Proof of Fatigue Strength of Ferritic and Austenitic ...library.sinap.ac.cn/db/hedianwencui201103/全文/41019190.pdf · stabilized German austenitic stainless steels in air and

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Proof of Fatigue Strength of Ferritic and Austenitic

Nuclear Components

E. Roos, K.-H. Herter , X. Schuler , T. Weißenberg

MPA Universität Stuttgart

35th MPA-Seminar

October 9, 2009 in Stuttgart

- 13.2 -

Abstract

For the construction, design and operation of nuclear components and systems the

appropriate technical codes and standards provide material data, detailed stress

analysis procedures and a design philosophy which guarantees a reliable behaviour

of the structural components throughout the specified lifetime. Especially for cyclic

stress evaluation the different codes and standards provide different fatigue analyses

procedures to be performed considering the various mechanical and thermal loading

histories and geometric complexities of the components. For the fatigue design

curves used as limiting criteria the influence of different factors like e.g., environment,

surface finish and temperature must be taken into consideration in an appropriate

way. Fatigue tests were performed with low alloy steels as well as with Nb- and Ti-

stabilized German austenitic stainless steels in air and simulated high temperature

boiling water reactor environment. The experimental results are compared and

valuated with the mean data curves in air as well as with mean data curves under

high temperature water environment published in the international literature.

1 Introduction

The basis for construction, design and operation of mechanical systems, structures

and components (SSC) are national technical codes and standards, like for nuclear

SSC the ASME-Code Section III [1], the German Nuclear Safety Standards KTA [2]

or the French RCC-M Code [3] and for non nuclear SSC e.g. the European standard

EN13445 [4]. The basic philosophy in the design of SSC is to demonstrate that the

integrity and the function is guaranteed throughout the lifetime. It is important that the

design concept accounts for most possible failure modes and provides rational

margins of safety against each type of failure mode. Some of the potential failure

modes which SSC designers should take into account are for example: Excessive

elastic deformation including elastic instability, excessive plastic deformation, brittle

fracture, fatigue and corrosion.

During design stage a complete picture of the stress state within the SSC obtained

by calculation or measurement of both mechanical and thermal stresses during

transient and steady state operation has to be created. It has to be demonstrated that

all stresses (primary, secondary) are within the allowable stress limits given by the

codes and standards, and that the usage factor developed by a fatigue analysis

(peak stresses) including the environmental effects are well below the limiting value

(cumulative fatigue life usage factor U<1).

It is possible to prevent failure modes caused by fatigue by imposing distinct limits on

the peak stresses at the highest loaded regions of the SSC or by reducing the load

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cycles since fatigue failure is related to and initiated by high local stresses/strains.

The design rules according to the technical codes and standards, [1, 2, 3, 4], provide

for explicit consideration of cyclic operation specific rules for assessing the

cumulative fatigue damage using design fatigue curves of allowable alternating loads

(allowable stress or strain amplitudes) vs. number of loading cycles (S-N curves),

caused by different specified or monitored load cycles. The influence of different

factors like welds, environment, surface finish, temperature, mean stress and size

must be taken into consideration in an appropriate way.

2 Fatigue approach for pressurized components

2.1 Fatigue S-N curves

Fatigue data are generally obtained from unwelded smooth cylindrical specimens

which were tested under strain control at room temperature and in air environment

with a fully reversed loading, i.e. strain ratio Rε=εU/εO=–1 and are plotted in the form

of nominal stress amplitude Sa vs. the number of cycles N to failure (mean data

curves). The total strain range Δεt obtained from the tests is converted to nominal

stress range 2Sa by multiplying the strain range by the modulus of elasticity E at test

temperature.

2ES2 t

a

εΔ⋅= (1)

Based on [5, 6] fatigue ε-N data can by expressed as

( ) ( )ClnBANln a −ε−= (2)

The current ASME as well as KTA best fit mean data curves [6, 7, 8, 11, 12] can be

written in terms of Eq. (2) as follows, categorized by the types of material. The fatigue

life for austenitic Cr-Ni steels is given by

( ) ( )1670029546 ,ln,,Nln a −ε−= (3)

for carbon steels by

( ) ( )0720027266 ,ln,,Nln a −ε−= (4)

and for low alloy ferritic steels by

( ) ( )1280023396 ,ln,,Nln a −ε−= (5)

The fatigue life to failure is defined as the number of cycles necessary for the tensile

stress to drop 25% from its peak or steady–state value during test, called N25. For a

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specimen size usually used in fatigue testing, e.g. 8-12 mm diameter cylindrical

specimens, this corresponds to a crack depth of about 3 mm [10].

The existing fatigue ε–N data to develop the S-N curves are categorized by the types

of material. Therefore most of the S-N curves given in the codes and standards are

to be applied for specific steels (e.g. distinguish between steels of different ultimate

tensile strength Rm).

