ML20043F640
| ML20043F640 | |
| Person / Time | |
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| Issue date: | 02/12/2020 |
| From: | Office of the Chief Human Capital Officer, Woodard Corp |
| To: | |
| Gary Callaway | |
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| Download: ML20043F640 (56) | |
Text
Chapter 12 EDG PERFORMANCE MONITORING AND MAINTENANCE
Learning Objectives This lesson will provide students an overview of:
- 1. Prescriptive vs. Predictive maintenance Which better?
- 2. Some regulatory requirements for maintenance, including "NRC Maintenance Rule"
- 3. Monitoring, trending, analysis of EDG and support system parameters, + fuel oil, lube oil, cooling water, etc.
- 4. Importance of baseline data, parameter trending, analysis+
- 5. Observations before, during, after EDG runs
Learning Objectives (continued)
- 6. Potential impact of maintenance on/in vicinity of EDG
- 7. Some EDG monitoring systems including human
- 8. Data on contribution of each EDG subsystem to failure rate
EDG Maintenance: Prescriptive vs. Predictive Prescriptive (Calendar-Based) Method Ch 1: Reasons *Diesel* engines picked for emergency power:
Long history of reliable service, frequently 6000+ hours/yr
'Factory' maintenance schedules inappropriate for NPP use. Why?
Prescriptive maintenance: unnecessary, intrusive inspections, disassembly, parts replacement, etc.
$$$, EDG out of service, potential for errors "If IAB, DFI"
EDG Maintenance: Prescriptive vs. Predictive Predictive (Condition-Based) Method More effective approach based on condition, determined by monitoring, trending, analysis Head off failure thru early warning signs: abnormal temperature, pressure, vibration, wear products, etc.
Techniques: Observation (logging), analyses of fuel oillube oil cooling water, engine analyzers, thermal (IR) scanning...
EDG reliability, less unscheduled down-time, reduced cost
Key Regulatory Documents 10 CFR 50.65: "Requirements for Monitoring Effectiveness of Maintenance at Nuclear Power Plants" AKA "NRC Maintenance Rule" Requires licensees to monitor performance of structures, systems, components against preset performance goals/criteria they establish, based on safety signif.
Reg Guide 1.160, "Monitoring the Effectiveness of Maintenance at Nuclear Power Plants" Provides guidance for implementing the "Maintenance Rule"
Key Regulatory Documents (continued)
NRC Inspection Manual, Chapter 0609, Appendix K:
"Maintenance Risk Assessment and Risk Management Significance Determination Process."
Tool for evaluating licensee maintenance program effectiveness using Significance Determination Process (SDP), plus Inspection Procedure 71111.13, "Maintenance Risk Assessment and Emergent Work Control."
NUMARC 93-01, Rev 1 (now NEI 1996a): Nuclear Management and Resource Councilnow Nuclear Energy Institute"Industry Guideline for Monitoring Effectiveness of Maintenance at Nuclear Power Plants." (Licensee guidance for the "Maintenance Rule")
Monitoring & Trending: Fundamentals Must understand present conditions for each EDG parameter optimum range/value, what is acceptable (limits).
Requires systematic trending of parameters during successive operating cycles/time periods...
Deviation alert investigation cause action GOAL: Predictable, need-based maintenance, with minimum unplanned down time...
Preferred monitoring techniques can be implemented with engine in service.
Monitoring & Trending: Fundamentals (cont)
Info from monitoring techniques may overlap different indications of same condition(s)... [examples]. Integrated analysis of data helps identify trends, problems.
Applying engine analyzers is complex, engine-specific, may be work in progress. Can at least warn change has occurred.
No one symptom /test /engine analyzer can tell full story Parameter monitoring useless without competent analysis by those with responsibility and authority to follow up results.
Monitoring: Prerequisites Equipment Calibration: Accuracy of gauges, meters, monitoring systems must be verified Licensee's equipment calibration system /service must be certified for compliance to ISO 170125 or MIL-STD-45662A (1985), "Calibration Systems Requirements" Ambient Conditions Data: Temperature of engine intake air and air or water used for cooling impact performance. Atmospheric pressure (primarily from altitude) is also significant. Record the ambient conditions relevant to engine performance.
Fuel Oil Quality Monitoring Diesel fuel characteristics can have profound impact on engine performance, even its life. Licensees required to have fuel oil monitoring program complying with ASTM D-975, "Limiting Requirements for Diesel Fuel Oils."
