current status of life assessment

8/18/2019 Current Status of Life Assessment

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Current Status of Life Assessment

Technologies & Life Management

Methodologies for Key Components of

Fossil Power Plants in China

Shu GuogangShu Guogang11 Chen GuoliangChen Guoliang22 Ren AiRen Ai11 Wang YanliWang Yanli22

1.Suzhou Nuclear Power Research Institute1.Suzhou Nuclear Power Research Institute

2. University of Science and Technology Beijing2. University of Science and Technology Beijing


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1.The History and Current Status of Fossil Power Plants in

China

2.The History and Current Status of Steels Used in Fossil Power

Plants in China

3.The Typical Life Assessment Technologies for Key

Components of Fossil Power Plants

4.Life Assessment Techniques Developed in China

5. The Current Statues of Life Management for Fossil Power

Plants in China


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Introduction

The total fossil power capacity has reached 384,500 MW by

the end of 2003 in China;

There are more than 300 fossil power units with the capacity

of 300 MW per unit or above;

The capacity of fossil power plants with more than 30 years’

operation has reached approximate 1500 MW;

The capacity of nuclear powerunits has reached about

7000MW.


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1. The History and Current Status of

Fossil Power Plants in China The equipment manufacturing industry for power generation in China was

initially set up in 1955 for 6 MW fossil power plants with the introduction

of manufacturing technologies from Czech Republic

In 1960s and 1970s, China self designed and manufactured fossil power

units with capacity of 125 MW, 200 MW and 300 MW

In early 1980s, China introduced manufacturing technologies for sub-

critical 300 MW and 600 MW generation units

In 2003, China’s first largest super-critical unit with a capacity of 900 MW

began commercial operation

At present, the power units under construction are mainly super-critical and

ultra-super-critical units


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The three series of fossil power plants in China

East European series with the representative of former Soviet

Union; Western series with representatives of US, Germany and

Japan;

The series with Chinese self-developed technologies.

The characteristics of above-mentioned three series

determine the diversities and complex of materials used inhigh-temperature components of fossil power plants in China.

It also determines the diversities and difficulties of life

assessment for those components in China.


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2.The History and Current Status of Steels

Used in Fossil Power Plants in China

In 1950s: The steels used in fossil power plants were mainly

carbon steel and low-alloy steel;

In 1960s and 1970s : China developed some heat-resistant

steels, e.g. 13SiMnMoVB (Chromium-free 7#),12MoVWBSiRe (Chromium-free 8#), 15MnPNbRe and

2Mn19A15sIMoTi, etc. Some are still using, e.g. boiler steels,

12Cr2MoWVB (steel-102); bolt steels, 20Cr1Mo1VnbTiB (1#

steel) and 2Cr1Mo1VtiB (2# steel); welded rotor steels,

25Cr2NiMoV.continuedcontinued


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During the period, China also introduced some German steels ,

St45. 8 , 13CrMo44 , 10CrMo910 (thin wall)、F11 、F12 、

19Mn5 、BHW38 etc.

In late 1980s, China introduced German and Japan steels

TP304H and TP347H, and also former Soviet Union stain-less

steels.

In 1980, steel T91 was first used in high-temperature super-

heaters of fossil power plants; In 1983, T91 and P91 were

certified by ASME as Grades SA213-T91 and SA335-P91.


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In early 1990s,China introduced steel T/P91.

The properties of T/P91 produced in China all meet GB5310-

1995 and ASME SA-213 requirements; But P91 is still not

used as commercial products until now.

The characteristic of steels used in China determines the

feature of life assessment for high temperature components .


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3.The Typical Life Assessment Technologies for Key

Components of Fossil Power Plants

The main aging mechanisms of high-temperature componentmaterials are creep, fatigue and creep-fatigue interaction etc.

The life assessment methods are decided by the different agingmechanisms：

(A) Piping or tube life assessment Involves removing samples from component and testing

Two main types

(1) Rupture tests (2) Creep tests

Tests are accelerated by increasing temperature or stress or both

Hence the methods involve extrapolation techniques

e.g(1)Isothermal extrapolation method;

(2)Iso-stress extrapolation method;

(3)Time-temperature parameters method (Larsen-Miller approach);mostly used for

life estimates of boiler tubes.(4)The projection concept.


