Improving Machinery Reliability 3 Episode 15 doc

Survey Data On MTTF vs Practices Survey sheets were sent to many engineers asking for their opinions on how life of pump components was effected by installation/operation/maintenance p

604 Iniproviizg Machinery Reliability

In spite of relatively high maintenance costs, the Society of Maintenance and Reli- ability (SMRP) Professionals reported in 1996 that more than 56% of U.S industries

do not have a comprehensive maintenance and reliability program Modern Power

Systems, July 1994, reported results from an EPRI study, which was independently collaborated by Chevron, that showed the execution of a predictive maintenance pro- gram on electric motors could reduce the cost of maintenance by more than 50%

Comparative Cost of Maintenance Strategies

Run to Failure EPRI Study $1 7-$19

Chevron

Preventative Maintenance

$1 1 -$13

$1 3

Predictive Maintenance

$ 7 4 9

$8

Figure A-3 Predictive maintenance practices for electric motors can reduce mainte-

nance costs by 50%)

Current Maintenance Methods Differ Significantly from Best Practice

SMRP surveyed their membership in the Spring 1996 and reported that only 44%

of their membership have integrated reliability and maintenance programs Surpris- ingly, 17% of the companies surveyed reported the absence of any reliability or pre- dictive maintenance program

Maintainability

No Reliability or

Maintainabilit

Reliability and Maintainability

Figure A-4 Do you have a reliability and maintainability process?'

Appendix A: Useful and Interesting Statistic 605

Deloitte and Touche in their study, “Maintenance Practices and Technologies,” report that management recognizes the importance of maintenance Diagnostics and predictive maintenance practice rank as high as traditional cost reduction programs

Min Plant Down Time

Figure A-5 Maintenance programs recognized to be of importance.’

The same Deloitte and Touche study shows that the majority of companies sur- veyed employed reactive maintenance strategies versus the preferred predictive and proactive capability with a high degree of automation

C L Hays, in his paper entitled, “Plant Maintenance and Diagnostics, Current Practice and Future Trends” at the P/PM conference in late 1996 summarized the disadvantage of a strict preventive maintenance policy based on a time-based overall

of a mechanical component

Figure A-6 shows the traditional “bathtub curve” that represents the probability of

a failure versus time for a random system Traditional preventative maintenance practice is based on “guessing” the appropriate time to replace a critical component

to avoid the expected downtime from a failure The premature replacement of a criti- cal component under the preventive maintenance strategy does not always result in improved uptime because the system may experience an untimely failure of the new component

Condition-based maintenance strategies (CBM) are key to improving the uptime

of a mechanical system CBM is based on the ability to proactively identify the root cause of failures, eliminate the source of failures, and to provide for predictive main- tenance methods These methods provide early detection of impending failures and thus provide for maximum system life without prematurely introducing an overall cycle as is shown in Figure A-6

Plant-wide Asset Management Provides Platform for Integrating Assets

The second Offshore Reliability Data Survey (OREDA) of ten large offshore petroleum producers in the North Sea provides an interesting view of the failure rates of major plant assets used for offshore oil production

606 Improving Machinery Reliability

Predictive maintenance assures early detection

of failures

I '

Figure A-7 is based on the failure rate data provided in the OREDA report and confirms the premise that rotating equipment affords the most significant opportuni-

ty for increased reliability and reduction of maintenance costs

Figure A-7 OREDA failure data

Appendix A: Useful and Interesting Statistic 607

maintenance strategies showing significant savings

Regulatory Advanced P/PM

Control Control Strategies

Figure A-9 Early adopters measuring savings from asset management?

608 Improving Machinery Reliability

The December 1995 P/PM Journal chronicles a study of varied pump mainte- nance practices and the value of using predictive maintenance strategies versus run

to fail An overall savings of 40 times the initial purchase price of the pump is

reported

Plantwide asset management provides the platform for integrating emerging main- tenance technologies built on the foundation of field device diagnostics Adoption of

open communication networks and planning with equipment suppliers will permit

realization of the vision of a plantwide asset management system that will reduce

maintenance costs by up to 70%

Early adopters of asset management strategies are already reporting benefits

One early adopter of the “islands of automation” approach has measured savings

of 1.75% versus 3.2% for regulatory control with less than 20% of the assets being monitored

References

1 Boynton, B and Lenz, G., “Plant Asset Management: An Integrated Maintenance Vision,” presented at 6th International Process Plant Reliability Conference, Houston, Texas, October 1997

Paul Barringer, P.E

Barringer & Associates, Inc

Manufacturing, Engineering, and Reliability Consultants P.O Box 3985

Humble, TX 77347-3985 Phone: 281-852-6810 FAX: 281-852-3749 hpaul@barringerl.com http://www barringerl.com

Reliability measures the capacity of equipment or processes to operate without failure for a specified interval when put into service and used correctly

Reliability Definitions

Probability of failure-free interval

Performing the intended function

Working for specified time intervals

Working under stated conditions

Certainty of no failures Performing any possible functions Functioning forever

Working under all possible conditions

Primary Measures Of Reliability

Mean time between failure is a primary yardstick for

measuring reliability

- If MTTF is Iasge compared to the missisn->aeliable

- If MTTF is short cornpared to the mission->unreliable!!