Diesel fuel specs are plant-specific. Why? Fuel parameters Flash point (°F): Influences ignition. Lowest fuel oil temp at which continuous vapor generation will sustain flame at free surface exposed to oxygen and ignition source. Fire codes encourage fuels with flash points of 65°C (150°F) or above.
Fuel Oil Quality Monitoring (continued)
Specific Gravity or API Gravity @ 60°F: Relates weight of fuel to water. Diesel fuels are lighter than water, so specific gravity
<1.0. However, API gravity index has *inverse* scale starting at 10.0 for H2O so lighter fuels have higher API gravity number.
Pour point (°F): Fuel temperature at which flow ceases...
Cloud point (°F): Fuel temperature at which paraffin (wax) in fuel starts forming crystals (looks "cloudy"). Filters, injection equipment can be clogged/ plugged by wax IN 94-19, S.M. NOTE Carbon residue, % by weight: Deposited carbon can foul injector tips, piston rings, exhaust valves.
Fuel Oil Quality Monitoring (continued)
Water and Sediment (% volume, by centrifuge): Indicates fuel cleanlinesscan impact fuel injection components. Sediment clogs filters, water promotes microbial growth (bio-fouling) in diesel fuel tanks. These promote microbiologically-induced corrosion (MIC), especially of steel pipe and tanks Color: Ranges from dark-amber to light-golden. Fuel color (darker or lighter) of less concern than color changes during storage (typically darkening) Unstable fuel (?)
Fuel Oil Quality Monitoring (continued)
Ash (% by weight): Non-combustible trace minerals and metals in fuels (silicon, vanadium, etc). Tend to have an abrasive or corrosive effect, or result in engine deposits.
Vanadium especially troublesome forms Vanadium Pentoxide (highly corrosive).
Distillation temperatures, (°F) at 90% and end points, at STP:
Relates to volatility or vaporization tendency of fuel during distillation. In lighter fuels, such as used in diesels at NPPs, 90% distillation point is often used. Lighter, more volatile fuel tends to have lower ignition points, can affect engine starting, running.
Fuel Oil Quality Monitoring (continued)
Viscosity @ 100°F (Saybolt Universal Sec, SUS): Relates to flow characteristics. Oils with lower API gravity numbers tend to be more viscous (thicker).
Sulfur (% by weight): Trace sulfur contaminates cause acid formation post-combustion, in presence of water vapor at the required temp. Sulfur lubricates, so the low sulfur fuels have additives to restore lubricity. Chapter 13 discusses potential issues with ultra-low sulfur fuel oil Copper strip corrosion test (comparative): Predicts copper corrosion characteristics of a fuel. Relevant for engines with Cu gaskets/components in fuel system.
Fuel Oil Quality Monitoring (continued)
Cetane number ignition quality test (comparative-qualitative).
A critical property of fuel relating to smooth engine operation.
Comparison is between Cetane with high ignition quality and Heptamethylonane with low ignition quality. Effects starting times and load acceptance response time. Higher Cetane #
provides more responsive starting, load acceptance. > 40 Heating value (BTU per lb.) Another critical property of fuel.
Diesels = heat engines (convert chemical energy into heat, to produce work). Fuels with higher heating values per pound tend to be lighter fuels. But lighter fuels have lower specific gravity (higher API gravity)
(con't)
Fuel Oil Quality Monitoring (continued)
Although lighter fuels have a higher BTU content per pound
("Heating Value"), they have a lower BTU content per gallon.
With diesel fuel storage, consumption monitored in gallons, BTUs per gallon is the critical parameter.
Diesels used in nuclear applications frequently had their fuel consumption tests performed using fuel oil with an API gravity of 28. If operated on lighter fuel (API gravity of 29 or above),
they have to burn more fuel to generate the heat to produce the same power output. That would place into question the sufficiency of on-site fuel oil storage for EDG systems. <28
Fuel Oil Quality Monitoring: Bottom Line
- 1. Time to determine acceptability of fuel oil shipments is before off-loading into on-site storage tanks. Proactive licensees will subject samples of delivered fuel to quality tests before accepting or permitting the fuel to be off-loaded
- 2. Does licensee's program periodically assess quality of fuel oil in tanks? Moisture (condensation/infiltration), deterioration of tanks (leaks/rusting), fuel aging, microbial growth impact fuel quality.
NOTE: Biodiesel has potential to cause a number of problems, discussed in Chapter 13.
Lube Oil Analysis and Trending Lube oil analysis can reveal much about engine internal condition.