Based on experimental ε–N data fatigue life models for estimating the fatigue lives of

these steels in air have been developed at ANL [10] as best-fits mean data. The

fatigue life, N, of carbon steels is represented by

).(ln.T..)Nln( a 11309751001206146 −ε−−= (6)

and for low-alloy ferritic steels by

).(ln.T..)Nln( a 15108081001204806 −ε−−= (7)

where εa is the applied strain amplitude (%), and T is the test temperature (°C). For

austenitic stainless steels in air at temperatures up to 400°C the fatigue data are best

represented by the equation

).(ln..)Nln( a 112092018916 −ε−= (8)

The design curves included in the codes were derived by introducing factors of 2 on

stress and 20 on cycles of the mean data curve concerned, whichever gave the

lowest curve and is meant to account for real effects (“scatter of data and material

variability”, “size effects”, “surface finish and environment”, [7, 8, 9, 10]) occurring

during plant operation.

2.2 Effects influencing the fatigue life

The use of the fatigue design curves is restricted in the nuclear codes and standards

to a specific maximum temperature below the creep range. Using design fatigue

curves it is necessary to adjust the allowable stresses if the modulus of elasticity E at

operating temperature is different from that one used for the design curves. In air, the

fatigue life of ferritic steels decreases with increasing temperature, however the effect

is small. For austenitic stainless steels the temperature has no significant effect on

the fatigue life plotted as S-N curve. In the nuclear codes and standards it is

supposed that the design S-N curves may accounted for any temperature effects by

the subfactor of 2 for “data scatter and material variability” [10]. This results in a

comparable reduction in fatigue life like in the European standard EN13445 [4] using

a temperature correction factor ft*.

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In the codes and standards there are different and specific requirements concerning

the surface finish of components especially for welded regions, for different vessel

and piping products and different joints. A special regard to the influence of surface

finish depending upon peak-to-valley height Rz is obvious. Depending on Rz for

carbon steel or low–alloy steel and for austenitic stainless steels the surface finish

would decrease fatigue life depending on the number of cycles. Surface finish may

be considered for number of cycles >103. Below this number of load cycles, the

influence of surface finish may be negligible, Figure 1.

0,01

0,10

1,00

10,00

10 100 1000 10000

Load Cycles / N

Str

ain

Am

plit

ud

e ε

a /

%

ASME Mean DataANL Mean Data polishedsmooth finishedroughened

Strain controlledRoom temperatureMaterial 20MnMoNi5-5

0,01

0,10

1,00

10,00

10 100 1000 10000

Load Cycles / N

Str

ain

Am

plit

ud

e ε

a /

%

ASME Mean DataANL Mean Data polishedsmooth finishedroughened


Figure 1: Influence of surface finish for ferritic low alloy steel in the very low cycle fatigue regime.

In nuclear codes and standards it is supposed that this effect is accounted for in the

subfactor for “surface finish and environment” of 4.

To account for this effect the procedure included in European standard EN13445 [4]

differentiate between unwelded SSC with correction factor fS and welded SCC fatigue

design curves for weld details.

During the last three decades great endeavours have been made to investigate the

influence of the coolant environment on fatigue life [13, 14, 15, 16]. Today it is

generally accepted that the Light Water Reactor (LWR) environment can have a

significant impact on the fatigue life of carbon and low alloy steels as well as on

austenitic stainless steels under given circumstances and has to be involved in

cumulative fatigue life considerations.

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The U.S. Nuclear Regulatory Commission (NRC) has recently issued the Regulatory

Guide 1.207 “Guidelines for Evaluating Fatigue Analyses Incorporating the Life

Reduction of Metal Components Due to the Effects of the Light-Water Reactor

Environment for New Reactors” [17]. This Regulatory Guide is based on the research

work and publications by ANL [13], which provide equations for mean fatigue life

curves in LWR environment of carbon steels, low alloy ferritic steels and austenitic

stainless steels, exemplarily shown in Figure 2.

10 100 1000 10000 100000 1000000

0,1

1

10

.

ASME III Design (KTA 3201.2)

Reg.Guide 1.207

New Air Design Curve

(Factor 2 / 12)

ANL mean air 2007

ANL mean water 2007

ASME mean air

austenitic SS ParameterT = 240 °Cε = 0.01 %/sFen = 3.55 (ANL)E240 °C = 183 000 MPa

Str

ain

Am

plit

ud

e ε

a / %

Load Cycles / N

Figure 2: Fatigue life curves for stainless steels

The ANL fatigue life model for LWR environments includes parameters for the effects

of temperature, strain rate, dissolved oxygen content in water and, in case of ferritic

steels, sulphur content of the steel.

The environmental effects are expressed in terms of an environmental correction

factor Fen as the ratio of fatigue life in air environment at room temperature to fatigue

life in LWR coolant at operating temperature.

waterair

en NNF = (9)

The Fen factor, depending on the above-mentioned parameters (temperature, strain

rate, oxygen, sulphur), is also used to estimate the environmental fatigue usage.

∑ ×= ienien FUU (10)

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This procedure is consistent with the methods proposed in Japan [18, 19, 20],

whereas the parameters to determine Fen are somewhat different in the Japanese

approach.