- Do you know your MTTF for rotating equipment?

- Do you know your MTTF for non-rotating equipment?

- Which cost you the most money for failures?

- How much UNreliability can you afford?

- How much UNreliabiIity can you correct?

- What's your Pareto list of the top 10 ten cost items?

-

F

5

g

- Where do you start the corrections and how much can you afford?

Reliability Problems = Business Problems

B

2

h)

0.5 1.0

Reliability Sensitivity to MTTF

0.135 0.368

High Reliability

Requires Long MTTF

5.0 10.0 15.0 20.0 30.0 40.0

Failures: Roots Of eiia bility Problems

Early Plant Life Frequency %

Basic Serial Reliability Models

Appendix B: Reliability Models 615

Practices used by engineering, maintenance, and operations are the foundation for

Reliability

Engineering Principles

New Enaineerina Tools To Solve

Old Nagging Problems

1 Solve the vital few problems

2 Reduce overall costs

3 Use bathtub curve concepts

4 Apply science 8 engineering

using new reliability tools

5 Make life cycle costing decisions

/ P \

The Issue

\

Total Maintenance

Total Productive Maintenance

Involve Production Penonnel In All

1 Aim for effective equipment use

Appropriate Maintenance Tasks Productive

2 Prevent losses by a PM team effort

meet your goal?

be within your control? I

Good Practices

Use Of Best-Of-Class Practices

1 Trained People At Various Levels

2 Good Procedures 8 Practices

3 New Techniques

4 Teamwork between Maintenance

L? Production Departments

Survey Data On MTTF vs Practices

Survey sheets were sent to many engineers asking for

their opinions on how life of pump components was

effected by installation/operation/maintenance practices-

opinions are used since hard facts are not available

Data returned by experts was consolidated, and

(generally) median results are reported below

The characteristics of best, good, and inferior practices

were identified and losses in component life are listed

In general, results from the survey seem realistic

although inferior trend data may be too pessimistic

The data follows trends reported in Bloch & Geitner’s

Pump Curve Characteristics

* Intrinsic reliability- is achieved at BEP

(and measured by mean time to failure)

Centrifugal pump curves are a wonderful advertising device leading naive engineers to believe the entire curve is useful for long

rhis is the correct point for

ichieving the greatest inherent

ife for the pump

Problems Causing Short Pump Life

I

Pump Curve Sensitivity For Pump Reliability

Operational problems noted on the pump curve decrease the intrinsic system reliability-so long life is obtained only for a small portion of the pump curve Best Efficiency Poin

I

Usable Portion Of Pump Curves

Pump Curve Sensitivity For Pump Reliability

Recirculation &

BeannglSeal Problems Best Practices->Long Life

Better Practices

Good Practices->Short Life

Low Bearing &

Low Seal Life

Best Efficiency

f-1

Deviations from BEP result in smaller

MTBF and incur more maintenance

problems along with higher costs

Excursions beyond BEP result in

short lives and unreliability How

much costs can you afford to incur?

% Flow

8

0

Pump Curve Practices-A Model

ow Bearing & Low Seal Life

Life Based On Best Practices For

Installation And Use For All

Features Except How Close The

Pump Operates To BEP

Loss Of Life From BEP Practice

n 9717 1.30 1 388.476 40.96

I

0.9726 2.50 389,045 39.40 0.8547 1.30 341,882 36.05 0.9712 1.30 388.476 40.96 0.9677 1.40 387,090 40.27 0.9712 1.20 388,476 41.71 0.9801 2.00 294,030 29.75

For All

Elect.+

Items

hours hours

N

Best Practices For Installation And Use Including Best BEP Practices Achieves 98% of Inherent System Life

Loss Of Life From BEP Practice

suction 14" case

Best Practices For I ~ s t a l l a t i ~ n And Use Except For Better BEP Brastices Ashieves 90% of Inherent System Life

Better BEP Practices = -20% to + I O % of BEP

Best Practices For Installation And Use Except For Good BEP Practices Achieves 75% of Inherent System Life