Take samples down-stream from supply pump, prior to filter, with system at normal operating temp, pressure. Analysis reveals:
Lubrication oil condition: Important properties viscosity, oxidation, total base number/total acid number (TBN/TAN),
additive concentrations.
Typical values for new oil should be available from oil supplier or producer. Set alert and action values for end-of-useful-life.
Lube Oil Analysis and Trending (continued)
Contamination: Usually due to the operating environment.
Those monitored include water, glycol, TBN/TAN, SOx or NOx (changes), fuel dilution, viscosity changes, and dirt (Si, etc).
Engine internal component condition: Engine condition/wear indicated by metal concentrations in oil. Engine wear metals of interest include iron, copper, lead, tin, chromium, aluminum, silver (as applicable). Specify expected wear metals of concern to lab performing lube oil analysis. Engine manufacturer's data used to set alert and action values for each
Lube Oil Analysis and Trending (continued)
Major engine problems have been missed due to inappropriate alert limits, no limits set, or lab reports not being reviewed in timely manner CASE EXAMPLE -- Crankcase Explosions: Engine failures occurred in which wear metal trends should have alerted operators well in advance. Cooper-Bessemer "KSV" engines in service at several NPPs had 13 crankcase "explosion" events... Reference IN 92-78.
S.M. Figures 12-1 and 12-2 are photographs of pistons from an engine after an explosion.
Figure 12-1 Piston with Advanced Tin Smear Tin removed from side of piston, exposing the base metal (dark area).
Some scoring of piston base metal, plus indication of sticking rings.
The direct result of inadequate lubrication (multiple underlying causes).
Figure, 12-2 shows this effect on another piston with more severe damage.
Figure 12-2 Failed Piston -- Tin Wiped Off Essentially all tin removed from sides, exposing the base metal (dark area).
Scoring of piston base metal, entrapped rings, and evidence of blowby.
The direct result of inadequate lubrication (multiple underlying causes).
Lube Oil Analysis and Trending (continued)
Root cause of Cooper KSV crankcase explosions was insufficient pistoncylinder liner lubrication. Multiple contributing factors:
Routine "fast start" tests with loading Very cold intake combustion air Oil scraper ring near bottom of piston, to reduce oil use in continuous-duty service. Also wrist pin end cap.
Corrective actions taken, no further KSV explosions reported.
What monitoring would have prevented it?
Being alert to crankcase pressure! Effective lube oil monitoring analysisfollow-up. An oil mist monitoring system
EDG / Support System Monitoring Engine and support system parameters provide general indication of mechanical condition, combustion performance.
To obtain valid results, run EDG at repeatable baseline conditions with monitored parameters stabilized before data collection.
Progressive/step changes in parameter values should be analyzed.
Following: List of parameters that should be monitored. Those with round bullet point (*) are required by IEEE 387-1995, Table 4 Others, identified with (), will assist engine/generator monitoring.
EDG/Support System Parameters to Monitor Pressures:
- Lube Oil: Engine Inlet
- Lube Oil: Turbo Inlet
- Lube Oil: Engine, Filter Differential
- Lube Oil: Turbo, Filter Differential
- Lube Oil: Engine Header
- Crankcase (Positive/Negative)
Fuel Oil (Pressure and Flow)
Cylinder Combustion Air Inlet Manifold Cylinder Inlet Manifold Boost Pressure
EDG/Support System Parameters to Monitor Temperatures:
- Lube Oil: Engine Inlet and Outlet
- Jacket Water: Engine Inlet, Outlet
- Exhaust: Each Power Cylinder
- Exhaust: Turbo Outlet
- Exhaust: Manifold (if applicable)
Cylinder Combustion Air Inlet Manifold Engine Bearings Generator Stator
EDG/Support System Parameters to Monitor Electrical:
- Frequency
- Power (KW)
- Reactive (KVAR)
- Current: Generator, All Phases
- Voltage: Generator, All Phases
- Current: Generator Field Voltage: Generator Field
EDG/Support System Parameters to Monitor Fluid Levels:
- Jacket Water: Standpipe/Expansion Tank Level Engine Lube Oil Sump Level Generator Bearing Oil Reservoir Level Other Parameters:
Engine speed Fuel rack settings All Alarmed Indications Ambient conditions (temperature, etc)
Engine hours (calendar time plot)
Engine Cooling Water Analysis Primary concerns for engine cooling water systems are:
Fouling and Scaling Impair heat transfer Component corrosion Potential leakage, failure Closed loop cooling water tests (typical): conductivity, chloride titration, Ph, antifreeze/additive concentrations, microbiological growth (count).