In Regulatory Guide 1.207 a new fatigue design curve in air is developed based on

the new ANL mean air curve [13], lowered by a factor of 2 on stress and a reduced

factor of 12 on cycles, respectively whichever is more conservative. Again this curve

does not include safety margins and the environmental effects have to be considered

on the basis of Fen as stated above.

2.3 Fatigue analysis

Introduced by ASME in the early 1960s [7, 8, 6] for many years all pressure vessel

fatigue design rules followed the ASME approach. They are based on the concept

that the fatigue life of any SSC can be estimated from the S-N curve (design curve)

for the material concerned, obtained from uni-axial fatigue tests on small polished

specimens (mean data curve), by applying an appropriate fatigue strength reduction

factor (FSRF) Kf to account for discontinuities or weld joints. Instead of using the

FSRF applicable to pressure vessels, the piping analysis employ stress indices (Ci

and Ki) or stress concentration factors Kt for local areas based on linear elastic

calculations. Initially the S-N curves covered lives up to only 106 cycles. The overall

design approach was directed mainly at high-strain low-cycle fatigue (LCF)

conditions and little attention was paid to weld details as sources of fatigue. The

design curves were derived by introducing factors of 2 on stress and 20 on cycles of

the mean data curve concerned, whichever gave the lowest curve and is meant to

account for real effects (“scatter of data and material variability”, “size effects”,

“surface finish and environment”, [7, 8, 9, 10]) occurring during plant operation. All

pressure vessel and piping fatigue design rules are based essentially on the same

approach based on data from primarily low-cycle fatigue (LCF) tests.

As demonstrated in Figure 3 fatigue analysis can be performed by different concepts

which must not necessarily yield in the same result. The approach used in nuclear

codes and standards [1, 2, 3] can be assigned to local concepts (local notch strain or

stress concepts) in principal based on linear elastic stress calculations using stress

indices resp. stress concentration factors to take into account the structural

discontinuities in the SSC including welds [9].

Conservatism in the fatigue analysis may arise from the overall fatigue evaluation

procedure in conjunction with the fatigue design curves. This includes:

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• Stress analysis rules based on linear elastic calculations using stress indices,

stress concentration factors and plastic correction factor Ke.

• Use of S-N curves instead of service life curves.

• Reduced notch effect at cyclic conditions (fatigue stress concentration factor

smaller compared to stress concentration factor under static loads).

• Use of specified design transients with high number of cycles.

Fatigue Strength AssessmentFatigue Strength Assessment

ExperimentalAssessment

ExperimentalAssessment Analytical / Numerical AssessmentAnalytical / Numerical Assessment

Global ConceptBased on external forces or based on

nominal stresses within the component sections in question



Local ConceptBased on local stresses and related to criticalvalues of local phenomena like crack initiation

or crack propagation



Nominal StressConcept


Structural StressConcept


Local Notch stressConcept


Crack PropagationConcept


Full ScaleComponent Test

Tests up to failure of thecomponent under typical

loading conditionsNF=f(loading),

eg. acc. to ASME-VIII, Div.2 or up to the tech-

nical crack initiation Ni=f(loading)






Nominal Stress-Woehler-Line

- Material- Geometry- Surface finish /

Weld qualityNominal Stress Collektive

- Loading sequence- Geometry- Load amplitude

Accumulation of damage

NF=f(σNom)

Structural Stress resp.Strain Woehler-Line


Weld qualityStructural Stress resp.Strain Collektive

- Loading sequence - Geometry- Load amplitude

Akkumulation of damage

NF=f(σStruc)

Strain Woehler-line /cyclic Stress-StrainCurve

- Material- Weld quality

Local Notch Stress- Geometry- Load amplitude

Stress-Strain History- Load-time function

Accumulation ofdamage

NI=f(σNotch)

Crack Growth Curve

(cyclic)- Material- Load amplitude

Load-Time Function ΔKeff- Geometry- Crack geometry

Crack Growth / LifetimeWoehler-Line / Service-Life Curves (crack init. Up tofailure, ΔσNom)

Fatigue Strength AssessmentFatigue Strength Assessment

ExperimentalAssessment

ExperimentalAssessment Analytical / Numerical AssessmentAnalytical / Numerical Assessment



























Nominal Stress-Woehler-Line


Weld qualityNominal Stress Collektive

- Loading sequence- Geometry- Load amplitude

Accumulation of damage

NF=f(σNom)

Structural Stress resp.Strain Woehler-Line


Weld qualityStructural Stress resp.Strain Collektive

- Loading sequence - Geometry- Load amplitude

Akkumulation of damage

NF=f(σStruc)

Strain Woehler-line /cyclic Stress-StrainCurve

- Material- Weld quality

Local Notch Stress- Geometry- Load amplitude

Stress-Strain History- Load-time function

Accumulation ofdamage

NI=f(σNotch)

Crack Growth Curve

(cyclic)- Material- Load amplitude

Load-Time Function ΔKeff- Geometry- Crack geometry

Crack Growth / LifetimeWoehler-Line / Service-Life Curves (crack init. Up tofailure, ΔσNom)

Figure 3: Different Methods to perform fatigue analysis

However the codes and standards permit the use of new and improved approaches

to fatigue analysis like e.g.

