ARIPPA 2012 Steam Turbine Maint for Optimized Availability (1)

8/21/2019 ARIPPA 2012 Steam Turbine Maint for Optimized Availability (1)

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2012 ARIPPA Technical Symposium

Steam Turbine Generator Maintenance for

Optimized Availability

David Branton, CEO

Turbine Generator Maintenance, Inc.


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Steam Turbine Generators

some statistics and history80% of all electricity in the world is generated by steam turbines driving

electrical generators:

10,632 TWH [terrawatt (1012) hours]World

3,244 TWHU.S. 1,485 TWHChina (expected to be 6,560 TWh by 2030)

Each American uses 13.6 mw-hrs/year vs Chineese 2.6 mw-

hrs/year

U.S. 46% coal, 20% NG, 7% hydro; China 70% coal, 20% hydro

The first practical steam turbine generator was designed and built by Sir

Charles Parsons in 1884 and generated 7.5 MW. Generation principles

remain the same.

GEs first production steam turbine generator was introduced in 1901 and

was rated at 500 KW; just two years later a 5000 KW unit went into

commercial service for Commonwealth Edison.


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Designing a Maintenance Plan

Qualitative Tools

Running Assessments

Periodic Minor Inspections

Objective Based Major Inspections

RequirementsMaximum unit availability

No unplanned outagesPredictable maintenance costs

OptionsMaximum efficiency

Maximum power output


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The turbine and generator are the largest single investment in a fossil power

plant and in many manufacturing and refining facilities. Proper maintenance is

required to maintain efficiency (cost of production) and availability (the amount

of time the unit is able to operate).

Efficiency issues

Steam leakage into the environment

Steam path steam leakage

Blade/nozzle erosion/deposits

Availability issues

Lubrication failures

Steam path failures

Control system malfunctions

Protective device malfunctions

Maintenance Issues


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Maintenance PlanningMaintenance planning considerations

Steam pressure/temperatures

Type of duty cycle

Speed of turbine and generator

Extraction, backpressure, condensing considerations

Over temperature/pressure operation

Environment of facility

Quality of water/steam

Expectations of plant

There is no one size fits all maintenance plan.


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Maintenance PlanningMaintenance planning considerations

Major inspections provide opportunities for availability and efficiency improvements

with minimum outage impact if planned properly.

Major Inspection outages can be better scheduled with qualitative rather thansubjective data

Availability of the turbine and generator and reliability of critical auxiliaries

can be optimized:

o Periodic Running Assessments combined with data trending and analysis

o Periodic minor (3-5 day) outages to inspect critical areas for issues

A combination of Running Assessments and Focused Minor

Inspections can assure availability and optimize major inspections.


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Turbine Generator MaintenanceOutage Cycle


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Running Assessments

Critical parametersVibration/Noise

Turbine inlet temperature fluctuations

Stage performance

Steam chemistry

Bearing temperatures

Pedestal expansion/lubrication/cleanliness

Electrical system grounding

Motor loading

Gland system integrity

Air in-leakage

Lubrication backup integrity

Lubrication cleanliness

Overspeed protectionGenerator partial discharge and rotor flux probe

Data must be monitored, collected, trended, analyzed,

and used for outage planning


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Running Assessments - Vibration Trending


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Running AssessmentsGrounding Brushes

Turbine Availability issue


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Running AssessmentsOil System Integrity

According to the International Association of Engineering Insurers

The highest frequency of turbine generator failures in the

10400 mw range has been lube oil incidents

Dirt and/water contamination

Loss of oil pressure


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Running AssessmentsDC Backup

Turbine Availability issue


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Running Assessments

Generator Rotor Windings

Shorted Turns in Pole A - Coil 5, Pole B - Coils 6 and 7

Magnetic Wedges in Coil 1note small signal


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Minor Inspection Scopes

Bearing Inspectionsevery two years

Critical inspections for availability

Standard Scope should include

Coupling alignment checks Disassembly and inspection of thrust bearing

- including total rotor travel and thrust clearance

Disassembly and inspection of journal bearings

- including UT and LPT

Oil system including the oil reservoir, pumps/motors, oil coolers

Maintenance oil flush Backup oil system integrity

Turbine shaft grounding maintenance

Check and calibrate protective devices including overspeed,

bearing temperatures and vibration

Generator borescope and electrical tests


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Minor InspectionsBearing Inspections