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(B) Turbine life assessment

Based on thermal fatigue damage model

Thick components experience damage during starting and stopping unit due

to thermal stress gradients

Magnitude of stress depends on rate of temperature change and

components size.


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(C) Header life assessment

Damage mechanisms ---creep and thermal fatigue from cyclic operationDC+ DF≤D

where Dc obtained from Robinson ’s Linear Life Fractions Rule

DF

obtained from Miners’s Linear Damage Rule

D : allowable damage

(D) Non-destructive and microstructural methods

Replication techniques

Cavitation damage

Microstructural change e.g carbide particle

Pearlite spheroidization ;

Sub-grain size and dislocation density changes.

Hardness

(E) Component integrity assessment


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4 Life Assessment Techniques Developed in China

Micro-area plasticity condition equation life assessment

techniques for component materials

Modified projection concept

Life assessment method of creep-fatigue interaction

The material life and component life---the creep curve

extrapolation method step by step


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Micro-area plasticity condition equation life

assessment techniques for component materials

The research results for steel 12Cr1MoV showThe research results for steel 12Cr1MoV show ：：

the fine carbides smaller than 50the fine carbides smaller than 50--100nm are still remaining inside100nm are still remaining inside

the grain after operation for 300,000 hours.the grain after operation for 300,000 hours.

Carbides have apparently grown up at grain boundaries. Even inCarbides have apparently grown up at grain boundaries. Even in

some areas the linked carbides have been formed, which causessome areas the linked carbides have been formed, which causes

weakness area adjacent to grain boundaries. Therefore, theweakness area adjacent to grain boundaries. Therefore, the

structural deterioration in grain boundaries area are key factor structural deterioration in grain boundaries area are key factor ss

affecting the service life of components.affecting the service life of components.


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0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40

China has developed a nanometer detection pin insertion method tomeasure the micro-plasticity ,try to establish the empirical relationship

between service life and strain coefficient.

12Cr1MoV12Cr1MoV

s t r a i n s e n s

i t i v i t y r a t i o m

（ × 1 0 - 3 )

operating time（×10

4

hr ）


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Modified projection concept

According to the Evans and Wilshire theory, the

relationship between θi values and creep strain can

be expressed by:

)1()1( 42 431 −+−= − t t

ee θ θ

θ θ θ ε

The creep strain at any time can be calculated when

the values of θi

were defined by the constant stress

creep test , the 105 hour creep life can be extrapolated

by short time creep test.

continuedcontinued


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China has started the research of life assessment of high

temperature components by using

projection concept in early1990s, and put forward a modified projection concept to

assess the life of components under low stress creep condition

and established modified concept equation for steels

12Cr1MoV and 10CrMo910, etc. commonly used in China

)1( 321 −+= − t

et θ

θ θ ε


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Modified projection concept considers more about the

creep curve features of low alloy steels under a constant

load. The primary creep could be ignored compare to the long

term secondary creep and tertiary creep under the low

stress condition. So the creep curve can be calculated byabove-mentioned equation.

t

ε

t

ε

（a） classic creep curve （ b） low-alloy steel long term creep curve


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For the i is the function of temperature and stress, The

1、

2、

3 values can be obtained from high stresscreep test. Therefore, the practical low stress creep curve

can be extrapolated in the power plants.

Now, the application has been extended to 8 power plants.


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Comparison of the calculation value and the test value for θ1、θ2、θ3

12Cr1MoV12Cr1MoV○○○○○

○○○○

11●●●●●

●●●●

22

33

c a l c u l a t e d v a l u e

tested value


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12Cr1MoV12Cr1MoV

T=540T=540℃℃

σσ=68.6MPa=68.6MPa

s t r a i n

( %

)

time (hrs)

Calculated low stress creep curve


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Life assessment method of creep-fatigue interaction

In 1980s and early 1990s, Chinese scholars carried out

a systematic research on creep-fatigue interaction for

high temperature steels used in power plants,

especially for those steels used to peaking units, and

established fracture characteristic diagram under creep-fatigue interaction with hold time.