• elastic plastic finite element calculations, which may result in lower stress/strain

amplitudes,

• improved (lower) plastic correction factors Ke and

• use of load cycles and temperature transients derived from on-line fatigue moni-

toring.

Furthermore the stress analysis procedure is based on strength hypotheses which

are fully verified for static loads and for fatigue strength (endurance limit). In the

- 13.9 -

range of fatigue strength for finite life appropriate strength hypotheses are still under

verification, especially when the principal stresses or strains change directions or

there is a phase shift in stress or strain components.

3 Experimental Investigations

3.1 Air environment

Tests in air environment at room

temperature, 288°C and 350°C were

performed under strain controlled

conditions and few under stress

controlled conditions, Figure 4. Test

material for the smooth cylindrical

specimens and smooth hollow

cylindrical specimens was low alloy

ferritic steel 20MnMoNi5-5 (similar to

ASTM A533, Gr. B, Cl. 2) and

stabilized austenitic stainless steel

X 10 CrNiNb 18 9 S (similar to ASTM

TP347) and X 6 CrNiTi 18 10 S

(similar to ASTM TP321).

The major results are as follows.

• For the low alloy ferritic steel

20MnMoNi5-5 the fatigue life data

at room temperature are shown in

Figure 5. Included are the ASME

mean data curve Eq. 5 and the

ANL mean data curve Eq. 7.

• For the low alloy ferritic steel 20MnMoNi5-5 the fatigue life data at temperatures

between 240 and 350oC are shown in Figure 6 and compared with the ASME

mean data curve Eq. 5 and the ANL mean data curve Eq. 7 (T=300oC).

Figure 4: Equipment for fatigue testing in air environment

- 13.10 -

0,01

0,10

1,00

10,00

10 100 1000 10000 100000 1000000 10000000

Load Cycles / N

Str

ain

Am

plit

ud

e ε

a /

%


ASME Mean Data Curve

ANL Mean Data CurveT = 20°C

Stress controlled

0,01

0,10

1,00

10,00

10 100 1000 10000 100000 1000000 10000000

Load Cycles / N

Str

ain

Am

plit

ud

e ε

a /

%




Stress controlled

Figure 5: Fatigue strain vs. life data for the low alloy ferritic steel 20MnMoNi5-5 in air

at room temperature

For more relevant ε–N data from MPA Universtät Stuttgart (MPA) tests for low alloy

ferritic steels (20MnMoNi5-5, 22NiMoCr3-7, 15MnNi6-3, 15NiCuMoNb5) at tempera-

tures up to 350oC are shown in Figure 7. Included are the ASME mean data curve

Eq. 5, the ANL mean data curve Eq. 7and a mean data curve representing the MPA

ε–N data by

).(ln..)Nln( a 1023024929945 −ε−= (11)

Between 103 and 105 load cycles there is a good conformity. In the very LCF and

HCF regime for a detailed evaluation more data are needed.

- 13.11 -

0,01

0,10

1,00

10,00

10 100 1000 10000 100000 1000000 10000000

Load Cycles / N

Str

ain

Am

plit

ud

e ε

a /

%

Strain controlledTemperatures 240-350oCMaterial 20MnMoNi5-5



0,01

0,10

1,00

10,00

10 100 1000 10000 100000 1000000 10000000

Load Cycles / N

Str

ain

Am

plit

ud

e ε

a /

%

Strain controlledTemperatures 240-350oCMaterial 20MnMoNi5-5



Figure 6: Fatigue strain vs. life data for the low alloy ferritic steel 20MnMoNi5-5 in air

at temperatures 240-350oC

0,01

0,10

1,00

10,00

10 100 1000 10000 100000 1000000 10000000

Load Cycles / N

Str

ain

Am

pli

tud

e ε

a

/ %

Strain controlledTemperatures 20-350oCMaterial: 20MnMoNi5-5

22NiMoCr3-715MnNi6-315NiCuMoNb5

MPA Data best-fit

Stress controlled



0,01

0,10

1,00

10,00

10 100 1000 10000 100000 1000000 10000000

Load Cycles / N

Str

ain

Am

pli

tud

e ε

a

/ %

Strain controlledTemperatures 20-350oCMaterial: 20MnMoNi5-5

22NiMoCr3-715MnNi6-315NiCuMoNb5

MPA Data best-fit

Stress controlled



Figure 7: MPA fatigue strain vs. life data for the low alloy ferritic steels in air at

temperatures up to 350oC

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For the stabilized austenitic stainless steels X6CrNiNb18-10 and X6CrNiTi18-10 the

fatigue life data at temperatures between room temperature and 350oC are plotted in

Figure 8 together with the ASME mean data curve Eq. 3, the ANL mean data curve

Eq. 8 and a mean data curve representing the MPA ε–N data by

).(ln.,)Nln( a 1025401891264246 −ε−= (12)

The MPA mean data curve is in very good agreement with the ANL mean data curve

for load cycles >103.

