The Use of Creep Data in Power · PDF fileAdvanced Gas cooled Reactor Degradation Mechanisms Creep, ... Use of Creep Data in Power Generation, ... 2/3 also allows “full inelastic

The Use of Creep Data in Power Generation

Mike Spindler Assessment Technology Group

The Use of Creep Data in Power Generation, NOT PROTECTIVELY MARKED2

Advanced Gas cooled Reactor Degradation Mechanisms

Creep, Oxidation and Irradiation20Cr25Ni Stainless, Nimonic PE16 and Graphite

Creep and Thermal Fatigue (Temp. >400-650°C) & Oxidation (CO2 & steam )

Fatigue Corrosion (Salt water)

Fatigue (rotating plant)


Rules of Creep

1st Rule of Creep:- No matter how much data you have you need more.

2nd Rule of Creep:- The more data you have the more difficult it is to

understand.

3rd Rule of Creep:- Nobody can agree on the right way of doing anything.


Engineering Disasters

‘Sultana’ Boiler explosion 27 April 1865,

1238 killed


Design Code Requirements for Creep DataASME II Part D and ASME VIII :- Stress to produce a creep rate of 0.01%/1000 h- Stress to cause rupture at the end of 100,000 h

- Base metal and appropriate weld metals and weldments at 50°C intervals and 50°C above the maximum intended use temperature.

ASME III-NH also requires:- Stress to a Total (elastic, plastic, primary, and secondary) Strain of 1%;- Stress to cause initiation of tertiary creep

IMechE Creep of Steels Working Party also provides- 0.1, 0.2, 0.5, 1, 2, 5% Creep Strain

BS EN 13445-3:2009- 1% Creep Strain- Rupture strength

RCC-MR- Time and creep strain at the end of primary, - min creep strain rate, - Time and creep strain at the initiation of tertiary.


Creep Testing Requirements for Design DataASME- Tests to 30,000 hours for extrapolation to 100,000 hours- Base metal and appropriate weld metals and weldments

at 50°C intervals and 50°C above the maximum intended use temperature.

TÜV - Min. 3 Casts Tested to 30,000hours

BS and European Standards, ISO 6303 and PD6605 and ECCC- x3 the test duration exceeded by data points from 5 Casts

at temperatures within 25°C of that specified- i.e. >70,000h testing for 200kh design- i.e. >80,000h testing for 250kh design


½CrMoV at 550°C

0

20

40

60

80

100

120

140

160

180

200

0 50000 100000 150000 200000 250000 300000 350000 400000Time (hours)

Stre

ss (M

Pa)

550°C PD6525 550°C

Beech 550°C AJB2 550°C

ISO 1978 550°C

End of life window (T 500 to 540°C)


ECCC RECOMMENDATIONS - VOLUME 5 Part I

INTERIM-MINIMUM REQUIREMENTS

TARGET-MINIMUM REQUIREMENTS

For 3 casts For 6 casts

3 tests at each of 3 temperatures, at intervals of 50 to 100°C

- 3 tests per temperature (different O) with tu,max 10kh

5 tests at each of 3 temperatures in the design application range at intervals of 25 to 50°C

- 4 tests per temperature (different O) with tu 40kh

- 1 test per temperature with tu,max40kh

http://www.ommi.co.uk/etd/eccc/advancedcreep/open.htm


Idealised Test Matrix for Creep to Rupture TestsCast Stress to produce mean Failure Time of (hours)

1,000 3,000 10,000 30,000 70,000

1

All 6 Casts tested at min. Three Temperatures 1. Typical Application Temperature to nearest 50°C2. Max. Application Temperature (i.e. 50°C above typical)3. 50°C above Maximum Application Temperature

Total 90 tests, ~234 years, cost very variable £250k-£2M

2

3

4

5

6


Large Multi-Source Data Set Such as Type 316H

10

100

1000

10 100 1000 10000 100000 1000000Time (hours)

Stre

ss (M

Pa)

482500550600650700800


Medium Single/Double Source Data Sets - NF709R

0

50

100

150

200

250

300

350

400

450

500

100 1000 10000 100000

Time (hours)

Line

ar S

tress

(Pro

prie

tary

Dat

a)

600°C 650°C 700°C 750°C800°C 600°C unfailed 650°C unfailed 700°C unfailed750°C unfailed 800°C unfailed 3S2T Model Multi-Region


Reheat Cracks - Creep Cracking

Note low primary stress (45MPa) and low temperature 510-535°C.

Predicted Life 180M hours!

Header Body Flank Position

S4 Weld after 55,000 hours 490-525°C

Nozzle


0

0.05

0.1

0.15

0.2

0.25

0.3

0 50 100 150 200 250 300

Time (hours)

True

Inel

astic

Stra

in (a

bs.)

