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

Transcription

1 Characterization of the Corrosion Scenarios on the Trans-Canada Pipeline (Alberta System) (Interim Report: Dec. 20, 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 1

2 Background 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%); T. R. Jack, et al, Materials Performance Nov. 1995; idid, March

3 Background 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. 3

4 Objectives 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. 4

5 Working electrode: A516 Grade 70 carbon steel, Φ1 cm 2, polished with silicon carbide paper to grit No.1200; Reference electrode: SCE; Counter electrode: Pt mesh (2x2 cm 2 ) ; Experimental Electrolytes: Sol-A: M NaHCO M NaCl M Na 2 SO M NaClO 4 (ph about 7.0 after purging Ar+5% CO 2 or O 2 + 5% CO 2 at 23ºC for 1 h); Sol-B: 0.15 M NaHCO M NaCl M Na 2 SO M NaClO 4 (ph about 7.0 after purging 100% CO 2 at 23ºC for 1 h). Instruments: Solartron 1480 Multistat, 1287 Potentiostat, 1255B FRA, PINE AFASR Rotator, Raman spectroscopy, and scanning electron microscopy. 5

6 Experimental Electrochemical cell, WE working electrode, CE counter electrode, RE reference electrode 6

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). 7

8 Experimental scenario 1 & 2 potential -1.3 V 1 min -1.1 V 1 min Eoc 5 h EIS Eoc 5 h EIS Eoc 5 h EIS time Static experiments for scenario 1 (anaerobic) and 2 (aerobic ) Ar+5% CO 2 or O 2 +5% CO 2 were purged during measurements 8

9 Results: Scenario 1 & potential (V vs SCE) Ar+5% CO 2 O 2 +5% CO 2 EIS time (h) Open-circuit potential measured on pipeline steel in Sol-A purged with Ar+5% CO 2 or O 2 +5% CO 2 mixed gases during the measurements at 23 ºC 9

10 Results: Scenario Z (Ω cm 2 ) theta (degree) 60 d 1 d 2 40 d frequency (Hz) Impedance measured on pipeline steel in Sol-A purged with Ar+5% CO 2 mixed gas during the measurements at 23 ºC 10

11 Results: Scenario Z (Ω cm 2 ) theta (degree) d 1 d 2 d frequency (Hz) Impedance measured on pipeline steel in Sol-A purged with O 2 +5% CO 2 mixed gas during the measurements at 23 ºC 11

12 Experimental scenario 1 & 2 (RDE) -0.4 V (scenario 1) 0.1 V (scenario 2) potential -1.3 V 1 min -1.1 V 1 min -1.2 V -1.2 V time Electrochemical experiments using RDE for scenario 1 and 2 Ar+5% CO 2 or O 2 +5% CO 2 was purged during measurements 12

13 Results: Cyclic voltammograms 8 6 Ar+5% CO 2 O 2 +5% CO 2 current (ma) potential (V vs SCE) Cyclic voltammograms measured on pipeline steel in Sol-A purged with Ar+5% CO 2 or O 2 +5% CO 2 mixed gases during measurements at 23 ºC 13

14 Results: Effect of rotation rate -0.4 (a) Ar+5% CO potential (V vs SCE) Rotation rate: 1, 2, 5, 8 and 15 Hz E-6 1E-5 1E-4 1E current density (A/cm 2 ) (b) O 2 +5% CO 2 Rotation rate: 1, 2, 5, 8 and 15 Hz E-6 1E-5 1E-4 1E current density (A/cm 2 ) Polarization curves measured on pipeline steel in Sol-A purged with (a) Ar+5% CO 2, and (b) O 2 +5% CO 2 mixed gases during the measurements at 23 ºC potential (V vs SCE) 14

15 Results: Effect of rotation rate V V V V V (a) 0-10 (b) 1/j (ma -1 ) /j (ma -1 ) V V V V V f -1/2 (s 0.5 ) f -1/2 (s 0.5 ) (a) anodic current (b) cathodic current Koutecky-Levich plots for pipeline steel in Sol-A purged with Ar+5% CO 2 mixed gas during the measurements at 23 ºC 15

16 Results: Effect of rotation rate /j (ma -1 ) V V V V V (a) 1/j (ma -1 ) V V V V V (b) f -1/2 (s 0.5 ) f -1/2 (s 0.5 ) (a) anodic current (b) cathodic current Koutecky-Levich plots for pipeline steel in Sol-A purged with O 2 +5% CO 2 mixed gas during the measurements at 23 ºC 16

