BPPTpresentation_06-08-2003

MPT-MATCOR

Ageing of Industrial PlantDr Jonathan Lloyd

CEO, MPT-Matcor Pte LtdSingapore

&Dr Nick Laycock

MPT New Zealand

MPT-MATCOR

Contents…..

• Principal Damage Mechanisms• Where do Losses Occur?• What Ages Industrial Plant• Effective Management of Ageing Plant• Plant Life Assessment• Benefits of RBI• Case Studies

MPT-MATCOR

The 3 main damagemechanisms

• Corrosion

• Fatigue

• Creep

MPT-MATCOR

Where do the major lossesoccur?

0 5 10 15 20 25 30 35

Piping

Tanks

Reactors

Drums

Heat Exchangers

Towers

Heaters & Boilers

Others

%

MPT-MATCOR

What “Ages” Industrial Plant?

• Obsolescence• Corrosion

– most significant damage mechanism by far• Metallurgical damage mechanisms

– exposure to high temperatures• Creep damage• Cyclic (fatigue) damage

MPT-MATCOR

Corrosion

• General Corrosion– well understood

• Stress CorrosionCracking– less well understood

• Pitting Corrosion– most unpredictable

MPT-MATCOR

Metallurgical Damage

• Reduced strengthfollowing thermallydrivenmicrostructuralchanges

MPT-MATCOR

Fatigue damage

• Initiation & growth ofcracks from stressconcentrators

• Requires fluctuatingstresses

• Higher start-up &shut down cycleswill usually lead topremature failure

MPT-MATCOR

Effective Management ofAgeing Plant

• Risk Based Inspection (RBI)

• Reliability Centred Maintenance (RCM)

• Adopting methodologies that:-– Quantify risk– Allocate inspection and maintenance

resources accordingly

MPT-MATCOR

What is Risk?

0 1 2 3 4 5

C onsequences O f Fa ilure

0

1

2

3

4

5

Prob

abili

ty O

f Fai

lure

H igh Risk

Low R isk

(Acceptable Ris k ?)

MPT-MATCOR

Objective of RBI and RCM is toachieve optimum use of resources

cost

cost

level of maintenancelevel of maintenance

operating costoperating costmaintenance costmaintenance cost

O&MO&Mcostcost

optimumoptimumunder maintainedunder maintained over maintainedover maintained

MPT-MATCOR

Why is old plant often written offtoo early…?• Early in life the owners have greater

incentive to identify the cause of aproblem and fix it

• As plant ages and capital cost is writtenoff and/or more efficient technologiescreate obsolescence - less incentive tospend money on fixing a problem

MPT-MATCOR

Most failures usually occur closethe beginning and end of plant life

Time

Freq

uenc

y of

Fai

lure

s

Comm

issioning

Phase Old

Age

MPT-MATCOR

Need for Plant LifeAssessment

• Plant designs often conservative• Designs based on average materials property

data• Life extension is usually possible• If capital has been written off during “design

life” the financial operating cost during theextended life of the plant is low and mayoutweigh other factors like obsolescence

MPT-MATCOR

When Remaining LifeAssessment Becomes Necessary

time (hours)time (hours)100,000100,000

design lifedesign life

absolute lifeabsolute life

life extensionlife extension

economic working lifeeconomic working life

remnant life assessment requiredremnant life assessment required

MPT-MATCOR

Starting Points for RBI• What material is it made from? (Carbon

steel, low-alloy steel, stainless etc.)

• What process fluids is it exposed to in andout of service?

• What temperatures and pressures/stressesis it exposed to?