Good BEP Practices = -30% to +15% of BEP

Responsibilities For Pump Curves

Engineering is responsible for designing the system

Operations is responsible for keeping the system at

the BEP and issuing maintenance work orders for

correcting impellers/pumps to re-center the BEP

when operating conditions change and BEP is no

longer in the target area

problems identified, Le., removing/replacing the

impeller to meet a size specified by engineering

for short life of bearings and seals

Maintenance is responsible for correcting the 0

Reliability & Costs Effects

Pump Curve Sensitivity Effects

Pump Curve Effects On Component

-

Impeller life Mtr Starter life

Mtr Winding life

Coupling life

-30% to *15% Of BEP

-

Straight Runs Of Suction Piping

create equal mechanical loads on pumps

Short runs of pipe produce unequal impeller loads and cause undesirable loads on the system

Unbalanced loads from short pipe runs produce undesirable vibration loads

The inlet pipe should be 2 sizes larger with special reducers for smooth entry of fluids into the pump

to achieve long life

Short runs of straight pipe result in short MTTF

Loss Of Life From Intake L/D Practice

$00 hp pump: 8" discharge' 10"

suction * 14" case

Good Practice

Best Practices For Installation And Use Except For Better L/D Practices Achieves 92% of Inherent System Life

Better Intake U D Practices = 6 to 8

s

R

0

G-

Best Practices For Installation And Use Except For Good LID Practices Achieves 76% of Inherent System Life

Good Intake U D Practices = I to 3

LID Suction Straight Run

Intake Piping Practice L/D Ratio Effects

LID Suction Straight Run Effects On

Impeller life Mtr Starter life

Rotational Shaft Alignment

Lack of rotational shaft alignment imposes higher mechanical loads on rotating elements which

shortens life

Poor alignment results in short MTTF

0 Good alignment results in long MTTF

Alignment is a three dimensional requirement

Jacking screws and shims are requirements for precision alignment-with limits for the number of shims allowed for corrections before a solid riser block is constructed and used

Standards must be set and maintained at operating conditions

8

a

Effects Of Practices o n Component Life

beta eta

Pump

Good Practice Replacements

Alignment

Practices Multiplier

Life Multiplier

* eta From

Practices 0.9240 0.8120 0.8498 0.8710

0 8498 0.8910 0.9350

1 .oooo

0.9350 1.0000

-

- =-Mea

~I 2.50 369,593 37.43 1.30 324,788 34.24 1.30 339,917 35.84 1.40 348.381 36.25 1.20 339,917 36.50 2.00 267,300 27.04 1.30 140,250 14.79

1 oo 150,000 17.12

1 .oo 280.500 32.02 1.20 300.000 32.21

time between system failures= 2.75

or= 24,060

loss= 2,148

For Ail

M e c h s Items

For All Elect.->

Items hours hours

Best Practices For Installation And Use Except For Better Rotational Alignment Achieves 92% of Inherent System Life

Better Rotational Alignment Practices = 50.003 inches or 50.025 mm

Loss Of Life From Rotational

Except For Effects Of

100 hp pump: 8" discharge" IO" G@ Practices on

Best Practices For Installation And Use Except For Good Rotational Alignment Achieves 65% of Inherent System Life

Good Rotational Alignment Practices = kO.009 inches or k0.229 mm

Rotational Alignment Effects

Rotational Shaft Alignment Error Effects

98%

150%

u) u)

0

CI

100%

Best Practices Better Practices Good Practices

iO.001inch or i0.025mm f0.003inch or t0.076mm t0.009inch or 20.229mm

System Life Includes Pump And Motor-All Other Features Use Best Practices Except As Noted

w

o\

Rotational Shaft Alignment Effects

Mechanical Pipe Alignment

Lack of pipe alignment imposes high mechanical loads

Good pipe alignment results in long MTBF

Poor pipe alignment results in short MTBF

-

3

Pipe alignment is a three dimensional requirement

No-load pipe alignment requires consideration of

temperature changes and the resulting physical

changes in pipe dimensions to reduce mechanical loads

Good pipe alignment practices require hand alignment

without use of mechanical assist to achieve long life in

service

Loss Of Life From Piping

Good Practice

100 hp pump: 8" discharge * 10"

suction * 14" case

Best Practices For Installation And Use Except For Better Piping Alignment Achieves 60% of Inherent System Life

Better Rotational Piping Practices = tO.010 inches or k0.254 mrn

P Loss Of Life From Piping

Alignment Practice

loss= 15,664 hours

Best Practices For Installation And Use Except For Good Piping Alignment Achieves 40% of Inherent System Life

Good Rotational Piping Practices = 20.125 inches or 23.175 mm