1. Reliability Risk Assessment
Ray Barlog, PE
March 24, 2015
“Service Measured to the Standard”
Cornerstone Electrical Consultants, Inc.

2. Safety and Reliability
Both deal with uncertainty, aim to reduce undesired outcomes
Safety mostly concerned with avoiding harm to humans
Reliability most often concerned with reducing economic losses - $$
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3. Cornerstone Electrical Consultants, Inc.
Risk
- An event that has a negative consequence and has a probability of occurring (not an opportunity)
Risk = Likelihood x Consequence
Reliability Risk = Failure Probability x $$ Impact
Reliability Risks are often not constant across time
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4. Cornerstone Electrical Consultants, Inc.
Risk
Do We Want To…………
Eliminate Risk?
Reduce Risk?
Manage Risk?
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5. Risk Management Process
Identify
Analyze
Evaluate
Respond
Control
Assessment
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6. Cornerstone Electrical Consultants, Inc.
Risk Assessment
The process of identifying, analyzing, and evaluating, and prioritizing risks
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7. Some Reliability Risk Assessment Methods
Functional FMEA Process FMEA Equipment FMEA Expected Value FMEA Fault Tree Analysis Qualitative Fault Tree What If Analysis
Bow Tie Analysis RAM Modeling Stochastic Life Cycle Cost Concept FMEA Event Tree Analysis Layer of Protection Analysis Markov Analysis
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8. Cornerstone Electrical Consultants, Inc.
3 Reliability RA Tools
Functional Failure Mode and Effects Analysis
Bow Tie Analysis
Reliability, Availability, Maintainability (RAM) Modeling
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9. Cornerstone Electrical Consultants, Inc.
FMEA
Probably the most common reliability risk assessment tool
Structured method
Best using team with diverse backgrounds
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10. Cornerstone Electrical Consultants, Inc.
FMEA
Came from Military Procedure MIL-P-1629, Procedures for Performing a Failure Mode, Effects and Criticality Analysis, dated November 9, 1949.
FMEA used and improved by NASA in the 1960's to improve and verify reliability of space program hardware.
Mil-Std-1629A used in the military and by commercial
Used in the Nuclear Power Industry for evaluating design risks
SAE J an FMEA standard used in the auto industry
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11. FMEA-asks the questions
What is the intended function?
How does it fail? ( failure mode )
How often do we expect the failure to occur?
How severe are the effects?
What are the potential causes of the failure?
How likely is the onset of failure to be detected?
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Common Example
Objective: Determine the most critical risk and its cause(s) for this boiler feed water system.
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Common Example
If 2 pumps fail, both boilers trip
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Common Example
P-1
P-2
P-3
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15. Cornerstone Electrical Consultants, Inc.
Risk Rating Factors
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16. Cornerstone Electrical Consultants, Inc.
FMEA Worksheet
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Bow Tie Analysis
A simple graphical tool that shows the link between potential causes, preventive and mitigating controls, and consequences of a risk event
Shows at a glance how risks are managed
Can be purely qualitative or semi-quantitative
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Reason’s Swiss Cheese
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Generalized Bow Tie
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Example Risk Matrix
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21. Bow Tie-Common Example
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22. Cornerstone Electrical Consultants, Inc.
RAM Model
RAM: Reliability, Availability, Maintainability
Reliability: Probability of surviving a given time interval without failure under given conditions
Availability: Average % time a system is in a state to perform a function
Maintainability: Probability of completion of a maintenance task in a given time interval
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23. Cornerstone Electrical Consultants, Inc.
RAM Model
A graphical and mathematical representation of system operation, dependency, and performance
Most quantitative of the three methods presented
Requires failure data, repair time data, and system operating logic
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24. RAM Model Building Block
Series
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25. RAM Model Building Block
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26. Cornerstone Electrical Consultants, Inc.
RAM Model-Example
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27. RAM Model-Typical Input
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RAM Model Results
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RAM Model Results
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Pros / Cons - FMEA
Tedious, Time Consuming
Requires robust risk matrix
Doesn't handle redundancy or multiple failures well
Doesn't handle dependencies well
Doesn’t handle increasing failure rates well
Structured, Thorough
Easy to Learn
Uses Group Knowledge
Requires no special software
Excellent for evaluating designs early in the process
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Pros / Cons – Bow Tie
Quantifying risk requires modification
Requires robust risk matrix
Software recommended for good documentation
Becomes complex with large systems
Excellent risk management communication tool
Easy to learn and interpret
Uses group knowledge to develop
Fairly quick to develop
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Pros / Cons – RAM Model
Can be labor and $$ intensive for large systems
Not easily understood by person not trained
Requires special analyst skills for model building
Quality of model depends on quality of data
Quantifies risks for prioritization
Estimates risks over time
Handles dependencies, redundancy, special ops rules
Evaluating “What Ifs” can be done quickly
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33. Cornerstone Electrical Consultants, Inc.
Final Thoughts
There is NO one best or universal method.
Use the simplest method that can help you meet the objective of your assessment with the minimum investment of time and resources.
Risk assessment alone is valueless- risks must be managed and that takes action.
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34. What are your questions?
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