1

Characterization of the Corrosion Scenarios on the Trans-Canada Pipeline (Alberta System)

(Interim Report: Dec. 20, 2005 -

Feb. 28, 2006)

P. Q. Wu, Z. Qin, and D. W. Shoesmith

The University of Western Ontario, London, Ontario, N6A 5B7

&

F. King

NOVA Research and Technology Center

Calgary, Alberta, Canada T2P 5H1

2

Six corrosion scenarios have been defined for

transmission pipelines based on TCPL/NRTC field

investigations:

1) Primary anaerobic corrosion (29%); 2) Primary aerobic corrosion (4%);3) Anaerobic corrosion turning aerobic (21%);4)

Primary anaerobic corrosion with sulfate-reducing

bacteria (SRB) (26%);

5)

Anaerobic corrosion with SRB turning aerobic (17%);

6)

Aerobic corrosion turning anaerobic with SRB (3%);

Background

T. R. Jack, et al, Materials Performance Nov. 1995; idid, March 1996.

3

These scenarios are useful in assessing the likely corrosion conditions and rates at various locations. However, since the corrosion product deposits and their influence on corrosion of pipeline steel are very complex, understanding of the corrosion mechanism of pipeline steel is not yet complete. Nova is developing a Permeable Coatings Model to predict the effect of cathodic protection on pipeline corrosion. A more complete understanding of the corrosion mechanism is needed.

Background

4

To investigate the electrochemical and chemical

processes involved in the film formation and

transformation processes (scenarios 1 to 3);

To provide a firmer mechanistic basis for the

Permeable Coatings Model developed by Nova to

predict the effect of cathodic protection on pipeline

corrosion.

Objectives

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Working electrode: A516 Grade 70 carbon steel, Φ1 cm2, polished with silicon carbide paper to grit No.1200;

Reference electrode: SCE;

Counter electrode: Pt mesh (2x2 cm2) ;

Electrolytes: Sol-A: 0.0075 M NaHCO3+0.001 M NaCl + 0.001 M Na2SO4 + 0.1 M NaClO4 (pH about 7.0 after purging Ar+5% CO2 or O2+ 5% CO2

at 23ºC for 1 h);Sol-B: 0.15 M NaHCO3 +0.001 M NaCl + 0.001 M Na2SO4 + 0.1 M NaClO4 (pH about 7.0 after purging 100% CO2 at 23ºC for 1 h).

Instruments: Solartron 1480 Multistat, 1287 Potentiostat, 1255B FRA, PINE AFASR Rotator, Raman spectroscopy, and scanning electron microscopy.

Experimental

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Experimental

Electrochemical cell, WE ––

working electrode, CE ––

counter electrode, RE ––

reference electrode

7

Research Approaches

Cyclic voltammetry (CV) with rotating disk electrode (RDE) technique;

Open-circuit potential technique;

Electrochemical Impedance Spectroscopy (EIS);

In-situ and ex-situ Raman spectroscopy;

Scanning electron microscopy (SEM).

8

-1.3 V 1 min

-1.1 V1 min

Eoc5 h

time

pote

ntia

l

Static experiments for scenario 1 (anaerobic) and 2 (aerobic )Ar+5% CO2

or O2

+5% CO2

were purged during measurements

Experimental – scenario 1 & 2

EIS

Eoc5 h

EIS

Eoc5 h

EIS

9

Results: Scenario 1 & 2

0 10 20 30 40 50 60 70-0.80

-0.75

-0.70

-0.65

-0.60

-0.55

-0.50

Ar+5% CO2 O2+5% CO2

EIS

pote

ntia

l (V

vs

SC

E)

time (h)Open-circuit potential measured on pipeline steel in Sol-A purged with Ar+5% CO2 or O2 +5% CO2 mixed gases during the measurements at 23 ºC

10

Results: Scenario 1

101

102

103

104

10-2 10-1 100 101 102 103 104 1050

20

40

60 d 1 d 2 d 3

Z (Ω

cm

2 )

- the

ta (d

egre

e)

frequency (Hz)Impedance measured on pipeline steel in Sol-A purged with Ar+5% CO2 mixed gas during the measurements at 23 ºC

11

Results: Scenario 2

Impedance measured on pipeline steel in Sol-A purged with O2 +5% CO2 mixed gas during the measurements at 23 ºC

101

102

103

10-2 10-1 100 101 102 103 104 1050

20

40 d 1 d 2 d 3

Z (Ω

cm

2 )

- the

ta (d

egre

e)

frequency (Hz)

12

Electrochemical experiments using RDE for scenario 1 and 2Ar+5% CO2

or O2

+5% CO2

was purged during measurements

-1.3 V 1 min

-1.1 V1 min

-1.2 V

-0.4 V (scenario 1)0.1 V (scenario 2)

-1.2 V

time

pote

ntia

lExperimental – scenario 1 & 2 (RDE)

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Results: Cyclic voltammograms