MPT-MATCOR

The 3 Phase Approach toRisk-Based Life Assessment

Phase I Phase I --calculationalcalculational approach approach-operational and design data-operational and design data-worst case material properties-worst case material properties

Phase II Phase II - field inspection- field inspection-input of condition assessment data-input of condition assessment data

Predictive Predictive assessment ofassessment ofcomponentcomponentintegrityintegrity

IsIspredicted life predicted life

greater than targetgreater than target

YESYESDefine optimum futureDefine optimum futureinspection scheduleinspection scheduleandandlife extension capacitylife extension capacity

NONOPhase III Phase III - refined analysis- refined analysis- material sampling/testing- material sampling/testing- detailed surveillance- detailed surveillance- complex stress analysis- complex stress analysis

Define optimum inspection and Define optimum inspection and refurbishment strategyrefurbishment strategy

MPT-MATCOR

The 3 Phase Approach to Risk-Based Life Assessment 1/3

• Phase 1: Review the plant designand history and identify those areas atrisk, perform inverse design calculationson a worst case (minimum materialsproperty and design conditions basis).Define an inspection workscope.

MPT-MATCOR










MPT-MATCOR

• Phase 2: Perform the inspectionworkscope defined in Phase 1 and inputactual field data into calculations. Theoutcome facilitates definition of futureinspection plans and/or the necessity forPhase 3.


MPT-MATCOR










MPT-MATCOR

• Phase 3: If Phase 2 indicates life isless than required, then more complexanalysis (e.g. sophisticated probabilisticcalculations, stress analysis andfracture mechanics) and removal of fieldsamples for laboratory testing may beconsidered necessary.


MPT-MATCOR










MPT-MATCOR

Ongoing Life Assessment

Identify Cons equencesof Failure

Es timate Probabilityof Failure Calculate the Ris k

Prepare RBI Plans :•Plant-Wide

•Item by Item

Ins pectEs timate Remaining Life

Identify:•Contro l Meas ures

•Monitoring Methods•Remedial Actions

Implement •Contro l Meas ures

•Monitoring Methods•Remedial Actions

MPT-MATCOR

Benefits of RBI• Ensures the safety of

employees and thepublic.

• Assists in ensuringplant reliability.

• Optimises inspectionresources.

• Assists inprogrammingmaintenance, repairsand modifications.

• Basis for extendinginspection intervals.

• Provides information forlife assessment studies.

• Input to failure analysisand performanceassessment.

• Comply with standardsand regulations.

MPT-MATCOR

• RBI should ensure that inspection methods: -– a) Detect the “expected” damage modes;– b) Produce sufficiently accurate data.

• To calculate remaining life: -– a) Identify on-line monitoring methods– b) Identify damage control methods (where

possible).

• If effectively applied RBI should: -– a) Increase operational life;– b) Increase plant availability; and– c) Minimise risk of failure.

MPT-MATCOR

Where and When Does DamageOccur? How to Manage?

• Consequences– Actual

consequencessometimes hard topredict, so considerworst outcomebased on relativehazards etc.

• Likelihood– Consider risk factors

from scientific andmechanistic standpoint

– Failure statistics andexperience on similarplants elsewhere

MPT-MATCOR

Case study:Heat Exchanger Tubes

• General corrosion is predictable and tolerable(quite easy to monitor/inspect)

• Pitting corrosion less predictable• But one isolated deepest pit may cause a

failure – do we need to inspect 100%?• No. The use of extreme value statistical

techniques can provide reasonable predictionof life based on good inspection data fromonly a 10% sample.

MPT-MATCOR

The ProblemRoutine inspection of a HE finds pitting, but only 10% of the tubes have been inspected.

⇒ What is the extent of damage in the tubes that were not inspected?

⇒ Without remedial action, when will the HE fail?

MPT-MATCOR

Condition AssessmentWhat is the extent of damage in the tubes that were not inspected?

Extreme Value (EV) statistical techniques can be used.

00.10.20.30.40.50.60.70.80.9

0 50 100 150 200 250 300 350 400

Pit depth (microns)

Prob

abili

ty d

ensi

ty

extreme values

00.005

0.010.015

0.020.025

0.030.035

0.04

100 120 140 160 180 200 220 240

Maximum pit depths per unitPr

obab

ility

den

sity

mean

All Pit Depths Extreme Pit Depths

(Type I distribution)

MPT-MATCOR

Condition AssessmentWhen the maximum pit depths follow a Type I distribution, the expected maximum pit depth scales logarithmically with the number of sample units.Similar rules apply to other EV distributions.Results for 10% of the tubes can be “scaled up” to 100% of the tubes.