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The fracture characteristic diagram with different

hold time

a l t e r n

a t i v e s t r e s s σ

a

( × 1 0

2 M

P a )

rupture life Nf (tr)

m e

a n s t r e s s σ m

( × 1 0

2 M P

a )

12Cr1MoV12Cr1MoV

σσmax=274.4MPamax=274.4MPa

T=588T=588℃℃

S t r e s s σ

Time (t)

σ max Hold

σ min

-hold 100s -hold 10s●- hold 0s


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First it is necessary to distinguish different fracture modes. There is adifferent prediction equation for creep rupture and fatigue rupture .

As to the power plant components operated for a long time, creep rupture is

the dominating factor. We can predict life with low part of figure below,

within which exists a saturated value of hold time that has a weak relation

to stress condition, it is to said that it isn’t necessary to consider the

influence of unit start up and shut down;

We can use the different hold time under a given maximum stress to

experimentally determine the saturated value, which is the basis of life

prediction for materials for which creep rupture is the dominant failure

mode.


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The material life and the component life---- the

creep curve extrapolation method step by step

The material life is different with component life:

There are differences between test conditions and actual

operation environment;

The samples may not be representative of the whole

component due to the dispersion of material properties.


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To solve the problem, China developed “the

creep curve extrapolation method step by step”

Measured

Short time

Long time

3

3

The measurement values before point 1 in Figure are approximated to obtaincurve 1, from which extrapolation can be made to point 2, then the measurementvalues before point 2 are approximated to obtain curve 2, from which extrapolationcan be made to point 3, then the measurement values before point 3 areapproximated to obtain curve 3. From here the prediction becomes fairly consistent

with the measurement curve (real line), the residual life can be accurately obtained.This is what is called extrapolation method).


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The advantages of “ the creep curve extrapolation

method step by step ”

The advantages of creep curves extrapolation can be fully

utilized, which evaluates the evolution of creep deformations

rather than life estimation only; The prediction and extrapolation can be made gradually, since

every prediction is made only with extrapolation of one

operating cycle instead of the whole life, therefore the accuracyof prediction and extrapolation can be greatly enhanced;

The application of method is not limited for pure creep

condition; it is still valid provided that creep deformation is stilla dominant one regardless of the presence of mechanical or

thermal fatigue. The effects caused by creep temperature and

stress fluctuation can also be estimated according to the creep

curves calculated based on typical creep temperature and stress

calculation; continuedcontinued


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The prediction and extrapolation can be made under

the conditions consistent with practical operating

conditions;

The prediction and extrapolation can be made forevery specific individual component rather than the

statistic average extrapolation;

This method can easily realize on-line prediction and

monitoring.

5 Th C t St t f Lif M t f


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5. The Current Statues of Life Management for

Fossil Power Plants in China

The life management of power plants has emphases on key

components that can be divided into three categories:

super-heater and reheater;

main steam pipe, reheater steam pipe and high-temperatureheader;

turbine rotor, cylinder and high-temperature bolt

The life management for components of nuclear power plants

is undergoing now.

Th d i i t ti l l f lif t f


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The administrative levels of life management for

components of fossil power plants in China

Provincial

electric power

institute

Level 1

(1) Gather historical operation data

(2) Design code calculations

Level 2(1)Operating temperatures and pressure,compared to design

(2)Some preliminary inspection

Level 3(1)Detailed inspection(2)Sample removal and testing(3)Detailed calculations(4)

Formulation and revision of industrystandard

Power plant

National electric

power institute

Informationexchange &

experience feedback

The three-level structure of life management system for power plants in China


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(A) Life management of high-temperature boiler tubes

The Main interface of life management system for boiler tubes


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(B)Life management of turbine rotor

History record of rotor in process of startup


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(C)Life management of header

Temperature history record of header


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The on-line assessment technology has developed and started

its use in China. With combination of predictive maintenance

and optimized operation, China has effectively realized the

life management and acquired remarkable achievements:

Reduced costly unscheduled service outages caused by

unexpected failures.

Extended the service life safely and economically

Eliminated the unnecessary or premature replacement ofcomponents and equipment


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THANKS !THANKS !THANKS !


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current status of life assessment

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