Cyclic

voltammograms

measured on pipeline steel in Sol-A purged with Ar+5% CO2

or O2

+5% CO2

mixed gases during measurements at 23 ºC

-1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0-2

0

2

4

6

8

curre

nt (m

A)

potential (V vs SCE)

Ar+5% CO2 O2+5% CO2

14

Results: Effect of rotation rate

-1.2

-1.0

-0.8

-0.6

-0.4

1E-6 1E-5 1E-4 1E-3 0.01

(a) Ar+5% CO2

Rotation rate: 1, 2, 5, 8 and 15 Hz

current density (A/cm2)

pote

ntia

l (V

vs S

CE)

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

1E-6 1E-5 1E-4 1E-3 0.01

(b) O2+5% CO2

Rotation rate: 1, 2, 5, 8 and 15 Hz

current density (A/cm2)po

tent

ial (

V vs

SC

E)

Polarization curves measured on pipeline steel in Sol-A purged with (a) Ar+5% CO2 , and (b) O2 +5% CO2 mixed gases during the measurements at 23 ºC

15

Koutecky-Levich plots for pipeline steel in Sol-A purged with Ar+5% CO2

mixed gas during the measurements at 23 ºC

0.2 0.4 0.6 0.8 1.00

20

40

60

80

(a) -0.72 V -0.74 V -0.76 V -0.78 V -0.80 V

1/j (

mA-1

)

f -1/2 (s0.5)0.2 0.4 0.6 0.8 1.0

-40

-30

-20

-10

0

(b)

-0.90 V -0.92 V -0.94 V -0.96 V -0.98 V

1/j (

mA-1

)

f -1/2 (s0.5)

(a) anodic current (b) cathodic current

Results: Effect of rotation rate

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Koutecky-Levich plots for pipeline steel in Sol-A purged with O2 +5% CO2

mixed gas during the measurements at 23 ºC

(a) anodic current (b) cathodic current

0.2 0.4 0.6 0.8 1.0

0

2

4

6

8

(a) -0.26 V -0.24 V -0.22 V -0.20 V -0.18 V

1/j (

mA-1

)

f -1/2 (s0.5)0.2 0.4 0.6 0.8 1.0

-2.0

-1.5

-1.0

-0.5

0.0

(b)

-0.90 V -0.92 V -0.94 V -0.96 V -0.98 V

1/j (

mA-1

)

f -1/2 (s0.5)

Results: Effect of rotation rate

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-1.3 V1 min -1.1 V

1 min

Eoc1 h

time

pote

ntia

l

Static electrochemical experiments for scenario 3Ar+5% CO2

or O2

+5% CO2

were purged during measurements

Eoc1-2 d

50 mV vs Eoc 1-2 d

EIS

Eoc1-2 d

EIS

Eoc1-2 d

EIS

5% CO2 +Ar100% CO2 5% CO2 +Ar 5% CO2 +O2

Experimental – scenario 3

0.15 M NaHCO3 + 0.1 M NaClO4

10-3 M NaCl + 10-3

M Na2 SO4 added

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Potential measured at 23ºC on pipeline steel in Sol-B purged with different gases during the measurements.

Results: Scenario 3

0 24 48 72 96 120 144-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.15M NaHCO3+0.1 M NaClO4

10-3 M NaCl+10-3 M Na2SO4

O2+5% CO2Ar+5% CO2100% CO2

EIS

EIS

EIS

pote

ntia

l (V

vs

SC

E)

time (h)

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Impedance measured at 23ºC on pipeline steel in Sol-B purged with different gases during the measurements.

Results: Scenario 3

100

101

102

103

104

105

10-2 10-1 100 101 102 103 104 1050

20

40

60

80

2.5 d 3.5 d 4.5 d

Z (Ω

cm

2 )

- the

ta (d

egre

e)

frequency (Hz)

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Open-circuit potential measured at 23ºC on pipeline steel in 0.001 M NaCl +0.001 M Na2

SO4

+ 0.1 M NaClO4

alternatively purged with Ar+5% CO2

and O2

+5% CO2

mixed gas during the measurements (No bicarbonate added, pH 5.5).

0 1 2 3 4 5 6-0.8

-0.7

-0.6

-0.5

EIS

EIS

EIS

Ar+5% CO2

O2+5% CO2

Ar+5% CO2

pote

ntia

l (V

vs

SC

E)

time (d)

Results: Scenario 3 (pH 5.5)

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EIS measured at 23 ºC on pipeline steel in 0.001 M NaCl +0.001 M Na2 SO4 + 0.1 M NaClO4 alternatively purged with Ar+5% CO2 and O2 +5% CO2 mixed gases during the measurements (No bicarbonate added, pH 5.5).

