, the no of running hrs. 354 against available 2208 due torefinery shut down.Start Stop HistoryNon availability of SLSS, 5Exhaust Pr. Low, 3Electrical System, 3Black Out, 2No power & steam demand, 3Load hunting issue, 3Instrument Malfunction, 1Major Overhauling, 1Total No. of Stops  Since Aug‐1221 Times925249336773872074471574174467271662274472074473372074172068973767274472073872010722477436417257446317447206747207447447206070200400600800Apr/12May/12Jun/12Jul/12Aug/12Sep/12Oct/12Nov/12Dec/12Jan/13Feb/13Mar/13Apr/13May/13Jun/13Jul/13Aug/13Sep/13Oct/13Nov/13Dec/13Jan/14Feb/14Mar/14Apr/14May/14Jun/14Jul/14Aug/14Sep/14Oct/14Nov/14Dec/14Jan/15Feb/15Mar/15Apr/15May/15Jun/15Jul/15Aug/15Sep/15Oct/15Monthly Running hoursBPTG OPER HRSObservations on steam path ComponentsSnap Chart and Causal Factor (RCA)Analysis of the Causal FactorWet Ambience In turbine during rotor standstill condition for longer duration• Machine commissioned in April 2012.• May’12 to July’12 ‐ in intermittent start stop condition. Same time, the steamlines were charged and possibility of steam ingress inside turbine casing existed.• July’14 to Sep’14 – machine stopped due to plant shutdown.• More than 21 stoppages since Aug 12.• BPSTG (Back Pressure Steam Turbine) flash tank ‐12 nos. drain lines : 9 no.intermittent (including 3 turbine casing drains) and 3 nos. continuous drains.• Continuous drains are from VHP (Very High Pressure) header & remain in serviceduring BPSTG trip condition too.• Back flow of flash steam from these continuous drains can createwet ambience in turbine during rotor standstill condition.• BPSTG drains from upstream and downstream of exhaust steam (LP)• Motor operated valve (MOV) are connected to same drain header,which has potential to create wet ambience in turbine during rotorstandstill condition. (Refer schematic)Analysis of the Causal FactorProprietary & ConfidentialBPTG Flash Tank Drain Details10BPTG Flash Tank1 2 53 46 78 9 11 12S No. Type of Drain Drain From Valve near flash tank1 Intermittent Casing MP Near Flash Tank2 Intermittent Casing LP Near Flash Tank3 Intermittent Aux Steam Drain Header No Isolation4 Intermittent Casing HP Near Flash Tank5 Intermittent Common Header under QC NRV, after QC NRV,LP VentNo Isolation6 Continuous ESV Drain No Isolation7 Intermittent LP Steam to VAM drain No Isolation8 Continuous VHP drain trap near Startup vent MOVNear Flash Tank9 Intermittent VHP drain by Pass near Startup vent MOVNear Flash Tank10 Continuous VHP drain trap near Flash Tank Near Flash Tank11 Intermittent VHP drain by Pass near Flash Tank Near Flash Tank12 Intermittent LP Exhaust Before Q C NRVNote: During site test as part of RCA, back flow of steam from flash tank to turbine casing  noted from HP  casing drain and back flow from LP exhaust line.Exhaust Steam Line DrainsBPSTG drains from upstream and downstream of exhaust steam (LP) MOV  connected to same drain header and has potential to create wet ambience in turbine during rotor standstill Graphics-Corrosion on Rotor and Carrier Blading 17ROTATING BLADES STATIONARY BLADES ROTATING & STATIONARY BLADES TO BE REPLACEDGUIDE BLADE CARRIER ‐ 1GUIDE BLADE CARRIER ‐ 2GUIDE BLADE CARRIER ‐ 3STAGESTAGESTAGESTAGESTAGEGUIDE BLADE CARRIER ‐ 1STAGEGUIDE BLADE CARRIER ‐ 3141516GUIDE BLADE CARRIER ‐ 2STAGESTAGESTAGESTAGESTAGESTAGE1819BPSTG TURBINE ROTOR8 9101112131 2 3 4 5 