QRMEC-Elsayed May 28 2013

8/12/2019 QRMEC-Elsayed May 28 2013

1/47

Reliability and Maintainability

Engineering: An Overview

E. A. ElsayedDepartment of Industrial and Systems Engineering

Rutgers University

New Jersey, USA

[email protected]

1


2/47

Brief Topics

Some initial thoughts and personal

experience Reliability definition

Reliability testing

Methods for improving reliability

Maintenance strategies: PM, FR,Inspection policies

Condition-based maintenance based oncurrent sensors technologies

2


3/47


4/47

Topics



Reliability testing




4


5/47

Reliability Economics

Oil Pipeline Shutdown (Hardware Failure)

BP shuts oilfield August 8, 2006

Damaged pipeline in Alaska affects 8% of U.S. oil

production; crude surges; record gas prices seen.

The threat of a stoppage also endangers Alaska's budget:Oil taxes account for more than 90 percent of its revenues.

BP officials have acknowledged they did not test the pipes

adequately using a so-called pig device which is run

through a pipe to gauge corrosion (utilizes ultrasound todetect corrosion).,,,inspection and maintenance strategies.

5


6/47

Reliability Engineering

Air Traffic Delays (Software Failure)

Nov 19 2009: A computer glitch caused flight

cancellations and delays across the U.S.

The problem involved the FAA computer systems

in Salt Lake City and Atlanta that handle

automated flight plans, forcing air traffic

controllers to revert to the much more time-

consuming approach of entering flight plans by

hand.

Software failure (7000 flights)

6


7/47

Global Impact: Oceanic Airspace

Data Link Communication Reliability

Oakland ARTCC

ARINC SITA

Ground

EarthStations

Uplink

7

Engine

MonitoringAOC or Aircraft

Operational

Communication

Position

Monitoring


8/47

Recall of Cars due to Degradation

October 1, 2012(Environmental conditions)

8

General Motors Co. recalled more than 40,000 cars sold inwarm-weather states because a plastic part might crack and

cause a fuel leak.

The recall affects vehicles sold or currently registered inArizona, California, Florida, Nevada or Texas. Owners in

Arkansas and Oklahoma also are included in the recall of the

2009 Cobalt and G5.

The vehicles have plastic parts connected to the fuel pump

which could crack. If the crack gets large enough, fuel could

leak out of the vehicle and cause a fire.


9/47

Reliability Definitions Measurements

When you a buy a product or service

you request high quality and high reliability

How do you measure it? What is high?

How long? Reliability: 0.99 at year 5, 0.999 at year 4

Time dependent qualityreliability

How do companies predict reliability and estimatewarranty?

Reliability of cold standby units New tires and oldtires

9


10/47

Maximum Reliability level

Reliability

WithRepairs

Time

NoRepairs

Some Initial Thoughts

Repairable and Non-Repairable

Another measure of reliability is availability (probability

that the system provides its functions when needed).

10


11/47

Some Initial Thoughts

Failure Rate During Life Cycle

Will you buy additional warranty?

Burn in and removal of early failures.

Time

Fa

ilureRate

Early Failures

ConstantFailure Rate

Increasing

FailureRate

11


12/47


13/47

13

Reliability Definitions

Reliability is a time dependent characteristic.

It can only be determined after an elapsed time but

can be predicted at any time.

It is the probability that a product or service will

operate properly for a specified period of time (design

life) under the design operating conditions without

failure.

13


14/47

14

Other Measures of Reliability

Availability is used for repairable systems

It is the probability that the system is operational atany random time t.

It can also be specified as a proportion of time thatthe system is available for use in a given interval(0,T).

Mission availabilityplay time, military products

One shot devicesmissiles, standby generators.

14


15/47

15

Other Measures of Reliability

Mean Time To Failure (MTTF): It is the average

time that elapses until a failure occurs.

It does not provide information about the distribution

of the TTF, hence we need to estimate the variance

of the TTF.

Mean Time Between Failure (MTBF): It is the

average time between successive failures.

It is used for repairable systems.

15


16/47


17/47

Brief Topics



Reliability testing




17


18/47

1818

Types of Reliability Testing

Highly accelerated life testing (HALT) Highly accelerated stress screening (HASS)

Accelerated life testing (ALT)

Degradation testing (DT) Accelerated Degradation Testing (ADT)

Acceptance test (AT)


19/47

19


20/47

2020

Purposes and Needs

1. Investigate failure modes and correct designs

2. Improve reliability during development

3. Demonstrate reliability for accepting a design

4. Predict reliability

5. Eliminate units with manufacturing defects

(infant mortality failures)

6. Accept or reject a products


21/47

2121

Idea of Accelerated Stress Testing

Compression and extrapolation

Use conditionSeverer condition

Life

Stress

Unknown

extrapolation

MTTF


22/47

Testing and Acceptance

Testing and Life Prediction:

Conduct extensive reliability testing for both

demonstration (acceptance of products) and life prediction.

Collect continuously to have constant assessment of thesystem reliability. Always assess the mean residual life to

determine the optimum time to replace the systemspecially in the wear out region..

Suppliers need to provide evidence of systems reliability.

22


23/47

Current Cycle Profile: -40 C to 125 C

New Cycle Profile: -65 C to 170 C

Stress type, stress loading, sample size, duration of

the test.???


24/47

2424

Summary of Reliability Testing

1 2 3 4 5 6

RDT X

RGT X

HALT X X

HASS X X

ALT X X

DT X X

ADT X X

Burn-in X

Acceptance X X


25/47

Brief Topics



Reliability testing




25


26/47


27/47

System Design Contd

System design: Implicit

RedundancyPumps connected in series.