Deformation data test 13156 (ruptured)

RofA test 13156 (ruptured)

Initial Loading

Elongation test 13156 (ruptured)

Last logged creep strain at failure

What Strain Data? – Deformation and Failure

.)abs(RofA1

1lnLtrue


Simple Primary Secondary Model

0

0.5

1

1.5

0 1000 2000 3000 4000Time (h)

Cre

ep S

train

(%)

1.E-04

1.E-03

1.E-02

Cre

ep S

train

Rat

e (%

/h)

Creep Strain Data (550°C 390MPa)Prediction (550°C 390MPa)Creep Strain Rate

t , at the end of primary creep

minimum creep rate

p a

t the

end

of p

rimar

y cr

eep

minpc ,MAX


Simple Primary, Secondary Tertiary Creep Deformation Model

s

r

p

tp (tp / tr tr

m

Tertiary

Secondary

Primary

+

+


Creep Data Converted to True Stress and True Inelastic Strain

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

0 0.05 0.1 0.15 0.2 0.25 0.3True Inelastic Strain (abs.)

Inel

astic

Stra

in R

ate

(1/h

)

0

50

100

150

200

250

300

350

400

450

True

Stre

ss (M

Pa)

Strain Rate

Average Rate

Stress

Loading

Last Logged

NeckingLocal Strain in neck


Creep-fatigue crack developmentPredominantly thermal loading conditions

Threshold

Instabilitylimit

Focus on creep fatigue crack initiation and early development under predominantly thermal loading conditions (R5 Volume 2/3)Design interest is crack initiationFor inspection management and remaining life assessment, crack development is of interest (R5 Volume 4/5)Within the cyclic plastic zoneBeyond the cyclic plastic zone (to

arrest?)Further growth is dependent on

magnitude of superimposed primary loadingWhether an instability reached is

considered by Fracture Codes, R6(Courtesy of : Dr S R Holdsworth EMPA Switzerland)


R5 Volume 2/3 Creep-fatigue crack initiation for defect free structuresThe integrity of a defect-free component is considered in Volume 2/3 by the following mechanisms:- Excessive plastic deformation- Creep rupture- Ratchetting or incremental collapse- Initiation of cracking due to combined creep and fatigue damage- Creep deformation enhanced by cyclic loadings

Design codes tend to use “elastic” calculations in the first instance, which are often excessively conservative. R5 Volume 2/3 uses “simplified inelastic analysis”, “reference stress” and “shakedown” concepts to give more realistic assessments while retaining some conservatism. R5 Volume 2/3 also allows “full inelastic analysis”.


For 35 year life- Cold shut downs 21 to 33- Operating hours 254k – 267k - Dwell times 8000 – 12500 hours

Fatigue damage negligible (<5x10-4)Creep damage - Temperature 530°C- Start of dwell stress 170MPa- Calculated creep damage 1.39- Residual stresses also contribute to failure

One example of creep-fatigue in service Superheater Tailpipes


Typical Creep-Fatigue Cycles

Stra in (%)

-0.4 -0.2 0.0 0.2 0.4

Stre

ss (M

Pa)

-200

-150

-100

-50

0

50

100

150

200(c) T30406Z1 Cycle 679=0.6%Z=1

Stra in (%)

-0.4 -0.2 0.0 0.2 0.4

Stre

ss (M

Pa)

-200

-150

-100

-50

0

50

100

150

200(a) TAGE_6Z1 Cycle 325=0.6%Z=1 Dwell at peak as seen during in-phase

thermal-mechanical cycling.

These cycles are common in laboratory tests

Intermediate dwell as seen during 90°out of phase’ thermal-mechanical cycling

These cycles are common in real plant


Time Fraction Best Estimate Predictions of Fatigue and Creep Damage

Bi-linear interaction with locus at (0.3,0.3)

Non-conservative at low strain ranges in Type 316H and Type 347 weld metal.

ht

fc T)(σt

dtd0 ,

01 Nd f

Creep Damage, Dc

0.01 0.1 1 10

Fatig

ue D

amag

e, D

f

0.01

0.1

1

10

Bi-Linear Interaction Locus at (0.3,0.3)x2/2Type 316H at 570°C Peak DwellsCast 304L at 650°C Peak DwellsCast 304L at 650°C Intermediate DwellsType 347 Weld at 650°C Peak DwellsType 347 Weld at 650°C Intermediate Dwells


Stress Modified Ductility Exhaustion (SMDE)Best Estimate Predictions of Fatigue and Creep Damage

Linear interaction

Decreased scatter about linear interaction for all tests.

Particularly, intermediate dwells Type 347 weld metal and Cast 304L and low strain ranges all materials.