7STAGESTAGESTAGECURTISESTAGESTAGESTAGESTAGESTAGE6DrainAction Plan Based on the AnalysisCausal Factor Root Cause Action TakenWet AmbienceInside Turbineleading tocorrosion onturbinecomponents.Back flow of steam to theturbine casing from:1.Casing Drains connected tocommon flash tank havingtotal 12 no drains connected.2.LP exhaust end drains.3.Machine stoppages forlonger duration.1. Shifting of turbine header drain trap and bypass valve (Before MOV) from flash tank to atmospheric drain.2. Shifting of Drain trap upstream Inlet valve, Trap root Inlet valve and Trap Bypass valve to approachable locations   3. Shifting of header after MOV drain trap and bypass valve from flash tank to atmospheric drain.4. Shifting of VAM Boiler Drain Trap and bypass valvecommon drain header (2”) from flash tank to atmosphericCausal Factor Root Cause Action TakenWet AmbienceInside Turbineleading tocorrosion onturbinecomponents.Back flow of steam to theturbine casing from:1.Casing Drains connected tocommon flash tank havingtotal 12 no drains connected.2.LP exhaust end drains.3.Machine stoppages forlonger duration.5. Shifting of Aux. Steam Drain Trap and bypass valvecommon drain header (4”) from flash tank toatmospheric.6. Shifting LP Exhaust After MOV Drain trap and drainbypass from flash tank to atmospheric7. Shifting of LP Exhaust After NRV Drain from flash tankto atmospheric and provision of Trap.8. Separation of Steam and oil Leak off drains.9. Provision of Break out flanges in HP/MP/LP Casingdrains.Action Plan Based on the AnalysisVHP HeaderPRESENT BPTG FLASH TANK PIPING CONNECTIONSVHP HeaderBPTG FLASH TANK  SUGGESTED PIPING CONNECTIONSBPTG VAM M/C LP STEAMVAM M/C LP STEAM DRAIN HEADER TD BFP AUXILIARY STEAMAUXILIARY STEAM DRAINHEADERESV LEAK OFFWARM UP DRAIN  MOV ‐1107FLASH TANK MOV 1103BEOREMOV DRAIN TRAP AND TRAP BYPASSMOV 1402MOV 1404PCV 1118PCV 1414AFTER  MOV DRAIN TRAP AND TRAP BYPASSATMOSPHERIC VENTLearningsBased on the turbine satisfactory performance after taking corrective actions,following learnings can be implemented horizontally across all steam turbines:1. Process Flow Diagrams must be verified at site during erection stage and duringhandover/take over. The same was overlooked in the subject case and resulted inhuge maintenance cost.2. During long shutdown of the turbine, OEM guidelines for preservation should befollowed. The same were not followed in our case leading to creation of wetambience inside turbine casing and hence corrosion on blades.3. In subject case, OEM recommended “The turbine unit will be protected againstinternal corrosion during prolonged shutdown of more than 2 weeks after coolingdown the turbine, by admitting Nitrogen into the turbine and maintain a lowpositive pressure of about 50 to 75 mm W.G. during whole time of shutdown atstandstill condition, the protection shall include all steam spaces including thegland sealing”.

Severe Corrosion On Rotor Blades of Back Pressure Type Steam Turbine Due to Unique Reason. What Went Wrong?

https://oaktrust.library.tamu.edu/bitstream/handle/1969.1/166831/07_Kumar.pdf?sequence=1&isAllowed=y

Severe Corrosion On Rotor Blades of Back Pressure Type Steam Turbine Due to Unique Reason. What Went Wrong?

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Severe Corrosion On Rotor Blades of Back Pressure Type Steam Turbine Due to Unique Reason. What Went Wrong?

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