0

50

100

150

200

250

300

1 10 100 1000 10000

Number of sample units

Expe

cted

max

imum

pit

dept

h

MPT-MATCOR

Condition AssessmentEconomiser with 392 tubes.30 tubes IRIS inspection.

Conventional EV analysis yields a maximum pit depth prediction of 4.5 mm. But the fit is not good and this estimate is unrealistic.

Using the GEV and ML estimation to the fit parameters, a maximum pit depth of 2.8 mm is predicted, with an upper 95% confidence limit of 3.7 mm. This is more likely to be correct.

MPT-MATCOR

Life PredictionEV techniques can also be used for life prediction.

00.005

0.010.015

0.020.025

0.030.035

0.04

100 120 140 160 180 200 220 240

Maximum pit depths per unit

Prob

abili

ty d

ensi

ty

mean

0

50

100

150

200

250

300

0 1 2 3 4 5

Days in service

Pit d

epth

(mic

rons

)mean-maximum expected maximum per 1000

Maximum Pit Depths in Sample Units at Day “X”

Maximum Pit Depths in Sample Units as Fn of Time

MPT-MATCOR

Life PredictionEV techniques can be used,

provided that:

Inspection data are available for a number of different times.Operating conditions in the future can reasonably be considered similar to those in the past.

P.J. Laycock, R.A. Cottis and P.A. Scarf, J. Electrochem. Soc., 137, 64-69 (1990).

MPT-MATCOR

Life PredictionPlant A: one HE with CW on the tube-side.

Microscopic inspection of three tubes extracted after one year of operationNDT results from 40 tubes after two years of operation.Fitted mean function obtained from a 4-parameter GEV fit. Type 1 EV maximum pit depth.

0

500

1000

1500

2000

2500

0 200 400 600 800 1000

Days in service

Pit d

epth

(mic

rons

)

observed data fitted mean function Type I whole HE return level

MPT-MATCOR

Case study 2:High temperature componentsWhen does creep occur?

– Carbon steels up to400oC creep is unlikely

– Low-alloy steels (e.g.2.25%Cr1%Mo etc) goodup to about 500oC

– Stainless steels up to600oC or more

– Inconel etc. even better

What inspection andmonitoring methods?

- Replication

- Hardness

- Dimensional checks

- Review operational history

MPT-MATCOR

Some more “exotic” damagemechanisms

• Hydrogen damage & metal dusting– Where carbon and low alloy steels

exposed to hydrogen in service– Also in boilers with poor BFW control

• Stress corrosion cracking– Expected where austenitic materials are

exposed to chlorides– Carbon steels exposed to extreme caustic

conditions

MPT-MATCOR

How is RBI being applied forcommercial gain withoutcompromising safety?

• Singapore PetrochemicalComplex (case study)– Many items of “statutory

equipment”– No creep damage or significant

corrosion– Used RBI to persuade

authorities to allow extendedinspection intervals from 2 yearsto as much as 5 years

– Millions $ in opportunity costsavings

– Used MPT’s RMS software

MPT-MATCOR

RBI in the Power Industry• RBI already widely adopted

• Boilers and other items arejust too big for 100%inspection

• Has led to significantreduction in boiler tubefailures and vastimprovements in overallreliability and availability

MPT-MATCOR

Conclusions• The optimum management of ageing

industrial plant assets beyond their originaldesign lives requires an ongoing risk-basedapproach.

• The benefits of RBI and RCM vastlyoutweigh their costs of implementation.

• The application of probabilistic techniquesis a necessity where operating conditionsare diverse and unpredictable, e.g. pittingcorrosion in condensers, or creep in high-temperature heat exchanger tubes.

Documents

BPPTpresentation_06-08-2003