CANMET-MTL

1

Metallurgical Factors in Stress Corrosion Cracking (SCC) and Hydrogen-Induced Cracking (HIC)Metallo-2007Indian Institute of Technology, Kanpurin Honour of Professor T. R. Anantharaman

Winston Revie and Mimoun ElboujdainiCANMET Materials Technology LaboratoryNatural Resources Canada, Ottawa, Canada

December 10, 2007

CANMET-MTL

2

CANMET-MTL

3

Outline Overview of Underground Oil and Gas Pipelines Hydrogen-Induced Cracking (HIC)

- Metallurgical and Environmental Variables- Inclusions

Stress Corrosion Cracking (SCC)- Metallurgical, Mechanical, Environmental,

and Electrochemical Variables- Inclusions

Conclusions What Does the Future Hold? Collaboration/A World without Borders Acknowledgements

I

n

s

i

d

e

O

u

t

s

i

d

e

CANMET-MTL

4

CANMET-MTL

5

Underground Pipeline2 Sides to Every Pipe

Soil, Microorganisms,Unstable Terrain

Flowing Oil, Gas, Brine

Steel, Coating

Flowing Oil, Gas,

Brine

CANMET-MTL

6

HIC in Steel Exposed to Sour Gas

CANMET-MTL

7

Hydrogen-InducedCracking (HIC)

Internal cracks caused by trapped hydrogen atoms.- Cracks parallel to

rolling plane. - Residual or applied

tensile stress not necessary for HIC.

CANMET-MTL

8

Prediction of HIC

1. Immersion, 4 days, in H2S-satd buffer solution, pH varied from 1.1 to 5.9

2. Diffusible hydrogen measured, glycerol displacement at 45oC

3. Coupons examined for cracking, ultrasonic C-scan, metallographic examination

CANMET-MTL

9

pHth and CHth

Environment pHth Lowest pH at which no HIC was

detected

Material CHth Highest hydrogen concentration in

the steel at which no HIC was detected

CANMET-MTL

10

Criterion for HIC

0

0 LH

cHth

cH0

cH0H2S/H2O

Steel

AirHIC

0

cH0 Concentration of H at the inner pipe surfacecHth Threshold H Concentration

No HIC

CANMET-MTL

11

Criterion for HIC

HIC occurs if:

cH0 > cHth

Environmental MaterialVariable Variable

CANMET-MTL

12

CANMET-MTL

13

Title

0

0.5

1

1.5

2

2.5

0 0.1 0.2 0.3 0.4 0.5Volume fraction of inclusions (%)

.

T

h

r

e

s

h

o

l

d

h

y

d

r

o

g

e

n

c

o

n

c

e

n

t

r

a

t

i

o

n

(

m

L

)

.

Volume Fraction of Inclusions, %

T

h

r

e

s

h

o

l

d

H

y

d

r

o

g

e

n

C

o

n

c

e

n

t

r

a

t

i

o

n

,

m

L

HIC and Inclusions

CANMET-MTL

14

Inclusions Inclusions in cracks are MnS, by EDX Provide sites for H to accumulate

Steel Crack Ca/SA Yes 0.15B Yes 0.50C Yes 0.96D Yes 1.31E No 2.62F No 2.50

Optimum Ca/S Ratio2

CANMET-MTL

15

Microstructures

CANMET-MTL

16

CANMET-MTL

17

Stress Corrosion Cracking Is

A cracking process that requiresthe simultaneous action of acorrosive and a sustained tensilestress.

CANMET-MTL

18

Requirements

1.Steel susceptible to SCC2.Tensile stress3.Potent environment

- Coating failure provides access of aqueous environment to pipe surface.

CANMET-MTL

19

Stress

Hoop stress- from internal pipe pressure

Axial stress- from soil movement or localized pipe bending

Residual stress - from pipe forming or steel making operations

Cyclic stress- Fluctuations in operating pressure

CANMET-MTL

20

From: N.E.B Report on SCC, MH-2-96 (1996)

Stresses in Pipelines

CANMET-MTL

21

CANMET-MTL

22

Types of SCC

Near-Neutral-pH SCC- Transgranular

High-pH SCC- Intergranular

Orientation:- Longitudinal- Circumferential

CANMET-MTL

23

Stages of SCC

1. Generation of Environment2. Initiation of SCC3. Propagation of SCC

CANMET-MTL

24

Development of 5 cracks, a, b, c, d and e, after the total exposure time shown, in X-65, max = 70% YS, R = 0.4 and f = 1 Hz in NS4 solution saturated with CO2, showing the correlation of crack initiation, pits and non-metallic inclusions and the interaction and coalescence of cracks. (Observations were made on replicas.)

e

d

c

b

aa

b

c

d

e

a

b

cd

e

a

b

c

d

e

b

c

d

e

a

Total Exposure Time 309 h

469 h747 h 1025 h

300 m

20 m

CANMET-MTL

25

200 m

a

b

c

e

a

b

c

e

(a) (b)

N = 2.69 x 106 CyclesN = 1.69 x 106 Cycles

20

dd

469 h 747 h

CANMET-MTL

26

EDX Spectrum Before Test After Test

(a)

(b)

(c)

CaAl

O

S

20 m

O

AlS Ca

Al

O

Ca

S Ca

Ca

Ca

S

S

Al

Al

Al-oxide

CaAlO3dark

CaS

CaS

All dissolved

EDS spectra and the morphologies associated with three inclusions in a X-65 steel sample before and after test at max= 90%YS, R=0.6 and f=0.1Hz in NS-4 solution saturated with N2/5%CO2. Note: Effect of S on corrosion around inclusions.