Creep Damage, Dc

0.01 0.1 1 10

Fatig

ue D

amag

e, D

f

0.01

0.1

1

10

Linear Interactionx2/2Type 316H at 570°C Peak DwellsCast 304L at 650°C Peak DwellsCast 304L at 650°C Intermediate DwellsType 347 Weld at 650°C Peak DwellsType 347 Weld at 650°C Intermediate Dwells

dtT

dht

inf

inSMc

0),,(

11exp. mninf TPA


Local Strain at Failure

Elongation =39.3%

RofA =74.4%

Ltrue =148.6% (ln(1/(1-RofA(abs.)))

1

10

100

1000

1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00

Creep Strain Rate (1/h)

Duc

tility

(%)

True Local 100MPaElong. 100MPaTrue Local 201MPaElong. 201MPa True Local

Elongation


1

10

100

1000

0.0000001 0.000001 0.00001 0.0001 0.001 0.01 0.1

Average Strain Rate (1/h)

True

Loc

al S

train

(%)

116 to 185201 to 247278 to 312324 to 401Fit 151Fit 224Fit 295Fit 372

Stress (MPa)

Fitting Creep Ductility Data

111

1, exp mncUf T

PAMIN


Prediction of Stress Relaxation

Secondary Creep Model Based on minimum creep rate under predicts stress relaxation.

RCC-MR Type Primary & secondary creep model over predicts stress relaxation.

Solution to slow the primary creep deformation prediction by including an internal stress term.

600°C 220MPa

0

50

100

150

200

250

0.01 0.1 1 10 100 1000 10000 100000 1000000Time (Hrs)

Stre

ss (M

Pa)

Data

Secondary

Primary & Secondary

550°C 230MPa

80

100

120

140

160

180

200

220

240

0.01 0.1 1 10 100 1000 10000 100000Time (Hrs)

Stre

ss (M

Pa)

Data

Secondary

Primary & Secondary


Effect of Internal Stress on Esshete 1250

200

250

300

350

400

450

500

550

0.01 0.1 1 10 100 1000 10000 100000

Time (h)

True

Str

ess

(MPa

)

NAE 523MPaNAF 471MPaPrimary & Secondary 523MPaPrimary & Secondary 471MPaWith Internal Stress 523MPaWith Internal Stress 471MPa

trt sfp exp1 miTruefp TPA exp.


Multiaxial Stress Rupture CriteriaThe lower shelf and combined CGF can be written as a multiaxial stress rupture criteria by including a power law stress dependence (n).

0

100

200

300

400

500

600

700

800

1 10 100 1000 10000 100000

Rupture Life (hrs)

Uniaxial

Torsion Tension

Pressure Tension

Notched Bar

Mul

tiaxi

al R

uptu

re S

tress


Plant States of Stress

0.333

0.417

0.500

0.583

0.667

0.5 1 1.5 2 2.51/equ

S 1/

equ

Notched Bars a/R=0.53 to 25

Biaxial

Plant Experience

Region where tests are needed

Max Principal/von Mises Stress

Dev

iato

ric/v

on M

ises

Stre

ss


Creep Crack Growth

t > ti

t = ti

t < ti

t = 0 Initial sharpcrack

Crack blunting

Formation of ashort crack

Creep crackgrowth

•Initiation

•Crack growth

•Fracture

•Creep rupture


Creep Crack Growth

0 500 1000 1500 2000 2500 300010

15

20

25

30

35

Time (h)

Cra

ck le

ngth

(mm

)


• C* is the creep analogue of contour integral J inelastic plastic fracture

• C* estimation is time dependent version of Jestimation

C* Parameter

refcref

*

refref

GEC

GEJ


Creep Crack Growth Testing

0 500 1000 1500 2000 2500 3000 3500

0.2

0.4

0.6

0.8

1Load line displacement (mm)

Hours

0 500 1000 1500 2000 2500 3000 3500

0.5

1

1.5

2

2.5

3

Hours

Crack growth (mm)

20 amp DC

32mm

p.d.output

50mm

p.d.output

p.d.output

4mm

Potentialmeasurementpoints

Displacement transducer(lvdt)


Creep Crack Growth Data

1E-07

1E-06

1E-05

1E-04

1E-03

1E-06 1E-05 1E-04 1E-03

C* [MPa m/h]

da/d

t [m

/h]

Sepc. 01Spec. 07cSpec. 08Spec. 10Spec. 15Spec. 14R66 UB: A=0.5Base Line Creep: A=0.2R66 Mean: A=0.1

R66 Mean

R66 Mean x 2

R66 Upper Bound

qACa *

Decreasing Ductility

Increasing Creep Rate


Finite Element Analysis – A Three Legged Stool

Software

Compatibility Equations

Equilibrium Equations

Material Properties


Finite Element Analysis – A Three Legged Stool

Documents

The Use of Creep Data in Power · PDF fileAdvanced Gas cooled Reactor Degradation Mechanisms Creep, ... Use of Creep Data in Power Generation, ... 2/3 also allows “full inelastic