environmentally assisted cracking - · pdf fileintegridad estructural, 2010-11 master...

Integridad Estructural, 2010-11Master Universitario en INGENIERÍA DE ESTRUCTURAS, CIMENTACIONES Y MATERIALES

Environmentally assisted cracking

Jesús Ruiz Hervías

Associate ProfessorMaterials Engineering Department

Civil Engineering SchoolTechnical University of Madrid, UPM

Integridad Estructural, 2010-11Master Universitario en INGENIERÍA DE ESTRUCTURAS, CIMENTACIONES Y MATERIALES 2

SUMMARY

•

Introduction•

SCC –

stress state

•

Corrosion

fatigue•

Corrective

actions

•

Example


INTRODUCTION

•

SCC: cracking

in aggressive

environments

under static

loads

•

C-F: cracking

in aggressive

environments

under cyclic

loads

•

Key problem: loads

much

lower

than

elastic

limit•

Importance: cracking

of

bridges, pipes, nuclear

components…


INTRODUCTION

•

Evidence: small

loads, not

too

aggressive environments

(season

cracking, H embrittlement)

•

SCC: load + environment

+ susceptible material–

Both

effects

cannot

produce cracking

separately

–

Scientic

and

technological

aspects

not

solved

•

SCC and CF: main

cause of

failure

in structures

Environment

StressMetallurgy

SCC FACTORS


INTRODUCTION

5

(M. Elices, Mecánica de la Fractura)


INTRODUCTION

•

Corrosion types


INTRODUCTION

•

SCC: different micromechanisms–

Intergranular

fracture

–

Transgranular

fracture


INTRODUCTION

•

Intergranular SCC–

Crack propagates

along

grain

boundaries


INTRODUCTION

•

Transgranular SCC–

Crack propagates

inside

grains


INTRODUCTION

Pressurized Water Reactor

Reactor’s pressure vessel typically housed in 8”

of steel


INTRODUCTION

Pressure vessel steel

Irradiation Assisted Stress Corrosion Cracking (IASCC) Radiation + Stress + Environment


INTRODUCTION

Gas and liquid pipelines

•

Two ruptures in 1995

•

Evidence SCC widespread on both gas and liquid pipelines

•

Since 1977 -

22 failures

–

12 ruptures, 10 leaks

National

Energy

Board, Canada


SCC –

STRESS STATE

13

•

Most

important

phenomena: most stressed

zone

–

Crack tip: Fracture Mechanics techniques

(KI

)

•

Experiments: failure time vs. KI–

SCC threshold: KISCC

–

Interval KISCC to

KIC : susceptibility range


SCC –

STRESS STATE

14

•

Experiments: crack growth

rate

vs. KI –

Quantify SCC life

–

Understand crack growth mechanisms

I and III: stress controlThreshold: KISCCFracture: KIC

II: Plateau, control by chemical process

Electrochemical parametersMaterial


SCC –

STRESS STATE

15

da/dt

vs. KI in a Ti alloy

in Hydrogen

Zone II, influence of:• Material• Environment


SCC –

Stress state

16

•

Zone

I: propagation

threshold, KISCC–

Tests with

positive geometries: 0K

a∂

>∂

1.12IK aσ π=

Crack, a

σ

σ


SCC –

STRESS STATE

17

•

Zone

I: propagation

threshold, KISCC–

Tests with

negative

geometries: 0K

a∂

<∂

3/2

2

34IEH uK

a=

In this

caseu=constant


SCC –

STRESS STATE

18

•

Crack propagation: (+) and

(-) geometries

0Ka

∂<

∂


SCC –

STRESS STATE

19

•

Example

of

different

geometries

2 2

2 3

3

3

12

8

a FGEB Ha Fu

EBH

=

=

( )3/2

1/23/2 2

2 3 34I

aF EH uK GEBH a

= = =

3/2

2 3 0IK Fa BH

∂= >

∂

3/2

3

3 02

IK EH ua a

∂= − <

∂

(+) geometry (-) geometry

Load control Displacement control


CORROSION FATIGUE

20

True

Corrosion-fatigue Fatigue -

SCC IntermediateFatigue-SCC

•

Corrosion-fatigue types


CORROSION FATIGUE

21

Frequency: the

lower the

value, the

higher

the

crack growth

rate

•

Factors: mechanical

load


CORROSION FATIGUE

22

Waveform: the

rising part

of

the

waveform

has the

largest influence

on

crack

growth

rate

•

Factors: mechanical

load


CORRECTIVE ACTIONS

23

•

Modification:•

Environment

•

Material•

Reduction of mechanical load


CORRECTIVE ACTIONS

24

•

Surface protection:•

Paintings

•

Chromium/Nickel

plating•

Carburation/nitruration

•

Introduction of compressive residual stresses:•

Cold rolling

•

Shot

peening•

Laser

shock processing

•

Carburation/nitruration


CORRECTIVE ACTIONS

25

•

Shot peening:•

Impact

at the

surface

•

Compressive

residual stresses

below

surface


CORRECTIVE ACTIONS

26

•

Shot peening:•

Improvement

of

fatigue life

http://www.metalimprovement.com/shotpeening_video_hi.php


REFERENCES

•

Elices, M. Mecánica de la Fractura. ETSI Caminos. Universidad Politécnica de Madrid, 1998

•

Broek, D. The

Practical

Use of

Fracture Mechanics, Kluwer, 1988

27


EXAMPLE

28

•

SCC – fatiga–

Fatiga (R=0.2, 0.5 Hz): calcular velocidad propagación grietas por corrosión fatiga (mm/ciclo):

•

ΔK=3 MPam0.5

•

ΔK=10 MPam0.5

•

ΔK=20 MPam0.5

•

Nota: si KImax

>KISCC → (da/dn)cf

= (da/dn)f+ (da/dn)scc•

Fatiga: da/dN(mm/ciclo)=4·10-9(ΔK)3, ΔK (MPam0.5)


EXAMPLE

29

•

SCC – fatiga

SCC

Fatiga


EXAMPLE

30

max minK K KΔ = −

min

max

KRK

=max 1

KKR

Δ=

−

0

1ISCCKKR

Δ=

−

( )0 1 ISCCK R KΔ = −0.5

0 0.8 5 4K MPamΔ = ⋅ =

0.5301

CIC

KK MPamR

Δ= =

−0.524CK MPamΔ =


EXAMPLE

31

0.51 03K MPam KΔ = < Δ

( ) 71 1.08 10 /mda A K mm c

dN−= Δ = ⋅

0.52 010K MPam KΔ = > Δ

0.53 020K MPam KΔ = > Δ

( )21m

SCC

da daA KdN dt ν

⎛ ⎞= Δ + ⎜ ⎟⎝ ⎠

6 6 514 10 3 10 10 /0.5

da mm cdN

− − −= ⋅ + ⋅ =

5 6 513.2 10 3 10 3.8 10 /0.5

da mm cdN

− − −= ⋅ + ⋅ = ⋅

environmentally assisted cracking - · pdf fileintegridad estructural, 2010-11 master...

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