Open loop cooling water tests usually track total dissolved solids, Ph, salt hardness, microbiological growth, ...
Jacket water inletoutlet temps can warn of fouling/scaling
Engine Exhaust Emissions Analysis Emissions testing reveals info on combustion performance and can help identify an engine in need of closer monitoring/adjustments.
Combustion Byproducts of Most Significance for the Engine:
Carbon Monoxide (CO) Measure of combustion efficiency.
Unburned hydrocarbons (HC) Possible crevice volume effect, flame quench, lubricating oil. Associated with engine condition and efficiency.
Particulate (soot) Possible rich unburned fuel spray/lube oil
Engine Exhaust Emissions Analysis (continued)
Additional Combustion Byproducts:
Nitrogen Oxides (NOx) From nitrogen reaction with high temp burned gases. Largely related to the combustion temperature (thermal NOx). Can be associated with injection timing, spray pattern, or air temperature issues.
Sulfur Oxides (SOx) Little value for engine monitoring now (ULS) fuel.
Increased emission levels from baseline may indicate timing changes, fuel system issue, general engine/cylinder condition.
"Engine Analyzers" for Monitoring Systems monitor cylinder pressures, temps, and/or vibration. Data integrated with crankshaft angle, fuel rack position. Supplemental equipment can monitor lube oil parameters on-line, as EDG runs:
These systems trend data, compare to baseline
$$$ but potentially powerful tool to monitor engines US Navy Integrated Condition Assessment System (ICAS)
Data from specific engine analyzer engine monitoring systems:
"Engine Analyzers" for Monitoring (continued)
Phased Cylinder Pressure Type - Data on individual cylinder pressure characteristics through engine cycles:
Peak firing pressure spreads, deviation Peak firing pressure angle (phased cylinder pressure)
Rate of cylinder pressure change (first derivative, psi/degree)
Mean effective pressure Indicated horsepower Reference compression pressure Reference exhaust/intake terminal pressure
Use of "Engine Analyzers" (continued)
Average cylinder peak pressure + peak pressure spread monitor engine deviation from baseline. Stress cylinder peak pressure.
When pressures excessive: damage (?)
NOTE: Matching peak firing pressures between cylinders within predetermined band = most accurate method to balance engine
("peak firing pressure balancing"). High cylinder peak pressure can occur for a variety of reasons. Cylinder with highest peak pressure *may* not be one with highest load. (Investigate, fix)
Figures 12-3 thru 12-6 show Phased Cylinder Pressure data.
Figure 12-3 EDG Diagnostic Report - PFP vs. Crank Angle (Right Bank)
Figure 12-4 EDG Diagnostic Report - PFP vs. Crank Angle (16 Cylinders)
Figure 12-5 EDG Diagnostic Report - PFP vs. Crank Angle (& Swept Volume (4L)
Figure 12-6 EDG Diagnostic Report - PFP vs. Crank Angle (& Swept Volume (2R)
Use of "Engine Analyzers" (continued)
Phased Engine Vibration (VT) and Ultrasonic (UT) Type: Monitor vibration, "listen" for ultrasonic frequency anomalies relating to:
Valve train condition Main bearing condition Piston to cylinder interaction Cylinder combustion characteristics Piston blow-by and cylinder-ring interaction Injector nozzle characteristics, injection pump status Magnitude and duration of exhaust blow-down event Turbocharger and/or supercharger status, including bearing Piston pin, articulated pin, or connecting rod bearing condition
A Practical Cylinder Balancing Method Engine balance assessed from temps, pressures in each cylinder.
Exhaust temp: Pyrometers just downstream of exhaust ports Cylinder press: Gauges at test ports open to combustion space Cylinder pressures are *preferred* means of balancing an engine.
Cylinder temperatures typically used to monitor cylinder balance during routine operation.
As a "rule of thumb" balanced engines will typically have:
Exhaust temperature deviations < 150°F (80°C)
Cylinder firing pressure deviations < 150 PSI
Good place for a break!
Crankcase Oil Mist Monitoring Crankcase oil mist detection systems warn of engine mechanical distress: cylinder wallpiston scuffing, incipient bearing failure, etc. Localized hot spots that boil lube oil, producing oil mist Normal crankcase oil mist concentration typically < 2 mg/liter Lower explosive limit (LEL) for lube oil mist is 50 mg/liter Performance issues in early systems hindered acceptance Now use signal processing to prevent false alarms at start-up.