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Uneven wear Varnish deposits


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Minor InspectionElectrical Discharge

through the Thrust Bearing


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Minor Inspection Scopes

Valve inspectionsevery two yearsCritical inspections for safety, efficiency, and control

Standard Scope should include:

Disassemble, clean, and inspect steam side

- Include all stop and control valves- Include all non return valves

- Seat integrity and contact

- Stem and stem seal integrity

Disassemble, clean and inspect control side

Check valve set points and travels

Perform protective systems inspections and calibration checks

Perform borescope inspections of steam inlet/nozzle

Perform generator borescope and maintenance tests


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Minor InspectionsValve Inspections


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Minor InspectionsValve InspectionsMinor InspectionsValve Inspections

LP Governor valve seat damage


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Proper planning can significantly reduce planned outage inspections.

Based on the turbine configuration, a major inspection can be completed in

26 weeks based on unit size.

The turbine-generator is almost always the critical path, and any generator

maintenance/repair must be placed in the same outage window.

Factors critical to achieving minimum outage durations:

Planning for the outage should begin after the last major inspection

and developed over a maintenance cycle of Running Assessments

and Minor Inspections. Most turbine and generator replacement parts

can be sourced from non-OEM suppliers with less lead time.

Develop contingency repair plansidentify potential scopes of work,

identify repair resources, and develop repair schedules.

Contract experienced turbine generator teams that understand the

unit and have the skills and tools necessary to handle the anomalies

and with minimum impact to the schedule.

Outage Implementation Major Inspections


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Major Inspection Findings Averting Forced Outage

HP Turbine

Nozzle box movement

First stage rotating buckets

Nozzle migration

Turbine wheel corrosion

LP Turbine

Last row blade migration

Generator

Rotor winding short Stator core overheating


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Major InspectionSteam PathHeat shield weld failure in stage 4


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Major InspectionSteam PathLocking pin failure in rotating stage 1


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Major InspectionSteam Path

Missing seals


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Nozzle migration downstream


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MajorSteam PathLast row blade migration


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Downstream side Upstream side

Major InspectionSteam PathCurtis stage severe damage


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Steam Turbine Design TypesAdvantages and DisadvantagesReaction vs. Impulse

Reaction designed turbines start out at a higher efficiencyless leakage

Impulse design turbines have fewer stages

Tip Leakage Root Leakage

Fig. C-F. Reinker, J.K., and Mason, P.B., Steam Turbines for Large

Power Applications, GER-3646D, GE Power Systems, Schenectady, NY.


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Major InspectionSteam PathStage efficiency improvement


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Boiler carryover


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Boiler carryover


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Major InspectionSteam Packing

Excessive clearances


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Major InspectionsGenerator

Stator and core


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Major InspectionGenerator

Rotor winding


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Major InspectionImplementation

Outage duration for a major inspection can be optimized by: Effective planningcontingency plan development, safety plan, quality plan

Team implementationdaily reporting and proactive management

Pre-Qualified personnelprofessional, resumes, down to working level

Defined and organized tools


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Steam turbine generators are rugged and with a comprehensive

maintenance program can operate reliably.

Using proper assessment techniques and performing strategic

minor inspections, Major Inspection intervals can be optimizedand performed predictably and cost efficiently.

Proper operation is imperative to maintain the equipment

performance but when anomalies occur, the potential impact

must be assessed.

A tailored maintenance program can greatly reduce operatingcosts by maintaining efficiency, availability, and reliability.

A planned and well organized outage plan/team can assure on-

time outage duration.

Conclusions

ARIPPA 2012 Steam Turbine Maint for Optimized Availability (1)

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