CANMET-MTL

27

Schematic of Inclusion

Sulfide, (soluble)

Oxide (insoluble)

In some cases, CaS envelopes oxide/aluminate inclusion.Aluminate inclusions have poor deformability, remain spherical.In polishing to 1 m diamond finish, use non-aqueous lubricant, oil-based diamond.

CANMET-MTL

28

CANMET-MTL

29

Focused ion beam images of crack in X-65 specimen after 4.15 x 106cycles, max = 70% YS, R = 0.4, f = 1 Hz, NS-4 solution, CO2 satd. (a) Plan view of crack, FIB secondary electron image, tilt 0 deg. (b) Enlargement of crack tip area in ion-milled cross-sectioned region, tilt 30 deg. (b) image in secondary ion mode,

(a)

X 25 m Y 25 m

CANMET-MTL

30

WrappedNot Wrapped

X-65 steel, max = 70% YS, R = 0.4, f = 1 Hz, in NS4 solution saturated with CO2. Right part of specimen in (a) was coated with PTFE film during the test interval between 469 and 747 h. No coating between the exposure of 747 and 1025 h (b).

747 h 1025 h

CANMET-MTL

31

Pipe Fatigue Precracking

CANMET-MTL

32

Full-Scale Pipe Test for SCC

CANMET-MTL

33

CANMET-MTL

34

Conclusions - 11. SCC promoted by:

1. Decreasing R (min./max. stress)2. Increasing frequency

2. Environment that leads to SCC is generated by the balance between:

CO2CP current

3. Inclusions provide initiation sites for pitting4. Pits provide initiation sites for SCC5. Proximity of several small cracks can lead to

linkage

CANMET-MTL

35

Conclusions 2

6. SCC Initiation SitesPitsInclusionsSurface geometric discontinuitiesCoating Disbondments

CANMET-MTL

36

Conclusions 3

7. Elongated inclusions provide H trap sites for HIC initiation

1. Good correlation between inclusion measurements and HIC

2. Lower volume fraction of inclusions ~ increased HIC resistance

3. Banded microstructure decreases HIC resistance

CANMET-MTL

37

What is the Main Question about Corrosion?

1. Will there be another failure? If?

2. When will the next failure occur? When?

3. Where will the next failure occur? Where?

What do YOU think?

CANMET-MTL

38

CANMET-MTL

39

100 Years of Corrosion R&D The Foundation

Sensors for Field Measurements

Instrumentation for Data Collection

Software for Data Analysisand Decision-making

Cellular Network/Satellite Communications

Information on Data & Decisions

Building on Success

CANMET-MTL

40

Intelligent Systems Are Built on

1. Knowledge of Corrosion2. Sensors3. Instrumentation4. Software5. Remote Communications

1960s: Design Corrosion Out2000s: Design Smart Systems for Corrosion Monitoring and

Decision-makingMonitoring online, in real time, all the time

Convergence of technologies provides new opportunities to manage corrosion.

CANMET-MTL

41

CANMET-MTL

42

CANMET-MTL

43

Corrosion Control Wagon

$$$

CANMET-MTL

44

A Strategy Meeting

Corrosion Control Wagon

$$$

CANMET-MTL

45

Corrosion Control Wagon

Team Leader

$$$

CANMET-MTL

46

Acknowledgements

Jenny Been Mahmoud ShehataJenny Jackman Yong-zhi WangDave Kiff Glenn WilliamsYves Lafrenire Wenyue ZhengRuel Ramsingh

GRIPRCICanadian Federal Interdepartmental

Program of Energy R&D (PERD)

CANMET-MTL

47

Last Thought

Managing corrosion is an investment in asset protection that should result in cost savings because, when corrosion is managed, the cost of failure by corrosion is saved.

CANMET-MTL

48

Knowing is not enough; we must apply.

Willing is not enough; we must do.

Goethe

Failure Prevention

CANMET-MTL

49

NS-4 Solution

483 mg/L NaHCO3 122 mg/L KCl 137 mg/L CaCl2 131 mg/L MgSO47H2O

Trang Web nay coi cung hay, vao coi thu di http://gaigoibaucat.xlphp.net

unTrang Web nay coi cung hay, vao coi thu di http://gaigoibaucat.xlphp.net

CANMET-MTL

50

Trang Web nay coi cung hay, vao coi thu di http://gaigoibaucat.xlphp.net

C:\WINDOWS\hinhem.scr