0,01

0,10

1,00

10,00

10 100 1000 10000 100000 1000000

Load Cycles / N

Str

ain

Am

plit

ud

e ε

a /

%

Strain controlled Temperatures 20-350oCMaterials: X10CrNiNb18-9

X10CrNiTi18-9

MPA Data best-fit

ANL Mean Data Curve


0,01

0,10

1,00

10,00

10 100 1000 10000 100000 1000000

Load Cycles / N

Str

ain

Am

plit

ud

e ε

a /

%

Strain controlled Temperatures 20-350oCMaterials: X10CrNiNb18-9

X10CrNiTi18-9

MPA Data best-fit

ANL Mean Data Curve


Figure 8: Fatigue strain vs. life data for the stabilized austenitic stainless steels

X 10 CrNiNb 18 9 S and X 10 CrNiTi 18 9 S in air at temperatures 20°C-350oC

• Cyclic tests with multi-axial loading (torsion or torsion with superimposed longitu-

dinal loading), Figure 9, fit into the mean data curves of the uniaxial cyclic tests,

Figure 10. The calculation of the equivalent stress amplitude according to ASME-

BPVC Section III, Subsection NH (based on the equivalent strain range, Eq. (13))

shows good results in comparison to the tests performed.

( ) ( ) ( ) ( ) ( )22222223

122

zxiyzixyixiziziyiyixiVi γΔ+γΔ+γΔ+εΔ−εΔ+εΔ−εΔ+εΔ−εΔν−

=εΔ∗

(13)

with ν*=0.5 for plastic und ν*=0.3 for elastic material behaviour.

- 13.13 -

Cooledspecimen grip

Heating device

Cooledspecimen grip

Specimen withthermo couple

Figure 9: Equipment for fatigue testing of hollow cylindrical specimens under tension-torsion loading in air environment

10

100

1000

10000

100000

10 100 1000 10000 100000 1000000

Load Cycles / N

Str

ess

Am

plit

ud

e

σV

a /

MP

a


Torsion with superimposed Axial Loading

90o Phase Shift

ANL Mean Data Curve

10

100

1000

10000

100000

10 100 1000 10000 100000 1000000

Load Cycles / N

Str

ess

Am

plit

ud

e

σV

a /

MP

a


Torsion with superimposed Axial Loading

90o Phase Shift

ANL Mean Data Curve

Figure 10: Fatigue stress vs. life data from hollow cylindrical specimen testing with

low alloy ferritic steel 20MnMoNi5-5 in air at room temperatures

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3.2 Simulated High temperature boiling water reactor environment

The investigations of environmental effects on fatigue life of stainless steels per-

formed in the USA and in Japan are predominantly based on unstabilized austenitic

stainless steels. There is a need to investigate whether the fatigue behaviour of the

niobium or titanium stabilized austenitic stainless steels used in German nuclear

power plants in contact with oxygenated high temperature (HT) water (boiling water

reactor BWR coolant) can be predicted by the curves and methods developed in the

USA and in Japan. In a second research program tests were performed with the low

alloy ferritic steel 22NiMoCr3-7.

Experiments at MPA [21], [22] are performed in a miniature autoclave, Figure 11,

which is fixed on the specimen shoulders and encloses the gauge length of the

specimen, similar to the test equipment at ANL [13]. The electrochemical potential is

measured in the same loop in a separate cell with an Ag/AgCl Electrochemical

Potential (ECP) electrode, Figure 11.

Al ignment Fix ture MT S6 09

Load Cel l M TS 661. 21B-02

Col le t Gr ip M TS 646. 10

PrüfmaschineLCFImit ECP Prüfbehälter(Ansicht vonhinten)

660

22

2

1

2

2

8

1 2

8

8 88

8

4 4

4 4

1

4

2

5 5

1 x3

6

Vorlauf Rücklauf

9 x2

7

miniature autoclavefor LCF-experimentsin BWR environment

autoclave forECP-measurement

Figure 11: Autoclave for Low Cycle Fatigue (LCF)-Experiment

3.2.1 Test with austenitic stainless steel

The specimens are machined from 2 nuclear grade pipe materials (wall thickness

35 mm and 45 mm, resp.) of the austenitic stainless steels X10CrNiNb18-9 and

X10CrNiTi18-9, stabilized with Ni and Ti, respectively, which are comparable to the

US steels A347 and A321, [21], Table 1. The specimens of steel X10CrNiTi18-9 are

additionally tested in a sensitized material state after an annealing treatment at 620

- 13.15 -

°C for 8 hours in order to simulate the depletion of solute Chromium as a result of a

welding procedure and post-weld heat treatment, respectively.