Results: Scenario 3 (pH 5.5)

101

102

103

104

10-2 10-1 100 101 102 103 104 1050

20

40

60

2 d 4 d 6 d

Z (Ω

cm

2 )

- the

ta (d

egre

e)

frequency (Hz)

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Results: Formation of Siderite

0 10 20 30 40 50-0.1

0.0

0.1

0.2

0.3

0.15 M NaHCO3+0.1 M NaClO4 at -0.682 V 0.15 M NaHCO3+0.1 M NaClO4 at -0.730 V 0.375 M NaHCO3+0.1 M NaClO4 at -0.730 V

curre

nt (m

A)

time (h)

Current measured on pipeline steel under potentiostatic control in x M NaHCO3 + 0.1 M NaClO4 purged with 100% CO2 gas during the measurements at 23 ºC

Raman

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Positions taken for ex-situ Raman analysis on pipeline steel after test for 16 h in 0.375 M NaHCO3

+ 0.1 M NaClO4

purged with 100% CO2

gas (pH 8.0)

Results: Formation of Siderite

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Raman spectra acquired on pipeline steel after test for 16 h in 0.375 M NaHCO3

+ 0.1 M NaClO4

purged with 100% CO2

gas

Results: Formation of Siderite

800 900 1000 1100 1200 13000

500

1000

1500

2000

Point 1 Point 2

1083

Inte

nsity

(a.u

.)

Raman shift (cm-1)

25In-situ Raman and electrochemical measurements

Experimental – scenario 3 (in-situ Raman)

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-1.3 V1 min

-1.1 V1 min

Eoc1 h

time

pote

ntia

l

In-situ Raman and electrochemical measurements

Eoc1 d

Eoc1 d

Open to air

Raman

Raman

Raman

100% CO2 Sealed

Experimental – scenario 3 (in-situ Raman)

50 mV vs Eoc 1 d

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Experimental – scenario 3 (in-situ Raman)

Positions taken for in-situ Raman analysis

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Experimental – scenario 3 (in-situ Raman)

In-situ Raman spectra acquired at spot 1 on pipeline steel immersed

in Sol- B for various times (2d –

sealed --

3d –

open –

4d)

0 400 800 1200 1600 20001000

2000

3000

4000

5000

6000

4 d3 d2 d

1083935

390298

Inte

nsity

(a.u

.)

Raman shift (cm-1)

FeOOH

ClO4-

CO2=

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Experimental – scenario 3 (in-situ Raman)

In-situ Raman spectra acquired at spot 2 on pipeline steel immersed

in Sol- B for various times (2d –

sealed --

3d –

open –

4d)

0 400 800 1200 1600 20001000

2000

3000

4000

5000

6000

4 d

3 d

2 d

1542

935

389298

Inte

nsity

(a.u

.)

Raman shift (cm-1)

FeOOH

ClO4-

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Experimental – scenario 3 (in-situ Raman)

In-situ Raman spectra acquired at spot 3 on pipeline steel immersed

in Sol- B for various times (2d –

sealed --

3d –

open –

4d)

0 400 800 1200 1600 20001000

2000

3000

4000

5000

6000

4 d

3 d

2 d

1083

1316

935

784

276

Inte

nsity

(a.u

.)

Raman shift (cm-1)

ClO4-

CO3=

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Experimental – scenario 3 (ex-situ Raman)

Position taken for ex-situ Raman analysis after 4 d test in Sol-B

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Experimental – scenario 3 (ex-situ Raman)

Ex-situ Raman spectrum acquired after 4 d test in Sol-B

200 400 600 800 1000 1200 1400 1600 1800 20000

1000

2000

3000

4000

5000

pt 1pt 2pt 3

386

1083

1650

664

281

Inte

nsity

(a.u

.)

Raman shift (cm-1)

FeOOH+FeCO3

FeOOH

Fe3 O4

FeCO3

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Summary

Effect of mass transport seems insignificant under anaerobic conditions, but the effect of oxygen diffusion on the corrosion of the steel is quite significant under aerobic conditions.The corrosion potentials of the pipeline steel are –0.75 V and –0.65 V respectively in anaerobic and aerobic conditions. The corrosion rate in aerobic conditions could be 10 times higher than that inanaerobic conditions.Different from scenario (2), when the conditions change from anaerobic to aerobic, the impedance does not change much, while the corrosion potential of pipeline steel shifts from –0.75 V to –0.22 V. These results may suggest that a film may be formed on the surface prior to the condition change.

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Investigation of scenarios (1) – (3) using a cell with

small solution volume and/or sacrificing Fe

Procedures to form siderite relatively quickly

Film characterization by in-situ + ex-situ Raman on

samples with and without pre-formed siderite

Corrosion rate measurements

EIS interpretations by equivalent circuits

Future Work

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Research in progress …

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Acknowledgements

NOVA Research and Technology Center for financial support;

Marek Odziemkowski, University of Waterloo, for

Raman spectroscopy analysis;

Surface Science Western for SEM and Raman spectroscopy analysis;

Members of Professor Shoesmith Group for friendship and assistance.