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

Reliability Risk Assessment

Ray Barlog, PE

Cornerstone Electrical Consultants, Inc.

“Service Measured to the Standard”

March 24, 2015

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 - $$


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


Risk

Do We Want To…………

Eliminate Risk?

Reduce Risk?

Manage Risk?


Risk Management Process


Identify

Analyze

EvaluateRespond

Control

Assessment

Risk Assessment

The process of identifying, analyzing, and evaluating, and prioritizing risks


Some Reliability Risk Assessment Methods

Bow Tie AnalysisRAM ModelingStochastic Life Cycle Cost Concept FMEA

Event Tree Analysis

Layer of Protection Analysis

Markov Analysis

Functional FMEAProcess FMEA

Equipment FMEA

Expected Value FMEA

Fault Tree Analysis

Qualitative Fault Tree

What If Analysis


3 Reliability RA Tools

• Functional Failure Mode and Effects Analysis

• Bow Tie Analysis

• Reliability, Availability, Maintainability (RAM) Modeling


FMEA

• Probably the most common reliability risk assessment tool

• Structured method

• Best using team with diverse backgrounds


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 J1739 - an FMEA standard used in the auto industry


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?Cornerstone Electrical Consultants, Inc.

Common Example


Objective: Determine the most critical risk and its cause(s) for this boiler feed water system.

Common Example


If 2 pumps fail, both boilers trip

Common Example


P-1 P-2 P-3

Risk Rating Factors


RATING

DEGREE OF

SEVERITY

QualitativeFAILURE

RATE (_/yr)DetectionCertainty

1 Less than $50K

Likelihood of occurrence is remote 1.00E-06

Almost certain that the potential failure will be found or prevented before producing an economic loss

100%

2 $50k to $100k

Low failure rate with supporting documentation

1.00E-05

Current controls may or may not detect impending failure

50%

3 $100k to $500k

Low failure rate without supporting documentation

1.00E-04

Current controls probably will not detect the potential failure 0%

4 $500k to $1mm

Occasional failures 1.00E-03

5 $1mm to $5mm

Medium Failure Rate 1.00E-02

6 $5mm to $10mm

Moderately High Failure Rate

1.00E-01

7 $10mm to $100mm

High Failure Rate 1

OCCURRENCE DETECTION

FMEA Worksheet


SubsystemFunction of Subsystem

Potential Failure Mode

O C C

Potential CausesS E V

Potential Failure EffectsD E T

R P N

Current Controls

Recommended Actions

Action Owner

42oo3 Pumps Fail Simultaneously due to seal failure

4

Boilers trip, Production Loss of $100k per day x 5 days plus $50k pump repair cost, Total $550k loss

2 32

Manual Condition Monitoring for vibration

Consider continuous vibration monitoring

Joe Engineer

31 Pump fails and auto-start for standby fails

3

Boilers trip, Production Loss of $100k per day x 5 days plus $60k repair cost. Total $560k loss

3 27Periodic Testing of Auto-Start

None NA

4Loss of Station Service Bus B

5

Boilers trip, Production Loss of $100k per day x 15 days plus $100k repair cost. Total $1.6mm loss

2 40Periodic ultrasonic corona testing

None NA

3Pump 1 fails and Station Service bus B fails

5

Boilers trip, Production Loss of $100k per day x 15 days plus $50k repair cost. Total $1.55mm loss

2 30Periodic ultrasonic corona testing

None NA

Loss of ALL feed water flow

Deliver feedwater to boilers at 2mmpph rate

Boiler Feed Pump System

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


Reason’s Swiss Cheese


Generalized Bow TieT

hrea

ts o

r C

ause

s

Con

sequ

ence

s

Cause 1

Cause 2

Cause 3

Cause 4

TOP EVENT

BarriersMitigations


Example Risk Matrix


A <$50k

B $50 to $500k

C $500k - $5mm

D $5mm-$50mm

E $50mm - $100mm

1 ( 1/yr)

2 (1/10yr)

3 (.001)/yr

4 (.0001)/yr

5 (.00001/yr)

Freq per Year or

Likelihood

Financial Consequence Severity

Bow Tie-Common Example


_ _ _ _

2 Medium 1 Weak 3 Strong 3 Strong

_ _ _ _

2 Medium 2 Medium 1 Weak 1 Weak

_ _ _

2 Medium 2 Medium 2 Medium

_

2 Medium

THREATS or CAUSES

BARRIERS / PREVENTIVE CONTROLS MITIGATIVE CONTROLS

Large Production Downtime Losses $550k-$5mm

CONSEQUENCES

2oo3 pumps fail due to seal failures F=1

Pump redundancy

Robust shaft and bearing design

Burner Trip System

3 Element BFW Control System

Boiler Tubes Damaged $10mm

TOP EVENTInadequate

BFW Flow to Boilers

One pump fails and auto-start fails F=1

Periodic testing of auto-start

Operator response

Quick Pump Repairs

Spares Stocking Strategy

Planned Repairs Prior to Major Damage

Significant Pump Repair Costs >$100k

Station Service Bus B Failure F=2

Corona testing to detect onset of failure

P-2 or P-3 fails and SS Bus A fails F=3

Corona testing to detect onset of failure

Use of Predictive Maintenance Techniques

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


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


RAM Model Building Block

• Series


RAM Model Building Block


RAM Model-Example


RAM Model-Typical Input


RAM Model Results


System Mean Availability 99.986%, +/- 0.052%

Average Annual Production Losses 2.457 mmLb/yr

Average Annual Production Losses $5,120/yr

Average Outage Duration 160.6 Hrs

Longest Duration Outage 372 Hrs

Shortest Duration Outage 0.34 Hrs

Results of 1000 Simulations, 20 Years in Length

System Life Cycle Performance Summary

RAM Model Results


Pros / Cons - FMEA


• Structured, Thorough

• Easy to Learn

• Uses Group Knowledge

• Requires no special software

• Excellent for evaluating designs early in the process

• 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

Pros / Cons – Bow Tie


• Excellent risk management communication tool

• Easy to learn and interpret

• Uses group knowledge to develop

• Fairly quick to develop

• Quantifying risk requires modification

• Requires robust risk matrix

• Software recommended for good documentation

• Becomes complex with large systems

Pros / Cons – RAM Model


• Quantifies risks for prioritization

• Estimates risks over time

• Handles dependencies, redundancy, special ops rules

• Evaluating “What Ifs” can be done quickly

• 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

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.

What are your questions?


Documents

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