Low cycle fatigue (LCF) tests are conducted in air and simulated BWR HT-water

environment at 240°C, the oxygen content of the water is adjusted to 400 ppb. In

addition to high purity water, few tests are performed at an increased conductivity of

0.8 µS/cm by dosing sulphate (90 ppb SO4 by adding highly diluted sulfuric acid

H2SO4). The flow velocity is quasi stagnant (0.004 m/s).

All experiments in water were preceded by a soaking period of 100 h at test

conditions. The LCF tests in water were conducted with strain amplitudes of 0.6, 0.9

and 1.2 % and an uniform strain rate of 0.01 %/s, Table 2 (strain rate in air 0.1 %/s).

Table 1: Specification of the tested materials

Test materials

Stainless steel 1.4550 (X 10 CrNiNb 18 9 S) 1), Nb – stabilized (C = 0,06 %)

from pipe with 35 mm wall thickness

Stainless steel 1.4541 (X 10 CrNiTi 18 9 S) 2), Ti – stabilized (C = 0,06 %)

from pipe with 45 mm wall thickness

● as delivered (solution annealed), EPR 3) - value = 0,3%·

● sensitised 620°C/8h, EPR - value = 1.3 – 1.4 % 1) acc. to current standard KTA 3201.1: X 6 CrNiNb 18 10 S 2) acc. to current standard KTA 3201.1: X 6 CrNiTi 18 10 S 3) EPR: Electrochemical Potentiokinetic Reactivation

Table 2: Test matrix of the LCF experiments with austenitic stainless steels

material material state εa [%] environment

1.4541 as delivered

0.6 0.9 1.2 air 240 °C

1.4550 as delivered 0.6 0.9 1.2 air 240 °C

1.4541 as delivered 0.6 0.9 1.2 water 240 °C

1.4541 sensitized 0.6 0.9 water 240 °C

1.4541 as delivered 0.6 0.9 sulphate 240 °C

1.4550 as delivered 0.9 1.2 water 240 °C

Strain rate in air: 0.1 %/s

Strain rate in water: 0.01 %/s

- 13.16 -

The fatigue life in simulated BWR environment is conservatively covered by the ANL

mean water curve for both austenitic stainless steels, Figure 12 and Figure 13. The

influence of the simulated BWR environment, characterized by the Fen factor, tends

to decrease with increasing strain amplitude. The fatigue life of the sensitized

material seems to be marginally reduced compared with the original solution

annealed material state of steel X10CrNiTi18-9, Figure 14, (reduction in average 4

and 12 % at strain amplitudes of 0.6 and 0.9 %, respectively), but with regard to the

low number of specimens there is no statistical evidence of this fact. For the

experiments in sulphate containing environment the decrease in fatigue life is quite

moderate in the range of 20 % compared to the results in high purity water, Figure

15, again all data points are conservatively covered by the ANL prediction curve.

100 1000 100000,2

0,3

0,4

0,5

0,6

0,7

0,80,91,0

2,0

.ε = 0.01 %/s

E 240 °C = 183 000 MPa

ANL water 2007 X10CrNiNb18-9 HT-water 240 °C

Str

ain

Am

plit

ud

e ε

a /

%

Load Cycles / N

ANL air 2007

ASME air

Figure 12: Fatigue life of Nb-stabilized austenitic stainless steel in HT-water compared

with ANL mean water curve

The results so far suggest that the fatigue life of the stabilized austenitic stainless

steels used in German nuclear power plants is similar to that of the unstabilized aus-

tenites of United States and Japan and can be reliably predicted by the existing me-

thods.

- 13.17 -

100 1000 100000,2

0,3

0,4

0,5

0,6

0,7

0,80,91,0

2,0

.ε = 0.01 %/sE 240 °C = 183 000 MPa

ANL water 2007 X10CrNiTi18-9

HT-water 240 °C

Str

ain

Am

plit

ud

e ε

a /

%

Load Cycles / N

ANL air 2007

ASME air

Figure 13: Fatigue life of Ti-stabilized austenitic stainless steel in HT-water compared with ANL mean water curve

100 1000 10000,2

0,3

0,4

0,5

0,6

0,7

0,80,91,0

2,0

.ε = 0.01 %/sE 240 °C = 183 000 MPa

ANL water 2007

X10CrNiTi18-9 sensitized HT-water 240 °C

Str

ain

Am

plit

ud

e ε

a /

%

Load Cycles / N

ANL air 2007

ASME air

Figure 14: Fatigue life of sensitized Ti-stabilized austenitic stainless steel in HT-water compared with ANL mean water curve

- 13.18 -

100 1000 100000,2

0,3

0,4

0,5

0,6

0,7

0,80,91,0

2,0

.ε = 0.01 %/sE 240 °C = 183 000 MPa

ANL water 2007

X10CrNiTi18-9 HT-Sulphate 240 °C

Str

ain

Am

plit

ud

e ε

a /

%

Load Cycles / N

ANL air 2007

ASME air

Figure 15: Fatigue life of Ti-stabilized austenitic stainless steel in HT sulphate water compared with ANL mean water curve

3.2.2 Tests with low alloy ferritic steel

Corresponding LCF experiments were performed with the ferritic steel 22NiMoCr3-7

(comparable to US steel A508, class 2) representative for reactor pressure vessel

(RPV) steels of European production [22]. The specimens were taken from a nuclear

grade vessel shell (wall thickness 143 mm without cladding) which was primarily

produced for a German nuclear power plant (BWR). In these LCF tests strain

amplitudes of 0.3, 0.5 and 0.9 % were applied at strain rates of 0.1 and 0.01 %/s.