Two consecutive failures for the system to fail

27


28/47

Brief Topics



Reliability testing




28


29/47

Failure Rate and Maintenance

Availability

Region 1, repair upon failure (FR)

Region 2, no PM

Region 3, PM, Condition-based, if possible.

Time

FailureRate

Early Failures

Constant

Failure Rate

Increasing

FailureRate

29


30/47

30

Distribut ion of the state

after maintenance

System State under Imperfect Maintenance

Time t

T1

> T2

> T3> T

4

0

ST

A

T

E

X(t) D

PM

R1 R+

1 R2R+

2

DF

R3R+

3 R4 R+

4 R5R+

5 R6R+

6

is the failure threshold while is preventive

maintenance threshold.FD PMD


31/47

Maintenance

Maintenance:

Time to perform maintenance is normally

recommended by the manufacturer of the equipmentoperating under normal conditionswhat is normal?

If the estimate of failure time is conservative, onerisks the replacement of items before its useful life.

If the estimate of failure time is optimistic, one risks

that the component or system may fail in service.

Use Condition-Based Maintenance

31


32/47

Brief Topics



Reliability testing



Condition-based maintenance based onadvances in sensors technologies

32


33/47

Technological Advances and Maintenance

Condition-based Maintenance

The recent advances in sensors technology,

chemical and physical non-destructive testing

(NDT), and sophisticated measurement techniques,

information processing, wireless communications

and internet capabilities have significantly impactedthe condition-based maintenance approach by

providing dynamic maintenance schedules that

minimize the cost, downtime and increase system

availability.

33


34/47

Condition-Based Maintenance Example

Otis Elevators / United Technologies

Remote Elevator Monitoring

It is an interconnected system of sensors,

monitors, circuits, hardware and software used

to collect, record, analyze and communicate

elevator data continuously monitors hundreds ofdifferent functions on elevators worldwide

(braking time, acceleration, deceleration, floor

level, door opening, forces on strands,..).

34


35/47

Condition-Based Maintenance Example

If the system detects a problem, it analyzes and

diagnoses the problems cause and location. Itmakes the service and aids Otis mechanic in

identifying the exact component(s) causing the

problem, which helps to facilitate a timely and

accurate resolution.

Issues:

Which component or subsystem?What is the indicator?

What is the alarm level of the indicator?

What is the action?35


36/47

3636

Most of mechanical components such as gears,

brakes, bearings exhibit degradation before

failure.

Ductile materials have degradation indicators:

change in its physical properties Electronic components such as resistors,

capacitors, diodes exhibit change in

performanceresistance drift as an example

Polymers and elastomers change properties with

time and stress

Degradation Indicators


37/47

3737

Examples of these indicators includehardness

which is a measure of degradation of elastomers. This is due to the fact that

elastomeric materials are critical to many

applications including hoses, seals and dampers

of various types and their hardness increases

over time to a critical level at which their ability

to absorb energy is severely degraded. This

may lead to cracks or excessive wear and

related failure modes in components

Degradation Indicators


38/47

38

Continuous-time Continuous-state

Degradation (Indicators)

Examples

Light intensity degradation of light emitting diode (LED)

Metal crack propagation

Wear of tires, brake system wear out, nozzle blocking.

Increase of stiffness of energy absorbing material.

Strength loss of steel beams due to corrosion


39/47

Degradation Path

39

dX t dt dW t

0 i idX t dt dW t X t x t W t


40/47

Brownian Motion: Parameters Estimation

Using the Maximum Likelihood Estimator we obtain the

parameters of the Brownian Motion degradation path as

40

2

1 1

2

2

2

1 1

1 1

n ni ii

i

i i

i i

n ni ii

i

i i

y mym v

n n

m t v t

y my

t n t n


41/47

First Passage Time Distribution

41

degradation 1

degradation 2

threshold 1

threshold 2

R l t D d ti t F il Ti


42/47

42

Relate Degradation to Failure Time

Distribution (First Passage Time)

:Failure time

0

10

20

30

40

50

0 20 40 60 80 100 120 140 160 180 200

Time

Data 1

&Exponential Fit 1

Data 2

&Exponential Fit 2

Data 3

&Exponential Fit 3

Data 4

&Exponential Fit 4

Critical Degradatio

Degradation vs Time( ) )R t t stProb(the 1 time for degradation measure to cross the failure threshold

Failure threshold


43/47

First Passage Time Distribution

43

In degradation modeling we set a degradation

threshold level at which the performance of the

system is considered unacceptable. The thresholdlevel is . The probability of failure can be

defined as

The time to cross the threshold level is referred to

as the first passage time. It has a distribution andits density function is given as shown next.

fD

1

fD t

F t P T t


44/47

Failure Data in Oil and Gas Industry

OREDA database:

MTBF motor driven dry-wet compressor unit

=1.8 year (It is really MTTF)

Major Failures: 80% of all forced outages are

caused by unforeseen liquid ingress into

compressor

44


45/47

Failure Data in Oil and Gas Industry

OREDA database:

Seal Failures: 80% of all seal failures are caused contamination

aging (elastomers)

Solution Analysis of 11,000 mechanical seal failures from

148 different reliability contract and alliance plant

sites over two years show that that 13% of theseal failures are attributable to lack of effective

corrective and preventive maintenance.

45


46/47


47/47

QRMEC-Elsayed May 28 2013

Documents

Transcript of QRMEC-Elsayed May 28 2013