Also provide calibrated oil mist concentrations Data logged to assess trends. Alertalarm levels can be set Figures 12-7A, -7B illustrate installed system (UK)
Figure 12-7A Crankcase Oil Mist Monitoring System Figure 12-7B Crankcase Oil Mist Monitoring System Infrared (IR) Scanning as a Monitoring Tool Engine, generator, electrical system, support equipment anomalies often result in pronounced temperature variations from norm:
Failing electrical termination Electric motor overloaded or bearing failing Generator winding or bearing overheating Engine cylinders with large variations in loading Failing electrical transformer, overloaded electrical circuit Portable IR imaging equipment is cost-effective tool. Take images at stabilized, steady-state conditions, compare to baseline data...
Figures 12-9A, 12-9B
Ordinary Visual Inspection IR Thermograph of Same Equipment Figure 12-9A IR Thermograph of Impending Failure
Overheating Bearing Electrical Termination One Leg of 3-Phase Fuse Block Figure 12-9B IR Thermographs of Impending Failures
Monitoring by Human Senses Visual observation + other human senses can identify equipment anomaliesoften better than high-tech, high-cost systems:
Visual inspection before EDG run (use check list) to verify readiness for operation, look for any problems Repeat after run. Verify configured for emergency use.
Non-Visual: Overheating transformer or motor will have odor, may be unusually hot to touch. Unusual noises should trigger action to determine what has changed Human senses compliment technology-based monitoring systems. (Always involved in assessing their data.)
Monitoring Summary NO monitoring scheme/system will provide complete, conclusive information on engine health, maintenance needs. Integration, analysis of data from ALL sources will enhance EDG reliability.
All successful predictive monitoring programs have:
Access to data collected under consistent and reproducible conditions. Baseline data for comparison.
Data review by experienced personnel with knowledge of engine design details, operations.
Clear responsibility and authority to obtain corrective action for anomalies with potential to impact readiness/reliability.
Selected Maintenance Topics EMD Lube Oil Change (Adverse Consequences)
Recommended oil had chlorinated additive: Unable to recycle Changed to oil used in rail service EMD engines. Wrist pin failures resulted because types of service were so different.
Additive was for extreme pressure service, also kept oil on surfaces during long shutdownsboth typical of NPP service.
Substitute oil lacked equivalent extreme pressure capabilities, or adherence qualities.
See IN 2002-22, "Degraded Bearing Surfaces in GM/EMD Emergency Diesel Generators" (includes consultant reports).
Selected Maintenance Topics (continued)
EDG Support Systems Major Contributors to Inoperability Events Long-term studies: Engine-mechanical problems cause just 5-10% of failures. Testimony to durability, reliability of diesels Engine monitoring still emphasized because failures can be catastrophic, major $$$ impact.
This statistic does support placing more emphasis on support system operability.
Figure 12-8 > Data on failure rates of EDG sub-systems.
Based on years of Licensee Event Reports (LERs)
Idaho National Engineering Laboratory (INEL) data is for 353 LERs, 1987-1993.
Southwest Research Institute (SwRI) data is based on 689 LERs, 1968-1982.
US Navy data is skewed by piston-cylinder failures with one engine family, plus a high rate of cooling water problems. Their Instrumentation and Control data do not correlate with the other sources.
Nuclear Plant Reliability Data System (by Institute of Nuclear Power Operations) includes many EDG event reports not in NRC's LER system due to being a non-demand situation, therefore not reported.
Figure 12-8 EDG Failures by Responsible System
Selected Maintenance Topics (continued)
Post-Maintenance Inspections Critical Many failures attributed to lack of effective post-maintenance inspection after any work done on EDG, any support systems, or just in vicinity. Examples in Chapter 13 Engine "Air Roll" or "Bar" Check Before any run following maintenance or idle period, perform "air roll" to verify freedom of movement. Cylinder test cocks open, fuel racks in "no fuel" position Licensee experience has proven worth of this procedure!
Not universal practice, but recommended by manufacturers.
Selected Maintenance Topics (continued)
Engine Owner Groups - Discussed in the Student Manual Long-Term Aging Concerns Heightened by plant license extensions Some licensees still routinely perform fast start - load tests Comprehensive EPRI Report on Diesel Engine Analyzers "Everything you wanted to know but were afraid to ask" Free download available at their web site (hard to find) http://my.epri.com/portal/server.pt?space=CommunityPage&cached=
true&parentname=ObjMgr&parentid=2&control=SetCommunity&Com munityID=404&RaiseDocID=TR-107135&RaiseDocType=Abstract_id
END OF CHAPTER 12