The water condition (high purity water, sulphate 90 ppb SO4) and temperature of

240°C was identical with the tests of austenitic material.

According to the procedure proposed by ANL and Regulatory Guide 1.207, the mean

data curve for the fatigue life in water environment depends on the strain rate, i.e. 2

different curves are calculated for the “fast” and the “slow” strain rate at test

conditions. The corresponding environmental correction factors according to ANL are

Fen = 2.57 for the high and Fen = 3.27 for the slow strain rate.

- 13.19 -

10 100 1000 10000 100000 1000000

0,1

1

10

Fen

= 3.27 (0.01 %/s)

HT-water 240 °C 0.1 %/s HT-water 240 °C 0.01 %/s

Fen

= 2.57 (0.1 %/s)

ANL water 20070.01 %/s


ASME mean air ferritic Steel 22NiMoCr3-7

Str

ain

Am

plit

ud

e /

%

Load Cycles / N

Figure 16: Results of the LCF experiments in high purity water at different strain rates.

Figure 16 shows the results of the LCF experiments in high purity water. At the fast

strain rate of 0.1 %/s the fatigue life of the specimens is in good accordance with the

corresponding mean data curve (denoted by ANL water 2007, 0.1 %/s), whereas at

the slow strain rate of 0.01 %/s, all experimental data are below the corresponding

mean data curve, i.e. in this case the effect of environment is underestimated for this

material. Investigations reveal that the cyclic stress-strain behaviour of this steel is

influenced by the strain rate, resulting in a higher hardening of the material at slow

strain rates, which might affect the sensitivity to corrosion effects under cyclic

loading. In air the strain rate has no influence on fatigue life.

In Figure 17 the fatigue behaviour at the fast strain rate of 0.1 %/s in sulphate is

compared with the experiments in high purity water. At strain amplitudes of 0.5 and

0.9 % hardly any influence of sulphate on fatigue life can be detected. Only at the

lowest strain amplitude of 0.3 %, associated with the longest exposure time in

environment, the fatigue life in sulphate tends to lower values.

At the slow strain rate of 0.01 %, only 2 experiments were performed at each strain

amplitude, Figure 18. As in high purity water all fatigue data in sulphate fall below the

ANL mean data curve. There is no significant effect of sulphate but a tendency to a

little lower average values compared with high purity water.

- 13.20 -

10 100 1000 10000 100000 1000000

0,1

1

10


ASME mean air

HT-Wasser 240 °C 0.1 %/s

Sulphate 240 °C 0.1 %/s

Fen

= 2.57 Sulphate Content 70-100 ppb

ferritic Steel 22NiMoCr3-7

Str

ain

Am

plit

ud

e /

%

Load Cycles / N Figure 17: Fatigue behaviour at the fast strain rate of 0.1 %/s in sulphate compared

with high purity water

10 100 1000 10000 100000 1000000

0,1

1

10


ASME mean air

HT-water 240 °C 0.01 %/s

Sulfat 240 °C 0.01 %/s

Fen

= 3.27 Sulphate Content 70-100 ppb

ferritic Steel 22NiMoCr3-7

Str

ain

Am

plit

ud

e

/ %

Load Cycles / N Figure 18: Fatigue behaviour at the slow strain rate of 0.01 %/s in sulphate compared

with high purity water

- 13.21 -

4 Conclusions

The results of fatigue tests performed at MPA in air environment to develop ε–N data

for the German low-alloy steels (e.g. 20MnMoNi5-5) are well represented by the new

ANL mean data curve for room temperature as well as for elevated temperatures

(slight decrease in fatigue life with increasing temperature).

For the German niobium or titanium stabilized austenitic stainless steels in air

environment the temperature has no significant effect on the fatigue life. This is in

conformity with the new ANL mean data curve to be applied up to 400oC.

The results of LCF experiments in simulated BWR water environment at 240°C show

a good correlation between fatigue life of German nuclear power plant materials and

international fatigue mean curves (ANL mean data curve). Only at low strain rates,

the environmental effects on fatigue life of the tested low alloy steel (22NimoCr3-7)

tend to be overestimated by the ANL mean data curve.

A sulphate content of the simulated BWR environment (90 ppb SO4) has no

significant influence on the fatigue behaviour.