17 Experimental scenario 3 100% CO 2 5% CO 2 +Ar 5% CO 2 +O 2 5% CO 2 +Ar EIS potential Eoc 1 h 50 mv vs Eoc 1-2 d Eoc 1-2 d EIS Eoc 1-2 d Eoc 1-2 d EIS -1.3 V 1 min -1.1 V 1 min 0.15 M NaHCO M NaClO M NaCl M Na 2 SO 4 added time Static electrochemical experiments for scenario 3 Ar+5% CO 2 or O 2 +5% CO 2 were purged during measurements 17

18 Results: Scenario potential (V vs SCE) % CO 2 Ar+5% CO M NaCl M Na 2 SO 4 O 2 +5% CO 2 EIS M NaHCO M NaClO 4 EIS EIS time (h) Potential measured at 23ºC on pipeline steel in Sol-B purged with different gases during the measurements. 18

19 Results: Scenario 3 Z (Ω cm 2 ) - theta (degree) d 3.5 d 4.5 d frequency (Hz) Impedance measured at 23ºC on pipeline steel in Sol-B purged with different gases during the measurements. 19

20 Results: Scenario 3 (ph 5.5) -0.5 potential (V vs SCE) Ar+5% CO 2 O 2 +5% CO 2 Ar+5% CO 2 EIS EIS EIS time (d) Open-circuit potential measured at 23ºC on pipeline steel in M NaCl M Na 2 SO M NaClO 4 alternatively purged with Ar+5% CO 2 and O 2 +5% CO 2 mixed gas during the measurements (No bicarbonate added, ph 5.5). 20

21 Results: Scenario 3 (ph 5.5) 10 4 Z (Ω cm 2 ) d 4 d 6 d - theta (degree) frequency (Hz) EIS measured at 23 ºC on pipeline steel in M NaCl M Na 2 SO M NaClO 4 alternatively purged with Ar+5% CO 2 and O 2 +5% CO 2 mixed gases during the measurements (No bicarbonate added, ph 5.5). 21

22 Results: Formation of Siderite M NaHCO M NaClO 4 at V 0.15 M NaHCO M NaClO 4 at V M NaHCO M NaClO 4 at V current (ma) Raman time (h) Current measured on pipeline steel under potentiostatic control in x M NaHCO M NaClO 4 purged with 100% CO 2 gas during the measurements at 23 ºC 22

23 Results: Formation of Siderite Positions taken for ex-situ Raman analysis on pipeline steel after test for 16 h in M NaHCO M NaClO 4 purged with 100% CO 2 gas (ph 8.0) 23

24 Results: Formation of Siderite 2000 Intensity (a.u.) Point 1 Point Raman shift (cm -1 ) Raman spectra acquired on pipeline steel after test for 16 h in M NaHCO M NaClO 4 purged with 100% CO 2 gas 24

25 Experimental scenario 3 (in-situ Raman) In-situ Raman and electrochemical measurements 25

26 Experimental scenario 3 (in-situ Raman) 100% CO 2 Sealed Open to air potential Eoc 1 h Raman Raman Eoc 1 d Raman 50 mv vs Eoc 1 d Eoc 1 d -1.3 V 1 min min V time In-situ Raman and electrochemical measurements 26

27 Experimental scenario 3 (in-situ Raman) Positions taken for in-situ Raman analysis 27

28 Experimental scenario 3 (in-situ Raman) FeOOH Intensity (a.u.) ClO CO 2 = 4 d 3 d 2 d Raman shift (cm -1 ) In-situ Raman spectra acquired at spot 1 on pipeline steel immersed in Sol- B for various times (2d sealed -- 3d open 4d) 28

29 Experimental scenario 3 (in-situ Raman) FeOOH Intensity (a.u.) ClO d d 2 d Raman shift (cm -1 ) In-situ Raman spectra acquired at spot 2 on pipeline steel immersed in Sol- B for various times (2d sealed -- 3d open 4d) 29

30 Experimental scenario 3 (in-situ Raman) Intensity (a.u.) ClO CO 3 = 4 d d 2 d Raman shift (cm -1 ) In-situ Raman spectra acquired at spot 3 on pipeline steel immersed in Sol- B for various times (2d sealed -- 3d open 4d) 30

31 Experimental scenario 3 (ex-situ Raman) Position taken for ex-situ Raman analysis after 4 d test in Sol-B 31

32 Experimental scenario 3 (ex-situ Raman) 1083 FeCO 3 Intensity (a.u.) FeOOH+FeCO FeOOH Fe 3 O pt 1 pt 2 pt Raman shift (cm -1 ) Ex-situ Raman spectrum acquired after 4 d test in Sol-B 32

33 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 in anaerobic 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. 33

34 Future Work 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 34

35 Research in progress 35

36 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. 36