Literatur

[1] Rules for Construction of Nuclear Power Plant Components. ASME Boiler and Pressure Vessel Code, Section III, Subsection NB, The American Society of Me-chanical Engineers (2007)

[2] Safety Standards of the Nuclear Safety Standards Commission (KTA). KTA Rules 3201 and 3211, Carl Heymanns Verlag KG, Cologne, latest edition

[3] French Design and Construction Rules for Mechanical Components of PWR Nu-clear Islands (RCC-M). AFCEN - Association Française pour la Construction des Ensembles Nucléaires, Paris

[4] European Standard EN 13445-3:2002 Unfired pressure vessels, Part 3: Design

[5] Coffin, L.F., A Study of the Effect of Cyclic Thermal Stresses on a Ductile Metal, Trans. ASME 76, 1954, pp. 931-950

[6] B. F. Langer., "Design of Pressure Vessels for Low-Cycle Fatigue", Journal of Basic Engineering, Vol. 84, 3 (1962)

[7] Criteria of Section III of the ASME Boiler and Pressure Vessel Code for Nuclear Vessels, the American Society of Mechanical Engineers, Library of Congress Catalog Card Number: 56-3934 (1963)

[8] Criteria of the ASME Boiler and Pressure Vessel Code for design by analysis in Section III and VIII, Division 2, the American Society of Mechanical Engineers, Library of Congress Catalog Card Number: 56-3934 (1969)

[9] Fatigue strength reduction and stress concentration factors for welds in pressure vessels and piping, Welding Research Council Bulletin, WRC 432, June 1998

- 13.22 -

[10] O. K. Chopra, W. J. Shack, Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials, NUREG/CR-6909, ANL-06/08, February 2007

[11] C. E. Jaske, W. J. O'Donnell, "Fatigue Design Criteria for Pressure Vessel Al-loys", Journal of Pressure Vessel Technology (1977)

[12] D. R. Diercks, "Development of Fatigue Design Curves for Pressure Vessel Al-loys using a Modified Langer Equation", Journal of Pressure Vessel Technology, Vol. 101 (1979)

[13] O. K. Chopra,, Effects of LWR Coolant Environments on Fatigue Design Curves of Carbon and Low Alloy Steels, NUREG/CR-6583, ANL-97/18, March 1998

[14] S. Rosinski, Materials Reliability Program (MRP), Evaluation of Fatigue Data Including Reactor Water Environmental Effects (MPR-49), EPRI Technical report 1003079, Dec. 2001

[15] H. D. Solomon, C. R. E. Amzallag, R. E. Delair, A. J. Vallee, Strain Controlled Fatigue of Type 304L SS in Air and PWR Water, 3rd Intern. Conference on Fa-tigue of Reactor Components, Seville, Spain, October 3 – 6, 2004

[16] M. Higuchi, Japanese Program Overview, 3rd Intern. Conference on Fatigue of Reactor Components, Seville, Spain, October 3 – 6, 2004

[17] Guidelines for Evaluating Fatigue Analyses Incorporating the Life Reduction of Metal Components due to the Effects of the Light-Water Reactor Environment for New Reactors, Regulatory Guide 1.207, U.S. Nuclear Regulatory Commis-sion, March 2007

[18] M. Nishimura, T. Nakamura, Y. Asada, TENPES Guidelines for Environmental Fatigue Evaluation in LWR Nuclear Power Plant in Japan, 2nd Intern. Confer-ence on Fatigue of Reactor Components, Snowbird, USA, July 29 – 31, 2002

[19] M. Higuchi, K. Sakaguchi, H. Akihiko, Y. Nomura, Revised and New Proposal of Environmental Fatigue Life Correction Factor (Fen) for Carbon and Low-Alloy Steels and Nickel Base Alloys in LWR Water Environments, Proceedings of PVP2006-ICPVT-11-93194, July 2006

[20] T. Nakamura, M. Higuchi, K. Takehiro, Y. Sugie, JSME Codes on Environmental Fatigue Evaluation, Proceedings of PVP2006-ICPVT-11-93305, July 2006

[21] T. Weissenberg, Zentrale Untersuchung und Auswertung von Herstellungsfeh-lern und Betriebsschäden im Hinblick auf druckführende Anlagenteile von Kern-kraftwerken, Arbeitspaket 3.1, Einfluss des Reaktorkühlmediums auf das Ermü-dungsverhalten austenitischer CrNi-Stähle, BMU-Vorhaben SR 2501, MPA Uni-versität Stuttgart, November 2007

[22] T. Weissenberg, Ermüdungsverhalten ferritischer Druckbehälter- und Rohrlei-tungsstähle in sauerstoffhaltigem Hochtemperaturwasser (Fatigue Behaviour of Ferritic Steels for Pressure Vessels and Piping in Oxygenated High Temperture Water), Final Report, Reactor Safety Research – Project No.: 1501309, MPA Universität Stuttgart, September 2009 (German Language)

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Proof of Fatigue Strength of Ferritic and Austenitic ...library.sinap.ac.cn/db/hedianwencui201103/全文/41019190.pdf · stabilized German austenitic stainless steels in air and